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The hydrocarboxyl radical , HOCO, is an unstable molecular radical important in combustion . It is formed by the reaction of the hydroxyl radical with carbon monoxide . Hydrocarboxyl then breaks up to form carbon dioxide and atomic hydrogen . Much of the carbon dioxide on Earth and Mars has been produced via the hydrocarboxyl radical. [ 2 ] HOCO formed from OH and CO initially is in an excited state. It can transfer energy to other molecules such as N 2 or other carbon monoxide molecules. [ 3 ]
The production of this radical during combustion was originally predicted by Ian W. M. Smith and Reinhard Zellner in 1973. [ 3 ] [ 4 ] The HOCO radical was detected in its deuterated form DOCO by Bryce J. Bjork, Thinh Q. Bui, and Jun Ye in 2016. [ 5 ] | https://en.wikipedia.org/wiki/Hydrocarboxyl |
This page provides supplementary chemical data on Hydrochloric acid .
The handling of this chemical may incur notable safety precautions. It is highly recommend that you seek the Material Safety Datasheet ( MSDS ) for this chemical from a reliable source and follow its directions. | https://en.wikipedia.org/wiki/Hydrochloric_acid_(data_page) |
Hydrochloric acid regeneration or HCl regeneration is a chemical process for the reclamation of bound and unbound HCl from metal chloride solutions such as hydrochloric acid . [ 1 ]
The commercially most relevant field of application for HCl regeneration processes is the recovery of HCl from waste pickle liquors from carbon-steel pickling lines. Other applications include the production of metal oxides such as, but not limited, to Al 2 O 3 and MgO, as well as rare-earth oxides, by pyrohydrolysis of aqueous metal chloride or rare-earth chloride solutions.
A number of different process routes are available. The most widely used is based on pyrohydrolysis and adiabatic absorption of hydrogen chloride in water, a process invented in the 1960s. However tightening environmental standards and stringent air permit policies render it increasingly difficult to establish new pyrohydrolysis-based acid regeneration plants.
The following processes for the regeneration of HCl from spent pickle liquors have been adopted by the ferrous metals processing industry:
Hydrothermal hydrolysis of hydrochloric SPL from carbon-steel pickling lines is a hydrometallurgical reaction, which takes place according to the following chemical formula:
12 FeCl 2 + 3 O 2 → 8 FeCl 3 + 2 Fe 2 O 3
2 FeCl 3 + 3 H 2 O → 6 HCl + Fe 2 O 3
Today hydrothermal hydrolysis, which operates at very low temperatures, consumes only a fraction of the energy other processes demand and produces virtually no emissions, is considered the most effective way to regenerate any given quantity of spent pickle liquor.
Known implementations of the hydrothermal HCl regeneration processes include the PORI process (1974 for J&L Steel, dismantled) and the optimized SMS Demag wet process (2008 for ThyssenKrupp Steel, under construction).
Pyrohydrolysis of hydrochloric spent pickle liquor from carbon steel pickling lines is a hydrometallurgical reaction which takes place according to the following chemical formulae:
4 FeCl 2 + 4 H 2 O + O 2 = 8 HCl + 2 Fe 2 O 3
2 FeCl 3 + 3 H 2 O = 6 HCl + Fe 2 O 3
The process is an inversion of the chemical descaling (pickling) process.
The metal chloride solution (in the most common case waste pickle liquor from a carbon steel pickling line) is fed to the venturi evaporator (III), where direct mass and heat exchange with the hot roast gas from the roaster (reactor/cyclone) takes place. The separator (IV) separates the gas and liquid phase of the venturi evaporator product. The liquid phase is re-circulated back to the venturi evaporator to increase mass and heat exchange performance.
Preconcentrated waste acid from the preconcentrator (III / IV) is injected into the reactor (I) by means of one or more spray booms (VIII) bearing one or more injection nozzles each. Injection takes place at reactor top at a pressure between 4 and 10 bar. The reactor is directly fired by tangentially mounted burners that create a hot swirl. Temperatures inside the reactor vary between 700 °C (burner level) and 370 °C (roast gas exit duct).
In the reactor the conversion of droplets of preconcentrated waste acid into iron oxide powder and hydrogen chloride gas takes place. Hydrogen Chloride leaves the reactor through the top, while iron oxide powder is removed from the reactor bottom by means of mechanical extraction devices. A cyclone (II) in the roast gas duct ensures separation and feed back of larger oxide particles carried by the roast gas.
In the absorption column (V) the hydrogen chloride compound of the saturated roast gas leaving the preconcentrator is adiabatically absorbed in water (which in many cases is acid rinse water from a carbon steel pickling line). Regenerated acid (typical strength: 18% wt/wt) is collected at absorption column bottom.
The roast gas is conveyed through the system by means of an exhaust gas fan (VI). Fans in plants provide pressure increases of approx. 200 mbar and are feedback-controlled to maintain a relative pressure of −3 mbar between reactor and atmosphere to avoid any overpressure-related leakage of acid gas.
To rinse the impeller and cool the gas as well as to remove remaining traces of HCl from the roast gas, the exhaust gas fan is commonly supplied with quenching water, which is separated from the exhaust gas stream by means of a mist eliminator (VII) at the pressure side of the fan.
In a final scrubber, commonly consisting of a combination of wet scrubbers such as venturi scrubbers (IX) and scrubber columns (X), remaining traces of HCl and dust are removed.
In some plant, absorption chemicals such as NaOH and Na 2 S 2 O 3 are used to bind HCl and Cl 2 (which is created under certain circumstances in several, but not all spray roasting reactors).
Pyrohydrolysis based acid regeneration processes produce a considerable amount of stack emissions containing HCl, particles and chlorine, which has led to numerous violations of the U.S. clean air act in the past. [ 2 ] | https://en.wikipedia.org/wiki/Hydrochloric_acid_regeneration |
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid , [ 1 ] while others extend the definition to include substances like aerosols and gels . The term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word suspension is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). The dispersed phase particles have a diameter of approximately 1 nanometre to 1 micrometre . [ 2 ] [ 3 ]
Some colloids are translucent because of the Tyndall effect , which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color.
Colloidal suspensions are the subject of interface and colloid science . This field of study began in 1845 by Francesco Selmi , [ 4 ] [ 5 ] [ 6 ] [ 7 ] who called them pseudosolutions, and expanded by Michael Faraday [ 8 ] and Thomas Graham , who coined the term colloid in 1861. [ 9 ]
Colloid : Short synonym for colloidal system. [ 10 ] [ 11 ]
Colloidal : State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm, or that in a system discontinuities are found at distances of that order. [ 10 ] [ 11 ] [ 12 ]
Colloids can be classified as follows:
Homogeneous mixtures with a dispersed phase in this size range may be called colloidal aerosols , colloidal emulsions , colloidal suspensions , colloidal foams , colloidal dispersions , or hydrosols .
Hydrocolloids describe certain chemicals (mostly polysaccharides and proteins ) that are colloidally dispersible in water . Thus becoming effectively "soluble" they change the rheology of water by raising the viscosity and/or inducing gelation. They may provide other interactive effects with other chemicals, in some cases synergistic, in others antagonistic. Using these attributes hydrocolloids are very useful chemicals since in many areas of technology from foods through pharmaceuticals , personal care and industrial applications, they can provide stabilization, destabilization and separation, gelation, flow control, crystallization control and numerous other effects. Apart from uses of the soluble forms some of the hydrocolloids have additional useful functionality in a dry form if after solubilization they have the water removed - as in the formation of films for breath strips or sausage casings or indeed, wound dressing fibers, some being more compatible with skin than others. There are many different types of hydrocolloids each with differences in structure function and utility that generally are best suited to particular application areas in the control of rheology and the physical modification of form and texture. Some hydrocolloids like starch and casein are useful foods as well as rheology modifiers, others have limited nutritive value, usually providing a source of fiber. [ 15 ]
The term hydrocolloids also refers to a type of dressing designed to lock moisture in the skin and help the natural healing process of skin to reduce scarring, itching and soreness.
Hydrocolloids contain some type of gel-forming agent, such as sodium carboxymethylcellulose (NaCMC) and gelatin. They are normally combined with some type of sealant, i.e. polyurethane to 'stick' to the skin.
A colloid has a dispersed phase and a continuous phase, whereas in a solution , the solute and solvent constitute only one phase. A solute in a solution are individual molecules or ions , whereas colloidal particles are bigger. For example, in a solution of salt in water, the sodium chloride (NaCl) crystal dissolves, and the Na + and Cl − ions are surrounded by water molecules. However, in a colloid such as milk, the colloidal particles are globules of fat, rather than individual fat molecules. Because colloid is multiple phases, it has very different properties compared to fully mixed, continuous solution. [ 16 ]
The following forces play an important role in the interaction of colloid particles: [ 17 ] [ 18 ]
The Earth’s gravitational field acts upon colloidal particles. Therefore, if the colloidal particles are denser than the medium of suspension, they will sediment (fall to the bottom), or if they are less dense, they will cream (float to the top). Larger particles also have a greater tendency to sediment because they have smaller Brownian motion to counteract this movement.
The sedimentation or creaming velocity is found by equating the Stokes drag force with the gravitational force :
where
and v {\displaystyle v} is the sedimentation or creaming velocity.
The mass of the colloidal particle is found using:
where
and ρ 1 − ρ 2 {\displaystyle \rho _{1}-\rho _{2}} is the difference in mass density between the colloidal particle and the suspension medium.
By rearranging, the sedimentation or creaming velocity is:
There is an upper size-limit for the diameter of colloidal particles because particles larger than 1 μm tend to sediment, and thus the substance would no longer be considered a colloidal suspension. [ 19 ]
The colloidal particles are said to be in sedimentation equilibrium if the rate of sedimentation is equal to the rate of movement from Brownian motion.
There are two principal ways to prepare colloids: [ 20 ]
The stability of a colloidal system is defined by particles remaining suspended in solution and depends on the interaction forces between the particles. These include electrostatic interactions and van der Waals forces , because they both contribute to the overall free energy of the system. [ 21 ]
A colloid is stable if the interaction energy due to attractive forces between the colloidal particles is less than kT , where k is the Boltzmann constant and T is the absolute temperature . If this is the case, then the colloidal particles will repel or only weakly attract each other, and the substance will remain a suspension.
If the interaction energy is greater than kT, the attractive forces will prevail, and the colloidal particles will begin to clump together. This process is referred to generally as aggregation , but is also referred to as flocculation , coagulation or precipitation . [ 22 ] While these terms are often used interchangeably, for some definitions they have slightly different meanings. For example, coagulation can be used to describe irreversible, permanent aggregation where the forces holding the particles together are stronger than any external forces caused by stirring or mixing. Flocculation can be used to describe reversible aggregation involving weaker attractive forces, and the aggregate is usually called a floc . The term precipitation is normally reserved for describing a phase change from a colloid dispersion to a solid (precipitate) when it is subjected to a perturbation. [ 19 ] Aggregation causes sedimentation or creaming, therefore the colloid is unstable: if either of these processes occur the colloid will no longer be a suspension.
Electrostatic stabilization and steric stabilization are the two main mechanisms for stabilization against aggregation.
A combination of the two mechanisms is also possible (electrosteric stabilization).
A method called gel network stabilization represents the principal way to produce colloids stable to both aggregation and sedimentation. The method consists in adding to the colloidal suspension a polymer able to form a gel network. Particle settling is hindered by the stiffness of the polymeric matrix where particles are trapped, [ 26 ] and the long polymeric chains can provide a steric or electrosteric stabilization to dispersed particles. Examples of such substances are xanthan and guar gum .
Destabilization can be accomplished by different methods:
Unstable colloidal suspensions of low-volume fraction form clustered liquid suspensions, wherein individual clusters of particles sediment if they are more dense than the suspension medium, or cream if they are less dense. However, colloidal suspensions of higher-volume fraction form colloidal gels with viscoelastic properties. Viscoelastic colloidal gels, such as bentonite and toothpaste , flow like liquids under shear, but maintain their shape when shear is removed. It is for this reason that toothpaste can be squeezed from a toothpaste tube, but stays on the toothbrush after it is applied.
The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple light scattering coupled with vertical scanning. [ 28 ] [ 29 ] [ 30 ] [ 31 ] This method, known as turbidimetry , is based on measuring the fraction of light that, after being sent through the sample, it backscattered by the colloidal particles. The backscattering intensity is directly proportional to the average particle size and volume fraction of the dispersed phase. Therefore, local changes in concentration caused by sedimentation or creaming, and clumping together of particles caused by aggregation, are detected and monitored. [ 32 ] These phenomena are associated with unstable colloids.
Dynamic light scattering can be used to detect the size of a colloidal particle by measuring how fast they diffuse. This method involves directing laser light towards a colloid. The scattered light will form an interference pattern, and the fluctuation in light intensity in this pattern is caused by the Brownian motion of the particles. If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion. This technique can confirm that aggregation has occurred if the apparent particle size is determined to be beyond the typical size range for colloidal particles. [ 21 ]
The kinetic process of destabilisation can be rather long (up to several months or years for some products). Thus, it is often required for the formulator to use further accelerating methods to reach reasonable development time for new product design. Thermal methods are the most commonly used and consist of increasing temperature to accelerate destabilisation (below critical temperatures of phase inversion or chemical degradation). Temperature affects not only viscosity, but also interfacial tension in the case of non-ionic surfactants or more generally interactions forces inside the system. Storing a dispersion at high temperatures enables to simulate real life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times.
Mechanical acceleration including vibration, centrifugation and agitation are sometimes used. They subject the product to different forces that pushes the particles / droplets against one another, hence helping in the film drainage. Some emulsions would never coalesce in normal gravity, while they do under artificial gravity. [ 33 ] Segregation of different populations of particles have been highlighted when using centrifugation and vibration. [ 34 ]
In physics , colloids are an interesting model system for atoms . [ 35 ] Micrometre-scale colloidal particles are large enough to be observed by optical techniques such as confocal microscopy . Many of the forces that govern the structure and behavior of matter, such as excluded volume interactions or electrostatic forces, govern the structure and behavior of colloidal suspensions. For example, the same techniques used to model ideal gases can be applied to model the behavior of a hard sphere colloidal suspension. Phase transitions in colloidal suspensions can be studied in real time using optical techniques, [ 36 ] and are analogous to phase transitions in liquids. In many interesting cases optical fluidity is used to control colloid suspensions. [ 36 ] [ 37 ]
A colloidal crystal is a highly ordered array of particles that can be formed over a very long range (typically on the order of a few millimeters to one centimeter) and that appear analogous to their atomic or molecular counterparts. [ 38 ] One of the finest natural examples of this ordering phenomenon can be found in precious opal , in which brilliant regions of pure spectral color result from close-packed domains of amorphous colloidal spheres of silicon dioxide (or silica , SiO 2 ). [ 39 ] [ 40 ] These spherical particles precipitate in highly siliceous pools in Australia and elsewhere, and form these highly ordered arrays after years of sedimentation and compression under hydrostatic and gravitational forces. The periodic arrays of submicrometre spherical particles provide similar arrays of interstitial voids , which act as a natural diffraction grating for visible light waves , particularly when the interstitial spacing is of the same order of magnitude as the incident lightwave. [ 41 ] [ 42 ]
Thus, it has been known for many years that, due to repulsive Coulombic interactions, electrically charged macromolecules in an aqueous environment can exhibit long-range crystal -like correlations with interparticle separation distances, often being considerably greater than the individual particle diameter. In all of these cases in nature, the same brilliant iridescence (or play of colors) can be attributed to the diffraction and constructive interference of visible lightwaves that satisfy Bragg’s law , in a matter analogous to the scattering of X-rays in crystalline solids.
The large number of experiments exploring the physics and chemistry of these so-called "colloidal crystals" has emerged as a result of the relatively simple methods that have evolved in the last 20 years for preparing synthetic monodisperse colloids (both polymer and mineral) and, through various mechanisms, implementing and preserving their long-range order formation. [ 43 ]
Colloidal phase separation is an important organising principle for compartmentalisation of both the cytoplasm and nucleus of cells into biomolecular condensates —similar in importance to compartmentalisation via lipid bilayer membranes , a type of liquid crystal . The term biomolecular condensate has been used to refer to clusters of macromolecules that arise via liquid-liquid or liquid-solid phase separation within cells. Macromolecular crowding strongly enhances colloidal phase separation and formation of biomolecular condensates .
Colloidal particles can also serve as transport vectors [ 44 ] of diverse contaminants in the surface water (sea water, lakes, rivers, freshwater bodies) and in underground water circulating in fissured rocks [ 45 ] (e.g. limestone , sandstone , granite ). Radionuclides and heavy metals easily sorb onto colloids suspended in water. Various types of colloids are recognised: inorganic colloids (e.g. clay particles, silicates, iron oxy-hydroxides ), organic colloids ( humic and fulvic substances). When heavy metals or radionuclides form pure colloids, the term " eigencolloid " is used to designate pure phases, i.e., pure Tc(OH) 4 , U(OH) 4 , or Am(OH) 3 . Colloids have been suspected for the long-range transport of plutonium on the Nevada Nuclear Test Site . They have been the subject of detailed studies for many years. However, the mobility of inorganic colloids is very low in compacted bentonites and in deep clay formations [ 46 ] because of the process of ultrafiltration occurring in dense clay membrane. [ 47 ] The question is less clear for small organic colloids often mixed in porewater with truly dissolved organic molecules. [ 48 ]
In soil science , the colloidal fraction in soils consists of tiny clay and humus particles that are less than 1μm in diameter and carry either positive and/or negative electrostatic charges that vary depending on the chemical conditions of the soil sample, i.e. soil pH . [ 49 ]
Colloid solutions used in intravenous therapy belong to a major group of volume expanders , and can be used for intravenous fluid replacement . Colloids preserve a high colloid osmotic pressure in the blood, [ 50 ] and therefore, they should theoretically preferentially increase the intravascular volume , whereas other types of volume expanders called crystalloids also increase the interstitial volume and intracellular volume . However, there is still controversy to the actual difference in efficacy by this difference, [ 50 ] and much of the research related to this use of colloids is based on fraudulent research by Joachim Boldt . [ 51 ] Another difference is that crystalloids generally are much cheaper than colloids. [ 50 ] | https://en.wikipedia.org/wiki/Hydrocolloid |
A hydrocupration is a chemical reaction whereby a ligated copper hydride species (Cu(I)H), reacts with a carbon-carbon or carbon-oxygen pi-system ; this insertion is typically thought to occur via a four-membered ring transition state , producing a new copper-carbon or copper-oxygen sigma-bond and a stable (generally) carbon-hydrogen sigma-bond. [ 1 ] In the latter instance (copper-oxygen), protonation (protodemetalation) is typical – the former (copper-carbon) has broad utility. [ 2 ] [ 3 ] The generated copper-carbon bond ( organocuprate ) has been employed in various nucleophilic additions to polar conjugated and non-conjugated systems and has also been used to forge (by way of reductive elimination or transmetalation ) new carbon-heteroatom bonds (Nitrogen, Boron, etc.). [ 3 ] [ 4 ]
While copper (I) hydride was the earliest known binary metal hydride (1800s), synthetic organic chemist’s interest in the reactivity of copper hydride complexes did not arise until nearly a century later; this interest came in the form of the now broadly utilized Stryker’s reagent (PPh3-modified CuH Hexamer) to affect hydrocuprations of unsaturated ketones – resulting in either 1,4 or 1,2 reduction (see Copper hydride , Stryker's reagent ). [ 2 ] [ 3 ] [ 5 ] While the discussed reactivity is still heavily utilized, hydrocupration has recently (early 21st century) been popularized in olefin functionalizations.
Many reactions utilizing ligated copper (I) hydride to functionalize olefins have been rendered catalytic and/or enantioselective . The scheme below details, in a generic sense, the catalytic cycle for popularized reactions in this realm – and, how they’ve been hypothesized to proceed. As it pertains to copper hydride-mediated hydroboration , after 1,2-migratory insertion (M.I.), a transmetalation can take place with pinacolborane (HBPin) to produce the hydroborated product and regenerate ligated copper (I) hydride. [ 4 ] [ 6 ]
For hydroalkylations (and hydroacylations ), the generated organocuprate (after initial migratory insertion) can perform nucleophilic substitution chemistry (SN2) with alkyl halides, carbonyls, and various other classical electrophiles; in this instance (and in the case of reactivity with an alkyl halide) a copper (I) halide salt is produced, which upon transmetalation with a metalated alkoxide additive produces a more thermodynamically stable metal halide salt and a copper (I) alkoxide. [ 7 ] [ 8 ] The latter species can undergo a final transmetalation with an alkyl hydrosilane ( stoichiometric ) to regenerate the active ligated copper (I) hydride catalyst and a thermodynamically stable silanol.
For hydroaminations , ligated copper (I) hydride undergoes a 1,2 migratory insertion; the resulting organocuprate can be reacted with an appropriate electrophilic amine source (such as the O-benzoylated hydroxylamine shown) to produce a highly energetic copper (III) intermediate. [ 3 ] [ 9 ] Reductive elimination between the carbon and nitrogen (forming C-N) produces the hydroaminated product along with a copper (I) alkoxide – which, similarly to the case of hydroalkylations/acylations, can undergo further transmetalation with an alkyl hydrosilane to regenerate the active ligated copper (I) hydride species. Alternative hypotheses to the amination step involve direct displacement or transmetalation, versus an oxidative addition to the polarized hydroxylamine. [ 10 ]
In 2013, the Buchwald group reported a copper-catalyzed hydroamination method for synthesizing chiral tertiary amines; similar work was disclosed by the Miura group ( Osaka University ) in the same year. [ 9 ] For about a decade, the group had published numerous papers employing ligated copper (I) hydride in 1,4-reductions of polar, conjugated systems – they postulated that their experience in performing this chemistry served as a platform for the hydroamination of alkenes shown.
In the case of activated olefins ( styrenyl -), the group observed markovnikov selectivity (presumably due to the stronger carbon-hydrogen bond formed simultaneously) and were able to render the reaction enantioselective through the utility of a chiral ligand (DTBM- SEGPHOS ). For unactivated ( aliphatic alkenes), the group observed anti-markovnikov selectivity exclusively – which, they theorize to be the result of a hydride migration from the copper catalyst to form the less sterically crowded terminal copper intermediate, where there is no electronic advantage as for styrenes to form the secondary alkyl-Cu intermediate; these reactions, at least in this initial publication, were not able to be rendered enantioselective. Notably, in subsequent publications the group has further diversified and improved this chemistry – where they’ve been able to render the aliphatic alkene reactions enantioselective, vary the electrophilic amine source, and broaden the substrate scope even further. [ 3 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ]
In 2015, the Buchwald group reported a copper-catalyzed enantioselective hydroalkylation of bromide tethered styrenyl-type olefins. [ 7 ] The synthesis of a variety of 4-, 5-, and 6-membered rings are reported – some of which are featured prominently in biologically active natural products and pharmaceuticals (substituted cyclobutanes , cyclopentanes , indanes , and saturated heterocycles ). Notably, competitive reduction of the alkyl halide by copper hydride was not observed under the optimized conditions – being a remarkable display of ligated copper (I) hydride’s chemoselectivity .
In 2020, the Buchwald group developed a copper-catalyzed enyne - nitrile coupling reaction – which, utilizes readily available building blocks to synthesize polysubstituted pyrroles . [ 15 ] Notably, this discovery stemmed from the group’s pursuit of performing intermolecular hydroacylations with hydrocuprated materials – the first examples being with ketones and aldehydes ; employing nitriles resulted in pyrrole formation. [ 3 ] While there is a pre-existing array of literature pertaining to polysubstituted pyrrole synthesis, the reported methodology allows for unique and modular retrosynthetic disconnections which differ from traditional condensation or substitution approaches to similar molecules. [ 16 ] | https://en.wikipedia.org/wiki/Hydrocupration |
In organic chemistry , hydrocyanation is a process for conversion of alkenes to nitriles . The reaction involves the addition of hydrogen cyanide and requires a catalyst if the substrate alkene is unactivated. This conversion is conducted on an industrial scale for the production of precursors to nylon. Direct hydrocyanation is rare in the laboratory because hydrogen cyanide is extremely toxic, but transfer variants can allow other nitrilic compounds to serve as hydrogen cyanide synthons .
Industrially, hydrocyanation is commonly performed on alkenes catalyzed by nickel complexes of phosphite ( P(OR) 3 ) ligands. A general reaction is shown: [ 1 ]
The reaction proceeds via oxidative addition of HCN to a low-valent metal complex to give a hydrido cyanide complex . Subsequently the alkene binds to the complex. The intermediate M(H)(CN)L n (alkene) then undergoes migratory insertion to give an alkylmetal cyanide. The cycle completes with reductive elimination of the nitrile, which is rate-limiting . Lewis acids , such as triphenylboron ( B(C 6 H 5 ) 3 ), speed elimination, increasing the overall reaction rate. [ 1 ]
Nickel-based catalysts deactivate when they formation of dicyanonickel(II) species, which are unreactive toward alkenes. The dicyanide arises via two pathways (L = phosphite): [ 1 ]
Most alkenes are prochiral , and their hydrocyanation generates chiral nitriles. Conventional hydrocyanation catalysts, e.g. Ni(P(OR) 3 ) 4 , catalyse the formation of racemic mixtures. When however the supporting ligands are chiral, the hydrocyanation can be highly enantioselective . For asymmetric hydrocyanation, popular chiral ligands are chelating aryl diphosphite complexes. [ 1 ] [ 2 ] [ 3 ]
Hydrocyanation was first reported by Arthur and Pratt in 1954, when they homogeneously catalyzed the hydrocyanation of linear alkenes. [ 4 ] The industrial process for catalytic hydrocyanation of butadiene to adiponitrile was invented by William C. Drinkard .
Carbonyls are well-known to add cyanide, in the cyanohydrin reaction ; and several variants on the Michael reaction are formal hydrocyanations. Simple conjugate addition leads to β-cyanoketones; direct addition to form a cyanohydrin sometimes induces a second addition to form β-cyano-cyanohydrins. Reaction conditions allows access to any of these products. [ 5 ]
Generally acidic conditions favor 1,2-adducts, while basic conditions favor 1,4-adducts. Additions of alkali metal cyanides , for instance, lead exclusively to 1,4-addition. [ 6 ] In contrast to alkali metal cyanides and cyanoaluminates, Lewis acidic cyanides, such as TMSCN , favor 1,2-addition. Acetylenic substrates undergo the reaction; however the scope of this reaction is limited and yields are often low. [ 5 ]
1,4-Addition to imines has been observed in a few cases, although imines are often base labile. [ 5 ]
Esters, [ 7 ] nitriles, [ 5 ] and other carbonyl derivatives also undergo conjugative hydrocyanation. When alkali metal cyanides are used, at least partial neutralization of the reaction medium is usually necessary. Neutralization can be accomplished through an acidic group on the substrate itself (internal neutralization). [ 5 ] or through the addition of an external acid (external neutralization). Acetic acid is commonly used for this purpose, in a procedure originally described by Lapworth. [ 5 ]
Conjugative hydrocyanation was used to prepare the steroidal D ring. [ 5 ] Diastereoselectivity is generally high in these addition reactions, and the resulting β-cyano carbonyl compounds can be converted to a number of steroidal products.
The most important industrial application is the nickel-catalyzed synthesis of adiponitrile ( NC−(CH 2 ) 4 −CN ) synthesis from buta-1,3-diene ( CH 2 =CH−CH=CH 2 ). Adiponitrile is a precursor to hexamethylenediamine ( H 2 N−(CH 2 ) 6 −NH 2 ), which is used for the production of certain kinds of Nylon . The DuPont ADN process to give adiponitrile is shown below:
This process consists of three steps: hydrocyanation of butadiene to a mixture of 2-methyl-butene-3-nitrile (2M3BM) and pentene-3-nitrile (3PN), an isomerization step from 2M3BM (not desired) to 3PN and a second hydrocyanation (aided by a Lewis acid cocatalyst such as aluminium trichloride or triphenylboron) to adiponitrile. [ 8 ]
Naproxen , an anti-inflammatory drug, is prepared via an asymmetric hydrocyanation of a vinylnaphthalene utilizing a phosphinite ( OPR 2 ) ligand, L . The enantioselectivity of this reaction is important because only the S enantiomer is medicinally desirable, whereas the R enantiomer produces harmful health effects. This reaction can produce the S enantiomer with >90% stereoselectivity . Upon recrystallization of the crude product, the optically pure nitrile can be obtained.
In transhydrocyanation , an equivalent of HCN is transferred from a cyanohydrin, e.g. acetone cyanohydrin , to another activated HCN acceptor. The transfer is an equilibrium process, initiated by base. The reaction can be driven by trapping or a superior acceptor, such as an aldehyde. [ 9 ]
Some hydrocyanation catalysts generate a reversible equilibrium, and can transfer HCN units between two different alkenes. [ 10 ] | https://en.wikipedia.org/wiki/Hydrocyanation |
Hydrocyclones are a type of cyclonic separators that separate product phases mainly on basis of differences in gravity with aqueous solutions as the primary feed fluid.
As opposed to dry or dust cyclones, which separate solids from gasses, hydrocyclones separate solids or different phase fluids from the bulk fluid. A hydrocyclone comprises a cylindrical shaped feed part with tangential feed; an overflow part with vortex finder; a conical part with an apex. A cyclone has no moving parts.
Product is fed into the hydrocyclone tangentially under a certain pressure. This creates a centrifugal movement, pushing the heavier phase outward and downward alongside the wall of the conical part. The decreasing diameter in the conical part increases the speed and so enhances the separation. Finally, the concentrated solids are discharged through the apex. The vortex finder in the overflow part creates a fast rotating upward spiral movement of the fluid in the centre of the conically shaped housing. The fluid is discharged through the overflow outlet.
The following parameters are decisive for good cyclone operation:
The main areas of application for hydrocyclones are: | https://en.wikipedia.org/wiki/Hydrocyclone |
Hydrodealkylation is a chemical reaction that often involves reacting an aromatic hydrocarbon , such as toluene , in the presence of hydrogen gas to form a simpler aromatic hydrocarbon devoid of functional groups . An example is the conversion of 1,2,4-trimethylbenzene to xylene . [ 1 ] This chemical process usually occurs at high temperature, at high pressure, or in the presence of a catalyst . These are predominantly transition metals , such as chromium or molybdenum .
This chemical reaction article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrodealkylation |
Hydrodefluorination ( HDF ) is a type of organic reaction in which in a substrate of a carbon–fluorine bond is replaced by a carbon–hydrogen bond . [ 1 ] [ 2 ] The topic is of some interest to scientific research. In one general strategy for the synthesis of fluorinated compounds with a specific substitution pattern, the substrate is a cheaply available perfluorinated hydrocarbon. An example is the conversion of hexafluorobenzene (C 6 F 6 ) to pentafluorobenzene (C 6 F 5 H) by certain zirconocene hydrido complexes . In this type of reaction the thermodynamic driving force is the formation of a metal-fluorine bond that can offset the cleavage of the very stable C-F bond. Other substrates that have been investigated are fluorinated alkenes .
Another reaction type is oxidative addition of a metal into a C-F bond [ 3 ] followed by a reductive elimination step in presence of a hydrogen source. For example, perfluorinated pyridine reacts with bis(cyclooctadiene)nickel(0) and triethylphosphine to the oxidative addition product and then with HCl to the ortho-hydrodefluorinated product.
In reductive hydrodefluorination the fluorocarbon is reduced in a series of single electron transfer steps through the radical anion , the radical and the anion with ultimate loss of a fluorine anion. An example is the conversion of pentafluorobenzoic acid to 3,4,5-tetrafluorobenzoic acid in a reaction of zinc dust in aqueous ammonia.
Specific systems that have been reported for fluoroalkyl group HDF are triethylsilane / carborane acid , [ 4 ] [ 5 ] and NiCl 2 (PCy 3 ) 2 / (LiAl(O-t-Bu) 3 H) [ 6 ] | https://en.wikipedia.org/wiki/Hydrodefluorination |
Hydrodemolition (also known as hydro demolition, hydroblasting, hydro blasting, hydromilling, waterblasting, and waterjetting) is a concrete removal technique which utilizes high-pressure water, often containing an abrasive material, to remove deteriorated and sound concrete as well as asphalt and grout . This process provides an excellent bonding surface for repair material and new coating applications. First developed in Europe in the 1980s, [ 1 ] this technology has become widely accepted for concrete removal and surface preparation throughout Europe and North America.
Hydrodemolition is not used as much for demolition as it is for surface restoration and protection projects. When concrete has deteriorated or the reinforcing steel has begun to corrode, it is necessary to remove any unsound concrete and reinforcing bars (rebar) in order to replace it with new concrete and maintain the integrity of the structure. This process has also been used to remove sound concrete that is not compromised in any way. This may be done to install a preventive cathodic protection system, or to remove concrete in structures in which vibration is a concern. Unlike jackhammers , hydrodemolition does not produce vibrations throughout a structure and therefore does not introduce micro fractures.
“Hydrodemolition can be used for horizontal, vertical, and overhead concrete removal and surface preparation on reinforced and non-reinforced structures. It is effective in removing concrete from around embedded metal elements such as reinforcing steel, expansion joints, anchorages, conduits, shear connectors, and shear studs. Hydrodemolition can be used for localized removals where deterioration is confined to small areas and for large area removals in preparation for a bonded overlay. This technology can also be used to remove existing coatings from concrete.”
The process of hydro scarification (a.k.a. hydroscarification or scarification) uses ultra high pressure water to remove the top surface of a concrete bridge or road surface. Usually the removal is within 1/4" to 3/4" at the most, but can be of any depth above the top layer of rebar . Removal of this type is done in order to provide a good microfracture-free surface for bonding with new, sound concrete. [ 2 ] Much like applying oil and chips to an asphalt road, this helps extend the useful life of the bridge decking and road surface by delaying the need for complete replacement.
Another application for hydro scarification is for decontamination, as for example is planned to be used in the Chernobyl New Safe Confinement for the concrete of Unit 4 of the Chernobyl Nuclear Power Plant .
Partial depth removal involves the selective removal of deteriorated concrete to a certain depth or of a concrete overlay to a depth exceeding 3/4". It is usually done in the case of concrete restoration projects where embedded objects such as rebar are substantial and need to be preserved. Hydrodemolition is ideal for concrete scarification at precision depths and preserving existing rebar for reuse. [ 3 ]
Complete removal of a concrete deck is done when it is too deteriorated to keep, but the structural concrete is adequate or can be easily repaired after the hydrodemolition has taken place. It can also be a preferred alternative where a bridge deck has been compromised during initial construction but not yet open to traffic. It allows the preservation of the reinforcement while the deck concrete can be fully replaced to meet the design intent and avoid the need for potential future repairs under traffic. Precast concrete beams are often used in structures such as bridges and parking garages. Hydrodemolition has been used successfully to remove concrete over these beams, where alternate methods such as jackhammers might have caused fracture of the beams.
This technology has been used on the following types of structures: bridge decks and substructures, parking structures , dams and spillways , water treatment facilities, tunnels and aqueducts , nuclear power plants , piers and docks, stadiums , warehouses, transfer stations, chemical plants, steel mills, and retaining walls .
Any process that is powerful enough to cut concrete can cut skin and bone. Operators of hydrodemolition equipment are required to wear protective equipment. For robotic hydrodemolition equipment, the operator wears steel-toed boots, eye protection, earmuffs and hard hat . Hand lance operators wear steel-toed boots, metatarsals, shin guards and sometimes body armor .
Hydrodemolition offers a number of environmental benefits. Hydrodemolition creates no dust pollution, reduces noise pollution, and the water used during the process can be collected after use to minimise any risk of contamination. Recently an innovative technology is available, which allows to clean and reuse the process-water after hydrodemolition. This makes in particular sense, when there is no fresh water access for feeding the high pressure pump. An Austrian company has developed the first mobile, container-based wastewater treatment device, which can be operated directly on site. [ 4 ] [ independent source needed ]
All types of surfaces can get dirty from excessive use and abuse, water and air pollution, and general exposure to the elements. These surfaces can be hydrocleaned using high pressure water or high pressure water mixed with an abrasive.
The use of high pressure and ultra high pressure water has been used to clean various coatings on concrete surfaces for the purpose of repair and reapplication. Coatings are used to protect concrete from the elements, rain, salt, and to create a friendlier surface for human use. Concrete can also be covered with carpet or tiles using a heavy duty glue or mastic. High pressure water can be used to clean these materials off when new carpet or tiles are desired.
Commercial and military airfields are required to maintain certain levels of friction on runways to prevent planes from skidding. Runway design, weather and amount of rubber remaining from tire wear all play a role in the level of friction of a landing strip. If too much rubber is present, the friction of the landing strip will be less, requiring more distance for landings, especially in wet weather. High pressure water can be used to remove rubber and restore required friction.
Cold cutting can be used to cut steel, concrete and other materials with the addition of an abrasive feed at the nozzle. Cold cutting is especially useful for cutting of pipes, vessels and tanks in areas where there is a requirement for no sparks or heat generated, such as chemical plants, oil rigs, or even residential neighborhoods, due to the lack of explosive force usually required to break concrete.
[ 5 ] | https://en.wikipedia.org/wiki/Hydrodemolition |
Hydrodenitrogenation ( HDN ) is an industrial process for the removal of nitrogen from petroleum . Organonitrogen compounds, even though they occur at low levels, are undesirable because they cause poisoning of downstream catalysts. Furthermore, upon combustion, organonitrogen compounds generate NOx , a pollutant. HDN is effected as general hydroprocessing , which traditionally focuses on hydrodesulfurization (HDS) because sulfur compounds are even more problematic. To some extent, hydrodeoxygenation (HDO) is also effected. [ 1 ]
Typical organonitrogen compounds in petroleum include quinolines and porphyrins and their derivatives. The total nitrogen content is typically less than 1% and the targeted levels are in the ppm range. As described in organic geochemistry , organonitrogen compounds are derivatives or degradation products of the compounds in the living matter that comprised the precursor to fossil fuels. In HDN, the organonitrogen compounds are treated at high temperatures with hydrogen in the presence of a catalyst , the net transformation being: [ 2 ]
The catalysts generally consist of cobalt and nickel as well as molybdenum disulfide or less often tungsten disulfide supported on alumina . The precise composition of the catalyst, i.e. Co/Ni and Mo/W ratios, are tuned for particular feedstocks. A wide variety of catalyst compositions have been considered, including metal phosphides . [ 3 ] | https://en.wikipedia.org/wiki/Hydrodenitrogenation |
Hydrodeoxygenation (HDO) is a hydrogenolysis process for removing oxygen from oxygen-containing compounds. Typical HDO catalysts commonly are sulfided nickel - molybdenum or cobalt -molybdenum on gamma alumina . An idealized reaction is: [ 1 ]
The first review on HDO was published in 1983. [ 2 ] HDO is of interest in producing biofuels , which are derived from oxygen-rich precursors like sugars or lipids. An example of a biomass refining process employing hydrodeoxygenation is the NEXBTL process.
HDO of biomass fast pyrolysis vapors under low hydrogen pressures have recently attracted a lot of attention. Bulk molybdenum trioxide (MoO3) was used as catalyst and found to completely deoxygenate cellulose, corn stover, and lignin pyrolysis vapors and produce a stream of hydrocarbons including aromatics, alkenes, and alkanes. [ 3 ] [ 4 ] From an economic viewpoint, only aromatics and alkenes should ideally be produced to enable product incorporation into the existing infrastructure. | https://en.wikipedia.org/wiki/Hydrodeoxygenation |
Hydrodesulfurization ( HDS ), also called hydrotreatment or hydrotreating , is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products , such as gasoline or petrol , jet fuel , kerosene , diesel fuel , and fuel oils . [ 1 ] [ 2 ] [ 3 ] The purpose of removing the sulfur, and creating products such as ultra-low-sulfur diesel , is to reduce the sulfur dioxide ( SO 2 ) emissions that result from using those fuels in automotive vehicles , aircraft , railroad locomotives , ships , gas or oil burning power plants , residential and industrial furnaces, and other forms of fuel combustion .
Another important reason for removing sulfur from the naphtha streams within a petroleum refinery is that sulfur, even in extremely low concentrations, poisons the noble metal catalysts ( platinum and rhenium ) in the catalytic reforming units that are subsequently used to upgrade the octane rating of the naphtha streams.
The industrial hydrodesulfurization processes include facilities for the capture and removal of the resulting hydrogen sulfide ( H 2 S ) gas. In petroleum refineries , the hydrogen sulfide gas is then subsequently converted into byproduct, sulfur (S) or sulfuric acid ( H 2 SO 4 ). In fact, the vast majority of the 64,000,000 metric tons of sulfur produced worldwide in 2005 was byproduct sulfur from refineries and other hydrocarbon processing plants. [ 4 ] [ 5 ]
An HDS unit in the petroleum refining industry is also often referred to as a hydrotreater and is the most common of the processing units found in a modern refinery. There are more than 1600 active hydrotreating units across more than 600 refineries globally with a combined capacity in excess of 400 million barrels per day (including all forms of hydrotreating but excluding hydrocracking and reforming processes). [ 6 ]
Although some reactions involving catalytic hydrogenation of organic substances were already known, the property of finely divided nickel to catalyze the fixation of hydrogen on hydrocarbon ( ethylene , benzene ) double bonds was discovered by the French chemist Paul Sabatier in 1897. [ 7 ] [ 8 ] Through this work, he found that unsaturated hydrocarbons in the vapor phase could be converted into saturated hydrocarbons by using hydrogen and a catalytic metal, laying the foundation of the modern catalytic hydrogenation process.
Soon after Sabatier's work, a German chemist, Wilhelm Normann , found that catalytic hydrogenation could be used to convert unsaturated fatty acids or glycerides in the liquid phase into saturated ones. He was awarded a patent in Germany in 1902 [ 9 ] and in Britain in 1903, [ 10 ] which was the beginning of what is now a worldwide industry.
In the mid-1950s, the first noble metal catalytic reforming process (the Platformer process ) was commercialized. At the same time, the catalytic hydrodesulfurization of the naphtha feed to such reformers was also commercialized. In the decades that followed, various proprietary catalytic hydrodesulfurization processes, such as the one depicted in the flow diagram below, have been commercialized. Currently, virtually all of the petroleum refineries worldwide have one or more HDS units.
By 2006, miniature microfluidic HDS units had been implemented for treating JP-8 jet fuel to produce clean feed stock for a fuel cell hydrogen reformer . [ 11 ] By 2007, this had been integrated into an operating 5 kW fuel cell generation system. [ 12 ]
Hydrogenation is a class of chemical reactions in which the net result is the addition of hydrogen (H). Hydrogenolysis is a type of hydrogenation and results in the cleavage of the C-X chemical bond , where C is a carbon atom and X is a sulfur (S), nitrogen (N) or oxygen (O) atom. The net result of a hydrogenolysis reaction is the formation of C-H and H-X chemical bonds. Thus, hydrodesulfurization is a hydrogenolysis reaction. Using ethanethiol ( C 2 H 5 SH ), a sulfur compound present in some petroleum products, as an example, the hydrodesulfurization reaction can be simply expressed as
For the mechanistic aspects of, and the catalysts used in this reaction see the section catalysts and mechanisms .
In an industrial hydrodesulfurization unit, such as in a refinery, the hydrodesulfurization reaction takes place in a fixed-bed reactor at elevated temperatures ranging from 300 to 400 °C and elevated pressures ranging from 30 to 130 atmospheres of absolute pressure, typically in the presence of a catalyst consisting of an alumina base impregnated with cobalt and molybdenum (usually called a CoMo catalyst). Occasionally, a combination of nickel and molybdenum (called NiMo) is used, in addition to the CoMo catalyst, for specific difficult-to-treat feed stocks, such as those containing a high level of chemically bound nitrogen.
The image below is a schematic depiction of the equipment and the process flow streams in a typical refinery HDS unit.
The liquid feed (at the bottom left in the diagram) is pumped up to the required elevated pressure and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid-gas mixture is preheated by flowing through a heat exchanger . The preheated feed then flows through a fired heater where the feed mixture is totally vaporized and heated to the required elevated temperature before entering the reactor and flowing through a fixed-bed of catalyst where the hydrodesulfurization reaction takes place.
The hot reaction products are partially cooled by flowing through the heat exchanger where the reactor feed was preheated and then flows through a water-cooled heat exchanger before it flows through the pressure controller (PC) and undergoes a pressure reduction down to about 3 to 5 atmospheres. The resulting mixture of liquid and gas enters the gas separator pressure vessel at about 35 °C and 3 to 5 atmospheres of absolute pressure.
Most of the hydrogen-rich gas from the gas separator vessel is recycle gas, which is routed through an amine contactor for removal of the reaction product H 2 S that it contains. The H 2 S -free hydrogen-rich gas is then recycled back for reuse in the reactor section. Any excess gas from the gas separator vessel joins the sour gas from the stripping of the reaction product liquid.
The liquid from the gas separator vessel is routed through a reboiled stripper distillation tower. The bottoms product from the stripper is the final desulfurized liquid product from hydrodesulfurization unit.
The overhead sour gas from the stripper contains hydrogen, methane , ethane , hydrogen sulfide , propane , and, perhaps, some butane and heavier components. That sour gas is sent to the refinery's central gas processing plant for removal of the hydrogen sulfide in the refinery's main amine gas treating unit and through a series of distillation towers for recovery of propane, butane and pentane or heavier components. The residual hydrogen, methane, ethane, and some propane is used as refinery fuel gas. The hydrogen sulfide removed and recovered by the amine gas treating unit is subsequently converted to elemental sulfur in a Claus process unit or to sulfuric acid in a wet sulfuric acid process or in the conventional Contact Process .
Note that the above description assumes that the HDS unit feed contains no olefins . If the feed does contain olefins (for example, the feed is a naphtha derived from a refinery fluid catalytic cracker (FCC) unit), then the overhead gas from the HDS stripper may also contain some ethene , propene , butenes and pentenes , or heavier components.
The amine solution to and from the recycle gas contactor comes from and is returned to the refinery's main amine gas treating unit.
The refinery HDS feedstocks (naphtha, kerosene, diesel oil, and heavier oils) contain a wide range of organic sulfur compounds, including thiols , thiophenes , organic sulfides and disulfides , and many others. These organic sulfur compounds are products of the degradation of sulfur containing biological components, present during the natural formation of the fossil fuel , petroleum crude oil.
When the HDS process is used to desulfurize a refinery naphtha, it is necessary to remove the total sulfur down to the parts per million range or lower in order to prevent poisoning the noble metal catalysts in the subsequent catalytic reforming of the naphthas.
When the process is used for desulfurizing diesel oils, the latest environmental regulations in the United States and Europe, requiring what is referred to as ultra-low-sulfur diesel (ULSD), in turn requires that very deep hydrodesulfurization is needed. In the very early 2000s, the governmental regulatory limits for highway vehicle diesel was within the range of 300 to 500 ppm by weight of total sulfur. As of 2006, the total sulfur limit for highway diesel is in the range of 15 to 30 ppm by weight. [ 13 ]
A family of substrates that are particularly common in petroleum are the aromatic sulfur-containing heterocycles called thiophenes . Many kinds of thiophenes occur in petroleum ranging from thiophene itself to more condensed derivatives, benzothiophenes and dibenzothiophenes . Thiophene itself and its alkyl derivatives are easier to hydrogenolyse, whereas dibenzothiophene, especially 4,6-dimethyldibenzothiophene is considered the most challenging substrates. Benzothiophenes are midway between the simple thiophenes and dibenzothiophenes in their susceptibility to HDS.
The main HDS catalysts are based on molybdenum disulfide ( MoS 2 ) together with smaller amounts of other metals. [ 14 ] The nature of the sites of catalytic activity remains an active area of investigation, but it is generally assumed basal planes of the MoS 2 structure are not relevant to catalysis, rather the edges or rims of these sheet. [ 15 ] At the edges of the MoS 2 crystallites, the molybdenum centre can stabilize a coordinatively unsaturated site (CUS), also known as an anion vacancy. Substrates, such as thiophene, bind to this site and undergo a series of reactions that result in both C-S scission and C=C hydrogenation. Thus, the hydrogen serves multiple roles—generation of anion vacancy by removal of sulfide, hydrogenation, and hydrogenolysis. A simplified diagram for the cycle is shown:
Most metals catalyse HDS, but it is those at the middle of the transition metal series that are most active. Although not practical, ruthenium disulfide appears to be the single most active catalyst, but binary combinations of cobalt and molybdenum are also highly active. [ 16 ] Aside from the basic cobalt-modified MoS 2 catalyst, nickel and tungsten are also used, depending on the nature of the feed. For example, Ni-W catalysts are more effective for hydrodenitrogenation . [ 17 ]
Metal sulfides are supported on materials with high surface areas. A typical support for HDS catalyst is γ- alumina . The support allows the more expensive catalyst to be more widely distributed, giving rise to a larger fraction of the MoS 2 that is catalytically active. The interaction between the support and the catalyst is an area of intense interest, since the support is often not fully inert but participates in the catalysis.
The basic hydrogenolysis reaction has a number of uses other than hydrodesulfurization.
The hydrogenolysis reaction is also used to reduce the nitrogen content of a petroleum stream in a process referred to as hydrodenitrogenation (HDN). The process flow is the same as that for an HDS unit.
Using pyridine ( C 5 H 5 N ), a nitrogen compound present in some petroleum fractionation products, as an example, the hydrodenitrogenation reaction has been postulated as occurring in three steps: [ 18 ] [ 19 ]
and the overall reaction may be simply expressed as:
Many HDS units for desulfurizing naphthas within petroleum refineries are actually simultaneously denitrogenating to some extent as well.
The hydrogenolysis reaction may also be used to saturate or convert alkenes into alkanes . The process used is the same as for an HDS unit.
As an example, the saturation of the olefin pentene can be simply expressed as:
Some hydrogenolysis units within a petroleum refinery or a petrochemical plant may be used solely for the saturation of olefins or they may be used for simultaneously desulfurizing as well as denitrogenating and saturating olefins to some extent. | https://en.wikipedia.org/wiki/Hydrodesulfurization |
Hydrodimerization is an organic reaction that couples two alkenes to give a symmetrical hydrocarbon. The reaction is often implemented electrochemically ; in that case the reaction is called electrodimerization . The reaction can also be induced with samarium diiodide , a one-electron reductant .
Hydrodimerization is the basis of the Monsanto adiponitrile synthesis : [ 1 ]
The reaction applies to a number electrophilic alkenes ( Michael acceptors ). [ 2 ] [ 3 ]
This electrochemistry -related article is a stub . You can help Wikipedia by expanding it .
This chemical process -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrodimerization |
Hydrodynamic Delivery (HD) is a method of DNA insertion in rodent models. Genes are delivered via injection into the bloodstream of the animal, and are expressed in the liver. This protocol is helpful to determine gene function, regulate gene expression, and develop pharmaceuticals in vivo. [ 1 ]
Hydrodynamic Delivery was developed as a way to insert genes without viral infection ( transfection ). The procedure requires a high-volume DNA solution to be inserted into the veins of the rodent using a high-pressure needle. [ 2 ] The volume of the DNA is typically 8-10% equal to 8-10% of the animal's body weight, and is injected within 5-7 seconds. [ 3 ] [ 4 ] The pressure of the insertion leads to cardiac congestion (increased pressure in the heart), allowing the DNA solution to flow through the bloodstream and accumulate in the liver. [ 2 ] The pressure expands the pores in the cell membrane, forcing the DNA molecules into the parenchyma , or the functional cells of the organ. [ 1 ] [ 5 ] [ 2 ] [ 4 ] In the liver, these cells are the hepatocytes . In less than two minutes after the injection, the pressure returns to natural levels, and the pores shrink back, trapping the DNA inside of the cell. After injection, the majority of genes are expressed in the liver of the animal over a long period of time. [ 6 ] [ 3 ]
Originally developed to insert DNA, further developments in HD have enabled the insertion of RNA, proteins, and short oligonucleotides into cells. [ 6 ]
The development of Hydrodynamic Delivery methods allows an alternative way to study in vivo experiments. This method has shown to be effective in small mammals, without the potential risks and complications of viral transfection. [ 7 ] Applications of these studies include: testing regulatory elements, generating antibodies, analyzing gene therapy techniques, and developing models for diseases. [ 8 ] Typically, genes are expressed in the liver, but the procedure can be altered to express genes in kidneys, lungs, muscles, heart, and pancreas. [ 2 ]
Hydrodynamic Delivery has been used to insert genes in an effort to combat genetic diseases. Since HD has mainly focused on small mammals such as rodents, its application in humans is limited. Ongoing research is increasing applications in large mammals and future clinical studies. Computer-assisted image-guided techniques allow surgeons to insert the needle or catheter in the precise site, while an automated injection device monitors and adjusts the pressure needed for optimal gene transmission.. [ 9 ] With more precise injections, the volume of DNA solution can be reduced to about 1% of the organism's body weight [ 3 ]
By using a catheter to conduct the injection, surgeons are able to express genes in organs other than the liver. Placing the catheter in alternate locations allows the DNA solution to reach the target, although genes are still expressed in the liver. [ 3 ]
Hydrodynamic DNA delivery is a useful tool for creating model systems for human disease. Using this technique, laboratories are able to study genetic diseases in vivo. Studies are able to insert oncogenes into lab animals to study treatments. [ 4 ] [ 10 ] In addition to gene transfer, HD has also been shown to work in tumor cells. [ 3 ] Metastatic cancer cells can be successfully delivered in model organisms in order to study specific cancers. [ 3 ] [ 4 ]
Alternative methods can be used to insert genes into an organism without a viral vector. These can be split into physical and chemical techniques. [ 2 ] [ 7 ]
Physical methods:
Chemical methods: | https://en.wikipedia.org/wiki/Hydrodynamic_delivery |
In microbiology , hydrodynamic focusing is a technique used to provide more accurate results when using flow cytometers or Coulter counters for determining the size of bacteria or cells . [ 1 ]
Cells are counted as they are forced to pass through a small channel (often referred to as a flow cell), causing disruptions in a laser light beam or electricity flow. These disruptions are analyzed by the instruments. It is difficult to create tunnels narrow enough for this purpose using ordinary manufacturing processes, as the diameter must be in the magnitude of micrometers, and the length of the tunnel should exceed several millimeters. The standard channel size used in most production flow cytometers is 250 by 250 micrometers.
Hydrodynamic focusing solves this problem by building up the walls of the tunnel from fluid, using the effects of fluid dynamics . A wide (hundreds of micrometers in diameter) tube made of glass or plastic is used, through which a "wall" of fluid called the sheath flow is pumped. The sample is injected into the middle of the sheath flow. If the two fluids differ enough in their velocity or density, they do not mix: they form a two-layer stable flow. [ 2 ]
This microbiology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrodynamic_focusing |
The hydrodynamic radius of a macromolecule or colloid particle is R h y d {\displaystyle R_{\rm {hyd}}} . The macromolecule or colloid particle is a collection of N {\displaystyle N} subparticles. This is done most commonly for polymers ; the subparticles would then be the units of the polymer. For polymers in solution, R h y d {\displaystyle R_{\rm {hyd}}} is defined by
where r i j {\displaystyle r_{ij}} is the distance between subparticles i {\displaystyle i} and j {\displaystyle j} , and where the angular brackets ⟨ … ⟩ {\displaystyle \langle \ldots \rangle } represent an ensemble average . [ 1 ] The theoretical hydrodynamic radius R h y d {\displaystyle R_{\rm {hyd}}} was originally an estimate by John Gamble Kirkwood of the Stokes radius of a polymer, and some sources still use hydrodynamic radius as a synonym for the Stokes radius.
Note that in biophysics , hydrodynamic radius refers to the Stokes radius, [ 2 ] or commonly to the apparent Stokes radius obtained from size exclusion chromatography . [ 3 ]
The theoretical hydrodynamic radius R h y d {\displaystyle R_{\rm {hyd}}} arises in the study of the dynamic properties of polymers moving in a solvent . It is often similar in magnitude to the radius of gyration . [ 4 ]
The mobility of non-spherical aerosol particles can be described by the hydrodynamic radius. In the continuum limit , where the mean free path of the particle is negligible compared to a characteristic length scale of the particle, the hydrodynamic radius is defined as the radius that gives the same magnitude of the frictional force, F d {\textstyle {\boldsymbol {F}}_{d}} as that of a sphere with that radius, i.e.
where μ {\textstyle \mu } is the viscosity of the surrounding fluid, and v {\textstyle {\boldsymbol {v}}} is the velocity of the particle. This is analogous to the Stokes' radius, however this is untrue as the mean free path becomes comparable to the characteristic length scale of the particulate - a correction factor is introduced such that the friction is correct over the entire Knudsen regime . As is often the case, [ 5 ] the Cunningham correction factor C {\textstyle C} is used, where:
where α , β , and γ {\textstyle \alpha ,\beta ,{\text{ and }}\gamma } were found by Millikan [ 6 ] to be: 1.234, 0.414, and 0.876 respectively. | https://en.wikipedia.org/wiki/Hydrodynamic_radius |
In civil engineering (specifically hydraulic engineering ), a hydrodynamic separator ( HDS ), also called a swirl separator, is a stormwater management device that uses cyclonic separation to control water pollution . They are designed as flow-through structures with a settling or separation unit to remove sediment and other pollutants. HDS are considered structural best management practices (BMPs), and are used to treat and pre-treat stormwater runoff , and are particularly suitable for highly impervious sites, such as roads, highways and parking lots. [ 1 ]
HDS systems use the physics of flowing water to remove a variety of pollutants and are characterized by an internal structure that either creates a swirling vortex or plunges the water into the main sump. [ 2 ] : 1 Along with supplemental features to reduce velocity, an HDS system is designed to separate floatables (trash, debris and oil) and settleable particles, like sediment, from stormwater. HDS systems are not effective for the removal of very fine solids or dissolved pollutants. [ 1 ] The systems are also subject to scour and sediment washout during large storm events, e.g. a 10-year storm . [ 2 ] : 42
A number of factors are relevant in selecting a hydrodynamic separator product for a site.
HDS systems should be sized based on treatment objectives including desired level of pollutant removal, drainage basin characteristics, climate of the region, and particle size to be targeted. Performance is also sensitive to water temperature, i.e. season. [ clarification needed ] Care must be taken to avoid routing excess flow through the device and compromising performance. Each vendor’s product has different pollutant removal rates that should be evaluated before selecting the system. [ 1 ]
The Technology Assessment Protocol-Ecology (TAPE) and Technology Acceptance and Reciprocity Partnership (TARP) are evaluation programs sponsored by several state agencies in the U.S. These programs include lab and field testing and provide specific sizing criteria for hydrodynamic separation systems. [ 3 ] [ 4 ] [ 5 ]
Currently, [ when? ] the Environmental & Water Resources Institute (a component of the American Society of Civil Engineers ) and ASTM International are developing comprehensive verification guidelines and standard test methods for assessing the performance of these devices. [ citation needed ]
HDS systems are not maintenance-intensive, when compared with land-based BMPs. Each manufactured system has a slightly different design, therefore maintenance and inspection requirements should be looked at closely when purchasing an HDS system. Vacuum trucks are typically used for maintenance, so unobstructed access to accumulated pollutants for removal is critical. [ 1 ]
Costs for HDS systems depend on site-specific conditions such as land characteristics, amount of runoff to be treated, system depth and performance requirements. Various brands of HDS systems differ in their treatment performance, and basing a decision solely on the installation and operating cost of a system may compromise system performance and the environment. Long-term maintenance costs should also be considered with overall costs when purchasing or selecting a stormwater BMP as initial installation and operating costs may not reflect the long-term investment needed to maintain the system. [ 1 ]
According to the U.S. Environmental Protection Agency (EPA), " Catch basin inserts may be more suitable when available land is limited, such as in urbanized areas. Swirl separators tend to need more space than catch basin inserts but can still function when space is limited." [ 1 ]
As stormwater regulations become increasingly stringent, many states and municipalities have developed criteria to govern the use and sizing of HDS systems, and publish lists that identify acceptable HDS systems. [ 6 ] Other jurisdictions evaluate the applicability of HDS on a site-specific basis. [ 7 ] It is increasingly common to use HDS as the first component of a treatment train, a combination of BMPs in series, to remove coarse solids and floatable pollutants that can rapidly clog other BMPs thus prolonging their maintenance cycle. | https://en.wikipedia.org/wiki/Hydrodynamic_separator |
In fluid dynamics , hydrodynamic stability is the field which analyses the stability and the onset of instability of fluid flows. The study of hydrodynamic stability aims to find out if a given flow is stable or unstable, and if so, how these instabilities will cause the development of turbulence . [ 1 ] The foundations of hydrodynamic stability, both theoretical and experimental, were laid most notably by Helmholtz , Kelvin , Rayleigh and Reynolds during the nineteenth century. [ 1 ] These foundations have given many useful tools to study hydrodynamic stability. These include Reynolds number , the Euler equations , and the Navier–Stokes equations . When studying flow stability it is useful to understand more simplistic systems, e.g. incompressible and inviscid fluids which can then be developed further onto more complex flows. [ 1 ] Since the 1980s, more computational methods are being used to model and analyse the more complex flows.
To distinguish between the different states of fluid flow one must consider how the fluid reacts to a disturbance in the initial state. [ 2 ] These disturbances will relate to the initial properties of the system, such as velocity , pressure , and density . James Clerk Maxwell expressed the qualitative concept of stable and unstable flow nicely when he said: [ 1 ]
"when an infinitely small variation of the present state will alter only by an infinitely small quantity the state at some future time, the condition of the system, whether at rest or in motion, is said to be stable but when an infinitely small variation in the present state may bring about a finite difference in the state of the system in a finite time, the system is said to be unstable."
That means that for a stable flow, any infinitely small variation, which is considered a disturbance, will not have any noticeable effect on the initial state of the system and will eventually die down in time. [ 2 ] For a fluid flow to be considered stable it must be stable with respect to every possible disturbance. This implies that there exists no mode of disturbance for which it is unstable. [ 1 ]
On the other hand, for an unstable flow, any variations will have some noticeable effect on the state of the system which would then cause the disturbance to grow in amplitude in such a way that the system progressively departs from the initial state and never returns to it. [ 2 ] This means that there is at least one mode of disturbance with respect to which the flow is unstable, and the disturbance will therefore distort the existing force equilibrium. [ 3 ]
A key tool used to determine the stability of a flow is the Reynolds number (Re), first put forward by George Gabriel Stokes at the start of the 1850s. Associated with Osborne Reynolds who further developed the idea in the early 1880s, this dimensionless number gives the ratio of inertial terms and viscous terms. [ 4 ] In a physical sense, this number is a ratio of the forces which are due to the momentum of the fluid (inertial terms), and the forces which arise from the relative motion of the different layers of a flowing fluid (viscous terms). The equation for this is [ 2 ] R e = inertial viscous = ρ u 2 μ u L = ρ u L μ = u L ν {\displaystyle R_{e}={\frac {\text{inertial}}{\text{viscous}}}={\frac {\rho u^{2}}{\frac {\mu u}{L}}}={\frac {\rho uL}{\mu }}={\frac {uL}{\nu }}} where
The Reynolds number is useful because it can provide cut off points for when flow is stable or unstable, namely the Critical Reynolds number R c {\displaystyle R_{c}} . As it increases, the amplitude of a disturbance which could then lead to instability gets smaller. [ 1 ] At high Reynolds numbers it is agreed that fluid flows will be unstable. High Reynolds number can be achieved in several ways, e.g. if μ {\displaystyle \mu } is a small value or if ρ {\displaystyle \rho } and u {\displaystyle {\text{u}}} are high values. [ 2 ] This means that instabilities will arise almost immediately and the flow will become unstable or turbulent. [ 1 ]
In order to analytically find the stability of fluid flows, it is useful to note that hydrodynamic stability has a lot in common with stability in other fields, such as magnetohydrodynamics , plasma physics and elasticity ; although the physics is different in each case, the mathematics and the techniques used are similar. The essential problem is modeled by nonlinear partial differential equations and the stability of known steady and unsteady solutions are examined. [ 1 ] The governing equations for almost all hydrodynamic stability problems are the Navier–Stokes equation and the continuity equation . The Navier–Stokes equation is given by: [ 1 ] ∂ u ∂ t + ( u ⋅ ∇ ) u − ν ∇ 2 u = − ∇ p 0 + b , {\displaystyle {\frac {\partial \mathbf {u} }{\partial t}}+(\mathbf {u} \cdot \nabla )\mathbf {u} -\nu \,\nabla ^{2}\mathbf {u} =-\nabla p_{0}+\mathbf {b} ,}
where
Here ∇ {\displaystyle \nabla } is being used as an operator acting on the velocity field on the left hand side of the equation and then acting on the pressure on the right hand side.
and the continuity equation is given by: D ρ D t + ρ ∇ ⋅ u = 0 {\displaystyle {\frac {D\mathbf {\rho } }{Dt}}+\rho \,\nabla \cdot \mathbf {u} =0} where D ρ D t {\displaystyle {\frac {D\mathbf {\rho } }{Dt}}} is the material derivative of the density.
Once again ∇ {\displaystyle \nabla } is being used as an operator on u {\displaystyle \mathbf {u} } and is calculating the divergence of the velocity.
But if the fluid being considered is incompressible , which means the density is constant, then D ρ D t = 0 {\displaystyle {\frac {D{\boldsymbol {\rho }}}{Dt}}=0} and hence: ∇ ⋅ u = 0 {\displaystyle \nabla \cdot \mathbf {u} =0}
The assumption that a flow is incompressible is a good one and applies to most fluids travelling at most speeds. It is assumptions of this form that will help to simplify the Navier–Stokes equation into differential equations, like Euler's equation, which are easier to work with.
If one considers a flow which is inviscid, this is where the viscous forces are small and can therefore be neglected in the calculations, then one arrives at Euler's equations : ∂ u ∂ t + ( u ⋅ ∇ ) u = − ∇ p 0 {\displaystyle {\frac {\partial \mathbf {u} }{\partial t}}+(\mathbf {u} \cdot \nabla )\mathbf {u} =-\nabla p_{0}}
Although in this case we have assumed an inviscid fluid this assumption does not hold for flows where there is a boundary. The presence of a boundary causes some viscosity at the boundary layer which cannot be neglected and one arrives back at the Navier–Stokes equation. Finding the solutions to these governing equations under different circumstances and determining their stability is the fundamental principle in determining the stability of the fluid flow itself.
To determine whether the flow is stable or unstable, one often employs the method of linear stability analysis. In this type of analysis, the governing equations and boundary conditions are linearized. This is based on the fact that the concept of 'stable' or 'unstable' is based on an infinitely small disturbance. For such disturbances, it is reasonable to assume that disturbances of different wavelengths evolve independently. (A nonlinear governing equation will allow disturbances of different wavelengths to interact with each other.)
Bifurcation theory is a useful way to study the stability of a given flow, with the changes that occur in the structure of a given system. Hydrodynamic stability is a series of differential equations and their solutions. A bifurcation occurs when a small change in the parameters of the system causes a qualitative change in its behavior,. [ 1 ] The parameter that is being changed in the case of hydrodynamic stability is the Reynolds number. It can be shown that the occurrence of bifurcations falls in line with the occurrence of instabilities. [ 1 ]
Laboratory experiments are a very useful way of gaining information about a given flow without having to use more complex mathematical techniques. Sometimes physically seeing the change in the flow over time is just as useful as a numerical approach and any findings from these experiments can be related back to the underlying theory. Experimental analysis is also useful because it allows one to vary the governing parameters very easily and their effects will be visible.
When dealing with more complicated mathematical theories such as Bifurcation theory and Weakly nonlinear theory, numerically solving such problems becomes very difficult and time-consuming but with the help of computers this process becomes much easier and quicker. Since the 1980s computational analysis has become more and more useful, the improvement of algorithms which can solve the governing equations, such as the Navier–Stokes equation, means that they can be integrated more accurately for various types of flow.
The Kelvin–Helmholtz instability (KHI) is an application of hydrodynamic stability that can be seen in nature. It occurs when there are two fluids flowing at different velocities. The difference in velocity of the fluids causes a shear velocity at the interface of the two layers. [ 3 ] The shear velocity of one fluid moving induces a shear stress on the other which, if greater than the restraining surface tension , then results in an instability along the interface between them. [ 3 ] This motion causes the appearance of a series of overturning ocean waves, a characteristic of the Kelvin–Helmholtz instability. Indeed, the apparent ocean wave-like nature is an example of vortex formation, which are formed when a fluid is rotating about some axis, and is often associated with this phenomenon.
The Kelvin–Helmholtz instability can be seen in the bands in planetary atmospheres such as Saturn and Jupiter , for example in the giant red spot vortex. In the atmosphere surrounding the giant red spot there is the biggest example of KHI that is known of and is caused by the shear force at the interface of the different layers of Jupiter's atmosphere. There have been many images captured where the ocean-wave like characteristics discussed earlier can be seen clearly, with as many as 4 shear layers visible. [ 5 ]
Weather satellites take advantage of this instability to measure wind speeds over large bodies of water. Waves are generated by the wind, which shears the water at the interface between it and the surrounding air. The computers on board the satellites determine the roughness of the ocean by measuring the wave height. This is done by using radar , where a radio signal is transmitted to the surface and the delay from the reflected signal is recorded, known as the "time of flight". From this meteorologists are able to understand the movement of clouds and the expected air turbulence near them.
The Rayleigh–Taylor instability is another application of hydrodynamic stability and also occurs between two fluids but this time the densities of the fluids are different. [ 6 ] Due to the difference in densities, the two fluids will try to reduce their combined potential energy . [ 7 ] The less dense fluid will do this by trying to force its way upwards, and the more dense fluid will try to force its way downwards. [ 6 ] Therefore, there are two possibilities: if the lighter fluid is on top the interface is said to be stable, but if the heavier fluid is on top, then the equilibrium of the system is unstable to any disturbances of the interface. If this is the case then both fluids will begin to mix. [ 6 ] Once a small amount of heavier fluid is displaced downwards with an equal volume of lighter fluid upwards, the potential energy is now lower than the initial state, [ 7 ] therefore the disturbance will grow and lead to the turbulent flow associated with Rayleigh–Taylor instabilities. [ 6 ]
This phenomenon can be seen in interstellar gas , such as the Crab Nebula . It is pushed out of the Galactic plane by magnetic fields and cosmic rays and then becomes Rayleigh–Taylor unstable if it is pushed past its normal scale height . [ 6 ] This instability also explains the mushroom cloud which forms in processes such as volcanic eruptions and atomic bombs.
Rayleigh–Taylor instability has a big effect on the Earth's climate. Winds that come from the coast of Greenland and Iceland cause evaporation of the ocean surface over which they pass, increasing the salinity of the ocean water near the surface, and making the water near the surface denser. This then generates plumes which drive the ocean currents . This process acts as a heat pump, transporting warm equatorial water North. Without the ocean overturning, Northern Europe would likely face drastic drops in temperature. [ 6 ]
The presence of colloid particles (typically with size in the range between 1 nanometer and 1 micron), uniformly dispersed in a binary liquid mixtures, is able to drive a convective hydrodynamic instability even though the system is initially in a condition of stable gravitational equilibrium (hence opposite to the Rayleigh-Taylor instability discussed above).
If a liquid contains a heavier molecular solute the concentration of which diminishes with the height, the system is gravitationally stable. Indeed, if a portion of fluid moves upwards due to a spontaneous fluctuation, it will end up being surrounded by less dense fluid and hence will be pushed back downwards. This mechanism thus inhibits convective motions. It has been shown, however, that this mechanism breaks down if the binary mixture contains uniformly dispersed colloidal particles. In that case, convective motions arise even if the system is gravitationally stable. [ 8 ] The key phenomenon to understand this instability is diffusiophoresis : in order to minimize the interfacial energy between colloidal particle and liquid solution, the gradient of molecular solute determines an internal migration of colloids which brings them upwards, thus depleting them at the bottom. In order words, since the colloids are slightly denser than the liquid mixture, this leads to a local increase of density with height. This instability, even in the absence of a thermal gradient, causes convective motions similar to those observed when a liquid is heated up from the bottom (known as Rayleigh-Bénard convection ), where the upward migration is due to thermal dilation, and leads to pattern formation . [ 8 ] This instability explains how animals get their intricate and distinctive patterns such as colorful stripes of tropical fish. [ 9 ] | https://en.wikipedia.org/wiki/Hydrodynamic_stability |
In fluid dynamics , helicity is, under appropriate conditions, an invariant of the Euler equations of fluid flow, having a topological interpretation as a measure of linkage and/or knottedness of vortex lines in the flow. This was first proved by Jean-Jacques Moreau in 1961 [ 1 ] and Moffatt derived it in 1969 without the knowledge of Moreau 's paper. This helicity invariant is an extension of Woltjer's theorem for magnetic helicity .
Let u ( x , t ) {\displaystyle \mathbf {u} (x,t)} be the velocity field and ∇ × u {\displaystyle \nabla \times \mathbf {u} } the corresponding vorticity field. Under the following three conditions, the vortex lines are transported with (or 'frozen in') the flow: (i) the fluid is inviscid ; (ii) either the flow is incompressible ( ∇ ⋅ u = 0 {\displaystyle \nabla \cdot \mathbf {u} =0} ), or it is compressible with a barotropic relation p = p ( ρ ) {\displaystyle p=p(\rho )} between pressure p and density ρ ; and (iii) any body forces acting on the fluid are conservative . Under these conditions, any closed surface S whose normal vectors are orthogonal to the vorticity (that is, n ⋅ ( ∇ × u ) = 0 {\displaystyle \mathbf {n} \cdot (\nabla \times \mathbf {u} )=0} ) is, like vorticity, transported with the flow.
Let V be the volume inside such a surface. Then the helicity in V , denoted H , is defined by the volume integral
For a localised vorticity distribution in an unbounded fluid, V can be taken to be the whole space, and H is then the total helicity of the flow. H is invariant precisely because the vortex lines are frozen in the flow and their linkage and/or knottedness is therefore conserved, as recognized by Lord Kelvin (1868). Helicity is a pseudo-scalar quantity: it changes sign under change from a right-handed to a left-handed frame of reference; it can be considered as a measure of the handedness (or chirality ) of the flow. Helicity is one of the four known integral invariants of the Euler equations; the other three are energy , momentum and angular momentum .
For two linked unknotted vortex tubes having circulations κ 1 {\displaystyle \kappa _{1}} and κ 2 {\displaystyle \kappa _{2}} , and no internal twist, the helicity is given by H = ± 2 n κ 1 κ 2 {\displaystyle H=\pm 2n\kappa _{1}\kappa _{2}} , where n is the Gauss linking number of the two tubes, and the plus or minus is chosen according as the linkage is right- or left-handed.
For a single knotted vortex tube with circulation κ {\displaystyle \kappa } , then, as shown by Moffatt & Ricca (1992), the helicity is given by H = κ 2 ( W r + T w ) {\displaystyle H=\kappa ^{2}(Wr+Tw)} , where W r {\displaystyle Wr} and T w {\displaystyle Tw} are the writhe and twist of the tube; the sum W r + T w {\displaystyle Wr+Tw} is known to be invariant under continuous deformation of the tube.
The invariance of helicity provides an essential cornerstone of the subject topological fluid dynamics and magnetohydrodynamics , which is concerned with global properties of flows and their topological characteristics.
In meteorology , [ 2 ] helicity corresponds to the transfer of vorticity from the environment to an air parcel in convective motion. Here the definition of helicity is simplified to only use the horizontal component of wind and vorticity , and to only integrate in the vertical direction, replacing the volume integral with a one-dimensional definite integral or line integral :
where
According to this formula, if the horizontal wind does not change direction with altitude , H will be zero as V h {\displaystyle V_{h}} and ∇ × V h {\displaystyle \nabla \times V_{h}} are perpendicular , making their scalar product nil. H is then positive if the wind veers (turns clockwise ) with altitude and negative if it backs (turns counterclockwise ). This helicity used in meteorology has energy units per units of mass [m 2 /s 2 ] and thus is interpreted as a measure of energy transfer by the wind shear with altitude, including directional.
This notion is used to predict the possibility of tornadic development in a thundercloud . In this case, the vertical integration will be limited below cloud tops (generally 3 km or 10,000 feet) and the horizontal wind will be calculated to wind relative to the storm in subtracting its motion:
where C → {\displaystyle {\vec {C}}} is the cloud motion relative to the ground.
Critical values of SRH ( S torm R elative H elicity) for tornadic development, as researched in North America , [ 3 ] are:
Helicity in itself is not the only component of severe thunderstorms , and these values are to be taken with caution. [ 4 ] That is why the Energy Helicity Index ( EHI ) has been created. It is the result of SRH multiplied by the CAPE ( Convective Available Potential Energy ) and then divided by a threshold CAPE:
This incorporates not only the helicity but the energy of the air parcel and thus tries to eliminate weak potential for thunderstorms even in strong SRH regions. The critical values of EHI: | https://en.wikipedia.org/wiki/Hydrodynamical_helicity |
In fluid dynamics and elasticity , hydroelasticity or flexible fluid-structure interaction (FSI), is a branch of science which is concerned with the motion of deformable bodies through liquids . The theory of hydroelasticity has been adapted from aeroelasticity , to describe the effect of structural response of the body on the fluid around it.
It is the analysis of the time-dependent interaction of hydrodynamic and elastic structural forces. Vibration of floating and submerged ocean structures/vessels encompasses this field of naval architecture .
Hydroelasticity is of concern in various areas of marine technology such as:
Analysis and design of marine structures or systems necessitates integration of hydrodynamics and structural mechanics; i.e. hydroelasticity plays the key role. There has been significant recent progress in research into the hydroelastic phenomena, and the topic of hydroelasticity is of considerable current interest. | https://en.wikipedia.org/wiki/Hydroelasticity |
Hydroextractors are machines which are used in the textile processing industry. These are mainly centrifuges . The wet material is placed in the extractor, which has a wall of perforated metal , generally stainless steel . The internal drum rotates at high speed, thus throwing out the water contained in it. The use of the hydroextractor significantly reduces the energy required to dry any material. Hydroextractors usually work on centrifugal force creating a high gravitational force, enhancing water extraction. Hence the water is separated and the product is obtained in a dry form.
This article about textiles is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydroextractor |
In organic chemistry , hydroformylation , also known as oxo synthesis or oxo process , is an industrial process for the production of aldehydes ( R−CH=O ) from alkenes ( R 2 C=CR 2 ). [ 1 ] [ 2 ] This chemical reaction entails the net addition of a formyl group ( −CHO ) and a hydrogen atom to a carbon-carbon double bond . This process has undergone continuous growth since its invention: production capacity reached 6.6 × 10 6 tons in 1995. It is important because aldehydes are easily converted into many secondary products. For example, the resultant aldehydes are hydrogenated to alcohols that are converted to detergents . Hydroformylation is also used in speciality chemicals , relevant to the organic synthesis of fragrances and pharmaceuticals . The development of hydroformylation is one of the premier achievements of 20th-century industrial chemistry .
The process entails treatment of an alkene typically with high pressures (between 10 and 100 atmospheres ) of carbon monoxide and hydrogen at temperatures between 40 and 200 °C. [ 3 ] In one variation, formaldehyde is used in place of synthesis gas. [ 4 ] Transition metal catalysts are required. Invariably, the catalyst dissolves in the reaction medium, i.e. hydroformylation is an example of homogeneous catalysis .
The process was discovered by the German chemist Otto Roelen in 1938 in the course of investigations of the Fischer–Tropsch process . Aldehydes and diethylketone were obtained when ethylene was added to an F-T reactor. Through these studies, Roelen discovered the utility of cobalt catalysts. HCo(CO) 4 , which had been isolated only a few years prior to Roelen's work, was shown to be an excellent catalyst. [ 5 ] [ 6 ] The term oxo synthesis was coined by the Ruhrchemie patent department, who expected the process to be applicable to the preparation of both aldehydes and ketones. Subsequent work demonstrated that the ligand tributylphosphine (PBu 3 ) improved the selectivity of the cobalt-catalysed process. The mechanism of Co-catalyzed hydroformylation was elucidated by Richard F. Heck and David Breslow in the 1960s. [ 7 ]
In 1968, highly active rhodium-based catalysts were reported. [ 8 ] Since the 1970s, most hydroformylation relies on catalysts based on rhodium . [ 9 ] Water-soluble catalysts have been developed. They facilitate the separation of the products from the catalyst. [ 10 ]
A key consideration of hydroformylation is the "normal" vs. "iso" selectivity . For example, the hydroformylation of propylene can afford two isomeric products, butyraldehyde or isobutyraldehyde :
These isomers reflect the regiochemistry of the insertion of the alkene into the M–H bond. Since both products are not equally desirable (normal is more stable than iso), much research was dedicated to the quest for catalyst that favored the normal isomer.
Markovnikov's rule addition of the cobalt hydride to primary alkenes is disfavored by steric hindrance between the cobalt centre and the secondary alkyl ligand. Bulky ligands exacerbate this steric hindrance. Hence, the mixed carbonyl/phosphine complexes offer a greater selectivity for anti-Markovnikov addition, thus favoring straight chain products ( n -) aldehydes. Modern catalysts rely increasingly on chelating ligands, especially diphosphites. [ 12 ]
Additionally, electron-rich the hydride complex are less proton-like. Thus, as a result, the electronic effects that normally favour the Markovnikov addition to an alkene are less applicable. Thus, electron-rich hydrides are more selective.
To suppress competing isomerization of the alkene, the rate of migratory insertion of the carbonyl into the carbon -metal bond of the alkyl must be relatively fast. The rate of insertion of the carbonyl carbon into the C-M bond is likely to be greater than the rate of beta-hydride elimination. [ 13 ]
Hydroformylation of prochiral alkenes creates new stereocenters . Using chiral phosphine ligands , the hydroformylation can be tailored to favor one enantiomer . [ 14 ] [ 15 ] Thus, for example, dexibuprofen , the (+)−( S )-enantiomer of ibuprofen , can be produced by enantioselective hydroformylation followed by oxidation.
The industrial processes vary depending on the chain length of the olefin to be hydroformylated, the catalyst metal and ligands, and the recovery of the catalyst. The original Ruhrchemie process produced propanal from ethylene and syngas using cobalt tetracarbonyl hydride as the catalyst . Today, industrial processes based on cobalt catalysts are mainly used for the production of medium- to long-chain olefins, whereas the rhodium-based catalysts are usually used for the hydroformylation of propene . The rhodium catalysts are significantly more expensive than cobalt catalysts. In the hydroformylation of higher molecular weight olefins the separation of the catalyst from the produced aldehydes is difficult.
The BASF-oxo process starts mostly with higher olefins and relies on cobalt carbonyl-based catalyst. [ 16 ] By conducting the reaction at low temperatures, one observes increased selectivity favoring the linear product. The process is carried out at a pressure of about 30 MPa and in a temperature range of 150 to 170 °C. The cobalt is recovered from the liquid product by oxidation to water-soluble Co 2 + , followed by the addition of aqueous formic or acetic acids . This process gives an aqueous phase of cobalt, which can then be recycled. Losses are compensated by the addition of cobalt salts. [ 17 ]
The Exxon process, also Kuhlmann- or PCUK – oxo process, is used for the hydroformylation of C6–C12 olefins. The process relies on cobalt catalysts. In order to recover the catalyst, an aqueous sodium hydroxide solution or sodium carbonate is added to the organic phase. By extraction with olefin and neutralization by addition of sulfuric acid solution under carbon monoxide pressure the metal carbonyl hydride can recovered. This is stripped out with syngas, absorbed by the olefin, and returned to the reactor. Similar to the BASF process, the Exxon process is carried out at a pressure of about 30 MPa and at a temperature of about 160 to 180 °C. [ 17 ]
The Shell process uses cobalt complexes modified with phosphine ligands for the hydroformylation of C7–C14 olefins. The resulting aldehydes are directly hydrogenated to the fatty alcohols , which are separated by distillation , which allows the catalyst to be recycled. The process has good selectivity to linear products, which find use as feedstock for detergents . The process is carried out at a pressure of about 4 to 8 MPa and at a temperature range of about 150–190 °C. [ 17 ]
The Union Carbide (UCC) process, also known as low-pressure oxo process (LPO), relies on a rhodium catalyst dissolved in high-boiling thick oil, a higher molecular weight condensation product of the primary aldehydes, for the hydroformylation of propene. The reaction mixture is separated in a falling film evaporator from volatile components. The liquid phase is distilled and butyraldehyde is removed as head product while the catalyst containing bottom product is recycled to the process. The process is carried out at about 1.8 MPa and 95–100 °C. [ 17 ]
The Ruhrchemie/Rhone–Poulenc process (RCRPP) relies on a rhodium catalyst with water-soluble TPPTS as ligand (Kuntz Cornils catalyst) for the hydroformylation of propene. [ 20 ] The tri- sulfonation of triphenylphosphane ligand provides hydrophilic properties to the organometallic complex. The catalyst complex carries nine sulfonate-groups and is highly soluble in water (about 1 kg L −1 ), but not in the emerging product phase. [ 21 ] The water-soluble TPPTS is used in about 50-fold excess, whereby the leaching of the catalyst is effectively suppressed. Reactants are propene and syngas consisting of hydrogen and carbon monoxide in a ratio of 1.1:1. A mixture of butyraldehyde and isobutyraldehyde in the ratio 96:4 is generated with few by-products such as alcohols, esters and higher boiling fractions. [ 21 ] The Ruhrchemie/Rhone-Poulenc-process is the first commercially available two-phase system in which the catalyst is present in the aqueous phase.
In the progress of the reaction an organic product phase is formed which is separated continuously by means of phase separation, wherein the aqueous catalyst phase remains in the reactor. [ 21 ]
The process is carried out in a stirred tank reactor where the olefin and the syngas are entrained from the bottom of the reactor through the catalyst phase under intensive stirring. The resulting crude aldehyde phase is separated at the top from the aqueous phase. The aqueous catalyst-containing solution is re-heated via a heat exchanger and pumped back into the reactor. [ 21 ] The excess olefin and syngas is separated from the aldehyde phase in a stripper and fed back to the reactor. The generated heat is used for the generation of process steam, which is used for subsequent distillation of the organic phase to separate into butyraldehyde and isobutyraldehyde. [ 21 ] Potential catalyst poisons coming from the synthesis gas migrate into the organic phase and removed from the reaction with the aldehyde. Thus, poisons do not accumulate, and the elaborate fine purification of the syngas can be omitted. [ 21 ]
A plant was built in Oberhausen in 1984, which was debottlenecked in 1988 and again in 1998 up to a production capacity of 500,000 t/a butanal. The conversion rate of propene is 98% and the selectivity to n-butanal is high. During the life time of a catalyst batch in the process less than 1 ppb rhodium is lost. [ 22 ]
Recipes have been developed for the hydroformylation on a laboratory scale, e.g. of cyclohexene . [ 3 ] [ 15 ]
Cobalt carbonyl and rhodium complexes catalyse the hydroformylation of formaldehyde and ethylene oxide to give hydroxyacetaldehyde and 3-hydroxypropanal , which can then be hydrogenated to ethylene glycol and propane-1,3-diol , respectively. The reactions work best when the solvent is basic (such as pyridine ). [ 23 ] [ 24 ]
In the case of dicobalt octacarbonyl or Co 2 (CO) 8 as a catalyst, pentan-3-one can arise from ethylene and CO, in the absence of hydrogen. A proposed intermediate is the ethylene-propionyl species [CH 3 C(O)Co(CO) 3 (ethylene)] which undergoes a migratory insertion to form [CH 3 COCH 2 CH 2 Co(CO) 3 ]. The required hydrogen arises from the water shift reaction . For details, see [ 25 ]
If the water shift reaction is not operative, the reaction affords a polymer containing alternating carbon monoxide and ethylene units. Such aliphatic polyketones are more conventionally prepared using palladium catalysts. [ 26 ]
Functionalized olefins such as allyl alcohol can be hydroformylated. The target product 1,4-butanediol and its isomer is obtained with isomerization free catalysts such as rhodium-triphenylphosphine complexes. The use of the cobalt complex leads by isomerization of the double bond to n- propanal . [ 27 ] The hydroformylation of alkenyl ethers and alkenyl esters occurs usually in the α-position to the ether or ester function.
The hydroformylation of acrylic acid and methacrylic acid in the rhodium-catalyzed process leads to the Markovnikov product in the first step. [ 28 ] By variation of the reaction conditions the reaction can be directed to different products. A high reaction temperature and low carbon monoxide pressure favors the isomerization of the Markovnikov product to the thermodynamically more stable β-isomer, which leads to the n-aldehyde. Low temperatures and high carbon monoxide pressure and an excess of phosphine, which blocks free coordination sites, can lead to faster hydroformylation in the α-position to the ester group and suppress the isomerization. [ 28 ]
Side reactions of the alkenes are the isomerization and hydrogenation of the double bond. While the alkanes resulting from hydrogenation of the double bond do not participate further in the reaction, the isomerization of the double bond with subsequent formation of the n-alkyl complexes is a desired reaction. The hydrogenation is usually of minor importance; However, cobalt-phosphine-modified catalysts can have an increased hydrogenation activity, where up to 15% of the alkene is hydrogenated.
Using tandem catalysis , systems have been developed for the one-pot conversion of akenes to alcohols. The first step is hydroformylation. [ 29 ]
Conditions for hydroformylation catalysis can induce degradation of supporting organophosphorus ligands. Triphenylphosphine is subject to hydrogenolysis , releasing benzene and diphenylphosphine. The insertion of carbon monoxide in an intermediate metal-phenyl bond can lead to the formation of benzaldehyde or by subsequent hydrogenation to benzyl alcohol . [ 30 ] One of the ligands phenyl-groups can be replaced by propene, and the resulting diphenylpropylphosphine ligand can inhibit the hydroformylation reaction due to its increased basicity. [ 30 ]
Although the original hydroformylation catalysts were based on cobalt, most modern processes rely on rhodium, which is expensive. There has therefore been interest in finding alternative metal catalysts. Examples of alternative metals include iron and ruthenium. [ 31 ] [ 32 ] | https://en.wikipedia.org/wiki/Hydroformylation |
A hydrogel is a biphasic material , a mixture of porous and permeable solids and at least 10% of water or other interstitial fluid . [ 1 ] [ 2 ] The solid phase is a water insoluble three dimensional network of polymers , having absorbed a large amount of water or biological fluids. [ 2 ] [ 3 ] [ 4 ] [ 5 ] Hydrogels have several applications, especially in the biomedical area, such as in hydrogel dressing . Many hydrogels are synthetic, but some are derived from natural materials. [ 6 ] [ 7 ] The term "hydrogel" was coined in 1894. [ 8 ]
The crosslinks which bond the polymers of a hydrogel fall under two general categories: physical hydrogels and chemical hydrogels. Chemical hydrogels have covalent cross-linking bonds , whereas physical hydrogels have non-covalent bonds . [ citation needed ] Chemical hydrogels can result in strong reversible or irreversible gels due to the covalent bonding. [ 9 ] Chemical hydrogels that contain reversible covalent cross-linking bonds, such as hydrogels of thiomers being cross-linked via disulfide bonds, are non-toxic and are used in numerous medicinal products. [ 10 ] [ 11 ] [ 12 ] Physical hydrogels usually have high biocompatibility, are not toxic, and are also easily reversible by simply changing an external stimulus such as pH, ion concentration ( alginate ) or temperature ( gelatine ); they are also used for medical applications. [ 13 ] [ 14 ] [ 15 ] [ 16 ] [ 17 ] Physical crosslinks consist of hydrogen bonds , hydrophobic interactions , and chain entanglements (among others). A hydrogel generated through the use of physical crosslinks is sometimes called a 'reversible' hydrogel. [ 13 ] Chemical crosslinks consist of covalent bonds between polymer strands. Hydrogels generated in this manner are sometimes called 'permanent' hydrogels.
Hydrogels are prepared using a variety of polymeric materials , which can be divided broadly into two categories according to their origin: natural or synthetic polymers. Natural polymers for hydrogel preparation include hyaluronic acid , chitosan , heparin , alginate , gelatin and fibrin . [ 18 ] Common synthetic polymers include polyvinyl alcohol , polyethylene glycol , sodium polyacrylate , acrylate polymers and copolymers thereof. [ 6 ] Whereas natural hydrogels are usually non-toxic, and often provide other advantages for medical use, such as biocompatibility , biodegradability , antibiotic / antifungal effect and improve regeneration of nearby tissue, their stability and strength is usually much lower than synthetic hydrogels. [ 19 ] There are also synthetic hydrogels that can be used for medical applications, such as polyethylene glycol (PEG) , polyacrylate , and polyvinylpyrrolidone (PVP) . [ 20 ]
There are two suggested mechanisms behind physical hydrogel formation, the first one being the gelation of nanofibrous peptide assemblies, usually observed for oligopeptide precursors. The precursors self-assemble into fibers, tapes, tubes, or ribbons that entangle to form non-covalent cross-links. The second mechanism involves non-covalent interactions of cross-linked domains that are separated by water-soluble linkers, and this is usually observed in longer multi-domain structures. [ 21 ] Tuning of the supramolecular interactions to produce a self-supporting network that does not precipitate, and is also able to immobilize water which is vital for to gel formation. Most oligopeptide hydrogels have a β-sheet structure , and assemble to form fibers, although α-helical peptides have also been reported. [ 22 ] [ 23 ] The typical mechanism of gelation involves the oligopeptide precursors self-assemble into fibers that become elongated, and entangle to form cross-linked gels.
One notable method of initiating a polymerization reaction involves the use of light as a stimulus. In this method, photoinitiators , compounds that cleave from the absorption of photons, are added to the precursor solution which will become the hydrogel. When the precursor solution is exposed to a concentrated source of light, usually ultraviolet irradiation, the photoinitiators will cleave and form free radicals, which will begin a polymerization reaction that forms crosslinks between polymer strands. This reaction will cease if the light source is removed, allowing the amount of crosslinks formed in the hydrogel to be controlled. [ 24 ] The properties of a hydrogel are highly dependent on the type and quantity of its crosslinks, making photopolymerization a popular choice for fine-tuning hydrogels. This technique has seen considerable use in cell and tissue engineering applications due to the ability to inject or mold a precursor solution loaded with cells into a wound site, then solidify it in situ. [ 25 ] [ 24 ]
Physically crosslinked hydrogels can be prepared by different methods depending on the nature of the crosslink involved. Polyvinyl alcohol hydrogels are usually produced by the freeze-thaw technique. In this, the solution is frozen for a few hours, then thawed at room temperature, and the cycle is repeated until a strong and stable hydrogel is formed. [ 26 ] Alginate hydrogels are formed by ionic interactions between alginate and double-charged cations. A salt, usually calcium chloride , is dissolved into an aqueous sodium alginate solution, that causes the calcium ions to create ionic bonds between alginate chains. [ 27 ] Gelatin hydrogels are formed by temperature change. A water solution of gelatin forms an hydrogel at temperatures below 37–35 °C, as Van der Waals interactions between collagen fibers become stronger than thermal molecular vibrations. [ 28 ]
Peptide based hydrogels possess exceptional biocompatibility and biodegradability qualities, giving rise to their wide use of applications, particularly in biomedicine; [ 2 ] as such, their physical properties can be fine-tuned in order to maximise their use. [ 2 ] Methods to do this are: modulation of the amino acid sequence, pH , chirality , and increasing the number of aromatic residues. [ 29 ] The order of amino acids within the sequence is crucial for gelation, as has been shown many times. In one example, a short peptide sequence Fmoc-Phe-Gly readily formed a hydrogel, whereas Fmoc-Gly-Phe failed to do so as a result of the two adjacent aromatic moieties being moved, hindering the aromatic interactions. [ 30 ] [ 31 ] Altering the pH can also have similar effects, an example involved the use of the naphthalene (Nap) modified dipeptides Nap-Gly-Ala, and Nap- Ala-Gly, where a drop in pH induced gelation of the former, but led to crystallisation of the latter. [ 32 ] A controlled pH decrease method using glucono-δ-lactone (GdL), where the GdL is hydrolysed to gluconic acid in water is a recent strategy that has been developed as a way to form homogeneous and reproducible hydrogels. [ 33 ] [ 34 ] The hydrolysis is slow, which allows for a uniform pH change, and thus resulting in reproducible homogenous gels. In addition to this, the desired pH can be achieved by altering the amount of GdL added. The use of GdL has been used various times for the hydrogelation of Fmoc and Nap-dipeptides. [ 33 ] [ 34 ] In another direction, Morris et al reported the use of GdL as a 'molecular trigger' to predict and control the order of gelation. [ 35 ] Chirality also plays an essential role in gel formation, and even changing the chirality of a single amino acid from its natural L-amino acid to its unnatural D-amino acid can significantly impact the gelation properties, with the natural forms not forming gels. [ 36 ] Furthermore, aromatic interactions play a key role in hydrogel formation as a result of π- π stacking driving gelation, shown by many studies. [ 37 ] [ 38 ]
Hydrogels also possess a degree of flexibility very similar to natural tissue due to their significant water content. As responsive " smart materials ", hydrogels can encapsulate chemical systems which upon stimulation by external factors such as a change of pH may cause specific compounds such as glucose to be liberated to the environment, in most cases by a gel–sol transition to the liquid state. Chemomechanical polymers are mostly also hydrogels, which upon stimulation change their volume and can serve as actuators or sensors .
Hydrogels have been investigated for diverse applications. By modifying the polymer concentration of a hydrogel (or conversely, the water concentration), the Young's modulus , shear modulus , and storage modulus can vary from 10 Pa to 3 MPa, a range of about five orders of magnitude. [ 40 ] A similar effect can be seen by altering the crosslinking concentration. [ 40 ] This much variability of the mechanical stiffness is why hydrogels are so appealing for biomedical applications, where it is vital for implants to match the mechanical properties of the surrounding tissues. [ 41 ] Characterizing the mechanical properties of hydrogels can be difficult especially due to the differences in mechanical behavior that hydrogels have in comparison to other traditional engineering materials. In addition to its rubber elasticity and viscoelasticity , hydrogels have an additional time dependent deformation mechanism which is dependent on fluid flow called poroelasticity . These properties are extremely important to consider while performing mechanical experiments. Some common mechanical testing experiments for hydrogels are tension , compression (confined or unconfined), indentation, shear rheometry or dynamic mechanical analysis . [ 40 ]
Hydrogels have two main regimes of mechanical properties: rubber elasticity and viscoelasticity :
In the unswollen state, hydrogels can be modelled as highly crosslinked chemical gels, in which the system can be described as one continuous polymer network. In this case:
G = N p k T = ρ R T M ¯ c {\displaystyle G=N_{p}kT={\rho RT \over {\overline {M}}_{c}}}
where G is the shear modulus , k is the Boltzmann constant, T is temperature, N p is the number of polymer chains per unit volume, ρ is the density, R is the ideal gas constant, and M ¯ c {\displaystyle {\overline {M}}_{c}} is the (number) average molecular weight between two adjacent cross-linking points. M ¯ c {\displaystyle {\overline {M}}_{c}} can be calculated from the swell ratio, Q , which is relatively easy to test and measure. [ 40 ]
For the swollen state, a perfect gel network can be modeled as: [ 40 ]
G swollen = G Q − 1 / 3 {\displaystyle G_{\textrm {swollen}}=GQ^{-1/3}}
In a simple uniaxial extension or compression test, the true stress, σ t {\displaystyle \sigma _{t}} , and engineering stress, σ e {\displaystyle \sigma _{e}} , can be calculated as:
σ t = G swollen ( λ 2 − λ − 1 ) {\displaystyle \sigma _{t}=G_{\textrm {swollen}}\left(\lambda ^{2}-\lambda ^{-1}\right)}
σ e = G swollen ( λ − λ − 2 ) {\displaystyle \sigma _{e}=G_{\textrm {swollen}}\left(\lambda -\lambda ^{-2}\right)}
where λ = l current / l original {\displaystyle \lambda =l_{\textrm {current}}/l_{\textrm {original}}} is the stretch. [ 40 ]
For hydrogels, their elasticity comes from the solid polymer matrix while the viscosity originates from the polymer network mobility and the water and other components that make up the aqueous phase. [ 42 ] Viscoelastic properties of a hydrogel is highly dependent on the nature of the applied mechanical motion. Thus, the time dependence of these applied forces is extremely important for evaluating the viscoelasticity of the material. [ 43 ]
Physical models for viscoelasticity attempt to capture the elastic and viscous material properties of a material. In an elastic material, the stress is proportional to the strain while in a viscous material, the stress is proportional to the strain rate. The Maxwell model is one developed mathematical model for linear viscoelastic response. In this model, viscoelasticity is modeled analogous to an electrical circuit with a Hookean spring, that represents the Young's modulus, and a Newtonian dashpot that represents the viscosity. A material that exhibit properties described in this model is a Maxwell material . Another physical model used is called the Kelvin-Voigt Model and a material that follow this model is called a Kelvin–Voigt material . [ 44 ] In order to describe the time-dependent creep and stress-relaxation behavior of hydrogel, a variety of physical lumped parameter models can be used. [ 40 ] These modeling methods vary greatly and are extremely complex, so the empirical Prony Series description is commonly used to describe the viscoelastic behavior in hydrogels. [ 40 ]
In order to measure the time-dependent viscoelastic behavior of polymers dynamic mechanical analysis is often performed. Typically, in these measurements the one side of the hydrogel is subjected to a sinusoidal load in shear mode while the applied stress is measured with a stress transducer and the change in sample length is measured with a strain transducer. [ 43 ] One notation used to model the sinusoidal response to the periodic stress or strain is:
in which G' is the real (elastic or storage) modulus, G" is the imaginary (viscous or loss) modulus.
Poroelasticity is a characteristic of materials related to the migration of solvent through a porous material and the concurrent deformation that occurs. [ 40 ] Poroelasticity in hydrated materials such as hydrogels occurs due to friction between the polymer and water as the water moves through the porous matrix upon compression. This causes a decrease in water pressure, which adds additional stress upon compression. Similar to viscoelasticity, this behavior is time dependent, thus poroelasticity is dependent on compression rate: a hydrogel shows softness upon slow compression, but fast compression makes the hydrogel stiffer. This phenomenon is due to the friction between the water and the porous matrix is proportional to the flow of water, which in turn is dependent on compression rate. Thus, a common way to measure poroelasticity is to do compression tests at varying compression rates. [ 45 ] Pore size is an important factor in influencing poroelasticity. The Kozeny–Carman equation has been used to predict pore size by relating the pressure drop to the difference in stress between two compression rates. [ 45 ]
Poroelasticity is described by several coupled equations, thus there are few mechanical tests that relate directly to the poroelastic behavior of the material, thus more complicated tests such as indentation testing, numerical or computational models are utilized. Numerical or computational methods attempt to simulate the three dimensional permeability of the hydrogel network.
The toughness of a hydrogel refers to the ability of the hydrogel to withstand deformation or mechanical stress without fracturing or breaking apart. A hydrogel with high toughness can maintain its structural integrity and functionality under higher stress. Several factors contribute to the toughness of a hydrogel including composition, crosslink density, polymer chain structure, and hydration level. The toughness of a hydrogel is highly dependent on what polymer(s) and crosslinker(s) make up its matrix as certain polymers possess higher toughness and certain crosslinking covalent bonds are inherently stronger. [ 46 ] Additionally, higher crosslinking density generally leads to increased toughness by restricting polymer chain mobility and enhancing resistance to deformation. The structure of the polymer chains is also a factor in that, longer chain lengths and higher molecular weight leads to a greater number of entanglements and higher toughness. [ 47 ] A good balance (equilibrium) in the hydration of a hydrogel leads is important because too low hydration causes poor flexibility and toughness within the hydrogel, but too high of water content can cause excessive swelling, weakening the mechanical properties of the hydrogel. [ 48 ] [ 49 ]
The hysteresis of a hydrogel refers to the phenomenon where there is a delay in the deformation and recovery of a hydrogel when it is subjected to mechanical stress and relieved of that stress. This occurs because the polymer chains within a hydrogel rearrange, and the water molecules are displaced, and energy is stored as it deforms in mechanical extension or compression. [ 50 ] When the mechanical stress is removed, the hydrogel begins to recover its original shape, but there may be a delay in the recovery process due to factors like viscoelasticity, internal friction, etc. [ 51 ] This leads to a difference between the stress-strain curve during loading and unloading. Hysteresis within a hydrogel is influenced by several factors including composition, crosslink density, polymer chain structure, and temperature .
The toughness and hysteresis of a hydrogel are especially important in the context of biomedical applications such as tissue engineering and drug delivery , as the hydrogel may need to withstand mechanical forces within the body, but also maintain mechanical performance and stability over time. [ 52 ] Most typical hydrogels, both natural and synthetic, have a positive correlation between toughness and hysteresis, meaning that the higher the toughness, the longer the hydrogel takes to recover its original shape and vice versa. [ 47 ] This is largely due to sacrificial bonds being the source of toughness within many of these hydrogels. Sacrificial bonds are non-covalent interactions such as hydrogen bonds , ionic interactions , and hydrophobic interactions , that can break and reform under mechanical stress. [ 53 ] The reforming of these bonds takes time, especially when there are more of them, which leads to an increase in hysteresis. However, there is currently research focused on the development of highly entangled hydrogels, which instead rely on the long chain length of the polymers and their entanglement to limit the deformation of the hydrogel, thereby increasing the toughness without increasing hysteresis as there is no need for the reformation of the bonds. [ 47 ]
The most commonly seen environmental sensitivity in hydrogels is a response to temperature. [ 54 ] Many polymers/hydrogels exhibit a temperature dependent phase transition, which can be classified as either an upper critical solution temperature (UCST) or lower critical solution temperature (LCST). UCST polymers increase in their water-solubility at higher temperatures, which lead to UCST hydrogels transitioning from a gel (solid) to a solution (liquid) as the temperature is increased (similar to the melting point behavior of pure materials). This phenomenon also causes UCST hydrogels to expand (increase their swell ratio) as temperature increases while they are below their UCST. [ 54 ] However, polymers with LCSTs display an inverse (or negative) temperature-dependence, where their water-solubility decreases at higher temperatures. LCST hydrogels transition from a liquid solution to a solid gel as the temperature is increased, and they also shrink (decrease their swell ratio) as the temperature increases while they are above their LCST. [ 54 ]
Applications can dictate for diverse thermal responses. For example, in the biomedical field, LCST hydrogels are being investigated as drug delivery systems due to being injectable (liquid) at room temp and then solidifying into a rigid gel upon exposure to the higher temperatures of the human body. [ 54 ] There are many other stimuli that hydrogels can be responsive to, including: pH, glucose, electrical signals, light , pressure , ions, antigens , and more. [ 54 ]
The mechanical properties of hydrogels can be fine-tuned in many ways beginning with attention to their hydrophobic properties. [ 54 ] [ 55 ] Another method of modifying the strength or elasticity of hydrogels is to graft or surface coat them onto a stronger/stiffer support, or by making superporous hydrogel (SPH) composites, in which a cross-linkable matrix swelling additive is added. [ 7 ] Other additives, such as nanoparticles and microparticles , have been shown to significantly modify the stiffness and gelation temperature of certain hydrogels used in biomedical applications. [ 56 ] [ 57 ] [ 58 ]
While a hydrogel's mechanical properties can be tuned and modified through crosslink concentration and additives, these properties can also be enhanced or optimized for various applications through specific processing techniques. These techniques include electro-spinning , 3D / 4D printing , self-assembly , and freeze-casting . One unique processing technique is through the formation of multi-layered hydrogels to create a spatially-varying matrix composition and by extension, mechanical properties. This can be done by polymerizing the hydrogel matrixes in a layer by layer fashion via UV polymerization. This technique can be useful in creating hydrogels that mimic articular cartilage, enabling a material with three separate zones of distinct mechanical properties. [ 59 ]
Another emerging technique to optimize hydrogel mechanical properties is by taking advantage of the Hofmeister series . Due to this phenomenon, through the addition of salt solution, the polymer chains of a hydrogel aggregate and crystallize, which increases the toughness of the hydrogel. This method, called " salting out ", has been applied to poly(vinyl alcohol) hydrogels by adding a sodium sulfate salt solution. [ 60 ] Some of these processing techniques can be used synergistically with each other to yield optimal mechanical properties. Directional freezing or freeze-casting is another method in which a directional temperature gradient is applied to the hydrogel is another way to form materials with anisotropic mechanical properties. Utilizing both the freeze-casting and salting-out processing techniques on poly(vinyl alcohol) hydrogels to induce hierarchical morphologies and anisotropic mechanical properties. [ 61 ] Directional freezing of the hydrogels helps to align and coalesce the polymer chains, creating anisotropic array honeycomb tube-like structures while salting out the hydrogel yielded out a nano-fibril network on the surface of these honeycomb tube-like structures. While maintaining a water content of over 70%, these hydrogels' toughness values are well above those of water-free polymers such as polydimethylsiloxane (PDMS), Kevlar , and synthetic rubber . The values also surpass the toughness of natural tendon and spider silk . [ 61 ]
The dominant material for contact lenses are acrylate- siloxane hydrogels. They have replaced hard contact lenses. One of their most attractive properties is oxygen permeability, which is required since the cornea lacks vasculature .
Hydrogels are three-dimensional network structures with high hydrophilicity that can absorb and retain large amounts of water. Due to their excellent biocompatibility, they are widely used in the field of biomaterials. The main feature of hydrogels is their high water content, which is similar to the aqueous environment in biological systems, making them ideal for applications in tissue engineering, drug delivery, wound dressings, and artificial skin. [ 91 ] Hydrogels can be classified into natural and synthetic types. Natural hydrogels, such as gelatin and chitosan, are derived from biological materials and offer good biodegradability and biocompatibility. Synthetic hydrogels, on the other hand, typically have higher mechanical strength and tunability but may exhibit lower biocompatibility. [ 92 ] Additionally, hydrogels can be categorized as environmental-responsive or non-responsive based on their response to external stimuli. Environmental-responsive hydrogels, which can react to changes in temperature, pH, or ion concentration, are particularly useful in drug delivery systems. Due to their tunability, hydrogels continue to expand their applications in the biomedical field and are expected to play a crucial role in various medical applications in the future.
Implanted or injected hydrogels have the potential to support tissue regeneration by mechanical tissue support, localized drug or cell delivery, [ 2 ] local cell recruitement or immunomodulation , or encapsulation of nanoparticles for local photothermal therapy or brachytherapy . [ 80 ] Polymeric drug delivery systems have overcome challenges due to their biodegradability, biocompatibility, and anti-toxicity. [ 93 ] [ 94 ] Materials such as collagen , chitosan, cellulose , and poly (lactic-co-glycolic acid) have been implemented extensively for drug delivery to organs such as eye, [ 95 ] nose, kidneys, [ 96 ] lungs, [ 97 ] intestines, [ 98 ] skin [ 99 ] and brain. [ 2 ] Future work is focused on reducing toxicity, improving biocompatibility, expanding assembly techniques [ 100 ]
Hydrogels have been considered as vehicles for drug delivery. [ 101 ] [ 77 ] [ 78 ] [ 79 ] They can also be made to mimic animal mucosal tissues to be used for testing mucoadhesive properties. [ 102 ] [ 103 ] They have been examined for use as reservoirs in topical drug delivery ; particularly ionic drugs, delivered by iontophoresis .
This article incorporates text by Jessica Hutchinson available under the CC BY 3.0 license. | https://en.wikipedia.org/wiki/Hydrogel |
The behavior of quantum dots (QDs) in solution and their interaction with other surfaces is of great importance to biological and industrial applications, such as optical displays, animal tagging , anti-counterfeiting dyes and paints, chemical sensing, and fluorescent tagging . However, unmodified quantum dots tend to be hydrophobic, which precludes their use in stable, water-based colloids . Furthermore, because the ratio of surface area to volume in a quantum dot is much higher than for larger particles, the thermodynamic free energy associated with dangling bonds on the surface is sufficient to impede the quantum confinement of excitons . Once solubilized by encapsulation in either a hydrophobic interior micelle or a hydrophilic exterior micelle, the QDs can be successfully introduced into an aqueous medium, in which they form an extended hydrogel network. In this form, quantum dots can be utilized in several applications that benefit from their unique properties, such as medical imaging and thermal destruction of malignant cancers. [ 1 ]
Quantum dots (QDs) are nano-scale semiconductor particles on the order of 2–10 nm in diameter. They possess electrical properties between those of bulk semi-conductors and individual molecules, as well as optical characteristics that make them suitable for applications where fluorescence is desirable, such as medical imaging. Most QDs synthesized for medical imaging are in the form of CdSe(ZnS) core(shell) particles. CdSe QDs have been shown to possess optical properties superior to organic dyes. [ 2 ] The ZnS shell has a two-fold effect:
Despite their potential for use as contrast agents for medical imaging techniques, their use in vivo is hindered by the cytotoxicity of cadmium . To address this issue, methods have been developed to “wrap” or “encapsulate” potentially-toxic QDs in bio-inert polymers to facilitate use in living tissue. While Cd-free QDs are commercially available, they are unsuitable for use as a substitute for organic contrasts. [ 4 ] Another issue with CdSe(ZnS) nanoparticles is significant hydrophobicity , which hinders their ability to enter solution with aqueous media, such as blood or spinal fluid . Certain hydrophilic polymers could be used to render the dots water-soluble.
One notable quantum dot encapsulation technique involves utilizing a double fluoroalkyl-ended polyethylene glycol molecule (R f -PEG) as a surfactant, which will spontaneously form micellular structures at its critical micelle concentration (CMC). The critical micelle concentration of the R f -PEG depends on the length of the PEG portion of the polymer. This molecule consists of a hydrophilic PEG backbone with two hydrophilic terminal groups (C n F 2n+1 -CH 2 CH 2 O) attached via isophorone diurethane. [ 5 ] It is synthesized by dehydrating a solution of 1,3-dimethyl-5-fluorouracil and PEG, mixing them in the presence of heavy water (D 2 O) via a sonicator to combine then. [ 6 ]
At the appropriate Krafft temperature and critical micelle concentration these molecules will form individual tear-drop loops, where the hydrophobic ends are attracted to one another, to other molecules, and also to the similarly hydrophobic QDs. This forms a loaded micelle with a hydrophilic outer shell and a hydrophobic core. [ 6 ]
When encapsulating hydrophobes in this way it is important to ensure the particle size is appropriate for the PEG backbone being utilized, as the number of PEG mer units (generally with a molecular weight of 6 kDa or 10 kDa) determines the maximum particle size that can be successfully contained at the core of the micelle.
To determine the average diameter, D, of the QDs, the following empirical equation is used:
Where
It is during encapsulation that the ZnS shell plays an especially important role, in that it helps prevent the agglomeration of CdSe particles that had no shell by occupying the previously mentioned bonds on the dot's surface; however, clumping can still occur through secondary forces that arise from common hydrophobicity. This can result in multiple particles within each micelle, which may negatively impact overall resolution. For this reason multiple combinations of PEG chain length and particle diameter are necessary to achieve optimal imaging properties.
After initial encapsulation the remaining molecules form connections between the individual micelles to form a network within the aqueous media called a hydrogel , creating a diffuse and relatively constant concentration of the encapsulated particle within the gel. The formation of hydrogels is a phenomenon observed in superabsorbent polymers , or "slush powders," in which the polymer, often in the form of a powder, absorbs water, becoming up to 99% liquid and 30-60 times larger in size. [ 7 ]
The diffusivity of spherical particles in a suspension is approximated by the Stokes–Einstein equation : [ 6 ]
Typical R f -PEG hydrogel diffusivities for 2 nm quantum dots are on the order of 10 −16 m 2 /s, so suspensions of quantum dots tend to be very stable. Hydrogel viscosity can be determined by using rheological techniques.
When encapsulating hydrophobic or potentially toxic materials it is important that the encapsulant remain intact while inside the body. Studying the rheological properties of the micelles permits identification and selection of the polymer that is most appropriate for use in long-term biological applications. R f -PEG exhibits superior rheological properties when used in vivo .
The properties of the polymer are influenced by the chain length. The correct chain length ensures that the encapsulant is not released over time. Avoiding the release of QDs and other toxic particles is critical to prevent unintentional cell necrosis in patients.
The length of the polymer is controlled by two factors:
Increasing the PEG length increases the solubility of the polymer. However, if the PEG chain is too long the micelle will become unstable. It has been observed that a stable hydrogel can only be formed with PEG backbones weighing between six and ten kilodaltons. [ 8 ]
On the other hand, increasing the length of the hydrophobic terminal groups decreases aqueous solubility. For a given PEG weight, if the hydrophobe is too short the polymer will just dissolve into the solution, and if it is too long the polymer won't dissolve at all. Generally, two end groups result in the highest conversion into micelles (91%): [ 8 ]
At molecular weights between 6 and 10 kilodaltons the R f -PEG hydrogel acts as a Maxwell material , which means the fluid has both viscosity and elasticity . This is determined by measuring the plateau modulus, the elastic modulus for a viscoelastic polymer is constant or "relaxed" when deformed, at a range of frequencies via oscillatory rheology. [ 9 ] [ 10 ] Plotting the first- vs second-order integrals of the modulus values, a Cole-Cole plot is obtained, which, when fitted to a Maxwell model, provides the following relationship:
Where
Based on the Maxwellian behavior of the hydrogel and observations of erosion via surface plasmon resonance (SPR) , the following data results for 3 common R f -PEG types at their specified concentrations: [ 11 ] [ 12 ]
X KC Y denotes X thousand daltons of molecular mass and Y carbon atoms.
These values can give us information on the degree of entanglement (or degree of cross linking, depending on what polymer is being considered). In general, higher degrees of entanglement leads to higher time required for the polymer to return to the undeformed state or relaxation times .
Hydrogel encapsulation of the QDs opens up a new range of applications, such as: | https://en.wikipedia.org/wiki/Hydrogel_encapsulation_of_quantum_dots |
Hydrogel fiber is a hydrogel made into a fibrous state, where its width is significantly smaller than its length. The hydrogel's specific surface area at fibrous form is larger than that of the bulk hydrogel, and its mechanical properties also changed accordingly. As a result of these changes, hydrogel fiber has a faster matter exchange rate and can be woven into different structures.
As a water swollen network with usually low toxicity, hydrogel fiber can be used in a variety of biomedical applications such as drug carrier, [ 1 ] optical sensor, [ 2 ] and actuator. [ 1 ]
But the production of hydrogel fiber can be challenging as the hydrogel is crosslinked and can not be shaped into a fibrous state after polymerization. To make hydrogel into a fibrous state, the pregel solution must be made into fibrous form and then crosslinked while maintaining this shape.
To produce hydrogel fiber, the solidification of the pregel solution is the most important step. The pregel solution needs to be solidified while maintaining its fibrous shape. To achieve this, several methods based on chemical crosslinking, phase change, rheological property change have been developed.
Change in physical interactions can be utilized for the solidification process, and the fibrous state is usually achieved outside of the extrusion nozzle. Due to the reversibility of those physical interactions, subsequent crosslinking is traditionally required. [ 3 ] [ 4 ] [ 5 ]
Hydrogel fiber can be produced by electrospinning with solidification done by the evaporation of the solvent. [ 3 ] The fibrous state is created by the combination of electrostatic repulsion and the surface tension of the solution. But subsequent crosslinking is usually needed to form a crosslinked network. One advantage of electrospun hydrogel fiber is that it has a diameter in range in the order between nm to μm, which is desirable for fast matter exchange. However, utilization of single fiber can be hard to achieve due to the weak mechanical strength of the microscopic fiber and its entanglements after production.
An example of this method would be the production of polyacrylamide (PAAM) semi-interpretation network developed by Tahchi et al. [ 3 ] Where the first linear PAAM (provide solidification) was mixed with AAM monomer (form subsequent network) and crosslinker N , N ′-methylenebisacrylamide (MBA). During the electrospinning process, the linear PAAM provided the required physical properties to achieve electrospinning, while the AAM monomer and MBA crosslinker were used to form a second crosslinked network inside the PAAM fiber. Although no crosslinking was formed between the first and second networks, the physical entanglement will prevent linear PAAM from leaking.
Through supramolecular chemistry, pregel solution can solidify through reversible supramolecular interactions such as host-guest interactions. [ 4 ] Such interaction can be manipulated through the mechanical force or the temperature. When energy exerted to the network is high enough, physical crosslinking point will break and the polymer will be at liquid state, after leaving the nozzle, the crosslinking can be rapidly formed to solidify the solution.
A case would be the Host–Guest Chemistry reported by Scherman et al. Where the formation of inclusion complex between Cucurbit[8]uril and 1-benzyl-3-vinylimidazolium bromide (BVIm) formed physical crosslinking point for the network. [ 4 ] The formation of this physical crosslinking point is controlled by the temperature of the solution. By heating up the solution and cooling it down rapidly at extrusion nuzzle, the hydogel fiber is formed. Also, subsequent crosslinking is performed to form a perment network.
Some hydrophilic polymer can be made into hydrogel fiber via melt-spinning method, where the solidification is done by the phase transition from the molten state. [ 5 ] Similar to the electro-spinning, the pregel solution was kept liquid in the container. After leaving the nuzzle at filament state, the fiber solidified after the encounter of cool ambient air and maintained their shape.
An example would be the meltspinning apparatus built by Long et al., where meltspinning of polylactic acid (PLA) and polycaprolactone (PCL) fiber are achieved. [ 5 ]
Similar to the draw spinning technique the direct ink writing technique utilized reversible physical solidification to produce hydrogel fibers. [ 6 ] The pregel solution was liqufied through shear thinning process which can be generated by adding microscopic particles such as mircrogel. After leaving the nuzzle, the hydrogel will solidify and retain their shape, and network will be made perment after crosslinking.
An example would be the production of the fiber developed by Lewis et al. [ 6 ] Where Silk fibroin was used to generate the desired shear-thinning properties. And the network was formed when the solvent was subsequently changed.
Similar to physical solidification, some chemical crosslinking methods have been developed to produce hydrogel fibers. And the key for the achievement of hydrogel production through the chemical crosslinking method is the effective separation between the formed network and the tube wall. [ 1 ]
Many microfluid device-based methods have been developed to produce hydrogel fibers. [ 1 ]
One of the most commonly used fiber production methods is the crosslinking of sodium alginate by CaCl 2 , where the formed calcium alginate will act as the crosslinking point to link the alginate chains together to form the network and solidified the polymer. Afterward, this alginate hydrogel fiber can be used as a template for the polymerization of secondary networks. Additionally, by controlling the fluid dynamics inside the microfluid device, the diameter and the shape of the resulting fiber can be tuned without doing modification to the devices. [ 1 ]
A practice would be the production of alginate solution reported by Yang et al . [ 7 ] They used the sodium alginate as core fluid and CaCl 2 as shealth fluid, the crosslinked network (hydrogel fiber) formed once this two fluid met, the laminar flow kept its tubular shape during the reaction.
Other photoinitiated free radical polymerization reactions can also be used for fiber production. [ 1 ] In this case, the shealth fluid was only used to separate the core fluid from the tube wall. Also, to achieve the solidification rapid enough, a more concentrated monomer solution was usually used.
An example would be the production of 4-hydroxybutyl acrylate fiber reported by Beebe et al. [ 8 ] The microfluid device they used was built with ethylvinyl acetate caplliary and PDMS rubber. The core fluid was a mixture of 4-hydroxybutyl acrylate , acrylic acid , ethyleneglycol dimethacrylate (crosslinker), 2,2′-dimethoxy-2-phenyl-acetonephenone (photoinitiator). The sheath fluid was only for separation. The crosslinked network was formed by free radical polymerization when the UV light met the core fluid.
Although only being able to produce short hydrogel fibers, production of hydrogel fiber by polymerizing the hydrogel network inside a tubular mold and push out the fiber forcefully can also be achieved. [ 9 ] But the friction will increase with the increasing length, and only short hydrogel fibers are feasible.
A case would be the production of poly(acrylamide- co -poly(ethylene glycol) diacrylate) fiber reported by yun et al. [ 9 ] The pregel solution was a mixture of AAM, poly(ethylene glycol) diacrylate (PEGDA, crosslinker), and 2-hydroxy-2-methylpropiophenone (photoinitiator). The mixture was injected into a tubular mold and extracted through hydrostatic force afterwards.
An interesting phenomenon called self-lubricate spinning can facilitate the demolding of the fiber and enables the continuous production of hydrogel fiber from tubular mold. [ 10 ] During the polymerization process, if an inert second polymer is present, it will be particularly expelled from the formed network and being able to move with relative ease. The linear polymer on the surface of the crosslinked network also contains water solvent due to the osmic pressure, thus, a lubrication layer is formed. Therefore, the solidified polymer fiber can exit the tube with decreased friction force and continuous production can be achieved.
An example would be the production the PAAM/PAMPS semi-interpenetration network hydrogel fiber reported by Zhao et al . [ 10 ] The pregel solution was the mixture of PAMPS, AAM, PEGDA (crosslinker), and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (photoinitiator). The pregel solution was fed into a PTFE tube at a constant speed, with UV light being used to initiate the reaction.
The surface morphology and shape of the cross-section can be observed via scanning electron microscope (SEM) imaging after removal of solvent. [ 1 ] Also, environmental scanning electron microscope (ESEM) can be used to observe wet hydrogel fibers. [ 10 ] But different treatments will affect the surface morphology of the hydrogel fiber drastically. If the hydrogel fiber was dried directly, a smooth surface would be obtained because of the collapse of the polymer network after the removal of the solvent. [ 1 ] If the hydrogel fiber was lyophilized, a porous surface will usually be found due to the pore-forming effect of the ice crystal. ESEM can directly observe the surface morphology. The resulting image usually indicates a smooth surface with some wrinkled formed due to the gradual loss of water. [ 10 ]
The mechanical properties of the fibers are tested, but the process can be tricky due to practical reasons. [ 11 ] The mechanical properties are tested with Universal Test Machine by fixing the hydrogel fibers between two holders. However, due to the compress of the holder, hydrogel fiber might have a trend to break at the holding point. [ 11 ] Also, the loss of water during the test will impact the resulting data, and precaution needs to be taken to meditate the loss. [ 9 ] And the tensile strength of the hydrogel fiber is usually smaller than 1 MPa. [ 10 ]
Optical properties are tested for optical sensing-related applications. [ 2 ] This can include light attenuation, refractive index, transmission, etc. [ 9 ] These optical properties are significantly influenced by the composition of the hydrogel.
Cell toxicity tests are performed for applications such as cell growth scaffolds. [ 12 ] By growing the cell with the ability to produce fluorescent protein, the growth of the cell can be monitored with fluorescent imaging techniques.
Transparent hydrogel fibers can be used as optical fiber, and stimuli-responsive functional groups can be grafted on to create optical sensors. [ 2 ] For example, in the research done by Yun et al. the glucose-sensitive phenylboronic acid was grafted onto the polymer network. When the glucose concentration changes, the adsorption of the phenylboronic acid will change accordingly and can be recorded with the light intensity at a certain wavelength.
Although suffering from poor mechanical strength, some approach has been made to construct hydrogel fiber with textile methods. [ 1 ] Also, the electrospun, meltspun, DIW method can produce hydrogel fiber structures at higher dimensions directly. [ 6 ] [ 13 ] [ 5 ]
Hydrogel fiber can be used to fabricate scaffolds for cell growth and drug release. [ 12 ] [ 1 ]
Stimuli-responsive hydrogel fibers can be used as actuators and soft robots. [ 10 ] [ 14 ] [ 15 ] [ 16 ] [ 17 ] By braiding the hydrogel fiber together, the force of the single fiber can be magnified. Also, due to the slipping between hydrogel fibers, the stain of the bending can be reduced to further enhance the performance. [ 10 ] | https://en.wikipedia.org/wiki/Hydrogel_fiber |
Hydrogen-bond catalysis is a type of organocatalysis that relies on use of hydrogen bonding interactions to accelerate and control organic reactions . In biological systems, hydrogen bonding plays a key role in many enzymatic reactions, both in orienting the substrate molecules and lowering barriers to reaction. [ 1 ] The field is relatively undeveloped compared to research in Lewis acid catalysis . [ 2 ]
Hydrogen-bond donors can catalyze reactions through a variety of mechanisms. Hydrogen bonding can stabilize anionic intermediates. They sequester anions, enabling the formation of reactive electrophilic cations. More acidic donors can act as general or specific acids, which activate electrophiles by protonation. A powerful approach is the simultaneous activation of both partners in a reaction, e.g. nucleophile and electrophile, termed "bifunctional catalysis". In all cases, the close association of the catalyst molecule to substrate also makes hydrogen-bond catalysis a powerful method of inducing enantioselectivity .
Hydrogen-bonding catalysts are often simple to make, relatively robust, and can be synthesized in high enantiomeric purity. New reactions catalyzed by hydrogen-bond donors are being discovered at an increasing pace, including asymmetric variants of common organic reactions, such as aldol additions, Diels-Alder cycloadditions and Mannich reactions . [ 3 ]
Many organic reactions involve the formation of tetrahedral intermediates through nucleophilic attack of functional groups such as aldehydes , amides or imines . In these cases, catalysis with hydrogen-bond donors is an attractive strategy since the anionic tetrahedral intermediates are better hydrogen-bond acceptors than the starting compound. This means that relative to the initial catalyst-substrate complex, the transition state, bearing more negative charge, is stabilized.
For example, in a typical acyl substitution reaction, the starting carbonyl compound is coordinated to the catalyst through one, two or possibly more hydrogen bonds. During the attack of the nucleophile, negative charge builds on the oxygen until the tetrahedral intermediate is reached. Therefore, the formally negative oxygen engages in a much stronger hydrogen bond than the starting carbonyl oxygen because of its increased negative charge. Energetically, this has the effect of lowering the intermediate and the transition state , thus accelerating the reaction.
This mode of catalysis is found in the active sites of many enzymes , such as the serine proteases . [ 4 ] In this example, the amide carbonyl is coordinated to two N–H donors. These sites of multiple coordination designed to promote carbonyl reactions in biology are termed " oxyanion holes ". Delivery of serine nucleophile forms a tetrahedral intermediate, which is stabilized by the increase hydrogen bonding to the oxyanion hole.
Many synthetic catalysts employ this strategy to activate a variety of electrophiles. Using a chiral BINOL catalyst, for instance, the Morita-Baylis-Hillman reaction involving the addition of enones to aldehydes can be effected with high enantioselectivity. [ 5 ] The nucleophile is an enolate-type species generated from the conjugate addition of PEt 3 to the enone, and adds enantioselectively to the aldehyde coordinated to catalyst.
In addition to carbonyls, other electrophiles such as imines can be used. For example, using a simple chiral thiourea catalyst, the asymmetric Mannich reaction of aromatic imines with silyl ketene acetals can be catalyzed with high ee in near quantitative conversion. [ 6 ] The mechanism of this reaction is not fully resolved and the reaction is very substrate-specific, only effective on certain aromatic electrophiles.
The scope of this mode of activation includes combinations of electrophiles, nucleophiles and catalyst structures. Furthermore, analogous reactions involving oxyanion intermediates such as enolate addition to nitroso compounds [ 7 ] or opening of epoxides [ 8 ] have also been catalyzed with this strategy.
Another strategy that has been explored is the stabilization of reactions that develop partial negative charges in the transition state. Examples of applications are most commonly reactions that are approximated concerted and pericyclic in nature. During the course of the reaction, one fragment develops partial negative character and the transition state can be stabilized by accepting hydrogen bond(s).
A demonstrative example is the catalysis of Claisen rearrangements of ester-substituted allyl vinyl ethers reported by the Jacobsen research group. [ 9 ] A chiral guanidinium catalyst was found to promote the reaction near room temperature with high enantioselectivity. During the transition state, the fragment coordinated to the amidinium catalyst develops partial anionic character due to the electronegativity of the oxygen and the electron-withdrawing ester group. This increases the strength of hydrogen bonding and lowers the transition state energy, thus accelerating the reaction.
Similarly, negative charge can develop in cycloaddition reactions such as the Diels-Alder reaction, when the partners are appropriately substituted. As a representative example, Rawal and coworkers developed a chiral catalyst based on α,α,α',α'-tetraaryl-2,2-disubstituted 1,3-dioxolane-4,5-dimethanol ( TADDOL ) that could catalyze Diels-Alder reactions. In the following example, the reaction with a highly electron-rich diene and an electron-poor dienophile is thought to develop significant negative charge on the enal fragment, and is the transition state is stabilized by increased hydrogen bonding to the TADDOL (Ar = 1-naphthyl). [ 10 ]
Hydrogen-bond catalysts can also accelerate reactions by assisting in the formation of electrophilic species through abstracting and coordinating an anion such as a halide. Urea and thiourea catalysts are the most common donors in anion-binding catalysis, and their ability to bind halides and other anions has been well established in the literature. [ 11 ] The use of chiral anion-binding catalysts can create an asymmetric ion pair and induce remarkable stereoselectivity.
One of the first reactions proposed to proceed through anion-binding catalysis is the Pictet-Spengler -type cyclization of hydroxy lactams with TMSCl under thiourea catalysis. [ 12 ] In the proposed mechanism, after initial substitution of the hydroxyl group with chloride, the key ion pair is formed. The activated iminium ion is closely associated with the chiral thiourea-bound chloride, and intramolecular cyclization proceeds with high stereoselectivity.
Asymmetric ion pairs can also be attacked in intermolecular reactions. In an interesting example, asymmetric addition of enol silane nucleophiles to oxocarbenium ions can be effected by catalytically forming the oxocarbenium through anion binding. [ 13 ] Starting from an acetal, the chloro ether is generated with boron trichloride and reacted with the enol silane and catalyst. The mechanism of formation of the oxocarbenium-thiourea-chloride complex is not fully resolved. It is thought that under the reaction conditions, the chloro ether can epimerize and thiourea can stereoselectively bind chloride to form a closely associated ion pair. This asymmetric ion pair is then attacked by the silane to generate alkylated product.
One example of the anion-binding mechanism is the hydrocyanation of imines catalyzed by Jacobsen's amido-thiourea catalyst depicted in the below diagram. This reaction is also one of the most extensively studied through computational, spectroscopic, labeling and kinetic experiments. [ 14 ] While direct addition of cyanide to a catalyst-bound imine was considered, an alternative mechanism involving formation of an iminium-cyanide ion pair controlled by catalyst was calculated to have a barrier that is lower by 20 kcal/mol. The proposed most likely mechanism begins with binding of the catalyst to HNC, which exists in equilibrium with HCN . This complex then protonates a molecule of imine, forming an iminium-cyanide ion pair with the catalyst binding and stabilizing the cyanide anion. The iminium is thought to also interact with the amide carbonyl on the catalyst molecule (see bifunctional catalysis below). The bound cyanide anion then rotates, and attacks the iminium through carbon. The investigators conclude that though imine-urea binding was observed through spectroscopy and was supported by early kinetic experiments, imine binding is off-cycle and all evidence points toward this mechanism involving thiourea-bound cyanide.
It is often difficult to distinguish between hydrogen-bond catalysis and general acid catalysis . [ 3 ] Hydrogen-bond donors can have varying acidity, from mild to essentially strong Brønsted acids like phosphoric acids. Looking at the extent of proton transfer over the course of the reaction is challenging and has not been investigated thoroughly in most reactions. Nevertheless, strong acid catalysts are often grouped with hydrogen-bond catalysts as they represent an extreme on this continuum and their catalytic behaviors share similarities. The mechanism of activation for these reactions involves initial protonation of the electrophilic partner. This has the effect of rendering the substrate more electrophilic and creating an ion pair, through which it is possible to transfer stereochemical information.
Asymmetric catalysis involving nearly complete protonation of substrate has been effective in Mannich reactions of aromatic aldimines with carbon nucleophiles. [ 15 ] In addition, aza- Friedel-Crafts reactions of furans , amidoalkylations of diazocarbonyl compounds, asymmetric hydrophosphonylation of aldimines and transfer hydrogenations have also been reported. [ 3 ] Chiral Brønsted acids are often easily prepared from chiral alcohols such as BINOLs, and many are already present in the literature due to their established utility in molecular recognition research. [ 16 ]
One of the main advantages of hydrogen-bond catalysis is the ability to construct catalysts that engage in multiple non-covalent interactions to promote the reaction. In addition to using hydrogen-bond donors to activate or stabilize a reactive center during the reaction, it is possible to introduce other functional groups, such as Lewis bases , arenes, or addition hydrogen-bonding sites to lend additional stabilization or to influence the other reactive partner.
For instance, the natural enzyme chorismate mutase , which catalyzes the Claisen rearrangement of chorismate, features many other interactions in addition to the hydrogen bonds involved in stabilizing the enolate-like fragment, which is an example of the anionic fragment stabilization strategy discussed above. [ 17 ] A key interaction is the stabilization of the other cationic allyl fragment through a cation-pi interaction in the transition state. The use of many additional hydrogen bonds has several putative purposes. The stabilization of multiple hydrogen bonds to the enzyme helps overcome the entropic cost of binding. Additionally, the interactions help hold the substrate in a reactive conformation, and the enzyme-catalyzed reaction has near-zero entropy of activation, while typical Claisen rearrangements in solution have very negative entropies of activation.
The use of cation-pi interactions has also been implemented in reactions with synthetic catalysts. A combination of anion-binding and cation-pi strategies can be used to effect enantioselective cationic polycyclizations. [ 18 ] In the transition state, it is proposed that the thiourea group binds chloride, while the aromatic system stabilizes the associated polyene cation. In support of this, increasing the size of the aromatic ring leads to improvements both in yield and stereoselectivity. The enantioselectivity correlates well with both the polarizability and the quadrupole moment of the aryl group.
Since such a large number of catalysts and reactions involve binding to electrophiles to stabilize the transition state, many bifunctional catalysts also present a Lewis-basic, hydrogen-bond acceptor site. As a representative example, Deng and coworkers have developed a thiourea-amine catalyst capable of promoting stereoselective Michael reactions. [ 19 ] In the proposed transition state, one of the thiourea N–H donors is coordinated to the Michael acceptor and will stabilize the negative charge buildup. The basic nitrogen lone pair acts as a hydrogen-bond acceptor to coordinate the nucleophile, but in the transition state acts as a general base to promote the nucleophilic enolate addition.
This motif of engaging both the nucleophilic and electrophilic partners in a reaction and stabilizing them in the transition state is very common in bifunctional catalysis and many more examples can be found in the article on thiourea organocatalysis .
A relatively new strategy of using synthetic oligopeptides to perform catalysis has yielded many examples of catalytic methods. [ 20 ] Peptides feature multiple potential sites for hydrogen bonding and it is generally not understood how these engage substrate or how they promote reaction. Peptides have the advantage of being extremely modular and often these catalysts are screened in large arrays. Highly enantioselective reactions have been discovered in this manner such as the aldol reaction depicted below.
Other transformations catalyzed by synthetic peptides include hydrocyanation, acylation, conjugate additions, aldehyde-imine couplings, aldol reaction and bromination. Although the nature of the transition states is unclear, in many examples small changes in the catalyst structure have dramatic effects on reactivity. It is hypothesized that a large number of hydrogen bonds both within the peptide and between catalyst and substrate must cooperate to meet the geometrical requirements for catalysis. Beyond this, understanding of catalyst design and mechanism has not yet progressed beyond requiring the testing of libraries of peptides.
The types of hydrogen-bond donors used in catalysis vary widely from reaction to reaction, even among similar catalytic strategies. While specific systems are often studied and optimized extensively, a general understanding of the optimal donor for a reaction or the relationship between catalyst structure and reactivity is greatly lacking. It is not yet practical to rationally design structures to promote a desired reaction with the desired selectivity. However, contemporary hydrogen-bond catalysis is primarily focused on a few types of systems that experimentally seem to be effective in a variety of situations. [ 21 ] These are termed "privileged structures". However, it is worth noting that other structural scaffolds and motifs have also shown promising results, such as metal-coordinated hydrogen-bond donors. [ 22 ]
In general, acidity of donor sites correlates well with the strength of the donor. For example, it is a common strategy to add electron-withdrawing aryl substituents on a thiourea catalyst, which can increase its acidity and thus the strength of its hydrogen bonding. However, it is still unclear how donor strength correlates with desired reactivity. Importantly, more acidic catalysts are not necessarily more effective. For instance, ureas are less acidic than thioureas by roughly 6 pKa units, but it is not generally true that ureas are significantly worse are catalyzing reactions. [ 28 ]
Furthermore, the effect of varying substituents on the catalyst is rarely well understood. Small substituent changes can completely change reactivity or selectivity. An example of this was in the optimization studies of a bifunctional Strecker reaction catalyst, one of the first well-studied thiourea catalysts. [ 29 ] Specifically, varying the X substituent on the salicylaldimine substituent, it was found that typical electron-withdrawing or electron-donating substituents had little effect on the rate, but ester substituents such as acetate or pivaloate seemed to cause noticeable rate acceleration. This observation is difficult to rationalize given that the X group is far from the reactive center during the course of the reaction and electronics do not seem to be the cause.
To date, there have been few examples of hydrogen-bond catalysis in the synthesis of natural products despite the large number of reactions being discovered. Generally, with high required catalyst loading and often extreme substrate specificity, hydrogen-bond catalysis is not yet useful.
In the Jacobsen synthesis of (+)-yohimbine, [ 30 ] an indole alkaloid, an early enantioselective Pictet-Spengler reaction using a pyrrole-substituted thiourea catalyst produced gram-scale quantities of product in 94% ee and 81% yield. The remainder of the synthesis was short, using a reductive amination and an intramolecular Diels-Alder reaction.
In 2008, Takemoto disclosed a concise synthesis of (−)-epibatidine that relied on a Michael cascade, catalyzed by a bifunctional catalyst. [ 31 ] After initial asymmetric Michael addition to the β-nitrostyrene , intramolecular Michael addition furnishes the cyclic ketoester product in 75% ee. Standard functional group manipulations and an intramolecular cyclization yields the natural product.
Aside from total synthesis, hydrogen-bond catalysis has been applied to the bulk synthesis of difficult-to-access chiral small molecules. An example is the gram-scale Strecker synthesis of unnatural amino acids using thiourea catalysis, reported in the journal Nature in 2009. [ 32 ] The catalyst, whether polymer-bound or homogeneous, is derived from natural tert-leucine and can catalyze (4 mol% catalyst loading) the formation of the Strecker product from benzhydryl amines and aqueous HCN. Hydrolysis of the nitrile and deprotections produces pure unnatural tert-leucine in 84% overall yield and 99% ee. | https://en.wikipedia.org/wiki/Hydrogen-bond_catalysis |
A hydrogen-donor solvent is hydrocarbon that transfers hydrogen to hydrogen-poor substrates, such as coal . The hydrogen-poor substrates could be a solute or suspension. The classic hydrogen-donor solvent (or just donor solvent) is tetrahydronaphthalene , [ 1 ] which converts to naphthalene by transfer of two equivalents of H 2 to the substrate. The enthalpy of hydrogenation of naphthalene is relatively low, which allows the tetrahydronaphthalene to be regenerated in the presence of high pressure H 2 . Catalysts are often used, such as molybdenum disulfide . Related hydrogen donor solvents or solvent components are dihydro phenanthrene and tetrahydroquinoline . [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/Hydrogen-donor_solvent |
A hydrogen-like atom (or hydrogenic atom ) is any atom or ion with a single valence electron . These atoms are isoelectronic with hydrogen . Examples of hydrogen-like atoms include, but are not limited to, hydrogen itself, all alkali metals such as Rb and Cs , singly ionized alkaline earth metals such as Ca + and Sr + and other ions such as He + , Li 2+ , and Be 3+ and isotopes of any of the above. A hydrogen-like atom includes a positively charged core consisting of the atomic nucleus and any core electrons as well as a single valence electron. Because helium is common in the universe, the spectroscopy of singly ionized helium is important in EUV astronomy, for example, of DO white dwarf stars.
The non-relativistic Schrödinger equation and relativistic Dirac equation for the hydrogen atom can be solved analytically, owing to the simplicity of the two-particle physical system. The one-electron wave function solutions are referred to as hydrogen-like atomic orbitals . Hydrogen-like atoms are of importance because their corresponding orbitals bear similarity to the hydrogen atomic orbitals.
Other systems may also be referred to as "hydrogen-like atoms", such as muonium (an electron orbiting an antimuon ), positronium (an electron and a positron ), certain exotic atoms (formed with other particles), or Rydberg atoms (in which one electron is in such a high energy state that it sees the rest of the atom effectively as a point charge ).
In the solution to the Schrödinger equation, which is non-relativistic, hydrogen-like atomic orbitals are eigenfunctions of the one-electron angular momentum operator L and its z component L z . A hydrogen-like atomic orbital is uniquely identified by the values of the principal quantum number n , the angular momentum quantum number l , and the magnetic quantum number m . The energy eigenvalues do not depend on l or m , but solely on n . To these must be added the two-valued spin quantum number m s = ± 1 ⁄ 2 , setting the stage for the Aufbau principle . This principle restricts the allowed values of the four quantum numbers in electron configurations of more-electron atoms. In hydrogen-like atoms all degenerate orbitals of fixed n and l , m and s varying between certain values (see below) form an atomic shell .
The Schrödinger equation of atoms or ions with more than one electron has not been solved analytically, because of the computational difficulty imposed by the Coulomb interaction between the electrons. Numerical methods must be applied in order to obtain (approximate) wavefunctions or other properties from quantum mechanical calculations. Due to the spherical symmetry (of the Hamiltonian ), the total angular momentum J of an atom is a conserved quantity. Many numerical procedures start from products of atomic orbitals that are eigenfunctions of the one-electron operators L and L z . The radial parts of these atomic orbitals are sometimes numerical tables or are sometimes Slater orbitals . By angular momentum coupling many-electron eigenfunctions of J 2 (and possibly S 2 ) are constructed.
In quantum chemical calculations hydrogen-like atomic orbitals cannot serve as an expansion basis, because they are not complete. The non-square-integrable continuum (E > 0) states must be included to obtain a complete set, i.e., to span all of one-electron Hilbert space. [ 1 ]
In the simplest model, the atomic orbitals of hydrogen-like atoms/ions are solutions to the Schrödinger equation in a spherically symmetric potential . In this case, the potential term is the potential given by Coulomb's law : V ( r ) = − 1 4 π ε 0 Z e 2 r {\displaystyle V(r)=-{\frac {1}{4\pi \varepsilon _{0}}}{\frac {Ze^{2}}{r}}} where
After writing the wave function as a product of functions: ψ ( r , θ , ϕ ) = R n l ( r ) Y ℓ m ( θ , ϕ ) {\displaystyle \psi (r,\theta ,\phi )=R_{nl}(r)Y_{\ell m}(\theta ,\phi )} (in spherical coordinates ), where Y ℓ m {\displaystyle Y_{\ell m}} are spherical harmonics , we arrive at the following Schrödinger equation: − ℏ 2 2 μ [ 1 r 2 ∂ ∂ r ( r 2 ∂ R ( r ) ∂ r ) − l ( l + 1 ) R ( r ) r 2 ] + V ( r ) R ( r ) = E R ( r ) , {\displaystyle -{\frac {\hbar ^{2}}{2\mu }}\left[{\frac {1}{r^{2}}}{\frac {\partial }{\partial r}}\left(r^{2}{\frac {\partial R(r)}{\partial r}}\right)-{\frac {l(l+1)R(r)}{r^{2}}}\right]+V(r)R(r)=ER(r),} where μ {\displaystyle \mu } is, approximately, the mass of the electron (more accurately, it is the reduced mass of the system consisting of the electron and the nucleus), and ℏ {\displaystyle \hbar } is the reduced Planck constant .
Different values of l give solutions with different angular momentum , where l (a non-negative integer) is the quantum number of the orbital angular momentum . The magnetic quantum number m (satisfying − l ≤ m ≤ l {\displaystyle -l\leq m\leq l} ) is the (quantized) projection of the orbital angular momentum on the z -axis. See here for the steps leading to the solution of this equation.
In addition to l and m , a third integer n > 0, emerges from the boundary conditions placed on R . The functions R and Y that solve the equations above depend on the values of these integers, called quantum numbers . It is customary to subscript the wave functions with the values of the quantum numbers they depend on. The final expression for the normalized wave function is: ψ n ℓ m = R n ℓ ( r ) Y ℓ m ( θ , ϕ ) {\displaystyle \psi _{n\ell m}=R_{n\ell }(r)\,Y_{\ell m}(\theta ,\phi )} R n ℓ ( r ) = ( 2 Z n a μ ) 3 ( n − ℓ − 1 ) ! 2 n ( n + ℓ ) ! e − Z r / n a μ ( 2 Z r n a μ ) ℓ L n − ℓ − 1 ( 2 ℓ + 1 ) ( 2 Z r n a μ ) {\displaystyle R_{n\ell }(r)={\sqrt {{\left({\frac {2Z}{na_{\mu }}}\right)}^{3}{\frac {(n-\ell -1)!}{2n{(n+\ell )!}}}}}e^{-Zr/{na_{\mu }}}\left({\frac {2Zr}{na_{\mu }}}\right)^{\ell }L_{n-\ell -1}^{(2\ell +1)}\left({\frac {2Zr}{na_{\mu }}}\right)} where:
parity due to angular wave function is ( − 1 ) ℓ {\displaystyle {\left({-1}\right)}^{\ell }} .
The quantum numbers n {\displaystyle n} , ℓ {\displaystyle \ell } and m {\displaystyle m} are integers and can have the following values: n = 1 , 2 , 3 , 4 , … {\displaystyle n=1,2,3,4,\dots } ℓ = 0 , 1 , 2 , … , n − 1 {\displaystyle \ell =0,1,2,\dots ,n-1} m = − ℓ , − ℓ + 1 , … , 0 , … , ℓ − 1 , ℓ {\displaystyle m=-\ell ,-\ell +1,\ldots ,0,\ldots ,\ell -1,\ell }
For a group-theoretical interpretation of these quantum numbers, see this article . Among other things, this article gives group-theoretical reasons why ℓ < n {\displaystyle \ell <n\,} and − ℓ ≤ m ≤ ℓ {\displaystyle -\ell \leq m\leq \,\ell } .
Each atomic orbital is associated with an angular momentum L . It is a vector operator , and the eigenvalues of its square L 2 ≡ L x 2 + L y 2 + L z 2 are given by: L ^ 2 Y ℓ m = ℏ 2 ℓ ( ℓ + 1 ) Y ℓ m {\displaystyle {\hat {L}}^{2}Y_{\ell m}=\hbar ^{2}\ell (\ell +1)Y_{\ell m}}
The projection of this vector onto an arbitrary direction is quantized . If the arbitrary direction is called z , the quantization is given by: L ^ z Y ℓ m = ℏ m Y ℓ m , {\displaystyle {\hat {L}}_{z}Y_{\ell m}=\hbar mY_{\ell m},} where m is restricted as described above. Note that L 2 and L z commute and have a common eigenstate, which is in accordance with Heisenberg's uncertainty principle . Since L x and L y do not commute with L z , it is not possible to find a state that is an eigenstate of all three components simultaneously. Hence the values of the x and y components are not sharp, but are given by a probability function of finite width. The fact that the x and y components are not well-determined, implies that the direction of the angular momentum vector is not well determined either, although its component along the z -axis is sharp.
These relations do not give the total angular momentum of the electron. For that, electron spin must be included.
This quantization of angular momentum closely parallels that proposed by Niels Bohr (see Bohr model ) in 1913, with no knowledge of wavefunctions.
In a real atom, the spin of a moving electron can interact with the electric field of the nucleus through relativistic effects, a phenomenon known as spin–orbit interaction . When one takes this coupling into account, the spin and the orbital angular momentum are no longer conserved , which can be pictured by the electron precessing . Therefore, one has to replace the quantum numbers l , m and the projection of the spin m s by quantum numbers that represent the total angular momentum (including spin ), j and m j , as well as the quantum number of parity .
See the next section on the Dirac equation for a solution that includes the coupling.
In 1928 in England Paul Dirac found an equation that was fully compatible with special relativity . The equation was solved for hydrogen-like atoms the same year (assuming a simple Coulomb potential around a point charge) by the German Walter Gordon . Instead of a single (possibly complex) function as in the Schrödinger equation, one must find four complex functions that make up a bispinor . The first and second functions (or components of the spinor) correspond (in the usual basis) to spin "up" and spin "down" states, as do the third and fourth components.
The terms "spin up" and "spin down" are relative to a chosen direction, conventionally the z direction. An electron may be in a superposition of spin up and spin down, which corresponds to the spin axis pointing in some other direction. The spin state may depend on location.
An electron in the vicinity of a nucleus necessarily has non-zero amplitudes for the third and fourth components. Far from the nucleus these may be small, but near the nucleus they become large.
The eigenfunctions of the Hamiltonian , which means functions with a definite energy (and which therefore do not evolve except for a phase shift), have energies characterized not by the quantum number n only (as for the Schrödinger equation), but by n and a quantum number j , the total angular momentum quantum number . The quantum number j determines the sum of the squares of the three angular momenta to be j ( j +1) (times ħ 2 , see Planck constant ). These angular momenta include both orbital angular momentum (having to do with the angular dependence of ψ) and spin angular momentum (having to do with the spin state). The splitting of the energies of states of the same principal quantum number n due to differences in j is called fine structure . The total angular momentum quantum number j ranges from 1/2 to n −1/2.
The orbitals for a given state can be written using two radial functions and two angle functions. The radial functions depend on both the principal quantum number n and an integer k , defined as:
where ℓ is the azimuthal quantum number that ranges from 0 to n −1. The angle functions depend on k and on a quantum number m which ranges from − j to j by steps of 1. The states are labeled using the letters S, P, D, F et cetera to stand for states with ℓ equal to 0, 1, 2, 3 et cetera (see azimuthal quantum number ), with a subscript giving j . For instance, the states for n =4 are given in the following table (these would be prefaced by n , for example 4S 1/2 ):
These can be additionally labeled with a subscript giving m . There are 2 n 2 states with principal quantum number n , 4 j +2 of them with any allowed j except the highest ( j = n −1/2) for which there are only 2 j +1. Since the orbitals having given values of n and j have the same energy according to the Dirac equation, they form a basis for the space of functions having that energy.
The energy, as a function of n and | k | (equal to j +1/2), is:
E n j = μ c 2 ( 1 + [ Z α n − | k | + k 2 − Z 2 α 2 ] 2 ) − 1 / 2 ≈ μ c 2 { 1 − Z 2 α 2 2 n 2 [ 1 + Z 2 α 2 n ( 1 | k | − 3 4 n ) ] } {\displaystyle {\begin{array}{rl}E_{n\,j}&=\mu c^{2}\left(1+\left[{\dfrac {Z\alpha }{n-|k|+{\sqrt {k^{2}-Z^{2}\alpha ^{2}}}}}\right]^{2}\right)^{-1/2}\\&\\&\approx \mu c^{2}\left\{1-{\dfrac {Z^{2}\alpha ^{2}}{2n^{2}}}\left[1+{\dfrac {Z^{2}\alpha ^{2}}{n}}\left({\dfrac {1}{|k|}}-{\dfrac {3}{4n}}\right)\right]\right\}\end{array}}}
(The energy of course depends on the zero-point used.) Note that if Z were able to be more than 137 (higher than any known element) then we would have a negative value inside the square root for the S 1/2 and P 1/2 orbitals, which means they would not exist. The Schrödinger solution corresponds to replacing the inner bracket in the second expression by 1. The accuracy of the energy difference between the lowest two hydrogen states calculated from the Schrödinger solution is about 9 ppm (90 μ eV too low, out of around 10 eV), whereas the accuracy of the Dirac equation for the same energy difference is about 3 ppm (too high). The Schrödinger solution always puts the states at slightly higher energies than the more accurate Dirac equation. The Dirac equation gives some levels of hydrogen quite accurately (for instance the 4P 1/2 state is given an energy only about 2 × 10 −10 eV too high), others less so (for instance, the 2S 1/2 level is about 4 × 10 −6 eV too low). [ 2 ] The modifications of the energy due to using the Dirac equation rather than the Schrödinger solution is of the order of α 2 , and for this reason α is called the fine-structure constant .
In the general case, the solution to the Dirac equation for quantum numbers n , k , and m , is:
Ψ = ( g n , k ( r ) r − 1 Ω k , m ( θ , ϕ ) i f n , k ( r ) r − 1 Ω − k , m ( θ , ϕ ) ) = ( g n , k ( r ) r − 1 ( k + 1 2 − m ) / ( 2 k + 1 ) Y k , m − 1 / 2 ( θ , ϕ ) − g n , k ( r ) r − 1 sgn k ( k + 1 2 + m ) / ( 2 k + 1 ) Y k , m + 1 / 2 ( θ , ϕ ) i f n , k ( r ) r − 1 ( − k + 1 2 − m ) / ( − 2 k + 1 ) Y − k , m − 1 / 2 ( θ , ϕ ) i f n , k ( r ) r − 1 sgn k ( − k + 1 2 + m ) / ( − 2 k + 1 ) Y − k , m + 1 / 2 ( θ , ϕ ) ) {\displaystyle \Psi ={\begin{pmatrix}g_{n,k}(r)r^{-1}\Omega _{k,m}(\theta ,\phi )\\if_{n,k}(r)r^{-1}\Omega _{-k,m}(\theta ,\phi )\end{pmatrix}}={\begin{pmatrix}g_{n,k}(r)r^{-1}{\sqrt {(k+{\tfrac {1}{2}}-m)/(2k+1)}}Y_{k,m-1/2}(\theta ,\phi )\\-g_{n,k}(r)r^{-1}\operatorname {sgn} k{\sqrt {(k+{\tfrac {1}{2}}+m)/(2k+1)}}Y_{k,m+1/2}(\theta ,\phi )\\if_{n,k}(r)r^{-1}{\sqrt {(-k+{\tfrac {1}{2}}-m)/(-2k+1)}}Y_{-k,m-1/2}(\theta ,\phi )\\if_{n,k}(r)r^{-1}\operatorname {sgn} k{\sqrt {(-k+{\tfrac {1}{2}}+m)/(-2k+1)}}Y_{-k,m+1/2}(\theta ,\phi )\end{pmatrix}}}
where the Ωs are columns of the two spherical harmonics functions shown to the right. Y a , b ( θ , ϕ ) {\displaystyle Y_{a,b}(\theta ,\phi )} signifies a spherical harmonic function:
in which P a b {\displaystyle P_{a}^{b}} is an associated Legendre polynomial . (Note that the definition of Ω may involve a spherical harmonic that doesn't exist, like Y 0 , 1 {\displaystyle Y_{0,1}} , but the coefficient on it will be zero.)
Here is the behavior of some of these angular functions. The normalization factor is left out to simplify the expressions.
From these we see that in the S 1/2 orbital ( k = −1), the top two components of Ψ have zero orbital angular momentum like Schrödinger S orbitals, but the bottom two components are orbitals like the Schrödinger P orbitals. In the P 1/2 solution ( k = 1), the situation is reversed. In both cases, the spin of each component compensates for its orbital angular momentum around the z axis to give the right value for the total angular momentum around the z axis.
The two Ω spinors obey the relationship:
To write the functions g n , k ( r ) {\displaystyle g_{n,k}(r)} and f n , k ( r ) {\displaystyle f_{n,k}(r)} let us define a scaled radius ρ:
with
where E is the energy ( E n j {\displaystyle E_{n\,j}} ) given above. We also define γ as:
g n , k ( r ) and f n , k ( r ) {\displaystyle g_{n,k}(r){\text{ and }}f_{n,k}(r)} are based on two generalized Laguerre polynomials of order n − | k | − 1 {\displaystyle n-|k|-1} and n − | k | {\displaystyle n-|k|} :
where A is a normalization constant involving the gamma function :
f is small compared to g (except at very small r ) because when k is positive the first terms dominate, and α is big compared to γ− k , whereas when k is negative the second terms dominate and α is small compared to γ− k . Note that the dominant term is quite similar to corresponding the Schrödinger solution – the upper index on the Laguerre polynomial is slightly less (2γ+1 or 2γ−1 rather than 2ℓ+1, which is the nearest integer), as is the power of ρ (γ or γ−1 instead of ℓ, the nearest integer). The exponential decay is slightly faster than in the Schrödinger solution.
The normalization factor makes the integral over all space of the square of the absolute value equal to 1.
When k = − n (which corresponds to the highest j possible for a given n , such as 1S 1/2 , 2P 3/2 , 3D 5/2 ...), then g n , k ( r ) {\displaystyle g_{n,k}(r)} and f n , k ( r ) {\displaystyle f_{n,k}(r)} are:
With A now reduced to:
Notice that because of the factor Zα, f ( r) is small compared to g ( r ). Also notice that in this case, the energy is given by
and the radial decay constant C by
Here is the 1S 1/2 orbital, spin up, without normalization:
Note that γ is a little less than 1, so the top function is similar to an exponentially decreasing function of r except that at very small r it theoretically goes to infinity. But the value of the r γ − 1 {\displaystyle r^{\gamma -1}} only surpasses 10 at a value of r smaller than 10 1 / ( γ − 1 ) , {\displaystyle 10^{1/(\gamma -1)},} which is a very small number (much less than the radius of a proton) unless Z is very large.
The 1S 1/2 orbital, spin down, without normalization, comes out as:
We can mix these in order to obtain orbitals with the spin oriented in some other direction, such as:
which corresponds to the spin and angular momentum axis pointing in the x direction. Adding i times the "down" spin to the "up" spin gives an orbital oriented in the y direction.
To give another example, the 2P 1/2 orbital, spin up, is proportional to:
(Remember that ρ = 2 r C {\displaystyle \rho =2rC} . C is about half what it is for the 1S orbital, but γ is still the same.)
Notice that when ρ is small compared to α (or r is small compared to ℏ c / ( μ c 2 ) {\displaystyle \hbar c/(\mu c^{2})} ) the "S" type orbital dominates (the third component of the bispinor).
For the 2S 1/2 spin up orbital, we have:
Now the first component is S-like and there is a radius near ρ = 2 where it goes to zero, whereas the bottom two-component part is P-like.
In addition to bound states, in which the energy is less than that of an electron infinitely separated from the nucleus, there are solutions to the Dirac equation at higher energy, corresponding to an unbound electron interacting with the nucleus. These solutions are not normalizable, but solutions can be found which tend toward zero as r goes to infinity (which is not possible when | E | < μ c 2 {\displaystyle |E|<\mu c^{2}} except at the above-mentioned bound-state values of E ). There are similar solutions with E < − μ c 2 . {\displaystyle E<-\mu c^{2}.} These negative-energy solutions are just like positive-energy solutions having the opposite energy but for a case in which the nucleus repels the electron instead of attracting it, except that the solutions for the top two components switch places with those for the bottom two.
Negative-energy solutions to Dirac's equation exist even in the absence of a Coulomb force exerted by a nucleus. Dirac hypothesized that we can consider almost all of these states to be already filled. If one of these negative-energy states is not filled, this manifests itself as though there is an electron which is repelled by a positively-charged nucleus. This prompted Dirac to hypothesize the existence of positively-charged electrons, and his prediction was confirmed with the discovery of the positron .
The Dirac equation with a simple Coulomb potential generated by a point-like non-magnetic nucleus was not the last word, and its predictions differ from experimental results as mentioned earlier. More accurate results include the Lamb shift (radiative corrections arising from quantum electrodynamics ) [ 3 ] and hyperfine structure . | https://en.wikipedia.org/wiki/Hydrogen-like_atom |
Hydrogen-oxidizing bacteria are a group of facultative autotrophs that can use hydrogen as an electron donor . They can be divided into aerobes and anaerobes . The former use hydrogen as an electron donor and oxygen as an acceptor while the latter use sulphate or nitrogen dioxide as electron acceptors . [ 1 ] Species of both types have been isolated from a variety of environments, including fresh waters, sediments, soils, activated sludge, hot springs, hydrothermal vents and percolating water. [ 2 ]
These bacteria are able to exploit the special properties of molecular hydrogen (for instance redox potential and diffusion coefficient) thanks to the presence of hydrogenases . [ 3 ] The aerobic hydrogen-oxidizing bacteria are facultative autotrophs, but they can also have mixotrophic or completely heterotrophic growth. Most of them show greater growth on organic substrates. The use of hydrogen as an electron donor coupled with the ability to synthesize organic matter, through the reductive assimilation of CO 2 , characterize the hydrogen-oxidizing bacteria.
Among the most represented genera of these organisms are Caminibacter , Aquifex , Ralstonia and Paracoccus .
Hydrogen is the most widespread element in the universe , representing around three-quarters of all atoms. [ 4 ] In the atmosphere , the concentration of molecular hydrogen (H 2 ) gas is about 0.5–0.6 ppm, and so it represents the second-most-abundant trace gas after methane . [ 3 ] H 2 can be used as energy source in biological processes because it has a highly negative redox potential ( E 0 ′ = –0.414 V). It can be coupled with O 2 , in oxidative respiration (2H 2 + O 2 → 2H 2 O), or with oxidized compounds, such as carbon dioxide or sulfate . [ 5 ]
In an ecosystem, hydrogen can be produced through abiotic and biological processes. The abiotic processes are mainly due to geothermal production [ 6 ] and serpentinization . [ 7 ]
In geothermal processes, hydrogen is usually present as a gas and may be obtained by different reactions:
1. Water may react with the silicon radical at high temperature:
Si· + H 2 O → SiOH + H·
H· + H· → H 2
2. A proposed reaction between iron oxides and water may occur at temperatures higher than 800 °C:
2FeO + H 2 O → Fe 2 O 3 + H 2
2Fe 3 O 4 + H 2 O → 3Fe 2 O 3 + H 2 [ 6 ]
Occurring at ambient temperature, serpentinization is an exothermic geochemical mechanism that takes place when ultramafic rocks from deep in the Earth rise and encounter water. This process can produce large quantities of H 2 , as well as methane and organic substances. [ 7 ]
The main biotic mechanisms that lead to the formation of hydrogen are nitrogen fixation and fermentation . The first happens in bacteria, such as cyanobacteria , that have a specialized enzyme, nitrogenase , which catalyzes the reduction of N 2 to NH 4 + . [ 8 ] [ 9 ] In addition, these microorganisms have another enzyme, hydrogenase , that oxidizes the H 2 released as a by-product. [ 4 ] If the nitrogen-fixing bacteria have low amounts of hydrogenase, excess H 2 can be released into the environment. [ 10 ] [ 11 ] The amount of hydrogen released depends on the ratio between H 2 production and consumption. [ 11 ] The second mechanism, fermentation , is performed by some anaerobic heterotrophic bacteria, in particular Clostridia , [ 12 ] that degrade organic molecules, producing hydrogen as one of the products. This type of metabolism mainly occurs in anoxic sites, such as lake sediments , deep-sea hydrothermal vents and the animal gut. [ 13 ]
The ocean is supersaturated with hydrogen, presumably as a result of these biotic processes. Nitrogen fixation is thought to be the major mechanism involved in the production of H 2 in the oceans. [ 3 ] Release of hydrogen in the oceans is dependent on solar radiation , with a daily peak at noon. [ 3 ] [ 14 ] [ 15 ] The highest concentrations are in the first metres near the surface, decreasing to the thermocline and reaching their minimum in the deep oceans. [ 3 ] Globally, tropical and subtropical oceans have the greatest abundance of H 2 . [ 3 ] [ 14 ] [ 16 ] [ 17 ]
H 2 is an important electron donor in hydrothermal vents . In this environment hydrogen oxidation represents a significant origin of energy, sufficient to conduct ATP synthesis and autotrophic CO 2 fixation, so hydrogen-oxidizing bacteria form an important part of the ecosystem in deep sea habitats. Among the main chemosynthetic reactions that take place in hydrothermal vents , the oxidation of sulphide and hydrogen holds a central role. In particular, for autotrophic carbon fixation, hydrogen oxidation metabolism is more favored than sulfide or thiosulfate oxidation, although less energy is released (only –237 kJ/mol compared to –797 kJ/mol). [ 18 ] To fix a mole of carbon during the hydrogen oxidation, one-third of the energy necessary for the sulphide oxidation is used. This is because hydrogen has a more negative redox potential than NAD(P)H. Depending on the relative amounts of sulphide, hydrogen and other species, energy production by oxidation of hydrogen can be as much as 10–18 times higher than production by the oxidation of sulphide. [ 19 ] [ 20 ]
Aerobic hydrogen-oxidizing bacteria, sometimes called knallgas bacteria, are bacteria that oxidize hydrogen with oxygen as final electron acceptor. These bacteria include Hydrogenobacter thermophilus , Cupriavidus necator , and Hydrogenovibrio marinus . There are both Gram positive and Gram negative knallgas bacteria.
Most grow best under microaerobic conditions because the hydrogenase enzyme is inhibited by the presence of oxygen and yet oxygen is still needed as a terminal electron acceptor in energy metabolism. [ 21 ]
The word Knallgas means " oxyhydrogen " (a mixture of hydrogen and oxygen, literally "bang-gas") in German .
Ocean surface water is characterized by a high concentration of hydrogen . [ 22 ] In 1989, an aerobic hydrogen-oxidizing bacterium was isolated from sea water. The MH-110 strain (aka DSM 11271, type strain of Hydrogenovibrio marinus [ 23 ] [ 24 ] ) is able to grow under normal temperature conditions and in an atmosphere (under a continuous gas flow system) characterized by an oxygen saturation of 40% (analogous characteristics are present in the surface water from which the bacteria were isolated, which is a fairly aerated medium). This differs from the usual behaviour of hydrogen-oxidizing bacteria, which in general thrive under microaerophilic conditions (<10% O 2 saturation). [ 25 ] [ 26 ]
This strain is also capable of coupling the hydrogen oxidation with the reduction of sulfur compounds such as thiosulfate and tetrathionate.
Knallgas bacteria are able to fix carbon dioxide using H 2 as their chemical energy source. Knallgas bacteria stand out from other hydrogen -oxidizing bacteria that, although using H 2 as energy source, are not able to fix CO 2 , as Knallgas do. [ 27 ]
This aerobic hydrogen oxidation (H 2 + O 2 ⟶ {\displaystyle \longrightarrow } H 2 O), also known as the Knallgas reaction, releases a considerable amount of energy, having a ΔG o of –237 kJ/mol. The energy is captured as a proton motive force for use by the cell.
The key enzymes involved in this reaction are the hydrogenases , which cleave molecular hydrogen and feed its electrons into the electron transport chain , where they are carried to the final acceptor, O 2 , extracting energy in the process. The hydrogen is ultimately oxidized to water, the end product. [ 28 ] The hydrogenases are divided into three categories according to the type of metal present in the active site. These enzymes were first found in Pseudomonas saccharophila , Alcaligenes ruhlandii and Alcaligenese eutrophus , in which there are two types of hydrogenases: cytoplasmic and membrane-bound. While the first enzyme takes up hydrogen and reduces NAD + to NADH for carbon fixation, the second is involved in the generation of the proton motive force. [ 29 ] [ 30 ] In most knallgas bacteria only the second is found. [ 31 ]
While these microorganisms are facultative autotrophs , some are also able to live heterotrophicically using organic substances as electron donors; in this case, the hydrogenase activity is less important or completely absent. [ 1 ]
However, knallgas bacteria, when growing as chemolithoautotrophs , can integrate a molecule of CO 2 to produce, through the Calvin–Benson cycle , biomolecules necessary for the cell: [ 32 ] [ 33 ]
6H 2 + 2O 2 + CO 2 ⟶ {\displaystyle \longrightarrow } (CH 2 O) + 5H 2 O
A study of Alcaligenes eutropha , a representative knallgas bacterium, found that at low concentrations of O 2 (about 10 mol %) and consequently with a low ΔH 2 /ΔCO 2 molar ratio (3.3), the energy efficiency of CO 2 fixation increases to 50%. Once assimilated, some of the carbon may be stored as polyhydroxybutyrate . [ 34 ] [ 35 ]
Given enough nutrients, H 2 , O 2 and CO 2 , many knallgas bacteria can be grown quickly in vats using only a small amount of land area. This makes it possible to cultivate them as an environmentally sustainable source of food and other products. For example, the polyhydroxybutyrate the bacteria produce can be used as a feedstock to produce biodegradable plastics in various eco-sustainable applications. [ 34 ] [ 35 ]
Solar Foods is a startup that has sought to commercialize knallgas bacteria for food production, using renewable energy to split hydrogen to grow a neutral-tasting, protein-rich food source for use in products such as artificial meat. [ 36 ] Research studies have suggested that knallgas cultivation is more environmentally friendly than traditional agriculture. [ 37 ] | https://en.wikipedia.org/wiki/Hydrogen-oxidizing_bacteria |
Hydrogen-terminated silicon surface is a chemically passivated silicon substrate where the surface Si atoms are bonded to hydrogen. [ 1 ] The hydrogen-terminated surfaces are hydrophobic, luminescent, and amenable to chemical modification. [ 2 ] Hydrogen-terminated silicon is an intermediate in the growth of bulk silicon from silane : [ 3 ] This termination is significant in the semiconductor industry due to its role in preventing oxidation and contamination of silicon surfaces, which is crucial for various applications including microelectronics and nanotechnology. [ 4 ]
Silicon wafers are treated with solutions of electronic-grade hydrofluoric acid in water, buffered water, or alcohol. One of the relevant reactions is simply removal of silicon oxides:
The key reaction however is the formation of the hydrosilane functional group.
atomic force microscope (AFM) has been used to manipulate hydrogen-terminated silicon surfaces. [ 5 ] [ 6 ]
Hydrogen termination removes dangling bonds . All surface Si atoms are tetrahedral. Hydrogen termination confers stability in ambient environments. So again, the surface is both clean (of oxides) and relatively inert . These materials can be handled in air without special care for several minutes. [ 7 ]
The Si-H bond in fact is stronger than the Si-Si bonds. Two kinds of Si-H centers are proposed, both featuring terminal Si-H bonds. One kind of site has one Si-H bond. The other kind of site features SiH 2 centers. [ 3 ]
Like organic hydrosilanes , the H-Si groups on the surface react with terminal alkenes and diazo groups. The reaction is called hydrosilylation . Many kinds of organic compounds with various functions can be introduced onto the silicon surface by the hydrosilylation of a hydrogen-terminated surface. The infrared spectrum of hydrogen-terminated silicon shows a band near 2090 cm −1 , not very different from νSi-H for organic hydrosilanes. [ 7 ]
One group proposed to use the material to create digital circuits made of quantum dots by removing hydrogen atoms from the silicon surface. [ 5 ] The hydrogen-terminated silicon surface is widely used in the fabrication of semiconductor devices. It serves as a precursor for various surface functionalization techniques and is also essential in the formation of silicon-on-insulator (SOI) wafers. [ 8 ]
Despite its stability, hydrogen-terminated silicon can gradually oxidize when exposed to air, forming a thin oxide layer. This process can be monitored using techniques such as X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). [ 9 ] | https://en.wikipedia.org/wiki/Hydrogen-terminated_silicon_surface |
A hydrogen analyzer is a device used to measure the hydrogen concentration in steels and alloys when the hydrogen concentration is unknown. [ 1 ] It also has industrial applications for corrosion monitoring .
This chemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrogen_analyzer |
The hydrogen anion , H − , is a negative ion of hydrogen, that is, a hydrogen atom that has captured an extra electron. The hydrogen anion is an important constituent of the atmosphere of stars , such as the Sun . In chemistry, this ion is called hydride . The ion has two electrons bound by the electromagnetic force to a nucleus containing one proton.
The binding energy of H − equals the binding energy of an extra electron to a hydrogen atom, called electron affinity of hydrogen. It is measured to be 0.754 195 (19) eV [ 2 ] or 0.027 716 16 (70) hartree (see Electron affinity (data page) ). The total ground state energy thus becomes −14.359 888 eV .
The hydrogen anion is the dominant bound-free opacity source at visible and near-infrared wavelengths in the atmospheres of stars like the Sun and cooler; [ 3 ] its importance was first noted in the 1930s. [ 4 ] The ion absorbs photons with energies in the range 0.75–4.0 eV, which ranges from the infrared into the visible spectrum. [ 5 ] [ 6 ] Most of the electrons in these negative ions come from the ionization of metals with low first ionization potentials, including the alkali metals and alkaline earths . The process which ejects the electron from the ion is properly called photodetachment rather than photoionization because the result is a neutral atom (rather than an ion) and a free electron.
H − also occurs in the Earth's ionosphere [ 5 ] and can be produced in particle accelerators . [ 7 ]
Its existence was first proven theoretically by Hans Bethe in 1929, [ 8 ] who used Hylleraas's variational method to show that H − is bound. He estimated its ground-state energy as −1.0506 Ry ( −0.5253 E h ), placing it below the hydrogen atom's ground state energy ( −0.5 E h ). H − is unusual because, in its free form, it has no bound excited states , as was finally proven in 1977. [ 9 ]
In chemistry, hydrogen has the formal oxidation state −1 in the hydride anion.
The term hydride is probably most often used to describe compounds of hydrogen with other elements in which the hydrogen is in the formal −1 oxidation state . In most such compounds the bonding between the hydrogen and its nearest neighbor is covalent. An example of a hydride is the borohydride anion ( BH − 4 ). | https://en.wikipedia.org/wiki/Hydrogen_anion |
The hydrogen assisted magnesiothermic reduction (" HAMR ") process is a thermochemical process to obtain titanium metal from titanium oxides. [ 1 ] [ 2 ]
A technical challenge in the production of titanium metal is the formation of oxide impurities. The Kroll process , which is widely used commercially, addresses this challenge by converting titanium ore (an oxide) into titanium tetrachloride (TiCl 4 ). This intermediate is readily purified. It is reduced to titanium metal with magnesium. This technology is both capital, energy, and carbon-intensive . One advantage of the Kroll process, and several like it, is that it starts with titanium ores (e.g., illmenite ), not a purified dioxide.
The HAMR technology also entails a two step process, starting with TiO 2 under an atmosphere of hydrogen gas. The product TiH 2 can be further processed to titanium metal through standard methods. The reduction of titanium oxides to titanium metal using magnesium does not occur. The novelty of the HAMR process is the inclusion of hydrogen. [ 3 ] | https://en.wikipedia.org/wiki/Hydrogen_assisted_magnesiothermic_reduction |
Hydrogen chloride Hydrogen fluoride Hydrogen iodide
Hydrogen astatide , also known as astatine hydride , astatane , astatidohydrogen or hydroastatic acid , is a chemical compound with the chemical formula HAt, consisting of an astatine atom covalently bonded to a hydrogen atom. [ 4 ] It thus is a hydrogen halide .
This chemical compound can dissolve in water to form hydroastatic acid, which exhibits properties very similar to the other five binary acids , and is in fact the strongest among them. However, it is limited in use due to its ready decomposition into elemental hydrogen and astatine, [ 5 ] as well as the short half-life of the various isotopes of astatine . Because the atoms have a nearly equal electronegativity , and as the At + ion has been observed, [ 6 ] dissociation could easily result in the hydrogen carrying the negative charge. Thus, a hydrogen astatide sample can undergo the following reaction:
This results in elemental hydrogen gas and astatine precipitate . Furthermore, a trend for hydrogen halides, or HX, is that enthalpy of formation becomes less negative, i.e., decreases in magnitude but increases in absolute terms, as the halide becomes larger. Whereas hydroiodic acid solutions are stable, the hydronium-astatide solution is clearly less stable than the water-hydrogen-astatine system. Finally, radiolysis from astatine nuclei could sever the H–At bonds.
Additionally, astatine has no stable isotopes . The most stable is astatine-210, which has a half-life of approximately 8.1 hours, making its chemical compounds especially difficult to work with, [ 7 ] as the astatine will quickly decay into other elements.
Hydrogen astatide can be produced by reacting astatine with hydrocarbons (such as ethane ): [ 8 ]
This reaction also produces the corresponding alkyl astatide, in this case ethyl astatide (astatoethane). | https://en.wikipedia.org/wiki/Hydrogen_astatide |
In chemistry , hydrogen atom abstraction , or hydrogen atom transfer ( HAT ), refers to a class of chemical reactions where a hydrogen free radical (a neutral hydrogen atom ) is removed from a substrate with another molecule. This process follows the general equation:
HAT reactions are common in various redox reactions , hydrocarbon combustion , and interactions involving cytochrome P450 that contain an Fe(V)O unit. The entity removing the hydrogen atom, known as the abstractor ( X• ), is often a radical itself, though in some instances, it may be a species with a closed electron shell , such as chromyl chloride . Hydrogen atom transfer can occur via a mechanism known as proton-coupled electron transfer . An illustrative synthetic instance of HAT is observed in iron zeolites , which facilitate the stabilization of alpha-oxygen . [ 1 ] [ 2 ] | https://en.wikipedia.org/wiki/Hydrogen_atom_abstraction |
Hydrogen auto-transfer , also known as borrowing hydrogen , is the activation of a chemical reaction by temporary transfer of two hydrogen atoms from the reactant to a catalyst and return of those hydrogen atoms back to a reaction intermediate to form the final product . [ 1 ] [ 2 ] [ 3 ] [ 4 ] Two major classes of borrowing hydrogen reactions exist: (a) those that result in hydroxyl substitution, [ 1 ] [ 2 ] and (b) those that result in carbonyl addition. [ 3 ] [ 4 ] In the former case, alcohol dehydrogenation generates a transient carbonyl compound that is subject to condensation followed by the return of hydrogen. In the latter case, alcohol dehydrogenation is followed by reductive generation of a nucleophile, which triggers carbonyl addition. As borrowing hydrogen processes avoid manipulations otherwise required for discrete alcohol oxidation and the use of stoichiometric organometallic reagents, they typically display high levels of atom-economy and, hence, are viewed as examples of Green chemistry .
The Guerbet reaction , reported in 1899, [ 5 ] is an early example of a hydrogen auto-transfer process. The Guerbet reaction converts primary alcohols to β-alkylated dimers via alcohol dehydrogenation followed by aldol condensation and reduction of the resulting enones. Application of the Guerbet reaction to the development of ethanol-to-butanol processes has garnered interest as a method for the production of renewable fuels . [ 6 ] In 1932 using heterogeneous nickel-catalysts Adkins reported the first alcohol aminations that occur through alcohol dehydrogenation-reductive amination. [ 7 ] Homogenous catalysts for alcohol amination based on rhodium and ruthenium were developed by Grigg [ 8 ] and Watanabe [ 9 ] in 1981. The first hydrogen auto-transfer processes that convert primary alcohols to products of carbonyl addition were reported by Michael J. Krische in 2007-2008 using homogenous iridium and ruthenium catalysts. [ 10 ] [ 11 ] [ 12 ]
Alcohol aminations are among the most commonly utilized borrowing hydrogen processes. [ 13 ] [ 14 ] [ 15 ] In reactions of this type, alcohol dehydrogenation is followed by reductive amination of the resulting carbonyl compound. This represents an alternative to two-step processes involving conversion of the alcohol to a halide or sulfonate ester followed by nucleophilic substitution
As shown below, alcohol amination has been used on kilogram scale by Pfizer for the synthesis of advanced pharmaceutical intermediates. [ 16 ] Additionally, AstraZeneca has used methanol as an alternative to conventional genotoxic methylating agents such as methyl iodide or dimethyl sulfate . [ 17 ] Nitroaromatics can also participate as amine precursors in borrowing hydrogen-type alcohol aminations. [ 18 ]
The formation of carbon–carbon bonds have been achieved through borrowing hydrogen-type indirect Wittig, [ 19 ] aldol, [ 20 ] Knoevenagel condensations [ 21 ] and also through various carbon nucleophiles. [ 22 ] [ 23 ] Related to the Guerbet reaction, Donohoe and coworkers have developed enantioselective borrowing hydrogen-type enolate alkylations. [ 24 ]
As exemplified by the Krische allylation , dehydrogenation of alcohol reactants can be balanced by reduction of allenes, dienes or allyl acetate to generate allylmetal-carbonyl pairs that combine to give products of carbonyl addition. [ 3 ] [ 4 ] In this way, lower alcohols are directly transformed to higher alcohols in a manner that significantly decreases waste. [ 25 ]
In 2008, borrowing hydrogen reactions of 1,3-enynes with alcohols to form products of carbonyl propargylation was discovered. [ 26 ] An enantioselective variant of this method was recently used in the total synthesis of leiodermatolide A. [ 27 ] | https://en.wikipedia.org/wiki/Hydrogen_auto-transfer |
In chemistry , a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force . It occurs when a hydrogen (H) atom, covalently bonded to a more electronegative donor atom or group ( Dn ), interacts with another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor ( Ac ). Unlike simple dipole–dipole interactions, hydrogen bonding arises from charge transfer (nB → σ*AH), orbital interactions, and quantum mechanical delocalization , making it a resonance-assisted interaction rather than a mere electrostatic attraction. [ 5 ]
The general notation for hydrogen bonding is Dn−H···Ac , where the solid line represents a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. [ 6 ] The most frequent donor and acceptor atoms are nitrogen (N), oxygen (O), and fluorine (F), due to their high electronegativity and ability to engage in stronger hydrogen bonding.
The term "hydrogen bond" is generally used for well-defined, localized interactions with significant charge transfer and orbital overlap, such as those in DNA base pairing or ice. In contrast, "hydrogen-bonding interactions" is a broader term used when the interaction is weaker, more dynamic, or delocalized, such as in liquid water, supramolecular assemblies (e.g.: lipid membranes , protein-protein interactions ), or weak C-H···O interactions. This distinction is particularly relevant in structural biology , materials science , and computational chemistry , where hydrogen bonding spans a continuum from weak van der Waals-like interactions to nearly covalent bonding. [ 5 ]
Hydrogen bonding can occur between separate molecules (intermolecular) or within different parts of the same molecule (intramolecular). [ 7 ] [ 8 ] [ 9 ] [ 10 ] Its strength varies considerably, depending on geometry, environment, and the donor-acceptor pair, typically ranging from 1 to 40 kcal/mol. [ 11 ] This places hydrogen bonds stronger than van der Waals interactions but generally weaker than covalent or ionic bonds .
Hydrogen bonding plays a fundamental role in chemistry, biology, and materials science. It is responsible for the anomalously high boiling point of water, the stabilization of protein and nucleic acid structures, and key properties of materials like paper, wool, and hydrogels. In biological systems, hydrogen bonds mediate molecular recognition, enzyme catalysis, and DNA replication, while in materials science, they contribute to self-assembly, adhesion, and supramolecular organization.
In a hydrogen bond, the electronegative atom not covalently attached to the hydrogen is named the proton acceptor, whereas the one covalently bound to the hydrogen is named the proton donor. This nomenclature is recommended by the IUPAC. [ 6 ] The hydrogen of the donor is protic and therefore can act as a Lewis acid and the acceptor is the Lewis base. Hydrogen bonds are represented as H···Y system, where the dots represent the hydrogen bond. Liquids that display hydrogen bonding (such as water) are called associated liquids . [ citation needed ]
Hydrogen bonds arise from a combination of electrostatics (multipole-multipole and multipole-induced multipole interactions), covalency (charge transfer by orbital overlap), and dispersion ( London forces ). [ 6 ]
In weaker hydrogen bonds, [ 13 ] hydrogen atoms tend to bond to elements such as sulfur (S) or chlorine (Cl); even carbon (C) can serve as a donor, particularly when the carbon or one of its neighbors is electronegative (e.g., in chloroform, aldehydes and terminal acetylenes). [ 14 ] [ 15 ] Gradually, it was recognized that there are many examples of weaker hydrogen bonding involving donor other than N, O, or F and/or acceptor Ac with electronegativity approaching that of hydrogen (rather than being much more electronegative). Although weak (≈1 kcal/mol), "non-traditional" hydrogen bonding interactions are ubiquitous and influence structures of many kinds of materials. [ citation needed ]
The definition of hydrogen bonding has gradually broadened over time to include these weaker attractive interactions. In 2011, an IUPAC Task Group recommended a modern evidence-based definition of hydrogen bonding, which was published in the IUPAC journal Pure and Applied Chemistry . This definition specifies:
The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X−H in which X is more electronegative than H, and an atom or a group of atoms in the same or another molecule, in which there is evidence of bond formation. [ 16 ]
Hydrogen bonds can vary in strength from weak (1–2 kJ/mol) to strong (161.5 kJ/mol in the bifluoride ion, HF − 2 ). [ 17 ] [ 18 ] Typical enthalpies in vapor include: [ 19 ]
The strength of intermolecular hydrogen bonds is most often evaluated by measurements of equilibria between molecules containing donor and/or acceptor units, most often in solution. [ 21 ] The strength of intramolecular hydrogen bonds can be studied with equilibria between conformers with and without hydrogen bonds. The most important method for the identification of hydrogen bonds also in complicated molecules is crystallography , sometimes also NMR-spectroscopy. Structural details, in particular distances between donor and acceptor which are smaller than the sum of the van der Waals radii can be taken as indication of the hydrogen bond strength. One scheme gives the following somewhat arbitrary classification: those that are 15 to 40 kcal/mol, 5 to 15 kcal/mol, and >0 to 5 kcal/mol are considered strong, moderate, and weak, respectively. [ 18 ]
Hydrogen bonds involving C-H bonds are both very rare and weak. [ 22 ]
The resonance assisted hydrogen bond (commonly abbreviated as RAHB) is a strong type of hydrogen bond. It is characterized by the π-delocalization that involves the hydrogen and cannot be properly described by the electrostatic model alone. This description of the hydrogen bond has been proposed to describe unusually short distances generally observed between O=C−OH··· or ···O=C−C=C−OH . [ 23 ]
The X−H distance is typically ≈110 pm , whereas the H···Y distance is ≈160 to 200 pm. The typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor. The following hydrogen bond angles between a hydrofluoric acid donor and various acceptors have been determined experimentally: [ 24 ]
Strong hydrogen bonds are revealed by downfield shifts in the 1 H NMR spectrum . For example, the acidic proton in the enol tautomer of acetylacetone appears at δ H {\displaystyle \delta _{\text{H}}} 15.5, which is about 10 ppm downfield of a conventional alcohol. [ 25 ]
In the IR spectrum, hydrogen bonding shifts the X−H stretching frequency to lower energy (i.e. the vibration frequency decreases). This shift reflects a weakening of the X−H bond. Certain hydrogen bonds - improper hydrogen bonds - show a blue shift of the X−H stretching frequency and a decrease in the bond length. [ 26 ] H-bonds can also be measured by IR vibrational mode shifts of the acceptor. The amide I mode of backbone carbonyls in α-helices shifts to lower frequencies when they form H-bonds with side-chain hydroxyl groups. [ 27 ] The dynamics of hydrogen bond structures in water can be probed by this OH stretching vibration. [ 28 ] In the hydrogen bonding network in protic organic ionic plastic crystals (POIPCs), which are a type of phase change material exhibiting solid-solid phase transitions prior to melting, variable-temperature infrared spectroscopy can reveal the temperature dependence of hydrogen bonds and the dynamics of both the anions and the cations. [ 29 ] The sudden weakening of hydrogen bonds during the solid-solid phase transition seems to be coupled with the onset of orientational or rotational disorder of the ions. [ 29 ]
Hydrogen bonding is of persistent theoretical interest. [ 30 ] According to a modern description O:H−O integrates both the intermolecular O:H lone pair ":" nonbond and the intramolecular H−O polar-covalent bond associated with O−O repulsive coupling. [ 31 ]
Quantum chemical calculations of the relevant interresidue potential constants ( compliance constants ) revealed [ how? ] large differences between individual H bonds of the same type. For example, the central interresidue N−H···N hydrogen bond between guanine and cytosine is much stronger in comparison to the N−H···N bond between the adenine-thymine pair. [ 32 ]
Theoretically, the bond strength of the hydrogen bonds can be assessed using NCI index, non-covalent interactions index , which allows a visualization of these non-covalent interactions , as its name indicates, using the electron density of the system. [ citation needed ]
Interpretations of the anisotropies in the Compton profile of ordinary ice claim that the hydrogen bond is partly covalent. [ 33 ] However, this interpretation was challenged [ 34 ] and subsequently clarified. [ 35 ]
Most generally, the hydrogen bond can be viewed as a metric -dependent electrostatic scalar field between two or more intermolecular bonds. This is slightly different from the intramolecular bound states of, for example, covalent or ionic bonds . However, hydrogen bonding is generally still a bound state phenomenon, since the interaction energy has a net negative sum. The initial theory of hydrogen bonding proposed by Linus Pauling suggested that the hydrogen bonds had a partial covalent nature. This interpretation remained controversial until NMR techniques demonstrated information transfer between hydrogen-bonded nuclei, a feat that would only be possible if the hydrogen bond contained some covalent character. [ 36 ]
The concept of hydrogen bonding once was challenging. [ 37 ] Linus Pauling credits T. S. Moore and T. F. Winmill with the first mention of the hydrogen bond, in 1912. [ 38 ] [ 39 ] Moore and Winmill used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than tetramethylammonium hydroxide . The description of hydrogen bonding in its better-known setting, water, came some years later, in 1920, from Latimer and Rodebush. [ 40 ] In that paper, Latimer and Rodebush cited the work of a fellow scientist at their laboratory, Maurice Loyal Huggins , saying, "Mr. Huggins of this laboratory in some work as yet unpublished, has used the idea of a hydrogen kernel held between two atoms as a theory in regard to certain organic compounds."
An ubiquitous example of a hydrogen bond is found between water molecules. In a discrete water molecule, there are two hydrogen atoms and one oxygen atom. The simplest case is a pair of water molecules with one hydrogen bond between them, which is called the water dimer and is often used as a model system. When more molecules are present, as is the case with liquid water, more bonds are possible because the oxygen of one water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with a hydrogen on another water molecule. This can repeat such that every water molecule is H-bonded with up to four other molecules, as shown in the figure (two through its two lone pairs, and two through its two hydrogen atoms). Hydrogen bonding strongly affects the crystal structure of ice , helping to create an open hexagonal lattice. The density of ice is less than the density of water at the same temperature; thus, the solid phase of water floats on the liquid, unlike most other substances. [ citation needed ]
Liquid water's high boiling point is due to the high number of hydrogen bonds each molecule can form, relative to its low molecular mass . Owing to the difficulty of breaking these bonds, water has a very high boiling point, melting point, and viscosity compared to otherwise similar liquids not conjoined by hydrogen bonds. Water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of bonds of a water molecule is up to four. [ 41 ]
The number of hydrogen bonds formed by a molecule of liquid water fluctuates with time and temperature. [ 42 ] From TIP4P liquid water simulations at 25 °C, it was estimated that each water molecule participates in an average of 3.59 hydrogen bonds. At 100 °C, this number decreases to 3.24 due to the increased molecular motion and decreased density, while at 0 °C, the average number of hydrogen bonds increases to 3.69. [ 42 ] Another study found a much smaller number of hydrogen bonds: 2.357 at 25 °C. [ 43 ] Defining and counting the hydrogen bonds is not straightforward however.
Because water may form hydrogen bonds with solute proton donors and acceptors, it may competitively inhibit the formation of solute intermolecular or intramolecular hydrogen bonds. Consequently, hydrogen bonds between or within solute molecules dissolved in water are almost always unfavorable relative to hydrogen bonds between water and the donors and acceptors for hydrogen bonds on those solutes. [ 44 ] Hydrogen bonds between water molecules have an average lifetime of 10 −11 seconds, or 10 picoseconds. [ 45 ]
A single hydrogen atom can participate in two hydrogen bonds. This type of bonding is called "bifurcated" (split in two or "two-forked"). It can exist, for instance, in complex organic molecules. [ 46 ] It has been suggested that a bifurcated hydrogen atom is an essential step in water reorientation. [ 47 ]
Acceptor-type hydrogen bonds (terminating on an oxygen's lone pairs) are more likely to form bifurcation (it is called overcoordinated oxygen, OCO) than are donor-type hydrogen bonds, beginning on the same oxygen's hydrogens. [ 48 ]
For example, hydrogen fluoride —which has three lone pairs on the F atom but only one H atom—can form only two bonds; ( ammonia has the opposite problem: three hydrogen atoms but only one lone pair).
Hydrogen bonding plays an important role in determining the three-dimensional structures and the properties adopted by many proteins. Compared to the C−C , C−O , and C−N bonds that comprise most polymers, hydrogen bonds are far weaker, perhaps 5%. Thus, hydrogen bonds can be broken by chemical or mechanical means while retaining the basic structure of the polymer backbone. This hierarchy of bond strengths (covalent bonds being stronger than hydrogen-bonds being stronger than van der Waals forces) is relevant in the properties of many materials. [ 49 ]
In these macromolecules, bonding between parts of the same macromolecule cause it to fold into a specific shape, which helps determine the molecule's physiological or biochemical role. For example, the double helical structure of DNA is due largely to hydrogen bonding between its base pairs (as well as pi stacking interactions), which link one complementary strand to the other and enable replication . [ citation needed ]
In the secondary structure of proteins , hydrogen bonds form between the backbone oxygens and amide hydrogens. When the spacing of the amino acid residues participating in a hydrogen bond occurs regularly between positions i and i + 4 , an alpha helix is formed. When the spacing is less, between positions i and i + 3 , then a 3 10 helix is formed. When two strands are joined by hydrogen bonds involving alternating residues on each participating strand, a beta sheet is formed. Hydrogen bonds also play a part in forming the tertiary structure of protein through interaction of R-groups. (See also protein folding ). [ citation needed ]
Bifurcated H-bond systems are common in alpha-helical transmembrane proteins between the backbone amide C=O of residue i as the H-bond acceptor and two H-bond donors from residue i + 4 : the backbone amide N−H and a side-chain hydroxyl or thiol H + . The energy preference of the bifurcated H-bond hydroxyl or thiol system is −3.4 kcal/mol or −2.6 kcal/mol, respectively. This type of bifurcated H-bond provides an intrahelical H-bonding partner for polar side-chains, such as serine , threonine , and cysteine within the hydrophobic membrane environments. [ 27 ]
The role of hydrogen bonds in protein folding has also been linked to osmolyte-induced protein stabilization. Protective osmolytes, such as trehalose and sorbitol , shift the protein folding equilibrium toward the folded state, in a concentration dependent manner. While the prevalent explanation for osmolyte action relies on excluded volume effects that are entropic in nature, circular dichroism (CD) experiments have shown osmolyte to act through an enthalpic effect. [ 50 ] The molecular mechanism for their role in protein stabilization is still not well established, though several mechanisms have been proposed. Computer molecular dynamics simulations suggest that osmolytes stabilize proteins by modifying the hydrogen bonds in the protein hydration layer. [ 51 ]
Several studies have shown that hydrogen bonds play an important role for the stability between subunits in multimeric proteins. For example, a study of sorbitol dehydrogenase displayed an important hydrogen bonding network which stabilizes the tetrameric quaternary structure within the mammalian sorbitol dehydrogenase protein family. [ 52 ]
A protein backbone hydrogen bond incompletely shielded from water attack is a dehydron . Dehydrons promote the removal of water through proteins or ligand binding . The exogenous dehydration enhances the electrostatic interaction between the amide and carbonyl groups by de-shielding their partial charges . Furthermore, the dehydration stabilizes the hydrogen bond by destabilizing the nonbonded state consisting of dehydrated isolated charges . [ 53 ]
Wool , being a protein fibre, is held together by hydrogen bonds, causing wool to recoil when stretched. However, washing at high temperatures can permanently break the hydrogen bonds and a garment may permanently lose its shape. [ citation needed ]
The properties of many polymers are affected by hydrogen bonds within and/or between the chains. Prominent examples include cellulose and its derived fibers, such as cotton and flax . In nylon , hydrogen bonds between carbonyl and the amide N H effectively link adjacent chains, which gives the material mechanical strength. Hydrogen bonds also affect the aramid fibre , where hydrogen bonds stabilize the linear chains laterally. The chain axes are aligned along the fibre axis, making the fibres extremely stiff and strong. Hydrogen-bond networks make both polymers sensitive to humidity levels in the atmosphere because water molecules can diffuse into the surface and disrupt the network. Some polymers are more sensitive than others. Thus nylons are more sensitive than aramids , and nylon 6 more sensitive than nylon-11 . [ citation needed ]
A symmetric hydrogen bond is a special type of hydrogen bond in which the proton is spaced exactly halfway between two identical atoms. The strength of the bond to each of those atoms is equal. It is an example of a three-center four-electron bond . This type of bond is much stronger than a "normal" hydrogen bond. The effective bond order is 0.5, so its strength is comparable to a covalent bond. It is seen in ice at high pressure, and also in the solid phase of many anhydrous acids such as hydrofluoric acid and formic acid at high pressure. It is also seen in the bifluoride ion [F···H···F] − . Due to severe steric constraint, the protonated form of Proton Sponge (1,8-bis(dimethylamino)naphthalene) and its derivatives also have symmetric hydrogen bonds ( [N···H···N] + ), [ 54 ] although in the case of protonated Proton Sponge, the assembly is bent. [ 55 ]
The hydrogen bond can be compared with the closely related dihydrogen bond , which is also an intermolecular bonding interaction involving hydrogen atoms. These structures have been known for some time, and well characterized by crystallography ; [ 56 ] however, an understanding of their relationship to the conventional hydrogen bond, ionic bond , and covalent bond remains unclear. Generally, the hydrogen bond is characterized by a proton acceptor that is a lone pair of electrons in nonmetallic atoms (most notably in the nitrogen , and chalcogen groups). In some cases, these proton acceptors may be pi-bonds or metal complexes . In the dihydrogen bond, however, a metal hydride serves as a proton acceptor, thus forming a hydrogen-hydrogen interaction. Neutron diffraction has shown that the molecular geometry of these complexes is similar to hydrogen bonds, in that the bond length is very adaptable to the metal complex/hydrogen donor system. [ 56 ]
The Hydrogen bond is relevant to drug design. According to Lipinski's rule of five the majority of orally active drugs have no more than five hydrogen bond donors and fewer than ten hydrogen bond acceptors. These interactions exist between nitrogen – hydrogen and oxygen –hydrogen centers. [ 57 ] Many drugs do not, however, obey these "rules". [ 58 ] | https://en.wikipedia.org/wiki/Hydrogen_bond |
physchem.ox.ac.uk
Hydrogen bromide is the inorganic compound with the formula HBr . It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming hydrobromic acid , which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by mass form a constant-boiling azeotrope mixture that boils at 124.3 °C (255.7 °F). Boiling less concentrated solutions releases H 2 O until the constant-boiling mixture composition is reached.
Hydrogen bromide , and its aqueous solution, hydrobromic acid , are commonly used reagents in the preparation of bromide compounds.
Hydrogen bromide and hydrobromic acid are important reagents in the production of organobromine compounds . [ 8 ] [ 9 ] [ 10 ] In an electrophilic addition reaction, HBr adds to alkenes:
The resulting alkyl bromides are useful alkylating agents , e.g., as precursors to fatty amine derivatives. Related free radical additions to allyl chloride and styrene give 1-bromo-3-chloropropane and phenylethylbromide , respectively.
Hydrogen bromide reacts with dichloromethane to give bromochloromethane and dibromomethane , sequentially:
These metathesis reactions illustrate the consumption of the stronger acid (HBr) and release of the weaker acid (HCl).
Allyl bromide is prepared by treating allyl alcohol with HBr:
HBr adds to alkynes to yield bromoalkenes. The stereochemistry of this type of addition is usually anti :
Also, HBr adds epoxides and lactones , resulting in ring-opening.
With triphenylphosphine , HBr gives triphenylphosphonium bromide, a solid "source" of HBr. [ 11 ]
Vanadium(III) bromide and molybdenum(IV) bromide were prepared by treatment of the higher chlorides with HBr. These reactions proceed via redox reactions: [ 12 ]
Hydrogen bromide (along with hydrobromic acid) is produced by combining hydrogen and bromine at temperatures between 200 and 400 °C. The reaction is typically catalyzed by platinum or asbestos . [ 9 ] [ 13 ]
HBr can be prepared by distillation of a solution of sodium bromide or potassium bromide with phosphoric acid or sulfuric acid : [ 14 ]
Concentrated sulfuric acid is less effective because it oxidizes HBr to bromine :
The acid may be prepared by:
Anhydrous hydrogen bromide can also be produced on a small scale by thermolysis of triphenylphosphonium bromide in refluxing xylene . [ 11 ]
Hydrogen bromide prepared by the above methods can be contaminated with Br 2 , which can be removed by passing the gas through a solution of phenol at room temperature in tetrachloromethane or other suitable solvent (producing 2,4,6-tribromophenol and generating more HBr in the process) or through copper turnings or copper gauze at high temperature. [ 13 ]
HBr is highly corrosive and, if inhaled, can cause lung damage. [ 15 ] | https://en.wikipedia.org/wiki/Hydrogen_bromide |
A hydrogen carrier is an organic macromolecule that transports atoms of hydrogen from one place to another inside a cell or from cell to cell for use in various metabolical processes. [ 1 ] Examples include NADPH , NADH , and FADH . The main role of these is to transport hydrogen atom to electron transport chain which will change ADP to ATP by adding one phosphate during metabolic processes (e.g. photosynthesis and respiration ). Hydrogen carrier participates in an oxidation-reduction reaction [ 2 ] by getting reduced due to the acceptance of a Hydrogen. The enzyme used in Glycolysis , [ 3 ] Dehydrogenase is used to attach the hydrogen to one of the hydrogen carrier. [ 4 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrogen_carrier |
The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide . At room temperature , it is a colorless gas , which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor . Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl.
Hydrogen chloride is a diatomic molecule , consisting of a hydrogen atom H and a chlorine atom Cl connected by a polar covalent bond . The chlorine atom is much more electronegative than the hydrogen atom, which makes this bond polar. Consequently, the molecule has a large dipole moment with a negative partial charge (δ−) at the chlorine atom and a positive partial charge (δ+) at the hydrogen atom. [ 9 ] In part because of its high polarity, HCl is very soluble in water (and in other polar solvents ).
Upon contact, H 2 O and HCl combine to form hydronium cations [H 3 O] + and chloride anions Cl − through a reversible chemical reaction :
The resulting solution is called hydrochloric acid and is a strong acid . The acid dissociation or ionization constant, K a , is large, which means HCl dissociates or ionizes practically completely in water. Even in the absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve in certain other solvents such as methanol :
Hydrogen chloride can protonate molecules or ions and can also serve as an acid- catalyst for chemical reactions where anhydrous (water-free) conditions are desired.
Because of its acidic nature, hydrogen chloride is a corrosive substance , particularly in the presence of moisture.
Frozen HCl undergoes a phase transition at 98.4 K (−174.8 °C; −282.5 °F). X-ray powder diffraction of the frozen material shows that the material changes from an orthorhombic structure to a cubic one during this transition. In both structures the chlorine atoms are in a face-centered array . However, the hydrogen atoms could not be located. [ 10 ] Analysis of spectroscopic and dielectric data, and determination of the structure of DCl (deuterium chloride) indicates that HCl forms zigzag chains in the solid, as does HF (see figure on right). [ 11 ]
The infrared spectrum of gaseous hydrogen chloride, shown on the left, consists of a number of sharp absorption lines grouped around 2886 cm −1 (wavelength ~3.47 μm). At room temperature, almost all molecules are in the ground vibrational state v = 0. Including anharmonicity the vibrational energy can be written as:
To promote an HCl molecule from the v = 0 to the v = 1 state, we would expect to see an infrared absorption about ν o = ν e + 2 x e ν e = 2880 cm −1 . However, this absorption corresponding to the Q-branch is not observed due to it being forbidden by symmetry. Instead, two sets of signals (P- and R-branches) are seen owing to a simultaneous change in the rotational state of the molecules. Because of quantum mechanical selection rules, only certain rotational transitions are permitted. The states are characterized by the rotational quantum number J = 0, 1, 2, 3, ... selection rules state that Δ J is only able to take values of ±1.
The value of the rotational constant B is much smaller than the vibrational one ν o , such that a much smaller amount of energy is required to rotate the molecule; for a typical molecule, this lies within the microwave region. However, the vibrational energy of HCl molecule places its absorptions within the infrared region, allowing a spectrum showing the rovibrational transitions of this molecule to be easily collected using an infrared spectrometer with a gas cell. The latter can even be made of quartz as the HCl absorption lies in a window of transparency for this material.
Naturally abundant chlorine consists of two isotopes, 35 Cl and 37 Cl, in a ratio of approximately 3:1. While the spring constants are nearly identical, the disparate reduced masses of H 35 Cl and H 37 Cl cause measurable differences in the rotational energy, thus doublets are observed on close inspection of each absorption line, weighted in the same ratio of 3:1.
Most hydrogen chloride produced on an industrial scale is used for hydrochloric acid production. [ 13 ]
In the 17th century, Johann Rudolf Glauber from Karlstadt am Main, Germany used sodium chloride salt and sulfuric acid for the preparation of sodium sulfate in the Mannheim process , releasing hydrogen chloride. Joseph Priestley of Leeds, England prepared pure hydrogen chloride in 1772, [ 14 ] and by 1808 Humphry Davy of Penzance , England had proved that the chemical composition included hydrogen and chlorine . [ 15 ]
Hydrogen chloride is produced by combining chlorine and hydrogen :
As the reaction is exothermic , the installation is called an HCl oven or HCl burner. The resulting hydrogen chloride gas is absorbed in deionized water , resulting in chemically pure hydrochloric acid. This reaction can give a very pure product, e.g. for use in the food industry.
The reaction can also be triggered by blue light. [ 16 ]
The industrial production of hydrogen chloride is often integrated with the formation of chlorinated and fluorinated organic compounds, e.g., Teflon , Freon , and other CFCs , as well as chloroacetic acid and PVC . Often this production of hydrochloric acid is integrated with captive use of it on-site. In the chemical reactions , hydrogen atoms on the hydrocarbon are replaced by chlorine atoms, whereupon the released hydrogen atom recombines with the spare atom from the chlorine molecule, forming hydrogen chloride. Fluorination is a subsequent chlorine-replacement reaction, producing again hydrogen chloride:
The resulting hydrogen chloride is either reused directly or absorbed in water, resulting in hydrochloric acid of technical or industrial grade.
Small amounts of hydrogen chloride for laboratory use can be generated in an HCl generator by dehydrating hydrochloric acid with either sulfuric acid or anhydrous calcium chloride . Alternatively, HCl can be generated by the reaction of sulfuric acid with sodium chloride: [ 17 ]
This reaction occurs at room temperature. Provided there is NaCl remaining in the generator and it is heated above 200 °C, the reaction proceeds further:
For such generators to function, the reagents should be dry.
Hydrogen chloride can also be prepared by the hydrolysis of certain reactive chloride compounds such as phosphorus chlorides , thionyl chloride ( SOCl 2 ), and acyl chlorides . For example, cold water can be gradually dripped onto phosphorus pentachloride ( PCl 5 ) to give HCl:
Most hydrogen chloride is consumed in the production of hydrochloric acid. It is also used in the production of vinyl chloride and many alkyl chlorides . [ 13 ] Trichlorosilane , a precursor to ultrapure silicon, is produced by the reaction of hydrogen chloride and silicon at around 300 °C. [ 18 ]
Around 900, the authors of the Arabic writings attributed to Jabir ibn Hayyan (Latin: Geber) and the Persian physician and alchemist Abu Bakr al-Razi (c. 865–925, Latin: Rhazes) were experimenting with sal ammoniac ( ammonium chloride ), which when it was distilled together with vitriol (hydrated sulfates of various metals) produced hydrogen chloride. [ 19 ] It is possible that in one of his experiments, al-Razi stumbled upon a primitive method to produce hydrochloric acid . [ 20 ] However, it appears that in most of these early experiments with chloride salts , the gaseous products were discarded, and hydrogen chloride may have been produced many times before it was discovered that it can be put to chemical use. [ 21 ]
One of the first such uses was the synthesis of mercury(II) chloride (corrosive sublimate), whose production from the heating of mercury either with alum and ammonium chloride or with vitriol and sodium chloride was first described in the De aluminibus et salibus ("On Alums and Salts"), an eleventh- or twelfth century Arabic text falsely attributed to Abu Bakr al-Razi and translated into Latin by Gerard of Cremona (1144–1187). [ 22 ]
Another important development was the discovery by pseudo-Geber (in the De inventione veritatis , "On the Discovery of Truth", after c. 1300) that by adding ammonium chloride to nitric acid , a strong solvent capable of dissolving gold (i.e., aqua regia ) could be produced. [ 23 ]
After the discovery in the late sixteenth century of the process by which unmixed hydrochloric acid can be prepared, [ 24 ] it was recognized that this new acid (then known as spirit of salt or acidum salis ) released vaporous hydrogen chloride, which was called marine acid air . In the 17th century, Johann Rudolf Glauber used salt ( sodium chloride ) and sulfuric acid for the preparation of sodium sulfate , releasing hydrogen chloride gas (see production, above). In 1772, Carl Wilhelm Scheele also reported this reaction and is sometimes credited with its discovery. Joseph Priestley prepared hydrogen chloride in 1772, and in 1810 Humphry Davy established that it is composed of hydrogen and chlorine . [ 25 ]
During the Industrial Revolution , demand for alkaline substances such as soda ash increased, and Nicolas Leblanc developed a new industrial-scale process for producing the soda ash. In the Leblanc process , salt was converted to soda ash, using sulfuric acid, limestone, and coal, giving hydrogen chloride as by-product. Initially, this gas was vented to air, but the Alkali Act 1863 prohibited such release, so then soda ash producers absorbed the HCl waste gas in water, producing hydrochloric acid on an industrial scale. Later, the Hargreaves process was developed, which is similar to the Leblanc process except sulfur dioxide , water, and air are used instead of sulfuric acid in a reaction which is exothermic overall. In the early 20th century the Leblanc process was effectively replaced by the Solvay process , which did not produce HCl. However, hydrogen chloride production continued as a step in hydrochloric acid production.
Historical uses of hydrogen chloride in the 20th century include hydrochlorinations of alkynes in producing the chlorinated monomers chloroprene and vinyl chloride , which are subsequently polymerized to make polychloroprene ( Neoprene ) and polyvinyl chloride (PVC), respectively. In the production of vinyl chloride, acetylene ( C 2 H 2 ) is hydrochlorinated by adding the HCl across the triple bond of the C 2 H 2 molecule, turning the triple into a double bond , yielding vinyl chloride.
The "acetylene process", used until the 1960s for making chloroprene , starts out by joining two acetylene molecules, and then adds HCl to the joined intermediate across the triple bond to convert it to chloroprene as shown here:
This "acetylene process" has been replaced by a process which adds Cl 2 to the double bond of ethylene instead, and subsequent elimination produces HCl instead, as well as chloroprene.
Hydrogen chloride forms corrosive hydrochloric acid on contact with water found in body tissue. Inhalation of the fumes can cause coughing , choking , inflammation of the nose, throat, and upper respiratory tract , and in severe cases, pulmonary edema , circulatory system failure, and death. [ 26 ] Skin contact can cause redness, pain , and severe chemical burns . Hydrogen chloride may cause severe burns to the eye and permanent eye damage.
The U.S. Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health have established occupational exposure limits for hydrogen chloride at a ceiling of 5 ppm (7 mg/m 3 ), [ 27 ] and compiled extensive information on hydrogen chloride workplace safety concerns. [ 28 ] | https://en.wikipedia.org/wiki/Hydrogen_chloride |
A hydrogen clathrate is a clathrate containing hydrogen in a water lattice. This substance is interesting due to its possible use to store hydrogen in a hydrogen economy . [ 1 ] [ 2 ] A recent review that accounts the state-of-the-art and future prospects and challenges of hydrogen storage as clathrate hydrates is reported by Veluswamy et al. (2014). [ 3 ] Another unusual characteristic is that multiple hydrogen molecules can occur at each cage site in the ice, one of only a very few guest molecule that forms clathrates with this property. The maximum ratio of hydrogen to water is 6 H 2 to 17 H 2 O. [ 4 ] It can be formed at 250K in a diamond anvil at a pressure of 300MPa (3000 Bars). It takes about 30 minutes to form, so this method is impractical for rapid manufacture. [ 5 ] The percent of weight of hydrogen is 3.77%. [ 4 ] The cage compartments are hexakaidecahedral and hold from two to four molecules of hydrogen. At temperatures above 160K the molecules rotate around inside the cage. Below 120K the molecules stop racing around the cage, and below 50K are locked into a fixed position. This was determined with deuterium in a neutron scattering experiment. [ 4 ]
Under higher pressures a 1:1 ratio clathrate can form. It crystallises in a cubic structure, where H 2 and H 2 O are both arranged in a diamond lattice. It is stable above 2.3 GPa. [ 6 ]
Under even higher pressures (over 38 GPa) there is a prediction of the existence of a clathrate with a cubic structure and a 1:2 ratio: 2H 2 •H 2 O. [ 7 ]
More complex clathrates can occur with hydrogen, water and other molecules such as methane , [ 8 ] and tetrahydrofuran . [ 9 ]
Since hydrogen and water ice are common constituents of the universe, it is very likely that under the right circumstances natural hydrogen clathrates will be formed. This could occur in icy moons for example. [ 8 ] Hydrogen clathrate was likely to be formed in the high pressure nebulae that formed the gas giants , but not to have formed in comets. [ 10 ] | https://en.wikipedia.org/wiki/Hydrogen_clathrate |
A hydrogen compressor is a device that increases the pressure of hydrogen by reducing its volume resulting in compressed hydrogen or liquid hydrogen .
Traditionally, applications for hydrogen compressors included Chlorine electrolyser and many chemical applications like the production of hydrogen peroxide (HPPO). The newer applications related to green and environmentally friendly technologies include fuel cells and electrolysis for hydrogen production . [ 1 ]
Hydrogen compressors are closely related to hydrogen pumps and gas compressors : both increase the pressure on a fluid and both can transport the fluid through a pipe . As gases are compressible, the compressor also reduces the volume of hydrogen gas, whereas the main result of a pump raising the pressure of a liquid is to allow the liquid hydrogen to be transported elsewhere.
A proven method to compress hydrogen is to apply reciprocating piston compressors. Widely used in refineries, they are the backbone of refining crude oil. Reciprocating piston compressors are commonly available as either oil-lubricated or non-lubricated; for high pressure (350 - 700 bar), non-lubricated compressors are preferred to avoid oil contamination of the hydrogen. Typical drive power is in the order of magnitude of Megawatts (300kW-15MW). Expert know-how on piston sealing and packing rings can ensure that reciprocating compressors outperform the competing technologies in terms of MTBO (Mean Time Between Overhaul).
An ionic liquid piston compressor is a hydrogen compressor based on an ionic liquid piston instead of a metal piston as in a piston-metal diaphragm compressor . [ 2 ]
A multi-stage electrochemical hydrogen compressor incorporates a series of membrane-electrode-assemblies (MEAs), similar to those used in proton-exchange membrane fuel cells ; this type of compressor has no moving parts and is compact. The electrochemical compressor works similar to a fuel cell, a voltage is applied to the membrane and the resulting electric current pulls hydrogen through the membrane. With electrochemical compression of hydrogen, a pressure of 14500 psi (1000bar or 100MPa) is achieved. A patent is pending claiming an exergy efficiency of 70 to 80% for pressures up to 10,000 psi or 700 bars. [ 3 ] A single stage electrochemical compression to 800 bar was reported in 2011. [ 4 ]
In a hydride compressor , thermal and pressure properties of a hydride are used to absorb low-pressure hydrogen gas at ambient temperatures and then release high-pressure hydrogen gas at higher temperatures; the bed of hydride is heated with hot water or an electric coil. [ 5 ]
Piston -metal diaphragm compressors are stationary high-pressure compressors, four-staged water-cooled, 11–15 kW, 30–50 Nm3/h 40 MPa for dispensation of hydrogen. [ 6 ] Since compression generates heat, the compressed gas is to be cooled between stages making the compression less adiabatic and more isothermal . The default assumption on diaphragm hydrogen compressors is an adiabatic efficiency of 70%. [ 7 ] Used in hydrogen stations .
The guided rotor compressor (GRC) is a positive-displacement rotary compressor based upon an envoluted [ check spelling ] trochoid geometry which utilizes a parallel trochoid curve to define its basic compression volume. [ 8 ] [ 9 ] It has a typical 80 to 85% adiabatic efficiency. [ 10 ]
The single-piston linear compressor uses dynamic counterbalancing, where an auxiliary movable mass is flexibly attached to a movable piston assembly and to the stationary compressor casing using auxiliary mechanical springs with zero vibration export at minimum electrical power and current consumed by the motor. [ 11 ] It is used in cryogenics
2023 saw the invention of a compressor cylinder which heats gas to multiply it's pressure. There is no pressure limit as any start pressure is multiplied. First public mention is in Patent Application No. PCT/AU2023/051351. | https://en.wikipedia.org/wiki/Hydrogen_compressor |
12.9 (in DMSO) [ 5 ]
Hydrogen cyanide (formerly known as prussic acid ) is a chemical compound with the formula HCN and structural formula H−C≡N . It is a highly toxic and flammable liquid that boils slightly above room temperature , at 25.6 °C (78.1 °F). HCN is produced on an industrial scale and is a highly valued precursor to many chemical compounds ranging from polymers to pharmaceuticals. Large-scale applications are for the production of potassium cyanide and adiponitrile , used in mining and plastics, respectively. [ 10 ] It is more toxic than solid cyanide compounds due to its volatile nature. A solution of hydrogen cyanide in water , represented as HCN( aq ), is called hydrocyanic acid . The salts of the cyanide anion are known as cyanides .
Whether hydrogen cyanide is an organic compound or not is a topic of debate among chemists, and opinions vary from author to author. [ example needed ] Traditionally, it is considered inorganic by a significant [ vague ] number [ quantify ] of authors. [ who? ] Contrary to this view, it is considered organic by other authors, [ who? ] because hydrogen cyanide belongs to the class of organic compounds known as nitriles which have the formula R−C≡N , where R is typically organyl group (e.g., alkyl or aryl ) or hydrogen . [ 11 ] In the case of hydrogen cyanide, the R group is hydrogen H, so the other names of hydrogen cyanide are methanenitrile and formonitrile. [ 2 ]
Hydrogen cyanide is a linear molecule , with a triple bond between carbon and nitrogen . The tautomer of HCN is HNC, hydrogen isocyanide . [ citation needed ]
Much literature has historically claimed that hydrogen cyanide smells of almonds or bitter almonds . However, there has been considerable confusion and disagreement over this, because the smell of household almond essence is due to benzaldehyde , which is released along with hydrogen cyanide from the breakdown of amygdalin present in some plant seeds, and thus is often mistaken for it. [ 12 ] [ 13 ] In an experiment to test what hydrogen cyanide smells like, the chemistry Youtuber Nigel Braun, a.k.a. NileRed , described the smell as " not at all like an almond " but like " weak bleach or chlorine " or " swimming pools ". [ 14 ]
About half of people are unable to detect the smell of hydrogen cyanide owing to a recessive genetic trait . [ 15 ]
The volatile compound has been used as inhalation rodenticide and human poison, as well as for killing whales. [ 16 ] Cyanide ions interfere with iron-containing respiratory enzymes. [ citation needed ]
Hydrogen cyanide is weakly acidic with a p K a of 9.2. It partially ionizes in water to give the cyanide anion, CN − . HCN forms hydrogen bonds with its conjugate base, species such as (CN − )(HCN) n . [ 17 ]
Hydrogen cyanide reacts with alkenes to give nitriles. The conversion, which is called hydrocyanation , employs nickel complexes as catalysts. [ 18 ]
Four molecules of HCN will tetramerize into diaminomaleonitrile . [ 19 ]
Metal cyanides are typically prepared by salt metathesis from alkali metal cyanide salts, but mercuric cyanide is formed from aqueous hydrogen cyanide: [ 20 ]
Hydrogen cyanide was first isolated in 1752 by French chemist Pierre Macquer who converted Prussian blue to an iron oxide plus a volatile component and found that these could be used to reconstitute it. [ 21 ] The new component was what is now known as hydrogen cyanide. It was subsequently prepared from Prussian blue by the Swedish chemist Carl Wilhelm Scheele in 1782, [ 22 ] and was eventually given the German name Blausäure ( lit . "Blue acid") because of its acidic nature in water and its derivation from Prussian blue. In English, it became known popularly as prussic acid.
In 1787, the French chemist Claude Louis Berthollet showed that prussic acid did not contain oxygen, [ 23 ] an important contribution to acid theory, which had hitherto postulated that acids must contain oxygen [ 24 ] (hence the name of oxygen itself, which is derived from Greek elements that mean "acid-former" and are likewise calqued into German as Sauerstoff ).
In 1811, Joseph Louis Gay-Lussac prepared pure, liquified hydrogen cyanide, [ 25 ] and in 1815 he deduced Prussic acid's chemical formula. [ 26 ]
The word cyanide for the radical in hydrogen cyanide was derived from its French equivalent, cyanure , which Gay-Lussac constructed from the Ancient Greek word κύανος for dark blue enamel or lapis lazuli , again owing to the chemical’s derivation from Prussian blue. Incidentally, the Greek word is also the root of the English color name cyan .
The most important process is the Andrussow oxidation invented by Leonid Andrussow at IG Farben in which methane and ammonia react in the presence of oxygen at about 1,200 °C (2,190 °F) over a platinum catalyst: [ 27 ]
In 2006, between 500 million and 1 billion pounds (between 230,000 and 450,000 t) were produced in the US. [ 28 ] Hydrogen cyanide is produced in large quantities by several processes and is a recovered waste product from the manufacture of acrylonitrile . [ 10 ]
Of lesser importance is the Degussa process ( BMA process ) in which no oxygen is added and the energy must be transferred indirectly through the reactor wall: [ 29 ]
This reaction is akin to steam reforming , the reaction of methane and water to give carbon monoxide and hydrogen .
In the Shawinigan Process, hydrocarbons , e.g. propane , are reacted with ammonia.
In the laboratory, small amounts of HCN are produced by the addition of acids to cyanide salts of alkali metals :
This reaction is sometimes the basis of accidental poisonings because the acid converts a nonvolatile cyanide salt into the gaseous HCN.
Hydrogen cyanide could be obtained from potassium ferricyanide and acid:
The large demand for cyanides for mining operations in the 1890s was met by George Thomas Beilby , who patented a method to produce hydrogen cyanide by passing ammonia over glowing coal in 1892. This method was used until Hamilton Castner in 1894 developed a synthesis starting from coal, ammonia, and sodium yielding sodium cyanide , which reacts with acid to form gaseous HCN.
HCN is the precursor to sodium cyanide and potassium cyanide , which are used mainly in gold and silver mining and for the electroplating of those metals. Via the intermediacy of cyanohydrins , a variety of useful organic compounds are prepared from HCN including the monomer methyl methacrylate , from acetone , the amino acid methionine , via the Strecker synthesis , and the chelating agents EDTA and NTA . Via the hydrocyanation process, HCN is added to butadiene to give adiponitrile , a precursor to Nylon-6,6 . [ 10 ]
HCN is used globally as a fumigant against many species of pest insects that infest food production facilities. Both its efficacy and method of application lead to very small amounts of the fumigant being used compared to other toxic substances used for the same purpose. [ 32 ] Using HCN as a fumigant also has less environmental impact, compared to some other fumigants such as sulfuryl fluoride , [ 33 ] and methyl bromide . [ 34 ]
HCN is obtainable from fruits that have a pit , such as cherries , apricots , apples , and nuts such as bitter almonds , from which almond oil and extract is made. Many of these pits contain small amounts of cyanohydrins such as mandelonitrile and amygdalin , which slowly release hydrogen cyanide. [ 35 ] [ 36 ] One hundred grams of crushed apple seeds can yield about 70 mg of HCN. [ 37 ] The roots of cassava plants contain cyanogenic glycosides such as linamarin , which decompose into HCN in yields of up to 370 mg per kilogram of fresh root. [ 38 ] Some millipedes , such as Harpaphe haydeniana , Desmoxytes purpurosea , and Apheloria release hydrogen cyanide as a defense mechanism, [ 39 ] as do certain insects, such as burnet moths and the larvae of Paropsisterna eucalyptus . [ 40 ] Hydrogen cyanide is contained in the exhaust of vehicles, and in smoke from burning nitrogen-containing plastics .
HCN has been measured in Titan's atmosphere by four instruments on the Cassini space probe , one instrument on Voyager , and one instrument on Earth. [ 41 ] One of these measurements was in situ , where the Cassini spacecraft dipped between 1,000 and 1,100 km (620 and 680 mi) above Titan's surface to collect atmospheric gas for mass spectrometry analysis. [ 42 ] HCN initially forms in Titan's atmosphere through the reaction of photochemically produced methane and nitrogen radicals which proceed through the H 2 CN intermediate, e.g., (CH 3 + N → H 2 CN + H → HCN + H 2 ). [ 43 ] [ 44 ] Ultraviolet radiation breaks HCN up into CN + H; however, CN is efficiently recycled back into HCN via the reaction CN + CH 4 → HCN + CH 3 . [ 43 ]
It has been postulated that carbon from a cascade of asteroids (known as the Late Heavy Bombardment ), resulting from interaction of Jupiter and Saturn, blasted the surface of young Earth and reacted with nitrogen in Earth's atmosphere to form HCN. [ 45 ]
Some authors [ who? ] have shown that neurons can produce hydrogen cyanide upon activation of their opioid receptors by endogenous or exogenous opioids. They have also shown that neuronal production of HCN activates NMDA receptors and plays a role in signal transduction between neuronal cells ( neurotransmission ). Moreover, increased endogenous neuronal HCN production under opioids was seemingly needed for adequate opioid analgesia , as analgesic action of opioids was attenuated by HCN scavengers. They considered endogenous HCN to be a neuromodulator . [ 46 ]
It has also been shown that, while stimulating muscarinic cholinergic receptors in cultured pheochromocytoma cells increases HCN production, in a living organism ( in vivo ) muscarinic cholinergic stimulation actually decreases HCN production. [ 47 ]
Leukocytes generate HCN during phagocytosis , and can kill bacteria , fungi , and other pathogens by generating several different toxic chemicals, one of which is hydrogen cyanide. [ 46 ]
The vasodilatation caused by sodium nitroprusside has been shown to be mediated not only by NO generation, but also by endogenous cyanide generation, which adds not only toxicity, but also some additional antihypertensive efficacy compared to nitroglycerine and other non-cyanogenic nitrates which do not cause blood cyanide levels to rise. [ 48 ]
HCN is a constituent of tobacco smoke . [ 49 ]
As a precursor to amino acids and nucleic acids, hydrogen cyanide has been proposed to have played a part in the origin of life . Compounds of special interest are oligomers of HCN including its trimer aminomalononitrile and tetramer diaminomaleonitrile , which can be described as (HCN)3 and (HCN)4, respectively. [ 50 ] Although the relationship of these chemical reactions to the origin of life theory remains speculative, studies in this area uncovered new pathways to organic compounds derived from the condensation of HCN (e.g. Adenine ). [ 51 ]
Because hydrogen cyanide is a precursor to nucleic acids, which are critical for terrestrial life, astronomers are incentivized to search for derivatives of HCN. [ 52 ]
HCN has been detected in the interstellar medium [ 53 ] and in the atmospheres of carbon stars . [ 54 ] Since then, extensive studies have probed formation and destruction pathways of HCN in various environments and examined its use as a tracer for a variety of astronomical species and processes. HCN can be observed from ground-based telescopes through a number of atmospheric windows. [ 55 ] The J=1→0, J=3→2, J= 4→3, and J=10→9 pure rotational transitions have all been observed. [ 53 ] [ 56 ] [ 57 ]
HCN is formed in interstellar clouds through one of two major pathways: [ 58 ] via a neutral-neutral reaction (CH 2 + N → HCN + H) and via dissociative recombination (HCNH + + e − → HCN + H). The dissociative recombination pathway is dominant by 30%; however, the HCNH + must be in its linear form. Dissociative recombination with its structural isomer, H 2 NC + , exclusively produces hydrogen isocyanide (HNC).
HCN is destroyed in interstellar clouds through a number of mechanisms depending on the location in the cloud. [ 58 ] In photon-dominated regions (PDRs), photodissociation dominates, producing CN (HCN + ν → CN + H). At further depths, photodissociation by cosmic rays dominate, producing CN (HCN + cr → CN + H). In the dark core, two competing mechanisms destroy it, forming HCN + and HCNH + (HCN + H + → HCN + + H; HCN + HCO + → HCNH + + CO). The reaction with HCO + dominates by a factor of ~3.5. HCN has been used to analyze a variety of species and processes in the interstellar medium. It has been suggested as a tracer for dense molecular gas [ 59 ] [ 60 ] and as a tracer of stellar inflow in high-mass star-forming regions. [ 61 ] Further, the HNC/HCN ratio has been shown to be an excellent method for distinguishing between PDRs and X-ray-dominated regions (XDRs). [ 62 ]
On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC , H 2 CO , and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) . [ 63 ] [ 64 ]
In February 2016, it was announced that traces of hydrogen cyanide were found in the atmosphere of the hot Super-Earth 55 Cancri e with NASA's Hubble Space Telescope . [ 65 ]
On 14 December 2023, astronomers reported the first time discovery, in the plumes of Enceladus , moon of the planet Saturn , of hydrogen cyanide, a possible chemical essential for life [ 66 ] as we know it, as well as other organic molecules , some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life ." [ 67 ] [ 68 ]
In World War I , hydrogen cyanide was used by the French from 1916 as a chemical weapon against the Central Powers , and by the United States and Italy in 1918. It was not found to be effective enough due to weather conditions. [ 69 ] [ 70 ] The gas is lighter than air and rapidly disperses up into the atmosphere. Rapid dilution made its use in the field impractical. In contrast, denser agents such as phosgene or chlorine tended to remain at ground level and sank into the trenches of the Western Front's battlefields. Compared to such agents, hydrogen cyanide had to be present in higher concentrations in order to be fatal.
A hydrogen cyanide concentration of 100–200 ppm in breathing air will kill a human within 10 to 60 minutes. [ 71 ] A hydrogen cyanide concentration of 2000 ppm (about 2380 mg/m 3 ) will kill a human in about one minute. [ 71 ] The toxic effect is caused by the action of the cyanide ion, which halts cellular respiration . It acts as a non-competitive inhibitor for an enzyme in mitochondria called cytochrome c oxidase . As such, hydrogen cyanide is commonly listed among chemical weapons as a blood agent . [ 72 ]
The Chemical Weapons Convention lists it under Schedule 3 as a potential weapon which has large-scale industrial uses. Signatory countries must declare manufacturing plants that produce more than 30 metric tons per year, and allow inspection by the Organisation for the Prohibition of Chemical Weapons .
Perhaps its most infamous use is Zyklon B (German: Cyclone B , with the B standing for Blausäure – prussic acid; also, to distinguish it from an earlier product later known as Zyklon A), [ 73 ] used in the Nazi German extermination camps of Majdanek and Auschwitz-Birkenau during World War II to kill Jews and other persecuted minorities en masse as part of their Final Solution genocide program. Hydrogen cyanide was also used in the camps for delousing clothing in attempts to eradicate diseases carried by lice and other parasites. One of the original Czech producers continued making Zyklon B under the trademark "Uragan D2" [ 74 ] until around 2015. [ 75 ]
During World War II , the US considered using it, along with cyanogen chloride , as part of Operation Downfall , the planned invasion of Japan, but President Harry Truman decided against it, instead using the atomic bombs developed by the secret Manhattan Project . [ 76 ]
Hydrogen cyanide was also the agent employed in judicial execution in some U.S. states , where it was produced during the execution by the action of sulfuric acid on sodium cyanide or potassium cyanide . [ 77 ]
Under the name prussic acid , HCN has been used as a killing agent in whaling harpoons, though it was quickly abandoned for being dangerous to the crew. [ 16 ] From the middle of the 18th century it was used in a number of poisoning murders and suicides. [ 78 ]
Hydrogen cyanide gas in air is explosive at concentrations above 5.6%. [ 79 ] | https://en.wikipedia.org/wiki/Hydrogen_cyanide |
The hydrogen cycle consists of hydrogen exchanges between biotic (living) and abiotic (non-living) sources and sinks of hydrogen-containing compounds.
Hydrogen (H) is the most abundant element in the universe. [ 1 ] On Earth, common H-containing inorganic molecules include water (H 2 O), hydrogen gas (H 2 ), hydrogen sulfide (H 2 S), and ammonia (NH 3 ). Many organic compounds also contain H atoms, such as hydrocarbons and organic matter . Given the ubiquity of hydrogen atoms in inorganic and organic chemical compounds, the hydrogen cycle is focused on molecular hydrogen, H 2 .
As a consequence of microbial metabolisms or naturally occurring rock-water interactions, hydrogen gas can be created. Other bacteria may then consume free H2, which may also be oxidised photochemically in the atmosphere or lost to space. Hydrogen is also thought to be an important reactant in pre-biotic chemistry and the early evolution of life on Earth, and potentially elsewhere in the Solar System . [ 2 ]
Abiotic sources of hydrogen gas include water-rock and photochemical reactions. Exothermic serpentinization reactions between water and olivine minerals liberate H 2 in the marine or terrestrial subsurface. [ 3 ] [ 4 ] In the ocean, hydrothermal vents erupt magma and altered seawater fluids including abundant H 2 , depending on the temperature regime and host rock composition. [ 5 ] [ 4 ] Molecular hydrogen can also be produced through photooxidation (via solar UV radiation ) of some mineral species such as siderite in anoxic aqueous environments. This may have been an important process in the upper regions of early Earth's Archaean oceans. [ 6 ]
Because H 2 is the lightest element, atmospheric H 2 can readily be lost to space via Jeans escape , an irreversible process that drives Earth's net mass loss . [ 7 ] Photolysis of heavier compounds not prone to escape, such as CH 4 or H 2 O, can also liberate H 2 from the upper atmosphere and contribute to this process. Another major sink of free atmospheric H 2 is photochemical oxidation by hydroxyl radicals (•OH), which forms water. [ citation needed ]
Anthropogenic sinks of H 2 include synthetic fuel production through the Fischer-Tropsch reaction and artificial nitrogen fixation through the Haber-Bosch process to produce nitrogen fertilizers . [ citation needed ]
Many microbial metabolisms produce or consume H 2 .
Hydrogen is produced by hydrogenases and nitrogenases enzymes in many microorganisms, some of which are being studied for their potential for biofuel production. [ 8 ] [ 9 ] These H 2 -metabolizing enzymes are found in all three domains of life , and out of known genomes over 30% of microbial taxa contain hydrogenase genes. [ 10 ] Fermentation produces H 2 from organic matter as part of the anaerobic microbial food chain [ 11 ] via light-dependent or light-independent pathways. [ 8 ]
Biological soil uptake is the dominant sink of atmospheric H 2 . [ 12 ] Both aerobic and anaerobic microbial metabolisms consume H 2 by oxidizing it in order to reduce other compounds during respiration . Aerobic H 2 oxidation is known as the Knallgas reaction. [ 13 ]
Anaerobic H 2 oxidation often occurs during interspecies hydrogen transfer in which H 2 produced during fermentation is transferred to another organism, which uses the H 2 to reduce CO 2 to CH 4 or acetate , SO 2− 4 to H 2 S, or Fe 3+ to Fe 2+ . Interspecies hydrogen transfer keeps H 2 concentrations very low in most environments because fermentation becomes less thermodynamically favorable as the partial pressure of H 2 increases. [ 11 ]
Hydrogen typically acts as an electron donor . [ 14 ] This quality has implications for global atmospheric chemistry , possibly delaying the degradation and increasing the abundance of greenhouse gases . This makes hydrogen an indirect greenhouse gas. [ 15 ] For example, H 2 can interfere with the removal of methane from the atmosphere . Typically, atmospheric CH 4 is oxidized by hydroxyl radicals ( • OH), but H 2 can also react with • OH to reduce it to H 2 O. [ 16 ]
Hydrothermal H 2 may have played a major role in pre-biotic chemistry . [ 17 ] Liberation of H 2 by serpentinization may have supported formation of the reactants proposed in the iron-sulfur world origin of life hypothesis. [ 18 ] The subsequent evolution of hydrogenotrophic methanogenesis is hypothesized as one of the earliest metabolisms on Earth . [ 19 ] [ 2 ]
Serpentinization can occur on any planetary body with chondritic composition. The discovery of H 2 on other ocean worlds , such as Enceladus , [ 20 ] [ 21 ] [ 22 ] suggests that similar processes are ongoing elsewhere in the Solar System , and potentially in other planetary systems as well. [ 13 ] | https://en.wikipedia.org/wiki/Hydrogen_cycle |
Hydrogen damage is the generic name given to a large number of metal degradation processes due to interaction with hydrogen atoms. Molecular gaseous hydrogen does not have the same effect as atoms or ions released into solid solution in the metal.
Carbon steels exposed to hydrogen at high temperatures experience high temperature hydrogen attack which leads to internal decarburization and weakening. [ 1 ] [ 2 ]
Atomic hydrogen diffusing through metals may collect at internal defects like inclusions and laminations and form molecular hydrogen. High pressures may be built up at such locations due to continued absorption of hydrogen leading to blister formation, growth and eventual bursting of the blister. Such hydrogen induced blister cracking has been observed in steels, aluminium alloys, titanium alloys and nuclear structural materials. Metals with low hydrogen solubility (such as tungsten) are more susceptible to blister formation. [ 3 ] While in metals with high hydrogen solubility like vanadium, hydrogen prefers to induce stable metal-hydrides instead of bubbles or blisters.
Flakes and shatter cracks are internal fissures seen in large forgings. Hydrogen picked up during melting and casting segregates at internal voids and discontinuities and produces these defects during forging. Fish-eyes are bright patches named for their appearance seen on fracture surfaces, generally of weldments. Hydrogen enters the metal during fusion-welding and produces this defect during subsequent stressing. Steel containment vessels exposed to extremely high hydrogen pressures develop small fissures or micro perforations through which fluids may leak.
Hydrogen lowers tensile ductility in many materials. In ductile materials, like austenitic stainless steels and aluminium alloys, no marked embrittlement may occur, but may exhibit significant lowering in tensile ductility (% elongation or % reduction in area) in tensile tests.
The best method of controlling hydrogen damage is to control contact between the metal and hydrogen. Many steps can be taken to reduce the entry of hydrogen into metals during critical operations like melting; casting; working (rolling, forging, etc.); welding; and surface preparation, like chemical cleaning, electroplating, and corrosion during their service life. Control of the environment and metallurgical control of the material to decrease its susceptibility to hydrogen are the two major approaches to reduce hydrogen damage.
There are various methods of adequately identifying and monitoring hydrogen damage, including ultrasonic echo attenuation method, amplitude-based backscatter , velocity ratio, creeping waves /time-of-flight measurement, pitch-catch mode shear wave velocity, advanced ultrasonic backscatter techniques (AUBT), time of flight diffraction (TOFD) , thickness mapping and in-situ metallography – replicas. [ 4 ] For hydrogen damage, the backscatter technique is used to detect affected areas in the material. To cross-check and confirm the findings of the backscatter measurement, the velocity ratio measurement technique is used. For the detection of micro and macro cracks , time of flight diffraction is a suitable method to use. | https://en.wikipedia.org/wiki/Hydrogen_damage |
Hydrogen darkening is a physical degradation of the optical properties of glass . Free hydrogen atoms are able to bind to the SiO 2 silica glass compound forming hydroxyl (OH)—a chemical compound that interferes with the passage of light through the glass .
The problem is particularly relevant to fiber-optic cables —particularly in oil and gas wells where fiber optic cables are used for distributed temperature sensing (DTS). Hydrogen can be present due to the cracking of hydrocarbons in the well. The darkening of the fiber can distort the DTS reading and possibly render the DTS system inoperable due to the optical loss budget being exceeded.
To prevent this, coatings such as carbon are applied to the fiber, and hydrogen capturing gels are used to buffer the fiber and other proprietary techniques may be used to prevent hydrogen atoms from reaching the glass fiber via the cable sheath .
This glass engineering or glass science related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrogen_darkening |
The hydrogen economy is an umbrella term for the roles hydrogen can play alongside low-carbon electricity to reduce emissions of greenhouse gases . The aim is to reduce emissions where cheaper and more energy-efficient clean solutions are not available. [ 2 ] In this context, hydrogen economy encompasses the production of hydrogen and the use of hydrogen in ways that contribute to phasing-out fossil fuels and limiting climate change .
Hydrogen can be produced by several means. Most hydrogen produced today is gray hydrogen , made from natural gas through steam methane reforming (SMR). This process accounted for 1.8% of global greenhouse gas emissions in 2021. [ 3 ] Low-carbon hydrogen , which is made using SMR with carbon capture and storage ( blue hydrogen ), or through electrolysis of water using renewable power ( green hydrogen ), accounted for less than 1% of production. [ 4 ] Virtually all of the 100 million tonnes [ 5 ] of hydrogen produced each year is used in oil refining (43% in 2021) and industry (57%), principally in the manufacture of ammonia for fertilizers, and methanol . [ 6 ] : 18, 22, 29
To limit global warming , it is generally envisaged that the future hydrogen economy replaces gray hydrogen with low-carbon hydrogen. As of 2024 it is unclear when enough low-carbon hydrogen could be produced to phase-out all the gray hydrogen. [ 7 ] The future end-uses are likely in heavy industry (e.g. high-temperature processes alongside electricity, feedstock for production of green ammonia and organic chemicals , as alternative to coal-derived coke for steelmaking ), long-haul transport (e.g. shipping, and to a lesser extent hydrogen-powered aircraft and heavy goods vehicles), and long-term energy storage. [ 8 ] [ 9 ] Other applications, such as light duty vehicles and heating in buildings, are no longer part of the future hydrogen economy, primarily for economic and environmental reasons. [ 10 ] [ 11 ] Hydrogen is challenging to store, to transport in pipelines, and to use. It presents safety concerns since it is highly explosive, and it is inefficient compared to direct use of electricity . Since relatively small amounts of low-carbon hydrogen are available, climate benefits can be maximized by using it in harder-to-decarbonize applications. [ 11 ]
As of 2023 [update] there are no real alternatives to hydrogen for several chemical processes in which it is currently used, such as ammonia production for fertilizer . [ 12 ] The cost of low- and zero-carbon hydrogen is likely to influence the degree to which it will be used in chemical feedstocks, long haul aviation and shipping, and long-term energy storage. Production costs of low- and zero-carbon hydrogen are evolving. Future costs may be influenced by carbon taxes , the geography and geopolitics of energy, energy prices, technology choices, and their raw material requirements.. [ 13 ] The U.S. Department of Energy's Hydrogen Hotshot Initiative seeks to reduce the cost of green hydrogen drop to $1 a kilogram during the 2030s, [ 14 ] though the cost of electrolyzers rose 50% between 2021 and 2024. [ 15 ]
The concept of a society that uses hydrogen as the primary means of energy storage was theorized by geneticist J. B. S. Haldane in 1923. Anticipating the exhaustion of Britain's coal reserves for power generation, Haldane proposed a network of wind turbines to produce hydrogen and oxygen for long-term energy storage through electrolysis , to help address renewable power's variable output . [ 16 ] The term "hydrogen economy" itself was coined by John Bockris during a talk he gave in 1970 at General Motors (GM) Technical Center. [ 17 ] Bockris viewed it as an economy in which hydrogen, underpinned by nuclear and solar power, would help address growing concern about fossil fuel depletion and environmental pollution, by serving as energy carrier for end-uses in which electrification was not suitable. [ 2 ] [ 18 ]
A hydrogen economy was proposed by the University of Michigan to solve some of the negative effects of using hydrocarbon fuels where the carbon is released to the atmosphere (as carbon dioxide, carbon monoxide, unburnt hydrocarbons, etc.). Modern interest in the hydrogen economy can generally be traced to a 1970 technical report by Lawrence W. Jones of the University of Michigan, [ 19 ] in which he echoed Bockris' dual rationale of addressing energy security and environmental challenges. Unlike Haldane and Bockris, Jones only focused on nuclear power as the energy source for electrolysis, and principally on the use of hydrogen in transport, where he regarded aviation and heavy goods transport as the top priorities. [ 20 ]
A spike in attention for the hydrogen economy concept during the 2000s was repeatedly described as hype by some critics and proponents of alternative technologies, [ 22 ] [ 23 ] [ 24 ] and investors lost money in the bubble . [ 25 ] Interest in the energy carrier resurged in the 2010s, notably with the forming of the World Hydrogen Council in 2017. Several manufacturers released hydrogen fuel cell cars commercially, with manufacturers such as Toyota, Hyundai, and industry groups in China having planned to increase numbers of the cars into the hundreds of thousands over the next decade. [ 26 ] [ 27 ]
The global scope for hydrogen's role in cars is shrinking relative to earlier expectations. [ 28 ] [ 29 ] By the end of 2022, 70,200 hydrogen vehicles had been sold worldwide, [ 30 ] compared with 26 million plug-in electric vehicles . [ 31 ]
Early 2020s takes on the hydrogen economy share earlier perspectives' emphasis on the complementarity of electricity and hydrogen, and the use of electrolysis as the mainstay of hydrogen production. [ 8 ] They focus on the need to limit global warming to 1.5 °C and prioritize the production, transportation and use of green hydrogen for heavy industry (e.g. high-temperature processes alongside electricity, [ 32 ] feedstock for production of green ammonia and organic chemicals, [ 8 ] as alternative to coal-derived coke for steelmaking ), [ 33 ] long-haul transport (e.g. shipping, aviation and to a lesser extent heavy goods vehicles), and long-term energy storage. [ 8 ] [ 9 ]
Hydrogen production globally was valued at over US$155 billion in 2022 and is expected to grow over 9% annually through 2030. [ 34 ]
In 2021, 94 million tonnes (Mt) of molecular hydrogen ( H 2 ) was produced. [ 35 ] Of this total, approximately one sixth was as a by-product of petrochemical industry processes. [ 4 ] Most hydrogen comes from dedicated production facilities, over 99% of which is from fossil fuels, mainly via steam reforming of natural gas (70%) and coal gasification (30%, almost all of which in China). [ 4 ] Less than 1% of dedicated hydrogen production is low carbon: steam fossil fuel reforming with carbon capture and storage , green hydrogen produced using electrolysis, and hydrogen produced from biomass . [ 4 ] CO 2 emissions from 2021 production, at 915 MtCO 2 , [ 36 ] amounted to 2.5% of energy-related CO 2 emissions [ 37 ] and 1.8% of global greenhouse gas emissions. [ 3 ]
Virtually all hydrogen produced for the current market is used in oil refining (40 Mt H 2 in 2021) and industry (54 MtH2). [ 6 ] : 18, 22 In oil refining, hydrogen is used, in a process known as hydrocracking , to convert heavy petroleum sources into lighter fractions suitable for use as fuels. Industrial uses mainly comprise ammonia production to make fertilizers (34 Mt H 2 in 2021), methanol production (15 Mt H 2 ) and the manufacture of direct reduced iron (5 Mt H 2 ). [ 6 ] : 29
Hydrogen gas is produced by several industrial methods. [ 38 ] Nearly all of the world's current supply of hydrogen is created from fossil fuels. [ 39 ] [ 40 ] Most hydrogen is gray hydrogen made through steam methane reforming . In this process, hydrogen is produced from a chemical reaction between steam and methane , the main component of natural gas. Producing one tonne of hydrogen through this process emits 6.6–9.3 tonnes of carbon dioxide. [ 41 ] When carbon capture and storage is used to remove a large fraction of these emissions, the product is known as blue hydrogen . [ 42 ]
Green hydrogen is usually understood to be produced from renewable electricity via electrolysis of water. [ 43 ] [ 44 ] Less frequently, definitions of green hydrogen include hydrogen produced from other low-emission sources such as biomass . [ 45 ] Producing green hydrogen is currently more expensive than producing gray hydrogen, and the efficiency of energy conversion is inherently low. [ 46 ] Other methods of hydrogen production include biomass gasification , methane pyrolysis , and extraction of underground hydrogen . [ 47 ] [ 48 ]
Green methanol is a liquid fuel that is produced from combining carbon dioxide and hydrogen ( CO 2 + 3 H 2 → CH 3 OH + H 2 O ) under pressure and heat with catalysts . It is a way to reuse carbon capture for recycling . Methanol can store hydrogen economically at standard outdoor temperatures and pressures , compared to liquid hydrogen and ammonia that need to use a lot of energy to stay cold in their liquid state . [ 50 ] In 2023 the Laura Maersk was the first container ship to run on methanol fuel. [ 51 ] Ethanol plants in the midwest are a good place for pure carbon capture to combine with hydrogen to make green methanol, with abundant wind and nuclear energy in Iowa , Minnesota , and Illinois . [ 52 ] [ 53 ] Mixing methanol with ethanol could make methanol a safer fuel to use because methanol doesn't have a visible flame in the daylight and doesn't emit smoke, and ethanol has a visible light yellow flame. [ 54 ] [ 55 ] [ 56 ] Green hydrogen production of 70% efficiency and a 70% efficiency of methanol production from that would be a 49% energy conversion efficiency . [ 57 ]
Hydrogen can be deployed as a fuel in two distinct ways: in fuel cells which produce electricity, and via combustion to generate heat. [ 59 ] When hydrogen is consumed in fuel cells, the only emission at the point of use is water vapor. [ 59 ] Combustion of hydrogen can lead to the thermal formation of harmful nitrogen oxides emissions. [ 59 ]
In the context of limiting global warming , low-carbon hydrogen (particularly green hydrogen ) is likely to play an important role in decarbonizing industry. [ 60 ] Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals, thus contributing to the decarbonization of industry alongside other technologies, such as electric arc furnaces for steelmaking. [ 32 ] However, it is likely to play a larger role in providing industrial feedstock for cleaner production of ammonia and organic chemicals. [ 60 ] For example, in steelmaking , hydrogen could function as a clean energy carrier and also as a low-carbon catalyst replacing coal-derived coke . [ 33 ]
The imperative to use low-carbon hydrogen to reduce greenhouse gas emissions has the potential to reshape the geography of industrial activities, as locations with appropriate hydrogen production potential in different regions will interact in new ways with logistics infrastructure, raw material availability, human and technological capital. [ 60 ]
Much of the interest in the hydrogen economy concept is focused on hydrogen vehicles , particularly planes . [ 61 ] [ 62 ] Hydrogen vehicles produce significantly less local air pollution than conventional vehicles. [ 63 ] By 2050, the energy requirement for transportation might be between 20% and 30% fulfilled by hydrogen and synthetic fuels . [ 64 ] [ 65 ] [ 66 ]
Hydrogen used to decarbonize transportation is likely to find its largest applications in shipping , aviation and to a lesser extent heavy goods vehicles, through the use of hydrogen-derived synthetic fuels such as ammonia and methanol , and fuel cell technology. [ 8 ] Hydrogen has been used in fuel cell buses for many years. It is also used as a fuel for spacecraft propulsion .
In the International Energy Agency 's 2022 Net Zero Emissions Scenario (NZE), hydrogen is forecast to account for 2% of rail energy demand in 2050, while 90% of rail travel is expected to be electrified by then (up from 45% today). Hydrogen's role in rail would likely be focused on lines that prove difficult or costly to electrify. [ 67 ] The NZE foresees hydrogen meeting approximately 30% of heavy truck energy demand in 2050, mainly for long-distance heavy freight (with battery electric power accounting for around 60%). [ 68 ]
Although hydrogen can be used in adapted internal combustion engines , fuel cells, being electrochemical , have an efficiency advantage over heat engines. Fuel cells are more expensive to produce than common internal combustion engines but also require higher purity hydrogen fuel than internal combustion engines. [ 69 ]
In the light road vehicle segment including passenger cars, by the end of 2022, 70,200 fuel cell electric vehicles had been sold worldwide, [ 30 ] compared with 26 million plug-in electric vehicles. [ 31 ] With the rapid rise of electric vehicles and associated battery technology and infrastructure, hydrogen's role in cars is minuscule. [ 28 ] [ 29 ]
Green hydrogen , from electrolysis of water , has the potential to address the variability of renewable energy output. [[Hydrogen energy]] is a clean fuel that produces only water when used in fuel cells. While most hydrogen comes from natural gas, green hydrogen from renewables offers a zero-emission alternative.Producing green hydrogen can both reduce the need for renewable power curtailment during periods of high renewables output and be stored long-term to provide for power generation during periods of low output. [ 70 ] [ 71 ]
An alternative to gaseous hydrogen as an energy carrier is to bond it with nitrogen from the air to produce ammonia, which can be easily liquefied, transported, and used (directly or indirectly) as a clean and renewable fuel . [ 72 ] [ 73 ] Among disadvantages of ammonia as an energy carrier are its high toxicity, energy efficiency of NH 3 production from N 2 and H 2 , and poisoning of PEM Fuel Cells by traces of non-decomposed NH 3 after NH 3 to N 2 conversion.
Numerous industry groups (gas networks, gas boiler manufacturers) across the natural gas supply chain are promoting hydrogen combustion boilers for space and water heating, and hydrogen appliances for cooking, to reduce energy-related CO 2 emissions from residential and commercial buildings. [ 74 ] [ 75 ] [ 11 ] The proposition is that current end-users of piped natural gas can await the conversion of and supply of hydrogen to existing natural gas grids , and then swap heating and cooking appliances, and that there is no need for consumers to do anything now. [ 74 ] [ 75 ] [ 11 ]
A review of 32 studies on the question of hydrogen for heating buildings, independent of commercial interests, found that the economics and climate benefits of hydrogen for heating and cooking generally compare very poorly with the deployment of district heating networks, electrification of heating (principally through heat pumps ) and cooking, the use of solar thermal , waste heat and the installation of energy efficiency measures to reduce energy demand for heat. [ 11 ] Due to inefficiencies in hydrogen production, using blue hydrogen to replace natural gas for heating could require three times as much methane , while using green hydrogen would need two to three times as much electricity as heat pumps. [ 11 ] Hybrid heat pumps, which combine the use of an electric heat pump with a hydrogen boiler, may play a role in residential heating in areas where upgrading networks to meet peak electrical demand would otherwise be costly. [ 11 ]
The widespread use of hydrogen for heating buildings would entail higher energy system costs, higher heating costs and higher environmental impacts than the alternatives, although a niche role may be appropriate in specific contexts and geographies. [ 11 ] If deployed, using hydrogen in buildings would drive up the cost of hydrogen for harder-to-decarbonize applications in industry and transport. [ 11 ]
As of 2019 [update] although technically possible production of syngas from hydrogen and carbon-dioxide from bio-energy with carbon capture and storage (BECCS) via the Sabatier reaction is limited by the amount of sustainable bioenergy available: [ 76 ] therefore any bio-SNG made may be reserved for production of aviation biofuel . [ 77 ]
In hydrogen pipelines and steel storage vessels, hydrogen molecules are prone to react with metals, causing hydrogen embrittlement and leaks in the pipeline or storage vessel. [ 78 ] Since it is lighter than air, hydrogen does not easily accumulate to form a combustible gas mixture. [ 78 ] However, even without ignition sources, high-pressure hydrogen leakage may cause spontaneous combustion and detonation . [ 78 ]
Hydrogen is flammable when mixed even in small amounts with air. Ignition can occur at a volumetric ratio of hydrogen to air as low as 4%. [ 79 ] In approximately 70% of hydrogen ignition accidents, the ignition source cannot be found, and it is widely believed by scholars that spontaneous ignition of hydrogen occurs. [ 78 ]
Hydrogen fire, while being extremely hot, is almost invisible, and thus can lead to accidental burns. [ 80 ] Hydrogen, like most gases, can cause asphyxiation in the absence of adequate ventilation. [ 81 ]
A hydrogen infrastructure is the infrastructure of points of hydrogen production , truck and pipeline transport, and hydrogen stations for the distribution and sale of hydrogen fuel , [ 82 ] and thus a crucial prerequisite before a successful commercialization of fuel cell technology. [ 83 ]
Hydrogen stations which are not situated near a hydrogen pipeline get supply via hydrogen tanks, compressed hydrogen tube trailers , liquid hydrogen trailers , liquid hydrogen tank trucks or dedicated onsite production. Pipelines are the cheapest way to move hydrogen over long distances compared to other options. Hydrogen gas piping is routine in large oil-refineries, because hydrogen is used to hydrocrack fuels from crude oil. The IEA recommends existing industrial ports be used for production and natural gas pipelines for transport, international co-operation and shipping. [ 84 ]
Several methods exist for storing hydrogen . These include mechanical approaches such as using high pressures and low temperatures, or employing chemical compounds that release H 2 upon demand. While large amounts of hydrogen are produced by various industries, it is mostly consumed at the site of production, notably for the synthesis of ammonia . For many years hydrogen has been stored as compressed gas or cryogenic liquid, and transported as such in cylinders, tubes, and cryogenic tanks for use in industry or as propellant in space programs. The overarching challenge is the very low boiling point of H 2 : it boils around 20.268 K (−252.882 °C or −423.188 °F). Achieving such low temperatures requires expending significant energy.
Xcel Energy is going to build two combined cycle power plants in the Midwest that can mix 30% hydrogen with the natural gas. [ 89 ] Intermountain Power Plant is being retrofitted to a natural gas/hydrogen power plant that can run on 30% hydrogen as well, and is scheduled to run on pure hydrogen by 2045. [ 90 ]
More widespread use of hydrogen in economies entails the need for investment and costs in its production, storage, distribution and use. Estimates of hydrogen's cost are therefore complex and need to make assumptions about the cost of energy inputs (typically gas and electricity), production plant and method (e.g. green or blue hydrogen), technologies used (e.g. alkaline or proton exchange membrane electrolysers), storage and distribution methods, and how different cost elements might change over time. [ 91 ] : 49–65 These factors are incorporated into calculations of the levelized costs of hydrogen (LCOH). The following table shows a range of estimates of the levelized costs of gray, blue, and green hydrogen, expressed in terms of US$ per kg of H 2 (where data provided in other currencies or units, the average exchange rate to US dollars in the given year are used, and 1 kg of H 2 is assumed to have a calorific value of 33.3kWh).
The range of cost estimates for commercially available hydrogen production methods is broad. As of 2022, gray hydrogen is cheapest to produce without a tax on its CO 2 emissions, followed by blue and green hydrogen. Blue hydrogen production costs are not anticipated to fall substantially by 2050, [ 94 ] [ 91 ] : 28 can be expected to fluctuate with natural gas prices and could face carbon taxes for uncaptured emissions. [ 91 ] : 79 The cost of electrolysers fell by 60% from 2010 to 2022, [ 95 ] before rising due to an increasing cost of capital . [ 25 ] The cost of electrolyzers rose 50% between 2021 and 2024. [ 15 ] Oxford Institute for Energy Studies nevertheless projects that the cost of green hydrogen is likely to fall significantly towards 2030 and 2050, [ 98 ] : 26 alongside the falling cost of renewable power generation. [ 99 ] [ 91 ] : 28 It is cheapest to produce green hydrogen with surplus renewable power that would otherwise be curtailed , which favors electrolyzers capable of responding to low and variable power levels . [ 98 ] : 5
A 2022 Goldman Sachs analysis anticipates that globally green hydrogen will achieve cost parity with grey hydrogen by 2030, earlier if a global carbon tax is placed on gray hydrogen. [ 13 ] In terms of cost per unit of energy, blue and gray hydrogen will always cost more than the fossil fuels used in its production, while green hydrogen will always cost more than the renewable electricity used to make it.
Subsidies for clean hydrogen production are much higher in the US and EU than in India. [ 100 ]
The distribution of hydrogen for the purpose of transportation is being tested around the world, particularly in the US ( California , Massachusetts ), Canada , Japan , the EU ( Portugal , Norway , the Netherlands , Denmark, Germany ), and Iceland .
An indicator of the presence of large natural gas infrastructures already in place in countries and in use by citizens is the number of natural gas vehicles present in the country. The countries with the largest amount of natural gas vehicles are (in order of magnitude): [ 101 ] Iran , China , Pakistan , Argentina , India , Brazil , Italy , Colombia , Thailand , Uzbekistan , Bolivia , Armenia , Bangladesh , Egypt , Peru , Ukraine , the United States . Natural gas vehicles can also be converted to run on hydrogen .
Also, in a few private homes, fuel cell micro-CHP plants can be found, which can operate on hydrogen, or other fuels as natural gas or LPG. [ 102 ] [ 103 ]
Western Australia 's Department of Planning and Infrastructure operated three Daimler Chrysler Citaro fuel cell buses as part of its Sustainable Transport Energy for Perth Fuel Cells Bus Trial in Perth from 2004 to 2007. [ 104 ]
By November 2020 the Australian Renewable Energy Agency (ARENA) had invested $55 million in 28 hydrogen projects, from early stage research and development to early stage trials and deployments. The agency's stated goal is to produce hydrogen by electrolysis for $2 per kilogram, announced by Minister for Energy and Emissions Angus Taylor in a 2021 Low Emissions Technology Statement. [ 105 ]
In October 2021, Queensland Premier Annastacia Palaszczuk and private investor Andrew Forrest announced that Queensland would be home to the world's largest hydrogen plant. [ 106 ]
In November 2024, the South Australian Government 's plan to spend A$593 million on a 200MW hydrogen energy plant near Whyalla was granted federal approval under the EPBC Act . The project is planned to be developed by the Office of Hydrogen Power SA, ATCO Australia , and BOC , [ 107 ] and intended "to supply additional grid stability for homes and businesses around the state, by using excess renewable energy generated from large-scale wind and solar farms to provide a consistent output of supply". Construction was scheduled to start in 2025, with completion and commissioning happening in 2026. [ 108 ]
Countries in the EU which have a relatively large natural gas pipeline system already in place include Belgium , Germany , France , and the Netherlands . [ 109 ] In 2020, The EU launched its European Clean Hydrogen Alliance (ECHA). [ 110 ] [ 111 ]
Green hydrogen has become more common in France. A €150 million Green Hydrogen Plan was established in 2019, and it calls for building the infrastructure necessary to create, store, and distribute hydrogen as well as using the fuel to power local transportation systems like buses and trains. Corridor H2, a similar initiative, will create a network of hydrogen distribution facilities in Occitania along the route between the Mediterranean and the North Sea. The Corridor H2 project will get a €40 million loan from the EIB . [ 112 ] [ 113 ]
German car manufacturer BMW has been working with hydrogen for years. [ quantify ] . [ 114 ] The German government has announced plans to hold tenders for 5.5 GW of new hydrogen-ready gas-fired power plants and 2 GW of "comprehensive H2-ready modernisations" of existing gas power stations at the end of 2024 or beginning of 2025 [ 115 ]
Iceland has committed to becoming the world's first hydrogen economy by the year 2050. [ 116 ] Iceland is in a unique position. Presently, [ when? ] it imports all the petroleum products necessary to power its automobiles and fishing fleet . Iceland has large geothermal resources, so much that the local price of electricity actually is lower than the price of the hydrocarbons that could be used to produce that electricity.
Iceland already converts its surplus electricity into exportable goods and hydrocarbon replacements. In 2002, it produced 2,000 tons of hydrogen gas by electrolysis, primarily for the production of ammonia (NH 3 ) for fertilizer. Ammonia is produced, transported, and used throughout the world, and 90% of the cost of ammonia is the cost of the energy to produce it.
Neither industry directly replaces hydrocarbons. Reykjavík , Iceland, had a small pilot fleet of city buses running on compressed hydrogen, [ 117 ] and research on powering the nation's fishing fleet with hydrogen is under way (for example by companies as Icelandic New Energy ). For more practical purposes, Iceland might process imported oil with hydrogen to extend it, rather than to replace it altogether.
The Reykjavík buses are part of a larger program, HyFLEET:CUTE, [ 118 ] operating hydrogen fueled buses in eight European cities. HyFLEET:CUTE buses were also operated in Beijing, China and Perth, Australia (see below). A pilot project demonstrating a hydrogen economy is operational on the Norwegian island of Utsira . The installation combines wind power and hydrogen power. In periods when there is surplus wind energy, the excess power is used for generating hydrogen by electrolysis . The hydrogen is stored, and is available for power generation in periods when there is little wind. [ citation needed ]
India is said to adopt hydrogen and H-CNG, due to several reasons, amongst which the fact that a national rollout of natural gas networks is already taking place and natural gas is already a major vehicle fuel. In addition, India suffers from extreme air pollution in urban areas. [ 119 ] [ 120 ] According to some estimates, nearly 80% of India's hydrogen is projected to be green, driven by cost declines and new production technologies. [ 121 ]
Currently however, hydrogen energy is just at the Research, Development and Demonstration (RD&D) stage. [ 122 ] [ 123 ] As a result, the number of hydrogen stations may still be low, [ 124 ] although much more are expected to be introduced soon. [ 125 ] [ 126 ] [ 127 ]
It planning open first hydrogen publication stations, The Ministry of Climate and Environment (MKiŚ) will soon schan competitions for 2-3 hydrogen refueling stations, Polish Deputy Minister in this ministry Krzysztof Bolesta. [ 128 ]
Saudi Arabia as a part of the NEOM project , is looking to produce roughly 1.2 million tonnes of green ammonia a year, beginning production in 2025. [ 129 ]
In Cairo, Egypt, Saudi real estate funding skyscraper project powered by hydrogen. [ 130 ]
The Ulsan Green Hydrogen Town is a hydrogen city project being developed in Ulsan . As of October 2024, 188km of underground pipelines have been laid to connect hydrogen produced as a byproduct from petrochemical complexes to the city center. [ 131 ]
The Turkish Ministry of Energy and Natural Resources and the United Nations Industrial Development Organization created the International Centre for Hydrogen Energy Technologies (UNIDO-ICHET) in Istanbul in 2004 and it ran to 2012. [ 132 ] In 2023 the ministry published a Hydrogen Technologies Strategy and Roadmap. [ 133 ]
The UK started a fuel cell pilot program in January 2004, the program ran two Fuel cell buses on route 25 in London until December 2005, and switched to route RV1 until January 2007. [ 134 ] The Hydrogen Expedition is currently working to create a hydrogen fuel cell-powered ship and using it to circumnavigate the globe, as a way to demonstrate the capability of hydrogen fuel cells. [ 135 ] In August 2021 the UK Government claimed it was the first to have a Hydrogen Strategy and produced a document. [ 136 ]
In August 2021, Chris Jackson quit as chair of the UK Hydrogen and Fuel Cell Association, a leading hydrogen industry association, claiming that UK and Norwegian oil companies had intentionally inflated their cost projections for blue hydrogen in order to maximize future technology support payments by the UK government. [ 137 ]
Several domestic U.S. automobile companies have developed vehicles using hydrogen, such as GM and Toyota. [ 138 ] However, as of February 2020, infrastructure for hydrogen was underdeveloped except in some parts of California. [ 139 ] The United States have their own hydrogen policy . [ citation needed ] A joint venture between NREL and Xcel Energy is combining wind power and hydrogen power in the same way in Colorado. [ 140 ] Hydro in Newfoundland and Labrador are converting the current wind-diesel Power System on the remote island of Ramea into a Wind-Hydrogen Hybrid Power Systems facility. [ 141 ] Five pump station hubs being delivered to heavy-duty H2 trucks in Texas. [ 142 ] Hydrogen City built Green by Hydrogen International (GHI), to planning open in 2026. [ 143 ]
In 2006, Florida’s infrastructure project was commissioned. [ 144 ] First opened Orlando as public bus transportation, Ford Motor Company announced putting a fleet of hydrogen-fueled Ford E-450. [ 145 ] [ 146 ] Liquidated hydrogen mobile system was constructed at Titusville. [ 147 ] [ 148 ] An FPL’s pilot clean hydrogen facility operated in Okeechobee County. [ 149 ]
A similar pilot project on Stuart Island uses solar power , instead of wind power , to generate electricity. When excess electricity is available after the batteries are fully charged, hydrogen is generated by electrolysis and stored for later production of electricity by fuel cell. [ 150 ] The US also have a large natural gas pipeline system already in place. [ 109 ]
Việt Nam Energy Association have included green hydrogenation support. [ 151 ] Australian clean energy company Pure Hydrogen Corporation Limited announced on July 22 that it has signed an MoU with Vietnam public transportation. [ 152 ] | https://en.wikipedia.org/wiki/Hydrogen_economy |
Hydrogen embrittlement ( HE ), also known as hydrogen-assisted cracking or hydrogen-induced cracking ( HIC ), is a reduction in the ductility of a metal due to absorbed hydrogen . Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs in steels , as well as in iron , nickel , titanium , cobalt , and their alloys. Copper , aluminium , and stainless steels are less susceptible to hydrogen embrittlement. [ 1 ] [ 2 ] [ 3 ] [ 4 ]
The essential facts about the nature of hydrogen embrittlement have been known since the 19th century. [ 5 ] [ 6 ] Hydrogen embrittlement is maximised at around room temperature in steels, and most metals are relatively immune to hydrogen embrittlement at temperatures above 150 °C. [ 7 ] Hydrogen embrittlement requires the presence of both atomic ("diffusible") hydrogen and a mechanical stress to induce crack growth, although that stress may be applied or residual . [ 2 ] [ 8 ] [ 9 ] Hydrogen embrittlement increases at lower strain rates . [ 1 ] [ 2 ] [ 10 ] In general, higher-strength steels are more susceptible to hydrogen embrittlement than mid-strength steels. [ 11 ]
Metals can be exposed to hydrogen from two types of sources: gaseous dihydrogen and atomic hydrogen chemically generated at the metal surface. Atomic hydrogen dissolves quickly into the metal at room temperature and leads to embrittlement. [ 6 ] Gaseous dihydrogen is found in pressure vessels and pipelines . Electrochemical sources of hydrogen include acids (as may be encountered during pickling , etching , or cleaning), corrosion (typically due to aqueous corrosion or cathodic protection ), and electroplating . [ 1 ] [ 2 ] Hydrogen can be introduced into the metal during manufacturing by the presence of moisture during welding or while the metal is molten . The most common causes of failure in practice are poorly controlled electroplating or damp welding rods .
Hydrogen embrittlement as a term can be used to refer specifically to the embrittlement that occurs in steels and similar metals at relatively low hydrogen concentrations , or it can be used to encompass all embrittling effects that hydrogen has on metals. These broader embrittling effects include hydride formation, which occurs in titanium and vanadium but not in steels, and hydrogen-induced blistering, which only occurs at high hydrogen concentrations and does not require the presence of stress. [ 10 ] However, hydrogen embrittlement is almost always distinguished from high temperature hydrogen attack (HTHA), which occurs in steels at temperatures above 204 °C and involves the formation of methane pockets. [ 12 ] The mechanisms (there are many) by which hydrogen causes embrittlement in steels are not comprehensively understood and continue to be explored and studied. [ 1 ] [ 13 ] [ 14 ]
Hydrogen embrittlement is a complex process involving a number of distinct contributing micro-mechanisms, not all of which need to be present. The mechanisms include the formation of brittle hydrides , the creation of voids that can lead to high-pressure bubbles, enhanced decohesion at internal surfaces and localised plasticity at crack tips that assist in the propagation of cracks. [ 14 ] There is a great variety of mechanisms that have been proposed [ 14 ] and investigated as to the cause of brittleness once diffusible hydrogen has been dissolved into the metal. [ 6 ] In recent years, it has become widely accepted that HE is a complex process dependent on material and environment so that no single mechanism applies exclusively. [ 15 ]
Hydrogen embrittles a variety of metals including steel, [ 19 ] [ 20 ] aluminium (at high temperatures only [ 21 ] ), and titanium . [ 22 ] Austempered iron is also susceptible, though austempered steel (and possibly other austempered metals) displays increased resistance to hydrogen embrittlement. [ 23 ] NASA has reviewed which metals are susceptible to embrittlement and which only prone to hot hydrogen attack: nickel alloys, austenitic stainless steels , aluminium and alloys, copper (including alloys, e.g. beryllium copper ). [ 2 ] Sandia has also produced a comprehensive guide. [ 24 ]
Steel with an ultimate tensile strength of less than 1000 MPa (~145,000 psi) or hardness of less than HRC 32 on the Hardness Rockwell Scale is not generally considered susceptible to hydrogen embrittlement. As an example of severe hydrogen embrittlement, the elongation at failure of 17-4PH precipitation hardened stainless steel was measured to drop from 17% to only 1.7% when smooth specimens were exposed to high-pressure hydrogen [ 2 ]
As the strength of steels increases, the fracture toughness decreases, so the likelihood that hydrogen embrittlement will lead to fracture increases. In high-strength steels , anything above a hardness of HRC 32 may be susceptible to early hydrogen cracking after plating processes that introduce hydrogen. They may also experience long-term failures any time from weeks to decades after being placed in service due to accumulation of hydrogen over time from cathodic protection and other sources. Numerous failures have been reported in the hardness range from HRC 32-36 and above; therefore, parts in this range should be checked during quality control to ensure they are not susceptible. [ citation needed ]
Testing the fracture toughness of hydrogen-charged, embrittled specimens is complicated by the need to keep charged specimens very cold, in liquid nitrogen, to prevent the hydrogen diffusing away. [ 26 ]
Copper alloys which contain oxygen can be embrittled if exposed to hot hydrogen. The hydrogen diffuses through the copper and reacts with inclusions of Cu 2 O , forming 2 metallic Cu atoms and H 2 O , which then forms pressurized bubbles of steam at the grain boundaries . This process can force the grains of the crystal lattice away from each other, in a process known as steam embrittlement . [ citation needed ]
Alloys of vanadium , nickel , and titanium have a high hydrogen solubility , and can therefore absorb significant amounts of hydrogen. This can lead to hydride formation, resulting in irregular volume expansion and reduced ductility (because metallic hydrides are fragile ceramic materials ). This is a particular issue when looking for non- palladium -based alloys for use in hydrogen separation membranes. [ 18 ]
While most failures in practice have been through fast failure, there is experimental evidence that hydrogen also affects the fatigue properties of steels. This is entirely expected given the nature of the embrittlement mechanisms proposed for fast fracture. [ 27 ] [ 16 ] In general hydrogen embrittlement has a strong effect on high- stress , low-cycle fatigue and very little effect on high-cycle fatigue. [ 2 ] [ 24 ]
Hydrogen embrittlement is a volume effect: it affects the volume of the material. Environmental embrittlement [ 2 ] is a surface effect where molecules from the atmosphere surrounding the material under test are adsorbed onto the fresh crack surface. This is most clearly seen from fatigue measurements where the measured crack growth rates [ 24 ] can be an order of magnitude higher in hydrogen than in air. That this effect is due to adsorption, which saturates when the crack surface is completely covered, is understood from the weak dependence of the effect on the pressure of hydrogen. [ 24 ]
Environmental embrittlement is also observed to reduce fracture toughness in fast fracture tests, but the severity is much reduced compared with the same effect in fatigue. [ 24 ]
Hydrogen embrittlement occurs when a previously embrittled material has low fracture toughness regardless of the atmosphere in which it is tested. Environmental embrittlement occurs when the low fracture toughness is only observed in that atmosphere.
During manufacture, hydrogen can be dissolved into the component by processes such as phosphating , pickling , electroplating , casting , carbonizing , surface cleaning , electrochemical machining , welding , hot roll forming , and heat treatments .
During service use, hydrogen can be dissolved into the metal from wet corrosion or through misapplication of protection measures such as cathodic protection . [ 2 ] In one case of failure during construction of the San Francisco–Oakland Bay Bridge galvanized (i.e. zinc-plated ) rods were left wet for 5 years before being tensioned . The reaction of the zinc with water introduced hydrogen into the steel. [ 28 ] [ 29 ] [ 30 ]
A common case of embrittlement during manufacture is poor arc welding practice, in which hydrogen is released from moisture, such as in the coating of welding electrodes or from damp welding rods . [ 22 ] [ 31 ] To avoid atomic hydrogen formation in the high temperature plasma of the arc , welding rods have to be perfectly dried in an oven at the appropriate temperature and duration before use. Another way to minimize the formation of hydrogen is to use special low-hydrogen electrodes for welding high-strength steels .
Apart from arc welding, the most common problems are from chemical or electrochemical processes which, by reduction of hydrogen ions or water, generate hydrogen atoms at the surface, which rapidly dissolve in the metal. One of these chemical reactions involves hydrogen sulfide ( H 2 S ) in sulfide stress cracking (SSC), a significant problem for the oil and gas industries. [ 32 ]
After a manufacturing process or treatment which may cause hydrogen ingress, the component should be baked to remove or immobilize the hydrogen. [ 29 ]
Hydrogen embrittlement can be prevented through several methods, all of which are centered on minimizing contact between the metal and hydrogen, particularly during fabrication and the electrolysis of water . Embrittling procedures such as acid pickling should be avoided, as should increased contact with elements such as sulfur and phosphate .
If the metal has not yet started to crack, hydrogen embrittlement can be reversed by removing the hydrogen source and causing the hydrogen within the metal to diffuse out through heat treatment . This de-embrittlement process, known as low hydrogen annealing or "baking", is used to overcome the weaknesses of methods such as electroplating which introduce hydrogen to the metal, but is not always entirely effective because a sufficient time and temperature must be reached. [ 33 ] Tests such as ASTM F1624 can be used to rapidly identify the minimum baking time (by testing using careful design of experiments , a relatively low number of samples can be used to pinpoint this value). Then the same test can be used as a quality control check to evaluate if baking was sufficient on a per-batch basis.
In the case of welding, often pre-heating and post-heating the metal is applied to allow the hydrogen to diffuse out before it can cause any damage. This is specifically done with high-strength steels and low alloy steels such as the chromium / molybdenum / vanadium alloys . Due to the time needed to re-combine hydrogen atoms into the hydrogen molecules, hydrogen cracking due to welding can occur over 24 hours after the welding operation is completed.
Another way of preventing this problem is through materials selection. This will build an inherent resistance to this process and reduce the need for post-processing or constant monitoring for failure. Certain metals or alloys are highly susceptible to this issue, so choosing a material that is minimally affected while retaining the desired properties would also provide an optimal solution. Much research has been done to catalogue the compatibility of certain metals with hydrogen. [ 24 ] Tests such as ASTM F1624 can also be used to rank alloys and coatings during materials selection to ensure (for instance) that the threshold of cracking is below the threshold for hydrogen-assisted stress corrosion cracking. Similar tests can also be used during quality control to more effectively qualify materials being produced in a rapid and comparable manner.
Coatings act as a barrier between the metal substrate and the surrounding environment, hindering the ingress of hydrogen atoms. Various techniques can be used to apply coatings, such as electroplating, chemical conversion coatings, or organic coatings. The choice of coating depends on factors such as the type of metal, the operating environment, and the specific requirements of the application.
Electroplating is a commonly used method to deposit a protective layer onto the metal surface. This process involves immersing the metal substrate into an electrolyte solution containing metal ions. By applying an electric current, the metal ions are reduced and form a metallic coating on the substrate. Electroplating can provide an excellent protective layer that enhances corrosion resistance and reduces the susceptibility to hydrogen embrittlement.
Chemical conversion coatings are another effective method for surface protection. These coatings are typically formed through chemical reactions between the metal substrate and a chemical solution. The conversion coating chemically reacts with the metal surface, resulting in a thin, tightly adhering protective layer. Examples of conversion coatings include chromate, phosphate, and oxide coatings. These coatings not only provide a barrier against hydrogen diffusion but also enhance the metal's corrosion resistance.
Organic coatings, such as paints or polymer coatings, offer additional protection against hydrogen embrittlement. These coatings form a physical barrier between the metal surface and the environment. They provide excellent adhesion, flexibility, and resistance to environmental factors. Organic coatings can be applied through various methods, including spray coating, dip coating , or powder coating . They can be formulated with additives to further enhance their resistance to hydrogen ingress.
Thermally sprayed coatings offer several advantages in the context of hydrogen embrittlement prevention. The coating materials used in this process are often composed of materials with excellent resistance to hydrogen diffusion, such as ceramics or cermet alloys. These materials have a low permeability to hydrogen, creating a robust barrier against hydrogen ingress into the metal substrate. [ 34 ]
Most analytical methods for hydrogen embrittlement involve evaluating the effects of (1) internal hydrogen from production and/or (2) external sources of hydrogen such as cathodic protection. For steels, it is important to test specimens in the lab that are at least as hard (or harder) as the final parts will be. Ideally, specimens should be made of the final material or the nearest possible representative, as fabrication can have a profound impact on resistance to hydrogen-assisted cracking.
There are numerous ASTM standards for testing for hydrogen embrittlement:
There are many other related standards for hydrogen embrittlement: | https://en.wikipedia.org/wiki/Hydrogen_embrittlement |
Hydrogen evolution reaction ( HER ) is a chemical reaction that yields H 2 . [ 1 ] The conversion of protons to H 2 requires reducing equivalents and usually a catalyst. In nature, HER is catalyzed by hydrogenase enzymes which rely on iron- and nickel-based catalysts. Commercial electrolyzers typically employ supported nickel-based catalysts. [ 2 ]
HER is a key reaction which occurs in the electrolysis of water for the production of hydrogen for both industrial energy applications, [ 3 ] as well as small-scale laboratory research. Due to the abundance of water on Earth, hydrogen production poses a potentially scalable process for fuel generation. This is an alternative to steam methane reforming [ 4 ] for hydrogen production, which has significant greenhouse gas emissions , and as such scientists are looking to improve and scale up electrolysis processes that have fewer emissions.
In acidic conditions, the hydrogen evolution reaction follows the formula: [ 5 ]
In neutral or alkaline conditions, the reaction follows the formula: [ 5 ]
Both of these mechanisms can be seen in industrial practices at the cathode side of the electrolyzer where hydrogen evolution occurs. In acidic conditions, it is referred to as proton exchange membrane electrolysis or PEM , while in alkaline conditions it is referred to simply as alkaline electrolysis . Historically, alkaline electrolysis has been the dominant method of the two, though PEM has recently began to grow due to the higher current density that can be achieved in PEM electrolysis. [ 6 ]
The HER process is more efficient in the presence of catalysts. Commercial alkaline electrolyzers use nickel-based catalysts at the cathode and steel at the anode. [ 2 ] Proton exchange membrane based technology is an alternative to conventional high pressure electrolyzers. [ 7 ] The alkalinity of the electrolyte in these processes enables the use of less expensive catalysts [ 3 ] In PEM electrolyzers, the standard catalyst for HER is platinum supported on carbon, or Pt/C, [ 7 ] used at the anode. The performance of a catalyst can be characterized by the level of adsorption of hydrogen into binding sites of the metal surface, as well as the overpotential of the reaction as current density increases. [ 3 ] Anion exchange membrane (AEM) water electrolyzers are newly developed electrolyzers. In AEM electrolyzers, the standard catalyst for HER is still non-precious metal-based catalysts, such as nickel or iron. [ 8 ]
The high cost and energy input from water electrolysis poses a challenge to the large scale implementation of hydrogen power. The electrolysis of water is only practical where energy is cheap. [ 2 ] While alkaline electroysis is commonly used, its limited current density capacity requires large electrical input, which poses both a cost and environmental concern due to the high carbon content of electricity in the many countries. [ 9 ] The electrocatalysts used for electrolysis of PEM electrolyzers currently account for about 5% of the total process cost, however, as this process is scaled up.
HER can also be an unwelcome side reaction that could compete with other reductions such as the electrolyzed nitrogen fixation or electrochemical reduction of carbon dioxide . Neither of these processes commercial, however. [ 10 ] HER does compete in chrome plating . | https://en.wikipedia.org/wiki/Hydrogen_evolution_reaction |
15 (in DMSO) [ 2 ]
Hydrogen fluoride (fluorane) is an inorganic compound with chemical formula H F . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid . It is the principal industrial source of fluorine , often in the form of hydrofluoric acid, and is an important feedstock in the preparation of many important compounds including pharmaceuticals and polymers such as polytetrafluoroethylene (PTFE). HF is also widely used in the petrochemical industry as a component of superacids . Due to strong and extensive hydrogen bonding , it boils near room temperature, a much higher temperature than other hydrogen halides .
Hydrogen fluoride is an extremely dangerous gas, forming corrosive and penetrating hydrofluoric acid upon contact with moisture . The gas can also cause blindness by rapid destruction of the corneas .
In 1771 Carl Wilhelm Scheele prepared the aqueous solution, hydrofluoric acid in large quantities, although hydrofluoric acid had been known in the glass industry before then.
French chemist Edmond Frémy (1814–1894) is credited with discovering hydrogen fluoride (HF) while trying to isolate fluorine .
HF is diatomic in the gas-phase. As a liquid, HF forms relatively strong hydrogen bonds , hence its relatively high boiling point. Solid HF consists of zig-zag chains of HF molecules. The HF molecules, with a short covalent H–F bond of 95 pm length, are linked to neighboring molecules by intermolecular H–F distances of 155 pm. [ 4 ] Liquid HF also consists of chains of HF molecules, but the chains are shorter, consisting on average of only five or six molecules. [ 5 ]
Hydrogen fluoride does not boil until 20 °C in contrast to the heavier hydrogen halides, which boil between −85 °C (−120 °F) and −35 °C (−30 °F). [ 6 ] [ 7 ] [ 8 ] This hydrogen bonding between HF molecules gives rise to high viscosity in the liquid phase and lower than expected pressure in the gas phase.
HF is miscible with water (dissolves in any proportion). In contrast, the other hydrogen halides exhibit limiting solubilities in water. Hydrogen fluoride forms a monohydrate HF . H 2 O with melting point −40 °C (−40 °F), which is 44 °C (79 °F) above the melting point of pure HF. [ 9 ]
Aqueous solutions of HF are called hydrofluoric acid . When dilute, hydrofluoric acid behaves like a weak acid, unlike the other hydrohalic acids, due to the formation of hydrogen-bonded ion pairs [ H 3 O + ·F − ]. However concentrated solutions are strong acids, because bifluoride anions are predominant, instead of ion pairs. In liquid anhydrous HF, self-ionization occurs: [ 10 ] [ 11 ]
which forms an extremely acidic liquid ( H 0 = −15.1 ).
Like water, HF can act as a weak base, reacting with Lewis acids to give superacids . A Hammett acidity function ( H 0 ) of about −28 is obtained with antimony pentafluoride (SbF 5 ) at a 1:1 molar ratio , forming fluoroantimonic acid . [ 12 ] [ 13 ]
Hydrogen fluoride is typically produced by the reaction between sulfuric acid and pure grades of the mineral fluorite : [ 14 ]
About 20% of manufactured HF is a byproduct of fertilizer production, which generates hexafluorosilicic acid . This acid can be degraded to release HF thermally and by hydrolysis:
In general, anhydrous hydrogen fluoride is more common industrially than its aqueous solution, hydrofluoric acid . Its main uses, on a tonnage basis, are as a precursor to organofluorine compounds and a precursor to cryolite for the electrolysis of aluminium. [ 14 ]
HF reacts with chlorocarbons to give fluorocarbons. An important application of this reaction is the production of tetrafluoroethylene (TFE), precursor to Teflon . Chloroform is fluorinated by HF to produce chlorodifluoromethane (R-22): [ 14 ]
Pyrolysis of chlorodifluoromethane (at 550-750 °C) yields TFE.
HF is a reactive solvent in the electrochemical fluorination of organic compounds. In this approach, HF is oxidized in the presence of a hydrocarbon and the fluorine replaces C–H bonds with C–F bonds . Perfluorinated carboxylic acids and sulfonic acids are produced in this way. [ 15 ]
1,1-Difluoroethane is produced by adding HF to acetylene using mercury as a catalyst. [ 15 ]
The intermediate in this process is vinyl fluoride or fluoroethylene, the monomeric precursor to polyvinyl fluoride .
The electrowinning of aluminium relies on the electrolysis of aluminium fluoride in molten cryolite. Several kilograms of HF are consumed per ton of Al produced. Other metal fluorides are produced using HF, including uranium tetrafluoride . [ 14 ]
HF is the precursor to elemental fluorine , F 2 , by electrolysis of a solution of HF and potassium bifluoride . The potassium bifluoride is needed because anhydrous HF does not conduct electricity. Several thousand tons of F 2 are produced annually. [ 16 ]
HF serves as a catalyst in alkylation processes in refineries. It is used in the majority of the installed linear alkyl benzene production facilities in the world. The process involves dehydrogenation of n -paraffins to olefins, and subsequent reaction with benzene using HF as catalyst. For example, in oil refineries "alkylate", a component of high- octane petrol ( gasoline ), is generated in alkylation units, which combine C 3 and C 4 olefins and iso -butane . [ 14 ]
Hydrogen fluoride is an excellent solvent. Reflecting the ability of HF to participate in hydrogen bonding, even proteins and carbohydrates dissolve in HF and can be recovered from it. In contrast, most non-fluoride inorganic chemicals react with HF rather than dissolving. [ 17 ]
Hydrogen fluoride is highly corrosive and a powerful contact poison. Exposure requires immediate medical attention. [ 18 ] It can cause blindness by rapid destruction of the corneas . Breathing in hydrogen fluoride at high levels or in combination with skin contact can cause death from an irregular heartbeat or from pulmonary edema (fluid buildup in the lungs). [ 18 ] | https://en.wikipedia.org/wiki/Hydrogen_fluoride |
A hydrogen fuel cell power plant is a type of fuel cell power plant (or station) which uses a hydrogen fuel cell to generate electricity for the power grid . They are larger in scale than backup generators such as the Bloom Energy Server and can be up to 60% efficient in converting hydrogen to electricity. There is little to no nitrous oxide produced in the fuel cell process, which is produced in the process of a combined cycle hydrogen power plant . If the hydrogen could be produced with electrolysis also known as green hydrogen , then this could be a solution to the energy storage problem of renewable energy . [ 1 ] [ 2 ]
The Shinincheon Bitdream Hydrogen Fuel Cell Power Plant in Incheon , South Korea can produce 78.96 MegaWatts of power. It opened in 2021 and is one of the first large scale fuel cell power plants for the grid , rather than just a backup generator . The plant will also purify the air by sucking in 2.4 tons of fine dust per year and filtering it out of the air. It will also produce hot water as a by-product that will be used to heat houses locally, also known as district heating . [ 3 ] [ 4 ]
Fuel cells produce a lot of hot water and a cogeneration or combined cycle could be used for further benefit or to produce more electricity with a steam turbine , increasing the efficiency to >80% using a Phosphoric acid fuel cell . [ 5 ] [ 6 ]
Further studies are needed to see if the water is potable . Places that are dry and have water shortages could use the water for agriculture or other greywater uses. [ 7 ] [ 8 ] Another use would be to use the hot water by-product for High-temperature electrolysis for more hydrogen fuel. [ 9 ]
High-temperature electrolysis at nuclear power plants could produce hydrogen at scale and more efficiently. The DOE Office of Nuclear Energy has demonstration projects to test 3 nuclear facilities in the United States at: | https://en.wikipedia.org/wiki/Hydrogen_fuel_cell_power_plant |
Hydrogen gas porosity is an aluminium casting defect in the form of a porosity or void in an aluminium casting caused by a high level of hydrogen gas (H 2 ) dissolved in the aluminium at liquid phase . The solubility of hydrogen in solid aluminium is much smaller than in liquid aluminium. As the aluminium freezes, some of the hydrogen comes out of solution and forms bubbles, creating porosity in the solid aluminium.
Aluminium foundries want to produce high-quality aluminum castings with minimum porosity. Hydrogen porosity can be reduced by reducing the amount of hydrogen in the liquid aluminium alloy, by degassing or sparging . (Sometimes a small hydrogen concentration is intentionally maintained; some very fine hydrogen porosity can be preferable to internal voids caused by shrinkage.) Directional solidification can drive impurities to one end of the casting.
Hydrogen forms whenever molten aluminium comes into contact with water vapor, and easily dissolves into the melt. The gas tends to come out of the solution and forms bubbles when the melt solidifies.
The detrimental effects arising from the presence of an excess of dissolved hydrogen in aluminium are numerous. Hydrogen causes porosity in aluminum products leading to many casting defects, reduced mechanical properties like fatigue and lower corrosion resistance. Several methods are used to reduce the amount of dissolved hydrogen from the melt, such as furnace fluxing prior to the casting process or using in-line degassing equipment [ 1 ] during the casting process.
An on-line method of measuring hydrogen in aluminum is then required to characterize and optimize the process, which helps ensure the quality of outgoing products and monitors the performance of these degassing processes. Traditional laboratory methods, such as hot extraction , are too expensive for routine quality assurance, and too slow for effective process control . The Reduced Pressure Test (RPT) is often used on the foundry floor. The RPT is a semi-quantitative method with limited accuracy that provides an indication of the hydrogen level.
A hydrogen analyzer [ 2 ] can be used for direct measurement of hydrogen in liquid aluminium. Direct monitoring of hydrogen is possible using an on-line quantitative measurement technology based on a closed-loop gas recirculation method though a porous ceramic probe.
Since its introduction in 1989, this gas recirculation method has been increasingly used by major aluminum producers. [ 3 ]
An example of analyzer for direct hydrogen measurement in liquid aluminium is the Accurity. It works with a probe immersed in liquid aluminium and it uses the closed-loop recirculation method.
The closed loop recirculation is a proven method of directly monitoring hydrogen in molten aluminium. A small volume of carrier gas, usually nitrogen, is brought in contact with the melt by means of an immersed probe, and is continuously recirculated in the closed loop until its hydrogen content reaches equilibrium with the vapor pressure of H 2 in the melt. The H 2 concentration in the gas is measured and converted into a reading of the gas concentration in the metal. This method is fast, reproducible, and accurate, and can be used online on the factory floor.
The amount of H 2 in the gas loop of the instrument is determined by a thermal conductivity sensor, which provides high reproducibility and a broad measurement range. | https://en.wikipedia.org/wiki/Hydrogen_gas_porosity |
In chemistry , hydrogen halides ( hydrohalic acids when in the aqueous phase) are diatomic , inorganic compounds that function as Arrhenius acids . The formula is H X where X is one of the halogens : fluorine , chlorine , bromine , iodine , astatine , or tennessine . [ 1 ] All known hydrogen halides are gases at standard temperature and pressure . [ 2 ]
The hydrogen halides are diatomic molecules with no tendency to ionize in the gas phase (although liquified hydrogen fluoride is a polar solvent somewhat similar to water). Thus, chemists distinguish hydrogen chloride from hydrochloric acid. The former is a gas at room temperature that reacts with water to give the acid. Once the acid has formed, the diatomic molecule can be regenerated only with difficulty, but not by normal distillation . Commonly the names of the acid and the molecules are not clearly distinguished such that in lab jargon, "HCl" often means hydrochloric acid, not the gaseous hydrogen chloride.
Hydrogen chloride, in the form of hydrochloric acid , is a major component of gastric acid .
Hydrogen fluoride, chloride and bromide are also volcanic gases .
The direct reaction of hydrogen with fluorine and chlorine gives hydrogen fluoride and hydrogen chloride, respectively. Industrially these gases are, however, produced by treatment of halide salts with sulfuric acid . Hydrogen bromide arises when hydrogen and bromine are combined at high temperatures in the presence of a platinum catalyst . The least stable hydrogen halide, HI, is produced less directly, by the reaction of iodine with hydrogen sulfide or with hydrazine . [ 1 ] : 809–815
The hydrogen halides are colourless gases at standard conditions for temperature and pressure (STP) except for hydrogen fluoride, which boils at 19 °C. Alone of the hydrogen halides, hydrogen fluoride exhibits hydrogen bonding between molecules, and therefore has the highest melting and boiling points of the HX series. From HCl to HI the boiling point rises. This trend is attributed to the increasing strength of intermolecular van der Waals forces , which correlates with numbers of electrons in the molecules. Concentrated hydrohalic acid solutions produce visible white fumes. This mist arises from the formation of tiny droplets of their concentrated aqueous solutions of the hydrohalic acid.
Upon dissolution in water, which is highly exothermic, the hydrogen halides give the corresponding acids. These acids are very strong, reflecting their tendency to ionize in aqueous solution yielding hydronium ions (H 3 O + ). With the exception of hydrofluoric acid, the hydrogen halides are strong acids , with acid strength increasing down the group. Hydrofluoric acid is complicated because its strength depends on the concentration owing to the effects of homoconjugation . As solutions in non-aqueous solvents, such as acetonitrile , the hydrogen halides are only modestly acidic however.
Similarly, the hydrogen halides react with ammonia (and other bases), forming ammonium halides:
In organic chemistry, the hydrohalogenation reaction is used to prepare halocarbons. For example, chloroethane is produced by hydrochlorination of ethylene : [ 5 ] | https://en.wikipedia.org/wiki/Hydrogen_halide |
The hydrogen hypothesis is a model proposed by William F. Martin and Miklós Müller in 1998 that describes a possible way in which the mitochondrion arose as an endosymbiont within a prokaryotic host in the archaea , giving rise to a symbiotic association of two cells from which the first eukaryotic cell could have arisen ( symbiogenesis ).
According to the hydrogen hypothesis: [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ]
The hypothesis differs from many alternative views within the endosymbiotic theory framework, which suggest that the first eukaryotic cells evolved a nucleus but lacked mitochondria, the latter arising as a eukaryote engulfed a primitive bacterium that eventually became the mitochondrion. The hypothesis attaches evolutionary significance to hydrogenosomes and provides a rationale for their common ancestry with mitochondria. Hydrogenosomes are anaerobic mitochondria that produce ATP by, as a rule, converting pyruvate into hydrogen, carbon dioxide and acetate . Examples from modern biology are known where methanogens cluster around hydrogenosomes within eukaryotic cells. Most theories within the endosymbiotic theory framework do not address the common ancestry of mitochondria and hydrogenosomes. The hypothesis provides a straightforward explanation for the observation that eukaryotes are genetic chimeras with genes of archaeal and eubacterial ancestry. Furthermore, it would imply that archaea and eukarya split after the modern groups of archaea appeared. Most theories within the endosymbiotic theory framework predict that some eukaryotes never possessed mitochondria. The hydrogen hypothesis predicts that no primitively mitochondrion-lacking eukaryotes ever existed. In the 15 years following the publication of the hydrogen hypothesis, this specific prediction has been tested many times and found to be in agreement with observation. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ]
In 2015, the discovery and placement of the Lokiarchaeota (an archaeal lineage possessing an expanded genetic repertoire including genes involved in membrane remodeling and actin cytoskeletal structure) as the sister group to eukaryotes called into question particular tenets of the hydrogen hypothesis, as Lokiarchaeota appear to lack methanogenesis. [ 6 ] | https://en.wikipedia.org/wiki/Hydrogen_hypothesis |
A hydrogen infrastructure is the infrastructure of points of hydrogen production , truck and pipeline transport, and hydrogen stations for the distribution and sale of hydrogen fuel , [ 1 ] and thus a crucial prerequisite before a successful commercialization of fuel cell technology. [ 2 ]
Hydrogen stations which are not situated near a hydrogen pipeline get supply via hydrogen tanks, compressed hydrogen tube trailers , liquid hydrogen trailers , liquid hydrogen tank trucks or dedicated onsite production. Pipelines are the cheapest way to move hydrogen over long distances compared to other options. Hydrogen gas piping is routine in large oil-refineries, because hydrogen is used to hydrocrack fuels from crude oil. The IEA recommends existing industrial ports be used for production and natural gas pipelines for transport, international co-operation and shipping. [ 3 ]
South Korea and Japan , [ 4 ] which as of 2019 lack international electrical interconnectors , are investing in the hydrogen economy . [ 5 ] In March 2020, the Fukushima Hydrogen Energy Research Field was opened in Japan, claiming to be the world's largest hydrogen production facility. [ 6 ] Much of the site is occupied by a solar array ; power from the grid is also used for electrolysis of water to produce hydrogen fuel. [ 7 ]
A hydrogen highway is a chain of hydrogen -equipped filling stations and other infrastructure along a road or highway which allow hydrogen vehicles to travel.
Hydrogen stations that are not situated near a hydrogen pipeline get deliveries of hydrogen tanks via compressed hydrogen tube trailers , liquid hydrogen trailers , liquid hydrogen tank trucks or dedicated onsite production. Government supported activities to expand hydrogen fuel infrastructure are ongoing in the US state of California, in some member states of the European Union, Japan and ellsewhere.
Hydrogen pipeline transport is a transportation of hydrogen through a pipe as part of the hydrogen infrastructure. Hydrogen pipeline transport is used to connect the point of hydrogen production or delivery of hydrogen with the point of demand, pipeline transport costs are similar to CNG , [ 8 ] the technology is proven, [ 9 ] however most hydrogen is produced on the place of demand with every 50 to 100 miles (80 to 161 km) an industrial production facility. [ 10 ] As of 2004 [update] , there are 900 miles (1,448 km) of low pressure hydrogen pipelines in the US and 930 miles (1,497 km) in Europe.
According to a 2024 research report, the United States has 1,600 miles (2,570 kilometers) of hydrogen pipelines; the global total stands at 2,800 miles (4,500 kilometers). [ 11 ] The World Economic Forum , in December 2023, estimated that Europe had approximately 1,600 kilometers of hydrogen pipelines. [ 12 ]
Hydrogen embrittlement (a reduction in the ductility of a metal due to absorbed hydrogen) is not a problem for hydrogen gas pipelines. Hydrogen embrittlement only happens with 'diffusible' hydrogen, i.e. atoms or ions. Hydrogen gas, however, is molecular (H 2 ), and there is a very significant energy barrier to splitting it into atoms. [ 13 ]
98% of hydrogen production uses the steam reforming method. [ 14 ] Methods such as electrolysis of water are also used. [ 15 ] The world's largest facility for producing electrolytic hydrogen fuel is claimed [ 16 ] to be the Fukushima Hydrogen Energy Research Field (FH2R), a 10MW-class hydrogen production unit, inaugurated on 7 March 2020, in Namie , Fukushima Prefecture . [ 17 ] The site occupies 180,000 square meters of land, much of which is occupied by a solar array ; but power from the grid is also used to conduct electrolysis of water to produce hydrogen fuel . [ 16 ]
Hydrogen may be transported through pipes .
Hydrogen pipeline transport is sometimes used to transport hydrogen from the point of production or delivery to the point of demand. Although hydrogen pipeline transport is technologically mature, [ 22 ] [ 23 ] and the transport costs are similar to those of CNG , [ 24 ] most hydrogen is produced in the place of demand, with an industrial production facility every 50 to 100 miles (80 to 161 km) [ 25 ]
For process metal piping at pressures up to 7,000 psi (48 MPa), high-purity stainless steel piping with a maximum hardness of 80 HRB is preferred. [ 26 ] This is because higher hardnesses are associated with lower fracture toughness so stronger, higher hardness steel is less safe.
Composite pipes are assessed like:
Fiber-Reinforced Polymer pipelines (or FRP pipeline) and reinforced thermoplastic pipes are researched. [ 27 ] [ 28 ] [ 29 ] [ 30 ]
Carrying hydrogen in steel pipelines (grades: API5L-X42 and X52; up to 1,000psi/7,000kPa, constant pressure/low pressure cycling) does not lead to hydrogen embrittlement . [ 31 ] Hydrogen is typically stored in steel cylinders without problems.
A hydrogen highway is a chain of hydrogen -equipped public filling stations , along a road or highway, that allows hydrogen powered cars to travel. [ 32 ] William Clay Ford Jr . has stated that infrastructure is one of three factors (also including costs and manufacturability in high volumes) that hold back the marketability of fuel cell cars. [3]
Hydrogen fueling stations generally receive deliveries of hydrogen by tanker truck from hydrogen suppliers. [ 33 ] An interruption at a hydrogen supply facility can shut down multiple hydrogen fueling stations. [ 34 ] A hydrogen fueling station costs between $1 million and $4 million to build. [ 35 ]
As of 2019, 98% of hydrogen is produced by steam methane reforming , which emits carbon dioxide. [ 14 ] The bulk of hydrogen is also transported in trucks, so pollution is emitted in its transportation. [ 33 ]
A hydrogen station is a storage or filling station for hydrogen fuel . [ 36 ] The hydrogen is dispensed by weight. [ 37 ] [ 38 ] There are two filling pressures in common use: H70 or 700 bar , and the older standard H35 or 350 bar. [ 39 ] As of 2021 [update] , around 550 filling stations were available worldwide. [ 39 ] According to H2stations.org by Ludwig-Bölkow-Systemtechnik (LBST), as of the end of 2023, there were 921 hydrogen refueling stations globally, [ 40 ] although this number clearly conflicts with those published by AFDC. [ 41 ] The distribution of these stations is highly uneven, with a concentration in East Asia, particularly in China, Japan and South Korea; Central Europe and California in the United States. Other regions have very few, if any, hydrogen refuelling stations. [ 40 ] [ 41 ]
Hydrogen fueling stations can be divided into off-site stations, where hydrogen is delivered by truck or pipeline, and on-site stations that produce and compress hydrogen for the vehicles. [ 42 ] [ 43 ]
Home hydrogen fueling stations are available to consumers. [ 44 ] A model that can produce 12 kilograms of hydrogen per day sells for $325,000. [ 45 ]
Solar powered water electrolysing hydrogen home stations are composed of solar cells , power converter , water purifier , electrolyzer , piping, hydrogen purifier , [ 46 ] oxygen purifier, compressor , [ 47 ] pressure vessels [ 48 ] and a hydrogen outlet. [ 49 ]
Hydrogen fuel is hazardous because of its low ignition energy, high combustion energy, and because it easily leaks from tanks. [ 50 ] Explosions at hydrogen filling stations have been reported. [ 51 ]
Hydrogen fuelling stations generally receive deliveries by truck from hydrogen suppliers. An interruption at a hydrogen supply facility can shut down multiple hydrogen fuelling stations due to an interruption of the supply of hydrogen. [ 52 ]
There are far fewer Hydrogen filling stations than gasoline fuel stations, which in the US alone numbered 168,000 in 2004. [ 53 ] Replacing the US gasoline infrastructure with hydrogen fuel infrastructure is estimated to cost a half trillion U.S. dollars. [ 54 ] A hydrogen fueling station costs between $1 million and $4 million to build. [ 55 ] In comparison, battery electric vehicles can charge at home or at public chargers. As of 2023, there are more than 60,000 public charging stations in the United States, with more than 160,000 outlets. [ 41 ] A public Level 2 charger, which comprise the majority of public chargers in the US, costs about $2,000, and DC fast chargers, of which there are more than 30,000 in the U.S., [ 41 ] generally cost between $100,000 and $250,000, [ 56 ] although Tesla superchargers are estimated to cost approximately $43,000. [ 57 ]
During refueling, the flow of cold hydrogen can cause frost to form on the dispenser nozzle, sometimes leading to the nozzle becoming frozen to the vehicle being refueled. [ 58 ]
Consulting firm Ludwig-Bölkow-Systemtechnik tracks global hydrogen filling stations and publishes a map. [ 59 ]
In 2019, there were 178 publicly available hydrogen fuel stations in operation. [ 60 ]
As of May 2023 [update] , there are 167 publicly available hydrogen fuel stations in operation in Japan. [ 61 ] [ 62 ] In 2012 there were 17 hydrogen stations, [ 63 ] and in 2021, there were 137 publicly available hydrogen fuel stations in Japan. [ 39 ]
By the end of 2023, China had built 354 hydrogen refueling stations. [ 64 ]
In 2019, there were 33 publicly available hydrogen fuel stations in operation in South Korea. [ 60 ] [ 65 ] In November 2023, however, due to hydrogen supply problems and broken stations, most fueling stations in South Korea offered no hydrogen. [ 66 ] 41 out of the 159 hydrogen stations in the country were listed as open, and some of these were rationing supplies of hydrogen. [ 67 ]
In 2019, there were 177 stations in Europe. [ 60 ] [ 68 ] [ 69 ] According to H2stations.org by Ludwig-Bölkow-Systemtechnik (LBST), there were 265 hydrogen refuelling stations in Europe by the end of 2023. [ 40 ]
As of June 2023, [update] there were 105 hydrogen fuel stations in Germany, [ 40 ] As of June 2023, [update] there were 5 publicly available hydrogen fuel stations in France, [ 68 ] 3 publicly available hydrogen fuel stations in Iceland, [ 68 ] one publicly available hydrogen fuel station in Italy, [ 68 ] 4 publicly available hydrogen fuel stations in The Netherlands, [ 68 ] 2 publicly available hydrogen fuel stations in Belgium, [ 68 ] 4 publicly available hydrogen fuel stations in Sweden, [ 68 ] 3 publicly available hydrogen fuel stations in Switzerland [ 68 ] and 6 publicly available hydrogen fuel stations in Denmark. [ 68 ] Everfuel, the only operator of hydrogen stations in Denmark, announced in 2023 the closure of all of its public hydrogen stations in the country. [ 70 ] [ 71 ]
As of June 2021, [update] there were 2 publicly available hydrogen fuel stations in Norway, both in the Oslo area. [ 72 ] Since the explosion at the hydrogen filling station in Sandvika in June 2019, the sale of hydrogen cars in Norway has halted. [ 73 ] In 2023, Everfuel announced the closure of its two public hydrogen stations in Norway and cancelled the opening of a third. [ 70 ] In 2024 Shell discontinued its hydrogen fuel projects in Norway. [ 74 ]
As of June 2020, [update] there were 11 publicly available hydrogen fuel stations in the United Kingdom, [ 68 ] but as of 2023, the number decreased to 5. [ 75 ] In 2022, Shell closed its three hydrogen stations in the UK, [ 76 ]
As of July 2023, there were 10 fueling stations in Canada, 9 of which were open to the public:
As of July 2024 [update] , there were 54 publicly accessible hydrogen refueling stations in the US, 53 of which were located in California, with one in Hawaii. [ 41 ]
In 2021, the first Australian publicly available hydrogen fuel station opened in Canberra , operated by ActewAGL . [ 86 ]
A hydrogen tank (other names- cartridge or canister) is used for hydrogen storage . [ 87 ] [ 88 ] [ 89 ] The first type IV hydrogen tanks for compressed hydrogen at 700 bars (70 MPa; 10,000 psi) were demonstrated in 2001, the first fuel cell vehicles on the road with type IV tanks are the Toyota FCHV , Mercedes-Benz F-Cell and the GM HydroGen4 .
Various applications have allowed the development of different H2 storage scenarios.
Recently, the Hy-Can [ 90 ] consortium has introduced a small one liter, 10 bars (1.0 MPa; 150 psi) format. Horizon Fuel Cells is now selling a refillable 3 megapascals (30 bar; 440 psi) metal hydride form factor for consumer use called HydroStik. [ 91 ]
In accordance with ISO/TS 15869 (revised):
This specification was replaced by ISO 13985:2006 and only applies to liquid hydrogen tanks.
Actual Standard EC 79/2009
Using magnesium [ 98 ] for hydrogen storage , a safe but weighty reversible storage technology. Typically the pressure requirement are limited to 10 bars (1.0 MPa; 150 psi).
The charging process generates heat whereas the discharge process will require some heat to release the H2 contained in the storage material. To activate these types of hydrides, at the current state of development you need to reach approximately 300 °C (572 °F). [ 99 ] [ 100 ] [ 101 ]
See also sodium aluminium hydride | https://en.wikipedia.org/wiki/Hydrogen_infrastructure |
2.8 (in acetonitrile) [ 3 ]
Hydrogen iodide (HI) is a diatomic molecule and hydrogen halide . Aqueous solutions of HI are known as hydroiodic acid or hydriodic acid, a strong acid . Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under standard conditions, whereas the other is an aqueous solution of the gas. They are interconvertible. HI is used in organic and inorganic synthesis as one of the primary sources of iodine and as a reducing agent .
HI is a colorless gas that reacts with oxygen to give water and iodine. With moist air, HI gives a mist (or fumes) of hydroiodic acid. It is exceptionally soluble in water, giving hydroiodic acid. One liter of water will dissolve 425 liters of HI gas, the most concentrated solution having only four water molecules per molecule of HI. [ 6 ]
Hydroiodic acid is an aqueous solution of hydrogen iodide. Commercial "concentrated" hydroiodic acid usually contains 48–57% HI by mass. The solution forms an azeotrope boiling at 127 °C with 57% HI, 43% water. The high acidity is caused by the dispersal of the ionic charge over the anion. The iodide ion radius is much larger than the other common halides , which results in the negative charge being dispersed over a large volume. This weaker H + ···I − interaction in HI facilitates dissociation of the proton from the anion and is the reason HI is the strongest acid of the hydrohalides.
The industrial preparation of HI involves the reaction of I 2 with hydrazine , which also yields nitrogen gas: [ 7 ]
When the synthesis is performed in water, the HI can be purified by distillation .
Anhydrous HI can be prepared by reaction of iodine with tetrahydronaphthalene : [ 8 ]
HI can also be distilled from a solution of NaI or other alkali iodide that is treated with the dehydration reagent phosphorus pentoxide (which gives phosphoric acid ). [ 9 ] Concentrated sulfuric acid is unsuited for acidifying iodides, as it oxidizes the iodide to elemental iodine.
An historical route to HI involves oxidation of hydrogen sulfide with aqueous iodine: [ 10 ]
Additionally, HI can be prepared by simply combining H 2 and I 2 : [ 9 ]
This method is usually employed to generate high-purity samples. For many years, this reaction was considered to involve a simple bimolecular reaction between molecules of H 2 and I 2 . However, when a mixture of the gases is irradiated with the wavelength of light equal to the dissociation energy of I 2 , about 578 nm, the rate increases significantly. This supports a mechanism whereby I 2 first dissociates into 2 iodine atoms, which each attach themselves to a side of an H 2 molecule and break the H−H bond : [ 11 ]
In the laboratory, yet another method involves hydrolysis of PI 3 , the iodine analog of PBr 3 . In this method, I 2 reacts with phosphorus to create phosphorus triiodide , which then reacts with water to form HI and phosphorous acid :
Solutions of hydrogen iodide are easily oxidized by air:
HI 3 is brown in color, which makes aged solutions of HI often appear dark.
Like HBr and HCl, HI adds to alkenes , [ 13 ] in a reaction that is subject to the same Markovnikov and anti-Markovnikov guidelines as HCl and HBr.
HI is also used in organic chemistry to convert primary alcohols into alkyl iodides . [ 14 ] This reaction is an S N 2 substitution , in which the iodide ion replaces the "activated" hydroxyl group (water):
HI is sometimes preferred over other hydrogen halides.
HI (or HBr ) can also be used to cleave ethers . Commonly, it is applied to the cleavage of aryl-alkyl ethers to give phenols and the alkyl iodide. [ 14 ] In the following idealized equation diethyl ether is split two equivalents of ethyl iodide :
The reaction is regioselective , as iodide tends to attack the less sterically hindered ether carbon.
HI was commonly employed as a reducing agent early on in the history of organic chemistry. Chemists in the 19th century attempted to prepare cyclohexane by HI reduction of benzene at high temperatures, but instead isolated the rearranged product, methylcyclopentane ( see the article on cyclohexane ). As first reported by Kiliani, [ 15 ] hydroiodic acid reduction of sugars and other polyols results in the reductive cleavage of several or even all hydroxy groups, although often with poor yield and/or reproducibility. [ 16 ] In the case of benzyl alcohols and alcohols with α-carbonyl groups, reduction by HI can provide synthetically useful yields of the corresponding hydrocarbon product ( ROH + 2HI → RH + H 2 O + I 2 ). [ 13 ] This process can be made catalytic in HI using red phosphorus to reduce the formed I 2 . [ 17 ]
Commercial processes for obtaining iodine all focus on iodide-rich brines . The purification begins by converting iodide to hydroiodic acid, which is then oxidized to iodine. The iodine is then separated by evaporation or adsorption. [ 18 ] | https://en.wikipedia.org/wiki/Hydrogen_iodide |
This page provides supplementary chemical data on hydrogen iodide .
The handling of this chemical may incur notable safety precautions. It is highly recommend that you seek the Material Safety Datasheet ( MSDS ) for this chemical from a reliable source such as SIRI , and follow its directions. | https://en.wikipedia.org/wiki/Hydrogen_iodide_(data_page) |
Hydrogen isocyanide is a chemical with the molecular formula HNC. It is a minor tautomer of hydrogen cyanide (HCN). Its importance in the field of astrochemistry is linked to its ubiquity in the interstellar medium .
Both hydrogen isocyanide and azanylidyniummethanide are correct IUPAC names for HNC. There is no preferred IUPAC name . The second one is according to the substitutive nomenclature rules , derived from the parent hydride azane ( NH 3 ) and the anion methanide ( CH − 3 ). [ 1 ]
Hydrogen isocyanide (HNC) is a linear triatomic molecule with C ∞v point group symmetry . It is a zwitterion and an isomer of hydrogen cyanide (HCN). [ 2 ] Both HNC and HCN have large, similar dipole moments , with μ HNC = 3.05 Debye and μ HCN = 2.98 Debye respectively. [ 3 ] These large dipole moments facilitate the easy observation of these species in the interstellar medium .
As HNC is higher in energy than HCN by 3920 cm −1 (46.9 kJ/mol), one might assume that the two would have an equilibrium ratio ( [ H N C ] [ H C N ] ) e q {\textstyle \left({\frac {[HNC]}{[HCN]}}\right)_{eq}} at temperatures below 100 Kelvin of 10 −25 . [ 4 ] However, observations show a very different conclusion; ( [ H N C ] [ H C N ] ) o b s e r v e d {\textstyle \left({\frac {[HNC]}{[HCN]}}\right)_{observed}} is much higher than 10 −25 , and is in fact on the order of unity in cold environments. This is because of the potential energy path of the tautomerization reaction; there is an activation barrier on the order of roughly 12,000 cm −1 for the tautomerization to occur, which corresponds to a temperature at which HNC would already have been destroyed by neutral-neutral reactions. [ 5 ]
In practice, HNC is almost exclusively observed astronomically using the J = 1→0 transition. This transition occurs at ~90.66 GHz, which is a point of good visibility in the atmospheric window , thus making astronomical observations of HNC particularly simple. Many other related species (including HCN) are observed in roughly the same window. [ 6 ] [ 7 ]
HNC is intricately linked to the formation and destruction of numerous other molecules of importance in the interstellar medium—aside from the obvious partners HCN, protonated hydrogen cyanide (HCNH + ) , and cyanide (CN) , HNC is linked to the abundances of many other compounds, either directly or through a few degrees of separation. As such, an understanding of the chemistry of HNC leads to an understanding of countless other species—HNC is an integral piece in the complex puzzle representing interstellar chemistry.
Furthermore, HNC (alongside HCN) is a commonly used tracer of dense gas in molecular clouds. Aside from the potential to use HNC to investigate gravitational collapse as the means of star formation, HNC abundance (relative to the abundance of other nitrogenous molecules) can be used to determine the evolutionary stage of protostellar cores. [ 3 ]
The HCO + /HNC line ratio is used to good effect as a measure of density of gas. [ 8 ] This information provides great insight into the mechanisms of the formation of (Ultra-)Luminous Infrared Galaxies ((U)LIRGs), as it provides data on the nuclear environment, star formation , and even black hole fueling. Furthermore, the HNC/HCN line ratio is used to distinguish between photodissociation regions and X-ray-dissociation regions on the basis that [HNC]/[HCN] is roughly unity in the former, but greater than unity in the latter.
The study of HNC is relatively straightforward, which is a major motivation for its research. Its J = 1→0 transition occurs in a clear portion of the atmospheric window, and it has numerous isotopomers that are easily studied. Additionally, its large dipole moment makes observations particularly simple. Moreover, HNC is a fundamentally simple molecule in its molecular nature. This makes the study of the reaction pathways that lead to its formation and destruction a good means of obtaining insight to the workings of these reactions in space. Furthermore, the study of the tautomerization of HNC to HCN (and vice versa), which has been studied extensively, has been suggested as a model by which more complicated isomerization reactions can be studied. [ 5 ] [ 9 ] [ 10 ]
HNC is found primarily in dense molecular clouds, though it is ubiquitous in the interstellar medium. Its abundance is closely linked to the abundances of other nitrogen-containing compounds. [ 11 ] HNC is formed primarily through the dissociative recombination of HNCH + and H 2 NC + , and it is destroyed primarily through ion-neutral reactions with H + 3 and C + . [ 12 ] [ 13 ] Rate calculations were done at 3.16 × 10 5 years, which is considered early time, and at 20 K, which is a typical temperature for dense molecular clouds. [ 14 ] [ 15 ]
These four reactions are merely the four most dominant, and thus the most significant in the formation of the HNC abundances in dense molecular clouds; there are dozens more reactions for the formation and destruction of HNC. Though these reactions primarily lead to various protonated species, HNC is linked closely to the abundances of many other nitrogen containing molecules, for example, NH 3 and CN. [ 11 ] The abundance HNC is also inexorably linked to the abundance of HCN, and the two tend to exist in a specific ratio based on the environment. [ 12 ] This is because the reactions that form HNC can often also form HCN, and vice versa, depending on the conditions in which the reaction occurs, and also that there exist isomerization reactions for the two species.
HCN (not HNC) was first detected in June 1970 by L. E. Snyder and D. Buhl using the 36-foot radio telescope of the National Radio Astronomy Observatory. [ 16 ] The main molecular isotope, H 12 C 14 N, was observed via its J = 1→0 transition at 88.6 GHz in six different sources: W3 (OH), Orion A, Sgr A(NH3A), W49, W51, DR 21(OH). A secondary molecular isotope, H 13 C 14 N, was observed via its J = 1→0 transition at 86.3 GHz in only two of these sources: Orion A and Sgr A(NH3A). HNC was then later detected extragalactically in 1988 using the IRAM 30-m telescope at the Pico de Veleta in Spain. [ 17 ] It was observed via its J = 1→0 transition at 90.7 GHz toward IC 342.
A number of detections have been made towards the end of confirming the temperature dependence of the abundance ratio of [HNC]/[HCN]. A strong fit between temperature and the abundance ratio would allow observers to spectroscopically detect the ratio and then extrapolate the temperature of the environment, thus gaining great insight into the environment of the species. The abundance ratio of rare isotopes of HNC and HCN along the OMC-1 varies by more than an order of magnitude in warm regions versus cold regions. [ 18 ] In 1992, the abundances of HNC, HCN, and deuterated analogs along the OMC-1 ridge and core were measured and the temperature dependence of the abundance ratio was confirmed. [ 6 ] A survey of the W 3 Giant Molecular Cloud in 1997 showed over 24 different molecular isotopes, comprising over 14 distinct chemical species, including HNC, HN 13 C, and H 15 NC. This survey further confirmed the temperature dependence of the abundance ratio, [HNC]/[HCN], this time even confirming the dependence of the isotopomers. [ 19 ]
These are not the only detections of importance of HNC in the interstellar medium. In 1997, HNC was observed along the TMC-1 ridge and its abundance relative to HCO + was found to be constant along the ridge—this led credence to the reaction pathway that posits that HNC is derived initially from HCO + . [ 7 ] One significant astronomical detection that demonstrated the practical use of observing HNC occurred in 2006, when abundances of various nitrogenous compounds (including HN 13 C and H 15 NC) were used to determine the stage of evolution of the protostellar core Cha-MMS1 based on the relative magnitudes of the abundances. [ 3 ]
On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN , HNC, H 2 CO , and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) . [ 20 ] [ 21 ] | https://en.wikipedia.org/wiki/Hydrogen_isocyanide |
Hydrogen isotope biogeochemistry (HIBGC) is the scientific study of biological, geological, and chemical processes in the environment using the distribution and relative abundance of hydrogen isotopes . Hydrogen has two stable isotopes, protium 1 H and deuterium 2 H, which vary in relative abundance on the order of hundreds of permil . The ratio between these two species can be called the hydrogen isotopic signature of a substance. Understanding isotopic fingerprints and the sources of fractionation that lead to variation between them can be applied to address a diverse array of questions ranging from ecology and hydrology to geochemistry and paleoclimate reconstructions. Since specialized techniques are required to measure natural hydrogen isotopic composition (HIC), HIBGC provides uniquely specialized tools to more traditional fields like ecology and geochemistry.
The study of hydrogen stable isotopes began with the discovery of deuterium by chemist Harold Urey . [ 1 ] Even though the neutron was not realized until 1932, [ 2 ] Urey began searching for "heavy hydrogen" in 1931. Urey and his colleague George Murphy calculated the redshift of heavy hydrogen from the Balmer series and observed very faint lines on a spectrographic study. To intensify the spectroscopic lines for publishable data, Murphy and Urey paired with Ferdinand Brickwedde and distilled a more concentrated pool of heavy hydrogen, now called deuterium . This work on hydrogen isotopes won Urey the 1934 Nobel Prize in Chemistry . [ 3 ]
Also in 1934, scientists Ernest Rutherford , Mark Oliphant , and Paul Harteck , produced the radioisotope tritium (hydrogen-3, 3 H) by hitting deuterium with high-energy nuclei. The deuterium used in the experiment was a generous gift of heavy water from UC Berkeley physicist Gilbert N. Lewis . [ 4 ] Bombarding deuterium produced two previously undetected isotopes, helium-3 ( 3 He) and 3 H. Rutherford and his colleagues successfully created 3 H, but incorrectly assumed that 3 He was the radioactive component. The work of Luis Walter Alvarez and Robert Cornog [ 5 ] first isolated 3 H and reversed Rutherford's incorrect notion. Alvarez reasoned that tritium was radioactive, but did not measure the half-life, though calculations at the time suggested >10 years. At the end of World War II , physical chemist Willard Libby detected the residual radioactivity of a tritium sample with a Geiger counter , [ 4 ] providing a more accurate understanding of the half-life , now accepted as 12.3 years. [ 6 ]
The discovery of hydrogen isotopes also impacted physics in the 1940s, as nuclear magnetic resonance spectroscopy was first invented. Organic chemists now use nuclear magnetic resonance (NMR) to map protein interactions [ 7 ] or identify small compounds, [ 8 ] but NMR was first a passion project of physicists. All three isotopes of hydrogen were found to have magnetic properties suitable for NMR spectroscopy. The first chemist to fully express an application of NMR was George Pake , who measured gypsum ( CaSO 4 ⋅ 2 H 2 O {\displaystyle {\ce {CaSO4.2H2O}}} ) as a crystal and powder. [ 9 ] The signal observed, called the Pake doublet , was from the magnetically active hydrogens in water. Pake then calculated the proton-proton bond length . NMR measurements were further revolutionized when commercial machines became available in the 1960s. Before this, NMR experiments involved constructing massive projects, locating large magnets, and hand wiring miles of copper coil. [ 10 ] Proton NMR remained the most popular technique throughout advancements in following decades, but 2 H and 3 H were used in other flavors of NMR spectroscopy. 2 H has a different magnetic moment and spin than 1 H, but generally a much smaller signal. Historically, deuterium NMR is a poor alternative to proton NMR, but has been used to study the behavior of lipids on cell membranes . [ 11 ] A variant of 2 H NMR called 2 H-SNIF has shown potential for understating position-specific isotope compositions and comprehending biosynthetic pathways. [ 12 ] Tritium is also used in NMR, [ 13 ] as it is the only nucleus more sensitive than 1 H, generating very large signals. However, tritium's radioactivity discouraged many studies of 3 H-NMR.
While tritium's radioactivity discourages use in spectroscopy , tritium is essential for nuclear weapons . Scientists began understanding nuclear energy as early as the 1800s, but large advancements were made in studies of the atomic bomb in the early 1940s. Wartime research, especially the Manhattan Project , greatly advanced the understanding of radioactivity . 3 H is a byproduct in reactors , a result of hitting lithium-6 with neutrons , producing almost 5 MeV of energy.
In boosted fission weapons a mix of 2 H and 3 H is heated until there is thermonuclear fusion to produce helium and free neutrons . [ 14 ] These fast neutrons then cause further fission, creating "boosting". In 1951, in Operation Greenhouse , a prototype named George, validated the proof of concept for such a weapon. [ 15 ] However, the first true boosted fission bomb, Greenhouse Item , was successfully tested in 1952, giving a 45.5-kiloton yield, nearly double that of an unboosted bomb. [ 15 ] The United States stopped producing tritium in nuclear reactors in 1988, [ 16 ] but nuclear tests in the 1950s added large spikes of radionuclides to the air, especially carbon-14 and 3 H. [ 17 ] [ 18 ] This complicated measurements for geologists using carbon dating . However, some oceanographers benefited from the 3 H increase, using the signal in the water to trace physical mixing of water masses. [ 19 ]
In biogeochemistry, scientists focused mainly on deuterium as a tracer for environmental processes, especially the water cycle . American geochemist Harmon Craig , once a graduate student of Urey, discovered the relationship between rainwater's hydrogen and oxygen isotope ratios. The linear correlation between the two heavy isotopes occurs worldwide and is called the global meteoric water line . [ 20 ] By the late 1960s, the focus of hydrogen isotopes shifted away from water and toward organic molecules . Plants use water to form biomass , but a 1967 study by Zebrowski, Ponticorvo, and Rittenberg found that the organic material in plants had less 2 H than the water source. [ 21 ] Zebrowski's research measured the deuterium concentration of fatty acids and amino acids derived from sediments in the Mohole drilling project . Further studies by Bruce Smith and Samuel Epstein in 1970 confirmed the depletion of 2 H in organics compared to environmental water. [ 22 ] Another duo in 1970, Schiegl and Vogel, analyzed the HIC as water became biomass, as biomass became coal and oil , and as oil became natural gas . [ 23 ] In each step they found 2 H further depleted. A landmark paper in 1980 by Marilyn Epstep, now M. Fogel, and Thomas Hoering titled "Biogeochemistry of the stable hydrogen isotopes" refined the links between organic materials and sources. [ 24 ]
In this early stage of hydrogen stable isotope study, most isotope compositions or fractionations were reported as bulk measurements of all organic or all inorganic matter . Some exceptions include cellulose [ 25 ] [ 26 ] and methane , [ 27 ] as these compounds are easily separated. Another advantage of methane for compound-specific measurements is the lack of hydrogen exchange. Cellulose has exchangeable hydrogen, but chemical derivatization can prevent swapping of cellulose hydrogen with water or mineral hydrogen sources. Cellulose and methane studies in the 1970s and 1980s set the standard for modern hydrogen isotope geochemistry.
Measurement of individual compounds was made possible in the late 1990s and early 2000s with advances in mass spectrometry . [ 28 ] The Thermo Delta+XL transformed measurements as the first instrument capable of compound specific isotope analysis. It was then possible to look at smaller samples with more precision. Hydrogen isotope applications quickly emerged in petroleum geochemistry by measuring oil, paleoclimatology by observing lipid biomarkers , and ecology by constructing trophic dynamics . Advances are underway in the clumped-isotope composition of methane [ 29 ] after development of the carbonate thermometer . [ 30 ] [ 31 ] Precise measurements are also enabling focus on microbial biosynthetic pathways involving hydrogen. [ 32 ] Ecologists studying trophic levels are especially interested in compound specific measurements for reconstructing past diets and tracing predator-prey relationships. [ 33 ] Highly advanced machines now promise position-specific hydrogen-isotope analysis of biomolecules and natural gas . [ 34 ]
All isotopes of an element have the same number of protons with varying numbers of neutrons. Hydrogen has three naturally occurring isotopes: 1 H, 2 H and 3 H; called protium (H), deuterium (D) and tritium (T), respectively. Both 1 H and 2 H are stable, while 3 H is unstable and beta-decays to 3 He. While there are some important applications of 3 H in geochemistry (such as its use as an ocean circulation tracer ) these will not be discussed further here.
The study of stable isotope biogeochemistry involves the description of the relative abundances of various isotopes in a certain chemical pool, as well as the way in which physicochemical processes change the fraction of those isotopes in one pool vs. another. Various type of notation have been developed to describe the abundance and change in the abundance of isotopes in these processes, and these are summarized below. In most cases only the relative amounts of an isotope are of interest, the absolute concentration of any one isotope is of little importance.
The most fundamental description of hydrogen isotopes in a system is the relative abundance of 2 H and 1 H. This value can be reported as isotope ratio 2 R or fractional abundance 2 F defined as:
and
where x H is amount of isotope x H. Fractional abundance is equivalent to mole fraction, and yields atom percent when multiplied by 100. In some instances atom percent excess is used, which reports the atom percent of a sample minus the atom percent of a standard.
Isotope ratios for a substance are often reported compared to a standard with known isotopic composition, and measurements of relative masses are always made in conjuncture with measuring a standard. For hydrogen, the Vienna Standard Mean Ocean Water standard is used which has an isotope ratio of 155.76±0.1 ppm. The delta value as compared to this standard is defined as:
These delta values are often quite small, and are usually reported as per mil values (‰) which come from multiplying the above equation by a factor of 1000.
The study of HIBGC relies on the fact that various physicochemical processes preferentially enrich or deplete 2 H relative to 1 H (see kinetic isotope effect [KIE], etc.). Various measures have been developed to describe the fractionation in an isotope between two pools, often the product and reactant of a physiochemical process. α notation describes the difference between two hydrogen pools A and B with the equation:
where δ 2 H A is the delta value of pool A relative to VSMOW. As many delta values do not vary greatly from one another the α value is often very close to unity. A related measure called epsilon (ε) is often used which is given simply by:
These values are often very close to zero, and are reported as per mill values by multiplying α − 1 by 1000. One final measure is Δ, pronounced "cap delta", which is simply:
2 H and 1 H are stable isotopes. Therefore, the 2 H/ 1 H ratio of a pool containing hydrogen, remains constant as long as no hydrogen is added or removed, a property known as conservation of mass . When two pools of hydrogen A and B mix with molar amounts of hydrogen m A and m B , each with their own starting fractional abundance of deuterium ( F A and F B ), then the fractional abundance of the resulting mixture is given by the following exact equation:
The terms with Σ represent the values for the combined pools. The following approximation is often used for calculations regarding the mixing of two pools with a known isotopic composition:
This approximation is convenient and applicable with little error in most applications having to deal with pools of hydrogen from natural processes. The maximum difference between the calculated delta ( δ ) value with the approximate and exact equations is given by the following equation:
This error is quite small for nearly all mixing of naturally occurring isotope values, even for hydrogen which can have quite large natural variations in δ values. [ 35 ] The estimation is usually avoided when unnaturally large δ values are encountered, which is especially common in isotopic labeling experiments.
Natural processes result in broad variations in the D/H ratio (DHR) in different pools of hydrogen. KIEs and physical changes such as precipitation and evaporation lead to these observed variations. Seawater varies slightly, between 0 and −10 per mil, while atmospheric water can vary between about −200‰ to +100‰. Biomolecules synthesized by organisms, retain some of the D/H signature of the water which they were grown on, plus a large fractionation factor which can be as great as several hundred ‰. Large D/H differences, of thousands of ‰, can be found between Earth and other planetary bodies such as Mars, likely due to variations in isotope fractionation during planet formation and the loss of hydrogen into space.
A number of common processes fractionate hydrogen isotopes to produce the isotope variations found in nature. Common physical processes include precipitation and evaporation. Chemical reactions can also heavily influence the partitioning of heavy and light isotopes between pools. The rate of a chemical reaction depends in part on the energies of the chemical bonds formed and broken in the reaction. Since different isotopes have different masses, the bond energies differ between isotopologues of a chemical species. This will result in a difference in the rate of a reaction for the different isotopologues, resulting in a fractionation of the different isotopes between the reactant and product in a chemical reaction. This is known as the kinetic isotope effect (KIE). A classic example of KIE is the DHR difference in the equilibrium between H 2 O and H 2 which can have an α value of as much as 3–4. [ 36 ]
In many areas of study the origin of a chemical or group of chemicals is of central importance. Questions such as the source of environmental pollutants, the origin of hormones in an athlete's body, or the authenticity of foods and flavorings are all examples where chemical compounds need to be identified and sourced. Hydrogen isotopes have found uses in these and many other diverse areas of study. Since many processes can affect the DHR of a given compound this ratio can be a diagnostic signature for compounds produced in a specific location or via a certain process. Once the DHRs of a number of sources are known the measurement of this ratio for a sample of unknown origin can often be used to link it back to a certain source or production method.
1 H, with one proton and no neutrons , is the most abundant nuclide in the Solar System , formed in the earliest rounds of stellar explosions after the Big Bang . [ 37 ] After the universe exploded into life, the hot and dense cloud of particles began to cool, first forming subatomic particles like quarks and electrons , which then condensed to form protons and neutrons . Elements larger than hydrogen and helium were produced with successive stars, forming from the energy released during supernovae .
Deuterium , 2 H, with one proton and one neutron, is also known to have cosmic origin. Like protium, deuterium was produced very early in the universe's history, during Big Bang nucleosynthesis (BBN). As protons and neutrons combined, helium-4 was produced with a deuterium intermediate. Alpha reactions with 4 He produce many of the larger elements that dominate today's Solar System. However, before the universe cooled, high-energy photons destroyed any deuterium, preventing larger element formation. This is called the deuterium bottleneck , a restriction on the timeline for nucleosynthesis . All of today's deuterium originated from this proton-proton fusion after enough cooling. [ 38 ]
Tritium , 3 H, with one proton and two neutrons, was produced by proton and neutron collisions in the early universe as well, but it has since radioactively decayed to helium-3 . Today's tritium cannot be from BBN, due to tritium's short half-life , 12.3 years. Today's 3 H concentration is instead governed by nuclear reactions and cosmic rays . The beta decay of 3 H to 3 He releases an electron and an antineutrino, and about 18 keV of energy. This is a low-energy decay, so the radiation cannot permeate skin. Tritium is thus only hazardous if directly ingested or inhaled. [ 39 ]
1 H is a spin-1/2 subatomic particle and therefore a fermion . Other fermions include neutrons , electrons , and tritium. Fermions are governed by the Pauli exclusion principle , where no two particles can have the same quantum number . [ 40 ] [ 41 ] However, bosons like deuterium and photons, are not bound by exclusion and multiple particles can occupy the same energy state. This fundamental difference in 1 H and 2 H manifests in many physical properties. Integer-spin particles like deuterium follow Bose–Einstein statistics while fermions with half-integer spins follow Fermi–Dirac statistics . Wave functions that describe multiple fermions must be antisymmetric with respect to swapping particles, while boson wave functions are symmetric. [ 42 ] Because bosons are indistinguishable and can occupy the same state, collections of bosons behave very differently than fermions at colder temperatures. As bosons are cooled and relaxed to the lowest energy state, phenomena like superfluidity and superconductivity occur. [ 43 ]
Isotopes differ by number of neutrons , which directly impacts physical properties based on mass and size. Normal hydrogen (protium, 1 H) has no neutron. Deuterium ( 2 H) has one neutron, and tritium ( 3 H) has two. Neutrons add mass to the atom, leading to different chemical physical properties . This effect is especially strong for hydrogen isotopes, since the added neutron doubles the mass from 1 H to 2 H. For heavier elements like carbon , nitrogen , oxygen , or sulfur , the mass difference is diluted.
Physical chemists often model chemical bonding with the quantum harmonic oscillator (QHO), simplifying a hydrogen-hydrogen bond as two balls connected by a spring. [ 41 ] [ 44 ] The QHO is based on Hooke's law and is a good approximation of the Morse potential that accurately describes bonding. Modeling H/ 2 H in a chemical reaction demonstrates the energy distributions of isotopes in products and reactants. Lower energy levels for the heavier isotope 2 H can be explained mathematically by the QHO's dependence on the inverse of the reduced mass μ. Thus, a larger reduced mass is a larger denominator and thus a smaller zero point energy and a lower energy state in the quantum well .
Calculating the reduced mass of a 1 H– 1 H bond versus a 2 H– 2 H bond gives:
The quantum harmonic oscillator has energy levels of the following form, where k is the spring constant and h is the Planck constant. [ 41 ]
The effects of this energy distribution manifest in the kinetic isotope effect (KIE) and the equilibrium isotope effect. [ 45 ] In a reversible reaction , under equilibrium conditions, the reaction proceeds forward and backward, distributing the isotopes to minimize thermodynamic free energy. Some time later, at equilibrium, more heavy isotopes will be on the product side. The stability of the lower energy drives the products to be enriched in 2 H relative to reactants. Conversely, under kinetic conditions, reactions are generally irreversible. The limiting step in the reaction is overcoming the activation energy barrier to reach an intermediate state. The lighter isotope has a higher energy state in the quantum well and will thus be preferentially formed into products. Thus under kinetic conditions the product will be relatively depleted in 2 H.
KIEs are common in biological systems and are especially important for HIBGC. KIEs usually result in larger fractionations than equilibrium reactions. In any isotope system, KIEs are stronger for larger mass differences. Light isotopes in most systems also tend to move faster but form weaker bonds. At high temperature, entropy explains a large signal in isotope composition. However, when temperature decreases isotope effects are more expressed and randomness plays less of a role. These general trends are exposed in further understanding of bond breaking, diffusion or effusion , and condensation or evaporation reactions.
One of the major complications in studying hydrogen isotopes is the issue of exchangeability. At many time scales, ranging from hours to geological epochs, scientists have to consider if the hydrogen moieties in studied molecules are the original species or if they represent exchange with water or mineral hydrogen near by. Research in this area is still inconclusive in regards to rates of exchange, but it is generally understood that hydrogen exchange complicates the preservation of information in isotope studies.
Hydrogen atoms easily separate from electronegative bonds such as hydroxyl bonds (O–H), nitrogen bonds (N–H), and thiol / mercapto bonds (S–H) on hour to day long timescales. This rapid exchange is particularly problematic for measurements of bulk organic matter with these functional groups because isotope compositions are more likely to reflect the source water and not the isotope effect. Therefore, records of paleoclimate that are not measuring ancient waters, rely on other isotopic markers. Advancements in the 1990s held promising potential to resolve this problem: samples were equilibrated with two variations of heavy water and compared. Their ratios represent an exchange factor that can calibrate measurements to correct for H/ 2 H swapping. [ 46 ]
For some time, researchers believed that large hydrocarbon molecules were impervious to hydrogen exchange, but recent work has identified many reactions that allow isotope reordering. The isotopic exchange becomes relevant at geologic time scales and has impacted work of biologists studying lipid biomarkers , and geologists studying ancient oil. Reactions responsible for exchange include [ 46 ] [ 47 ]
Detailed kinetics of these reactions have not been determined. However, it is known that clay minerals catalyze ionic hydrogen exchange faster than other minerals. [ 48 ] Thus hydrocarbons formed in clastic environments exchange more than those in carbonate settings. Aromatic and tertiary hydrogen also have greater exchange rates than primary hydrogen. This is due to the increasing stability of associated carbocations . [ 49 ] Primary carbocations are considered too unstable to exist and have never been isolated in an FT-ICR spectrometer . [ 50 ] On the other hand, tertiary carbocations are relatively stable and are often intermediates in organic chemistry reactions. This stability, which increases the likelihood of proton loss, is due to the electron donation of nearby carbon atoms. Resonance and nearby lone pairs can also stabilize carbocations via electron donation . Aromatic carbons are thus relatively easy to exchange.
Many of these reactions have a strong temperature dependence; higher temperature typically accelerates exchange. However, different mechanisms may prevail at each temperature window. Ion exchange , for example, is most significant at low temperature. In such low-temperature environments, there is potential for preserving the original hydrogen isotope signal over hundreds of millions of years. [ 51 ] However, many rocks in geologic time have reached significant thermal maturity . Even by the onset of the oil window it appears that much of the hydrogen has exchanged. Recently, scientists have explored a silver lining: hydrogen exchange is a zero order kinetic reaction (for carbon bound hydrogen at 80–100°C, the half-times are likely 10 4 –10 5 years). [ 51 ] Applying the mathematics of rate constants would allow extrapolation to original isotopic compositions. While this solution holds promise, there is too much disagreement in the literature for robust calibrations.
Vapor isotope effects occur for 1 H, 2 H, and 3 H; since each isotope has different thermodynamic properties in the liquid and gas phases. [ 52 ] For water, the condensed phase is more enriched while the vapor is more depleted. For example, rain condensing from a cloud, is heavier than the vapor starting point. Generally, the large variations in deuterium concentration in water are from fractionations between liquid, vapor, and solid reservoirs. In contrast to the fractionation pattern of water, non-polar molecules like oils and lipids, have gaseous counterparts enriched with deuterium relative to the liquid. [ 28 ] This is thought to be associated with the polarity from hydrogen bonding in water that does not interfere in long-chain hydrocarbons.
Due to physical and chemical fractionation processes, the variations in the isotopic compositions of elements are reported, and the standard atomic weights of hydrogen isotopes have been published by IUPAC 's Commission on Atomic Weights and Isotopic Abundances. The HICs are reported relative to the International Atomic Energy Agency (IAEA) reference water. In the equilibrium isotope reactions of H/ 2 H in general, enrichment of the heavy isotope is observed in the compound with the higher oxidation state . However, in our natural environment, HIC varies greatly depending on the sources and organisms due to complexities of interacting elements in disequilibrium states. In this section, the observed variations in HIC of water sources (hydrosphere), living organisms (biosphere), organic substances (geosphere), and extraterrestrial materials in the Solar system are described.
Variations in δD of different water sources and ice caps are observed due to evaporation and condensation processes. (See section 6 for more details.) When seawater is well-mixed, the δD at equilibrium is near 0‰ (‰ SMOW) with a DHR of 155.76 ppm. However, continuous variations in δD are caused by evaporation or precipitation processes which lead to disequilibrium in fractionation processes. A large HIC gradient occurs in surface waters of the oceans, and the fluctuation value in the Northwest Atlantic surface water is around 20‰. According to the data examining the southern supersegment of the Pacific Ocean , as latitude decreases from 65˚S to 40˚S, δD fluctuates between around −50‰ and −70‰. [ 54 ]
The HIC of seawater (not just surface water) is mostly in the range of 0‰ to −10‰. The estimates of δD for different parts of the ocean across the world are shown on the map. [ 55 ]
Typical δDs for ice sheets in the polar regions range from around −400‰ to −300‰ (‰SMOW). [ 57 ] Ice caps' δDs are affected by distance from open ocean, latitude, atmospheric circulation, and the amount of insolation and temperature. The temperature change affects the HIC of ice caps, so the HIC of ice can give estimates for the historical climate cycles such as the timelines for interglacial and glacial periods . [See section 7.2. Paleo-reconstruction for more details]
The δDs of ice caps from 70 km south of Vostok Station and in East Antarctica are −453.7‰ and −448.4‰ respectively, and are shown on the map. [ 58 ]
The analysis done based on satellite measurement data, estimates δD for the air in various parts of the world. The general trend is that δD is more negative at higher latitude, so air above Antarctica and the Arctic is D-depleted to around −230‰ to −260‰ or even lower.
The estimated atmospheric δDs are shown on the map. [ 60 ]
A vast portion of global atmospheric water vapor comes from the Western Pacific near the tropics, (mean 2009) and the HIC of air depends on temperature and humidity. Hot, humid regions generally have higher δD. [ 61 ] Water vapor in the air is in general more depleted than terrestrial water sources, since 1 H 2 16 O evaporates faster than 1 H 2 H 16 O due to higher vapor pressure. On the other hand, rain water is in general more enriched than atmospheric water vapor. [ 62 ] [ 63 ]
δDs of annual precipitation in different regions of the world are shown on the map. [ 65 ] The precipitation is more D-enriched near the equator in the Tropics . The δDs generally fall in the range of around −30 ~ −150‰ in the northern hemisphere and −30~+30‰ over land areas of the southern hemisphere. In North America, the δD of average monthly precipitation across regions is lower in January (ranging up to around −300‰ in Canada) than in July (up to around −190‰). [ 65 ]
The overall mean precipitation is determined by the balance between evaporation of water from the oceans and other surface water and condensation of water vapor in the form of rain. Net evaporation should equal net precipitation, and the δD for precipitation is around −22‰ (global average). [ 66 ] The Global Network of Isotopes in Precipitation (GNIP) investigates and monitors the isotopic composition of precipitation at various sites all over the world. The mean precipitation can be estimated by the equation, δ 2 H = 8.17(±0.07) δ 18 O + 11.27(±0.65)‰ VSMOW. (Rozanski et al., 1993) This equation is the slightly modified version from the general global meteoric water line (GMWL) equation, δ 2 H = 8.13δ 18 O + 10.8, which provides the average relationship between δ 2 H and δ 18 O of natural terrestrial waters. [ 66 ] [ 67 ]
The δDs vs. VSMOW of lakes in different regions are shown on the map. [ 69 ] The general pattern observed, indicates that δDs of surface waters including lakes and rivers, are similar to that of local precipitation. [ 70 ]
The isotopic composition of soil is controlled by the input of precipitation . Therefore, the δD of soil is similar to that of local precipitation. However, due to evaporation, soil tends to be more D-enriched than precipitation. The degree of enrichment varies greatly depending on atmospheric humidity, local temperature as well as the depth of the soil beneath the surface. According to the study by Meinzer et al. (1999), as the depth in the soil increases, the δD of soil water decreases. [ 70 ]
The factors affecting δD of algal lipids are: δD of water, algal species (up to 160%), lipid type (up to 170%), salinity (+0.9±0.2% per PSU), growth rate (0 ~ −30% per day) and temperature (−2 ~ −8% per °C).
In a study by Zhang et al. (2009), the δDs of fatty acids in Thalassiosira pseudonana chemostat cultures were −197.3‰, −211.2‰ and −208.0‰ for C14, C16 and C18 fatty acids respectively. The δD of C16 fatty acid in the algae A. e. unicocca at 25°C, was determined using the empirical equation y = 0.890 x − 91.730, where x is the δD of water at harvest. For another algal species, B. v. aureus , the equation was y = 0.869 x − 74.651. [ 71 ]
The degree of D/H fractionation in most algal lipids increases with increasing temperature and decreases with increasing salinity. The growth rates have different impacts on the D/H fractionation depending on the species types. [ 72 ]
The δD of lipids from phytoplankton is largely affected by δD of water, and there seems to be a linear correlation between those two values. The δD of most other biosynthetic products in phytoplankton or cyanobacteria are more negative than that of the surrounding water. [ 73 ] The δD values of fatty acids in methanotrophs living in seawater lie between −50 and −170‰, and that of sterols and hopanols range between −150 and −270‰. [ 74 ] [ 75 ]
The HIC of photoautotrophs can be estimated using the equation,
where R l , R w , and R s are the DHRs of lipids, water, and substrates, respectively. X w is the mole fraction of lipid H derived from external water, whereas α l/w and α l/s denote the net isotopic fractionations associated with uptake and utilization of water and substrate hydrogen, respectively.
For phototrophs , R l is calculated assuming that X w = 1. The isotopic fractionation between lipids and methane ( α l/m ) is 0.94 for fatty acids and 0.79 for isoprenoid lipids. The isotopic fractionation between lipids and water ( α l/w ) is 0.95 for fatty acids and 0.85 for isoprenoid lipids. For plants and algae , the isotopic fractionation between lipids and methane ( α l/m ) is 0.94 for fatty acids and 0.79 for isoprenoid lipids. [ 74 ]
Source: [ 71 ]
δDs for n-C 29 alkane (‰) vs. VSMOW for different plant groups are as follows. Here, y {\displaystyle y} represents δDs for n-C 29 alkane(‰) vs. VSMOW, and x {\displaystyle x} represents δDs for mean annual precipitation (‰) vs. VSMOW). [ 76 ]
For plant leaf wax , the relative humidity, the timing of leaf wax formation and the growth conditions including light levels affect the D/H fractionation of plant wax. From the Craig–Gordon model, it can be understood that leaf water in the growth chamber gasses is significantly D-enriched due to transpiration. [ 77 ]
The global abundance of 2 H in plants is in the following order: phenylpropanoids > carbohydrates > bulk material > hydrolyzable lipids > steroids. [ 78 ] In plants, δDs of carbohydrates, which typically range around −70‰ to −140‰, are good indicators of the photosynthetic metabolism. Photosynthetically produced hydrogen which is bound to carbon backbones is ~100‰–170‰ more D-depleted than the water in plant tissues.
Heterotrophic processing of carbohydrates involves isomerization of triose phosphates and interconversion between fructose-6-phosphate and glucose-6-phosphate . These cellular processes promote the exchange between organic H and H 2 O within the plant tissues leading to around 158‰ of D-enrichment of those exchanged sites. [ 79 ] The δD of C 3 plants such as sugar beet , orange and grape ranges from −132‰ to −117‰, and that of C 4 plants such as sugar cane and maize ranges from −91‰ to −75‰. The δD of Crassulacean acid metabolism (CAM) such as pineapple is estimated at around −75‰. [ 78 ] Sugar beet and sugar cane contain sucrose, and maize contain glucose. Orange and pineapple are the sources of glucose and fructose .
The deuterium content of the sugars from the above plant species are not distinctive. In C 3 plants, hydrogen attached to carbons in 4 and 5 positions of the glucose typically comes from NADPH in the photosynthetic pathway, and is found to be more D-enriched. Whereas in C 4 plants, hydrogen attached to carbons 1 and 6 positions is more D-enriched. D-enrichment patterns in CAM species tend to be closer to that in C 3 species. [ 80 ]
The HIC of leaf water is variable during the biosynthesis, and the enrichment in the whole leaf can be described by the equation, △D leaf = △D e × ([1 − e −p ]/P) [ 81 ] [ 76 ]
The typical δD of bulk plant is around −160‰, while δDs for cellulose and lignin are −110‰ and −70‰ respectively. [ 78 ]
HIC in animal tissues is hard to estimate due to complexities in the diet intake and the isotopic composition of surrounding water sources. When fish species were investigated, average HIC of proteins was in a large range of −128‰ ~ +203‰. In the bulk tissue of organisms, all lipids were found to be D-depleted, and the values of δD for lipids tend to be lower than that for proteins. The average δD for Chironomid and fish protein was estimated to be in the range of −128‰ to +203‰. [ 82 ]
Most hydrogen in heterotrophic tissues comes from water not from diet sources, but the proportion coming from water varies. In general, hydrogen from water is transferred to NADPH and then taken up to the tissues. An apparent trophic effect (compounding effect) can be observed for δD in heterotrophs, so significant D-enrichments result from the intake of surrounding water the in aquatic food webs. The δD of proteins in animal tissues are in cases affected more by diet sources than by surrounding water. [ 82 ]
Though different δDs for the same class of compounds may arise in different organisms growing in water with the same δD, those compounds generally have the same δD within each organism itself. [See Section 7.5. Ecology for more details]
δDs of fatty acids in living organisms, are typically −73‰ to −237‰. The δDs of individual fatty acids vary widely between cultures (−362‰ to +331‰), but typically by less than around 30‰ between different fatty acids from the same species. [ 71 ]
The differences in δD for the compounds within the same lipid class is generally less than 50‰, whereas the difference falls in the range of 50‰–150‰ for the compounds in different lipid classes. [ 71 ]
δDs for typical lipid groups are determined using the following equation:
Polyisoprenoid lipids are more depleted than acetogenic (n-alkyl) lipids with more negative δDs.
‡ Enrichment relative to water
Source: [ 83 ]
The isotopic composition of alkenones often reflect the isotopic enrichment or depletion of the surrounding environment, and δDs of alkenones in different regions are shown on the map. [ 87 ] [ 88 ]
Source: [ 90 ]
According to the studies by Reddings et al., δDs for coals from various sources range from around −90‰ to −170‰. [ 91 ]
The δDs of coals in different regions are shown on the map. [ 92 ] [ 93 ]
Source: [ 94 ]
Methane produced by marine methanogens is typically more D-enriched than methane produced by methanogens grown in freshwater. δDs for thermogenic methane range from −275‰ to −100‰, and from −400‰ to −150‰ for microbial methane. [ 95 ]
The δD of atmospheric H 2 is around +180‰, the biggest δD known for natural terrestrials (mole fraction 2 H: 183.8 ppm). The δD of natural gas from a Kansas well is around −836‰ (mole fraction 2 H: 25.5 ppm) [ 96 ]
In electrolysis of water , hydrogen gas is produced at the cathode, but incomplete electrolysis of water may cause isotopic fractionation leading to enrichment of 2 H in the sample water and the production of hydrogen gas with deuterium components.
The δDs of hydroxyl-bearing minerals of the mantle were estimated at −80‰ ~ −40‰ via analysis of the isotopic composition for juvenile water. Hydrogen minerals generally have large isotope effects, and the isotopic composition often follows the pattern observed for precipitation.
The D/H fractionations in clays such as kaolinite, illite, smectite are in most cases consistent when no significant external forces are applied under constant temperature and pressure.
The following is an empirically determined equation for estimating the D/H fractionation factor:
1000 In α kaolinite-water = −2.2 × 10 6 × T −2 − 7.7. [ 98 ]
The δDs vs. ‰SMOW for hydrogen minerals found in mantle , metamorphic rock, shales , marine clays , marine carbonates and sedimentary rocks are shown in the table. [ 57 ]
Variations of DHR in the Solar System [ 99 ]
The DHRs of Jupiter and Saturn are nearly in the order of 10 −5 , and the DHRs of Uranus and Neptune are closer to 10 −4 . [ 102 ]
Hydrogen is the most abundant element in the universe. Variations in isotopic composition of extraterrestrial materials stem from planetary accretion or other planetary processes such as atmospheric escape, and are larger for H and N than for C and O. The preservation of D-enrichment is observed in chondritic meteorites , interplanetary dust particles and cometary Volatiles .
From the helium isotope abundance data, the cosmic DHR is estimated at around 20 ppm: much lower than the terrestrial DHR of 150 ppm. The enrichment of D/H from the proto-solar reservoir occurs for most of the planets except for Jupiter and Saturn, the massive gaseous planets. The DHRs of the atmospheres of Venus and Mars are ~2 × 10 −2 and ~8 × 10 −4 respectively. The DHRs of Uranus and Neptune are larger than that of protosolar reservoir by a factor of ~3 due to their deuterium-rich icy cores. The DHRs for comets are much larger than the values for the planets in the Solar System with δD of around 1000‰. [ 103 ]
The HICs in the galaxy and the Solar System are shown in the table.
DHR can be determined with a combination of different preparation techniques and instruments for different purposes. There are several types of HIC measurement: (i) organic hydrogen or water are converted to H 2 first, followed by high-precision isotope-ratio mass spectrometry (IRMS) measurement; (ii) 2 H/ 1 H and 18 O/ 16 O are directly measured as H 2 O by laser spectroscopy also with high precision; (iii) the intact molecules are directly measured by NMR or mass spectrometry with lower precision than IRMS.
Conversion to simple molecules (i.e. H 2 for hydrogen) is required prior to IRMS for stable isotopes. This is for several reasons with regard to hydrogen:
The classical offline preparation for the conversion is combustion over CuO at >800°C in sealed quartz tubes, followed by the isolation of resulting water and the reduction to H 2 over hot metal at 400 ~1000°C on a vacuum line. [ 105 ] The produced gas is then directly injected into the dual-inlet mass spectrometer for measurement. [ 104 ] The metals used for reduction to H 2 includes U, Zn, Cr, Mg and Mn, etc. U and Zn had been widely used since the 1950s [ 25 ] [ 106 ] [ 107 ] [ 108 ] [ 109 ] [ 110 ] until Cr [ 111 ] was successfully employed in the late 1990s.
The offline combustion/reduction has the highest accuracy and precision for HIC measurement without limits for sample types. The analytical uncertainty is typically 1~2‰ in δD. Thus it is still used today when highest levels of precision are required. However, the offline preparation procedure is very time-consuming and complicated. It also requires a large sample (several 100 mg). Thus, online preparation based on combustion/reduction coupled with the subsequent continuous flow-IRMS (CF-IRMS) system has been more often used nowadays. Chromium reduction or high temperature conversion are the dominant online preparation methods for detection of HIC by IRMS.
TC/EA (or HTC, high temperature conversion; HTP, high temperature pyrolysis ; HTCR, high temperature carbon reduction) is an "online" or "continuous flow" preparation method typically followed by IRMS detection. This is a "bulk" technique that measures all the hydrogen in a sample and provides the average isotope signal. The weighed sample is placed in a tin or silver capsule and dropped into a pyrolysis tube of TC/EA. The tube is made of glassy carbon with glassy carbon filling, so oxygen isotopes can be measured simultaneously without oxygen exchange with ceramic (Al 2 O 3 ) surface. [ 113 ] The molecules are then reduced into CO and H 2 at high temperature (>1400°C) in the reactor. The gaseous products are separated through gas chromatography (GC) using helium as the carrier gas, followed by a split-flow interface, and finally detected by IRMS. TC/EA method can be problematic for organic compounds with halogen or nitrogen due to the competition between the pyrolysis byproducts (e.g. HCl and HCN) and H 2 formation. [ 114 ] [ 115 ] In addition, it is susceptible to contamination with water, so samples must be scrupulously dried.
An adaption of this method is to determine the non-exchangeable (C-H) and exchangeable hydrogen (bounds to other elements, e.g. O, S and N) in organic matter. The samples are equilibrated with water in sealed autosampler carousels at 115°C and then transferred into pyrolysis EA followed by IRMS measurement. [ 116 ]
TC/EA method is quick with fairly high precision (~1‰). It was limited to solid samples; however, liquid sample recently can also be measured in TC/EA-IRMS system by adapting an autosampler for liquids. The drawback of TC/EA is the relatively big sample size (~ mg), which is smaller than offline combustion/reduction but larger than GC/pyrolysis. It cannot separate different compounds as GC/pyrolysis does and thus only the average for the whole sample can be provided, which is also a drawback for some research.
GC-interface (combustion or pyrolysis) is also an online preparation method followed by IRMS detection. This is a 'compound-specific' method, allowing separation of analytes prior to measurement and thus providing information about the isotopic composition of each individual compound. After GC separation, samples are converted to smaller gaseous molecules for isotope measurements. GC/pyrolysis uses the pyrolysis interface between GC and IRMS for the conversion of H and O in the molecules into H 2 and CO. GC-IRMS was first introduced by Matthews and Hayes in the late 1970s, [ 117 ] and was later used for δ 13 C, δ 15 N, δ 18 O and δ 34 S. Helium is used as the carrier gas in the GC systems. However, the separation of DH (m/z=3) signal from the tail of 4 He + beam was problematic due to the intense signal of 4 He + . [ 118 ] During the early 1990s, intense efforts were made in solving the difficulties to measure δD by GC/pyrolysis-IRMS. In 1999, Hilkert et al. developed a robust method by integrating the high temperature conversion (TC) into GC-IRMS and adding a pre-cup electrostatic sector and a retardation lens in front of the m/z=3 cup collector. Several different groups were working on this at the same time. [ 118 ] [ 119 ] [ 120 ] [ 121 ] This GC/pyrolysis-IRMS based on TC has been widely used for δD measurement nowadays. The commercial products of GC-IRMS include both combustion and pyrolysis interfaces so that δ 13 C and δD can be measured simultaneously.
The significant advantage of GC/pyrolysis method for HIC measurement is that it can separate different compounds in the samples. It requires the smallest sample size (typically ~200 ng [ 119 ] ) relative to other methods and has a high precision of 1~5 ‰. But this method is relatively slow and limited to the samples which can be applied in GC system.
Laser spectroscopy (or cavity ring-down spectroscopy , CRDS) is able to directly measure 2 H/ 1 H, 17 O/ 16 O and 18 O/ 16 O isotopic composition in water or methane. The use of laser spectroscopy on hydrogen isotopes was first reported by Bergamaschi et al. in 1994. [ 122 ] They directly measured 12 CH 3 D/ 12 CH 4 in atmospheric methane using a lead salt tunable diode laser spectroscopy. The development of CRDS was first reported by O'Keefe et al. in 1988. [ 123 ] In 1999, Kerstel et al. successfully applied this technique to determine HIC in water. [ 124 ] The system consists of a laser and a cavity equipped with high finesse reflectivity mirrors. Laser light is injected into the cavity, where the resonance takes place due to the constructive interference. The laser then is turned off. The decay of light intensity is measured. In the presence of a water sample, the photo-absorption by water isotopologues follows the kinetic law . The optical spectrum is obtained by recording ring-down time of the H 2 O spectral features of interest at certain laser wavelength. The concentration of each isotopologue is proportional to the area under each measured isotopologue spectral feature. [ 125 ]
Laser spectroscopy is quick, simple, and relatively cheap; and the equipment is portable. So it can be used in the field for measuring water samples. 2 H/ 1 H and 18 O/ 16 O can be determined simultaneously from a single injection. It requires a small sample size, < 1 μL for water. Typical precision is ~ 1‰. However, this is a compound-specific instrument, i.e. only one specific compound can be measured. And coexisting organic compounds (i.e. ethanol ) could interfere with the optical light absorption features of water, resulting in cross-contamination.
2 H-Site-specific Natural Isotope Fractionation-Nuclear Magnetic Resonance ( 2 H-SNIF-NMR ) is a type of NMR specialized in measuring the 2 H concentration of organic molecules at natural abundances. The NMR spectra distinguish hydrogen atoms in different chemical environments (e.g. the order of carbon that hydrogen binds to, adjacent functional groups, and even geminal positions of methylene groups), making it a powerful tool for position-specific isotope analysis . The chemical shift (in frequency units) of 2 H is 6.5x lower than that of 1 H. Thus, it is hard to resolve 2 H peaks. To provide enough resolution to separate 2 H peaks, high-strength magnetic field instruments (~11.4T) [ 126 ] are applied. Use of NMR to study hydrogen isotopes of natural products , was pioneered by Gerard Martin and his co-workers in the 1980s. [ 127 ] For several decades it has been developed and expanded. The D/H NMR measurement is sometimes coupled with IR-MS measurement to create a referential standard. [ 128 ] The sensitivity of SNIF-NMR is relatively low, typically requiring ~1 mmol of samples for each measurement. [ 129 ] The precision with respect to isotope ratio is also poor compared to mass spectrometry. Even state-of-art instruments can only measure DHR with around 50~200‰ error depending on the compound. [ 130 ] [ 131 ] [ 132 ] Therefore, so far technique can only distinguish the large D/H variations in preserved materials. In 2007, Philippe Lesot and his colleagues advanced this technique with a 2-dimensional NMR using chiral liquid crystals (CLC) instead of isotropic solvents to dissolve organic molecules. [ 133 ] This enables the measurements of quadrupolar doublets for each nonequivalent deuterium atom. Thus reduces peak overlaps and provides more detailed information of hydrogen chemical environment. [ 131 ]
Mainstream uses of 2 H-SNIF-NMR have been in source attribution, forensics and biosynthetic pathway studies. (See also Gray's section "Source attribution and Forensics") When measuring sugar compounds, a timesaving strategy is to convert them into ethanol through fermentation because 2 H-SNIF NMR for ethanol is well established. [ 128 ] Several studies [ 128 ] [ 134 ] have proved that hydrogen isotopes on the methyl and methylene position of the resulting ethanol is not affected by either fermentation rate or media. Another example is the study of monoterpenes. since the 1980s SNIF-NMR study of α-pinene has found large variations in DHR among its sites. Particularly ex-C 2 position has a strong depletion (~-750‰), which was in disagreement with accepted biosynthetic mechanism (mevalonate mechanism) at that time, and lead to new development in pathways. More recently, Ina Ehlers published their work on the D6 S /D6 R ratios of glucose molecules. The stereochemical diteterium distribution was found to correlate to photorespiration/photosynthesis ratios. Photorespiration/photosynthesis ratios are driven by CO 2 fertilization, [ 132 ] thus this might lead to new proxies in reconstructing paleo-CO 2 concentration. Work has also been done for long-chain fatty acids and found that even-numbered sites, which are thought to be derived from C 2 position of the acetyl group, are more enriched in 2 H than odd-numbered hydrogen that come from C1 position of the acetyl group. [ 129 ] Duan et al. reported a strong KIE during the desaturation from oleic acid to linoleic acid. [ 135 ]
In summary, the underlying physics of SNIF-NMR enables it to measure isotopomers . Another advantage of NMR measurement over mass spectrometry is that it analyzes samples non-destructively. 2 H SNIF-NMR has been well industrialized in source identification and forensics, and has contributed much to biochemical pathway studies. The application of 2 H SNIF-NMR to geological records is sporadic and still needs exploring.
Conventionally, mass spectrometry, such as gas chromatography-mass spectrometry ( GC-MS ) and gas chromatography -time of flight( GC-TOF ), is a common technique for analyzing isotopically labeled molecules . [ 136 ] [ 137 ] This method involves ionizing and analyzing isotopologues of an intact organic molecule of interest rather than its products of pyrolysis or conversion. However, it does not work for natural abundance hydrogen isotopes because conventional mass spectrometers do not have enough mass-resolving power to measure the 13 C/D isotopologues of intact organic molecules or molecular fragments at natural abundance. For example, to resolve the single D substituted isotopologue peak of any hydrocarbons one will have to be able to at least exclude single 13 C substituted isotopologue peak, which sits at the same cardinal mass yet 0.0029 amu lighter and is of orders of magnitude more abundant.
Recent advances in analytical instruments enable direct measurement of natural abundance DHRs in organic molecules. The new instruments have the same framework as any conventional gas source IRMS , but incorporate new features such as larger magnetic sector, double focusing sectors, quadrupole mass filter and multi-collectors. Two commercial examples are the Nu Panorama [ 138 ] and the Thermo Scientific 253 Ultra. [ 139 ] These instruments generally have good sensitivity and precision. Using only tens of nanomoles of methane, the Ultra can achieve a stable high precision of ~0.1‰ error in δD. [ 140 ] One of the first examples of this type of measurement has been clumped isotopes of methane.(See section of "natural gas" in Fossil fuels) Another strength of this kind of instruments is the ability to do site-specific isotopic ratio measurements. This technique is based on measuring DHRs of fragments from the ion source (e.g. CH 3 CH + 2 of propane molecule) that samples hydrogen atoms from different parts of the molecule. [ 141 ]
In summary, direct molecular mass-spectrometry has been commonly used to measure laboratory spiked isotope tracers. Recently advanced high resolution gas source isotope ratio mass spectrometers can measure hydrogen isotopes of organic molecules directly. These mass spectrometers can provide high precision and high sensitivity. The drawback of this type of instruments includes high cost, and standardization difficulty. Also, studying site-specific isotopes with mass spectrometry is less straightforward and needs more constraints than the SNIF-NMR method, and can only distinguish isotopologues but not isotopomers .
Water is the main source of hydrogen for all living things, so the isotopic composition of environmental water is a first-order control on that of the biosphere. The water (hydrological) cycle moves water around Earth's surface, significantly fractionating the hydrogen isotopes in water. [ 142 ] As the atmosphere's main moisture source, the ocean has a fairly uniform HIC across the globe around 0‰ (VSMOW). [ 143 ] Variations of δD larger than 10‰ in the ocean are generally confined to surface water due to evaporation, sea ice formation, and addition of meteoric water by precipitation, rivers or icebergs. [ 142 ] In the water cycle, the two main processes that fractionate hydrogen isotopes from seawater are evaporation and condensation. Oxygen isotopic composition ( 18 O/ 16 O) of water is also an important tracer in the water cycle, and cannot be separated from hydrogen isotopes when we talk about isotope fractionation processes associated with water.
When water evaporates from the ocean to the air, both equilibrium and kinetic isotope effects occur to determine the hydrogen and oxygen isotopic composition of the resulting water vapor. At the water-air interface, a stagnant boundary layer is saturated with water vapor (100% relative humidity ), and the isotopic composition of water vapor in the boundary layer reflects an equilibrium fractionation with liquid water. The liquid-vapor equilibrium fractionations for hydrogen and oxygen isotopes are temperature-dependent: [ 144 ]
The amount of liquid-vapor equilibrium fractionation for hydrogen isotopes is about 8x that of oxygen isotopes at Earth surface temperatures, which reflects the relative mass differences of the two isotope systems: 2 H is 100% heavier than 1 H, 18 O is 12.5% heavier than 16 O. Above the boundary layer, there is a transition zone with relative humidity less than 100%, and there is a kinetic isotope fractionation associated with water vapor diffusion from the boundary layer to the transition zone, which is empirically related to the relative humidity (h): [ 145 ]
The KIE associated with diffusion reflects the mass difference of the heavy-isotope water molecules H 2 H 16 O and H 2 18 O relative to the normal isotopolog (H 2 16 O).
After water evaporates to the air, condensation and precipitation transport it and return it to the surface. Water vapor condenses in ascending air masses that develop a lower temperature and saturation vapor pressure. Since the cooling and condensation happen relatively slowly, it is a process with equilibrium isotope effects. However, as water vapor is progressively condensed and lost from the air during moisture transport, the isotopic composition of the remaining vapor, as well as the resulting precipitation, can be largely depleted due to the process of Rayleigh distillation . The equation for Rayleigh distillation is: [ 146 ]
R r / R 0 = f α − 1 {\displaystyle R_{r}/R_{0}=f^{\alpha -1}}
where R 0 is the isotope ratio in the initial water vapor, R r is the isotope ratio in the remaining water vapor after some condensation, f is the fraction of water vapor remaining in the air, and α is the liquid-vapor equilibrium fractionation factor (α=1+ε). The isotopic composition of the resulting precipitation (R p ) can be derived from the composition of the remaining vapor:
R p / R r = ( 1 + δ p ) / ( 1 + δ r ) = α = 1 + ε {\displaystyle R_{p}/R_{r}=(1+\delta _{p})/(1+\delta _{r})=\alpha =1+\varepsilon }
As f decreases progressively during condensation, the remaining vapor becomes more and more depleted of the heavy isotopes, and the depletion becomes larger as f approaches zero. Rayleigh distillation can explain some first-order spatial patterns observed in the isotopic composition of precipitation across the globe, including isotopic depletion from the tropics to the poles, isotopic depletion from coastal to inland regions, and isotopic depletion with elevation over a mountain range, [1] all of which are associated with progressive moisture loss during transport. The Rayleigh distillation model can also be used to explain the strong correlation between δD and δ 18 O in global precipitation, expressed as the global meteoric water line (GMWL): δD = 8δ 18 O+10 [ 147 ] (later updated to δD = 8.17±0.07 δ 18 O+11.27±0.65 [ 41 ] ) The slope of the GMWL reflects the relative magnitude of hydrogen and oxygen isotope fractionation during condensation. The intercept of GMWL is non-zero (called deuterium-excess, or d-excess), which means ocean water does fall on GMWL. This is associated with the KIE during evaporation when water vapor diffuses from the saturated boundary layer to the unsaturated transition zone, and cannot be explained by the Rayleigh model. Nevertheless, the robust pattern in GMWL strongly suggests a single dominant moisture source to the global atmosphere, which is the tropical West Pacific. It should also be pointed out that a local meteoric water line can have a different slope and intercept from the GMWL, due to differences in humidity and evaporation intensity at different places. [ 145 ] Hydrogen and oxygen isotopes in water thus serve as an excellent tracer of the hydrological cycle both globally and locally.
Based on the processes that fractionate isotopes in the water cycle, isotopic composition of meteoric water can be used to infer related environmental variables such as air temperature, precipitation amount, past elevations, lake levels, as well as to trace moisture sources. These studies form the field of isotope hydrology. Examples of isotope hydrology applications include:
Isotopic composition of precipitation can be used to infer changes in air temperature based on the Rayleigh process. Lower temperature corresponds to lower saturation vapor pressure, which leads to more condensation that drives the residual vapor toward isotope depletion. The resulting precipitation thus has a more negative δD and δ 18 O value at lower temperature. This precipitation isotope thermometer is more sensitive at lower temperatures, and widely applied at high latitudes. For example, δD and δ 18 O were found to have a temperature sensitivity of 8‰/°C and 0.9‰/°C in Antarctic snow, and a sensitivity of 5.6‰/°C and 0.69‰/°C across Arctic sites. [ 148 ] δD and δ 18 O of ice cores in Greenland, Antarctica and alpine glaciers are important archives of temperature change in the geological past.
In contrast to temperature control at high latitudes, the isotopic composition of precipitation in the tropics is mainly influenced by rainfall amount (negative correlation). This "amount effect" is also observed for summer precipitation in the subtropics. [ 41 ] [ 148 ] Willi Dansgaard, who first proposed the term "amount effect", suggested several possible reasons for the correlation: (1) As cooling and condensation progress, the rainfall isotopic composition reflects an integrated isotopic depletion by the Rayleigh process; (2) A small amount of rainfall is more likely to be influenced by evaporation and exchange with surrounding moisture, which tend to make it more isotopically enriched. At low latitudes, the amount effect for δ 18 O is around −1.6‰/100mm precipitation increase at island stations, and −2.0‰/100mm at continental stations. [ 148 ] It was also noted that the amount effect was most pronounced when comparing isotopic composition of monthly precipitation at different places in the tropics. [ 148 ] The amount effect is also expected for HIC, but there are not as many calibration studies. Across southeast Asia, the δD sensitivity to monthly precipitation amount varies between −15 and −25‰/100mm depending on location. [ 149 ] In temperate regions, the isotopic composition of precipitation is dominated by rainfall amount in summer, but more controlled by temperature in the winter. [ 148 ] The amount effect may also be complicated by changes in regional moisture sources. [ 150 ] Reconstructions of rainfall amount in the tropics in the geological past are mostly based on δ 18 O of speleothems [ 151 ] [ 152 ] or δD of biogenic lipids, [ 153 ] [ 154 ] both of which are thought of as proxies for the isotopic composition of precipitation.
Hydrogen and oxygen isotopes also work as tracers for water budget in terrestrial reservoirs, including lakes, rivers, groundwater and soil water. For a lake, both the amount of water in the lake and the isotopic composition of the water are determined by a balance between inputs (precipitation, stream and ground water inflow) and outputs (evaporation, stream and ground water outflow). [ 142 ] The isotopic composition of lake water can often be used to track evaporation, which causes isotope enrichment in the lake water, as well as a δD-δ 18 O slope that is shallower than the meteoric water line. [ 155 ] The isotopic composition of river water is highly variable and have complicated sources over different timescales, but can generally be treated as a two-endmember mixing problem, a base-flow endmember (mainly ground water recharge) and an overland-flow endmember (mainly storm events). The isotope data suggest that the long-term integrated base-flow endmember is more important in most rivers, even during peak flows in summer. [ 142 ] Systematic river isotope data were collected across the world by the Global Network of Isotopes in Rivers (GNIR) [2] Archived 2016-05-13 at the Wayback Machine .The isotopic composition of groundwater can also be used to trace its sources and flow paths. An example is a groundwater isotope mapping study in Sacramento, California , which showed lateral flow of river water with a distinct isotope composition into the groundwater that developed a significant water table depression due to pumping for human use. [ 156 ] The same study also showed an isotopic signal of agricultural water being recharged into the giant alluvial aquifer in California 's Central Valley. [ 156 ] Finally, the isotopic composition of soil water is important for the study of plants. Below the water table, the soil has a relatively constant source of water with a certain isotopic composition. Above the water table, the isotopic composition of soil water is enriched by evaporation until a maximum at the surface. The vertical profile of isotopic composition of soil water is maintained by the diffusion of both liquid and vapor water. [ 157 ] A comparison of soil water and plant xylem water δD can be used to infer the depth at which plant roots get water from the soil. [ 158 ]
The isotopic compositions of ice cores from continental ice sheets and alpine glaciers have been developed as temperature proxies since the 1950s. Samuel Epstein was one of the first to show the applicability of this proxy by measuring oxygen isotopes in Antarctic snow, and also pointed out complications in the stable isotope-temperature correlation caused by the history of the air masses from which the snow formed. [ 160 ] Ice cores in Greenland and Antarctica can be thousands of meters thick and record snow isotopic composition of the past few glacial-interglacial cycles. Ice cores can be dated by layer counting on the top and ice flow modeling at depth, with additional age constraints from volcanic ash. [ 161 ] Cores from Greenland and Antarctica can be aligned in age at high-resolution by comparing globally well-mixed trace gas (e.g. CH 4 ) concentrations in the air bubbles trapped in the cores. [ 162 ] Some of the first ice core records from Greenland and Antarctica with age estimates go back to the last 10 5 years, and showed a depletion in δD and δ 18 O in the last ice age. [ 163 ] [ 164 ] The ice core record has since been extended to the last 800,000 years in Antarctica, [ 165 ] and at least 250,000 years in Greenland. [ 166 ] One of the best δD-based ice core temperature records is from the Vostok ice core in Antarctica, which goes back to 420,000 years. [ 159 ] The δD-temperature (of the inversion layer where snow forms) conversion in east Antarctica based on modern spatial gradient of δD (9‰/°C) is ΔT I =(ΔδD ice -8Δδ 18 O sw )/9, which takes into account variations in seawater isotopic composition caused by global ice volume changes. [ 159 ] Many local effects can influence ice δD in addition to temperature. These effects include moisture origin and transport pathways, evaporation conditions and precipitation seasonality, which can be accounted for in more complicated models. [ 167 ] Nevertheless, the Vostok ice core record shows some very important results: (1) A consistent δD depletion of ~70‰ during the last four glacial periods compared to interglacial times, corresponding to a cooling of 8°C in Antarctica; (2) A consistent drop of atmospheric CO 2 concentration by 100 ppmv and CH 4 drop by ~300 ppbv during glacial times relative to interglacials, suggesting a role of greenhouse gases in regulating global climate; (3) Antarctic air temperature and greenhouse gas concentration changes precede global ice volume and Greenland air temperature changes during glacial terminations, and greenhouse gases may be an amplifier of insolation forcing during glacial-interglacial cycles. [ 159 ] Greenland ice core isotope records, in addition to showing glacial-interglacial cycles, also shows millennial-scale climate oscillations that may reflect reorganization in ocean circulation caused by ice melt charges. [ 166 ] [ 168 ] [ 169 ] [ 170 ] There have also been ice core records generated in alpine glacials on different continents. A record from the Andes Mountains in Peru shows a temperature decrease of 5-6°C in the tropics during the last ice age. [ 171 ] A record from the Tibetan plateau shows a similar isotope shift and cooling during the last ice age. [ 172 ] Other existing alpine glacial isotope records include Mount Kilimanjaro in Tanzania, Mount Altai and West Belukha Plateau in Russia, Mount Logan in Canada, the Fremont Glacier in Wyoming, USA, and the Illimani Ice Core in Bolivia, most of which cover an interval of the Holocene epoch. [3]
The isotopic composition of biomolecules preserved in the sedimentary record can be used as a proxy for paleoenvironment reconstructions. Since water is the main hydrogen source for photoautotrophs , the HIC of their biomass can be related to the composition of their growth water and thereby used to gain insight into some properties of ancient environments. [ 173 ] Studying hydrogen isotopes can be very valuable, as hydrogen is more directly related to climate than other relevant stable isotope systems. However, hydrogen atoms bonded to oxygen, nitrogen, or sulfur are exchangeable with environmental hydrogen, which makes this system less straightforward [ 174 ] [ref to earlier H exchange section]. To study the HIC of biomolecules, it is preferable to use compounds where the hydrogen is largely bound to carbon, and thus not exchangeable on experimental timescales. By this criterion, lipids are a much better subject for hydrogen isotope studies than sugars or amino acids.
The net fractionation between source water and lipids is denoted ε l/w :
where w refers to the water, and l refers to the lipids.
While the δD of source water is the biggest influence on the δD of lipids, [ 175 ] discrepancies between fractionation factor values obtained from the slope and from the intercept of the regression suggest that the relationship is more complex than a two-pool fractionation. [ 176 ] In other words, there are multiple fractionation steps that must be taken into account in understanding the isotopic composition of lipids.
The carbon-bonded HIC of cellulose , as inherited from leaf water, has the potential to preserve the original meteoric water signal. This was first demonstrated in the 1970s. [ 25 ] [ 177 ] In a systematic survey across North America, tree cellulose δD was found to have temperature sensitivity 5.8‰/°C, similar to precipitation δD sensitivity of 5.6‰/°C. [ 178 ] This spatial correlation may be complicated by local effects of soil evaporation and leaf transpiration, [ 178 ] and the spatial gradient may not be representative of temporal changes in tree ring cellulose at a single place. The mechanism that generates the δD signal in cellulose from meteoric water is not fully understood, but at least includes leaf water transpiration, synthesis of carbohydrates, synthesis of cellulose from photosynthetic sugars, and exchange of sugars with xylem water. [ 179 ] Modeling studies show that observed tree ring cellulose δD can be produced when 36% of the hydrogen in sugars can exchange with xylem water, and effects such as humidity and rainfall seasonality may complicate the cellulose δD proxy. [ 179 ] Despite these complications, tree ring δD have been used for paleoclimate reconstructions of the past few millennia. For example, a tree ring cellulose δD records from pine trees in the White Mountains , California shows a 50‰ depletion from 6800 year ago to present. The cooling trend since the mid-Holocene thermal maximum is consistent with ice core and pollen records, but the corresponding magnitude of cooling is elusive due to complicated influences from local effects such as humidity and soil water composition. [ 180 ] The meaning of isotopes in cellulose and its applications is still an area of active study.
Terrestrial plants make leaf waxes to coat the surfaces of their leaves, to minimize water loss. These waxes are largely straight-chain n -alkyl lipids. They are insoluble, non-volatile, chemically inert, and resistant to degradation, making them easily preserved in the sedimentary record, and therefore good targets as biomarkers . [ 181 ]
The main water source for land plants is soil water, which largely resembles the HIC of rain water, but varies between environments and with enrichment by precipitation , depletion by evaporation , and exchange with atmospheric water vapor. There can be a significant offset between the δD value of source water and the δD value of leaf water at the site of lipid biosynthesis. No fractionation is associated with water uptake by roots, a process usually driven by capillary tension, with the one exception of xerophytes that burn ATP to pump water in extremely arid environments (with a roughly 10‰ depletion). [ 182 ] However, leaf water can be substantially enriched relative to soil water due to transpiration , an evaporative process which is influenced by temperature, humidity, and the composition of surrounding water vapor. The leaf water HIC can be described with a modified Craig-Gordon model, [ 183 ] where ΔD e is the steady state enrichment of leaf water, ε eq is the temperature-dependent equilibrium fractionation between liquid water and vapor, ε k is the KIE from diffusion between leaf internal air space and the atmosphere, ΔD v is the leaf/air disequilibrium, e a is atmospheric vapor pressure, and e i is internal leaf vapor pressure.
The Péclet effect, which describes the opposing forces of advection and diffusion can be added to the model as
where E is transpiration rate, L is length scale of transport, C is concentration of water, and D is diffusion coefficient.
While the role of rain water δD as the fundamental control on the final δD of lipids is well documented, [ 184 ] the importance of fractionation effects from rain water to soil water and leaf water on ε l/w is appreciated but remains poorly understood. [ 173 ] [ 185 ]
Organic biomolecules are generally depleted relative to the δD of leaf water. [ 173 ] However, differences between organisms, biosynthetic pathways, and biological roles of different molecules can lead to huge variability in fractionation; the diversity of lipid biomarkers spans a 600‰ range of δD values. [ 186 ] Lipid biosynthesis is biochemically complex, involving multiple enzyme-dependent steps that can lead to isotope fractionations. There are three major pathways of lipid biosynthesis, known as the mevalonate pathway , the acetogenic pathway , and the 1-deoxyD-xylulose-5-phosphate/2-methylerythroyl-4-phosphate pathway . [ 187 ] The acetogenic pathway is responsible for the production of n -alkyl lipids like leaf waxes, and is associated with a smaller δD depletion relative to source water than the other two lipid biosynthesis pathways. [ 32 ] [ 188 ] While leaf water is the main source of hydrogen in leaf biomolecules, relatively depleted hydrogen from acetate or NADPH is often added during biosynthesis, and contributes to the HIC of the final molecule. Secondary hydrogen exchange reactions, meaning hydrogenation and dehydrogenation reactions outside of the primary biosynthetic pathway, also contribute substantially to the variability of lipid HIC. [ 189 ]
It is important to note that biological differences in fractionation stem not only from biochemical differences between different molecules, but also from physiological differences between different organisms. For example, the δDs of multiple leaf wax molecules are enriched in shrubs (median ~ −90‰) relative to trees (median ~ −135‰), which themselves are enriched relative to both C 3 (median ~ −160‰) and C 4 grasses (median ~ −140‰). [ 173 ] Between individual species, substantial variation in δD has been documented. [ 190 ] [ 191 ] [ 192 ] [ 193 ] Other physiological factors that contribute to variable leaf wax δD values include the seasonal timing of leaf development, [ 194 ] response to external stress or environmental variability, [ 195 ] and the presence or absence of stomata [ 184 ]
It can be difficult to distinguish between physiological factors and environmental factors, when many physiological adaptations are directly related to environment.
Several environmental factors have been shown to contribute to leaf wax δD variability, in addition to environmental effects on the δD of source water. Humidity is known to impact lipid δD at moderate humidity levels, but not at particularly high (>80%) or low (<40%) humidity levels, and a broad trend of enriched δDs, meaning smaller ε l/w , is seen in arid regions. [ 173 ] [ 175 ] [ 190 ] Temperature and sunlight intensity, both correlated to latitude, have strong effects on the rates of metabolism and transpiration, and by extension on ε l/w . [ 196 ] Also, the average chain length of leaf wax molecules varies with geographic latitude, and ε l/w has been shown to increase with increasing chain length. [ 184 ]
When using biomarkers as a proxy for reconstructing ancient environments, it is important to be aware of the biases inherent in the sedimentary record. Leaf matter incorporated into sediment is largely deposited in the autumn, so seasonal variations in leaf waxes must be considered accordingly. [ 184 ] Furthermore, sediments average leaf waxes over lots of different plants in both space and time, making it difficult to calibrate the biological constraints on ε l/w . [ 173 ] Finally, preservation of biomolecules in the geologic record does not faithfully represent whole ecosystems, and there is always the threat of hydrogen exchange, particularly if the sediments are subjected to high temperatures.
The HIC of leaf waxes can be summarized as the δD of rain water, with three main fractionation steps: evaporation from soil water, transpiration from leaf water, and lipid biosynthesis, which can be combined and measured as the net fractionation, ε l/w . [ 173 ] With ever-improving measurement techniques for single molecules, and correlation with other independent proxies in the geological record that can help constrain some variables, investigating the HIC of leaf waxes can be extremely productive. Leaf wax δD data has been successfully applied to improving our understanding of climate driven changes in terrestrial hydrology, by showing that ocean circulation and surface temperature have a significant effect on continental precipitation. [ 197 ] [ 198 ] Leaf wax δD values have also been used as records of paleoaltimetry to reconstruct the elevation gradients in ancient mountain ranges based on the effect of altitude on rain water δD. [ 199 ] [ 200 ]
Another group of molecules often used in paleoreconstructions are alkenones , long-chain largely unsaturated lipids produced exclusively by coccolithophores . Coccolithophores are marine haptophyte algae, and include the globally iconic species Emiliania huxleyi , one of the main CaCO 3 producers in the ocean. The δDs of alkenones are highly correlated to the δDs of seawater, and so can be used to reconstruct paleoenvironmental properties that constrain the isotopic composition of sea water. The most notable reconstruction that alkenone δD values are applied to is the salinity of ancient oceans.
Both the δDs of sea water and the fractionations associated with hyptophyte biochemistry (ε bio ) are fairly well understood, so alkenones can be readily used to observe the secondary effect of salinity on δD. [ 201 ] There is a well established positive linear correlation between salinity and ε l/w , on the order of a ~3‰ change in fractionation per salinity unit. [ 202 ] Hypothesized mechanisms for this effect include enrichment of D in intracellular water due to reduced exchange with extracellular water at higher salinity, [ 203 ] removal of H from intracellular water due to increased production of solutes to maintain osmotic pressure at higher salinity, [ 204 ] and lower haptophyte growth rates at higher salinity [ 173 ]
Alkenone δDs have been used successfully to reconstruct past salinity changes in the Mediterranean Sea, [ 205 ] Black Sea, [ 206 ] [ 207 ] Panama Basin, [ 208 ] and Mozambique Channel. [ 201 ] As an extension of salinity, this data was also used to draw further conclusions about ancient environments, such as ancient freshwater flooding events, [ 205 ] [ 206 ] and the evolution of plankton in response to environmental changes [ 207 ]
The possibility of using water isotope depletion with elevation to reconstruct paleoaltimetry was demonstrated as early as the late 1960s, when Caltech geochemist Samuel Epstein tried to collect rainwater at different elevations in a single storm. [ 209 ] The δ 18 O and δD lapse rates vary within -1 to -5‰/km and -10 to -40‰/km respectively, but can vary with locations and seasons, and are not exactly linear with altitude. [ 210 ] [ 211 ] [ 212 ] One of the first studies in stable isotope paleoaltimetry demonstrated a meteoric water δD signature of -90 to -139‰ in fluid inclusions in quartz and adularia in an epithermal gold-silver deposit in Nevada, and suggested the applicability of stable isotopes in reconstruction of ancient topography in the Great Basin . [ 213 ] The hydrogen and oxygen isotopes of hydrous silicate minerals have since then been used to reconstruct topographic histories in mountain ranges across the world, including the North American Cordillera, the Rocky Mountains, the Himalayas, the European Alps, and Southern Alps in New Zealand. [ 209 ] Lab experiments with clay minerals have shown that the hydrogen and oxygen isotope compositions are relatively resistant to alteration at moderate temperature (<100°C), and can preserve the original meteoric water signal. [ 214 ] One important effect of mountain ranges on rainfall stable isotopes is the rain shadow effect, in which an isotopic depletion happens in precipitation on the leeward side compared to the windward side. A change in the difference in isotopic composition of precipitation on the two sides of a mountain can be used to infer the magnitude of the rain shadow effect. [ 209 ] In one such study, an isotope enrichment was observed in smectite on the east side of the Sierra Nevada in California from mid- Miocene to late Pliocene , suggesting a decrease in elevation during this period. [ 215 ] Another study found δDs around −140‰ in muscovite in the North America Cordillera during the early Eocene , which would suggest an elevation 1km higher than today at the time. [ 216 ] In addition to hydrous minerals, hydrogen isotopes in biomarkers such as leaf waxes have also been developed for paleoaltimetry studies. The δD lapse rate in leaf waxes (−21‰/km) falls in the range of meteoric water observations. [ 212 ] [ 217 ] As an example study, leaf wax δD data has been used to confirm hydrous mineral paleoaltimetry for the high elevation of the Sierra Nevada during the Eocene. [ 200 ]
The HIC of oil , gas and coal is an important geochemical tool to study the formation, storage, migration and many other processes. The HIC signal of fossil fuels results from both inheritance of source material and water as well as fractionations during hydrocarbon generation and subsequent alteration by processes such as isotopic exchange or biodegradation . When interpreting HIC data of sedimentary organic matter one must take all the processes that might have an isotope effect into consideration.
Almost all the organic hydrogen is exchangeable to some extent. Isotopic exchange of organic hydrogen will reorder the distribution of deuterium and often incorporate external hydrogen. Generally, more mature materials are more heavily exchanged. With effective exchange, aliphatic hydrogen can finally reach isotopic equilibrium at the final stage. Equilibrium fractionation factor varies between hydrogen sites. For example, aliphatic hydrogen isotope fractionation depends on the carbon atom that the hydrogen atom bonds with. To first order , alkyl HIC follows this trend: δD Primary carbon < δD Secondary carbon < δD Tertiary carbon . [ 218 ] The fractionation factors between carbon sites also decrease with increasing temperature. This can be potentially used as a thermo-history indicator. [ 141 ] The fractionation between whole molecule and water can be estimated by averaging all hydrogen-positions, and this leads to a relatively small variation of equilibrium fractionation between different groups of hydrocarbons and water. A theoretical prediction estimated this to be −80‰ to −95‰ for steranes , −90‰ to −95‰ for hopanes , and −70‰ to −95‰ for typical cycloparaffins at 0−100°C. [ 219 ] At the temperature of the oil window and gas window, the equilibrium fractionation between different group of organic molecules is relatively small, as compared with large primary signals.
The study of hydrogen isotopes of fossil fuels has been applied as proxies and tools in the following aspects:
The first stage that sedimentary organic matter (SOM) experiences after deposition is diagenesis . During diagenesis, biological decomposition can alter the DHR of organics. Several experimental studies have shown that some biodegraded materials become slightly enriched in D (less than 50‰). Most organics become kerogen by the end of diagenesis. Generally, δD of kerogen spans a wide range. Many factors contribute to the kerogen we observe in geologic records , including:
Research on the Australian basins showed that δD of lacustrine algal sourced kerogen with terrestrial contributions varies from −105‰ to −200‰, and δD of kerogen from near-coastal depositional environment has a narrower range, −75‰ to −120‰. [ 224 ] The smaller span in DHRs of coastal kerogen is thought to reflect the relatively stable regional climate. Pedentchouk and his colleagues reported δD values of -70‰ to -120‰ in immature to low mature kerogen from early Cretaceous lacustrine sediments in West Africa. [ 221 ]
Coals are from type III kerogen mostly derived from land plants, which should have a primary D/H signal sensitive to local meteoric water. Reddings et al. analyzed coals of various origins and found them randomly scattered across the range of −90‰ to −170‰. [ 225 ] Rigby et al. found D contents decrease from −70‰ to −100‰ with increasing maturity in coal from Bass Basin and attributed this to latter exchange with low D water. [ 226 ] Smith et al. studied H isotopes of coal samples from Antarctica and Australia. They found a strong negative correlation between δD and inferred paleolatitude. For coal samples originating near the Equator , δD is around −50‰, while for those originating from polar regions, δD is around −150‰. [ 227 ] This δD trend along latitude is consistent meteoric water trend and thus is an evidence that coals can preserve much of the original signals.
There are two types of approach to study the alteration of DHRs of kerogen during catagenesis: (1) laboratory incubation of organic matter that enables mechanistic study with controlled experiments; (2) natural sample measurement that provides information of combined effects over geologic timescales. The complex composition and chemistry of kerogen complicates the results. Nevertheless, most research on HIC of kerogen show D enrichment with increasing maturity. Type II kerogen (marine derived) from New Albany Shale is reported to have δD rise from −120‰ to −70‰ as vitrinite reflectance increase from 0.3% to 1.5%. [ 228 ] Two main mechanisms have been proposed for enrichment. One of them is kinetic fractionation during hydrocarbon generation while the other is isotopic exchange with surrounding water. Anhydrous incubation experiments have shown that the products are generally more D-depleted than their precursors, causing enrichment in residual kerogen. Schimmelmann et al. studied the relationship between terrestrially-derived oil and their source rock kerogens from four Australian Basins. They found that on average the oil is depleted to corresponding kerogen by 23‰. [ 224 ] Hydrous incubation experiments suggest that 36–79% of bulk organic hydrogen may come from water at moderate maturity. While still under debate, it appears likely that incorporation of water hydrogen isotopes is the more dominant process for kerogen D- enrichment during catagenesis. [ 46 ]
In summary, D content of kerogen and coal is complicated and hard to resolve due to the complex chemistry. Nevertheless, studies have found the possible correlation between coal δD and paleo-latitude.
Commonly, HIC of natural gas from the same well has a trend of δD methane < δD ethane < δD propane < δD C4+ . This is because most natural gas is thought to be generated by stepwise thermal cracking that is mostly irreversible and thus governed by normal kinetic isotope effects (KIE) that favor light isotopes. The same trend, known as "the normal order", [ 229 ] holds for carbon isotopes in natural gas. For example, Angola gas reportedly has a methane δD range of −190‰ to −140‰, an ethane δD of −146‰ to −107‰, a propane δD of −116‰ to −90‰, and a butane δD of −118‰ to −85‰. [ 230 ] However, some recent studies show that opposite patterns could also exist, meaning δD methane > δD ethane > δD propane . This phenomenon is often called 'isotopic reversal' or 'isotopic rollover'. The isotopic order could also be partly reversed, like δD methane > δD ethane < δD propane or δD methane < δD ethane > δD propane . [ 229 ] Burruss et al. found that in the deepest samples of northern Appalachian basin the hydrogen isotopic order for methane and ethane is reversed. [ 231 ] Liu et al., also found partial reversal in oil-related gas from the Tarim Basin. [ 229 ] The mechanism causing this reversal is still unknown. Possible explanations include mixing between gases of different maturities and sources, oxidation of methane, etc. Jon Telling et al., synthesized isotopically reversed (in both C and H) low-molecular alkanes using gas-phase radical recombination reactions in electrical discharge experiments, providing another possible mechanism. [ 232 ]
Methane is the main component of natural gas. Geosphere methane is intriguing for the large input of microbial methanogenesis . This process exhibits a strong KIE, resulting in greater D-depletion in methane relative to other hydrocarbons . δD ranges from −275‰ to −100‰ in thermogenic methane, and from −400‰ to −150‰ in microbial methane. [ 95 ] Also, methane formed by marine methanogens is generally enriched in D relative to methane from freshwater methanogens . δD of methane has been plotted together with other geochemical tools (like δ 13 C, gas wetness) to categorize and identify natural gas. A δD-δ 13 C diagram (sometimes called CD diagram, Whiticar diagram, or Schoell diagram) is widely used to place methane in one of the three distinct groups: thermogenic methane that is higher in both δ 13 C and δD; marine microbial methane that is more depleted in 13 C and freshwater microbial methane that is more depleted in D. Hydrogenotrophic methanogenesis produces less D-depleted methane relative to acetoclastic methanogenesis. The location where the organism lives and substrate concentration also affect isotopic composition: rumen methanogenesis, which occurs in a more closed system and with higher partial pressures of hydrogen, exhibits a greater fractionation (−300 to −400‰) than wetland methanogenesis (−250 to −170‰). [ 233 ] [ 234 ]
Recent advances in analytical chemistry have enabled high-precision measurements of multiply substituted (or 'clumped') isotopologues like 13 CH 3 2 H. This is a novel tool for studying methane formation. This proxy is based on the abundance of clumped isotopologues of methane, which should be enriched compared to the stochastic distribution at thermodynamic equilibrium because the reduced zero-point energy for heavy-heavy isotope bonding is more than twice the reduced zero-point energy of heavy-light isotope bonding. [ 235 ] The extent of enrichment decreases with increasing temperature, as higher entropy tends to randomize isotope distribution. Stolper et al. established this temperature calibration using laboratory equilibrated methane and field methane from known formation temperature, and applied this to several gas reservoirs to study natural gas formation and mixing. [ 236 ] Wang et al. also reported strong non-equilibrium isotope effect in methane clumped isotopes from lab-cultured methanogens and field samples. [ 237 ] These methane samples have relatively low abundance of clumped isotopologues, sometimes even lower than the stochastic distribution. This indicates that there are irreversible steps in enzymatic reactions during methanogenesis [ 237 ] that fractionation against clumped isotopologues to create the depleted signal. Isotope clumping in methane has proven a robust proxy, and scientists are now moving towards higher-order alkane molecules like ethane for further work. [ 238 ]
Oil is generally a product of thermal breakdown of type I and type II kerogen during catagenesis . The HIC should reflect the source kerogen signal, generation fractionation, isotopic exchange and other maturation effects. Thermal maturation at the oil window can erase much of the HIC primary signals. The formation of oil involves breaking C-C and C-H bonds, resulting in depletion of 13 C and 2 H in the products and enrichment in the residual reactants due to KIEs. Yongchun Tang and his colleagues modeled this process based on laboratory-calibrated kinetics data and found that the frequency factor ratio for D/H is 1.07. [ 239 ] Moreover, oil is also affected by isotope fractionation from phase changes . However, the behavior of oil gas-liquid fractionation differs from water as the vapor phase of oil is 2 H-enriched. [ 51 ] This depletes residual oil as it gets evaporated. Biodegradation of oil is also expected to fractionate hydrogen isotopes, as enzymatic breaking of C-H bond has a normal KIE. Several degradation experiments show that this fractionation is generally mild, ranging from −11‰ to −79‰. [ 51 ] This process should also enrich partially degraded oil. Finally, oil stored in a reservoir often had migrated through subsurface (aka geochromatography) from another source region, interacting with water. No data has been published to confirm the fractionation associated with migration, yet theoretical prediction shows that this is likely to be very small. [ 51 ]
Many studies of natural samples have shown slight increases in δD with thermal maturity. Amane Waseda reported δD of oil samples in northeast Japan to increase from around −130‰ to around −110‰ with higher maturity. [ 240 ] At low thermal maturity , dos Santos Neto and Hayes reported δD of saturate fraction of oil in Portiguar Basin derived from a lacustrine environment is -90‰, and from a marine-evaporitic environment is -120‰ to −135‰. [ 46 ] [ 85 ]
Bulk analysis of oil, which yields a complex mixture of organic compounds , obscures much of the valuable information. Switching to compound-specific study greatly expanded our understanding of hydrogen isotopes of oil. Analyzing HIC at the compound level avoids problems from differences in exchange rates, simplifies sources and products relationships, and draws a much more detailed picture. [ 51 ] δDs of n - alkanes are generally thought to be representative of oil as they are the major components. Schimmelmann et al. confirmed that alkane fractions have almost the same DHRs as whole oils . [ 224 ] Depending on source material type and maturity, δD of n -alkanes can vary from −100‰ to −180‰. A common phenomenon of various oil and matured rock derived n-alkanes is a trend of increasing δD with chain length. For example, Li et al. analyzed oils from the Western Canada Sedimentary Basin and found δD increased between 20‰ and 40‰ from C 13 to C 27 . [ 241 ] This "isotope slope" is an artifact of kinetic fractionation associated with thermal cracking of carbon chains. This trend has been experimentally reproduced and theoretically modeled by Tang et al. [ 223 ]
N-alkanes are also known to preserve detailed information of source material. Li et al. studied oils from the marine-derived Upper Cretaceous Second White Speckled Shale and found strong depleted signal around −180‰ in C 12 -C 18 . The low δD of this marine samples was explained by the discharge of a large high latitude river. [ 241 ] Schimmelmann et al. found that the δD of the oil sampled from coaly facies of the Crayfish group reaches down to −230‰ where as those sampled from algal facies of the same group are around −100‰. Such huge variation is hard to explain by any other causes than Australia splitting from Antarctica in late Cretaceous. [ 51 ] Another special case reported by Xiong et al. [ 242 ] studied Ordovician carbonates from Bohai Bay Basin. They found big differences between δD of n-alkanes, reflecting that the original signal is preserved rather than being homogenized. The result is not obvious as the sample is very mature (inferred vitrinite reflectance R 0 up to 2.3). Thus this is strong evidence that carbonate systems have much lower catalytic efficiency of hydrogen exchange on hydrocarbons. Strong enrichment (~40‰) in odd carbon numbered alkanes to even carbon numbered alkanes is also found in some subset of samples and the reason is unclear at this point. This odd-even effect is also observed in immature clastic sediments . [ 243 ]
Ecohydrology is concerned with the interaction between ecosystems and water cycling, from measuring the small scale drainage of water into soil to tracking the broad movements of water evaporating from trees. Because deuterium acts as a conservative tracer , it works well for tracking water movement through plants and ecosystems . Though water movement in single-process phenomena such as evaporation is relatively simple to track, many systems (e.g. cloud forests ) in the environment have multiple sources, and tracking water movement becomes more complicated. [ 244 ] Isotope spiking can also be done to determine water transport through soil and into plants by injecting deuterated water directly into the ground. [ 245 ]
Stable isotope analysis of xylem water can be used to follow the movement of water from soil into the plants and therefore provide a record of the depth of water acquisition. An advantage to using xylem water is that in theory, the HIC should directly reflect the input water without being affected by leaf transpiration. For example, Dawson and Ehleringer used this approach to determine whether trees that grow next to streams are using the surface waters from that stream. [ 246 ] Water from the surface would have the same isotopic composition as the stream, while water from farther below in the ground would be from past precipitation inputs. In this case, younger trees had a xylem water isotopic composition very close to the adjacent stream and likely used surface waters to get established. Older trees had depleted xylem water relative to the stream, reflecting that they source their water from deeper underground. [ 246 ] Other stable isotope studies have also determined that plants in redwood forests do not just take up water from their roots but acquire a significant proportion of water via stomatal uptake on leaves. [ 247 ]
Plant water can be used to characterize other plant physiological processes that affect the water cycle ; for example, leaf water is widely used for modeling transpiration [ 248 ] and water-use efficiency (WUE). [ 249 ] In transpiration, the Craig-Gordon model for lake water enrichment through evaporation [ 250 ] has been found experimentally to fit well for modelling leaf water enrichment. [ 251 ] Transpiration can be measured by direct injection of deuterated water into the base of the tree, trapping all water vapor transpired from the leaves and measuring the subsequent condensate. [ 252 ] Water use can also be measured and is calculated from a heavy water injection as follows:
where WU is water use in kg/day, M is mass of deuterated water injected in grams, T is the final day of the experiment, C i is concentration of deuterium at time interval i in grams/kilogram, and Δt i is the length of time interval i in days. Though the calculated water use via thermal-dissipation-probing of some tropical plants such as bamboos, correlates strongly with measured water use found by tracking D 2 O movement, the exact values are not the same. [ 253 ] In fact, with the legume tree Gliricidia sepium , which produces a heartwood, transpired water did not even correlate strongly with injected 2 H 2 O concentrations, which would further complicate water use measurements from direct injections. This possibly occurred because heartwoods could accumulate heavy water rather than move the water directly through xylem and to leaves. [ 253 ]
WUE, the ratio of carbon fixation to transpiration, has previously been associated with 13 C/ 12 C ratios using the equation:
where
HIC can be useful in tracking animal migration . [ 254 ] Animals with metabolically inert tissue (e.g. feathers or hair) synthesize that tissue using hydrogen from source water and food, but ideally do not incorporate subsequent water during migration. Because δD varies geographically, the difference between animal tissue δD and post-migration water δD, after accounting for the biological fractionation of assimilation, can provide information regarding animal movement. In monarch butterflies , for example, wing chitin is metabolically inert after it is built, so it can reflect the isotopic composition of the environmental water at the time and location of wing growth. This then creates a record of butterfly origin and can be used to determine migration distance. [ 255 ] This approach can also be used in bats and birds, using hair and feathers, respectively. [ 256 ] [ 257 ] Since rainwater becomes depleted as elevation increases, this method can also track altitudinal migration. However, this is technically hard to do, and the resolution seems to be too poor to track small altitudinal changes. [ 257 ] 2 H is most useful in tracking movement of species between areas with large continental water variation, since species movement can be complicated by the similarity of local water δD between places. For example, source water from Baja California may have the same δD as water from Maine. [ 258 ] Further, a proportion of the HIC in the tissue can exchange with water and complicate the interpretation of measurements. To determine this percentage of isotopic exchange, which varies according to local humidity levels, standards of metabolically inert tissue from the species of interest can be constructed and equilibriated to local conditions. This allows measured δD from different regions to be compared against each other. [ 259 ]
Assimilation of diet into tissue has a tissue-specific fractionation known as the trophic discrimination factor. Diet sources can be tracked through a food web via deuterium isotope profiles, though this is complicated by deuterium having two potential sources – water and food. Food more strongly impacts δD than does exchange with surrounding water, and that signal is seen across trophic levels. [ 260 ] However, different organisms derive organic hydrogen in varying ratios of water to food: for example, in quail, 20-30% of organic hydrogen was from water and the remainder from food. The precise percentage of hydrogen from water, depended on tissue source and metabolic activity. [ 261 ] In chironomids , 31-47% of biomass hydrogen derived from water, [ 260 ] and in microbes as much as 100% of fatty acid hydrogen can be derived from water depending on substrate. [ 186 ] In caterpillars, diet δD from organic matter correlates linearly with tissue δD. The same relationship does not appear to hold consistently for diet δD from water, however – water derived from either the caterpillar or its prey plant is more 2 H-enriched than their organic material. Going up trophic levels from prey (plant) to predator (caterpillar) results in an isotopic enrichment. [ 262 ] This same trend of enrichment is seen in many other animals - carnivores, omnivores, and herbivores - and seems to follow 15 N relative abundances. Carnivores at the same trophic level tend to exhibit the same level of 2 H enrichment. [ 263 ] Because, as mentioned earlier, the amount of organic hydrogen produced from water varies between species, a model of trophic level related to absolute fractionation is difficult to make if the participating species are not known. Consistency in measuring the same tissues is also important, as different tissues fractionate deuterium differently. In aquatic systems, tracking trophic interactions is valuable for not only understanding the ecology of the system, but also for determining the degree of terrestrial input. [ 33 ] [ 264 ] The patterns of deuterium enrichment consistent within trophic levels is a useful tool for assessing the nature of these interactions in the environment. [ 33 ]
Biological deuterium fractionation through metabolism is very organism and pathway dependent, resulting in a wide variability in fractionations. [ 186 ] [ 265 ] Despite this, some trends still hold. Hydrogen isotopes tend to fractionate very strongly in autotrophs relative to heterotrophs during lipid biosynthesis - chemoautotrophs produce extremely depleted lipids, with the fractionation ranging from roughly −200 to −400‰. [ 266 ] This has been observed both in laboratory-grown cultures fed a known quantity of deuterated water and in the environment. [ 186 ] [ 267 ] Proteins, however, do not follow as significant a trend, with both heterotrophs and autotrophs capable of generating large and variable fractionations. [ 266 ] In part, kinetic fractionation of the lighter isotope during formation of reducing equivalents NADH and NADPH result in lipids and proteins that are isotopically lighter.
Salinity appears to play a role in the degree of deuterium fractionation as well; more saline waters affect growth rate, the rate of hydrogen exchange, and evaporation rate. All of these factors influence lipid δD upon hydrogen being incorporated into biomass. In coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica , alkenone δD has been found to correlate strongly to organism growth rate divided by salinity. [ 202 ] The relationship between deuterium fractionation and salinity could potentially be used in paleoenvironment reconstruction with preserved lipids in the rock record to determine, for example, ocean salinity at the time of organismal growth. However, the degree of fractionation is not necessarily consistent between organisms, complicating the determination of paleosalinity with this method. [ 202 ] There also appears to be a negative correlation between growth rate and fractionation in these coccolithophores. Further experiments on unicellular algae Eudorina unicocca and Volvox aureus show no effect of growth rate (controlled by nitrogen limitation) on fatty acid δD. However, sterols become more D-depleted as growth rate increases, [ 268 ] in agreement with alkenone isotopic composition in coccolithophores. Overall, although there are some strong trends with lipid δD, the specific fractionations are compound-specific. As a result, any attempt to create a salinometer through δD measurements will necessarily be specific to a single compound type.
An important goal of environmental chemistry is tracing the source and degradation of pollutants. Various methods have been used for fingerprinting pools of environmental pollutants such as the bulk chemical composition of a spill, [ 269 ] isotope ratios of the bulk chemical mixture, [ 270 ] or isotope ratios of individual constituent compounds. Stable isotopes of carbon and hydrogen can be used as complementary fingerprinting techniques for natural gas. [ 271 ] The DHR of hydrocarbons from the Deepwater Horizon oil spill was used to verify that they were likely from the Macondo well. [ 272 ] HICs have also been used as a measure of the relative amount of biodegradation that has occurred in oil reservoirs in China, [ 273 ] and studies on pure cultures of n-alkane degrading organisms have shown a chain-length dependence on the amount of hydrogen isotope fractionation during degradation. [ 274 ] Additional studies have also shown hydrogen isotope effects in the degradation of methyl tert-butyl ether [ 275 ] and toluene [ 276 ] [ 277 ] that have been suggested to be useful in the evaluation of the level of degradation of these polluting compounds in the environment. In both cases the residual unreacted compounds became 2 H-enriched to a few tens of ‰, with variations exhibited between different organisms and degree of reaction completeness. These observations of heavy residual compounds have been applied to field observations of biodegradation reactions such as removal of benzene and ethylbenzene, [ 278 ] which imparted a D/H fractionation of 27 and 50 ‰, respectively. Also, analysis of o-xylene in a polluted site showed high residual DHRs after biodegradation, consistent with activation of C-H bonds being a rate limiting step in this process [ 279 ]
Stable isotope ratios have found uses in various instances where the authenticity or origin of a chemical compound is called into question. Such situations include assessing the authenticity of food, wine and natural flavors; drug screening in sports (see doping in sport ); pharmaceuticals; illicit drugs; and even helping identify human remains. In these cases it is often not enough to detect or quantify a certain compound, since the question is the origin of the compound. The strength of hydrogen isotope analysis in answering these questions is that the DHR of a natural product is often related to the natural water DHRs in the area where the product was formed (see: Hydrologic cycle ). Since DHRs vary significantly between different areas, this can be a powerful tool in locating the original source of many different substance.
Foods, flavorings and scents are often sold with the guarantee that chemical additives come from natural sources. This claim becomes hard to test when the chemical compound has a known structure and is readily synthesized in a lab. Authentication of claims about the origins of these chemicals has made good use of various stable isotopes, including those of hydrogen. Combined carbon and hydrogen isotope analysis has been used to test the authenticity of (E)-methyl cinnamate , [ 280 ] γ-decalactone and δ-decalactone . [ 281 ] Hydrogen and nitrogen isotope ratios have been used for the authentication of alkylpyrazines used as "natural" coffee flavorings . [ 282 ]
The isotope ratio of carbon in athletes' steroids has been used to determine whether these steroids came from the athlete's body or an outside source. This test has been used in a number of high-profile anti-doping cases and has various benefits over simply characterizing the concentration of various compounds. Attempts are being made to create similar tests based on stable hydrogen isotopes [ 283 ] which could be used to complement the existing testing methods. One concern with this method was that the natural steroids produced by the human body may vary significantly based on the 2 H content of drinking water, leading to false detection of doping based on HIC differences. This concern has been addressed in a recent study which concluded that the effect of DHR of drinking water did not pose an insurmountable source of error for this anti-doping testing strategy. [ 284 ]
The pharmaceutical industry has revenues of hundreds of billions of dollars a year globally . With such a large industry counterfeiting and copyright infringement are serious issues, and hydrogen isotope fingerprinting has become a useful tool in verifying the authenticity of various drugs. As described in the preceding sections, the utility of DHRs is highest when combined with measurements of other isotope ratios. In an early study on the stable isotope compositions of tropicamide , hydrocortisone , quinine and tryptophan ; carbon, nitrogen, oxygen and hydrogen stable isotopes were analyzed by EA-IRMS; clear distinctions were able to be made between manufacturers and even batches of the drugs based on their isotope signatures. [ 285 ] In this study it was determined that the hydrogen and oxygen isotope ratios were the two best fingerprints for distinguishing between different drug sources. A follow-up study analyzing naproxen from various lots and manufacturers also showed similar ability to distinguish between sources of the drugs. [ 286 ] The use of these isotope signatures could not only be used to distinguish between different manufacturers, but also between different synthetic pathways for the same compound. [ 287 ] These studies relied on the natural variations that occurred in the synthesis of these drugs, but other studies have used starting ingredients that are intentionally labeled D and 13 C, and showed that these labels could be traced into the final pharmaceutical product. [ 288 ] DHRs can also be determined for specific sites in a drug by 2 H NMR, and has been used to distinguish between different synthetic methods for ibuprofen and naproxen in one study, [ 289 ] and prozac and fluoxetine in another. [ 290 ] These studies show that bulk DHR information for EA-IRMS, and site-specific DHRs from 2 H NMR have great utility for pharmaceutical drug authenticity testing.
The sources and production mechanisms of illegal drugs has been another area that has seen successful application of hydrogen isotope characterization. Usually, as with other applications of stable isotope techniques, results are best when data for multiple stable isotopes are compared with one another. δ 2 H, δ 13 C and δ 15 N have been used together to analyze tablets of MDA and MDMA and has successfully identified differences which could be used to differentiate between different sources or production mechanisms. [ 291 ] The same combination of stable isotopes with the addition of δ 18 O was applied to heroin and associated packaging and could successfully distinguish between different samples. [ 292 ] Analysis using deuterium NMR was also able to shed light on the origin and processing of both cocaine and heroin . [ 293 ] In the case of heroin this site-specific natural isotopic fraction measured by deuterium NMR (SNIF-NMR) method could be used for determining the geographic origin of the molecule by analyzing so-called natural sites (which were present in the morphine from which heroin is made), as well as gaining information on the synthesis process by analyzing the artificial sites (added during drug processing).
The geographic variation in DHR in human drinking water is recorded in hair. Studies have shown a very strong relation between an individual's hair and drinking water DHRs. [ 294 ]
Since tap water DHR depends strongly on geography, a person's hair DHR can be used to determine regions where they most likely lived during hair growth. This idea has been used in criminal investigations to try to constrain the movements of a person prior to their death, in much the same way DHRs have been used to track animal migration . By analyzing sections of hair of varying ages, one can determine in what D/H regions a person was living at a specific time before their death. [ 295 ] | https://en.wikipedia.org/wiki/Hydrogen_isotope_biogeochemistry |
The hydrogen line , 21 centimeter line , or H I line [ a ] is a spectral line that is created by a change in the energy state of solitary , electrically neutral hydrogen atoms . It is produced by a spin -flip transition, which means the direction of the electron's spin is reversed relative to the spin of the proton. This is a quantum state change between the two hyperfine levels of the hydrogen 1 s ground state . The electromagnetic radiation producing this line has a frequency of 1 420 .405 751 768 (2) MHz (1.42 GHz), [ 1 ] which is equivalent to a wavelength of 21.106 114 054 160 (30) cm in a vacuum . According to the Planck–Einstein relation E = hν , the photon emitted by this transition has an energy of 5.874 326 184 1116 (81) μ eV [ 9.411 708 152 678 (13) × 10 −25 J ]. The constant of proportionality , h , is known as the Planck constant .
The hydrogen line frequency lies in the L band , which is located in the lower end of the microwave region of the electromagnetic spectrum . It is frequently observed in radio astronomy because those radio waves can penetrate the large clouds of interstellar cosmic dust that are opaque to visible light . The existence of this line was predicted by Dutch astronomer H. van de Hulst in 1944, then directly observed by E. M. Purcell and his student H. I. Ewen in 1951. Observations of the hydrogen line have been used to reveal the spiral shape of the Milky Way , to calculate the mass and dynamics of individual galaxies, and to test for changes to the fine-structure constant over time. It is of particular importance to cosmology because it can be used to study the early Universe. Due to its fundamental properties, this line is of interest in the search for extraterrestrial intelligence . This line is the theoretical basis of the hydrogen maser .
An atom of neutral hydrogen consists of an electron bound to a proton . The lowest stationary energy state of the bound electron is called its ground state . Both the electron and the proton have intrinsic magnetic dipole moments ascribed to their spin , whose interaction results in a slight increase in energy when the spins are parallel, and a decrease when antiparallel. The fact that only parallel and antiparallel states are allowed is a result of the quantum mechanical discretization of the total angular momentum of the system. When the spins are parallel, the magnetic dipole moments are antiparallel (because the electron and proton have opposite charge), thus one would expect this configuration to actually have lower energy just as two magnets will align so that the north pole of one is closest to the south pole of the other. This logic fails here because the wave functions of the electron and the proton overlap; that is, the electron is not spatially displaced from the proton, but encompasses it. The magnetic dipole moments are therefore best thought of as tiny current loops. As parallel currents attract, the parallel magnetic dipole moments (i.e., antiparallel spins) have lower energy. [ 2 ]
In the ground state, the spin-flip transition between these aligned states has an energy difference of 5.874 33 μeV . When applied to the Planck relation , this gives:
where λ is the wavelength of an emitted photon, ν is its frequency , E is the photon energy, h is the Planck constant , and c is the speed of light in a vacuum. In a laboratory setting, the hydrogen line parameters have been more precisely measured as:
in a vacuum. [ 3 ]
This transition is highly forbidden with an extremely small transition rate of 2.9 × 10 −15 s −1 , [ 4 ] and a mean lifetime of the excited state of around 11 million years. [ 3 ] Collisions of neutral hydrogen atoms with electrons or other atoms can help promote the emission of 21 cm photons. [ 5 ] A spontaneous occurrence of the transition is unlikely to be seen in a laboratory on Earth, but it can be artificially induced through stimulated emission using a hydrogen maser . [ 6 ] It is commonly observed in astronomical settings such as hydrogen clouds in our galaxy and others. Because of the uncertainty principle , its long lifetime gives the spectral line an extremely small natural width , so most broadening is due to Doppler shifts caused by bulk motion or nonzero temperature of the emitting regions. [ 7 ]
During the 1930s, it was noticed that there was a radio "hiss" that varied on a daily cycle and appeared to be extraterrestrial in origin. After initial suggestions that this was due to the Sun, it was observed that the radio waves seemed to propagate from the centre of the Galaxy . These discoveries were published in 1940 and were noted by Jan Oort who knew that significant advances could be made in astronomy if there were emission lines in the radio part of the spectrum. He referred this to Hendrik van de Hulst who, in 1944, predicted that neutral hydrogen could produce radiation at a frequency of 1 420 .4058 MHz due to two closely spaced energy levels in the ground state of the hydrogen atom . [ 8 ]
The 21 cm line (1420.4 MHz) was first detected in 1951 by Ewen and Purcell at Harvard University , [ 9 ] and published after their data was corroborated by Dutch astronomers Muller and Oort, [ 10 ] and by Christiansen and Hindman in Australia. After 1952 the first maps of the neutral hydrogen in the Galaxy were made, and revealed for the first time the spiral structure of the Milky Way . [ 11 ] [ 12 ]
The 21 cm spectral line appears within the radio spectrum (in the L band of the UHF band of the microwave window ). Electromagnetic energy in this range can easily pass through the Earth's atmosphere and be observed from the Earth with little interference. [ 13 ] The hydrogen line can readily penetrate clouds of interstellar cosmic dust that are opaque to visible light . [ 14 ] Assuming that the hydrogen atoms are uniformly distributed throughout the galaxy, each line of sight through the galaxy will reveal a hydrogen line. The only difference between each of these lines is the Doppler shift that each of these lines has. Hence, by assuming circular motion , one can calculate the relative speed of each arm of our galaxy. The rotation curve of our galaxy has been calculated using the 21 cm hydrogen line. It is then possible to use the plot of the rotation curve and the velocity to determine the distance to a certain point within the galaxy. However, a limitation of this method is that departures from circular motion are observed at various scales. [ 15 ]
Hydrogen line observations have been used indirectly to calculate the mass of galaxies, [ 16 ] to put limits on any changes over time of the fine-structure constant , [ 17 ] and to study the dynamics of individual galaxies. The magnetic field strength of interstellar space can be measured by observing the Zeeman effect on the 21-cm line; a task that was first accomplished by G. L. Verschuur in 1968. [ 18 ] In theory, it may be possible to search for antihydrogen atoms by measuring the polarization of the 21-cm line in an external magnetic field. [ 19 ]
Deuterium has a similar hyperfine spectral line at 91.6 cm (327 MHz), and the relative strength of the 21 cm line to the 91.6 cm line can be used to measure the deuterium-to-hydrogen (D/H) ratio. One group in 2007 reported D/H ratio in the galactic anticenter to be 21 ± 7 parts per million. [ 20 ]
The line is of great interest in Big Bang cosmology because it is the only known way to probe the cosmological " dark ages " from recombination (when stable hydrogen atoms first formed) to the reionization epoch. After including the redshift range for this period, this line will be observed at frequencies from 200 MHz to about 15 MHz on Earth. [ 21 ] It potentially has two applications. First, by mapping the intensity of redshifted 21 centimeter radiation it can, in principle, provide a very precise picture of the matter power spectrum in the period after recombination. [ 22 ] Second, it can provide a picture of how the universe was re‑ionized, [ 23 ] as neutral hydrogen which has been ionized by radiation from stars or quasars will appear as holes in the 21 cm background. [ 24 ] [ 7 ]
However, 21 cm observations are very difficult to make. Ground-based experiments to observe the faint signal are plagued by interference from television transmitters and the ionosphere , [ 23 ] so they must be made from very secluded sites with care taken to eliminate interference. Space based experiments, including on the far side of the Moon (where they would be sheltered from interference from terrestrial radio signals), have been proposed to compensate for this. [ 25 ] Little is known about other foreground effects, such as synchrotron emission and free–free emission on the galaxy. [ 26 ] Despite these problems, 21 cm observations, along with space-based gravitational wave observations, are generally viewed as the next great frontier in observational cosmology, after the cosmic microwave background polarization . [ 27 ]
The Pioneer plaque , attached to the Pioneer 10 and Pioneer 11 spacecraft, portrays the hyperfine transition of neutral hydrogen and used the wavelength as a standard scale of measurement. For example, the height of the woman in the image is displayed as eight times 21 cm, or 168 cm. Similarly the frequency of the hydrogen spin-flip transition was used for a unit of time in a map to Earth included on the Pioneer plaques and also the Voyager 1 and Voyager 2 probes. On this map, the position of the Sun is portrayed relative to 14 pulsars whose rotation period circa 1977 is given as a multiple of the frequency of the hydrogen spin-flip transition. It is theorized by the plaque's creators that an advanced civilization would then be able to use the locations of these pulsars to locate the Solar System at the time the spacecraft were launched. [ 28 ] [ 29 ]
The 21 cm hydrogen line is considered a favorable frequency by the SETI program in their search for signals from potential extraterrestrial civilizations. In 1959, Italian physicist Giuseppe Cocconi and American physicist Philip Morrison published "Searching for interstellar communications", a paper proposing the 21 cm hydrogen line and the potential of microwaves in the search for interstellar communications. According to George Basalla, the paper by Cocconi and Morrison "provided a reasonable theoretical basis" for the then-nascent SETI program. [ 30 ] Similarly, Pyotr Makovetsky proposed SETI use a frequency which is equal to either
or
Since π is an irrational number , such a frequency could not possibly be produced in a natural way as a harmonic , and would clearly signify its artificial origin. Such a signal would not be overwhelmed by the H I line itself, or by any of its harmonics. [ 31 ] | https://en.wikipedia.org/wiki/Hydrogen_line |
Hydrogen peroxide is a chemical compound with the formula H 2 O 2 . In its pure form, it is a very pale blue [ 5 ] liquid that is slightly more viscous than water . It is used as an oxidizer , bleaching agent, and antiseptic , usually as a dilute solution (3%–6% by weight) in water for consumer use and in higher concentrations for industrial use. Concentrated hydrogen peroxide, or " high-test peroxide ", decomposes explosively when heated and has been used as both a monopropellant and an oxidizer in rocketry . [ 6 ]
Hydrogen peroxide is a reactive oxygen species and the simplest peroxide , a compound having an oxygen–oxygen single bond . It decomposes slowly into water and elemental oxygen when exposed to light, and rapidly in the presence of organic or reactive compounds. It is typically stored with a stabilizer in a weakly acidic solution in an opaque bottle. Hydrogen peroxide is found in biological systems including the human body. Enzymes that use or decompose hydrogen peroxide are classified as peroxidases .
The boiling point of H 2 O 2 has been extrapolated as being 150.2 °C (302.4 °F), approximately 50 °C (90 °F) higher than water. In practice, hydrogen peroxide will undergo potentially explosive thermal decomposition if heated to this temperature. It may be safely distilled at lower temperatures under reduced pressure. [ 7 ]
Hydrogen peroxide forms stable adducts with urea ( hydrogen peroxide–urea ), sodium carbonate ( sodium percarbonate ) and other compounds. [ 8 ] An acid-base adduct with triphenylphosphine oxide is a useful "carrier" for H 2 O 2 in some reactions.
Hydrogen peroxide ( H 2 O 2 ) is a nonplanar molecule with (twisted) C 2 symmetry ; this was first shown by Paul-Antoine Giguère in 1950 using infrared spectroscopy . [ 9 ] [ 10 ] Although the O−O bond is a single bond , the molecule has a relatively high rotational barrier of 386 cm −1 (4.62 kJ / mol ) for rotation between enantiomers via the trans configuration, and 2460 cm −1 (29.4 kJ/mol) via the cis configuration. [ 11 ] These barriers are proposed to be due to repulsion between the lone pairs of the adjacent oxygen atoms and dipolar effects between the two O–H bonds. For comparison, the rotational barrier for ethane is 1040 cm −1 (12.4 kJ/mol).
The approximately 100° dihedral angle between the two O–H bonds makes the molecule chiral . It is the smallest and simplest molecule to exhibit enantiomerism . It has been proposed that the enantiospecific interactions of one rather than the other may have led to amplification of one enantiomeric form of ribonucleic acids and therefore an origin of homochirality in an RNA world . [ 12 ]
The molecular structures of gaseous and crystalline H 2 O 2 are significantly different. This difference is attributed to the effects of hydrogen bonding , which is absent in the gaseous state. [ 13 ] Crystals of H 2 O 2 are tetragonal with the space group D 4 4 or P 4 1 2 1 2. [ 14 ]
In aqueous solutions , hydrogen peroxide forms a eutectic mixture, exhibiting freezing-point depression down as low as −56 °C; pure water has a freezing point of 0 °C and pure hydrogen peroxide of −0.43 °C. The boiling point of the same mixtures is also depressed in relation with the mean of both boiling points (125.1 °C). It occurs at 114 °C. This boiling point is 14 °C greater than that of pure water and 36.2 °C less than that of pure hydrogen peroxide. [ 15 ]
Hydrogen peroxide is most commonly available as a solution in water. For consumers, it is usually available from pharmacies at 3 and 6 wt% concentrations. The concentrations are sometimes described in terms of the volume of oxygen gas generated; one milliliter of a 20-volume solution generates twenty milliliters of oxygen gas when completely decomposed. For laboratory use, 30 wt% solutions are most common. Commercial grades from 70% to 98% are also available, but due to the potential of solutions of more than 68% hydrogen peroxide to be converted entirely to steam and oxygen (with the temperature of the steam increasing as the concentration increases above 68%) these grades are potentially far more hazardous and require special care in dedicated storage areas. Buyers must typically allow inspection by commercial manufacturers.
Hydrogen peroxide has several structural analogues with H m X−XH n bonding arrangements (water also shown for comparison). It has the highest (theoretical) boiling point of this series (X = O, S, N, P). Its melting point is also fairly high, being comparable to that of hydrazine and water, with only hydroxylamine crystallising significantly more readily, indicative of particularly strong hydrogen bonding. Diphosphane and hydrogen disulfide exhibit only weak hydrogen bonding and have little chemical similarity to hydrogen peroxide. Structurally, the analogues all adopt similar skewed structures, due to repulsion between adjacent lone pairs .
Hydrogen peroxide is produced by various biological processes mediated by enzymes .
Hydrogen peroxide has been detected in surface water, in groundwater, and in the atmosphere . It can also form when water is exposed to UV light. [ 16 ] Sea water contains 0.5 to 14 μg/L of hydrogen peroxide, and freshwater contains 1 to 30 μg/L. [ 17 ] Concentrations in air are about 0.4 to 4 μg/m 3 , varying over several orders of magnitude depending in conditions such as season, altitude, daylight and water vapor content. In rural nighttime air it is less than 0.014 μg/m 3 , and in moderate photochemical smog it is 14 to 42 μg/m 3 . [ 18 ]
The amount of hydrogen peroxide in biological systems can be assayed using a fluorometric assay . [ 19 ]
Alexander von Humboldt is sometimes said to have been the first to report the first synthetic peroxide, barium peroxide , in 1799 as a by-product of his attempts to decompose air, although this is disputed due to von Humboldt's ambiguous wording. [ 20 ] Nineteen years later Louis Jacques Thénard recognized that this compound could be used for the preparation of a previously unknown compound, which he described as eau oxygénée ("oxygenated water") — subsequently known as hydrogen peroxide. [ 21 ] [ 22 ] [ 23 ]
An improved version of Thénard's process used hydrochloric acid , followed by addition of sulfuric acid to precipitate the barium sulfate byproduct. This process was used from the end of the 19th century until the middle of the 20th century. [ 24 ]
The bleaching effect of peroxides and their salts on natural dyes had been known since Thénard's experiments in the 1820s, but early attempts of industrial production of peroxides failed. The first plant producing hydrogen peroxide was built in 1873 in Berlin . The discovery of the synthesis of hydrogen peroxide by electrolysis with sulfuric acid introduced the more efficient electrochemical method. It was first commercialized in 1908 in Weißenstein , Carinthia , Austria. The anthraquinone process , which is still used, was developed during the 1930s by the German chemical manufacturer IG Farben in Ludwigshafen . The increased demand and improvements in the synthesis methods resulted in the rise of the annual production of hydrogen peroxide from 35,000 tonnes in 1950, to over 100,000 tonnes in 1960, to 300,000 tonnes by 1970; by 1998 it reached 2.7 million tonnes. [ 17 ]
Early attempts failed to produce neat hydrogen peroxide. Anhydrous hydrogen peroxide was first obtained by vacuum distillation . [ 25 ]
Determination of the molecular structure of hydrogen peroxide proved to be very difficult. In 1892, the Italian physical chemist Giacomo Carrara (1864–1925) determined its molecular mass by freezing-point depression , which confirmed that its molecular formula is H 2 O 2 . [ 26 ] H 2 O=O seemed to be just as possible as the modern structure, and as late as in the middle of the 20th century at least half a dozen hypothetical isomeric variants of two main options seemed to be consistent with the available evidence. [ 27 ] In 1934, the English mathematical physicist William Penney and the Scottish physicist Gordon Sutherland proposed a molecular structure for hydrogen peroxide that was very similar to the presently accepted one. [ 28 ] [ 29 ]
In 1994, world production of H 2 O 2 was around 1.9 million tonnes and grew to 2.2 million in 2006, [ 30 ] most of which was at a concentration of 70% or less. In that year, bulk 30% H 2 O 2 sold for around 0.54 USD / kg , equivalent to US$1.50/kg (US$0.68/ lb ) on a "100% basis". [ 31 ] [ clarification needed ]
Today, hydrogen peroxide is manufactured almost exclusively by the anthraquinone process , which was originally developed by BASF in 1939. It begins with the reduction of an anthraquinone (such as 2-ethylanthraquinone or the 2-amyl derivative) to the corresponding anthrahydroquinone, typically by hydrogenation on a palladium catalyst . In the presence of oxygen , the anthrahydroquinone then undergoes autoxidation : the labile hydrogen atoms of the hydroxy groups transfer to the oxygen molecule, to give hydrogen peroxide and regenerating the anthraquinone. Most commercial processes achieve oxidation by bubbling compressed air through a solution of the anthrahydroquinone, with the hydrogen peroxide then extracted from the solution and the anthraquinone recycled back for successive cycles of hydrogenation and oxidation. [ 31 ] [ 32 ]
The net reaction for the anthraquinone-catalyzed process is: [ 31 ]
The economics of the process depend heavily on effective recycling of the extraction solvents, the hydrogenation catalyst and the expensive quinone .
Hydrogen peroxide was once prepared industrially by hydrolysis of ammonium persulfate :
[NH 4 ] 2 S 2 O 8 was itself obtained by the electrolysis of a solution of ammonium bisulfate ( [NH 4 ]HSO 4 ) in sulfuric acid . [ 33 ]
Small amounts are formed by electrolysis, photochemistry , electric arc , and related methods. [ 34 ]
A commercially viable route for hydrogen peroxide via the reaction of hydrogen with oxygen favours production of water but can be stopped at the peroxide stage. [ 35 ] [ 36 ] One economic obstacle has been that direct processes give a dilute solution uneconomic for transportation. None of these has yet reached a point where it can be used for industrial-scale synthesis.
Hydrogen peroxide is about 1000 times stronger as an acid than water. [ 37 ]
Hydrogen peroxide disproportionates to form water and oxygen with a Δ H o of −2884.5 kJ / kg [ 38 ] and a Δ S of 70.5 J/(mol·K):
The rate of decomposition increases with rise in temperature, concentration, and pH . H 2 O 2 is unstable under alkaline conditions. Decomposition is catalysed by various redox-active ions or compounds, including most transition metals and their compounds (e.g. manganese dioxide ( MnO 2 ), silver , and platinum ). [ 39 ]
The redox properties of hydrogen peroxide depend on pH. In acidic solutions, H 2 O 2 is a powerful oxidizer .
Sulfite ( SO 2− 3 ) is oxidized to sulfate ( SO 2− 4 ).
Under alkaline conditions, hydrogen peroxide is a reductant. When H 2 O 2 acts as a reducing agent, oxygen gas is also produced. For example, hydrogen peroxide will reduce sodium hypochlorite and potassium permanganate , which is a convenient method for preparing oxygen in the laboratory:
The oxygen produced from hydrogen peroxide and sodium hypochlorite is in the singlet state .
Hydrogen peroxide also reduces silver oxide to silver :
Although usually a reductant, alkaline hydrogen peroxide converts Mn(II) to the dioxide:
In a related reaction, potassium permanganate is reduced to Mn 2+ by acidic H 2 O 2 : [ 5 ]
Hydrogen peroxide is frequently used as an oxidizing agent . Illustrative is oxidation of thioethers to form sulfoxides , such as conversion of thioanisole to methyl phenyl sulfoxide : [ 40 ] [ 41 ]
Alkaline hydrogen peroxide is used for epoxidation of electron-deficient alkenes such as acrylic acid derivatives, [ 42 ] and for the oxidation of alkylboranes to alcohols , the second step of hydroboration-oxidation . It is also the principal reagent in the Dakin oxidation process.
Hydrogen peroxide is a weak acid, forming hydroperoxide or peroxide salts with many metals.
It also converts metal oxides into the corresponding peroxides. For example, upon treatment with hydrogen peroxide, chromic acid ( CrO 3 and H 2 SO 4 ) forms a blue peroxide CrO(O 2 ) 2 .
The aerobic oxidation of glucose in the presence of the enzyme glucose oxidase produces hydrogen peroxide. The conversion affords gluconolactone : [ 43 ]
Superoxide dismutases (SOD)s are enzymes that promote the disproportionation of superoxide into oxygen and hydrogen peroxide. [ 44 ]
Peroxisomes are organelles found in virtually all eukaryotic cells. [ 45 ] They are involved in the catabolism of very long chain fatty acids , branched chain fatty acids , D -amino acids , polyamines , and biosynthesis of plasmalogens and ether phospholipids , which are found in mammalian brains and lungs. [ 46 ] They produce hydrogen peroxide in a process catalyzed by flavin adenine dinucleotide (FAD): [ 47 ]
Hydrogen peroxide arises by the degradation of adenosine monophosphate , which yields hypoxanthine . Hypoxanthine is then oxidatively catabolized first to xanthine and then to uric acid , and the reaction is catalyzed by the enzyme xanthine oxidase : [ 48 ]
Hypoxanthine
Xanthine oxidase
Xanthine
Xanthine oxidase
Uric acid
The degradation of guanosine monophosphate yields xanthine as an intermediate product which is then converted in the same way to uric acid with the formation of hydrogen peroxide. [ 48 ]
Catalase , another peroxisomal enzyme, uses this H 2 O 2 to oxidize other substrates, including phenols , formic acid , formaldehyde , and alcohol , by means of a peroxidation reaction:
thus eliminating the poisonous hydrogen peroxide in the process.
This reaction is important in liver and kidney cells, where the peroxisomes neutralize various toxic substances that enter the blood. Some of the ethanol humans drink is oxidized to acetaldehyde in this way. [ 49 ] In addition, when excess H 2 O 2 accumulates in the cell, catalase converts it to H 2 O through this reaction:
Glutathione peroxidase , a selenoenzyme , also catalyzes the disproportionation of hydrogen peroxide.
The reaction of Fe 2+ and hydrogen peroxide is the basis of the Fenton reaction , which generates hydroxyl radicals , which are of significance in biology:
The Fenton reaction explains the toxicity of hydrogen peroxides because the hydroxyl radicals rapidly and irreversibly oxidize all organic compounds, including proteins , membrane lipids , and DNA . [ 50 ] Hydrogen peroxide is a significant source of oxidative DNA damage in living cells. DNA damage includes formation of 8-Oxo-2'-deoxyguanosine among many other altered bases, as well as strand breaks, inter-strand crosslinks, and deoxyribose damage. [ 51 ] By interacting with Cl − , hydrogen peroxide also leads to chlorinated DNA bases. [ 51 ] Hydroxyl radicals readily damage vital cellular components, especially those of the mitochondria . [ 52 ] [ 53 ] [ 54 ] The compound is a major factor implicated in the free-radical theory of aging , based on its ready conversion into a hydroxyl radical .
Eggs of sea urchin , shortly after fertilization by a sperm, produce hydrogen peroxide. It is then converted to hydroxyl radicals (HO•), which initiate radical polymerization , which surrounds the eggs with a protective layer of polymer .
The bombardier beetle combines hydroquinone and hydrogen peroxide, leading to a violent exothermic chemical reaction to produce boiling, foul-smelling liquid that partially becomes a gas ( flash evaporation ) and is expelled through an outlet valve with a loud popping sound. [ 55 ] [ 56 ] [ 57 ]
As a proposed signaling molecule , hydrogen peroxide may regulate a wide variety of biological processes. [ 58 ] [ 59 ] At least one study has tried to link hydrogen peroxide production to cancer. [ 60 ]
About 60% of the world's production of hydrogen peroxide is used for pulp- and paper-bleaching . [ 30 ] The second major industrial application is the manufacture of sodium percarbonate and sodium perborate , which are used as mild bleaches in laundry detergents . A representative conversion is:
Sodium percarbonate, which is an adduct of sodium carbonate and hydrogen peroxide, is the active ingredient in such laundry products as OxiClean and Tide laundry detergent . When dissolved in water, it releases hydrogen peroxide and sodium carbonate. [ 24 ] By themselves these bleaching agents are only effective at wash temperatures of 60 °C (140 °F) or above and so, often are used in conjunction with bleach activators , which facilitate cleaning at lower temperatures.
Hydrogen peroxide has also been used as a flour bleaching agent and a tooth and bone whitening agent.
It is used in the production of various organic peroxides with dibenzoyl peroxide being a high volume example. [ 61 ] Peroxy acids , such as peracetic acid and meta -chloroperoxybenzoic acid also are produced using hydrogen peroxide. Hydrogen peroxide has been used for creating organic peroxide -based explosives, such as acetone peroxide . It is used as an initiator in polymerizations . Hydrogen peroxide reacts with certain di- esters , such as phenyl oxalate ester (cyalume), to produce chemiluminescence ; this application is most commonly encountered in the form of glow sticks .
The reaction with borax leads to sodium perborate , a bleach used in laundry detergents:
Hydrogen peroxide is used in certain waste-water treatment processes to remove organic impurities. In advanced oxidation processing , the Fenton reaction [ 62 ] [ 63 ] gives the highly reactive hydroxyl radical (•OH). This degrades organic compounds, including those that are ordinarily robust, such as aromatic or halogenated compounds . [ 64 ] It can also oxidize sulfur -based compounds present in the waste; which is beneficial as it generally reduces their odour. [ 65 ]
Hydrogen peroxide may be used for the sterilization of various surfaces, [ 66 ] including surgical instruments, [ 67 ] and may be deployed as a vapour ( VHP ) for room sterilization. [ 68 ] H 2 O 2 demonstrates broad-spectrum efficacy against viruses, bacteria, yeasts, and bacterial spores. [ 69 ] [ 70 ] In general, greater activity is seen against Gram-positive than Gram-negative bacteria; however, the presence of catalase or other peroxidases in these organisms may increase tolerance in the presence of lower concentrations. [ 71 ] Lower levels of concentration (3%) will work against most spores; higher concentrations (7 to 30%) and longer contact times will improve sporicidal activity. [ 70 ] [ 72 ]
Hydrogen peroxide is seen as an environmentally safe alternative to chlorine -based bleaches, as it degrades to form oxygen and water and it is generally recognized as safe as an antimicrobial agent by the U.S. Food and Drug Administration (FDA). [ 73 ]
High-concentration H 2 O 2 is referred to as "high-test peroxide" (HTP). It can be used as either a monopropellant (not mixed with fuel) or the oxidizer component of a bipropellant rocket . Use as a monopropellant takes advantage of the decomposition of 70–98% concentration hydrogen peroxide into steam and oxygen. The propellant is pumped into a reaction chamber, where a catalyst, usually a silver or platinum screen, triggers decomposition, producing steam at over 600 °C (1,100 °F), which is expelled through a nozzle , generating thrust . H 2 O 2 monopropellant produces a maximal specific impulse ( I sp ) of 161 s (1.6 kN·s /kg). Peroxide was the first major monopropellant adopted for use in rocket applications. Hydrazine eventually replaced hydrogen peroxide monopropellant thruster applications primarily because of a 25% increase in the vacuum specific impulse. [ 74 ] Hydrazine (toxic) and hydrogen peroxide (less toxic [ACGIH TLV 0.01 and 1 ppm respectively]) are the only two monopropellants (other than cold gases) to have been widely adopted and utilized for propulsion and power applications. [ citation needed ] The Bell Rocket Belt , reaction control systems for X-1 , X-15 , Centaur , Mercury , Little Joe , as well as the turbo-pump gas generators for X-1, X-15, Jupiter, Redstone and Viking used hydrogen peroxide as a monopropellant. [ 75 ] The RD-107 engines (used from 1957 to present) in the R-7 series of rockets decompose hydrogen peroxide to power the turbopumps.
In bipropellant applications, H 2 O 2 is decomposed to oxidize a burning fuel. Specific impulses as high as 350 s (3.5 kN·s/kg) can be achieved, depending on the fuel. Peroxide used as an oxidizer gives a somewhat lower I sp than liquid oxygen but is dense, storable, and non-cryogenic and can be more easily used to drive gas turbines to give high pressures using an efficient closed cycle . It may also be used for regenerative cooling of rocket engines. Peroxide was used very successfully as an oxidizer in World War II German rocket motors (e.g., T-Stoff , containing oxyquinoline stabilizer, for both the Walter HWK 109-500 Starthilfe RATO externally podded monopropellant booster system and the Walter HWK 109-509 rocket motor series used for the Me 163 B), most often used with C-Stoff in a self-igniting hypergolic combination, and for the low-cost British Black Knight and Black Arrow launchers. Presently, HTP is used on ILR-33 AMBER [ 76 ] and Nucleus [ 77 ] suborbital rockets.
In the 1940s and 1950s, the Hellmuth Walter KG –conceived turbine used hydrogen peroxide for use in submarines while submerged; it was found to be too noisy and require too much maintenance compared to diesel-electric power systems. Some torpedoes used hydrogen peroxide as oxidizer or propellant. Operator error in the use of hydrogen peroxide torpedoes was named as possible causes for the sinking of HMS Sidon and the Russian submarine Kursk . [ 78 ] SAAB Underwater Systems is manufacturing the Torpedo 2000. This torpedo, used by the Swedish Navy , is powered by a piston engine propelled by HTP as an oxidizer and kerosene as a fuel in a bipropellant system. [ 79 ] [ 80 ]
Hydrogen peroxide has various domestic uses, primarily as a cleaning and disinfecting agent.
Diluted H 2 O 2 (between 1.9% and 12%) mixed with aqueous ammonia has been used to bleach human hair . The chemical's bleaching property lends its name to the phrase " peroxide blonde ". [ 81 ] Hydrogen peroxide is also used for tooth whitening . It may be found in most whitening toothpastes. Hydrogen peroxide has shown positive results involving teeth lightness and chroma shade parameters. [ 82 ] It works by oxidizing colored pigments onto the enamel where the shade of the tooth may become lighter. [ further explanation needed ] Hydrogen peroxide may be mixed with baking soda and salt to make a homemade toothpaste. [ 83 ]
Hydrogen peroxide reacts with blood as a bleaching agent, and so if a blood stain is fresh, or not too old, liberal application of hydrogen peroxide, if necessary in more than single application, will bleach the stain fully out. After about two minutes of the application, the blood should be firmly blotted out. [ 84 ] [ 85 ]
Hydrogen peroxide may be used to treat acne , [ 86 ] although benzoyl peroxide is a more common treatment.
The use of dilute hydrogen peroxide as an oral cleansing agent has been reviewed academically to determine its usefulness in treating gingivitis and plaque . Although there is a positive effect when compared with a placebo, it was concluded that chlorhexidine is a much more effective treatment. [ 87 ]
Some horticulturists and users of hydroponics advocate the use of weak hydrogen peroxide solution in watering solutions. Its spontaneous decomposition releases oxygen that enhances a plant's root development and helps to treat root rot (cellular root death due to lack of oxygen) and a variety of other pests. [ 88 ] [ 89 ]
For general watering concentrations, around 0.1% is in use. This can be increased up to one percent for antifungal actions. [ 90 ] Tests show that plant foliage can safely tolerate concentrations up to 3%. [ 91 ]
Hydrogen peroxide is used in aquaculture for controlling mortality caused by various microbes. In 2019, the U.S. FDA approved it for control of Saprolegniasis in all coldwater finfish and all fingerling and adult coolwater and warmwater finfish, for control of external columnaris disease in warm-water finfish, and for control of Gyrodactylus spp. in freshwater-reared salmonids. [ 92 ] Laboratory tests conducted by fish culturists have demonstrated that common household hydrogen peroxide may be used safely to provide oxygen for small fish. The hydrogen peroxide releases oxygen by decomposition when it is exposed to catalysts such as manganese dioxide .
Hydrogen peroxide may be used in combination with a UV-light source to remove yellowing from white or light grey acrylonitrile butadiene styrene (ABS) plastics to partially or fully restore the original color. In the retrocomputing scene, this process is commonly referred to as retrobright .
Regulations vary, but low concentrations, such as 5%, are widely available and legal to buy for medical use. Most over-the-counter peroxide solutions are not suitable for ingestion. Higher concentrations may be considered hazardous and typically are accompanied by a safety data sheet (SDS). In high concentrations, hydrogen peroxide is an aggressive oxidizer and will corrode many materials, including human skin. In the presence of a reducing agent , high concentrations of H 2 O 2 will react violently. [ 93 ] While concentrations up to 35% produce only "white" oxygen bubbles in the skin (and some biting pain) that disappear with the blood within 30–45 minutes, concentrations of 98% dissolve paper. However, concentrations as low as 3% can be dangerous for the eye because of oxygen evolution within the eye. [ 94 ]
High-concentration hydrogen peroxide streams, typically above 40%, should be considered hazardous due to concentrated hydrogen peroxide's meeting the definition of a DOT oxidizer according to U.S. regulations if released into the environment. The EPA Reportable Quantity (RQ) for D001 hazardous wastes is 100 pounds (45 kg), or approximately 10 US gallons (38 L), of concentrated hydrogen peroxide.
Hydrogen peroxide should be stored in a cool, dry, well-ventilated area and away from any flammable or combustible substances. It should be stored in a container composed of non-reactive materials such as stainless steel or glass (other materials including some plastics and aluminium alloys may also be suitable). [ 95 ] As it breaks down quickly when exposed to light, it should be stored in an opaque container, and pharmaceutical formulations typically come in brown bottles that block light. [ 96 ]
Hydrogen peroxide, either in pure or diluted form, may pose several risks, the main one being that it forms explosive mixtures upon contact with organic compounds. [ 97 ] Distillation of hydrogen peroxide at normal pressures is highly dangerous. It is corrosive, especially when concentrated, but even domestic-strength solutions may cause irritation to the eyes, mucous membranes , and skin. [ 98 ] Swallowing hydrogen peroxide solutions is particularly dangerous, as decomposition in the stomach releases large quantities of gas (ten times the volume of a 3% solution), leading to internal bloating. Inhaling over 10% can cause severe pulmonary irritation. [ 99 ]
With a significant vapour pressure (1.2 kPa at 50 °C), [ 100 ] hydrogen peroxide vapour is potentially hazardous. According to U.S. NIOSH, the immediately dangerous to life and health (IDLH) limit is only 75 ppm. [ 101 ] The U.S. Occupational Safety and Health Administration (OSHA) has established a permissible exposure limit of 1.0 ppm calculated as an 8-hour time-weighted average (29 CFR 1910.1000, Table Z-1). [ 97 ] Hydrogen peroxide has been classified by the American Conference of Governmental Industrial Hygienists (ACGIH) as a "known animal carcinogen, with unknown relevance on humans". [ 102 ] For workplaces where there is a risk of exposure to the hazardous concentrations of the vapours, continuous monitors for hydrogen peroxide should be used. Information on the hazards of hydrogen peroxide is available from OSHA [ 97 ] and from the ATSDR. [ 103 ]
Historically, hydrogen peroxide was used for disinfecting wounds, partly because of its low cost and prompt availability compared to other antiseptics . [ 104 ]
There is conflicting evidence on hydrogen peroxide's effect on wound healing. Some research finds benefit, while other research find delays and healing inhibition. [ 105 ] Its use for home treatment of wounds is generally not recommended. [ 106 ] 1.5–3% hydrogen peroxide is used as a disinfectant in dentistry, especially in endodotic treatments together with hypochlorite and chlorhexidine and 1–1.5% is also useful for treatment of inflammation of third molars (wisdom teeth). [ 107 ]
Practitioners of alternative medicine have advocated the use of hydrogen peroxide for various conditions, including emphysema , influenza , AIDS , and in particular cancer . [ 108 ] There is no evidence of effectiveness and in some cases it has proved fatal. [ 109 ] [ 110 ] [ 111 ] [ 112 ]
Both the effectiveness and safety of hydrogen peroxide therapy is scientifically questionable. Hydrogen peroxide is produced by the immune system, but in a carefully controlled manner. Cells called phagocytes engulf pathogens and then use hydrogen peroxide to destroy them. The peroxide is toxic to both the cell and the pathogen and so is kept within a special compartment, called a phagosome . Free hydrogen peroxide will damage any tissue it encounters via oxidative stress , a process that also has been proposed as a cause of cancer. [ 113 ] Claims that hydrogen peroxide therapy increases cellular levels of oxygen have not been supported. The quantities administered would be expected to provide very little additional oxygen compared to that available from normal respiration. It is also difficult to raise the level of oxygen around cancer cells within a tumour, as the blood supply tends to be poor, a situation known as tumor hypoxia .
Large oral doses of hydrogen peroxide at a 3% concentration may cause irritation and blistering to the mouth, throat, and abdomen as well as abdominal pain, vomiting, and diarrhea. [ 109 ] Ingestion of hydrogen peroxide at concentrations of 35% or higher has been implicated as the cause of numerous gas embolism events resulting in hospitalisation. In these cases, hyperbaric oxygen therapy was used to treat the embolisms. [ 114 ]
Intravenous injection of hydrogen peroxide has been linked to several deaths. [ 115 ] [ 111 ] [ 112 ] The American Cancer Society states that "there is no scientific evidence that hydrogen peroxide is a safe, effective, or useful cancer treatment." [ 110 ] Furthermore, the therapy is not approved by the U.S. FDA.
Bibliography | https://en.wikipedia.org/wiki/Hydrogen_peroxide |
Hydrogen peroxide–urea (also called Hyperol , artizone , urea hydrogen peroxide , and UHP ) is a white crystalline solid chemical compound composed of equimolar amounts of hydrogen peroxide and urea . It contains solid and water -free hydrogen peroxide, which offers a higher stability and better controllability than liquid hydrogen peroxide when used as an oxidizing agent . Often called carbamide peroxide in dentistry , it is used as a source of hydrogen peroxide when dissolved in water for bleaching , disinfection and oxidation .
For the preparation of the complex, urea is dissolved in 30% hydrogen peroxide (molar ratio 2:3) at temperatures below 60 °C. upon cooling this solution, hydrogen peroxide–urea precipitates out in the form of small platelets. [ 2 ]
Akin to water of crystallization , hydrogen peroxide cocrystallizes with urea with the stoichiometry of 1:1. The compound is simply produced (on a scale of several hundred tonnes a year) by the dissolution of urea in excess concentrated hydrogen peroxide solution, followed by crystallization . [ 3 ] The laboratory synthesis is analogous. [ 4 ]
The solid state structure of this adduct has been determined by neutron diffraction . [ 5 ]
Hydrogen peroxide–urea is a readily water-soluble, odorless, crystalline solid, which is available as white powder or colorless needles or platelets. [ 2 ] Upon dissolving in various solvents, the 1:1 complex dissociates back to urea and hydrogen peroxide. So just like hydrogen peroxide , the (erroneously) so-called adduct is an oxidizer but the release at room temperature in the presence of catalysts proceeds in a controlled manner. Thus the compound is suitable as a safer substitute for the unstable aqueous solution of hydrogen peroxide. Because of the tendency for thermal decomposition, which accelerates at temperatures above 82 °C, [ 6 ] it should not be heated above 60 °C, particularly in pure form.
The solubility of commercial samples varies from 0.05 g/mL [ 7 ] to more than 0.6 g/mL. [ 8 ]
Hydrogen peroxide–urea is mainly used as a disinfecting and bleaching agent in cosmetics and pharmaceuticals. [ 3 ] As a drug, this compound is used in some preparations for the whitening of teeth . [ 3 ] [ 9 ] [ 10 ] It is also used to relieve minor inflammation of gums, oral mucosal surfaces and lips including canker sores and dental irritation, [ 11 ] and to emulsify and disperse earwax . [ 12 ]
Carbamide peroxide is also suitable as a disinfectant, e.g. for germ reduction on contact lens surfaces or as an antiseptic for mouthwashes , ear drops or for superficial wounds and ulcers .
In the laboratory, it is used as a more easily handled replacement for hydrogen peroxide . [ 4 ] [ 13 ] [ 14 ] It has proven to be a stable, easy-to-handle and effective oxidizing agent which is readily controllable by a suitable choice of the reaction conditions. It delivers oxidation products in an environmentally friendly manner and often in high yields especially in the presence of organic catalysts such as cis -butenedioic anhydride [ 15 ] or inorganic catalysts such as sodium tungstate . [ 16 ]
It converts thiols selectively to disulfides, [ 15 ] secondary alcohols to ketones, [ 16 ] sulfides to sulfoxides and sulfones, [ 17 ] nitriles to amides, [ 17 ] [ 18 ] and N -heterocycles to amine oxides . [ 17 ] [ 19 ]
Hydroxybenzaldehydes are converted to dihydroxybenzenes ( Dakin reaction ) [ 17 ] [ 20 ] and give, under suitable conditions, the corresponding benzoic acids. [ 20 ]
It oxidizes ketones to esters, in particular cyclic ketones, such as substituted cyclohexanones [ 21 ] or cyclobutanones [ 22 ] to give lactones ( Baeyer–Villiger oxidation ).
The epoxidation of various alkenes in the presence of benzonitrile yields oxiranes in yields of 79 to 96%. [ 23 ]
The oxygen atom transferred to the alkene originates from the peroxoimide acid formed intermediately from benzonitrile. The resulting imidic acid tautomerizes to the benzamide.
The compound acts as a strong oxidizing agent and can cause skin irritation and severe eye damage. [ 24 ] Urea–hydrogen peroxide was also found to be an insensitive but powerful secondary explosive . [ 25 ] [ 26 ] | https://en.wikipedia.org/wiki/Hydrogen_peroxide–urea |
Hydrogen pinch analysis (HPA) is a hydrogen management method that originates from the concept of heat pinch analysis . HPA is a systematic technique for reducing hydrogen consumption and hydrogen generation through integration of hydrogen-using activities or processes in the petrochemical industry , petroleum refineries hydrogen distribution networks and hydrogen purification. [ 1 ]
A mass analysis is done by representing the purity and flowrate for each stream from the hydrogen consumers (sinks), such as hydrotreaters , hydrocrackers , isomerization units and lubricant plants and the hydrogen producers (sources), such as hydrogen plants and naphtha reformers, streams from hydrogen purifiers , membrane reactors , pressure swing adsorption and continuous distillation and off-gas streams from low- or high-pressure separators. The source-demand diagram shows bottlenecks, surplus or shortages. The hydrogen pinch is the purity at which the hydrogen network has neither hydrogen surplus nor deficit. [ 2 ]
After the analysis REFOPT from the Centre for Process Integration at The University of Manchester is used as a tool for process integration with which the process is optimized. [ 3 ] The methodology was also developed into commercial software by companies such as Linnhoff March and AspenTech . The Aspen product incorporated the work of Nick Hallale (formerly a lecturer at University of Manchester) and was the first method to consider multiple components, rather than a pseudo-binary mixture of hydrogen and methane.
The first assessment based on cost and value composite curves of hydrogen resources of a hydrogen network was proposed by Tower et al. (1996). Alves developed the hydrogen pinch analysis approach based on the concept of heat pinch analysis in 1999. [ 4 ] Nick Hallale and Fang Liu extended this original work, adding pressure constraints and mathematical programming for optimisation. This was followed by developments at AspenTech, producing commercial software for industrial application.
Nick Hallale, Ian Moore, Dennis Vauk, "Hydrogen optimization at minimal investment", Petroleum Technology Quarterly (PTQ), Spring (2003) | https://en.wikipedia.org/wiki/Hydrogen_pinch |
Hydrogen purification is any technology used to purify hydrogen . The impurities in hydrogen gas depend on the source of the H2, e.g., petroleum, coal, electrolysis, etc. The required purity is determined by the application of the hydrogen gas. For example, ultra-high purified hydrogen is needed for applications like proton exchange membrane fuel cells . [ 1 ]
The default large-scale purification of H 2 produced in oil refineries exploits its very low boiling point of −253 °C. Most impurities have boiling points well above this temperature. Low temperature methods can be complemented by scrubbing to remove particular impurities. [ 1 ]
Hydrogen can be purified by passing through a membrane composed of palladium and silver . Permeability of the former to hydrogen was discovered back in the 1860s. [ 2 ] An alloy with a ca. 3:1 ratio for Pd:Ag is more structural robust than pure Pd, which is the active component that allows the selective diffusion of H 2 through it. Diffusion is faster near 300 °C. This method has been used for purification of hydrogen on a laboratory scale, but not in industry. Silver-palladium membranes are unstable toward alkenes and sulfur-containing compounds. [ 1 ]
Dense thin-metal membrane purifiers are compact, relatively inexpensive and simple to use. [ 3 ] [ 4 ]
Pressure swing adsorption is used for the removal of carbon dioxide (CO 2 ) as the final step in the large-scale commercial synthesis of hydrogen . It can also remove methane , carbon monoxide , nitrogen , moisture and in some cases, argon , from hydrogen.
Hydrogen purifiers are used in metalorganic vapour phase epitaxy reactors for LED production. [ 5 ]
Fuel cell electric vehicles commonly use polymer electrolyte membrane fuel cells (PEMFC) that are susceptible to a range of impurities. Impurities impact PEMFC using a range of mechanisms, these may include poisoning the anode hydrogen oxidation reaction catalysts, reducing the ionic conductivity of the ionomer and membrane, altering wetting behaviour of components or blocking porosity in diffusion media. The impact of some impurities like carbon monoxide , formic acid , or formaldehyde is reversible with PEMFC performance recovering once the supply of impurity is removed. Other impurities, for example sulphurous compounds, may cause irreversible degradation. [ 6 ] The permissible limits of hydrogen impurities are shown below.
Efforts to assess the compliance of hydrogen supplied by hydrogen refuelling stations against the ISO-14687 standard have been performed. [ 8 ] [ 9 ] [ 10 ] While the hydrogen was generally found to be 'good' [ 8 ] violations of the standard have been reported, most frequently for nitrogen, water and oxygen.
Combustion applications are generally more tolerant of hydrogen impurities than PEFMC, as such the ISO-14687 standard for permissible impurities is less strict. [ 11 ] This standard has itself been criticised with revisions proposed to make it more lenient and therefore suitable for hydrogen distributed through a repurposed gas network. [ 12 ]
The presence of impurities in hydrogen depends on the feedstock and the production process. Hydrogen produced by electrolysis of water may routinely include trace oxygen and water. Hydrogen produced by reforming of hydrocarbons contains carbon dioxide and carbon monoxide as well as sulphur compounds. [ 12 ] Some impurities may be added deliberately, for example odorants to aid detection of gas leaks. [ 14 ]
As the permissible concentrations for many impurities are very low this sets stringent demands on the sensitivity of the analytical methods. Moreover, the high reactivity of some impurities requires use of a properly passivated sampling and analytical systems. [ 15 ] Sampling of hydrogen of is challenging and care must be taken to ensure that impurities are not introduced to the sample and that impurities do not absorb on or react within the sampling equipment, there are currently different methods for sampling but rely on filling a gas cylinder from the refuelling nozzle of a refuelling station. [ 16 ] Efforts are underway to standardise and compare sampling strategies. [ 17 ] [ 18 ] A combination of different instruments is needed to assess hydrogen samples for all of the components listed in ISO 14687-2. [ 19 ] Techniques suitable for individual impurities are indicated in the table below.
or CRDS
Techniques such as electrochemical sensors [ 22 ] [ 23 ] and mass spectrometry. [ 24 ] | https://en.wikipedia.org/wiki/Hydrogen_purification |
Hydrogen selenide is an inorganic compound with the formula H 2 Se. This hydrogen chalcogenide is the simplest and most commonly encountered hydride of selenium . H 2 Se is a colorless, flammable gas under standard conditions. It is the most toxic selenium compound [ 3 ] with an exposure limit of 0.05 ppm over an 8-hour period. [ 4 ] [ 5 ] Even at extremely low concentrations, this compound has a very irritating smell resembling that of decayed horseradish or "leaking gas", but smells of rotten eggs at higher concentrations.
H 2 Se adopts a bent structure with a H−Se−H bond angle of 91° [ citation needed ] . Consistent with this structure, three IR -active vibrational bands are observed: 2358, 2345, and 1034 cm −1 . [ 6 ]
The properties of H 2 S and H 2 Se are similar, although the selenide is more acidic with p K a = 3.89 and the second p K a = 11, [ 6 ] or 15.05 ± 0.02 at 25 °C. [ 7 ]
Industrially, it is produced by treating elemental selenium at T > 300 °C with hydrogen gas. [ 8 ] A number of routes to H 2 Se have been reported, which are suitable for both large and small scale preparations. In the laboratory, H 2 Se is usually prepared by the action of water on Al 2 Se 3 , concomitant with formation of hydrated alumina . A related reaction involves the acid hydrolysis of FeSe. [ 9 ]
H 2 Se can also be prepared by means of different methods based on the in situ generation in aqueous solution using boron hydride , Marsh test and Devarda's alloy . According to the Sonoda method, H 2 Se is generated from the reaction of H 2 O and CO on Se in the presence of Et 3 N . [ 10 ] H 2 Se can be purchased in cylinders.
Elemental selenium can be recovered from H 2 Se through a reaction with aqueous sulfur dioxide (SO 2 ).
Its decomposition is used to prepare the highly pure element.
H 2 Se is commonly used in the synthesis of Se-containing compounds. It adds across alkenes. Illustrative is the synthesis of selenoureas from cyanamides : [ 11 ]
H 2 Se gas is used to dope semiconductors with selenium.
Hydrogen selenide is hazardous, being the most toxic selenium compound [ 3 ] and far more toxic than its congener hydrogen sulfide . The threshold limit value is 0.05 ppm. The gas acts as an irritant at concentrations higher than 0.3 ppm, which is the main warning sign of exposure; below 1 ppm, this is "insufficient to prevent exposure", while at 1.5 ppm the irritation is "intolerable". [ 5 ] Exposure at high concentrations, even for less than a minute, causes the gas to attack the eyes and mucous membranes; this causes cold-like symptoms for at least a few days afterwards. In Germany, the limit in drinking water is 0.008 mg/L, and the US EPA recommends a maximum contamination of 0.01 mg/L. [ 8 ] [ 12 ]
Despite being extremely toxic, no human fatalities have yet been reported. It is suspected that this is due to the gas' tendency to oxidise to form red selenium in mucous membranes; elemental selenium is less toxic than selenides are. [ 4 ] | https://en.wikipedia.org/wiki/Hydrogen_selenide |
A hydrogen sensor is a gas detector that detects the presence of hydrogen . They contain micro-fabricated point-contact hydrogen sensors and are used to locate hydrogen leaks. They are considered low-cost, compact, durable, and easy to maintain as compared to conventional gas detecting instruments. [ 1 ]
There are five key issues with hydrogen detectors: [ 2 ]
There are various types of hydrogen microsensors, which use different mechanisms to detect the gas. [ 4 ] Palladium is used in many of these, because it selectively absorbs hydrogen gas and forms the compound palladium hydride . [ 5 ] Palladium-based sensors have a strong temperature dependence which makes their response time too large at very low temperatures. [ 6 ] Palladium sensors have to be protected against carbon monoxide , sulfur dioxide and hydrogen sulfide .
Several types of optical fibre surface plasmon resonance (SPR) sensor are used for the point-contact detection of hydrogen:
Sensors are typically calibrated at the manufacturing factory and are valid for the service life of the unit.
Siloxane enhances the sensitivity and reaction time of hydrogen sensors. [ 5 ] Detection of hydrogen levels as low as 25 ppm can be achieved; far below hydrogen's lower explosive limit of around 40,000 ppm. | https://en.wikipedia.org/wiki/Hydrogen_sensor |
In heterogeneous catalysis , hydrogen molecules can be adsorbed and dissociated by the metal catalyst. Hydrogen spillover is the migration of hydrogen atoms from the metal catalyst onto the nonmetal support or adsorbate. [ 1 ] [ 2 ] Spillover , generally, is the transport of a species adsorbed or formed on a surface onto another surface. [ 3 ] Hydrogen spillover can be characterized by three major steps, the first being where molecular hydrogen is split via dissociative chemisorption into its constitutive atoms on a transition metal catalyst surface, followed by migration from the catalyst to the substrate, culminating in their diffusion throughout the substrate surfaces and/or in the bulk materials. [ 4 ]
The mechanism behind hydrogen spillover has been long disputed. [ 5 ] Khoobiar’s work in 1964 marks the nascency of the spillover concept. [ 3 ] In his findings, yellow WO 3 can be reduced by H 2 to a blue compound with the use of a platinum catalyst. [ 3 ] Since the phenomenon was not found when using Al 2 O 3 as the catalyst, he claimed that the dissociative chemisorption of H 2 molecules on the Pt particles created hydrogen atoms. [ 3 ] The hydrogen atoms migrated from the Pt surface to the WO 3 particles and reduced them to blue WO 3−x particles. [ 3 ]
Essentially, hydrogen atoms would migrate from a hydrogen-rich to a hydrogen-poor surface. [ 3 ] However, these atoms are usually not generated on the surface of a support metal. [ 3 ] Hence, the two conditions for hydrogen spillover include the creation of hydrogen atoms (requires catalysts capable of dissociating and absorbing hydrogen) and the ability of hydrogen atoms to be transported.
Attempts to characterize the mechanism of hydrogen spillover have seen the use of radiation photoelectron spectroscopy to analyze the shift between different oxidation states of the support (commonly metal oxides) via their respective emission spectra . [ 6 ] In general, the mechanism is thought to proceed via the transfer of neutral hydrogen atoms to the support upon overcoming an activation energy barrier. [ 6 ] This has even been observed at temperatures as low as 180K in metal-organic framework (MOF) catalysts laced with Palladium nanoparticles (PdnP’s). [ 5 ] Upon transfer to the support, they assume the role of Lewis bases where they donate electrons and reversibly reduce the sorbent. [ 5 ] Additionally, the hydrodesulfurization of dibenzothiophene show that hydroxyl groups seem to favor the migration of spillover hydrogen, whereas sodium cations may trap the spillover hydrogen and are detrimental to hydrogenation pathway. [ 7 ]
Recently the mechanism of hydrogen spillover has been described using a precisely nanofabricated model system and single-particle spectromicroscopy . [ 1 ] Occurrence of hydrogen spillover on reducible supports such as titanium oxide is established, yet questions remain about whether hydrogen spillover can take place on nonreducible supports such as aluminium oxide . The study shows a convincing proof of the spillover effect at well-defined distances away from the metal catalyst explaining why hydrogen spillover is slower on an aluminum oxide catalyst support than on a titanium oxide catalyst support. The results reveal that hydrogen spillover is fast and efficient on titanium oxide, and extremely slow and short-ranged on aluminium oxide. A recent study has shown that the metal oxide supports that are able to perform hydrogen spillover can catalyze hydrogenation reactions more efficiently (even at room temperature) by supported Pd catalysts. [ 8 ]
Hydrogen spillover increases with adsorption temperature and metal dispersion. [ 9 ] A correlation has been reported between available surface area and the capacity for hydrogen storage . For PdnP-containing MOFs, in the presence of saturated metal particles, the capacity for hydrogen spillover only relied on the sorbent’s surface area and pore size. [ 6 ] On catalysts such as platinum or nickel, atomic hydrogen can be generated at a high frequency. [ 9 ] Through surface diffusion, multi-functional transport of hydrogen atoms can enhance a reaction and even regenerate a catalyst. [ 9 ] However, problems present in the strength of the hydrogen-support bond; too strong of an interaction would hinder its extraction via reverse spillover and nullify its function as a fuel cell. [ 6 ] Conversely, too weak a bond and the hydrogens are easily lost to the environment. [ 5 ]
With burgeoning interest in alternative energy sources, the prospect of hydrogen’s role as a fuel has become a major driving force for the optimization of storage methods, particularly at ambient temperatures where their application would be more practical for common use. [ 5 ] [ 10 ] Hydrogen spillover has emerged as a possible technique for achieving high-density hydrogen storage at near-ambient conditions in lightweight, solid-state materials as adsorbents. [ 4 ] [ 11 ] Hydrogen storage in carbon materials can be significantly enhanced by spillover techniques. [ 12 ] [ 13 ] Current trends include the use of metal-organic frameworks (MOFs) and other porous materials with high surface area for such storage, including but not exclusive to nanocarbons (e.g. graphene , carbon nanotubes ), [ 10 ] [ 11 ] zeolites , and nanostructured materials. [ 11 ] Hydrogen atom diffusion on nanostructured graphitic carbon materials is primarily governed by physisorption of hydrogen atoms. [ 4 ] Singled-walled nanotubes and multi-walled nanotubes are the best acceptor of spilt over hydrogen atoms. [ 11 ]
Another recent study has shown that the synthesis of methanol from both CO and CO 2 over Cu/ZrO 2 involves the spillover of H atoms formed on Cu to the surface of ZrO 2 . [ 14 ] The atomic H then participates in the hydrogenation of carbon-containing species to methanol. [ 14 ] | https://en.wikipedia.org/wiki/Hydrogen_spillover |
Several methods exist for storing hydrogen . These include mechanical approaches such as using high pressures and low temperatures, or employing chemical compounds that release H 2 upon demand. While large amounts of hydrogen are produced by various industries, it is mostly consumed at the site of production, notably for the synthesis of ammonia . For many years hydrogen has been stored as compressed gas or cryogenic liquid, and transported as such in cylinders, tubes, and cryogenic tanks for use in industry or as propellant in space programs. The overarching challenge is the very low boiling point of H 2 : it boils around 20.268 K (−252.882 °C or −423.188 °F). Achieving such low temperatures requires expending significant energy.
Although molecular hydrogen has very high energy density on a mass basis, partly because of its low molecular weight , as a gas at ambient conditions it has very low energy density by volume. If it is to be used as fuel stored on board a vehicle, pure hydrogen gas must be stored in an energy-dense form to provide sufficient driving range. Because hydrogen is the smallest molecule, it easily escapes from containers. Its effective 100-year global warming potential (GWP100) is estimated to be 11.6 ± 2.8.
Compressed hydrogen is a storage form whereby hydrogen gas is kept under pressures to increase the storage density. Compressed hydrogen in hydrogen tanks at 350 bar (5,000 psi) and 700 bar (10,000 psi) are used for hydrogen tank systems in vehicles, based on type IV carbon-composite technology. [ clarification needed ] [ 1 ] Car manufacturers including Honda [ 2 ] and Nissan [ 3 ] have been developing this solution.
Liquid hydrogen tanks for cars, producing for example the BMW Hydrogen 7 . Japan has a liquid hydrogen (LH2) storage site in Kobe port. [ 4 ] Hydrogen is liquefied by reducing its temperature to −253 °C, similar to liquefied natural gas (LNG) which is stored at −162 °C. A potential efficiency loss of only 12.79% can be achieved, or 4.26 kW⋅h/kg out of 33.3 kW⋅h/kg. [ 5 ]
Chemical storage could offer high storage performance due to the high storage densities. For example, supercritical hydrogen at 30 °C and 500 bar only has a density of 15.0 mol/L while methanol has a hydrogen density of 49.5 mol H 2 /L methanol and saturated dimethyl ether at 30 °C and 7 bar has a density of 42.1 mol H 2 /L dimethyl ether. [ citation needed ]
Regeneration of storage material is problematic. A large number of chemical storage systems have been investigated. H 2 release can be induced by hydrolysis reactions or catalyzed dehydrogenation reactions . Illustrative storage compounds are hydrocarbons, boron hydrides , ammonia , and alane etc. [ 7 ] A most promising chemical approach is electrochemical hydrogen storage, as the release of hydrogen can be controlled by the applied electricity. [ 8 ] Most of the materials listed below can be directly used for electrochemical hydrogen storage.
Nanomaterials , particularly those produced by ball mill and severe plastic deformation , offer an alternative that overcomes the two major barriers of bulk materials, rate of sorption and activation. [ 9 ] High-entropy alloy materials such as TiZrCrMnFeNi also show advantages of fast and reversible hydrogen storage at room temperature with good storage capacity for stationary applications. [ 10 ] [ 11 ]
Enhancement of sorption kinetics and storage capacity can be improved through nanomaterial-based catalyst doping, as shown in the work of the Clean Energy Research Center in the University of South Florida . [ 12 ] This research group studied LiBH 4 doped with nickel nanoparticles and analyzed the weight loss and release temperature of the different species. They observed that an increasing amount of nanocatalyst lowers the release temperature by approximately 20 °C and increases the weight loss of the material by 2-3%. The optimum amount of Ni particles was found to be 3 mol%, for which the temperature was within the limits established (around 100 °C) and the weight loss was notably greater than the undoped species.
The rate of hydrogen sorption improves at the nanoscale due to the short diffusion distance in comparison to bulk materials. They also have favorable surface-area-to-volume ratio .
The release temperature of a material is defined as the temperature at which the desorption process begins. The energy or temperature to induce release affects the cost of any chemical storage strategy. If the hydrogen is bound too weakly, the pressure needed for regeneration is high, thereby cancelling any energy savings. The target for onboard hydrogen fuel systems is roughly <100 °C for release and <700 bar for recharge (20–60 kJ/mol H 2 ). [ 13 ] A modified van 't Hoff equation , relates temperature and partial pressure of hydrogen during the desorption process. The modifications to the standard equation are related to size effects at the nanoscale.
ln ( p H 2 ) = Δ H ( r ) R T + 3 V m γ r R T + Δ S ( r ) R {\displaystyle \ln(p_{\mathrm {H_{\mathrm {2} }} })={\frac {\Delta H(r)}{RT}}+{\frac {3V_{\mathrm {m} }\gamma }{rRT}}+{\frac {\Delta S(r)}{R}}}
Where p H 2 is the partial pressure of hydrogen, Δ H is the enthalpy of the sorption process (exothermic), Δ S is the change in entropy , R is the ideal gas constant , T is the temperature in Kelvin, V m is the molar volume of the metal, r is the radius of the nanoparticle and γ is the surface free energy of the particle.
From the above relation we see that the enthalpy and entropy change of desorption processes depend on the radius of the nanoparticle. Moreover, a new term is included that takes into account the specific surface area of the particle and it can be mathematically proven that a decrease in particle radius leads to a decrease in the release temperature for a given partial pressure. [ 14 ]
Current approach to reduce CO 2 includes capturing and storing from facilities across the world. However, storage poses technical and economic barriers preventing global scale application. To utilize CO 2 at the point source, CO 2 hydrogenation is a realistic and practical approach. Conventional hydrogenation reduces unsaturated organic compounds by addition of H 2 . One method of CO 2 hydrogenation is via the methanol pathway. Methanol can be used to produce long chain hydrocarbons. Some barriers of CO 2 hydrogenation includes purification of captured CO 2 , H 2 source from splitting water and energy inputs for hydrogenation. For industrial applications, CO 2 is often converted to methanol. Until now, much progress has been made for CO 2 to C1 molecules. However, CO 2 to high value molecules still face many roadblocks and the future of CO 2 hydrogenation depends on the advancement of catalytic technologies. [ 15 ]
Metal hydrides , such as MgH 2 , NaAlH 4 , LiAlH 4 , LiH , LaNi 5 H 6 , TiFeH 2 , ammonia borane , and palladium hydride represent sources of stored hydrogen. There are three main classes of metal hydrides: [ 16 ] [ 17 ]
Here are the properties of some metal hydrides: [ 18 ]
Again the persistent problems are the % weight of H 2 that they carry and the reversibility of the storage process. [ 19 ] Some are easy-to-fuel liquids at ambient temperature and pressure, whereas others are solids which could be turned into pellets. These materials have good energy density , although their specific energy is often worse than the leading hydrocarbon fuels.
An alternative method for lowering dissociation temperatures is doping with activators. This strategy has been used for aluminium hydride , but the complex synthesis makes the approach unattractive. [ 20 ]
Proposed hydrides for use in a hydrogen economy include simple hydrides of magnesium [ 21 ] or transition metals and complex metal hydrides , typically containing sodium , lithium , or calcium and aluminium or boron . Hydrides chosen for storage applications provide low reactivity (high safety) and high hydrogen storage densities. Leading candidates are lithium hydride , sodium borohydride , lithium aluminium hydride and ammonia borane . A French company McPhy Energy is developing the first industrial product, based on magnesium hydride, already sold to some major clients such as Iwatani and ENEL.
Reversible hydrogen storage is exhibited by frustrated Lewis pair , which produces a borohydride. [ 22 ] [ 23 ] [ 24 ]
The phosphino-borane on the left accepts one equivalent of hydrogen at one atmosphere and 25 °C and expels it again by heating to 100 °C. The storage capacity is 0.25 wt%.
Traditional MgH 2 stores 7.6 wt% hydrogen, but its high desorption temperature (>300 °C) limits applications. Mg-Ti-V nanocomposites can reduce the desorption temperature to below 200 °C, which improved usability in fuel cell vehicles (FCVs). Carbon-coordinated MgH 2 exhibits 80% of improvement on cycling stability over 1000 cycles. [ 25 ]
LiBH 4 + MgH 2 composites stored about 11 wt% of hydrogen, which is one of the highest capacities reported. And ammonia borane (H₃NBH₃) releases 12 wt% hydrogen at moderate temperatures (~100–150 °C), making it a promising on-board storage candidate. [ 17 ]
Hydrogen can be produced using aluminium by reacting it with water. [ 26 ] It was previously believed that, to react with water, aluminium must be stripped of its natural oxide layer using caustic substances, alloys, [ 27 ] or mixing with gallium (which produces aluminium nanoparticles that allow 90% of the aluminium to react). [ 28 ] It has since been demonstrated that efficient reaction is possible by increasing the temperature and pressure of the reaction. [ 29 ] The byproduct of the reaction to create hydrogen is aluminium oxide , which can be recycled back into aluminium with the Hall–Héroult process , making the reaction theoretically renewable. Although this requires electrolysis, which consumes a large amount of energy, the energy is then stored in the aluminium (and released when the aluminium is reacted with water).
Mg-based hydrogen storage materials can be generally fell into three categories, i.e., pure Mg, Mg-based alloys, and Mg-based composites. Particularly, more than 300 sorts of Mg-based hydrogen storage alloys have been receiving extensive attention [ 30 ] because of the relatively better overall performance. Nonetheless, the inferior hydrogen absorption/desorption kinetics rooting in the overly undue thermodynamic stability of metal hydride make the Mg-based hydrogen storage alloys currently not appropriate for the real applications, and therefore, massive attempts have been dedicated to overcoming these shortages. Some sample preparation methods, such as smelting, powder sintering, diffusion, mechanical alloying, the hydriding combustion synthesis method, surface treatment, and heat treatment, etc., have been broadly employed for altering the dynamic performance and cycle life of Mg-based hydrogen storage alloys. Besides, some intrinsic modification strategies, including alloying, [ 31 ] [ 32 ] [ 33 ] [ 34 ] nanostructuring, [ 35 ] [ 36 ] [ 37 ] doping by catalytic additives, [ 38 ] [ 39 ] and acquiring nanocomposites with other hydrides, [ 40 ] [ 41 ] etc., have been mainly explored for intrinsically boosting the performance of Mg-based hydrogen storage alloys. [ 42 ] Like aluminium, magnesium also reacts with water to produce hydrogen. [ 43 ]
Of the primary hydrogen storage alloys progressed formerly, Mg and Mg-based hydrogen storage materials are believed to provide the remarkable possibility of the practical application, on account of the advantages as following: 1) the resource of Mg is plentiful and economical. Mg element exists abundantly and accounts for ≈2.35% of the earth's crust with the rank of the eighth; 2) low density of merely 1.74 g cm-3; 3) superior hydrogen storage capacity. The theoretical hydrogen storage amounts of the pure Mg is 7.6 wt % (weight percent), [ 44 ] [ 45 ] [ 46 ] and the Mg2Ni is 3.6 wt%, respectively. [ 42 ]
Lithium alanate (LiAlH 4 ) was synthesized for the first time in 1947 by dissolution of lithium hydride in an ether solution of aluminium chloride. [ 47 ] LiAlH 4 has a theoretical gravimetric capacity of 10.5 wt %H 2 and dehydrogenates in the following three steps: [ 48 ] [ 49 ] [ 50 ] 3LiAlH 4 ↔ Li 3 AlH 6 + 3H 2 + 2Al (423–448 K; 5.3 wt %H 2 ; ∆H = −10 kJ·mol−1 H 2 ); Li 3 AlH 6 ↔ 3LiH + Al + 1.5H 2 (453–493 K; 2.6 wt %H 2 ; ∆H = 25 kJ·mol−1 H 2 ); 3LiH + 3Al ↔ 3LiAl + 3/2H 2 (>673 K; 2.6 wt %H 2 ; ∆H = 140 kJ·mol−1 H 2 ). [ 51 ] The first two steps lead to a total amount of hydrogen released equal to 7.9 wt %, which could be attractive for practical applications, but the working temperatures and the desorption kinetics are still far from the practical targets. Several strategies have been applied in the last few years to overcome these limits, such as ball-milling and catalysts additions. [ 52 ] [ 53 ] [ 54 ] [ 55 ] [ 56 ] [ 51 ]
Potassium Alanate (KAlH 4 ) was first prepared by Ashby et al. [ 57 ] by one-step synthesis in toluene, tetrahydrofuran, and diglyme. Concerning the hydrogen absorption and desorption properties, this alanate was only scarcely studied. Morioka et al., [ 58 ] by temperature programmed desorption (TPD) analyses, proposed the following dehydrogenation mechanism: 3KAlH 4 →K 3 AlH 6 + 2Al + 3H 2 (573 K, ∆H = 55 kJ·mol−1 H 2 ; 2.9 wt %H 2 ), K 3 AlH 6 → 3KH + Al + 3/2H 2 (613 K, ∆H = 70 kJ·mol−1 H 2 ; 1.4 wt %H 2 ), 3KH → 3K + 3/2H 2 (703 K, 1.4 wt %H 2 ). These reactions were demonstrated reversible without catalysts addition at relatively low hydrogen pressure and temperatures. The addition of TiCl3 was found to decrease the working temperature of the first dehydrogenation step of 50 K, [ 59 ] but no variations were recorded for the last two reaction steps. [ 51 ]
Unsaturated organic compounds can store huge amounts of hydrogen. These Liquid Organic Hydrogen Carriers (LOHC) are hydrogenated for storage and dehydrogenated again when the energy/hydrogen is needed. Using LOHCs, relatively high gravimetric storage densities can be reached (about 6 wt-%) and the overall energy efficiency is higher than for other chemical storage options such as producing methane from the hydrogen . [ 60 ] Both hydrogenation and dehydrogenation of LOHCs requires catalysts. [ 61 ] It was demonstrated that replacing hydrocarbons by hetero-atoms, like N, O etc. improves reversible de/hydrogenation properties.
Research on LOHC was concentrated on cycloalkanes at an early stage, with its relatively high hydrogen capacity (6-8 wt %) and production of CO x -free hydrogen. [ 61 ] Heterocyclic aromatic compounds (or N-Heterocycles) are also appropriate for this task. A compound featuring in LOHC research is N-Ethylcarbazole [ de ] (NEC) [ 62 ] but many others do exist. [ 63 ] Dibenzyltoluene , which is already used as a heat transfer fluid in industry, was identified as potential LOHC. With a wide liquid range between -39 °C (melting point) and 390 °C (boiling point) and a hydrogen storage density of 6.2 wt% dibenzyltoluene is ideally suited as LOHC material. [ 64 ] Formic acid has been suggested as a promising hydrogen storage material with a 4.4wt% hydrogen capacity. [ 65 ]
Cycloalkanes reported as LOHC include cyclohexane, methyl-cyclohexane and decalin. The dehydrogenation of cycloalkanes is highly endothermic (63-69 kJ/mol H 2 ), which means this process requires high temperature. [ 61 ] Dehydrogenation of decalin is the most thermodynamically favored among the three cycloalkanes, and methyl-cyclohexane is second because of the presence of the methyl group. [ 66 ] Research on catalyst development for dehydrogenation of cycloalkanes has been carried out for decades. Nickel (Ni), Molybdenum (Mo) and Platinum (Pt) based catalysts are highly investigated for dehydrogenation. However, coking is still a big challenge for catalyst's long-term stability. [ 67 ] [ 68 ]
The temperature required for hydrogenation and dehydrogenation drops significantly for heterocycles vs simple carbocycles. [ 69 ] Among all the N-heterocycles, the saturated-unsaturated pair of dodecahydro-N-ethylcarbazole (12H-NEC) and NEC has been considered as a promising candidate for hydrogen storage with a fairly large hydrogen content (5.8wt%). [ 70 ] The figure on the top right shows dehydrogenation and hydrogenation of the 12H-NEC and NEC pair. The standard catalyst for NEC to 12H-NEC is Ru and Rh based. The selectivity of hydrogenation can reach 97% at 7 MPa and 130 °C-150 °C. [ 61 ] Although N-Heterocyles can optimize the unfavorable thermodynamic properties of cycloalkanes, a lot of issues remain unsolved, such as high cost, high toxicity and kinetic barriers etc. [ 61 ]
The imidazolium ionic liquids such alkyl(aryl)-3-methylimidazolium N-bis(trifluoromethanesulfonyl)imidate salts can reversibly add 6–12 hydrogen atoms in the presence of classical Pd/C or Ir0 nanoparticle catalysts and can be used as alternative materials for on-board hydrogen-storage devices. These salts can hold up to 30 g L −1 of hydrogen at atmospheric pressure. [ 71 ]
Formic acid is a highly effective hydrogen storage material, although its H 2 density is low. Carbon monoxide free hydrogen has been generated in a very wide pressure range (1–600 bar). A homogeneous catalytic system based on water-soluble ruthenium catalysts selectively decompose HCOOH into H 2 and CO 2 in aqueous solution. [ 72 ] This catalytic system overcomes the limitations of other catalysts (e.g. poor stability, limited catalytic lifetimes, formation of CO) for the decomposition of formic acid making it a viable hydrogen storage material. [ 73 ] And the co-product of this decomposition, carbon dioxide, can be used as hydrogen vector by hydrogenating it back to formic acid in a second step. The catalytic hydrogenation of CO 2 has long been studied and efficient procedures have been developed. [ 74 ] [ 75 ] Formic acid contains 53 g L −1 hydrogen at room temperature and atmospheric pressure. By weight, pure formic acid stores 4.3 wt% hydrogen. Pure formic acid is a liquid with a flash point 69 °C (cf. gasoline −40 °C, ethanol 13 °C). 85% formic acid is not flammable.
Ammonia (NH 3 ) releases H 2 in an appropriate catalytic reformer. Ammonia provides high hydrogen storage densities as a liquid with mild pressurization and cryogenic constraints: It can also be stored as a liquid at room temperature and pressure when mixed with water. Ammonia is the second most commonly produced chemical in the world and a large infrastructure for making, transporting, and distributing ammonia exists. Ammonia can be reformed to produce hydrogen with no harmful waste, or can mix with existing fuels and under the right conditions burn efficiently. Since there is no carbon in ammonia, no carbon by-products are produced; thereby making this possibility a "carbon neutral" option for the future. Pure ammonia burns poorly at the atmospheric pressures found in natural gas fired water heaters and stoves. Under compression in an automobile engine it is a suitable fuel for slightly modified gasoline engines. Ammonia is a suitable alternative fuel because it has 18.6 MJ/kg energy density at NTP and carbon-free combustion byproducts. [ 76 ]
Ammonia has several challenges to widespread adaption as a hydrogen storage material. Ammonia is a toxic gas with a potent odor at standard temperature and pressure. [ 77 ] Additionally, advances in the efficiency and scalability of ammonia decomposition are needed for commercial viability, as fuel cell membranes are highly sensitive to residual ammonia and current decomposition techniques have low yield rates. [ 78 ] A variety of transition metals can be used to catalyze the ammonia decomposition reaction, the most effective being ruthenium . This catalysis works through chemisorption , where the adsorption energy of N 2 is less than the reaction energy of dissociation. [ 79 ] Hydrogen purification can be achieved in several ways. Hydrogen can be separated from unreacted ammonia using a permeable, hydrogen-selective membrane. [ 80 ] It can also be purified through the adsorption of ammonia, which can be selectively trapped due to its polarity. [ 81 ]
In September 2005 chemists from the Technical University of Denmark announced a method of storing hydrogen in the form of ammonia saturated into a salt tablet. They claim it will be an inexpensive and safe storage method. [ 82 ] [ needs update ]
Hydrazine breaks down in the cell to form nitrogen and hydrogen / [ 83 ] Silicon hydrides and germanium hydrides are also candidates of hydrogen storage materials, as they can subject to energetically favored reaction to form covalently bonded dimers with loss of a hydrogen molecule. [ 84 ] [ 85 ]
Prior to 1980, several compounds were investigated for hydrogen storage including complex borohydrides, or aluminohydrides, and ammonium salts. These hydrides have an upper theoretical hydrogen yield limited to about 8.5% by weight. Amongst the compounds that contain only B, N, and H (both positive and negative ions), representative examples include: amine boranes, boron hydride ammoniates, hydrazine-borane complexes, and ammonium octahydrotriborates or tetrahydroborates. Of these, amine boranes (and especially ammonia borane ) have been extensively investigated as hydrogen carriers. During the 1970s and 1980s, the U.S. Army and Navy funded efforts aimed at developing hydrogen/deuterium gas-generating compounds for use in the HF/DF and HCl chemical lasers , and gas dynamic lasers. Earlier hydrogen gas-generating formulations used amine boranes and their derivatives. Ignition of the amine borane(s) forms boron nitride (BN) and hydrogen gas. In addition to ammonia borane
(H 3 BNH 3 ), other gas-generators include diborane diammoniate, H 2 B(NH 3 ) 2 BH 4 . [ citation needed ]
In this case hydrogen remains in physical forms, i.e., as gas, supercritical fluid, adsorbate, or molecular inclusions. Theoretical limitations and experimental results are considered [ 86 ] concerning the volumetric and gravimetric capacity of glass microvessels, microporous, and nanoporous media, as well as safety and refilling-time demands. Because hydrogen is the smallest molecule, it easily escapes from containers and during transfer from container to container. While it does not directly contribute to radiative forcing , hydrogen is estimated to have an effective 100-year global warming potential of 11.6 ± 2.8 due to its impact on processes such as atmospheric methane oxidation and tropospheric ozone production. [ 87 ] [ 88 ]
Zeolites are microporous and highly crystalline aluminosilicate materials. As they exhibit cage and tunnel structures, they offer the potential for the encapsulation of non-polar gases such as H 2 . In this system, hydrogen is physisorbed on the surface of the zeolite pores through a mechanism of adsorption that involves hydrogen being forced into the pores under pressure and low temperature. [ 89 ] Therefore, similar to other porous materials, its hydrogen storage capacity depends on the BET surface area , pore volume, the interaction of molecular hydrogen with the internal surfaces of the micropores, and working conditions such as pressure and temperature. [ 90 ]
Research shows that the channel diameter is also one of the parameters determining this capacity, especially at high pressure. In this case, an effective material should exhibit a large pore volume and a channel diameter close to the kinetic diameter of the hydrogen molecule (d H =2.89 Å). [ 89 ]
Table below shows the hydrogen uptake of several zeolites at liquid nitrogen temperature (77K):
Activated carbons are highly porous amorphous carbon materials with high apparent surface area. Hydrogen physisorption can be increased in these materials by increasing the apparent surface area and optimizing pore diameter to around 7 Å. [ 92 ] These materials are of particular interest due to the fact that they can be made from waste materials, such as cigarette butts which have shown great potential as precursor materials for high-capacity hydrogen storage materials. [ 93 ] [ 94 ]
Graphene can store hydrogen efficiently. The H 2 adds to the double bonds giving graphane . The hydrogen is released upon heating to 450 °C. [ 95 ] [ 96 ]
Hydrogen carriers based on nanostructured carbon (such as carbon buckyballs and nanotubes ) have been proposed. However, hydrogen content amounts up to ≈3.0-7.0 wt% at 77K which is far from the value set by US Department of Energy (6 wt% at nearly ambient conditions). [ citation needed ]
To realize carbon materials as effective hydrogen storage technologies, carbon nanotubes (CNTs) have been doped with MgH 2 . [ 12 ] The metal hydride has proven to have a theoretical storage capacity (7.6 wt%) that fulfills the United States Department of Energy requirement of 6 wt%, but has limited practical applications due to its high release temperature. The proposed mechanism involves the creation of fast diffusion channels by CNTs within the MgH 2 lattice. Fullerene substances are other carbonaceous nanomaterials that have been tested for hydrogen storage in this center. Fullerene molecules are composed of a C 60 close-caged structure, that allows for hydrogenation of the double bonded carbons leading to a theoretical C 60 H 60 isomer with a hydrogen content of 7.7 wt%. However, the release temperature in these systems is high (600 °C).
Metal–organic frameworks represent another class of synthetic porous materials that store hydrogen and energy at the molecular level. MOFs are highly crystalline inorganic-organic hybrid structures that contain metal clusters or ions (secondary building units) as nodes and organic ligands as linkers. When guest molecules (solvent) occupying the pores are removed during solvent exchange and heating under vacuum, porous structure of MOFs can be achieved without destabilizing the frame and hydrogen molecules will be adsorbed onto the surface of the pores by physisorption. Compared to traditional zeolites and porous carbon materials, MOFs have very high number of pores and surface area which allow higher hydrogen uptake in a given volume. Thus, research interests on hydrogen storage in MOFs have been growing since 2003 when the first MOF-based hydrogen storage was introduced. Since there are infinite geometric and chemical variations of MOFs based on different combinations of SBUs and linkers, many researches explore what combination will provide the maximum hydrogen uptake by varying materials of metal ions and linkers. [ citation needed ]
Temperature, pressure and composition of MOFs can influence their hydrogen storage ability. The adsorption capacity of MOFs is lower at higher temperature and higher at lower temperatures. With the rising of temperature, physisorption decreases and chemisorption increases. [ 97 ] For MOF-519 and MOF-520, the isosteric heat of adsorption decreased with pressure increase. [ 98 ] For MOF-5, both gravimetric and volumetric hydrogen uptake increased with increase in pressure. [ 97 ] The total capacity may not be consistent with the usable capacity under pressure swing conditions. For instance, MOF-5 and IRMOF-20, which have the highest total volumetric capacity, show the least usable volumetric capacity. [ 99 ] Absorption capacity can be increased by modification of structure. For example, the hydrogen uptake of PCN-68 is higher than PCN-61. [ 100 ] Porous aromatic frameworks (PAF-1), which is known as a high surface area material, can achieve a higher surface area by doping. [ 101 ]
There are many different ways to modify MOFs, such as MOF catalysts, MOF hybrids, MOF with metal centers and doping. MOF catalysts have high surface area, porosity and hydrogen storage capacity. However, the active metal centers are low. MOF hybrids have enhanced surface area, porosity, loading capacity and hydrogen storage capacity. Nevertheless, they are not stable and lack active centers. Doping in MOFs can increase hydrogen storage capacity, but there might be steric effect and inert metals have inadequate stability. There might be formation of interconnected pores and low corrosion resistance in MOFs with metal centers, while they might have good binding energy and enhanced stability. These advantages and disadvantages for different kinds of modified MOFs show that MOF hybrids are more promising because of the good controllability in selection of materials for high surface area, porosity and stability. [ 97 ]
In 2006, chemists achieved hydrogen storage concentrations of up to 7.5 wt% in MOF-74 at a low temperature of 77 K . [ 102 ] [ 103 ] In 2009, researchers reached 10 wt% at 77 bar (1,117 psi) and 77 K with MOF NOTT-112. [ 104 ] Most articles about hydrogen storage in MOFs report hydrogen uptake capacity at a temperature of 77K and a pressure of 1 bar because these conditions are commonly available and the binding energy between hydrogen and the MOF at this temperature is large compared to the thermal vibration energy. Varying several factors such as surface area, pore size, catenation, ligand structure, and sample purity can result in different amounts of hydrogen uptake in MOFs.
In 2020, researchers reported that NU-1501-Al, an ultraporous metal–organic framework (MOF) based on metal trinuclear clusters, yielded "impressive gravimetric and volumetric storage performances for hydrogen and methane", with a hydrogen delivery capacity of 14.0% w/w, 46.2 g/litre. [ 105 ] [ 106 ]
Cryo-compressed storage of hydrogen is the only technology that meets 2015 DOE targets for volumetric and gravimetric efficiency (see "CcH2" on slide 6 in [ 107 ] ).
Furthermore, another study has shown that cryo-compression exhibits interesting cost advantages: ownership cost (price per mile) and storage system cost (price per vehicle) are actually the lowest when compared to any other technology (see third row in slide 13 of [ 108 ] ).
Like liquid storage, cryo-compressed uses cold hydrogen (20.3 K and slightly above) in order to reach a high energy density. However, the main difference is that, when the hydrogen would warm-up due to heat transfer with the environment ("boil off"), the tank is allowed to go to pressures much higher (up to 350 bars versus a couple of bars for liquid storage). As a consequence, it takes more time before the hydrogen has to vent, and in most driving situations, enough hydrogen is used by the car to keep the pressure well below the venting limit. [ citation needed ]
Consequently, it has been demonstrated that a high driving range could be achieved with a cryo-compressed tank : more than 650 miles (1,050 km) were driven with a full tank mounted on a hydrogen-fueled engine of Toyota Prius . [ 109 ] Research is still underway to study and demonstrate the full potential of the technology. [ 110 ]
As of 2010, the BMW Group has started a thorough component and system level validation of cryo-compressed vehicle storage on its way to a commercial product. [ 111 ]
H 2 caged in a clathrate hydrate was first reported in 2002, but requires very high pressures to be stable. In 2004, researchers showed solid H 2 -containing hydrates could be formed at ambient temperature and tens of bars by adding small amounts of promoting substances such as THF . [ 112 ] [ 113 ] These clathrates have a theoretical maximum hydrogen densities of around 5 wt% and 40 kg/m 3 .
A team of Russian, Israeli and German scientists have collaboratively developed an innovative technology based on glass capillary arrays for the safe infusion, storage and controlled release of hydrogen in mobile applications. [ 114 ] [ 115 ] The C.En technology has achieved the United States Department of Energy (DOE) 2010 targets for on-board hydrogen storage systems. [ 116 ] DOE 2015 targets can be achieved using flexible glass capillaries and cryo-compressed method of hydrogen storage. [ 117 ]
Hollow glass microspheres (HGM) can be utilized for controlled storage and release of hydrogen. HGMs with a diameter of 1 to 100 μm, a density of 1.0 to 2.0 gm/cc and a porous wall with openings of 10 to 1000 angstroms are considered for hydrogen storage. The advantages of HGMs for hydrogen storage are that they are nontoxic, light, cheap, recyclable, reversible, easily handled at atmospheric conditions, capable of being stored in a tank, and the hydrogen within is non-explosive. [ 118 ] Each of these HGMs is capable of containing hydrogen up to 150 MPa without the heaviness and bulk of a large pressurized tank. All of these qualities are favorable in vehicular applications. Beyond these advantages, HGMs are seen as a possible hydrogen solution due to hydrogen diffusivity having a large temperature dependence. At room temperature, the diffusivity is very low, and the hydrogen is trapped in the HGM. The disadvantage of HGMs is that to fill and outgas hydrogen effectively the temperature must be at least 300 °C which significantly increases the operational cost of HGM in hydrogen storage. [ 119 ] The high temperature can be partly attributed to glass being an insulator and having a low thermal conductivity ; this hinders hydrogen diffusivity , and subsequently a higher temperature is required to achieve the desired storage capacity.
To make this technology more economically viable for commercial use, research is being done to increase the efficiency of hydrogen diffusion through the HGMs. One study done by Dalai et al. sought to increase the thermal conductivity of the HGM through doping the glass with cobalt . In doing so they increased the thermal conductivity from 0.0072 to 0.198 W/m-K at 10 wt% Co. Increases in hydrogen adsorption though were only seen up to 2 wt% Co (0.103 W/m-K) as the metal oxide began to cover pores in the glass shell. This study concluded with a hydrogen storage capacity of 3.31 wt% with 2 wt% Co at 200 °C and 10 bar. [ 118 ]
A study done by Rapp and Shelby sought to increase the hydrogen release rate through photo-induced outgassing in doped HGMs in comparison to conventional heating methods. The glass was doped with optically active metals to interact with the high-intensity infrared light . The study found that 0.5 wt% Fe 3 O 4 doped 7070 borosilicate glass had hydrogen release increase proportionally to the infrared lamp intensity. In addition to the improvements to diffusivity by infrared alone, reactions between the hydrogen and iron-doped glass increased the Fe 2+ /Fe 3+ ratio which increased infrared absorption therefore further increasing the hydrogen yield. [ 120 ]
As of 2020, the progress made in studying HGMs has increased its efficiency but it still falls short of Department of Energy targets for this technology. The operation temperatures for both hydrogen adsorption and release are the largest barrier to commercialization . [ 121 ]
Unlike mobile applications, hydrogen density is not a huge problem for stationary applications. As for mobile applications, stationary applications can use established technology:
Underground hydrogen storage [ 124 ] is the practice of hydrogen storage in caverns , salt domes and depleted oil and gas fields. Large quantities of gaseous hydrogen have been stored in caverns by ICI for many years without any difficulties. [ 125 ] The storage of large quantities of liquid hydrogen underground can function as grid energy storage . The round-trip efficiency is approximately 40% (vs. 75–80% for pumped-hydro (PHES) ), and the cost is slightly higher than pumped hydro, if only a limited number of hours of storage is required. [ 126 ] Another study referenced by a European staff working paper found that for large scale storage, the cheapest option is hydrogen at €140/MWh for 2,000 hours of storage using an electrolyser, salt cavern storage and combined-cycle power plant. [ 123 ] : 15 The European project Hyunder [ 127 ] indicated in 2013 that for the storage of wind and solar energy an additional 85 caverns are required as it cannot be covered by PHES and CAES systems. [ 128 ] A German case study on storage of hydrogen in salt caverns found that if the German power surplus (7% of total variable renewable generation by 2025 and 20% by 2050) would be converted to hydrogen and stored underground, these quantities would require some 15 caverns of 500,000 cubic metres each by 2025 and some 60 caverns by 2050 – corresponding to approximately one third of the number of gas caverns currently operated in Germany. [ 129 ] In the US, Sandia Labs are conducting research into the storage of hydrogen in depleted oil and gas fields, which could easily absorb large amounts of renewably produced hydrogen as there are some 2.7 million depleted wells in existence. [ 130 ]
Underground hydrogen storage is the practice of hydrogen storage in caverns , [ 131 ] [ 132 ] salt domes and depleted oil / gas fields . [ 133 ] [ 134 ] Large quantities of gaseous hydrogen have been stored in caverns for many years. [ 135 ] [ failed verification – see discussion ] [ unreliable source? ] The storage of large quantities of hydrogen underground in solution-mined salt domes , [ 136 ] aquifers , [ 137 ] excavated rock caverns, or mines can function as grid energy storage , [ 138 ] essential for the hydrogen economy . [ 139 ] By using a turboexpander the electricity needs for compressed storage on 200 bar amounts to 2.1% of the energy content. [ 140 ]
The Chevron Phillips Clemens Terminal in Texas has stored hydrogen since the 1980s in a solution-mined salt cavern. The cavern roof is about 2,800 feet (850 m) underground. The cavern is a cylinder with a diameter of 160 feet (49 m), a height of 1,000 feet (300 m), and a usable hydrogen capacity of 1,066 million cubic feet (30.2 × 10 ^ 6 m 3 ), or 2,520 metric tons (2,480 long tons; 2,780 short tons). [ 141 ]
Salt caverns are artificially created by injecting water from the surface into a well in the rock salt, where rock salt is a polycrystalline material made of NaCl, halite. Locations such as salt domes or bedded salt are usually picked for salt caverns' creation. Salt caverns can reach a maximum depth of 2000 m and a maximum volume capacity of 1,000,000 m3. The frequency of injection and withdrawal cycles ranges between 10 and 12 cycles per year. The leak rate is around 1%. [ 142 ] [ 143 ]
Due to the physiochemical properties of the rock salt, salt caverns exhibit multiple advantages. Key characteristics are low water content, low porosity and permeability, and its chemical inertia towards hydrogen. [ 144 ] Permeability is a key parameter in underground hydrogen storage, which affects its ability to seal. Though studies have found dilatancy and extensional fracture can cause significant permeability increase, rock salt crystal's recrystallization, which is a grain boundaries healing process, may contribute to its mechanical stiffness and permeability recovery. [ 145 ] Its plastic properties prevent the formation and spread of fractures and protect it from losing its tightness, which is particularly important for hydrogen storage. [ 144 ] Some of the disadvantages of salt caverns include lower storage capacity, large amount of water needed, and the effect of corrosion. Cushion gas is needed to avoid creep due to pressure drop when withdrawing gas from the reservoir. Though the need for cushion gas is relatively small, around 20%, the operational cost can still add up when working with a larger storage capacity. Cost is another big concern, where the cost of construction and operation are still high. [ 143 ] [ 146 ]
Though people have experience with storing natural gas, storing hydrogen is a lot more complex. Factors such as hydrogen diffusivity in solids cause restrictions in salt cavern storage. Microbial activity is under extensive research worldwide because of its impact on hydrogen loss. As a result of methanogenic bacteria's bacterial metabolism, carbon dioxide and hydrogen are consumed and methane is produced, which leads to the loss of hydrogen stored in the salt caverns. [ 147 ] [ 146 ]
A cavern sized 800 m tall and 50 m diameter can hold hydrogen equivalent to 150 GWh. [ 153 ] [ 154 ]
Power to gas is a technology which converts electrical power to a gas fuel . There are two methods: the first is to use the electricity for water splitting and inject the resulting hydrogen into the natural gas grid; the second, less efficient method is used to convert carbon dioxide and hydrogen to methane , (see natural gas ) using electrolysis and the Sabatier reaction . A third option is to combine the hydrogen via electrolysis with a source of carbon (either carbon dioxide or carbon monoxide from biogas , from industrial processes or via direct air-captured carbon dioxide ) via biomethanation , [ 155 ] [ 156 ] where biomethanogens (archaea) consume carbon dioxide and hydrogen and produce methane within an anaerobic environment. This process is highly efficient, as the archaea are self-replicating and only require low-grade (60 °C) heat to perform the reaction.
Another process has also been achieved by SoCalGas to convert the carbon dioxide in raw biogas to methane in a single electrochemical step, representing a simpler method of converting excess renewable electricity into storable natural gas. [ 157 ]
The UK has completed surveys and is preparing to start injecting hydrogen into the gas grid as the grid previously carried 'town gas' which is a 50% hydrogen-methane gas formed from coal. Auditors KPMG found that converting the UK to hydrogen gas could be £150bn to £200bn cheaper than rewiring British homes to use electric heating powered by lower-carbon sources. [ 158 ]
Excess power or off peak power generated by wind generators or solar arrays can then be used for load balancing in the energy grid. Using the existing natural gas system for hydrogen, Fuel cell maker Hydrogenics and natural gas distributor Enbridge have teamed up to develop such a power to gas system in Canada. [ 159 ]
Pipeline storage of hydrogen where a natural gas network is used for the storage of hydrogen. Before switching to natural gas , the German gas networks were operated using towngas , which for the most part (60-65%) consisted of hydrogen. The storage capacity of the German natural gas network is more than 200,000 GW·h which is enough for several months of energy requirement. By comparison, the capacity of all German pumped storage power plants amounts to only about 40 GW·h. The transport of energy through a gas network is done with much less loss (<0.1%) than in a power network (8%). The use of the existing natural gas pipelines for hydrogen was studied by NaturalHy. [ 160 ]
Portability is one of the biggest challenges in the automotive industry , where high density storage systems are problematic due to safety concerns.
High-pressure tanks weigh much more than the hydrogen they can hold. For example, in the 2014 Toyota Mirai , a full tank contains only 5.7% hydrogen, the rest of the weight being the tank. [ 161 ]
System densities are often around half those of the working material, thus while a material may store 6 wt% H 2 , a working system using that material may only achieve 3 wt% when the weight of tanks, temperature and pressure control equipment, etc., is considered. [ citation needed ]
Due to its clean-burning characteristics, hydrogen is a clean fuel alternative for the automotive industry. Hydrogen-based fuel could significantly reduce the emissions of greenhouse gases such as CO 2 , SO 2 and NO x . Three problems for the use of hydrogen fuel cells (HFC) are efficiency, size, and safe onboard storage of the gas. Other major disadvantages of this emerging technology involve cost, operability and durability issues, which still need to be improved from the existing systems. To address these challenges, the use of nanomaterials has been proposed as an alternative option to the traditional hydrogen storage systems. The use of nanomaterials could provide a higher density system and increase the driving range towards the target set by the DOE at 300 miles. Carbonaceous materials such as carbon nanotube and metal hydrides are the main focus of research. They are currently being considered for onboard storage systems due to their versatility, multi-functionality, mechanical properties and low cost with respect to other alternatives. [ 162 ]
The introduction of nanomaterials in onboard hydrogen storage systems may be a major turning point in the automotive industry. However, storage is not the only aspect of the fuel cell to which nanomaterials may contribute. Different studies have shown that the transport and catalytic properties of Nafion membranes used in HFCs can be enhanced with TiO 2 / SnO 2 nanoparticles. [ 162 ] The increased performance is caused by an improvement in hydrogen splitting kinetics due to catalytic activity of the nanoparticles. Furthermore, this system exhibits faster transport of protons across the cell which makes HFCs with nanoparticle composite membranes a promising alternative.
Another application of nanomaterials in water splitting has been introduced by a research group at Manchester Metropolitan University in the UK using screen-printed electrodes consisting of a graphene -like material. [ 163 ] Similar systems have been developed using photoelectrochemical techniques .
Increasing gas pressure improves the energy density by volume making for smaller container tanks. The standard material for holding pressurised hydrogen in tube trailers is steel (there is no hydrogen embrittlement problem with hydrogen gas). Tanks made of carbon and glass fibres reinforcing plastic as fitted in Toyota Mirai and Kenworth trucks are required to meet safety standards. Few materials are suitable for tanks as hydrogen being a small molecule tends to diffuse through many polymeric materials. The most common on board hydrogen storage in 2020 vehicles was hydrogen at pressure 700bar = 70MPa. The energy cost of compressing hydrogen to this pressure is significant. [ citation needed ]
Pressurized gas pipelines are always made of steel and operate at much lower pressures than tube trailers.
Alternatively, higher volumetric energy density liquid hydrogen or slush hydrogen may be used. However, liquid hydrogen is cryogenic and boils at 20.268 K (−252.882 °C or −423.188 °F). Cryogenic storage cuts weight but requires large liquification energies. The liquefaction process, involving pressurizing and cooling steps, is energy intensive. [ 164 ] The liquefied hydrogen has lower energy density by volume than gasoline by approximately a factor of four, because of the low density of liquid hydrogen – there are actually more oxidizable hydrogen atoms in a litre of gasoline (116 grams) than there are in a litre of pure liquid hydrogen (71 grams). Like any other liquid at cryogenic temperatures , the liquid hydrogen storage tanks must also be well insulated to minimize boil off.
Japan has a liquid hydrogen (LH2) storage facility at a terminal in Kobe, and was expected to receive the first shipment of liquid hydrogen via LH2 carrier in 2020. [ 165 ] Hydrogen is liquified by reducing its temperature to −253 °C, similar to liquified natural gas (LNG) which is stored at −162 °C. A potential efficiency loss of 12.79% can be achieved, or 4.26 kWh/kg out of 33.3 kWh/kg. [ 166 ]
The Hydrogen Storage Materials research field is vast, having tens of thousands of published papers. [ 167 ] According to Papers in the 2000 to 2015 period collected from Web of Science and processed in VantagePoint bibliometric software, a scientometric review of research in hydrogen storage materials was constituted. According to the literature, hydrogen energy went through a hype-cycle type of development in the 2000s. Research in Hydrogen Storage Materials grew at increasing rates from 2000 to 2010. Afterwards, growth continued but at decreasing rates, and a plateau was reached in 2015. Looking at individual country output, there is a division between countries that after 2010 inflected to a constant or slightly declining production, such as the European Union countries, the US and Japan, and those whose production continued growing until 2015, such as China and South Korea. The countries with most publications were China, the EU and the United States, followed by Japan. China kept the leading position throughout the entire period, and had a higher share of hydrogen storage materials publications in its total research output. [ 168 ]
Among materials classes, Metal-Organic Frameworks were the most researched materials, followed by Simple Hydrides. Three typical behaviors were identified:
However, current physisorption technologies are still far from being commercialized. The experimental studies are executed for small samples less than 100 g. [ 169 ] The described technologies require high pressure and/or low temperatures as a rule. Therefore, at their current state of the art these techniques are not considered as a separate novel technology but as a type of valuable add-on to current compression and liquefaction methods.
Physisorption processes are reversible since no activation energy is involved and the interaction energy is very low. In materials such as metal–organic frameworks , porous carbons, zeolites, clathrates, and organic polymers, hydrogen is physisorbed on the surface of the pores. In these classes of materials, the hydrogen storage capacity mainly depends on the surface area and pore volume. The main limitation of use of these sorbents as H 2 storage materials is weak van der Waals interaction energy between hydrogen and the surface of the sorbents. Therefore, many of the physisorption based materials have high storage capacities at liquid nitrogen temperature and high pressures, but their capacities become very low at ambient temperature and pressure. [ citation needed ]
LOHC , liquid organic hydrogen storage systems is a promising technique for future hydrogen storage. LOHC are organic compounds that can absorb and release hydrogen through chemical reactions . These compounds are characterized by the fact that they can be loaded and un-loaded with considerable amounts of hydrogen in a cyclic process. In principle, every unsaturated compound (organic molecules with C-C double or triple bonds ) can take up hydrogen during hydrogenation . This technique ensures that the release of compounds into the atmosphere are entirely avoided in hydrogen storage. Therefore, LOHCs is an attractive way to provide wind and solar energy for mobility applications in the form of liquid energy carrying molecules of similar energy storage densities and manageability as today's fossil fuels. [ 170 ] [ obsolete source ] | https://en.wikipedia.org/wiki/Hydrogen_storage |
Hydrogen sulfide is a chemical compound with the formula H 2 S . It is a colorless chalcogen-hydride gas , and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. [ 11 ] Swedish chemist Carl Wilhelm Scheele is credited with having discovered the chemical composition of purified hydrogen sulfide in 1777. [ 12 ]
Hydrogen sulfide is toxic to humans and most other animals by inhibiting cellular respiration in a manner similar to hydrogen cyanide . When it is inhaled or its salts are ingested in high amounts, damage to organs occurs rapidly with symptoms ranging from breathing difficulties to convulsions and death. [ 13 ] [ 14 ] Despite this, the human body produces small amounts of this sulfide and its mineral salts, and uses it as a signalling molecule . [ 15 ]
Hydrogen sulfide is often produced from the microbial breakdown of organic matter in the absence of oxygen, such as in swamps and sewers; this process is commonly known as anaerobic digestion , which is done by sulfate-reducing microorganisms . It also occurs in volcanic gases , natural gas deposits, and sometimes in well-drawn water.
Hydrogen sulfide is slightly denser than air. A mixture of H 2 S and air can be explosive.
In general, hydrogen sulfide acts as a reducing agent , as indicated by its ability to reduce sulfur dioxide in the Claus process . Hydrogen sulfide burns in oxygen with a blue flame to form sulfur dioxide ( SO 2 ) and water :
If an excess of oxygen is present, sulfur trioxide ( SO 3 ) is formed, which quickly hydrates to sulfuric acid :
It is slightly soluble in water and acts as a weak acid ( p K a = 6.9 in 0.01–0.1 mol/litre solutions at 18 °C), giving the hydrosulfide ion HS − . Hydrogen sulfide and its solutions are colorless. When exposed to air, it slowly oxidizes to form elemental sulfur, which is not soluble in water. The sulfide anion S 2− is not formed in aqueous solution. [ 16 ]
H 2 S and H 2 O exchange protons rapidly. This behavior is the basis of technologies for the purification of deuterium oxide ("heavy water" or D 2 O ), which exploits the easy distillation of these compounds. [ 17 ]
At pressures above 90 GPa ( gigapascal ), hydrogen sulfide becomes a metallic conductor of electricity. When cooled below a critical temperature this high-pressure phase exhibits superconductivity . The critical temperature increases with pressure, ranging from 23 K at 100 GPa to 150 K at 200 GPa. [ 18 ] If hydrogen sulfide is pressurized at higher temperatures, then cooled, the critical temperature reaches 203 K (−70 °C), which was the highest accepted superconducting critical temperature until the discovery of Lanthanum decahydride in 2019. By substituting a small part of sulfur with phosphorus and using even higher pressures, it has been predicted that it may be possible to raise the critical temperature to above 0 °C (273 K) and achieve room-temperature superconductivity . [ 19 ]
Hydrogen sulfide decomposes without a presence of a catalyst under atmospheric pressure around 1200 °C into hydrogen and sulfur. [ 20 ]
Hydrogen sulfide reacts with metal ions to form metal sulfides, which are insoluble, often dark colored solids. This behavior is the basis of the use of hydrogen sulfide as a reagent in the qualitative inorganic analysis of metal ions. In these analyses, heavy metal (and nonmetal ) ions (e.g., Pb(II), Cu(II), Hg(II), As(III)) are precipitated from solution upon exposure to H 2 S . The components of the resulting solid are then identified by their reactivity. Lead(II) acetate paper is used to detect hydrogen sulfide because it readily converts to lead(II) sulfide , which is black. [ 21 ] [ 22 ]
Hydrogen sulfide is also responsible for tarnishing on various metals including copper and silver ; the chemical responsible for black toning found on silver coins is silver sulfide ( Ag 2 S ), which is produced when the silver on the surface of the coin reacts with atmospheric hydrogen sulfide. [ 23 ] Coins that have been subject to toning by hydrogen sulfide and other sulfur-containing compounds may have the toning add to the numismatic value of a coin based on aesthetics, as the toning may produce thin-film interference , resulting in the coin taking on an attractive coloration. [ 24 ] Coins can also be intentionally treated with hydrogen sulfide to induce toning, though artificial toning can be distinguished from natural toning, and is generally criticised among collectors. [ 25 ]
Hydrogen sulfide is most commonly obtained by its separation from sour gas , which is natural gas with a high content of H 2 S . It can also be produced by treating hydrogen with molten elemental sulfur at about 450 °C. Hydrocarbons can serve as a source of hydrogen in this process. [ 26 ]
The very favorable thermodynamics for the hydrogenation of sulfur implies that the dehydrogenation (or cracking ) of hydrogen sulfide would require very high temperatures. [ 27 ]
A standard lab preparation is to treat ferrous sulfide with a strong acid in a Kipp generator :
For use in qualitative inorganic analysis , thioacetamide is used to generate H 2 S :
Many metal and nonmetal sulfides, e.g. aluminium sulfide , phosphorus pentasulfide , silicon disulfide liberate hydrogen sulfide upon exposure to water: [ 28 ]
This gas is also produced by heating sulfur with solid organic compounds and by reducing sulfurated organic compounds with hydrogen.
It can also be produced by mixing ammonium thiocyanate to concentrated sulphuric acid and adding water to it.
Hydrogen sulfide can be generated in cells via enzymatic or non-enzymatic pathways. Three enzymes catalyze formation of H 2 S : cystathionine γ-lyase (CSE), cystathionine β-synthetase (CBS), and 3-mercaptopyruvate sulfurtransferase (3-MST). [ 29 ] CBS and CSE are the main proponents of H 2 S biogenesis, which follows the trans-sulfuration pathway. [ 30 ] These enzymes have been identified in a breadth of biological cells and tissues, and their activity is induced by a number of disease states. [ 31 ] These enzymes are characterized by the transfer of a sulfur atom from methionine to serine to form a cysteine molecule. [ 30 ] 3-MST also contributes to hydrogen sulfide production by way of the cysteine catabolic pathway. [ 31 ] [ 30 ] Dietary amino acids, such as methionine and cysteine serve as the primary substrates for the transulfuration pathways and in the production of hydrogen sulfide. Hydrogen sulfide can also be derived from proteins such as ferredoxins and Rieske proteins . [ 31 ]
Sulfate-reducing (resp. sulfur-reducing ) bacteria generate usable energy under low-oxygen conditions by using sulfates (resp. elemental sulfur) to oxidize organic compounds or hydrogen; this produces hydrogen sulfide as a waste product. [ 32 ]
H 2 S in the body acts as a gaseous signaling molecule with implications for health and in diseases. [ 29 ] [ 33 ] [ 34 ] [ 35 ]
Hydrogen sulfide is involved in vasodilation in animals, as well as in increasing seed germination and stress responses in plants. [ 36 ] Hydrogen sulfide signaling is moderated by reactive oxygen species (ROS) and reactive nitrogen species (RNS). [ 36 ] H 2 S has been shown to interact with the NO pathway resulting in several different cellular effects, including the inhibition of cGMP phosphodiesterases, [ 37 ] as well as the formation of another signal called nitrosothiol. [ 36 ] Hydrogen sulfide is also known to increase the levels of glutathione, which acts to reduce or disrupt ROS levels in cells. [ 36 ]
The field of H 2 S biology has advanced from environmental toxicology to investigate the roles of endogenously produced H 2 S in physiological conditions and in various pathophysiological states. [ 38 ] H 2 S has been implicated in cancer, in Down syndrome and in vascular disease. [ 39 ] [ 40 ] [ 41 ] [ 42 ]
At lower concentrations, it stimulates mitochondrial function via multiple mechanisms including direct electron donation. [ 43 ] [ 44 ] However, at higher concentrations, it inhibits Complex IV of the mitochondrial electron transport chain, which effectively reduces ATP generation and biochemical activity within cells. [ 36 ]
Hydrogen sulfide is mainly consumed as a precursor to elemental sulfur. This conversion, called the Claus process , involves partial oxidation to sulfur dioxide. The latter reacts with hydrogen sulfide to give elemental sulfur. The conversion is catalyzed by alumina. [ 45 ]
Many fundamental organosulfur compounds are produced using hydrogen sulfide. These include methanethiol , ethanethiol , and thioglycolic acid . [ 26 ] Hydrosulfides can be used in the production of thiophenol . [ 46 ]
Upon combining with alkali metal bases, hydrogen sulfide converts to alkali hydrosulfides such as sodium hydrosulfide and sodium sulfide :
Sodium sulfides are used in the paper making industry. Specifically, salts of SH − break bonds between lignin and cellulose components of pulp in the Kraft process . [ 26 ]
As indicated above, many metal ions react with hydrogen sulfide to give the corresponding metal sulfides. Oxidic ores are sometimes treated with hydrogen sulfide to give the corresponding metal sulfides which are more readily purified by flotation .Metal parts are sometimes passivated with hydrogen sulfide. Catalysts used in hydrodesulfurization are routinely activated with hydrogen sulfide. [ 26 ]
Volcanoes and some hot springs (as well as cold springs ) emit some H 2 S . Hydrogen sulfide can be present naturally in well water, often as a result of the action of sulfate-reducing bacteria . [ 47 ] [ better source needed ] Hydrogen sulfide is produced by the human body in small quantities through bacterial breakdown of proteins containing sulfur in the intestinal tract; it therefore contributes to the characteristic odor of flatulence. It is also produced in the mouth ( halitosis ). [ 48 ]
A portion of global H 2 S emissions are due to human activity. By far the largest industrial source of H 2 S is petroleum refineries : The hydrodesulfurization process liberates sulfur from petroleum by the action of hydrogen. The resulting H 2 S is converted to elemental sulfur by partial combustion via the Claus process , which is a major source of elemental sulfur. Other anthropogenic sources of hydrogen sulfide include coke ovens, paper mills (using the Kraft process), tanneries and sewerage . H 2 S arises from virtually anywhere where elemental sulfur comes in contact with organic material, especially at high temperatures. Depending on environmental conditions, it is responsible for deterioration of material through the action of some sulfur oxidizing microorganisms. It is called biogenic sulfide corrosion . [ citation needed ]
In 2011 it was reported that increased concentrations of H 2 S were observed in the Bakken formation crude, possibly due to oil field practices, and presented challenges such as "health and environmental risks, corrosion of wellbore, added expense with regard to materials handling and pipeline equipment, and additional refinement requirements". [ 49 ]
Besides living near gas and oil drilling operations, ordinary citizens can be exposed to hydrogen sulfide by being near waste water treatment facilities, landfills and farms with manure storage. Exposure occurs through breathing contaminated air or drinking contaminated water. [ 50 ]
In municipal waste landfill sites , the burial of organic material rapidly leads to the production of anaerobic digestion within the waste mass and, with the humid atmosphere and relatively high temperature that accompanies biodegradation , biogas is produced as soon as the air within the waste mass has been reduced. If there is a source of sulfate bearing material, such as plasterboard or natural gypsum (calcium sulfate dihydrate), under anaerobic conditions sulfate reducing bacteria converts this to hydrogen sulfide. These bacteria cannot survive in air but the moist, warm, anaerobic conditions of buried waste that contains a high source of carbon – in inert landfills, paper and glue used in the fabrication of products such as plasterboard can provide a rich source of carbon [ 51 ] – is an excellent environment for the formation of hydrogen sulfide.
In industrial anaerobic digestion processes, such as waste water treatment or the digestion of organic waste from agriculture , hydrogen sulfide can be formed from the reduction of sulfate and the degradation of amino acids and proteins within organic compounds. [ 52 ] Sulfates are relatively non-inhibitory to methane forming bacteria but can be reduced to H 2 S by sulfate reducing bacteria , of which there are several genera. [ 53 ]
A number of processes have been designed to remove hydrogen sulfide from drinking water . [ 54 ]
Hydrogen sulfide is commonly found in raw natural gas and biogas. It is typically removed by amine gas treating technologies. In such processes, the hydrogen sulfide is first converted to an ammonium salt, whereas the natural gas is unaffected. [ 57 ] [ 58 ]
The bisulfide anion is subsequently regenerated by heating of the amine sulfide solution. Hydrogen sulfide generated in this process is typically converted to elemental sulfur using the Claus Process .
The underground mine gas term for foul-smelling hydrogen sulfide-rich gas mixtures is stinkdamp . Hydrogen sulfide is a highly toxic and flammable gas ( flammable range : 4.3–46%). It can poison several systems in the body, although the nervous system is most affected. [ citation needed ] The toxicity of H 2 S is comparable with that of carbon monoxide . [ 59 ] It binds with iron in the mitochondrial cytochrome enzymes , thus preventing cellular respiration . Its toxic properties were described in detail in 1843 by Justus von Liebig . [ 60 ]
Even before hydrogen sulfide was discovered, Italian physician Bernardino Ramazzini hypothesized in his 1713 book De Morbis Artificum Diatriba that occupational diseases of sewer-workers and blackening of coins in their clothes may be caused by an unknown invisible volatile acid (moreover, in late 18th century toxic gas emanation from Paris sewers became a problem for the citizens and authorities). [ 61 ]
Although very pungent at first (it smells like rotten eggs [ 62 ] ), it quickly deadens the sense of smell, creating temporary anosmia , [ 63 ] so victims may be unaware of its presence until it is too late. Safe handling procedures are provided by its safety data sheet (SDS) . [ 64 ]
Since hydrogen sulfide occurs naturally in the body, the environment, and the gut, enzymes exist to metabolize it. At some threshold level, believed to average around 300–350 ppm, the oxidative enzymes become overwhelmed. Many personal safety gas detectors, such as those used by utility, sewage and petrochemical workers, are set to alarm at as low as 5 to 10 ppm and to go into high alarm at 15 ppm. Metabolism causes oxidation to sulfate, which is harmless. [ 65 ] Hence, low levels of hydrogen sulfide may be tolerated indefinitely. [ citation needed ]
Exposure to lower concentrations can result in eye irritation, a sore throat and cough , nausea, shortness of breath, and fluid in the lungs . [ 59 ] These effects are believed to be due to hydrogen sulfide combining with alkali present in moist surface tissues to form sodium sulfide , a caustic . [ 66 ] These symptoms usually subside in a few weeks.
Long-term, low-level exposure may result in fatigue , loss of appetite, headaches , irritability, poor memory, and dizziness . Chronic exposure to low level H 2 S (around 2 ppm ) has been implicated in increased miscarriage and reproductive health issues among Russian and Finnish wood pulp workers, [ 67 ] but the reports have not (as of 1995) been replicated.
Short-term, high-level exposure can induce immediate collapse, with loss of breathing and a high probability of death. If death does not occur, high exposure to hydrogen sulfide can lead to cortical pseudolaminar necrosis , degeneration of the basal ganglia and cerebral edema . [ 59 ] Although respiratory paralysis may be immediate, it can also be delayed up to 72 hours. [ 68 ]
Inhalation of H 2 S resulted in about 7 workplace deaths per year in the U.S. (2011–2017 data), second only to carbon monoxide (17 deaths per year) for workplace chemical inhalation deaths. [ 69 ]
Treatment involves immediate inhalation of amyl nitrite , injections of sodium nitrite , or administration of 4-dimethylaminophenol in combination with inhalation of pure oxygen, administration of bronchodilators to overcome eventual bronchospasm , and in some cases hyperbaric oxygen therapy (HBOT). [ 59 ] HBOT has clinical and anecdotal support. [ 74 ] [ 75 ] [ 76 ]
Hydrogen sulfide was used by the British Army as a chemical weapon during World War I . It was not considered to be an ideal war gas, partially due to its flammability and because the distinctive smell could be detected from even a small leak, alerting the enemy to the presence of the gas. It was nevertheless used on two occasions in 1916 when other gases were in short supply. [ 77 ]
On September 2, 2005, a leak in the propeller room of a Royal Caribbean Cruise Liner docked in Los Angeles resulted in the deaths of 3 crewmen due to a sewage line leak. As a result, all such compartments are now required to have a ventilation system. [ 78 ] [ 79 ]
A dump of toxic waste containing hydrogen sulfide is believed to have caused 17 deaths and thousands of illnesses in Abidjan , on the West African coast, in the 2006 Côte d'Ivoire toxic waste dump . [ 80 ]
In September 2008, three workers were killed and two suffered serious injury, including long term brain damage, at a mushroom growing company in Langley , British Columbia . A valve to a pipe that carried chicken manure , straw and gypsum to the compost fuel for the mushroom growing operation became clogged, and as workers unclogged the valve in a confined space without proper ventilation the hydrogen sulfide that had built up due to anaerobic decomposition of the material was released, poisoning the workers in the surrounding area. [ 81 ] An investigator said there could have been more fatalities if the pipe had been fully cleared and/or if the wind had changed directions. [ 82 ]
In 2014, levels of hydrogen sulfide as high as 83 ppm were detected at a recently built mall in Thailand called Siam Square One at the Siam Square area. Shop tenants at the mall reported health complications such as sinus inflammation, breathing difficulties and eye irritation. After investigation it was determined that the large amount of gas originated from imperfect treatment and disposal of waste water in the building. [ 83 ]
In 2014, hydrogen sulfide gas killed workers at the Promenade shopping center in North Scottsdale, Arizona , USA [ 84 ] after climbing into 15 ft deep chamber without wearing personal protective gear . "Arriving crews recorded high levels of hydrogen cyanide and hydrogen sulfide coming out of the sewer."
In November 2014, a substantial amount of hydrogen sulfide gas shrouded the central, eastern and southeastern parts of Moscow . Residents living in the area were urged to stay indoors by the emergencies ministry. Although the exact source of the gas was not known, blame had been placed on a Moscow oil refinery. [ 85 ]
In June 2016, a mother and her daughter were found dead in their still-running 2006 Porsche Cayenne SUV against a guardrail on Florida's Turnpike , initially thought to be victims of carbon monoxide poisoning . [ 86 ] [ 87 ] Their deaths remained unexplained as the medical examiner waited for results of toxicology tests on the victims, [ 88 ] until urine tests revealed that hydrogen sulfide was the cause of death. A report from the Orange-Osceola Medical Examiner's Office indicated that toxic fumes came from the Porsche's starter battery , located under the front passenger seat. [ 89 ] [ 90 ]
In January 2017, three utility workers in Key Largo, Florida , died one by one within seconds of descending into a narrow space beneath a manhole cover to check a section of paved street. [ 91 ] In an attempt to save the men, a firefighter who entered the hole without his air tank (because he could not fit through the hole with it) collapsed within seconds and had to be rescued by a colleague. [ 92 ] The firefighter was airlifted to Jackson Memorial Hospital and later recovered. [ 93 ] [ 94 ] A Monroe County Sheriff officer initially determined that the space contained hydrogen sulfide and methane gas produced by decomposing vegetation. [ 95 ]
On May 24, 2018, two workers were killed, another seriously injured, and 14 others hospitalized by hydrogen sulfide inhalation at a Norske Skog paper mill in Albury, New South Wales . [ 96 ] [ 97 ] An investigation by SafeWork NSW found that the gas was released from a tank used to hold process water . The workers were exposed at the end of a 3-day maintenance period. Hydrogen sulfide had built up in an upstream tank, which had been left stagnant and untreated with biocide during the maintenance period. These conditions allowed sulfate-reducing bacteria to grow in the upstream tank, as the water contained small quantities of wood pulp and fiber . The high rate of pumping from this tank into the tank involved in the incident caused hydrogen sulfide gas to escape from various openings around its top when pumping was resumed at the end of the maintenance period. The area above it was sufficiently enclosed for the gas to pool there, despite not being identified as a confined space by Norske Skog. One of the workers who was killed was exposed while investigating an apparent fluid leak in the tank, while the other who was killed and the worker who was badly injured were attempting to rescue the first after he collapsed on top of it. In a resulting criminal case , Norske Skog was accused of failing to ensure the health and safety of its workforce at the plant to a reasonably practicable extent. It pleaded guilty, and was fined AU$1,012,500 and ordered to fund the production of an anonymized educational video about the incident. [ 98 ] [ 99 ] [ 96 ] [ 100 ]
In October 2019, an Odessa, Texas employee of Aghorn Operating Inc. and his wife were killed due to a water pump failure. Produced water with a high concentration of hydrogen sulfide was released by the pump. The worker died while responding to an automated phone call he had received alerting him to a mechanical failure in the pump, while his wife died after driving to the facility to check on him. [ 101 ] A CSB investigation cited lax safety practices at the facility, such as an informal lockout-tagout procedure and a nonfunctioning hydrogen sulfide alert system. [ 102 ]
The gas, produced by mixing certain household ingredients, was used in a suicide wave in 2008 in Japan. [ 103 ] The wave prompted staff at Tokyo's suicide prevention center to set up a special hotline during " Golden Week ", as they received an increase in calls from people wanting to kill themselves during the annual May holiday. [ 104 ]
As of 2010, this phenomenon has occurred in a number of US cities, prompting warnings to those arriving at the site of the suicide. [ 105 ] [ 106 ] [ 107 ] [ 108 ] [ 109 ]
In 2020, H 2 S ingestion was used as a suicide method by Japanese pro wrestler Hana Kimura . [ 110 ]
In 2024, Lucy-Bleu Knight, stepdaughter of famed musician Slash , also used H 2 S ingestion to commit suicide. [ 111 ]
Hydrogen sulfide is a central participant in the sulfur cycle , the biogeochemical cycle of sulfur on Earth. [ 112 ]
In the absence of oxygen , sulfur-reducing and sulfate-reducing bacteria derive energy from oxidizing hydrogen or organic molecules by reducing elemental sulfur or sulfate to hydrogen sulfide. Other bacteria liberate hydrogen sulfide from sulfur-containing amino acids ; this gives rise to the odor of rotten eggs and contributes to the odor of flatulence .
As organic matter decays under low-oxygen (or hypoxic ) conditions (such as in swamps, eutrophic lakes or dead zones of oceans), sulfate-reducing bacteria will use the sulfates present in the water to oxidize the organic matter, producing hydrogen sulfide as waste. Some of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides, which are not water-soluble. These metal sulfides, such as ferrous sulfide FeS, are often black or brown, leading to the dark color of sludge .
Several groups of bacteria can use hydrogen sulfide as fuel, oxidizing it to elemental sulfur or to sulfate by using dissolved oxygen, metal oxides (e.g., iron oxyhydroxides and manganese oxides ), or nitrate as electron acceptors. [ 113 ]
The purple sulfur bacteria and the green sulfur bacteria use hydrogen sulfide as an electron donor in photosynthesis , thereby producing elemental sulfur. This mode of photosynthesis is older than the mode of cyanobacteria , algae , and plants , which uses water as electron donor and liberates oxygen.
The biochemistry of hydrogen sulfide is a key part of the chemistry of the iron-sulfur world . In this model of the origin of life on Earth, geologically produced hydrogen sulfide is postulated as an electron donor driving the reduction of carbon dioxide. [ 114 ]
Hydrogen sulfide is lethal to most animals, but a few highly specialized species ( extremophiles ) do thrive in habitats that are rich in this compound. [ 115 ]
In the deep sea, hydrothermal vents and cold seeps with high levels of hydrogen sulfide are home to a number of extremely specialized lifeforms, ranging from bacteria to fish. [ which? ] [ 116 ] Because of the absence of sunlight at these depths, these ecosystems rely on chemosynthesis rather than photosynthesis . [ 117 ]
Freshwater springs rich in hydrogen sulfide are mainly home to invertebrates, but also include a small number of fish: Cyprinodon bobmilleri (a pupfish from Mexico), Limia sulphurophila (a poeciliid from the Dominican Republic ), Gambusia eurystoma (a poeciliid from Mexico), and a few Poecilia (poeciliids from Mexico). [ 115 ] [ 118 ] Invertebrates and microorganisms in some cave systems, such as Movile Cave , are adapted to high levels of hydrogen sulfide. [ 119 ]
Hydrogen sulfide has often been detected in the interstellar medium. [ 120 ] It also occurs in the clouds of planets in our solar system. [ 121 ] [ 122 ]
Hydrogen sulfide has been implicated in several mass extinctions that have occurred in the Earth's past. In particular, a buildup of hydrogen sulfide in the atmosphere may have caused, or at least contributed to, the Permian-Triassic extinction event 252 million years ago. [ 123 ] [ 124 ] [ 125 ]
Organic residues from these extinction boundaries indicate that the oceans were anoxic (oxygen-depleted) and had species of shallow plankton that metabolized H 2 S . The formation of H 2 S may have been initiated by massive volcanic eruptions, which emitted carbon dioxide and methane into the atmosphere, which warmed the oceans, lowering their capacity to absorb oxygen that would otherwise oxidize H 2 S . The increased levels of hydrogen sulfide could have killed oxygen-generating plants as well as depleted the ozone layer, causing further stress. Small H 2 S blooms have been detected in modern times in the Dead Sea and in the Atlantic Ocean off the coast of Namibia . [ 123 ] | https://en.wikipedia.org/wiki/Hydrogen_sulfide |
Hydrogen sulfide chemosynthesis is a form of chemosynthesis which uses hydrogen sulfide . [ 1 ] It is common in hydrothermal vent microbial communities [ 2 ] [ 3 ] Due to the lack of light in these environments this is predominant over photosynthesis . [ 4 ]
Giant tube worms use bacteria in their trophosome to fix carbon dioxide (using hydrogen sulfide as their energy source) and produce sugars and amino acids . [ 5 ] Some reactions produce sulfur:
In the above process, hydrogen sulfide serves as a source of electrons for the reaction. [ 6 ] Instead of releasing oxygen gas while fixing carbon dioxide as in photosynthesis , hydrogen sulfide chemosynthesis produces solid globules of sulfur in the process.
Mechanism of Action
In deep sea environments, different organisms have been observed to have the ability to oxidize reduced compounds such as hydrogen sulfide. [ 7 ] Oxidation is the loss of electrons in a chemical reaction. [ 8 ] Most chemosynthetic bacteria form symbiotic associations with other small eukaryotes [ 9 ] The electrons that are released from hydrogen sulfide will provide the energy to sustain a proton gradient across the bacterial cytoplasmic membrane. This movement of protons will eventually result in the production of adenosine triphosphate. The amount of energy derived from the process is also dependent on the type of final electron acceptor. [ 10 ]
Other Examples Of Chemosynthetic Organisms (using H 2 S as electron donor)
Across the world, researchers have observed different organisms in various locations capable of carrying out the process. Yang and colleagues in 2011 surveyed five Yellowstone thermal springs of varying depths and observed that the distribution of chemosynthetic microbes coincided with temperature as Sulfurihydrogenibiom was found at higher temperatures while Thiovirga inhabited cooler waters [ 11 ] Miyazaki et al., in 2020 also found an endosymbiont capable of hydrogen sulfide chemosynthesis which contained campylobacter species and a gastropod from the genus Alviniconcha oxidise hydrogen sulfide in the Indian Ocean [ 12 ] Furthermore, chemosynthetic bacteria such as purple sulfur bacteria have yellow globules of sulfur visible in their cytoplasm. [ 13 ] | https://en.wikipedia.org/wiki/Hydrogen_sulfide_chemosynthesis |
A hydrogen tanker or liquid hydrogen tanker is a tank ship designed for transporting liquefied hydrogen .
The World Energy Network research program of the Japanese New Sunshine Project was divided into 3 phases [ 1 ] during the period 1993 to 2002, its goal was to study the distribution of liquid hydrogen with hydrogen tankers [ 2 ] based on the LNG carrier technology of self-supporting tank designs such as the prismatic and spherical tank. Further research on maritime transport of hydrogen was done in the development for safe utilization and infrastructure of hydrogen project (2003–2007). [ 3 ]
Similar to an LNG carrier the boil off gas can be used for propulsion of the ship. [ 4 ]
The "Suiso Frontier" collected a cargo of liquid hydrogen from the port of Hastings in Victoria , Australia on 28 January 2022 and arrived back in Kobe , Japan at the end of February, 2022 with the cargo. [ 5 ] A second cargo was collected from the Hastings terminal in May, 2022 with a return to Japan in June 2022. [ 6 ]
In November 2022, Approval in Principle (AiP) was granted by Nippon Kaiji Kyokai (ClassNK) for Kawasaki Heavy Industries 's dual fuel generator engine using hydrogen gas as fuel , which will be installed on a 160,000 m 3 liquefied hydrogen carrier developed by Kawasaki. Kawasaki intends to conduct a demonstration test of this engine after installing it on a large-scale liquefied hydrogen carrier which is planned to be commercialized in the mid-2020s. [ 4 ] [ 7 ] In June 2023, Kawasaki Heavy Industries announced its completion of technological development for a cargo containment system (CCS) to be used in large liquefied hydrogen carriers. [ 8 ]
This merchant ship article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrogen_tanker |
Hydrogen technologies are technologies that relate to the production and use of hydrogen as a part hydrogen economy . Hydrogen technologies are applicable for many uses.
Some hydrogen technologies are carbon neutral and could have a role in preventing climate change and a possible future hydrogen economy . Hydrogen is a chemical widely used in various applications including ammonia production, oil refining and energy. [ 1 ] The most common methods for producing hydrogen on an industrial scale are: Steam reforming , oil reforming , coal gasification , water electrolysis . [ 2 ]
Hydrogen is not a primary energy source , because it is not naturally occurring as a fuel . It is, however, widely regarded as an ideal energy storage medium, due to the ease with which electricity can convert water into hydrogen and oxygen through electrolysis and can be converted back to electrical power using a fuel cell or hydrogen turbine. [ 3 ] There are a wide number of different types of fuel and electrolysis cells. [ 4 ]
The potential environmental impact depends primarily on the methods used to generate hydrogen as a fuel.
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Forze Hydrogen-Electric Racing Team Delft
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Possible future aircraft using precooled jet engines include Reaction Engines Skylon and the Reaction Engines A2 .
The following rockets were/are partially or completely propelled by hydrogen fuel: | https://en.wikipedia.org/wiki/Hydrogen_technologies |
Hydrogen telluride is the inorganic compound with the formula H 2 Te . A hydrogen chalcogenide and the simplest hydride of tellurium , it is a colorless gas. Although unstable in ambient air, the gas can exist long enough to be readily detected by the odour of rotting garlic at extremely low concentrations; or by the revolting odour of rotting leeks at somewhat higher concentrations. Most compounds with Te–H bonds ( tellurols ) are unstable with respect to loss of H 2 . H 2 Te is chemically and structurally similar to hydrogen selenide , both are acidic. The H–Te–H angle is about 90°. Volatile tellurium compounds often have unpleasant odours, reminiscent of decayed leeks or garlic. [ 2 ]
Electrolytic methods have been developed. [ 3 ]
H 2 Te can also be prepared by hydrolysis of the telluride derivatives of electropositive metals. [ 4 ] The typical hydrolysis is that of aluminium telluride :
Other salts of Te 2− such as MgTe and sodium telluride can also be used. Na 2 Te can be made by the reaction of Na and Te in anhydrous ammonia . [ 5 ] The intermediate in the hydrolysis, HTe − , can be isolated as salts as well. NaHTe can be made by reducing tellurium with NaBH 4 . [ 5 ]
Hydrogen telluride cannot be efficiently prepared from its constituent elements, in contrast to H 2 Se. [ 3 ]
H 2 Te is an endothermic compound, degrading to the elements at room temperature:
Light accelerates the decomposition. It is unstable in air, being oxidized to water and elemental tellurium: [ 6 ]
It is almost as acidic as phosphoric acid ( K a = 8.1×10 −3 ), having a K a value of about 2.3×10 −3 . [ 6 ] It reacts with many metals to form tellurides. [ 7 ] | https://en.wikipedia.org/wiki/Hydrogen_telluride |
Hydrogen transport involves the use of technology to transport hydrogen from the point of generation to the point of use.
Hydrogen can be transported in a variety of forms.
Hydrogen can be transported in gaseous form, typically in a pipeline. Because hydrogen gas is highly reactive, the pipeline or other container must be able to resist interacting with the gas. Hydrogen's low density at atmospheric pressure means that gas transport is suitable only for low volume requirements. [ 1 ]
Hydrogen switches to the liquid phase at −253 °C (−423.4 °F). Thus, transporting liquid hydrogen requires sophisticated refrigeration technologies such as cryogenic tanker trucks and liquefaction plants. [ 1 ]
Hydrogen can be reacted with other elements to form a variety of compounds. This allows it to be transported in either liquid (e.g., water) or solid form. One variation on this concept is to transport atomic silicon, produced using renewable energy . Mixing silicon with water separates water's oxygen from its hydrogen without requiring additional energy. The hydrogen can then be oxidixed with the oxygen (or air) to produce energy (with water as the only byproduct). [ 2 ]
Mechanochemistry refers to chemical reactions triggered by mechanical forces as opposed to heat, light, or electric potential . Ball milling can crush material such as boron nitride or graphene , allowing hydrogen gas to be absorbed by the powder, storing the hydrogen. The hydrogen can be released by heating the powder. These techniques offer the potential of substantial net energy savings. [ 3 ]
Hydrogen transport must address various safety threats.
It is highly flammable, requiring little energy to ignite. However, it is low density (0.0837 g/L), which allows leaked gas to rapidly dissipate, rather than accumulate as a higher density gas might, such as chlorine (3.214 g/L). [ 4 ]
Liquid hydrogen requires such low temperatures that leaks may solidify other air components such as nitrogen and oxygen . Solid oxygen can mix with liquid hydrogen, forming a mixture that could self-ignite. A jet fire can also ignite. [ 4 ]
At high concentrations, hydrogen gas is an asphyxiant , but is not otherwise toxic. [ 5 ]
ISO Technical Committee 197 is developing standards governing hydrogen applications. Standards are available onboard systems, fuel tanks and vehicle refueling systems and for production (including electrolysis and steam methane reformers ). [ 4 ]
Individual jurisdictions such as Italy have developed additional standards. [ 4 ] | https://en.wikipedia.org/wiki/Hydrogen_transport |
A hydrogen turboexpander-generator or generator-loaded expander for hydrogen gas is an axial flow turbine or radial expander for energy recovery through which a high pressure hydrogen gas is expanded to produce work used to drive an electrical generator . It replaces the control valve or regulator where the pressure drops to the appropriate pressure for the low-pressure network. A turboexpander generator can help recover energy losses and offset electrical requirements and CO 2 emissions.
Per stage, 200 bar is handled with up to 15,000 kW power and a maximum expansion ratio of 14, the generator loaded expander for hydrogen gas is fitted with an automatic thrust balance , a dry gas seal , and a programmable logic control with remote monitoring and diagnostics. [ 1 ]
Hydrogen turboexpander-generators are used for hydrogen pipeline transport in combination with hydrogen compressors and energy recovery in underground hydrogen storage . A variation is the compressor loaded turboexpanders which are used in the liquefaction of gases such as liquid hydrogen . [ 2 ] | https://en.wikipedia.org/wiki/Hydrogen_turboexpander-generator |
A hydrogenase mimic or bio-mimetic is an enzyme mimic of hydrogenases .
One of the more interesting applications of hydrogenases is to produce hydrogen , due its capacity to catalyze its redox reaction:
In the field of hydrogen production, the incorporation of chemical compounds in electrochemical devices to produce molecular hydrogen has been a topic of huge interest in the recent years due to the possibility of using hydrogen as a replacement of the fossil fuels as an energetic carrier. This approach of using materials inspired by natural models to do the same function as their natural counterparts is called bio-mimetic approach. Nowadays this approach has received a big impulse due to the availability of high-resolution crystal structures of several hydrogenases obtained with different techniques. The technical details of these hydrogenases are stored in electronic databases at disposition to who may be interested.
This information has allowed scientists to determine the important parts of the enzyme necessary to catalyze the reaction and determine the pathway of the reaction in a very detailed way. Which allow to have a very good comprehension of what is necessary to catalyze the same reaction using artificial components.
Several studies have demonstrated the possibility to develop chemical cells inspired by biological models to produce molecular hydrogen , for example: Selvaggi et al. [ 1 ] explored the possibility to use energy captured by the PSII, developing for that goal, an organic-inorganic hybrid system replacing the PSII protein complex by microspheres of TiO 2 a photo-inducible compound. In order to get the hydrogen production, the TiO 2 microspheres were covered with hydrogenases extracted from the marine thermophile Pyrococcus furiosus , in that way the energy of the light was captured by the TiO 2 microspheres and used to generate protons and electrons from water with the subsequent production of 29 μmol de H 2 hour −1 .
The obtained results from immobilization of hydrogenases on the surface of electrodes have demonstrated the viability of incorporating these enzymes in electrochemical cells, due to their ability to produce gaseous hydrogen through a redox reaction. (Hallenbeck and Benemann [ 2 ] ). This opens the possibility of using biomimetic compounds in electrodes to generate hydrogen.
Until the present day several bio-mimetic compounds have been developed: Collman et al. [ 3 ] produced ruthenium porphyrins, furthermore of the bio-mimetic compounds published by the research teams of Rauchfuss, Darensbourg and Pickett (in Artero and Fontecave [ 4 ] ) who developed bio-mimetic compounds of the [Fe] hydrogenase . More recently Manor and Rauchfuss [ 5 ] presented a very interesting mimic compound based in the [NiFe] hydrogenase with bidirectional properties, this compound has the characteristic that it carries two borane protected cyanide ligands at the iron atom. Some works about bio-mimetic compounds of hydrogenases are summarized in table 1.
Bridged Fe-dimer
complexes
columns (PGC)
m-(SCH(CH 3 )CH(CH 3 )S)eFe 2 (CO) 6 , m-(SCH 2 CH(CH 2 OH)S)eFe 2 (CO) 6 ,
Table 1. Bio-mimetic compounds of hydrogenases
However, obtaining bio-mimetic compounds able to hydrogen production on an industrial scale still is elusive. For that reason, the research of this topic is a hot spot in science which has taken the efforts of researchers around the world. Recently a review of the works done in bio-mimetic compounds was published by Schilter et al. . [ 22 ] Showing that some studies have got promising results in bio-mimetic compounds synthesized in laboratory.
Recently the possibility of study such compounds using molecular modeling assisted by informatic software has opened new possibilities in the study of the redox reaction of biomimetic compounds. For example, using "Density Functional Theory" (DFT) computer modeling made it possible to propose a pathway for H 2 binding and splitting on the catalytic center of a hydrogenase active site model (Greco [ 23 ] ). Other example of the application of computational modeling in the study of hydrogenases is the work done by Breglia et al. , [ 24 ] whose results shows the chemical pathway of how oxygen inhibited the redox reaction of [NiFe] hydrogenases .
The Fe-only hydrogenases are particularly common enzymes for synthetic organometallic chemists to mimic. This interest is motivated by the inclusion of high field ligands like cyano and CO ( metal carbonyl ) in the first coordination sphere of the pertinent di-iron cluster. Free cyano and carbonyl ligands are toxic to many biological systems. So, their inclusion in this system suggests they play pivotal roles. These high field ligands may ensure the iron centers at the active site remain in a low spin state throughout the catalytic cycle. In addition, there is bridging di thiolate between the two iron centers. This dithiolate has a three atom backbone in which the identity of the central atom is still undetermined; it models crystallographically as a CH 2 , NH or O group. There is reason to believe that this central atom is an amine which functions as a Lewis base . This amine combined with Lewis acidic iron centers makes the enzyme a bifunctional catalyst which can split hydrogen between a proton acceptor and a hydride acceptor or produce hydrogen from a proton and hydride.
Since none of the ligands on the iron centers are part of the enzyme's amino acid backbone, they can not be investigated through site-directed mutagenesis , but enzyme mimicry is a feasible approach.
Many elegant structural mimics have been synthesized reproducing the atomic content and connectivity of the active site. [ 25 ] The work by Pickett is a prime example of this field. [ 26 ] The catalytic activity of these mimics do not however compare to the native enzyme. In contrast, functional mimics, also known as bio-inspired catalysts , aim to reproduce only the functional features of an enzyme often through the use of different atomic content and connectivity from that found in the native enzymes. Functional mimics have made advances in the reactive chemistry and have implications on the mechanistic activity of the enzyme as well as acting as catalysts in their own right. [ 27 ] [ 28 ] [ 29 ] | https://en.wikipedia.org/wiki/Hydrogenase_mimic |
Hydrogenated MDI ( H 12 MDI or 4,4′-diisocyanato dicyclohexylmethane ) is an organic compound in the class known as isocyanates . [ 1 ] More specifically, it is an aliphatic diisocyanate. It is a water white liquid at room temperature and is manufactured in relatively small quantities. It is also known as 4,4'-methylenedi(cyclohexyl isocyanate) or methylene bis(4-cyclohexylisocyanate) [ 2 ] and has the formula CH 2 [(C 6 H 10 )NCO] 2 .
The product is manufactured by hydrogenation of methylene diphenyl diisocyanate . It may also be manufactured by phosgenation of 4,4-Diaminodicyclohexylmethane .
Aliphatic diisocyanates are not used in the production of polyurethane foam as the cost is too high and foam is very much a commodity. It is used in special applications for polyurethane , such as enamel coatings which are resistant to abrasion and degradation from ultraviolet light . There are also multiple patents where prepolymers based on it are used in golf ball production. [ 3 ] It is available commercially under the tradename of Desmodur W from Covestro - formerly Bayer Material Science. It is used as a reactive building block for the preparation of other chemical products such as isocyanate terminated prepolymers and other urethane polymers. [ 4 ] The isocyanate groups can undergo addition reactions at room temperature with compounds which contain active hydrogens especially amines and polyols. Polyurethane resins based on this diisocyanate have good flexibility and mechanical strength. The polymers formed tend to have abrasion and hydrolysis resistance as well as retaining gloss and physical properties upon weathering. The resins based on this material are useful in coatings for flooring, roofing, maintenance and adhesives, and sealants. They find use in the coatings , adhesives , sealants and elastomers (CASE) applications. [ 5 ] [ 6 ] A prepolymer made from H 12 MDI and incorporating dimethylol propionic acid can also be converted to light stable polyurethane dispersions . [ 7 ] [ 8 ] | https://en.wikipedia.org/wiki/Hydrogenated_MDI |
Hydrogenated starch hydrolysates ( HSHs ), also known as polyglycitol syrup (INS 964), are mixtures of several sugar alcohols (a type of sugar substitute). Hydrogenated starch hydrolysates were developed by the Swedish company Lyckeby Starch in the 1960s. [ 1 ] The HSH family of polyols is an approved food ingredient in Canada, Japan, and Australia. HSH sweeteners provide 40 to 90% sweetness relative to table sugar .
Hydrogenated starch hydrolysates are produced by the partial hydrolysis of starch – most often corn starch, but also potato starch or wheat starch. This creates dextrins ( glucose and short glucose chains). The hydrolyzed starch (dextrin) then undergoes hydrogenation to convert the dextrins to sugar alcohols.
Hydrogenated starch hydrolysates are similar to sorbitol : if the starch is completely hydrolyzed so that only single glucose molecules remain, then after hydrogenation the result is sorbitol. Because in HSHs the starch is not completely hydrolyzed, a mixture of sorbitol, maltitol , and longer chain hydrogenated saccharides (such as maltotriitol) is produced. When no single polyol is dominant in the mix, the generic name hydrogenated starch hydrolysates is used. However, if 50% or more of the polyols in the mixture are of one type, it can be labeled as "sorbitol syrup", or "maltitol syrup", etc.
Hydrogenated starch hydrolysates are used commercially in the same way as other common sugar alcohols. They are often used as both a sweetener and as a humectant (moisture-retaining ingredient). As a crystallization modifier, they can prevent syrups from forming crystals of sugar. It is used to add bulk, body, texture, and viscosity to mixtures, and can protect against damage from freezing and drying. HSH products are generally blended with other sweeteners, both caloric and artificial.
Similar to xylitol , hydrogenated starch hydrolysates are not readily fermented by oral bacteria and are used to formulate sugarless products that do not promote dental caries .
HSHs are also more slowly absorbed in the digestive tract, thus, have a reduced glycemic potential relative to glucose. However, they do have a laxative effect when consumed in large amounts. [ 2 ] | https://en.wikipedia.org/wiki/Hydrogenated_starch_hydrolysates |
Hydrogenation is a chemical reaction between molecular hydrogen (H 2 ) and another compound or element, usually in the presence of a catalyst such as nickel , palladium or platinum . The process is commonly employed to reduce or saturate organic compounds . Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, often an alkene . Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogenation reduces double and triple bonds in hydrocarbons . [ 1 ]
Hydrogenation has three components, the unsaturated substrate, the hydrogen (or hydrogen source) and, invariably, a catalyst . The reduction reaction is carried out at different temperatures and pressures depending upon the substrate and the activity of the catalyst.
The same catalysts and conditions that are used for hydrogenation reactions can also lead to isomerization of the alkenes from cis to trans . This process is of great interest because hydrogenation technology generates most of the trans fat in foods. A reaction where bonds are broken while hydrogen is added is called hydrogenolysis , a reaction that may occur to carbon-carbon and carbon-heteroatom ( oxygen , nitrogen or halogen ) bonds. Some hydrogenations of polar bonds are accompanied by hydrogenolysis.
For hydrogenation, the obvious source of hydrogen is H 2 gas itself, which is typically available commercially within the storage medium of a pressurized cylinder. The hydrogenation process often uses greater than 1 atmosphere of H 2 , usually conveyed from the cylinders and sometimes augmented by "booster pumps". Gaseous hydrogen is produced industrially from hydrocarbons by the process known as steam reforming . [ 2 ] For many applications, hydrogen is transferred from donor molecules such as formic acid , isopropanol , and dihydroanthracene . [ 3 ] These hydrogen donors undergo dehydrogenation to, respectively, carbon dioxide , acetone , and anthracene . These processes are called transfer hydrogenations .
An important characteristic of alkene and alkyne hydrogenations, both the homogeneously and heterogeneously catalyzed versions, is that hydrogen addition occurs with " syn addition ", with hydrogen entering from the least hindered side. [ 4 ] This reaction can be performed on a variety of different functional groups .
With rare exceptions, H 2 is unreactive toward organic compounds in the absence of metal catalysts. The unsaturated substrate is chemisorbed onto the catalyst, with most sites covered by the substrate. In heterogeneous catalysts, hydrogen forms surface hydrides (M-H) from which hydrogens can be transferred to the chemisorbed substrate. Platinum , palladium , rhodium , and ruthenium form highly active catalysts, which operate at lower temperatures and lower pressures of H 2 . Non-precious metal catalysts, especially those based on nickel (such as Raney nickel and Urushibara nickel ) have also been developed as economical alternatives, but they are often slower or require higher temperatures. The trade-off is activity (speed of reaction) vs. cost of the catalyst and cost of the apparatus required for use of high pressures. Notice that the Raney-nickel catalysed hydrogenations require high pressures: [ 8 ] [ 9 ]
Catalysts are usually classified into two broad classes: homogeneous and heterogeneous . Homogeneous catalysts dissolve in the solvent that contains the unsaturated substrate. Heterogeneous catalysts are solids that are suspended in the same solvent with the substrate or are treated with gaseous substrate.
Some well known homogeneous catalysts are indicated below. These are coordination complexes that activate both the unsaturated substrate and the H 2 . Most typically, these complexes contain platinum group metals, especially Rh and Ir.
Homogeneous catalysts are also used in asymmetric synthesis by the hydrogenation of prochiral substrates. An early demonstration of this approach was the Rh-catalyzed hydrogenation of enamides as precursors to the drug L-DOPA . [ 10 ] To achieve asymmetric reduction, these catalyst are made chiral by use of chiral diphosphine ligands. [ 11 ] Rhodium catalyzed hydrogenation has also been used in the herbicide production of S-metolachlor, which uses a Josiphos type ligand (called Xyliphos). [ 12 ] In principle asymmetric hydrogenation can be catalyzed by chiral heterogeneous catalysts, [ 13 ] but this approach remains more of a curiosity than a useful technology.
Heterogeneous catalysts for hydrogenation are more common industrially. In industry, precious metal hydrogenation catalysts are deposited from solution as a fine powder on the support, which is a cheap, bulky, porous, usually granular material, such as activated carbon , alumina , calcium carbonate or barium sulfate . [ 14 ] For example, platinum on carbon is produced by reduction of chloroplatinic acid in situ in carbon. Examples of these catalysts are 5% ruthenium on activated carbon, or 1% platinum on alumina. Base metal catalysts, such as Raney nickel , are typically much cheaper and do not need a support. Also, in the laboratory, unsupported (massive) precious metal catalysts such as platinum black are still used, despite the cost.
As in homogeneous catalysts, the activity is adjusted through changes in the environment around the metal, i.e. the coordination sphere . Different faces of a crystalline heterogeneous catalyst display distinct activities, for example. This can be modified by mixing metals or using different preparation techniques. Similarly, heterogeneous catalysts are affected by their supports.
In many cases, highly empirical modifications involve selective "poisons". Thus, a carefully chosen catalyst can be used to hydrogenate some functional groups without affecting others, such as the hydrogenation of alkenes without touching aromatic rings, or the selective hydrogenation of alkynes to alkenes using Lindlar's catalyst . For example, when the catalyst palladium is placed on barium sulfate and then treated with quinoline , the resulting catalyst reduces alkynes only as far as alkenes. The Lindlar catalyst has been applied to the conversion of phenylacetylene to styrene . [ 15 ]
Transfer hydrogenation uses hydrogen-donor molecules other than molecular H 2 . These "sacrificial" hydrogen donors, which can also serve as solvents for the reaction, include hydrazine , formic acid , and alcohols such as isopropanol. [ 18 ]
In organic synthesis , transfer hydrogenation is useful for the asymmetric hydrogenation of polar unsaturated substrates, such as ketones , aldehydes and imines , by employing chiral catalysts .
Polar substrates such as nitriles can be hydrogenated electrochemically , using protic solvents and reducing equivalents as the source of hydrogen. [ 19 ]
The addition of hydrogen to double or triple bonds in hydrocarbons is a type of redox reaction that can be thermodynamically favorable. For example, the addition of hydrogen to ethene has a Gibbs free energy change of -101 kJ·mol −1 , which is highly exothermic . [ 11 ] In the hydrogenation of vegetable oils and fatty acids, for example, the heat released, about 25 kcal per mole (105 kJ/mol), is sufficient to raise the temperature of the oil by 1.6–1.7 °C per iodine number drop.
However, the reaction rate for most hydrogenation reactions is negligible in the absence of catalysts. The mechanism of metal-catalyzed hydrogenation of alkenes and alkynes has been extensively studied. [ 20 ] First of all isotope labeling using deuterium confirms the regiochemistry of the addition:
On solids, the accepted mechanism is the Horiuti- Polanyi mechanism: [ 21 ] [ 22 ]
In the third step, the alkyl group can revert to alkene, which can detach from the catalyst. Consequently, contact with a hydrogenation catalyst allows cis-trans -isomerization. The trans -alkene can reassociate to the surface and undergo hydrogenation. These details are revealed in part using D 2 (deuterium), because recovered alkenes often contain deuterium.
For aromatic substrates, the first hydrogenation is slowest. The product of this step is a cyclohexadiene, which hydrogenate rapidly and are rarely detected. Similarly, the cyclohexene is ordinarily reduced to cyclohexane.
In many homogeneous hydrogenation processes, [ 23 ] the metal binds to both components to give an intermediate alkene-metal(H) 2 complex. The general sequence of reactions is assumed to be as follows or a related sequence of steps:
Alkene isomerization often accompanies hydrogenation. This important side reaction proceeds by beta-hydride elimination of the alkyl hydride intermediate: [ 24 ]
Often the released olefin is trans.
The hydrogenation of nitrogen to give ammonia is conducted on a vast scale by the Haber–Bosch process, [ 25 ] consuming an estimated 1% of the world's energy supply .
Oxygen can be partially hydrogenated to give hydrogen peroxide , although this process has not been commercialized. One difficulty is preventing the catalysts from triggering decomposition of the hydrogen peroxide to form water. [ 26 ] [ 27 ]
Catalytic hydrogenation has diverse industrial uses. Most frequently, industrial hydrogenation relies on heterogeneous catalysts. [ 2 ]
The food industry hydrogenates vegetable oils to convert them into solid or semi-solid fats that can be used in spreads, candies, baked goods, and other products like margarine . Vegetable oils are made from polyunsaturated fatty acids (having more than one carbon-carbon double bond). Hydrogenation eliminates some of these double bonds. [ 28 ]
In petrochemical processes, hydrogenation is used to convert alkenes and aromatics into saturated alkanes (paraffins) and cycloalkanes (naphthenes), which are less toxic and less reactive. Relevant to liquid fuels that are stored sometimes for long periods in air, saturated hydrocarbons exhibit superior storage properties. On the other hand, alkenes tend to form hydroperoxides , which can form gums that interfere with fuel handling equipment. For example, mineral turpentine is usually hydrogenated. Hydrocracking of heavy residues into diesel is another application. In isomerization and catalytic reforming processes, some hydrogen pressure is maintained to hydrogenolyze coke formed on the catalyst and prevent its accumulation.
Hydrogenation is a useful means for converting unsaturated compounds into saturated derivatives. Substrates include not only alkenes and alkynes, but also aldehydes, imines, and nitriles, [ 29 ] which are converted into the corresponding saturated compounds, i.e. alcohols and amines. Thus, alkyl aldehydes, which can be synthesized with the oxo process from carbon monoxide and an alkene, can be converted to alcohols. E.g. 1-propanol is produced from propionaldehyde, produced from ethene and carbon monoxide. Xylitol , a polyol , is produced by hydrogenation of the sugar xylose , an aldehyde. Primary amines can be synthesized by hydrogenation of nitriles , while nitriles are readily synthesized from cyanide and a suitable electrophile. For example, isophorone diamine, a precursor to the polyurethane monomer isophorone diisocyanate , is produced from isophorone nitrile by a tandem nitrile hydrogenation/reductive amination by ammonia, wherein hydrogenation converts both the nitrile into an amine and the imine formed from the aldehyde and ammonia into another amine.
The earliest hydrogenation was that of the platinum-catalyzed addition of hydrogen to oxygen in the Döbereiner's lamp , a device commercialized as early as 1823. The French chemist Paul Sabatier is considered the father of the hydrogenation process. In 1897, building on the earlier work of James Boyce , an American chemist working in the manufacture of soap products, he discovered that traces of nickel catalyzed the addition of hydrogen to molecules of gaseous hydrocarbons in what is now known as the Sabatier process . For this work, Sabatier shared the 1912 Nobel Prize in Chemistry . Wilhelm Normann was awarded a patent in Germany in 1902 and in Britain in 1903 for the hydrogenation of liquid oils, which was the beginning of what is now a worldwide industry. The commercially important Haber–Bosch process , first described in 1905, involves hydrogenation of nitrogen. In the Fischer–Tropsch process , reported in 1922 carbon monoxide, which is easily derived from coal, is hydrogenated to liquid fuels.
In 1922, Voorhees and Adams described an apparatus for performing hydrogenation under pressures above one atmosphere. [ 30 ] The Parr shaker, the first product to allow hydrogenation using elevated pressures and temperatures, was commercialized in 1926 based on Voorhees and Adams' research and remains in widespread use. In 1924 Murray Raney developed a finely powdered form of nickel, which is widely used to catalyze hydrogenation reactions such as conversion of nitriles to amines or the production of margarine.
In the 1930s, Calvin discovered that copper(II) complexes oxidized H 2 . The 1960s witnessed the development of well defined homogeneous catalysts using transition metal complexes, e.g., Wilkinson's catalyst (RhCl(PPh 3 ) 3 ). Soon thereafter cationic Rh and Ir were found to catalyze the hydrogenation of alkenes and carbonyls. [ 31 ] In the 1970s, asymmetric hydrogenation was demonstrated in the synthesis of L-DOPA , and the 1990s saw the invention of Noyori asymmetric hydrogenation . [ 32 ] The development of homogeneous hydrogenation was influenced by work started in the 1930s and 1940s on the oxo process and Ziegler–Natta polymerization .
For most practical purposes, hydrogenation requires a metal catalyst. Hydrogenation can, however, proceed from some hydrogen donors without catalysts. Illustrative hydrogen donors include diimide and aluminium isopropoxide , the latter illustrated by the Meerwein–Ponndorf–Verley reduction . Some metal-free catalytic systems have been investigated. One such system for reduction of ketones consists of tert -butanol and potassium tert-butoxide and very high temperatures. [ 33 ] The reaction depicted below describes the hydrogenation of benzophenone :
A chemical kinetics study [ 34 ] found this reaction is first-order in all three reactants suggesting a cyclic 6-membered transition state .
Another system for metal-free hydrogenation is based on the phosphine - borane , compound 1 , which has been called a frustrated Lewis pair . It reversibly accepts dihydrogen at relatively low temperatures to form the phosphonium borate 2 which can reduce simple hindered imines . [ 35 ]
The reduction of nitrobenzene to aniline has been reported to be catalysed by fullerene , its mono-anion, atmospheric hydrogen and UV light. [ 36 ]
Today's bench chemist has three main choices of hydrogenation equipment:
The original and still a commonly practised form of hydrogenation in teaching laboratories, this process is usually effected by adding solid catalyst to a round bottom flask of dissolved reactant which has been evacuated using nitrogen or argon gas and sealing the mixture with a penetrable rubber seal. Hydrogen gas is then supplied from a H 2 -filled balloon . The resulting three phase mixture is agitated to promote mixing. Hydrogen uptake can be monitored, which can be useful for monitoring progress of a hydrogenation. This is achieved by either using a graduated tube containing a coloured liquid, usually aqueous copper sulfate or with gauges for each reaction vessel.
Since many hydrogenation reactions such as hydrogenolysis of protecting groups and the reduction of aromatic systems proceed extremely sluggishly at atmospheric temperature and pressure, pressurised systems are popular. In these cases, catalyst is added to a solution of reactant under an inert atmosphere in a pressure vessel . Hydrogen is added directly from a cylinder or built in laboratory hydrogen source, and the pressurized slurry is mechanically rocked to provide agitation, or a spinning basket is used. [ 37 ] Recent advances in electrolysis technology have led to the development of high pressure hydrogen generators , which generate hydrogen up to 1,400 psi (100 bar) from water. Heat may also be used, as the pressure compensates for the associated reduction in gas solubility.
Flow hydrogenation has become a popular technique at the bench and increasingly the process scale. [ citation needed ] This technique involves continuously flowing a dilute stream of dissolved reactant over a fixed bed catalyst in the presence of hydrogen. Using established high-performance liquid chromatography technology, this technique allows the application of pressures from atmospheric to 1,450 psi (100 bar). Elevated temperatures may also be used. At the bench scale, systems use a range of pre-packed catalysts which eliminates the need for weighing and filtering pyrophoric catalysts.
Catalytic hydrogenation is done in a tubular plug-flow reactor packed with a supported catalyst. The pressures and temperatures are typically high, although this depends on the catalyst. Catalyst loading is typically much lower than in laboratory batch hydrogenation, and various promoters are added to the metal, or mixed metals are used, to improve activity, selectivity and catalyst stability. The use of nickel is common despite its low activity, due to its low cost compared to precious metals.
Gas liquid induction reactors (hydrogenator) are also used for carrying out catalytic hydrogenation. [ 38 ] | https://en.wikipedia.org/wiki/Hydrogenation |
In chemistry, the hydrogenation of carbon–nitrogen double bonds is the addition of the elements of dihydrogen (H 2 ) across a carbon–nitrogen double bond, forming amines or amine derivatives. [ 1 ] Although a variety of general methods have been developed for the enantioselective hydrogenation of ketones, [ 2 ] methods for the hydrogenation of carbon–nitrogen double bonds are less general. Hydrogenation of imines is complicated by both syn / anti isomerization and tautomerization to enamines, which may be hydrogenated with low enantioselectivity in the presence of a chiral catalyst. [ 3 ] Additionally, the substituent attached to nitrogen affects both the reactivity and spatial properties of the imine, complicating the development of a general catalyst system for imine hydrogenation. Despite these challenges, methods have been developed that address particular substrate classes, such as N -aryl, N -alkyl, and endocyclic imines.
If the complex is chiral and non-racemic and the substrate is prochiral, an excess of a single enantiomer of a chiral product can result. [ 4 ]
Hydrogen for the reduction of C=N double bond can either be provided by hydrogen gas (H 2 ) or transferred from sources of H 2 , such as alcohols and formic acid. The process is usually catalyzed by transition metal complexes . For metal catalyzed reactions, the transfer of H 2 to the imine can proceed by either inner sphere or outer sphere mechanisms.
Relevant to the inner sphere mechanism are the two modes by which imines can coordinate, as a π or as a σ-donor ligand. The pi-imines are also susceptible to conversion to iminium ligands upon N-protonation. The binding mode for the imine is unclear, both η 1 (σ-type) and η 2 (π-type). The final step in the mechanism is release of the amine. [ 5 ] In some iridium-catalyzed hydrogenations, the mechanism is believed to proceed via a monohydride species. The oxidation state of iridium is always +3.
Examples: [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ]
Ruthenium(II) complexes of amine ligands are known for engaging in the outer-sphere mechanism, during which the imine/iminium substrate does not bind to the metal center directly. Instead, substrate receives the elements of H 2 by interaction with Ru-H and N-H sites. [ 12 ] [ 13 ] This process is utilized by the Shvo catalyst and many ruthenium amine complexes. One such complex is Baratta's catalyst RuCl 2 (PPh 3 ) 2 (ampy) (ampy = 2- picolylamine ) for transfer hydrogenation . [ 14 ]
Because the substituents attached to the imine nitrogen exert a profound influence on reactivity, few general catalyst systems exist for the enantioselective hydrogenation of imines and imine derivatives. However, catalyst systems have been developed that catalyze hydrogenation of particular classes of imines with high enantioselectivity and yield. This section describes some of these systems and is organized by the substitution pattern of the imine.
α-Carboxy imines are attractive precursors for α-amino acids. Organocatalytic reduction of these substrates is possible using a Hantzsch ester and a chiral phosphoric acid catalyst. [ 15 ]
Imine hydrogenation provides a practical route to chiral amines. [ 16 ] Metolachlor is the active ingredient in the widely used herbicide Dual Magnum. A key step in its industrial production involves the enantioselective reduction of an N -aryl imine. This reduction is achieved with extremely high turnover number (albeit moderate enantioselectivity) through the use of a specialized catalyst system consisting of [Ir(COD)Cl] 2 , modified Josiphos ligand 3 , and acid and iodide additives. [ 17 ]
Imines may be reduced enantioselectively using stoichiometric amounts of chiral metal hydrides. [ 18 ] Such methods have the advantage that they are easy to implement. Reduction with hydrosilanes is a second alternative to transition-metal catalyzed hydrogenation. [ 19 ] | https://en.wikipedia.org/wiki/Hydrogenation_of_carbon–nitrogen_double_bonds |
Hydrogenics is a developer and manufacturer of hydrogen generation and fuel cell products based on water electrolysis and proton-exchange membrane (PEM) technology. [ 2 ] [ 3 ] Hydrogenics is divided into two business units: OnSite Generation and Power Systems. Onsite Generation is headquartered in Oevel, Belgium and had 73 full-time employees as of December 2013. [ 4 ] Power Systems is based in Mississauga , Ontario , Canada, with a satellite facility in Gladbeck , Germany . [ 4 ] It had 62 full-time employees as of December 2013. [ 4 ] Hydrogenics maintains operations in Belgium , Canada and Germany with satellite offices in the United States , Indonesia , Malaysia and Russia . [ 4 ]
The OnSite Generation business segment is based on water electrolysis technology, which involves the decomposition of water into oxygen ( O 2 ) and hydrogen gas ( H 2 ) by passing an electric current through a liquid electrolyte . [ 4 ] The resultant hydrogen gas is then captured and used for industrial gas applications, hydrogen fueling applications, and is used to store renewable and surplus energy in the form of hydrogen gas. [ 4 ] Hydrogenics' HySTAT electrolyzer products can be used both indoors and outdoors. [ 4 ]
The Power Systems business segment is based on PEM fuel cell technology, which transforms chemical energy resulting from the electrochemical reaction of hydrogen and oxygen into electrical energy. (Edgar) Its HyPM products can handle electrical power outputs ranging from 1 kilowatt to 1 megawatt . [ 4 ] The company also develops and delivers hydrogen generation products based on PEM water electrolysis. [ 4 ]
Power-to-Gas is an energy process and storage technology, which takes the excess power generated by wind turbines , solar power , or biomass power plants and converts carbon dioxide and water into methane using electrolysis , enabling it be stored. [ 5 ] [ 6 ] [ 7 ] The excess electricity can then be held in existing reserves, including power and natural gas grids. [ 6 ] [ 7 ] This allows for seasonally adjusted storage of significant amounts of power and the provision of CO 2 -neutral fuels in the form of the resulting renewable energy source gas. [ 6 ] [ 7 ]
In 1988, Hydrogenics was founded under the name Traduction Militech Translation Inc. [ 8 ] In 1995, it entered into the fuel cell technology development business and Traduction Militech Translation changed its name to Hydrogenics in 1990. [ 8 ]
In 2002, Hydrogenics acquired EnKAT GmbH, which formed its Hydrogenics Europe division. [ 9 ] It also acquired Greenlight Power Technologies, Inc., a competing fuel cell testing business, in 2003. [ 9 ] A year later, in 2004, the company acquired Stuart Energy, a manufacturer of hydrogen-generation products based on alkaline electrolyte technology. [ 8 ] [ 10 ]
In 2007, Hydrogenics narrowed the focus of its fuel cell activities by exiting the fuel cell testing business and working more on forklift power and backup power markets. [ 8 ] That same year, Heliocentris partnered with Hydrogenics and SMA Solar Technologie to incorporate Hydrogenics' fuel cell power modules into stationary backup power systems. [ 8 ]
In September 2010, Hydrogenics formed an alliance with CommScope Inc. , a Hickory, North Carolina –based multinational telecommunications company. [ 11 ] Per the alliance, CommScope invested US$8.5 million in Hydrogenics as part of a joint product development program. [ 8 ] [ 12 ]
Hydrogenics signed a Memorandum of Understanding (MoU) with Iwatani Corporation, a Japanese industrial energy company, in April 2012. [ 13 ] The companies began to collaborate on hydrogen solutions in the Japanese energy market, including utility-scale hydrogen energy storage, hydrogen generation and fuelling, fuel cell integration, and industrial hydrogen generation. [ 13 ] Later that month Hydrogenics and Enbridge Inc. entered into a joint venture to develop utility-scale energy storage beginning in Ontario . [ 12 ] [ 14 ] Under the agreement, hydrogen produced during periods of excess renewable generation will be injected into Enbridge's existing natural gas pipeline network. [ 14 ] In June 2013, Hydrogenics announced that its Power-to-Gas facility was operational with the first direct injection of hydrogen into a gas pipeline. [ 15 ]
Hydrogenics entered into a joint venture with South Korea –based Kolon Water & Energy to provide power generation in that country in June 2014. [ 16 ]
In 2019 Hydrogenics was acquired in large parts by Cummins as part of their New Power division. Hydrogenics is now owned 81% by Cummins and 19% by Air Liquide. The name of the company has since been changed to Accelera. [ 1 ]
In June 2000, General Motors and Hydrogenics released their codeveloped HydroGen1, a vehicle powered by a first generation proton exchange membrane fuel cell system. [ 8 ] The following year, in October, the two companies developed low-pollution technology to power cars and trucks. [ 17 ]
In December 2002, Natural Resources Canada (NRCan) selected Hydrogenics to develop a next-generation hybrid fuel cells bus; Hydrogenics integrated its vehicle-to-grid technology into a 12.5 meter New Flyer Inverno 40i transit bus . [ 8 ] Hydrogenics' FC Hybrid Tecnobus midibus was exhibited in Europe in 2005. [ 8 ]
In January 2010, Hydrogenics began development of a next-generation power system to be used for surface mobility applications on the moon for the Canadian Space Agency . [ 2 ] The system includes an electrolyzer that produces both hydrogen and oxygen using solar power , and a fuel cell system that can be used for mobility, auxiliary, and life support systems . [ 2 ] Heliocentris and FAUN Umwelttechnick collaborated with Hydrogenics to develop a hybrid waste disposal vehicle for BSR (Berliner Stadtreinigung) in August of that year. [ 8 ]
In July 2012, Hydrogenics joined a consortium with EU members to build the world's largest steady state hydrogen storage facility in the Puglia region of Italy . [ 18 ] The system is part of the R&D smart grid project "INGRID." [ 12 ] [ 18 ]
In April 2013, Hydrogenics won a contract to supply a 1 megawatt hydrogen energy storage system to German utility E.ON in Hamburg . [ 19 ] The system will use electrolyzers based on Hydrogenics' proton exchange membrane (PEM) technology for hydrogen production and use excess power generated from regional renewable energy sources, primarily wind energy. [ 19 ] In November the first of E.ON's P2G facilities provided by Hydrogenics became operational. [ 15 ] The Falkenhagen facility uses wind-powered electrolysis equipment to transform water to hydrogen, which is then mixed with natural gas. [ 3 ] [ 15 ]
In February 2014, Hydrogenics was awarded two projects with the United Kingdom government. [ 20 ] Hydrogenics will provide its technology to build hydrogen fuel stations throughout the UK. [ 12 ] [ 20 ]
Hydrogenics was selected as a Preferred Respondent for a power-to-gas project in Ontario by the Independent Electricity System Operator . [ 21 ] [ 22 ] (IESO), a corporation responsible for operating the electricity market and directing the operation of the bulk electrical system in the province of Ontario, Canada, in July 2014. | https://en.wikipedia.org/wiki/Hydrogenics |
Hydrogenography is a combinatorial method based on the observation of optical changes on the metal surface by hydrogen absorption . [ 1 ] The method allows the examination of thousands of combinations of alloy samples in a single batch.
In the 1996 report of the method, thin films were coated with yttrium and lanthanum topped with a layer of palladium for the diffusion of hydrogen. The rate of absorption of hydrogen resulted in typical optical properties. [ 2 ] In the 2008 report magnesium , titanium and nickel are eroded and sputtering deposited in different ratios onto a transparent film in a thin layer of 100 nanometres following exposure to hydrogen in different amounts resulting in optical differences. [ 3 ] | https://en.wikipedia.org/wiki/Hydrogenography |
Hydrogenotrophs are organisms that are able to metabolize molecular hydrogen as a source of energy .
An example of hydrogenotrophy is performed by carbon dioxide -reducing organisms [ 1 ] which use CO 2 and H 2 to produce methane (CH 4 ) by the following reaction:
Other hydrogenotrophic metabolic pathways include acetogenesis , sulfate reduction , and other hydrogen oxidizing bacteria . Those that metabolize methane are called methanogenic . [ 2 ] Hydrogenotrophs belong to a group of organisms known as methanogens , organisms that carry out anaerobic processes that are responsible for the production of methane through carbon dioxide reduction. Methanogens also include a group of organisms called methylotrophs , organisms that can use single-carbon molecules or molecules with no carbon-carbon bonds. [ 3 ]
Hydrogenotrophic bacteria were first experimented with by NASA in the 1960s in order to find a replenishable food source. [ 4 ] Hydrogenotrophic bacteria have been found to have a high protein and carbohydrate content and have been a guiding principle in developing sustainable agricultural methods. [ citation needed ] Experimentation has revealed that hydrogenotrophic bacteria can convert carbon dioxide into food more rapidly than plants, making them an efficient and sustainable alternative to implement into plant-based high-protein diets and as a substitute in products that use plant extracts and oils. [ 5 ]
In September 2022, finnish biotech startup Solar Foods received its first food regulatory approval [ 6 ] from the Singapore Food Agency (SFA) for a protein supplement ( Solein ) derived from hydrogenotrophic microorganisms, [ 7 ] and has since started production in a commercial-scale facility. [ 6 ]
Hydrogenotrophs are commonly found in the human gut, along with other fermentative bacteria which live in symbiosis with one another. [ 4 ] They are also found in soils and in sediments of freshwater and marine ecosystems around the world. [ 8 ]
This microbiology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrogenotroph |
Hydrogen–deuterium exchange (also called H–D or H/D exchange) is a chemical reaction in which a covalently bonded hydrogen atom is replaced by a deuterium atom, or vice versa. It can be applied most easily to exchangeable protons and deuterons, where such a transformation occurs in the presence of a suitable deuterium source, without any catalyst. The use of acid, base or metal catalysts, coupled with conditions of increased temperature and pressure, can facilitate the exchange of non-exchangeable hydrogen atoms, so long as the substrate is robust to the conditions and reagents employed. This often results in perdeuteration: hydrogen-deuterium exchange of all non-exchangeable hydrogen atoms in a molecule.
An example of exchangeable protons which are commonly examined in this way are the protons of the amides in the backbone of a protein . [ 1 ] [ 2 ] [ 3 ] The method gives information about the solvent accessibility of various parts of the molecule, and thus the tertiary structure of the protein. The theoretical framework for understanding hydrogen exchange in proteins was first described by Kaj Ulrik Linderstrøm-Lang and he was the first to apply H/D exchange to study proteins. [ 4 ]
In protic solution exchangeable protons such as those in hydroxyl or amine group exchange protons with the solvent . If D 2 O is solvent, deuterons will be incorporated at these positions. The exchange reaction can be followed using a variety of methods (see Detection). Since this exchange is an equilibrium reaction, the molar amount of deuterium should be high compared to the exchangeable protons of the substrate. For instance, deuterium is added to a protein in H 2 O by diluting the H 2 O solution with D 2 O (e.g. tenfold). Usually exchange is performed at physiological pH (7.0–8.0) where proteins are in their most native ensemble of conformational states. [ 5 ] [ 6 ]
The H/D exchange reaction can also be catalysed, by acid, base or metal catalysts such as platinum. For the backbone amide hydrogen atoms of proteins, the minimum exchange rate occurs at approximately pH 2.6, on average. By performing the exchange at neutral pH and then rapidly changing the pH, the exchange rates of the backbone amide hydrogens can be dramatically slowed, or quenched . The pH at which the reaction is quenched depends on the analysis method. For detection by NMR, the pH may be moved to around 4.0–4.5. For detection by mass spectrometry, the pH is dropped to the minimum of the exchange curve, pH 2.6. In the most basic experiment, the reaction is allowed to take place for a set time before it is quenched.
The deuteration pattern of a molecule that has undergone H/D exchange can be maintained in aprotic environments. However, some methods of deuteration analysis for molecules such as proteins, are performed in aqueous solution, which means that exchange will continue at a slow rate even after the reaction is quenched. Undesired deuterium-hydrogen exchange is referred to as back-exchange and various methods have been devised to correct for this.
H–D exchange was measured originally by the father of hydrogen exchange Kaj Ulrik Linderstrøm-Lang using density gradient tubes. In modern times, H–D exchange has primarily been monitored by the methods: NMR spectroscopy , mass spectrometry and neutron crystallography . Each of these methods have their advantages and drawbacks.
Hydrogen and deuterium nuclei are grossly different in their magnetic properties. Thus it is possible to distinguish between them by NMR spectroscopy . Deuterons will not be observed in a 1 H NMR spectrum and conversely, protons will not be observed in a 2 H NMR spectrum. Where small signals are observed in a 1 H NMR spectrum of a highly deuterated sample, these are referred to as residual signals. They can be used to calculate the level of deuteration in a molecule. Analogous signals are not observed in 2 H NMR spectra because of the low sensitivity of this technique compared to the 1 H analysis. Deuterons typically exhibit very similar chemical shifts to their analogous protons. Analysis via 13 C NMR spectroscopy is also possible: the different spin values of hydrogen ( 1 / 2 ) and deuterium (1) gives rise to different splitting multiplicities. NMR spectroscopy can be used to determine site-specific deuteration of molecules.
Another method uses HSQC spectra. Typically HSQC spectra are recorded at a series of timepoints while the hydrogen is exchanging with the deuterium. Since the HSQC experiment is specific for hydrogen, the signal will decay exponentially as the hydrogen exchanges. It is then possible to fit an exponential function to the data, and obtain the exchange constant. This method gives residue -specific information for all the residues in the protein simultaneously [ 7 ] [ 8 ] The major drawback is that it requires a prior assignment of the spectrum for the protein in question. This can be very labor-intensive, and usually limits the method to proteins smaller than 25 kDa . Because it takes minutes to hours to record a HSQC spectrum, amides that exchange quickly must be measured using other pulse sequences.
Hydrogen–deuterium exchange mass spectrometry (HX-MS or HDX-MS) can determine the overall deuterium content of molecules which have undergone H/D exchange. Because of the sample preparation required, it is typically considered to provide an accurate measurement of non-exchangeable hydrogen atoms only. It can also involve H/D exchange in the gas phase [ 9 ] or solution phase exchange prior to ionization. [ 3 ] It has several advantages in NMR spectroscopy with respect to analysis of H–D exchange reactions: much less material is needed, the concentration of sample can be very low (as low as 0.1 uM), the size limit is much greater, and data can usually be collected and interpreted much more quickly. [ 10 ]
The deuterium nucleus is twice as heavy as the hydrogen nucleus because it contains a neutron as well as a proton. Thus a molecule that contains some deuterium will be heavier than one that contains all hydrogen. As a protein is increasingly deuterated, the molecular mass increases correspondingly. Detecting the change in the mass of a protein upon deuteration was made possible by modern protein mass spectrometry, first reported in 1991 by Katta and Chait. [ 11 ]
Determining site specific deuteration via mass spectrometry is more complicated than using NMR spectroscopy. For example, the location and relative amount of deuterium exchange along the peptide backbone can be determined roughly by subjecting the protein to proteolysis after the exchange reaction has been quenched. Individual peptides are then analyzed for overall deuteration of each peptide fragment. Using this technique the resolution of deuterium exchange is determined by the size of the peptides produced during digestion. [ 12 ] Pepsin , an acid protease , is commonly used for proteolysis, as the quench pH must be maintained during the proteolytic reaction. To minimize the back-exchange, proteolysis and subsequent mass spectrometry analysis must be done as quickly as possible. HPLC separation of the peptic digest is often carried out at low temperature just prior to electrospray mass spectrometry to minimize back-exchange. More recently, UPLC has been used due to its superior separation capabilities. [ 13 ]
It was proposed in 1999 that it might be possible to achieve single-residue resolution by using collision-induced dissociation (CID) fragmentation of deuterated peptides in conjunction with tandem mass spectrometry . It was soon discovered that CID causes "scrambling" of the deuterium position within the peptides. [ 14 ] [ 15 ] However, fragmentation produced by MALDI in-source decay (ISD), electron capture dissociation (ECD), and electron transfer dissociation (ETD) proceed with little or no scrambling under the correct experimental conditions. [ 16 ] [ 17 ] [ 18 ] Scrambling of the isotopic labeling is caused by collisional heating prior to dissociation of the ion and while CID do cause scrambling, collisional heating can also occur during ionization and ion transport. [ 19 ] However, by careful optimization of instrument parameters which cause ion heating, hydrogen scrambling can be minimized to a degree which preserves the solution phase isotopic labeling until fragmentation can be performed using a technique where scrambling does not occur. [ 17 ] [ 18 ] [ 20 ] [ 21 ] More recently, ultraviolet photodissociation (UVPD) has also been investigated as a possible fragmentation technique to localize deuterium within peptides and proteins. [ 22 ] [ 23 ] In this regard, the conclusions have been mixed, while it is possible to obtain UVPD fragments which has not undergone scrambling under certain conditions, others have shown that scrambling can occur for both peptides and proteins during the UVPD fragmentation step itself. [ 22 ] [ 23 ] The theory consolidating these apparent contradictions has to do with the dual fragmentation pathway that may arise from UV irradiation of peptides and proteins, i.e. direct and statistical dissociation. [ 24 ] That is, if experimental conditions favor direct dissociation and the precursor ion is kept at low internal energies before and during fragmentation the deuterium level of the resulting fragments will correspond to the non-scrambled precursor. [ 22 ] However, experimental conditions may favor statistical dissociation during UV irradiation, especially at long irradiation times and low gas pressure, leading to internal conversion of the electronic excitation energy contributed by the UV photons. [ 23 ] The result is vibrational excitation of the irradiated molecule which in turn undergo scrambling.
Hydrogen–deuterium exchange of fast-exchanging species (e.g. hydroxyl groups) can be measured at atomic resolution quantitatively by neutron crystallography, and in real time if exchange is conducted during the diffraction experiment.
High intensity neutron beams are generally generated by spallation at linac particle accelerators such as the Spallation Neutron Source . Neutrons diffract crystals similarly to X-rays and can be used for structural determination. Hydrogen atoms, with between one and zero electrons in a biological setting, diffract X-rays poorly and are effectively invisible under normal experimental conditions. Neutrons scatter from atomic nuclei, and are therefore capable of detecting hydrogen and deuterium atoms.
Hydrogen atoms are routinely replaced with deuterium, which introduce a strong and positive scattering factor. It is often sufficient to replace only the solvent and labile hydrogen atoms in a protein crystal by vapor diffusion. In such a structure the occupancy of an exchangeable deuterium atom in a crystal will refine from 0-100%, directly quantifying the amount of exchange.
Perdeuteration of one component of a multi-component system can provide contrast for neutron scattering experiments, where the contrast obtained by using deuterated solvents is insufficient. [ citation needed ]
It is not possible to determine the structure of a protein with H/D exchange other than neutron crystallography nor is it possible to define secondary structural elements. The reasons for this are related to the way in which protein structure slows exchange. Exchange rates are a function of two parameters: solvent accessibility and hydrogen bonding. Thus an amide which is part of an intramolecular hydrogen bond will exchange slowly if at all, while an amide on the surface of protein hydrogen bonded to water will exchange rapidly. Amides buried from the solvent but not hydrogen bonded may also have very slow exchange rates. Because both solvent accessibility and hydrogen bonding contribute to the rate of exchange, it becomes difficult to attribute a given exchange rate to a structural element without crystallography or NMR structural data.
H–D exchange has been used to characterize the folding pathway of proteins, by refolding the protein under exchange conditions. In a forward exchange experiment (H to D), a pulse of deuterium is added after various amounts of refolding time. The parts of the structure that form rapidly will be protected and thus not exchanged, whereas areas that fold late in the pathway will be exposed to the exchange for longer periods of time. Thus H/D exchange can be used to determine the sequence of various folding events. Factors determining the time resolution of this approach are the efficiency of mixing and how quickly the quench can be performed after the labeling.
H–D exchange has been used to characterize protein structures [ 25 ] and protein–protein interactions. [ 26 ] The exchange reaction needs to be carried out with the isolated proteins and with the complex. The exchanging regions are then compared. If a region is buried by the binding, the amides in this region may be protected in the complex and exchange slowly. However, one must bear in mind that H–D exchange cannot be used to locate binding interfaces for all protein-protein interactions. Some protein-protein interactions are driven by electrostatic forces of side chains and are unlikely to change the exchange rate of backbone amide hydrogens, particularly if the amide hydrogens are located in stable structural elements such as alpha helices .
Lastly, H–D exchange can be used to monitor conformational changes in proteins as they relate to protein function. If conformation is altered as result of post-translational modification , enzyme activation, drug binding or other functional events, there will likely be a change to H/D exchange that can be detected. [ 27 ]
HDXsite is an online websever which includes some applications such as HDX modeller increasing the resolution of experimental HDX data and modeling protection factors for individual residues. [ 28 ] [ 29 ] | https://en.wikipedia.org/wiki/Hydrogen–deuterium_exchange |
Hydrogeomorphology has been defined as “an interdisciplinary science that focuses on the interaction and linkage of hydrologic processes with landforms or earth materials and the interaction of geomorphic processes with surface and subsurface water in temporal and spatial dimensions.” [ 1 ] The term 'hydro-geomorphology’ designates the study of landforms caused by the action of water. [ 2 ] By this definition hydro-geomorphology is inseparable part of geomorphology moreover fluvial geomorphology, because water is one of the most important agents in forming and shaping of landforms. [ 3 ] From the groundwater point of view integration of geological, structural and hydrological data with hydro-geomorphologic data is very much useful in finding out the groundwater potential zones with fruitful results. The science relating to the geographical, geological, and hydrological aspects of water bodies and to changes to these aspects in response to low variations and to natural and human caused events, such as heavy rainfall or channel straightening is the hydro-geomorphology.
Hydrogeomorphology describes and evaluates the environment, in which water circulates, thus providing the information to understand the situation and to make the proper decisions. [ 4 ] Quantitative study of drainage basin provides the theoretical base for the hydrogeomorphic approach, suggesting that certain unvarying drainage basin characters can be correlated to the hydrologic response of a basin. The measurable description of a drainage basin can be grouped in to linear aspect of channel network, areal aspect of drainage basin, relief aspect of channel system and basin form. Hydro-geomorphology is science that deals with occurrences of water with respect to landform. [ 5 ] Hydrogeomorphology of a drainage basin is a function of rainfall kinematics , surface topography , drainage basin morphology and runoff etc. All these aspects are regarded as the potential to describe hydrogeomorphic properties of the drainage basin. Because of non-availability of hydrological data, discharge data and sediment load data over a sufficient period of time in ungauged catchments, various investigators have used the drainage basin parameters to study the hydrogeomorphology of the drainage basin. Hydrogeomorphic studies of drainage basin often suffer a setback due to lack of long-term data. Therefore, there is need to extrapolate the results of few small subsystems to other hydrologically and geomorphologically similar basins, which mostly remain ungauged for want of enormous resource and time involved in instrumentation and monitoring them. Importance of hydrology for geomorphological purposes has been increasingly appreciated among geomorphologists in the last few decades. Earlier geomorphologists were bounded to use different unconventional approach to evaluate the characteristics of rivers and drainage basins to get proper idea of various aspects of the water crisis.
R. E. Horton pioneered the hydrologic and hydromorphometric analysis of basin and provided a rational and systematic base. He framed the geomorphic parameters with hydrologic parameters of the drainage system. Thus hydrological criteria not only assist the geomorphologists to evaluate the hydrogeomorphic characteristics of a drainage basin also facilitate their extrapolation in space and time. Mark M. Brinson proposed A Hydrogeomorphic Classification for Wetlands in 1993. [ 6 ] | https://en.wikipedia.org/wiki/Hydrogeomorphology |
Hydrogeophysics is a cross-disciplinary area of research that uses geophysics to determine parameters (characteristics; measurements of limitations or boundaries) and monitor processes for hydrological studies of matters such as water resources, contamination, and ecological studies. [ 1 ] The field uses knowledge and researchers from geology, hydrology, physics, geophysics, engineering, statistics, and rock physics. It uses geophysics to provide quantitative information about hydrogeological parameters, using minimally invasive methods. Hydrogeophysics differs from geophysics in its specific uses and methods. Although geophysical knowledge and methods have existed and grown over the last half century for applications in mining and petroleum industries, hydrogeological study sites have different subsurface conditions than those industries. Thus, the geophysical methods for mapping subsurface properties combine with hydrogeology to use proper, accurate methods to map shallow hydrological study sites. [ 2 ]
The field of hydrogeophysics developed out of a need to use minimally invasive methods for determining and studying hydrogeological parameters and processes. Determination of hydrogeological parameters is important for finding water resources, which is a growing need, and learning about water contamination, which has become relevant with the growing use of potentially hazardous chemicals.
The methods and knowledge of geophysics had been developed for mining and petroleum industries, which involve consolidated subsurface environments with high pressure and temperature. Since the subsurface environments in hydrogeological studies are less consolidated and have low temperature and pressure, combining geophysics with hydrogeology was necessary to develop proper geophysical methods that work for hydrological purposes. [ 2 ]
Traditional hydrogeological methods for characterizing the subsurface usually involved drilling and taking soil samples from the site, which can disturb the study site, cost too much time or money, or expose researchers and people to harmful chemicals and contaminants. They also only provide localized information, rather than the necessary field-scale information. Using geophysical methods and digital technology allows hydrogeologists to more quickly study hydrological characteristics on a larger scale with a lower cost and less invasive techniques.
A Hydrogeophysics Advanced Study Institute was held at the Trest Castle in the Czech Republic in July 2002 and funded by NATO when they acknowledged the necessity for fully developed, minimally invasive procedures for investigating and monitoring hydrogeological processes and parameters in shallow subsurface conditions. The institute brought together geophysicists working in hydrogeological characterization with hydrogeologists interested in using geophysical methods and data for characterization. This group, plus other international researchers, discussed the possibilities and challenges of using geophysical methods for investigating hydrogeological parameters.
They determined the main obstacles of hydrogeophysics are gaps in the knowledge and understanding of the correlation between hydrogeological parameters and geophysical characteristics, and difficulty in being able to integrate those different sets of information. One of the biggest challenges is using an organized, methodical, and efficient way to combine geophysical and hydrogeological data sets that measure different parameters over different spatial scales. This is the largest obstacle because the foundation of hydrogeophysics is integrating hydrogeology with geophysics. [ 3 ]
There are many different methods for determining subsurface properties and features that can be done from different locations/ proximities to the study sites:
Geophysics helps to learn about many hydrogeological matters such as:
These parameters are then used to investigate matters including searching for underground water resources, aquifer control or contamination from sea water or industrial sources, and storing harmful substances underground. Having a good measurement of these hydrogeological parameters helps to better understand water contamination transport and develop more sustainable water resources. [ 4 ] | https://en.wikipedia.org/wiki/Hydrogeophysics |
A hydrograph is a graph showing the rate of flow ( discharge ) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in units of cubic meters per second (m³/s) or cubic feet per second (cfs).
Hydrographs often relate changes of precipitation to changes in discharge over time. [ 1 ] The term can also refer to a graph showing the volume of water reaching a particular outfall , or location in a sewerage network. Graphs are commonly used in the design of sewerage , more specifically, the design of surface water sewerage systems and combined sewers .
Other related terms include: [ 2 ]
Types of hydrographs include: [ 4 ]
A stream hydrograph is commonly determining the influence of different hydrologic processes on discharge from the subject catchment. Because the timing, magnitude, and duration of groundwater return flow differs so greatly from that of direct runoff, separating and understanding the influence of these distinct processes is key to analyzing and simulating the likely hydrologic effects of various land use, water use, weather, and climate conditions and changes.
However, the process of separating “baseflow” from “direct runoff” is an inexact science. In part this is because these two concepts are not, themselves, entirely distinct and unrelated. Return flow from groundwater increases along with overland flow from saturated or impermeable areas during and after a storm event; moreover, a particular water molecule can easily move through both pathways en route to the watershed outlet. Therefore, separation of a purely “baseflow component” in a hydrograph is a somewhat arbitrary exercise. Nevertheless, various graphical and empirical techniques have been developed to perform these hydrograph separations. The separation of base flow from direct runoff can be an important first step in developing rainfall-runoff models for a watershed of interest—for example, in developing and applying unit hydrographs as described below.
A unit hydrograph (UH) is the hypothetical unit response of a watershed (in terms of runoff volume and timing) to a unit input of rainfall. [ 5 ] It can be defined as the direct runoff hydrograph (DRH) resulting from one unit (e.g., one cm or one inch) of effective rainfall occurring uniformly over that watershed at a uniform rate over a unit period of time. As a UH is applicable only to the direct runoff component of a hydrograph (i.e., surface runoff ), a separate determination of the baseflow component is required.
A UH is specific to a particular watershed, and specific to a particular length of time corresponding to the duration of the effective rainfall. That is, the UH is specified as being the 1-hour, 6-hour, or 24-hour UH, or any other length of time up to the time of concentration of direct runoff at the watershed outlet. Thus, for a given watershed, there can be many unit hydrographs, each one corresponding to a different duration of effective rainfall.
The UH technique provides a practical and relatively easy-to-apply tool for quantifying the effect of a unit of rainfall on the corresponding runoff from a particular drainage basin . [ 6 ] UH theory assumes that a watershed's runoff response is linear, time-invariant, and that the effective rainfall occurs uniformly over the entirety of the watershed. In the real world, none of these assumptions are strictly true. Nevertheless, the application of UH methods typically yields a reasonable approximation of the flood response of natural watersheds. The linear assumptions underlying UH theory allow for the variation in storm intensity over time (i.e., the storm hyetograph ) to be simulated by applying the principles of superposition and proportionality to separate storm components to determine the resulting cumulative hydrograph. This allows for a relatively straightforward calculation of the hydrograph response to any arbitrary rain event.
An instantaneous unit hydrograph is a further refinement of the concept; for an IUH, the input rainfall is assumed to all take place at a discrete point in time (obviously, this isn't the case for actual rainstorms). Making this assumption can greatly simplify the analysis involved in constructing a unit hydrograph, and it is necessary for the creation of a geomorphologic instantaneous unit hydrograph.
The creation of a GIUH is possible given nothing more than topologic data for a particular drainage basin. In fact, only the number of streams of a given order, the mean length of streams of a given order, and the mean land area draining directly to streams of a given order are absolutely required (and can be estimated rather than explicitly calculated if necessary). It is therefore possible to calculate a GIUH for a basin without any data about stream height or flow, which may not always be available.
In subsurface hydrology ( hydrogeology ), a hydrograph is a record of the water level (the observed hydraulic head in wells screened across an aquifer ).
Typically, a hydrograph is recorded for monitoring of heads in aquifers during non-test conditions (e.g., to observe the seasonal fluctuations in an aquifer). When an aquifer test is being performed, the resulting observations are typically called drawdown , since they are subtracted from pre-test levels and often only the change in water level is dealt with.
Raster hydrographs are pixel-based plots for visualizing and identifying variations and changes in large multidimensional data sets. Originally developed by Keim (2000) [ 7 ] they were first applied in hydrology by Koehler (2004) [ 8 ] as a means of highlighting inter-annual (long-term) and intra-annual (e.g., seasonality ) changes in streamflow.
The raster hydrographs in the USGS WaterWatch, like those developed by Koehler, depict years on the y-axis and days along the x-axis. Users can choose to plot streamflow (actual values or log values), streamflow percentile, or streamflow class (from 1, for low flow, to 7 for high flow), for Daily, 7-Day, 14-Day, and 28-Day streamflow. For a more comprehensive description of raster hydrographs, see Strandhagen et al. (2006). [ 9 ]
A Lag-1 hydrograph is a graph of discharge which can be accomplished without a time axis (Koehler 2022). [ 10 ] This technique allows data properties such as Q, dQ/dt, and d 2 Q/dt 2 , and trends of increasing, decreasing or no change flow to be readily seen and understood on a single graph. Flow pulse reference lines can easily be added and interpreted. The methodology is based on the time-series serial correlation lag-1 graph and uses the normally unwanted (but still valuable) autocorrelation present within the streamflow data.
The x-axis represents the discharge for a date, Q t , while the y-axis represents the discharge for the next day, Q t+1 .
Data preparation and plotting methods are identical to an autocorrelation lag 1 plot, where 1 indicates a 1-day or daily time step. The table below shows how the time-series discharge are shifted. It is critical that the temporal sequence is maintained for the data. Thinking of the x values as “flow for today” and the y values as “flow for tomorrow” helps visualize the order of the data. | https://en.wikipedia.org/wiki/Hydrograph |
Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of oceans , seas , coastal areas , lakes and rivers , as well as with the prediction of their change over time, for the primary purpose of safety of navigation and in support of all other marine activities, including economic development, security and defense, scientific research, and environmental protection. [ 1 ]
The origins of hydrography lay in the making of charts to aid navigation, by individual mariners as they navigated into new waters. These were usually the private property, even closely held secrets, of individuals who used them for commercial or military advantage. As transoceanic trade and exploration increased, hydrographic surveys started to be carried out as an exercise in their own right, and the commissioning of surveys was increasingly done by governments and special hydrographic offices. National organizations, particularly navies , realized that the collection, systematization and distribution of this knowledge gave it great organizational and military advantages. Thus were born dedicated national hydrographic organizations for the collection, organization, publication and distribution of hydrography incorporated into charts and sailing directions.
Prior to the establishment of the United Kingdom Hydrographic Office , Royal Navy captains were responsible for the provision of their own charts. In practice this meant that ships often sailed with inadequate information for safe navigation, and that when new areas were surveyed, the data rarely reached all those who needed it. The Admiralty appointed Alexander Dalrymple as Hydrographer in 1795, with a remit to gather and distribute charts to HM Ships. Within a year existing charts from the previous two centuries had been collated, and the first catalog published. [ 2 ] The first chart produced under the direction of the Admiralty , was a chart of Quiberon Bay in Brittany , and it appeared in 1800.
Under Captain Thomas Hurd the department received its first professional guidelines, and the first catalogs were published and made available to the public and to other nations as well. In 1829, Rear-Admiral Sir Francis Beaufort , as Hydrographer, developed the eponymous Scale , and introduced the first official tide tables in 1833 and the first " Notices to Mariners " in 1834. The Hydrographic Office underwent steady expansion throughout the 19th century; by 1855, the Chart Catalogue listed 1,981 charts giving a definitive coverage over the entire world, and produced over 130,000 charts annually, of which about half were sold. [ 3 ]
The word hydrography comes from the Ancient Greek ὕδωρ ( hydor ), "water" and γράφω ( graphō ), "to write".
Large-scale hydrography is usually undertaken by national or international organizations which sponsor data collection through precise surveys and publish charts and descriptive material for navigational purposes. The science of oceanography is, in part, an outgrowth of classical hydrography. In many respects the data are interchangeable, but marine hydrographic data will be particularly directed toward marine navigation and safety of that navigation. Marine resource exploration and exploitation is a significant application of hydrography, principally focused on the search for hydrocarbons .
Hydrographical measurements include the tidal , current and wave information of physical oceanography. They include bottom measurements, with particular emphasis on those marine geographical features that pose a hazard to navigation such as rocks, shoals , reefs and other features that obstruct ship passage. Bottom measurements also include collection of the nature of the bottom as it pertains to effective anchoring. Unlike oceanography, hydrography will include shore features, natural and manmade, that aid in navigation. Therefore, a hydrographic survey may include the accurate positions and representations of hills , mountains and even lights and towers that will aid in fixing a ship's position, as well as the physical aspects of the sea and seabed.
Hydrography, mostly for reasons of safety, adopted a number of conventions that have affected its portrayal of the data on nautical charts. For example, hydrographic charts are designed to portray what is safe for navigation, and therefore will usually tend to maintain least depths and occasionally de-emphasize the actual submarine topography that would be portrayed on bathymetric charts . The former are the mariner 's tools to avoid accident. The latter are best representations of the actual seabed, as in a topographic map, for scientific and other purposes. Trends in hydrographic practice since c. 2003–2005 have led to a narrowing of this difference, with many more hydrographic offices maintaining "best observed" databases, and then making navigationally "safe" products as required. This has been coupled with a preference for multi-use surveys, so that the same data collected for nautical charting purposes can also be used for bathymetric portrayal.
Even though, in places, hydrographic survey data may be collected in sufficient detail to portray bottom topography in some areas, hydrographic charts only show depth information relevant for safe navigation and should not be considered as a product that accurately portrays the actual shape of the bottom. The soundings selected from the raw source depth data for placement on the nautical chart are selected for safe navigation and are biased to show predominantly the shallowest depths that relate to safe navigation. For instance, if there is a deep area that can not be reached because it is surrounded by shallow water, the deep area may not be shown. The color filled areas that show different ranges of shallow water are not the equivalent of contours on a topographic map since they are often drawn seaward of the actual shallowest depth portrayed. A bathymetric chart does show marine topology accurately. Details covering the above limitations can be found in Part 1 of Bowditch's American Practical Navigator . Another concept that affects safe navigation is the sparsity of detailed depth data from high resolution sonar systems. In more remote areas, the only available depth information has been collected with lead lines. This collection method drops a weighted line to the bottom at intervals and records the depth, often from a rowboat or sail boat. There is no data between soundings or between sounding lines to guarantee that there is not a hazard such as a wreck or a coral head waiting there to ruin a sailor's day. Often, the navigation of the collecting boat does not match today's GPS navigational accuracies. The hydrographic chart will use the best data available and will caveat its nature in a caution note or in the legend of the chart.
A hydrographic survey is quite different from a bathymetric survey in some important respects, particularly in a bias toward least depths due to the safety requirements of the former and geomorphologic descriptive requirements of the latter. Historically, this could include echosoundings being conducted under settings biased toward least depths, but in modern practice hydrographic surveys typically attempt to best measure the depths observed, with the adjustments for navigational safety being applied after the fact.
Hydrography of streams will include information on the stream bed, flows , water quality and surrounding land. Basin or interior hydrography pays special attention to rivers and potable water although if collected data is not for ship navigational uses, and is intended for scientific usage, it is more commonly called hydrometry or hydrology .
Hydrography of rivers and streams is also an integral part of water management. Most reservoirs in the United States use dedicated stream gauging and rating tables to determine inflows into the reservoir and outflows to irrigation districts, water municipalities and other users of captured water. River/stream hydrographers use handheld and bank mounted devices, to capture a sectional flow rate of moving water through a section and or current.
Uncrewed Surface Vessels (USVs) and are commonly used for hydrographic surveys - they are often equipped with some sort of sonar. Single-beam echosounders, multibeam echosounders , and side scan sonars are all frequently used in hydrographic applications. The knowledge gained from these surveys aid in disaster planning, port and harbor maintenance, and various other coastal planning activities. [ 4 ] [ 5 ]
Hydrographic services in most countries are carried out by specialized hydrographic offices . The international coordination of hydrographic efforts lies with the International Hydrographic Organization .
The United Kingdom Hydrographic Office is one of the oldest, supplying a wide range of charts covering the globe to other countries, allied military organizations and the public.
In the United States, the hydrographic charting function has been carried out since 1807 by the Office of Coast Survey of the National Oceanic and Atmospheric Administration within the U.S. Department of Commerce and the U.S. Army Corps of Engineers . [ 6 ] [ 7 ] | https://en.wikipedia.org/wiki/Hydrography |
Hydroids are a life stage for most animals of the class Hydrozoa , small predators related to jellyfish .
Some hydroids such as the freshwater Hydra are solitary, with the polyp attached directly to the substrate . When these produce buds, they become detached and grow on as new individuals.
The majority of hydroids are colonial . The original polyp is anchored to a solid substrate and forms a bud which remains attached to its parent. This in turn buds and in this way a stem is formed. The arrangement of polyps and the branching of the stem is characteristic of the species.
Some species have the polyps budding directly off the stolon which roots the colony. The polyps are connected by epidermis which surrounds a gastrovascular cavity. The epidermis secretes a chitinous skeleton which supports the stem and in some hydroids, the skeleton extends into a cup shape surrounding the polyp.
Most of the polyps are gastrozooids or feeding polyps, but some are specialised reproductive structures known as gonozooids . In some species, further specialised zooids are formed. [ 1 ] | https://en.wikipedia.org/wiki/Hydroid_(zoology) |
Hydroinformatics is a branch of informatics which concentrates on the application of information and communications technologies (ICTs) in addressing the increasingly serious problems of the equitable and efficient use of water for many different purposes. Growing out of the earlier discipline of computational hydraulics , the numerical simulation of water flows and related processes remains a mainstay of hydroinformatics, which encourages a focus not only on the technology but on its application in a social context.
On the technical side, in addition to computational hydraulics , hydroinformatics has a strong interest in the use of techniques originating in the so-called artificial intelligence community, such as artificial neural networks or recently support vector machines and genetic programming . These might be used with large collections of observed data for the purpose of data mining for knowledge discovery, or with data generated from an existing, physically based model in order to generate a computationally efficient emulator of that model for some purpose.
Hydroinformatics recognises the inherently social nature of the problems of water management and of decision-making processes, and strives to understand the social processes by which technologies are brought into use. Since the problems of water management are most severe in the majority world, while the resources to obtain and develop technological solutions are concentrated in the hands of the minority, the need to examine these social processes are particularly acute.
Hydroinformatics draws on and integrates hydraulics , hydrology , environmental engineering and many other disciplines. It sees application at all points in the water cycle from atmosphere to ocean, and in artificial interventions in that cycle such as urban drainage and water supply systems. It provides support for decision making at all levels from governance and policy through management to operations.
Hydroinformatics has a growing world-wide community of researchers and practitioners, and postgraduate programmes in Hydroinformatics are offered by many leading institutions. The Journal of Hydroinformatics provides a specific outlet for Hydroinformatics research, [ 1 ] and the community gathers to exchange ideas at the biennial conferences. These activities are coordinated by the joint IAHR , [ 2 ] IWA , [ 3 ] IAHS [ 4 ] Hydroinformatics Section .
Classic Soft-Computing Techniques is the first volume of the three, in the Handbook of HydroInformatics series ( Elsevier ) by Saeid Eslamian .
Handbook of HydroInformatics, Volume II: Advanced Machine Learning Techniques presents both the art of designing good learning algorithms, as well as the science of analyzing an algorithm's computational and statistical properties and performance guarantees
Handbook of HydroInformatics Volume III: Water Data Management Best Practices presents the latest and most updated data processing techniques that are fundamental to Water Science and Engineering disciplines. | https://en.wikipedia.org/wiki/Hydroinformatics |
Hydroiodic acid (or hydriodic acid ) is a colorless liquid. It is an aqueous solution of hydrogen iodide with the chemical formula H I ( aq ) . It is a strong acid , in which hydrogen iodide is ionized completely in an aqueous solution. Concentrated aqueous solutions of hydrogen iodide are usually 48% to 57% HI by mass. [ 2 ]
Hydroiodic acid reacts with oxygen in air to give iodine :
Like hydrogen halides , hydroiodic acid adds to alkenes to give alkyl iodides . It can also be used as a reducing agent , for example in the reduction of aromatic nitro compounds to anilines . [ 3 ]
The Cativa process is a major end use of hydroiodic acid, which serves as a co-catalyst for the production of acetic acid by the carbonylation of methanol . [ 4 ] [ 5 ]
Hydroiodic acid is listed as a U.S. Federal DEA List I Chemical , owing to its use as a reducing agent related to the production of methamphetamine from ephedrine or pseudoephedrine (recovered from nasal decongestant pills). [ 6 ] | https://en.wikipedia.org/wiki/Hydroiodic_acid |
For the use of hydrologists, ecologists, and water-resource managers in the study of surface water flows in the United States, the United States Geological Survey created a hierarchical system of hydrologic units.
Originally a four-tier system divided into regions , sub-regions, accounting units, and cataloging units, each unit was assigned a unique Hydrologic Unit Code (HUC). As first implemented the system had 21 regions, 221 subregions, 378 accounting units, and 2,264 cataloging units. [ 1 ] [ 2 ] Over time the system was changed and expanded. [ 3 ] As of 2010 there are six levels in the hierarchy, represented by hydrologic unit codes from 2 to 12 digits long, called regions , subregions, basins , subbasins, watersheds, and subwatersheds. The table below describes the system's hydrologic unit levels and their characteristics, along with example names and codes. [ 4 ]
The original delineation of units, down to subbasins (cataloging units), was done using 1:250,000 scale maps and data. The newer delineation work on watersheds and subwatersheds was done using 1:24,000 scale maps and data. As a result, the subbasin boundaries were changed and adjusted in order to conform to the higher resolution watersheds within them. Changes to subbasin boundaries resulted in changes in area sizes. Therefore, older data using "cataloging units" may differ from newer, higher resolution data using "subbasins". [ 5 ]
The regions (1st level hydrologic units) are geographic areas that contain either the drainage area of a major river, such as the Missouri region, or the combined drainage areas of a series of rivers, such as the Texas–Gulf region. Each subregion includes the area drained by a river system, a reach of a river and its tributaries in that reach, a closed basin or basins, or a group of streams forming a coastal drainage area. [ 6 ] Regions receive a two-digit code. The following levels are designated by the addition of another two digits. [ 7 ]
The hierarchy was designed and the units subdivided so that almost all the subbasins (formerly called cataloging units) are larger than 700 square miles (1,800 km 2 ). Larger closed basins were subdivided until their subunits were less than 700 square miles. [ 6 ] The 10-digit watersheds were delineated to be between 40,000 and 250,000 acres in size, and the 12-digit subwatersheds between 10,000 and 40,000 acres. [ 5 ] In addition to the hydrologic unit codes, each hydrologic unit was assigned a name corresponding to the unit's principal hydrologic feature or to a cultural or political feature within the unit. [ 6 ] The boundaries of the hydrologic units usually correspond to drainage basins with some exceptions; for example, subregion 1711, called "Puget Sound", includes all U.S. drainage into not only Puget Sound but also the Strait of Georgia , Strait of Juan de Fuca , and the Fraser River . [ 8 ] Also, region and subregion boundaries end at the U.S. international boundary. [ 6 ]
The various subdivisions of this system are not necessarily synonymous with watersheds for a number of reasons. As one analysis put it: "The hydrologic unit framework is in fact composed mostly of watersheds and pieces of watersheds. The pieces include units that drain to segments of streams, remnant areas, noncontributing areas, and coastal or frontal units that can include multiple watersheds draining to an ocean or large lake. Hence, half or more of the hydrologic units are not watersheds as the name of the framework Watershed Boundary Dataset (WBD) implies. Nonetheless, hydrologic units and watersheds are commonly treated as synonymous, and this misapplication and misunderstanding can have some serious scientific and management consequences." [ 9 ]
Aquifers of the United States are organized by national principal aquifer codes and names assigned by the National Water Information System (NWIS). Aquifers are identified by a geohydrologic unit code (a three-digit number related to the age of the formation) followed by a 4 or 5 character abbreviation for the geologic unit or aquifer name. [ 10 ] | https://en.wikipedia.org/wiki/Hydrologic_unit_system_(United_States) |
HEPEX is an international initiative bringing together hydrologists, meteorologists, researchers and endusers to develop advanced probabilistic hydrological forecast techniques for improved flood, drought and water management. HEPEX was launched in 2004 as an independent, cooperative international scientific activity. During the first meeting, the overarching goal was defined as
to develop and test procedures to produce reliable hydrological ensemble forecasts, and to demonstrate their utility in decision making related to the water, environmental and emergency management sectors
Key questions of HEPEX are :
The applications of Hydrological Ensemble Predictions span across large spatio-temporal scales ranging from short-term and very localized predictions to global climate change modeling.
HEPEX is organised around six major themes:
HEPEX is currently co-chaired by NOAA , the European Centre for Medium-Range Weather Forecast and the European Commission Joint Research Centre . Co-chairs are elected during plenary HEPEX meetings.
There is no formal membership for HEPEX. The HEPEX community is established through active participation of scientists, end users and decision makers in research, discussions and exchange of information on topics related to probabilistic hydrological predictions for floods, droughts, water management or related topics.
The community has been very active with growing importance. Information on the initiative and the possibility to actively contribute to ongoing discussions can be found on the HEPEX website . HEPEX webinars can be followed online with the possibility to participate in the discussion. They are then transferred for online viewing here. | https://en.wikipedia.org/wiki/Hydrological_Ensemble_Prediction_Experiment |
A hydrological code or hydrologic unit code is a sequence of numbers or letters (a geocode ) that identify a hydrological unit or feature, such as a river , river reach , lake , or area like a drainage basin (also called watershed in North America) or catchment.
One system, developed by Arthur Newell Strahler , known as the Strahler stream order , ranks streams based on a hierarchy of tributaries. Each segment of a stream or river within a river network is treated as a node in a tree, with the next segment downstream as its parent. When two first-order streams come together, they form a second-order stream. When two second-order streams come together, they form a third-order stream, and so on.
Another example is the system of assigning IDs to watersheds devised by Otto Pfafstetter [ pt ] , known as the Pfafstetter Coding System or the Pfafstetter System. Drainage areas are delineated in a hierarchical fashion, with "level 1" watersheds at continental scales, subdivided into smaller level 2 watersheds, which are divided into level 3 watersheds, and so on. Each watershed is assigned a unique number, called a Pfafsetter Code, based on its location within the overall drainage system. [ 1 ]
A comprehensive coding system is in use in Europe. This system codes from the ocean to the so-called primary catchment. The system determines a set of oceans or endorheic systems identified by a letter. These systems are subdivided into a maximum of 9 seas. The seas are numbered 1 to 9. Seas lying far from the ocean, for example the Black Sea receive a higher number. The seas are delimited using the so-called definitions made by the International Hydrographic Organization in 1953. The coasts of these seas are defined clockwise from north west to south east from the strait where the sea connects to the ocean or the other seas.
Subsequently every watershed along this coast is assigned a number using the Pfafstetter Coding System . This implies that the four largest watersheds are selected and receive numbers 2,4,6, or 8. The watersheds in between the large systems receive numbers 3, 5, and 7. Numbers 1 and 9 are used for the small watersheds on the edges of the strait. The smaller systems can subsequently be numbered recursively or kept together for grouping purpose.
Landmasses (Continent and Islands) are also numbered in a logical manner, along a clock-wise oriented sea. For Europe containing many inner seas this feature helps to read the relative location of a hydrological object in the sea. | https://en.wikipedia.org/wiki/Hydrological_code |
Hydrological optimization applies mathematical optimization techniques (such as dynamic programming , linear programming , integer programming , or quadratic programming ) to water-related problems. These problems may be for surface water , groundwater , or the combination. The work is interdisciplinary, and may be done by hydrologists , civil engineers , environmental engineers , and operations researchers .
Groundwater and surface water flows can be studied with hydrologic simulation . A typical program used for this work is MODFLOW . However, simulation models cannot easily help make management decisions, as simulation is descriptive. Simulation shows what would happen given a certain set of conditions. Optimization, by contrast, finds the best solution for a set of conditions. Optimization models have three parts:
To use hydrological optimization, a simulation is run to find constraint coefficients for the optimization. An engineer or manager can then add costs or benefits associated with a set of possible decisions, and solve the optimization model to find the best solution.
Partial differential equations (PDEs) are widely used to describe hydrological processes, suggesting that a high degree of accuracy in hydrological optimization should strive to incorporate PDE constraints into a given optimization . Common examples of PDEs used in hydrology include:
Other environmental processes to consider as inputs include: | https://en.wikipedia.org/wiki/Hydrological_optimization |
An hydrological transport model is a mathematical model used to simulate the flow of rivers, streams , groundwater movement or drainage front displacement , and calculate water quality parameters. These models generally came into use in the 1960s and 1970s when demand for numerical forecasting of water quality and drainage was driven by environmental legislation , and at a similar time widespread access to significant computer power became available. Much of the original model development took place in the United States and United Kingdom , but today these models are refined and used worldwide.
There are dozens of different transport models that can be generally grouped by pollutants addressed, complexity of pollutant sources, whether the model is steady state or dynamic, and time period modeled. Another important designation is whether the model is distributed (i.e. capable of predicting multiple points within a river) or lumped. In a basic model, for example, only one pollutant might be addressed from a simple point discharge into the receiving waters . In the most complex of models, various line source inputs from surface runoff might be added to multiple point sources , treating a variety of chemicals plus sediment in a dynamic environment including vertical river stratification and interactions of pollutants with in-stream biota . In addition watershed groundwater may also be included. The model is termed "physically based" if its parameters can be measured in the field.
Often models have separate modules to address individual steps in the simulation process. The most common module is a subroutine for calculation of surface runoff, allowing variation in land use type, topography , soil type, vegetative cover , precipitation and land management practice (such as the application rate of a fertilizer ). The concept of hydrological modeling can be extended to other environments such as the oceans , but most commonly (and in this article) the subject of a river watershed is generally implied.
In 1850, T. J. Mulvany was probably the first investigator to use mathematical modeling in a stream hydrology context, although there was no chemistry involved. [ 1 ] By 1892 M.E. Imbeau had conceived an event model to relate runoff to peak rainfall, again still with no chemistry. [ 2 ] Robert E. Horton ’s seminal work [ 3 ] on surface runoff along with his coupling of quantitative treatment of erosion [ 4 ] laid the groundwork for modern chemical transport hydrology.
Physically based models (sometimes known as deterministic, comprehensive or process-based models) try to represent the physical processes observed in the real world. Typically, such models contain representations of surface runoff, subsurface flow, evapotranspiration, and channel flow, but they can be far more complicated. "Large scale simulation experiments were begun by the U.S. Army Corps of Engineers in 1953 for reservoir management on the main stem of the Missouri River". This, [ 5 ] and other early work that dealt with the River Nile [ 6 ] [ 7 ] and the Columbia River [ 8 ] are discussed, in a wider context, in a book published by the Harvard Water Resources Seminar, that contains the sentence just quoted. [ 9 ] Another early model that integrated many submodels for basin chemical hydrology was the Stanford Watershed Model (SWM). [ 10 ] The SWMM ( Storm Water Management Model ), the HSPF (Hydrological Simulation Program – FORTRAN) and other modern American derivatives are successors to this early work.
In Europe a favoured comprehensive model is the Système Hydrologique Européen (SHE), [ 11 ] [ 12 ] which has been succeeded by MIKE SHE and SHETRAN . MIKE SHE is a watershed-scale physically based, spatially distributed model for water flow and sediment transport . Flow and transport processes are represented by either finite difference representations of partial differential equations or by derived empirical equations. The following principal submodels are involved:
This model can analyze effects of land use and climate changes upon in-stream water quality, with consideration of groundwater interactions.
Worldwide a number of basin models have been developed, among them RORB ( Australia ), Xinanjiang ( China ), Tank model ( Japan ), ARNO ( Italy ), TOPMODEL ( Europe ), UBC ( Canada ) and HBV ( Scandinavia ), MOHID Land ( Portugal ). However, not all of these models have a chemistry component. Generally speaking, SWM, SHE and TOPMODEL have the most comprehensive stream chemistry treatment and have evolved to accommodate the latest data sources including remote sensing and geographic information system data.
In the United States, the Corps of Engineers, Engineer Research and Development Center in conjunction with a researchers at a number of universities have developed the Gridded Surface/Subsurface Hydrologic Analysis GSSHA model. [ 13 ] [ 14 ] [ 15 ] GSSHA is widely used in the U.S. for research and analysis by U.S. Army Corps of Engineers districts and larger consulting companies to compute flow, water levels, distributed erosion, and sediment delivery in complex engineering designs. A distributed nutrient and contaminant fate and transport component is undergoing testing. GSSHA input/output processing and interface with GIS is facilitated by the Watershed Modeling System (WMS). [ 16 ]
Another model used in the United States and worldwide is V flo , a physics-based distributed hydrologic model developed by Vieux & Associates, Inc. [ 17 ] V flo employs radar rainfall and GIS data to compute spatially distributed overland flow and channel flow. Evapotranspiration, inundation, infiltration, and snowmelt modeling capabilities are included. Applications include civil infrastructure operations and maintenance, stormwater prediction and emergency management, soil moisture monitoring, land use planning , water quality monitoring, and others.
These models based on data are black box systems, using mathematical and statistical concepts to link a certain input (for instance rainfall ) to the model output (for instance runoff ). Commonly used techniques are regression , transfer functions , neural networks and system identification . These models are known as stochastic hydrology models. Data based models have been used within hydrology to simulate the rainfall-runoff relationship, represent the impacts of antecedent moisture and perform real-time control on systems.
A key component of a hydrological transport model is the surface runoff element, which allows assessment of sediment, fertilizer , pesticide and other chemical contaminants. Building on the work of Horton, the unit hydrograph theory was developed by Dooge in 1959. [ 18 ] It required the presence of the National Environmental Policy Act and kindred other national legislation to provide the impetus to integrate water chemistry to hydrology model protocols. In the early 1970s the U.S. Environmental Protection Agency (EPA) began sponsoring a series of water quality models in response to the Clean Water Act . An example of these efforts was developed at the Southeast Water Laboratory, [ 19 ] one of the first attempts to calibrate a surface runoff model with field data for a variety of chemical contaminants.
The attention given to surface runoff contaminant models has not matched the emphasis on pure hydrology models, in spite of their role in the generation of stream loading contaminant data. In the United States the EPA has had difficulty interpreting [ 20 ] diverse proprietary contaminant models and has to develop its own models more often than conventional resource agencies, who, focused on flood forecasting, have had more of a centroid of common basin models. [ 21 ]
Liden applied the HBV model to estimate the riverine transport of three different substances, nitrogen , phosphorus and suspended sediment [ 22 ] in four different countries: Sweden , Estonia , Bolivia and Zimbabwe . The relation between internal hydrological model variables and nutrient transport was assessed. A model for nitrogen sources was developed and analysed in comparison with a statistical method. A model for suspended sediment transport in tropical and semi-arid regions was developed and tested. It was shown that riverine total nitrogen could be well simulated in the Nordic climate and riverine suspended sediment load could be estimated fairly well in tropical and semi-arid climates. The HBV model for material transport generally estimated material transport loads well. The main conclusion of the study was that the HBV model can be used to predict material transport on the scale of the drainage basin during stationary conditions, but cannot be easily generalised to areas not specifically calibrated. In a different work, Castanedo et al. applied an evolutionary algorithm to automated watershed model calibration. [ 23 ]
The United States EPA developed the DSSAM Model to analyze water quality impacts from land use and wastewater management decisions in the Truckee River basin, an area which include the cities of Reno and Sparks, Nevada as well as the Lake Tahoe basin. The model [ 24 ] satisfactorily predicted nutrient, sediment and dissolved oxygen parameters in the river. It is based on a pollutant loading metric called "Total Maximum Daily Load" (TMDL). The success of this model contributed to the EPA's commitment to the use of the underlying TMDL protocol in EPA's national policy for management of many river systems in the United States . [ 25 ]
The DSSAM Model is constructed to allow dynamic decay of most pollutants; for example, total nitrogen and phosphorus are allowed to be consumed by benthic algae in each time step, and the algal communities are given a separate population dynamic in each river reach (e.g. based upon river temperature). Regarding stormwater runoff in Washoe County , the specific elements within a new xeriscape ordinance were analyzed for efficacy using the model. For the varied agricultural uses in the watershed, the model was run to understand the principal sources of impact, and management practices were developed to reduce in-river pollution. Use of the model has specifically been conducted to analyze survival of two endangered species found in the Truckee River and Pyramid Lake : the Cui-ui sucker fish (endangered 1967) and the Lahontan cutthroat trout (threatened 1970). | https://en.wikipedia.org/wiki/Hydrological_transport_model |
Hydrology (from Ancient Greek ὕδωρ ( húdōr ) ' water ' and -λογία ( -logía ) ' study of ' ) is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle , water resources , and drainage basin sustainability. A practitioner of hydrology is called a hydrologist . Hydrologists are scientists studying earth or environmental science , civil or environmental engineering , and physical geography . [ 1 ] Using various analytical methods and scientific techniques, they collect and analyze data to help solve water related problems such as environmental preservation , natural disasters , and water management . [ 1 ]
Hydrology subdivides into surface water hydrology, groundwater hydrology ( hydrogeology ), and marine hydrology. Domains of hydrology include hydrometeorology , surface hydrology , hydrogeology , drainage-basin management, and water quality .
Oceanography and meteorology are not included because water is only one of many important aspects within those fields.
Hydrological research can inform environmental engineering, policy , and planning .
Hydrology has been subject to investigation and engineering for millennia. Ancient Egyptians were one of the first to employ hydrology in their engineering and agriculture, inventing a form of water management known as basin irrigation. [ 3 ] Mesopotamian towns were protected from flooding with high earthen walls. Aqueducts were built by the Greeks and Romans , while history shows that the Chinese built irrigation and flood control works. The ancient Sinhalese used hydrology to build complex irrigation works in Sri Lanka , also known for the invention of the Valve Pit which allowed construction of large reservoirs, anicuts and canals which still function.
Marcus Vitruvius , in the first century BC, described a philosophical theory of the hydrologic cycle, in which precipitation falling in the mountains infiltrated the Earth's surface and led to streams and springs in the lowlands. [ 4 ] With the adoption of a more scientific approach, Leonardo da Vinci and Bernard Palissy independently reached an accurate representation of the hydrologic cycle. It was not until the 17th century that hydrologic variables began to be quantified.
Pioneers of the modern science of hydrology include Pierre Perrault , Edme Mariotte and Edmund Halley . By measuring rainfall, runoff, and drainage area, Perrault showed that rainfall was sufficient to account for the flow of the Seine. Mariotte combined velocity and river cross-section measurements to obtain a discharge value, again in the Seine. Halley showed that the evaporation from the Mediterranean Sea was sufficient to account for the outflow of rivers flowing into the sea. [ 5 ]
Advances in the 18th century included the Bernoulli piezometer and Bernoulli's equation , by Daniel Bernoulli , and the Pitot tube , by Henri Pitot . The 19th century saw development in groundwater hydrology, including Darcy's law , the Dupuit-Thiem well formula, and Hagen-Poiseuille 's capillary flow equation.
Rational analyses began to replace empiricism in the 20th century, while governmental agencies began their own hydrological research programs. Of particular importance were Leroy Sherman's unit hydrograph , the infiltration theory of Robert E. Horton , and C.V. Theis' aquifer test/equation describing well hydraulics.
Since the 1950s, hydrology has been approached with a more theoretical basis than in the past, facilitated by advances in the physical understanding of hydrological processes and by the advent of computers and especially geographic information systems (GIS). (See also GIS and hydrology )
The central theme of hydrology is that water circulates throughout the Earth through different pathways and at different rates. The most vivid image of this is in the evaporation of water from the ocean, which forms clouds. These clouds drift over the land and produce rain. The rainwater flows into lakes, rivers, or aquifers. The water in lakes, rivers, and aquifers then either evaporates back to the atmosphere or eventually flows back to the ocean, completing a cycle. Water changes its state of being several times throughout this cycle.
The areas of research within hydrology concern the movement of water between its various states, or within a given state, or simply quantifying the amounts in these states in a given region. Parts of hydrology concern developing methods for directly measuring these flows or amounts of water, while others concern modeling these processes either for scientific knowledge or for making a prediction in practical applications.
Ground water is water beneath Earth's surface, often pumped for drinking water. [ 1 ] Groundwater hydrology ( hydrogeology ) considers quantifying groundwater flow and solute transport. [ 6 ] Problems in describing the saturated zone include the characterization of aquifers in terms of flow direction, groundwater pressure and, by inference, groundwater depth (see: aquifer test ). Measurements here can be made using a piezometer . Aquifers are also described in terms of hydraulic conductivity, storativity and transmissivity. There are a number of geophysical methods [ 7 ] for characterizing aquifers. There are also problems in characterizing the vadose zone (unsaturated zone). [ 8 ]
Infiltration is the process by which water enters the soil. Some of the water is absorbed, and the rest percolates down to the water table . The infiltration capacity, the maximum rate at which the soil can absorb water, depends on several factors. The layer that is already saturated provides a resistance that is proportional to its thickness, while that plus the depth of water above the soil provides the driving force ( hydraulic head ). Dry soil can allow rapid infiltration by capillary action ; this force diminishes as the soil becomes wet. Compaction reduces the porosity and the pore sizes. Surface cover increases capacity by retarding runoff, reducing compaction and other processes. Higher temperatures reduce viscosity , increasing infiltration. [ 9 ] : 250–275
Soil moisture can be measured in various ways; by capacitance probe , time domain reflectometer or tensiometer . Other methods include solute sampling and geophysical methods. [ 10 ]
Hydrology considers quantifying surface water flow and solute transport, although the treatment of flows in large rivers is sometimes considered as a distinct topic of hydraulics or hydrodynamics. Surface water flow can include flow both in recognizable river channels and otherwise. Methods for measuring flow once the water has reached a river include the stream gauge (see: discharge ), and tracer techniques. Other topics include chemical transport as part of surface water, sediment transport and erosion.
One of the important areas of hydrology is the interchange between rivers and aquifers. Groundwater/surface water interactions in streams and aquifers can be complex and the direction of net water flux (into surface water or into the aquifer) may vary spatially along a stream channel and over time at any particular location, depending on the relationship between stream stage and groundwater levels.
In some considerations, hydrology is thought of as starting at the land-atmosphere boundary [ 11 ] and so it is important to have adequate knowledge of both precipitation and evaporation. Precipitation can be measured in various ways: disdrometer for precipitation characteristics at a fine time scale; radar for cloud properties, rain rate estimation, hail and snow detection; rain gauge for routine accurate measurements of rain and snowfall; satellite for rainy area identification, rain rate estimation, land-cover/land-use, and soil moisture, snow cover or snow water equivalent for example. [ 12 ]
Evaporation is an important part of the water cycle. It is partly affected by humidity, which can be measured by a sling psychrometer . It is also affected by the presence of snow, hail, and ice and can relate to dew, mist and fog. Hydrology considers evaporation of various forms: from water surfaces; as transpiration
from plant surfaces in natural and agronomic ecosystems. Direct measurement of evaporation can be obtained using Simon's evaporation pan .
Detailed studies of evaporation involve boundary layer considerations as well as momentum, heat flux, and energy budgets.
Remote sensing of hydrologic processes can provide information on locations where in situ sensors may be unavailable or sparse. It also enables observations over large spatial extents. Many of the variables constituting the terrestrial water balance, for example surface water storage, soil moisture , precipitation , evapotranspiration , and snow and ice , are measurable using remote sensing at various spatial-temporal resolutions and accuracies. [ 13 ] Sources of remote sensing include land-based sensors, airborne sensors and satellite sensors which can capture microwave , thermal and near-infrared data or use lidar , for example.
In hydrology, studies of water quality concern organic and inorganic compounds, and both dissolved and sediment material. In addition, water quality is affected by the interaction of dissolved oxygen with organic material and various chemical transformations that may take place. Measurements of water quality may involve either in-situ methods, in which analyses take place on-site, often automatically, and laboratory-based analyses and may include microbiological analysis .
Observations of hydrologic processes are used to make predictions of the future behavior of hydrologic systems (water flow, water quality). [ 14 ] One of the major current concerns in hydrologic research is "Prediction in Ungauged Basins" (PUB), i.e. in basins where no or only very few data exist. [ 15 ]
The aims of Statistical hydrology is to provide appropriate statistical methods for analyzing and modeling various parts of the hydrological cycle. [ 16 ] By analyzing the statistical properties of hydrologic records, such as rainfall or river flow, hydrologists can estimate future hydrologic phenomena. When making assessments of how often relatively rare events will occur, analyses are made in terms of the return period of such events. Other quantities of interest include the average flow in a river, in a year or by season.
These estimates are important for engineers and economists so that proper risk analysis can be performed to influence investment decisions in future infrastructure and to determine the yield reliability characteristics of water supply systems. Statistical information is utilized to formulate operating rules for large dams forming part of systems which include agricultural, industrial and residential demands.
Hydrological models are simplified, conceptual representations of a part of the hydrologic cycle. They are primarily used for hydrological prediction and for understanding hydrological processes, within the general field of scientific modeling . Two major types of hydrological models can be distinguished: [ 17 ]
Recent research in hydrological modeling tries to have a more global approach to the understanding of the behavior of hydrologic systems to make better predictions and to face the major challenges in water resources management.
Water movement is a significant means by which other materials, such as soil, gravel, boulders or pollutants, are transported from place to place. Initial input to receiving waters may arise from a point source discharge or a line source or area source , such as surface runoff . Since the 1960s rather complex mathematical models have been developed, facilitated by the availability of high-speed computers. The most common pollutant classes analyzed are nutrients , pesticides , total dissolved solids and sediment . | https://en.wikipedia.org/wiki/Hydrology |
Hydrology in Practice is a hydrology textbook by British hydrologist Elizabeth M. Shaw . The book was originally published in 1983 by Van Nostrand Reinhold (UK) Co. Ltd. [ citation needed ] and the most recent fourth edition was published in July 2010 by CRC Press , [ 2 ] a division of Taylor & Francis. The book has been described as both an introductory text and a resource for professionals.
The third edition of the book is separated into three parts which discuss hydrological measurements, hydrological analysis, and engineering applications.
Hydrology in Practice has been described by CRC Press as "likely to be the course text for every undergraduate / MSc hydrology course in the UK". [ 3 ]
The book has been reviewed by the Quarterly Journal of the Royal Meteorological Society , [ 4 ] the Journal of the American Water Resources Association , [ 5 ] the Hydrological Sciences Journal , [ 6 ] and the Journal of Hydrology , [ 7 ] along with being cited in many scientific journals . In a review of the third edition, the Hydrological Sciences Journal described the book as "an excellent compendium of techniques and methods of hydrological measurement and data analysis". The book is also recommended reading at Dartmouth College , [ 8 ] Utah State University , [ 9 ] the University of Malta , [ 10 ] the American Institute of Hydrology , [ 11 ] and the Polytechnic University of Catalonia , [ 12 ] among others. | https://en.wikipedia.org/wiki/Hydrology_in_Practice |
Fishing Creek is a tributary of the Susquehanna River , in Columbia County, Pennsylvania , in the United States. Hydrology involves the discharge , the pH , the chemical hydrology , the dams , and the water temperature . Data has been gathered from a United States Geological Survey gauging station near Bloomsburg, Pennsylvania . The pH of the waters in the Fishing Creek watershed ranges from 4.9 to 8.5 in various places.
Approximately 1 mile (2 km) downstream of Orangeville, Fishing Creek's discharge averages 615 cubic feet per second (17.4 m 3 /s ) per second and its median discharge is 361 cubic feet per second (10.2 m 3 /s) second. The creek's lowest recorded discharge rate in that location is 90 cubic feet per second (2.5 m 3 /s) in 1962 and its highest was 2,580 cubic feet per second (73 m 3 /s) in 1981. [ 1 ] Further upstream, in Benton, Fishing Creek's discharge is almost always less than 720 cubic feet per second (20 m 3 /s), and is far lower during the summer, usually approaching 0. The typical discharge of Fishing Creek at this location is around 540 cubic feet per second (15 m 3 /s). The streambeds of West Branch and East Branch Fishing Creeks commonly run dry in the summer. In dry years, they are dry for 105 days on average, while in wet years they are on average dry for 5 days. [ 2 ]
At a stream gauging station near Bloomsburg, Fishing Creek's discharge ranged between 10 cubic feet per second (0.28 m 3 /s) and 5,350 cubic feet per second (151 m 3 /s) between 2002 and 2012. The lowest discharge recorded during this time occurred on November 9, 2004. The highest discharge recorded during this time occurred on September 23, 2003. [ 3 ]
Near Benton, Fishing Creek's pH ranges from around 5.6 to around 7.25. Near Camp Lavigne, it ranges from 5.5 to 7.1. East Branch Fishing Creek is the only stream in the watershed whose pH drops below 5.5. Its pH can be as low as 4.9. West Creek and Coles Creek are the least acidic streams in the Fishing Creek watershed. Their pH is usually above 6.3 and often above 7. Typically, Fishing Creek and its tributaries are not at risk for being too acidic for the optimal health of fish , but in early spring during snowmelts , the pH levels near the limit that brook trout can tolerate. [ 2 ] Fishing Creek's waters are acidic due to acid rain . [ 4 ]
The waters of Fishing Creek at a gauging station near Bloomsburg had pH levels ranging from 5.8 to 8.5 between 2002 and 2012. The lowest pH during that time (5.8) occurred on December 17, 2003. The highest pH during that time (8.5) occurred on February 14, 2012. The average pH during that time and at that location was 7.242. [ 3 ]
The concentration of dissolved oxygen in Fishing Creek has been measured to range from approximately 5 to 17.5 milligrams per liter at Benton. In a 14-month period from May 2010 to July 2011, the dissolved oxygen level for the streams in the Fishing Creek watershed was highest in February 2011 and lowest in June, July, or August 2010, depending on the stream. A site on Fishing Creek, near Camp Lavigne, had slightly less fluctuation; there it ranged from 8 to 17 milligrams per liter of dissolved oxygen. [ 2 ]
The concentration of hydrogen ions in the waters of Fishing Creek near Bloomsburg between 2002 and 2012 ranged from 0.00001 to 0.00153 milligrams per liter. The date of the lowest concentration of hydrogen ions at that location was on March 1 and July 16, 2003. The date of the highest concentration of hydrogen ions at the location on the creek was December 17, 2003. The average concentration of hydrogen ions was 0.0001 milligrams per liter. [ 3 ]
The total concentration of nitrogen in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from 0.52 to 2.8 milligrams per liter. The date during which the lowest concentration of nitrogen occurred was October 14, 2009. The date of the highest concentration was on January 13, 2003. The average concentration of nitrogen between 2002 and 2012 was 1.212 milligrams per liter. [ 3 ]
The concentration of dissolved oxygen in Fishing Creek near Bloomsburg between 2002 and 2012 ranged between 4.1 and 17.1 milligrams per liter. The lowest concentration of dissolved oxygen in the creek during that period and at that location occurred on July 25, 2005. The highest concentration of dissolved oxygen occurred on January 6, 2009. The average concentration of dissolved oxygen was 10.942 milligrams per liter. [ 3 ]
Fishing Creek contains dissolved aluminum but in most places not enough to be toxic , although some of its tributaries have aluminum concentrations approaching lethal levels for fish. The only tributary of Fishing Creek which contains dissolved aluminum in concentrations of over 100 micrograms per liter is East Branch Fishing Creek . Fishing Creek itself and all of its other tributaries had dissolved aluminum concentrations of less than 70 micrograms per liter. This concentration is linked to the thawing of soils, as demonstrated by the fact that aluminum levels in Fishing Creek peak in March and April and drop to almost zero in the summer. [ 2 ]
The total concentration of calcium in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from 5.5 milligrams per liter to 26 milligrams per liter. The lowest concentration of calcium occurred on February 6, 2008. The highest concentration of calcium occurred on June 18, 2012. The average concentration of calcium was 7.532 milligrams per liter. [ 3 ]
The total concentration of magnesium in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from 1.5 milligrams per liter to 6.7 milligrams per liter. The lowest concentration of magnesium occurred on November 1, 2006. The highest concentration of magnesium occurred on June 18, 2012. The average concentration of calcium is 1.748 milligrams per liter. [ 3 ]
The total concentration of iron in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from 40 micrograms per liter to 5730 micrograms per liter. The lowest concentration of iron occurred on April 6, 2006, November 12, 2008, and June 18, 2012. The highest concentration of iron occurred on July 5, 2011. The average concentration of iron was 397.37 micrograms per liter. [ 3 ]
The total concentration of manganese in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from less than 10 to 240 micrograms per liter, not counting the times that its presence was "verified but not quantified". [ 3 ] The lowest concentration of manganese occurred on November 20, 2002. The highest concentration of manganese occurred on September 23, 2003. The average concentration was approximately 42 micrograms per liter. [ 3 ]
In all times between 2002 and 2012 that the concentration of copper in the waters of Fishing Creek at the gauging station near Bloomsburg was measured, it was under 10 milligrams per liter. The concentration was under 4 micrograms per liter all but one of the times that it was measured. The concentration of lead in the waters of Fishing Creek was always under 1 microgram per liter, as measured between 2002 and 2012 at the gauging station near Bloomsburg. The concentration of nickel was always under 4 micrograms per liter all the times it was measured and its presence quantified between 2002 and 2012. The concentration of strontium was only measured once, on February 14, 2012. The concentration was 90 micrograms per liter. [ 3 ]
The concentration of zinc in the waters of Fishing Creek has been under 5 micrograms per liter all the times that it was detected and measured. The other time, on April 11, 2012, it was 10 micrograms per liter. The concentration of selenium has only been measured once, on February 14, 2012. It was under 7 micrograms per liter. [ 3 ]
The concentration of carbon dioxide in the waters of Fishing Creek near Bloomsburg between 2002 and 2012 ranged from 0.3 to 34 milligrams per liter. The date during which there was the lowest concentration of carbon dioxide was April 6, 2006 and February 14, 2012. The date during which there was the highest concentration of carbon dioxide at the location on the creek was December 17, 2003. The average concentration of carbon dioxide was 2.04 milligrams per liter. [ 3 ]
The total concentration of ammonia in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from less than 0.02 milligrams per liter to 0.06 milligrams per liter. The highest concentration of ammonia occurred on May 19, 2009. The total concentration of nitrates in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 was always less than 0.04 milligrams per liter. [ 3 ]
The total concentration of phosphates in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from less than 0.031 milligrams per liter to 0.11 milligrams per liter. The highest concentration of phosphates occurred on May 19, 2009. The total concentration of phosphorus itself in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from less than 0.01 milligrams per liter to 0.575 milligrams per liter. The highest phosphorus concentration occurred on July 5, 2011. [ 3 ]
The total concentration of sulfates in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from 6.8 to 34.5 milligrams per liter. However, the second highest concentration was only 15.2 milligrams per liter. The highest concentration of sulfates occurred on February 14, 2012. The lowest concentration occurred on September 23, 2003. The average concentration was 10.57 milligrams per liter. [ 3 ]
The total concentration of caffeine in the waters of Fishing Creek near Bloomsburg between 2002 and 2012 ranged from an estimated 0.012 micrograms per liter to less than 0.2 micrograms per liter. The highest concentration occurred on November 12, 2008 and May 19, 2009. The lowest concentration occurred on February 6, 2008. The average concentration was approximately 0.099 micrograms per liter. [ 3 ]
The total concentration of acetaminophen in the waters of Fishing Creek near Bloomsburg between 2002 and 2012 ranged from an estimated 7 nanograms per liter to 88 nanograms per liter. The lowest concentration occurred on August 25, 2008 and the highest concentration occurred on March 17, 2009. The average concentration was approximately 63 nanograms per liter. [ 3 ]
The total concentration of codeine in the waters of Fishing Creek near Bloomsburg has been measured several times. It was under 0.04 micrograms per liter all the times that it was measured. [ 3 ]
The total concentration of phenols in the waters of Fishing Creek near Bloomsburg has been measured once, on November 9, 2004. The concentration was less than five micrograms per liter. The total concentration of chlortetracycline and oxytetracycline in the waters of Fishing Creek near Bloomsburg between 2002 and 2012 have also both been measured several times. The concentrations of both compounds was always less than 0.01 micrograms per liter. Sulfamethazine is another chemical whose concentration has been measured in the waters of Fishing Creek. Its concentration is always less than 5 nanograms per liter. [ 3 ]
The concentration of dehydronifedipine in the waters of Fishing Creek has also been measured a number of times. On February 6, 2008, April 3, 2008, June 10, 2008, and August 25, 2008, the concentration was the lowest, at less than 0.06 micrograms per liter. On November 12, 2008, March 17, 2009, May 19, 2009, and July 8, 2009, the concentration was at its highest, at less than 0.08 micrograms per liter. The average concentration is 0.07 micrograms per liter. [ 3 ]
The concentration of cotinine in the waters of Fishing Creek was measured eight times in 2008 and 2009. All of these times, the concentration was less than 26 nanograms per liter. The concentration of diltiazem was also measured eight times in 2008 and 2009. [ 3 ]
The total concentration of dissolved solids at Fishing Creek near Bloomsburg between 2002 and 2012 ranged from less than 2 to 166 milligrams per liter. The lowest concentration during that time occurred on January 13, 2003; May 19, 2003; October 21, 2003; December 17, 2003; March 14, 2005; May 5, 2005; February 8, 2006; April 6, 2006; August 3, 2006; January 4, 2007; May 24, 2007; July 11, 2007; December 4, 2007; and April 3, 2008. The highest concentration during that time occurred on September 23, 2003. [ 3 ]
The total concentration of azithromycin in Fishing Creek near Bloomsburg between 2002 and 2012 was less than 5 nanograms per liter every time it was measured. The total concentration of carbamazepine in Fishing Creek in the same place and time ranged from approximately 1 nanogram per liter to less than 40 nanograms per liter. The lowest concentration occurred on February 6, 2008. The highest concentration occurred several times in 2008 and 2009. [ 3 ]
The total concentration of diphenhydramine in Fishing Creek ranged from approximately 2 to less than 40 nanograms per liter. The lowest concentration occurred on June 10, 2008. The highest concentration occurred once in 2008 and three times in 2009. The average concentration was 22.125 nanograms per liter. [ 3 ]
The concentration of fecal coliform has been measured once, on November 9, 2004. Its concentration was under 20 M-FC 0.45uMF col per 100 milliliters. [ 3 ]
The concentration of E coli in the waters of Fishing Creek at the gauging station near Bloomsburg between 2002 and 2012 ranged from less than 3 to 150 m-TEC MF water col per 100 milliliters. The lowest concentration occurred on April 3, 2008. The highest concentration occurred on February 6, 2008. The average concentration was 58.14 m-TEC MF water col per 100 milliliters. [ 3 ]
The concentration of enterococcus in the waters of Fishing Creek at the gauging station near Bloomsburg has ranged from under 3 to 680 m-E MF water col per 100 milliliters. The lowest concentration occurred on November 12, 2008 and the highest concentration occurred on February 6, 2008. The average concentration was 120.71 m-E MF water col per 100 milliliters. [ 3 ]
There is a lowhead dam referred to by locals as Boone's Dam on Fishing Creek near where the creek flows past Bloomsburg. A dam was built on Fishing Creek in the northern reaches of Bloomsburg with the purpose of powering nearby Irondale furnaces. [ 5 ] [ 6 ] Additionally, a dam was built on Fishing Creek about 2 miles (3 km) north of Bloomsburg in 1818 by John Barton. [ 7 ] In the 1800s and early 1900s there were two other dams on Fishing Creek. One was in Orange Township, and the other, a 212-foot (65 m) concrete dam, was in Orangeville. [ 8 ] A dam known as the Benton Dam was built on upper Fishing Creek, directly upstream of Benton. [ 2 ]
The highest water temperature of a stream in the Fishing Creek watershed is that of West Creek, which can reach 77 °F (25 °C) in the summer. The water temperature of Fishing Creek in Benton can reach 75 °F (24 °C) in the summer. The water temperature of Coles Creek, a tributary of Fishing Creek, only reaches 66 to 68 °F (19 to 20 °C) in the summer. In the winter, the water temperature of the main stem of Fishing Creek is around 32 °F (0 °C), and West Branch Fishing Creek's temperature can reach as low as 28 °F (−2 °C) in the winter, making it the coldest stream in the watershed during winter. [ 2 ]
At a gauging station near Bloomsburg, the water temperature ranged from 32°F (0.1°C) to 78°F (25.7°C) between November 2002 and November 2012. The lowest water temperature of the creek occurred on January 10, 2011. The highest water temperature of the creek in this location occurred on August 3, 2006. The average water temperature in August on Fishing Creek near Bloomsburg is approximately 22.67°C. The average water temperature in January on Fishing Creek near Bloomsburg is approximately 1.92°C. The average water temperature of Fishing Creek for every water temperature measurement on the creek near Bloomsburg between 2002 and 2012 is approximately 12.03°C. [ 3 ] | https://en.wikipedia.org/wiki/Hydrology_of_Fishing_Creek_(North_Branch_Susquehanna_River_tributary) |
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