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ISASMELT Construction is expected to be completed by mid-2014, and the capital cost is estimated at US$650 million. The estimated operating cost was given as US$69 per tonne of concentrate. The Kansanshi copper smelter project is estimated to be worth US$340–500 million per year in reduced concentrate freight costs, export duties and sulfuric acid costs. In addition to treating copper concentrates, furnaces have also been built to treat secondary (scrap) copper materials. In the early 1990s, technical personnel from the then Union Miniére worked with MIM Holdings personnel to develop an ISASMELT-based process to treat scrap materials and residues containing copper and lead. Union Miniére operated a smelter at Hoboken, near Antwerpen in Belgium, that specialised in recycling scrap non-ferrous materials. The test work program was undertaken using an test rig at MIM Holdings’ lead refinery, Britannia Refined Metals, at Northfleet in the United Kingdom. A demonstration plant was designed by MIM Holdings personnel and operated for several months at the Hoboken smelter site. The new smelter was commissioned in the final quarter of 1997 and in 2007 was treating up to 300,000 t/y of secondary materials. The installation of the furnace replaced "a large number of unit processes" and substantially reduced operating costs at the Hoboken smelter. Umicore’s Hoboken plant uses a two-step process in a single furnace. The first step involves the oxidation of the feed to form a copper matte and a lead-rich slag | https://en.wikipedia.org/wiki?curid=39223191 |
ISASMELT The slag is then tapped and the remaining copper matte is then converted to blister copper. The lead-rich slag is subsequently reduced in a blast furnace to produce lead metal, while the copper is refined and the contained precious metals recovered. The then Hüttenwerke Kayser smelter at Lünen in Germany installed an plant in 2002 to replace three blast furnaces and one Peirce-Smith converter used for smelting scrap copper. The company was subsequently bought by Norddeutsche Affinerie AG, which in turn became Aurubis AG. The process used at the Lünen smelter involves charging the furnace with copper residues and scrap containing between 1 and 80% copper and then melting it in a reducing environment. This produces a "black copper phase" and a low-copper silica slag. Initially the black copper was converted to blister copper in the furnace. However, in 2011 the smelter was expanded as part of the "KRS Plus" project. A top-blown rotary converter is now used to convert the black copper and the furnace runs continuously in smelting mode. The installation of the furnace increased the overall copper recovery in the plant by reducing losses to slag, reduced the number of furnaces in operation, decreased the waste gas volume, and decreased energy consumption by more than 50%. The production capacity exceeds the original design by 40%. | https://en.wikipedia.org/wiki?curid=39223191 |
Bacterial Filtration Efficiency or BFE is a measurement of a respirator material's resistance to penetration of bacteria. Results are reported as percent efficiency and correlate with the ability of the fabric to resist bacterial penetration. Higher numbers in this test indicate better barrier efficiency. Wrap fabrics were compared based on grade as well as basis weight. . Kimberly-Clark uses a test procedure where samples were challenged with a biological aerosol of Staphylococcus aureus and the results employ a ratio of the bacterial challenge counts to sample effluent counts, to determine percent bacterial filtration efficiency (%BFE). Surgical mask standards in China, Europe, and the United States measure BFE by using particles of size 3.0 μm. | https://en.wikipedia.org/wiki?curid=39226969 |
Corrosion under insulation (CUI) is a severe form of localized external corrosion that occurs in carbon and low alloy steel equipment that has been insulated. This form of corrosion occurs when water is absorbed by or collected in the insulation. The equipment begins to corrode as it is exposed to water and oxygen. CUI is common in refineries and process plants that typically operate equipment at high temperatures. | https://en.wikipedia.org/wiki?curid=39228729 |
Configurational mechanics is a subdiscipline of continuum mechanics in which particular emphasis is placed on reckoning from the perspective of the material manifold. By contrast, in classical mechanics, reckoning is commonly made from the perspective of spatial coordinates. | https://en.wikipedia.org/wiki?curid=39230475 |
Yurii Sh. Matros Yurii Shaevich Matros () is a scientist in the field of chemical engineering, known for his achievement in the theory and practice of heterogeneous catalytic processes. He is acknowledged as a “Godfather” of realization of catalytic processes in forced unsteady state conditions. Matros developed a catalytic reactor with periodic changes of direction of flow rate in packed bed of catalyst (named in literature as “reverse process” or “Matros Reactor”). This reactor is widely known in scientific and applied literature as an example of an application of developed theory of forced unsteady processes. Yurii Matros has a full doctoral degree of science and is a professor. Matros was born in Odessa, Ukraine in 1937. As an overachieving student, he graduated from Odessa National Polytechnic University in 1959 with a red diploma (highest academic distinction). After four years of research at this university, while simultaneously working at the Novosibirsk chemical plant, he received his PhD degree in 1964. His science career was developed at the Boreskove Institute of Catalysis in its world-famous science center in the academic city of Novosibirsk (Akademgorodok), where in 1974 he received the degree of full doctor of chemical engineering and the official academic title of professor. Afterwards he became the head of the department which studied unsteady state processes in catalysis. His more than thirty years of academic and applied research has been focused on the gas-solid fixed and fluidized bed reactors | https://en.wikipedia.org/wiki?curid=39235307 |
Yurii Sh. Matros In the 1960s and 1970s, he analyzed various levels of mathematical modeling of catalytic reactors, beginning with the reaction process over the catalyst surface and ending with the processes in catalyst pellet and catalytic reactor itself. As one of the first researchers in the field, he described non-standard patterns of fixed bed reactor behavior, such as wrong way behavior and multiplicity of steady-state solutions. He contributed greatly to the theory of formation and movement of creeping fronts through the packed bed. His main scientific results, however, were developed from the 1970s to 1995. These results showed a new direction in theory and practice of forced unsteady-state processes in heterogeneous catalytic reactors as a way to significantly increase the efficiency of catalytic processes as a whole. Matros faced criticism by his opponents who claimed that he wants to construct a "perpetuum mobile". In reality, however, his theory was proven to be true, and now most chemical engineering science teams of universities and industry use it. The most frequently encountered example of unsteady-state operation is the reverse flow system (Matros reactor) in which the flow through reactor with fixed bed of catalysts is periodically reversed in order to store heat and/or mass, to regenerate heat/catalysts in situ, or to avoid kinetic limitation of a system at equilibrium | https://en.wikipedia.org/wiki?curid=39235307 |
Yurii Sh. Matros Former president of the Siberian Branch of Academy of Sciences of USSR (1925–2013) (now Russian Academy of Sciences), Gury Marchuk remarked that this was the most influential idea in chemistry during last 50 years. Matros is one of the scientists of the Academy of Sciences who consistently brought his scientific achievements directly to industrial practice. His more than forty patents indicate his great interest in realizing, and he realized, his scientific basic knowledge in different industrial applications. Most of the current commercial applications are encountered in environmental cleanup, especially in the catalytic elimination of VOCs from industrial and commercial exhausts, SO oxidation in sulfuric acid production, NOx reduction. Matros has been directly involved in the development, design and startup of dozens of industrial units. Potential applications include a number of partial oxidation processes and treatment of vehicular exhaust. His achievements have become the basis for a scientific school, which focuses on unsteady state processes in catalysis and which attracts post graduate students and collaboration among scientists from the former Soviet Union and other countries, such as Bulgaria, Hungary, India, Belgium, France, Switzerland, Poland, Germany, China, Italy and the United States. His books were published in Russian, English and Chinese, and they have now become reference books in most chemical engineering university departments across the world | https://en.wikipedia.org/wiki?curid=39235307 |
Yurii Sh. Matros Matros is the organizer and chairman of the traditional International Conference of Unsteady State Process in Catalysis which takes place periodically in Russia, Canada, Japan or the United States, every 3 to 4 years on average. Matros is often invited to give plenary lectures (PL) at prestigious international conferences. There are only two examples: 1. XIX International Conference on Chemical Reactors CHEMREACTOR-19, September 5–9, 2010, Vienna, Austria; PL by Matros was "How to Design Optimal Catalytic Reactor." The lecture was dedicated to Professor Mikhail Slin'ko. 2. International Conference took place in Novosibirsk, Russia in June 2007. It was dedicated to the 100-year anniversary of academician Boreskov's birthday. The PL was about a new type of catalytic processes based on forced unsteady state conditions, was presented by Matros. It was written: “An excellent lecture delivered by Prof. J. Matros, ... to create a fundamentally new type of catalytic processes based on non-stationary mode. ... The lecture was summarized the application of this technology in the industry around the world over the last several decades.” Matros’ role in international conferences reflects recognition in this field of science. In 1992, as a famous scientist, Matros received a green card on the basis of recommendations given by about 25 world authorities in chemical engineering: James Wei (Dean, Pomeroy and Betty Perry Smith Professor, School of Engineering and Applied Science, Princeton, NJ, USA); Larry D | https://en.wikipedia.org/wiki?curid=39235307 |
Yurii Sh. Matros Schmidt (Professor, University of Minnesota, Minneapolis, MN, USA); W. Harmon Ray (Steenbock Professor of Engineering, University of Wisconsin, Madison, WI, USA); Dan Luss (Cullen Professor and Chairman, University of Houston, TX, USA); Gilbert F. Froment (Directeur: Professor, Dr. Ir., Universiteit Gent, Belgiё); Gerhart Eigenberger (Professor. Dr. Ing., Universitat Stuttgart, Head of Institut f. Chemische Verfahrenstechnik, Germany); Dr. Blumenberg, BASF (Vice President, Process Chemistry, Ludwigshafen, Germany); Professor, Dr. Ir. von Dierendock (Senior Research Fellow, prof. of RUG, DSM; Dr. Jan J. Lerou (Du Pont, Wilmington, Delaware, Director of Research) and others. All of them reflected their own experience of scientific collaboration with Y. Matros. One example of a recommendation includes the following fragment from BASF, signed by Vice President of Process Chemistry, Blumenberg, on April 27, 1992: “He is one of the most famous chemical engineers, who are concerned with reactor technology ... BASF as one of the largest and most experienced chemical companies worldwide has acknowledged this by inviting Prof. Matros as a speaker on the occasion of its 125th anniversary in 1990 ... Prof. Matros has, besides his excellent research work, emphasized sharing of his knowledge with the scientific community. Excellent textbooks and numerous publications have contributed to the spread of scientific progress around the world | https://en.wikipedia.org/wiki?curid=39235307 |
Yurii Sh. Matros ” Another example of a recommendation includes the following fragment from the Head of Institute of Chemishe Verfahrenstechick of the University Stuttgart, Prof. Gerhat Eigenberger from April 23, 1992: “This letter attests to academic and experimental credentials of Dr. Y. Sh. Matros ... Dr. Matros is director on leave of the Department of Unsteady State Catalysis Processes in Novosibirsk, Russia. The institute of Catalysis is the best known and the highly respected institution on Catalysis in the whole former Soviet Union, and Dr. Matros is certainly one of its internationally best known researchers and representatives. Among his many achievements in the field of catalytic reaction engineering, I consider as highest his contributions to the dynamic operation of fixed bed reactors with periodic flow reversal, which is now referred to as the «Matros reactor» concept ...” Here are a few references on publications concerning Matros’ scientific and applied significance: In 1993 Matros founded a scientific consulting company called Matros Technologies, Inc. (MT) which gained recognition and became well known in the development different catalytic processes based on reversed-flow reactor conception. In 2008 MT received two awards: "80th anniversary of Yurii Matros" Boreskov Institute of Catalysis SB RAS. September 16, 2017. http://en.catalysis.ru/news/detail | https://en.wikipedia.org/wiki?curid=39235307 |
Yurii Sh. Matros php?ID=32213 Matros’ achievements and scientific activity is reflected in more than 40 patents, 300 publications of which he is the author or coauthor, 5 books of which he is the author, 7 books of which he is the editor-in-chief with and without coauthors. | https://en.wikipedia.org/wiki?curid=39235307 |
Vivergo Fuels is a bio-ethanol producer, headquartered in Hessle, East Riding of Yorkshire, but whose plant is based at Salt End, Kingston upon Hull, England. The company produces bio-fuels from locally sourced wheat and besides producing bio-ethanol, a by-product of animal feed is also part of the bio-fuel process. The company's plant was subject to a shutdown between November 2017 and April 2018 whilst demand for their product was low. The company blamed the United Kingdom government for not ruling that bio-fuel additives to petrol should be greater than 4.75%. It is the largest manufacturer of bio-ethanol in the United Kingdom and the second largest producer in Europe. Vivergo was first proposed in 2007 as a joint venture between AB Sugar, BP and DuPont. The company had £350 million ($400 million) invested into it and opened for business in July 2013, with both AB Sugar and BP taking a 47% share and DuPont the remaining 6%. In May 2015, BP pulled out of the venture and sold its stake to AB Sugar, giving them 94% of the company. The construction phase was beset by industrial action in March 2011; Vivergo had employed a company to build the plant, but it was behind schedule and so fired the company and sought another contractor to complete the task. This left 400 workers unemployed and the GMB union believed that Vivergo should continue to employ the workers whilst the search for a new contractor was completed | https://en.wikipedia.org/wiki?curid=39236938 |
Vivergo Fuels Redhall, a Wakefield-based company, was awarded the £18 million contract to design and build the plant in February 2010. The project was to have been completed by the end of 2010, but by the time of the industrial action, it was four months behind schedule. Redhall later successfully sued Vivergo for breach of contract. The company receives over of wheat per year and from that produces of bio-ethanol with of animal feed as by-product. The wheat is sourced from over 900 farms across Yorkshire and Lincolnshire with the bulk coming from the East Riding of Yorkshire. Wheat sourced from this region is high in starch which makes it ideal to process into bio-ethanol. The animal feed is sold on to over 800 farms across the United Kingdom. When the plant was opened, Frontier Agriculture had an exclusive contract to supply the transport from farms to the Vivergo plant. The plant was deliberately located on the Humber Estuary to take advantage of the ability of the east coast ports to export bulk liquids via ship-borne transport. Its location close to the major wheat producing areas in eastern England made it ideal. The next rival in terms of bio-fuels in the United Kingdom, is the Ensus plant on Teesside, which whilst producing less bio-ethanol and animal feed, also produces over of carbon dioxide gas for the drinks industry, something that Vivergo does not. This makes Vivergo the largest producer of bio-ethanol in the United Kingdom and the second largest producer in Europe | https://en.wikipedia.org/wiki?curid=39236938 |
Vivergo Fuels In November 2017, the plant was subject to an enforced closure by the company. Vivergo claimed that the business was unsustainable due to the government not adhering to its own Renewable Transport Fuel Obligation (RTFO) policy. Currently, the company produces E5, an up 5% blending product that is meant to be mixed with petrol in a 5:95% mix. Vivergo wish to produce E10, this would see an increase from 4.75% bio-fuels additives into petrol to 9.75% by 2020. After some government debate and agreement, the RTFO was adopted by the government, and was implemented in April 2018. The plant re-opened for business in April 2018 with E10 becoming law by 2020. | https://en.wikipedia.org/wiki?curid=39236938 |
Kabat numbering scheme The is a scheme for the numbering of amino acid residues in antibodies based upon variable regions. The scheme is useful when comparing these variable regions between antibodies. Its foundations were laid by the American biomedical scientist Elvin A. Kabat, who started collecting and aligning amino acid sequences of human and mouse Bence Jones proteins and immunoglobulin light chains in 1969. Another numbering scheme is the Chothia numbering system. | https://en.wikipedia.org/wiki?curid=39241335 |
Scandium sulfate is the scandium salt of sulfuric acid and has the formula Sc(SO). It is used in agriculture as a very dilute solution as a seed treatment to improve the germination of corn, peas, wheat, and other plants. | https://en.wikipedia.org/wiki?curid=39241652 |
Froth treatment (Athabasca oil sands) Bitumen froth treatment is a process used in the Athabasca oil sands (AOS) bitumen recovery operations to remove fine inorganics—water and mineral particles—from bitumen froth, by diluting the bitumen with a light hydrocarbon solvent—either naphthenic or paraffinic—to reduce the viscosity of the froth and to remove contaminants that were not removed in previous water-based gravity recovery phases. Bitumen with a high viscosity or with too many contaminants, is not suitable for transporting through pipelines or refining. The original and conventional naphthenic froth treatment (NFT) uses a naphtha solvent with the addition of chemicals. Paraffinic Solvent Froth Treatment (PSFT), which was first used commercially in the Albian Sands in the early 2000s, results in a cleaner bitumen with lower levels of contaminates, such as water and mineral solids. Following froth treatments, bitumen can be further upgraded using "heat to produce synthetic crude oil by means of a coker unit." Oil sand consists of a matrix of solid mineral material—quartz sand and clays, water, and the hydrocarbon, bitumen, which is the heaviest form of petroleum. According to the United Nations Institute for Training and Research, bitumen's normal viscosity is greater than 10 mPa s and its density is greater than 1000kg/m. Oil sands, before processing, comprise fine particles of silt and clay, that are 44 microns or less, and coarse particles of sand and rock, that are larger than 44 microns | https://en.wikipedia.org/wiki?curid=39242726 |
Froth treatment (Athabasca oil sands) Each grain of quartz sand, which is extremely abrasive and has an angular shapes, is "completely enveloped within bitumen". Each sand grain is surrounded by a thin film of water and bitumen covers the aqueous layer and the angular sand grain. The bitumen-and water-covered grains of quartz sand stick to one another. When untreated, the highly abrasive oil sands would damage pipelines, trucks, and all the equipment used in mining and operations. As well, the viscosity of bitumen changes with heat and cold. It is like molasses when warm, and will freeze when cold. Bitumen as a hydrocarbon, is considered to be a valuable energy resource. The more bitumen in an oil sands deposit, the more valuable it is. If a deposit contains less than 6% of bitumen it is not worth mining. The oil sands deposit has to have at least 18% of bitumen has to be economically viable. Bitumen production in 2004 included six inter-related and integrated processes or units—mining, utilities, extraction, froth treatment, water management, oil sands tailings ponds, and upgrading, according to a 2004 article in the "Canadian Journal of Chemical Engineering" (CJCE). The frothing treatment is part of an integrated process. Due to its high viscosity, heavy oil is much more challenging to produce and transport. Viscosity—the "internal resistance to the flow of fluid", is a physical property of crude oil—and an important parameter in the development and design of ultimate oil recovery and effective fluid flow pipelines | https://en.wikipedia.org/wiki?curid=39242726 |
Froth treatment (Athabasca oil sands) Viscosity is one of the pressure–volume–temperature (PVT) properties that is estimated during the different stages of oil exploration, production, recovery, and transportation. In bitumen, asphaltenes, which are often defined as the fraction which cannot be dissolved in n-heptane, impact negatively in oils sands operations—they "impart high viscosity to crude oils" and can cause a "myriad of production problems." Asphaltenes are molecular substances found in crude oil along with saturates—saturated hydrocarbons such as alkanes, aromatic hydrocarbons, and resins, known as (SARA). The first stage of the extraction process, used by oil sands operators in commercial operations, is a modified Clark hot water extraction (CHWE) process which was developed by Karl Adolf Clark's (1888–1966) in the 1920s. According to a 2017 "Oil Sands Magazine" article, after bitumen froth has been separated using the first stage of the bitumen recovery process—water-based gravity separation—the solution contains on average "60% bitumen, 30% water and 10% fine solids." The gravity separation vessel—the Primary Separation Cell (PSC), Primary Separation Vessel (PSV) or the SepCell—recovers 90% of the bitumen. During this process bitumen froth is produced. The froth is highly aerated—full of air bubble—and requires deaeration before it can be pumped to a Froth Storage Tank. The second stage is the froth treatment | https://en.wikipedia.org/wiki?curid=39242726 |
Froth treatment (Athabasca oil sands) The quality of bitumen froth prior to the frothing treatment—a solvent-based gravity separation treatment—is "too low to be processed by an upgrader or refinery." The water-based gravity separation alone cannot remove the remaining contaminants, which are 10 to 15% solids and up to 40% water. Froth treatments use a light hydrocarbon to lower the viscosity of the bitumen, releasing the fine particles and water, resulting in a cleaner diluted bitumen stream. The micrometer-sized inorganic mineral contaminants in the bitumen froth, after the first stage of processing, consist of fine silt and clay and the "water-in-oil emulsion droplets." These droplets, formed during the water-based bitumen extraction process, are the most challenging to remove. These emulsified water droplets are further stabilized by the micro-sized particles of quartz sand. Water-in-oil emulsions are "easy to destabilize" when fine mineral particles are removed. During an effective froth treatment removal process, the fine—micro sized—mineral particles form larger aggregates which facilitates the destabilization of the emulsified water droplets. During the integrated froth treatment, a light hydrocarbon—either a naphthenic or paraffinic solvent—is added to the froth to reduce the bitumen's viscosity and to remove the fine inorganic particles with a more "effective gravity separation". A 2013, American Chemical Society (ACS) described bitumen froth treatment as an "integrated process step in the Athabasca oil sands bitumen recovery operations | https://en.wikipedia.org/wiki?curid=39242726 |
Froth treatment (Athabasca oil sands) Its objective is to separate mineral solids and water from the bitumen froth. The bitumen froth is diluted with naphthenic or paraffinic solvents to lower its viscosity to facilitate the separation. Bitumen froth treatment is the "removal of inorganics (mineral particles and water droplets) from a bitumen organic solvent solution." The solvent to bitumen ratio (S/B) changes the dynamics of the water-in-diluted bitumen—dilbit—emulsions. By 2006, there were two commercialized froth treatment processes in the province of Alberta. At that time, they were called the "Syncrude Process," which involved "dilution with an aromatic solvent followed by centrifugation" and the "Albian Process," which involved "dilution with a paraffinic solvent followed by gravity settling." Following the frothing process, the bitumen may require more upgrading before it can be transported through pipelines. Processors that use the newer technology of Paraffinic Solvent Froth Treatment (PSFT), which has been in commercial use since 2002, no longer require this stage of upgrading, which represents a significant reduction in the cost of processing. The original—and more conventional—naphthenic froth treatment (NFT), does require an ungrader. In order to produce a marketable synthetic crude oil from oil sands bitumen, the heavy oil can only be processed at special refineries that include a complex heavy oil upgrader with a coker unit | https://en.wikipedia.org/wiki?curid=39242726 |
Froth treatment (Athabasca oil sands) In Canada, the Regina, Saskatchewan-Co-op Refinery Complex—formerly the Consumers Co-operative Refinery Limited (CCRL)—has a heavy oil upgrader section of the plant with the necessary Coker unit capable of processing the oil sands product, such as Lloydminster heavy oil, which is a component in the Western Canadian Select (WCS). The original and conventional froth treatment uses a solvent naphtha with the addition of chemicals to destabilize the emulsion. For thirty years, from the 1970s to the early 2000s, the only technology available in the oils sands industry for bitumen recovery, was Naphthenic Froth Treatment (NFT). In an article published in 2002 in the journal, "Chemosphere", which has been cited over 100 times, the authors said that naphthenic acids are present in Athabasca oil sands (AOL) tailings pond water (TPW) at an estimated concentration of 81 mg/l., which is too low a level for TPW to be considered a viable source for commercial recovery. They studied a solvent-based laboratory bench procedure developed to "efficiently extract naphthenic acids from bulk volumes of Athabasca oil sands tailings pond water (TPW)." The same authors had published the oft-cited 2001 article in the Society of Toxicology's "Toxicological Sciences", in which they stated that "naphthenic acids are the most significant environmental contaminants resulting from petroleum extraction from oil sands deposits | https://en.wikipedia.org/wiki?curid=39242726 |
Froth treatment (Athabasca oil sands) " They found that "under worst-case exposure conditions, acute toxicity is unlikely in wild mammals exposed to naphthenic acids" in [Athabasca oil sands] (AOS) tailings pond water, "but repeated exposure may have adverse health effects." In 1990, the Paraffinic Solvent Froth Treatment (PSFT) was developed with research contributed by CanmetENERGY. Syncrude patented the process in 1994 and "made the use rights available to all members of an oil sands Froth Treatment consortium, allowing the process to be implemented at other oil sands operations." PFT reduces the "viscosity of the bitumen, enabling water and solids removal by gravity separation". It also precipitates asphaltenes, which bind with water and solids" resulting in a cleaner bitumen that is "virtually free of impurities." This creates a cleaner bitumen with lower levels of aqueous and mineral contaminants. In 2011 SNC Lavalin entered into a C$650-million contract to build a PSFT plant in the Athabaska oil sands region in 2012, the first in the Canadian oil sands industry. The first commercialization of the Paraffinic Froth Treatment (PFT) was undertaken by the Athabasca Oil Sands Project (AOSP), in the Regional Municipality of Wood Buffalo in the early 2000s. AOSP, also known as Albian Sands—is a joint venture between Canadian Natural Resources (CNRL) (70%), Chevron Canada (20%), and Shell Canada (10%) AOSP consists of the Muskeg River Mine, Jack Pine Mine and the Scotford Upgrader. CNRL purchased Shell's shares in 2017 | https://en.wikipedia.org/wiki?curid=39242726 |
Froth treatment (Athabasca oil sands) PSFT technology is also in use at Imperial Oil's Kearl Oil Sands, and Teck Resources's Fort Hills open-pit oil sands mining operation. Teck plans on using it at its proposed massive Frontier open-pit oil sands mining operation. PSFT technology, which eliminates the use of an upgrader, has a "lower GHG intensity than about half of the oil currently refined in the U.S.", according to Teck. By 2011, projected costs for Imperial Oil's Kearl "mega-mine" had increased to "C$10.9 billion from initial estimates of C$8 billion." Imperial cut costs by using the frothing technique " instead of building an upgrader to process raw bitumen." There are a number of research projects on improving and evaluating innovations in froth treatment. The industry-funded and provincial government mandated, Alberta Energy Regulator (AER) regulates bitumen mining in the province. The AER's "Directive 082: Operating Criteria - Resource Recovery Requirements for Oil Sands Mine and Processing Plants" sets minimum recovery rates for all oil sands operations in the province. Oils sands deposits have varying ore grades with some having higher bitumen content than others. | https://en.wikipedia.org/wiki?curid=39242726 |
Büchner–Curtius–Schlotterbeck reaction The Buchner–Curtius–Schlotterbeck reaction is the reaction of aldehydes or ketones with aliphatic diazoalkanes to form homologated ketones. It was first described by Eduard Buchner and Theodor Curtius in 1885 and later by Fritz Schlotterbeck in 1907. Two German chemists also preceded Schlotterbeck in discovery of the reaction, Hans von Pechmann in 1895 and Viktor Meyer in 1905. The reaction has since been extended to the synthesis of β-keto esters from the condensation between aldehydes and diazo esters. The general reaction scheme is as follows: The reaction yields two possible carbonyl compounds (I and II) along with an epoxide (III). The ratio of the products is determined by the reactant used and the reaction conditions. The general mechanism is shown below. The resonating arrow (1) shows a resonance contributor of the diazo compound with a lone pair of electrons on the carbon adjacent to the nitrogen. The diazo compound then does a nucleophilic attack on the carbonyl-containing compound (nucleophilic addition), producing a tetrahedral intermediate (2). This intermediate decomposes by the evolution of nitrogen gas forming the tertiary carbocation intermediate (3). The reaction is then completed either by the reformation of the carbonyl through an 1,2-rearrangement or by the formation of the epoxide. There are two possible carbonyl products: one formed by migration of R (4) and the other by migration of R (5) | https://en.wikipedia.org/wiki?curid=39242968 |
Büchner–Curtius–Schlotterbeck reaction The relative yield of each possible carbonyl is determined by the migratory preferences of the R-groups. The epoxide product is formed by an intramolecular addition reaction in which a lone pair from the oxygen attacks the carbocation (6). This reaction is exothermic due to the stability of nitrogen gas and the carbonyl containing compounds. This specific mechanism is supported by several observations. First, kinetic studies of reactions between diazomethane and various ketones have shown that the overall reaction follows second order kinetics. Additionally, the reactivity of two series of ketones are in the orders ClCCOCH > CHCOCH > CHCOCH and cyclohexanone > cyclopentanone > cycloheptanone > cyclooctanone. These orders of reactivity are the same as those observed for reactions that are well established as proceeding through nucleophilic attack on a carbonyl group. The reaction was originally carried out in diethyl ether and routinely generated high yields due to the inherent irreversibly of the reaction caused by the formation of nitrogen gas. Though these reactions can be carried out at room temperature, the rate does increase at higher temperatures. Typically, the reaction is carried out at less than refluxing temperatures. The optimal reaction temperature is determined by the specific diazoalkane used. Reactions involving diazomethanes with alkyl or aryl substituents are exothermic at or below room temperature. Reactions involving diazomethanes with acyl or aroyl substituents require higher temperatures | https://en.wikipedia.org/wiki?curid=39242968 |
Büchner–Curtius–Schlotterbeck reaction The reaction has since been modified to proceed in the presence of Lewis acids and common organic solvents such as THF and dichloromethane. Reactions generally run at room temperature for about an hour, and the yield ranges from 70%-80% based on the choice of Lewis acid and solvent. Steric effects of the alkyl substituents on the carbonyl reactant have been shown to affect both the rates and yields of Büchner–Curtius–Schlotterbeck reaction. Table 1 shows the percent yield of the ketone and epoxide products as well as the relative rates of reaction for the reactions between several methyl alkyl ketones and diazomethane. The observed decrease in rate and increase in epoxide yield as the size of the alkyl group becomes larger indicates a steric effect. Ketones and aldehydes with electron-withdrawing substituents react more readily with diazoalkanes than those bearing electron-donating substituents (Table 2). In addition to accelerating the reaction, electron-withdrawing substituents typically increase the amount of epoxide produced (Table 2). The effects of substituents on the diazoalkanes is reversed relative to the carbonyl reactants: electron-withdrawing substituents decrease the rate of reaction while electron-donating substituents accelerate it. For example, diazomethane is significantly more reactive than ethyl diazoacetate, though less reactive than its higher alkyl homologs (e.g. diazoethane). Reaction conditions may also affect the yields of carbonyl product and epoxide product | https://en.wikipedia.org/wiki?curid=39242968 |
Büchner–Curtius–Schlotterbeck reaction In the reactions of "o"-nitrobenzaldehyde, "p"-nitrobenzaldehyde, and phenylacetaldehyde with diazomethane, the ratio of epoxide to carbonyl is increased by the inclusion of methanol in the reaction mixture. The opposite influence has also been observed in the reaction of piperonal with diazomethane, which exhibits increased carbonyl yield in the presence of methanol. The ratio of the two possible carbonyl products (I and II) obtained is determined by the relative migratory abilities of the carbonyl substituents (R and R). In general, the R-group most capable of stabilizing the partial positive charge formed during the rearrangement migrates preferentially. A prominent exception to this general rule is hydride shifting. The migratory preferences of the carbonyl R-groups can be heavily influenced by solvent and diazoalkane choice. For example, methanol has been shown to promote aryl migration. As shown below, if the reaction of piperanol (IV) with diazomethane is carried out in the absence of methanol, the ketone obtained though a hydride shift is the major product (V). If methanol is the solvent, an aryl shift occurs to form the aldehyde (VI), which cannot be isolated as it continues to react to form the ketone (VII) and the epoxide (VIII) products. The diazoalkane employed can also determine relative yields of products by influencing migratory preferences, as conveyed by the reactions of "o"-nitropiperonal with diazomethane and diazoethane | https://en.wikipedia.org/wiki?curid=39242968 |
Büchner–Curtius–Schlotterbeck reaction In the reaction between "o"-nitropiperonal (IX) and diazomethane, an aryl shift leads to production of the epoxide (X) in 9 to 1 excess of the ketone product (XI). When diazoethane is substituted for diazomethane, a hydride shift produces the ketone (XII), the only isolable product. The can be used to facilitate one carbon ring expansions when the substrate ketone is cyclic. For instance, the reaction of cyclopentanone with diazomethane forms cyclohexanone (shown below). The Büchner ring expansion reactions utilizing diazoalkanes have proven to be synthetically useful as they can not only be used to form 5- and 6-membered rings, but also more unstable 7- and 8-membered rings. An acyl-diazomethane can react with an aldehyde to form a β-diketone in the presence of a transition metal catalyst (SnCl in the example shown below). β-Diketones are common biological products, and as such, their synthesis is relevant to biochemical research. Furthermore, the acidic β-hydrogens of β-diketones are useful for broader synthetic purposes, as they can be removed by common bases. Acyl-diazomethane can also add to esters to form β-keto esters, which are important for fatty acid synthesis. As mentioned above, the acidic β-hydrogens also have productive functionality. The can also be used to insert a methylene bridge between a carbonyl carbon and a halogen of an acyl halide. This reaction allows conservation of the carbonyl and halide functionalities | https://en.wikipedia.org/wiki?curid=39242968 |
Büchner–Curtius–Schlotterbeck reaction It is possible to isolate nitrogen-containing compounds using the Büchner–Curtius–Schlotterbeck reaction. For example, an acyl-diazomethane can react with an aldehyde in the presence of a DBU catalyst to form isolable α-diazo-β-hydroxy esters (shown below). | https://en.wikipedia.org/wiki?curid=39242968 |
Hydrodefluorination (HDF) is a type of organic reaction in which in a substrate a carbon–fluorine bond is replaced by a carbon–hydrogen bond. 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 (CF) to pentafluorobenzene (CFH) 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 followed by a reductive elimination step in presence of a hydrogen source. For example, perfluoronated 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, and NiCl(PCy) / (LiAl(O-t-Bu)H) | https://en.wikipedia.org/wiki?curid=39244732 |
Klyne–Prelog system In stereochemistry, the (named for William Klyne and Vladimir Prelog) for describing conformations about a single bond offers a more systematic means to unambiguously name complex structures, where the torsional or dihedral angles are not found to occur in 60° increments. Klyne notation views the placement of the substituent on the front atom as being in regions of space called anti/syn and clinal/periplanar relative to a reference group on the rear atom. A plus (+) or minus (–) sign is placed at the front to indicate the sign of the dihedral angle. Anti or syn indicates the substituents are on opposite sides or the same side, respectively. Clinal substituents are found within 30° of either side of a dihedral angle of 60° (from 30° to 90°), 120° (90°–150°), 240° (210°–270°), or 300° (270°–330°). Periplanar substituents are found within 30° of either 0° (330°–30°) or 180° (150°–210°). Juxtaposing the designations produces the following terms for the conformers of butane ("see Alkane stereochemistry for an explanation of conformation nomenclature"): gauche butane is "syn-clinal" ("+sc" or "–sc", depending on the enantiomer), anti butane is "anti-periplanar", and eclipsed butane is "syn-periplanar". | https://en.wikipedia.org/wiki?curid=39253041 |
Oil mist refers to oil droplets suspended in the air in the size range 1~10 μm. may form when high pressure fuel oil, lubricating oil, hydraulic oil, or other oil is sprayed through a narrow crack, or when leaked oil connects with a high temperature surface, vaporizes, and comes in contact with low air temperature. This happens while the fluids interact with the moving parts during machining. Smaller oil droplets than oil mist are difficult to generate under normal circumstances. Bigger oil droplets than oil mist remain in spray form; this has the advantage of a higher ignition temperature. It sinks easily, reducing fire hazard. inside the crankcase can cause a bigger problem. When the concentration of oil mist increases and reaches the lowest explosion level (LEL; 50 mg/ℓ, as defined by the IACS), explosion may occur when the mist contacts surfaces of over or a spark. The International Association of Classification Societies (IACS) mandates that all ships with a cylinder diameter greater than 300mm or engine power over 2,250 kW must be equipped with either bearing temperature detectors or oil mist detectors. In regards to occupational exposures, the Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health have set occupational exposure limits at 5 ppm over an eight-hour time-weighted average, with a short-term exposure limit at 10 ppm | https://en.wikipedia.org/wiki?curid=39259290 |
Oil mist 1 International Maritime Organization (IMO) 2 International Association of Classification Societies Ltd unified requirements concerning MACHINERY INSTALLATIONS 3 Oil Companies International Marine Forum Ship Inspection Report (SIRE) Programme/ Vessel Inspection Questionnaires for Oil Tankers, Combination Carriers, Shuttle Tankers, Chemical Tankers and Gas Carriers | https://en.wikipedia.org/wiki?curid=39259290 |
Spectral line shape describes the form of a feature, observed in spectroscopy, corresponding to an energy change in an atom, molecule or ion. Ideal line shapes include Lorentzian, Gaussian and Voigt functions, whose parameters are the line position, maximum height and half-width. Actual line shapes are determined principally by Doppler, collision and proximity broadening. For each system the half-width of the shape function varies with temperature, pressure (or concentration) and phase. A knowledge of shape function is needed for spectroscopic curve fitting and deconvolution. An atomic transition is associated with a specific amount of energy, "E". However, when this energy is measured by means of some spectroscopic technique, the line is not infinitely sharp, but has a particular shape. Numerous factors can contribute to the broadening of spectral lines. Broadening can only be mitigated by the use of specialized techniques, such as Lamb dip spectroscopy. The principal sources of broadening are: Observed spectral line shape and line width are also affected by instrumental factors. The observed line shape is a convolution of the intrinsic line shape with the instrument transfer function. Each of these mechanisms, and others, can act in isolation or in combination. If each effect is independent of the other, the observed line profile is a convolution of the line profiles of each mechanism. Thus, a combination of Doppler and pressure broadening effects yields a Voigt profile | https://en.wikipedia.org/wiki?curid=39260084 |
Spectral line shape A Lorentzian line shape function can be represented as where "L" signifies a Lorentzian function standardized, for spectroscopic purposes, to a maximum value of 1; "formula_3" is a subsidiary variable defined as where formula_5 is the position of the maximum (corresponding to the transition energy "E"), "p" is a position, and "w" is the full width at half maximum (FWHM), the width of the curve when the intensity is half the maximum intensity (this occurs at the points formula_6). The unit of formula_5, formula_8 and formula_9 is typically wavenumber or frequency. The variable "x" is dimensionless and is zero at formula_10. The Gaussian line shape has the standardized form, The subsidiary variable, "x", is defined in the same way as for a Lorentzian shape. Both this function and the Lorentzian have a maximum value of 1 at "x" = 0 and a value of 1/2 at "x"=±1. The third line shape that has a theoretical basis is the Voigt function, a convolution of a Gaussian and a Lorentzian, where σ and γ are half-widths. The computation of a Voigt function and its derivatives are more complicated than a Gaussian or Lorentzian. A spectroscopic peak may be fitted to multiples of the above functions or to sums or products of functions with variable parameters. The above functions are all symmetrical about the position of their maximum. Asymmetric functions have also been used. For atoms in the gas phase the principal effects are Doppler and pressure broadening | https://en.wikipedia.org/wiki?curid=39260084 |
Spectral line shape Lines are relatively sharp on the scale of measurement so that applications such as atomic absorption spectroscopy (AAS) and Inductively coupled plasma atomic emission spectroscopy (ICP) are used for elemental analysis. Atoms also have distinct x-ray spectra that are attributable to the excitation of inner shell electrons to excited states. The lines are relatively sharp because the inner electron energies are not very sensitive to the atom's environment. This is applied to X-ray fluorescence spectroscopy of solid materials. For molecules in the gas phase, the principal effects are Doppler and pressure broadening. This applies to rotational spectroscopy, rotational-vibrational spectroscopy and vibronic spectroscopy. For molecules in the liquid state or in solution, collision and proximity broadening predominate and lines are much broader than lines from the same molecule in the gas phase. Line maxima may also be shifted. Because there are many sources of broadening, the lines have a stable distribution, tending towards a Gaussian shape. The shape of lines in a nuclear magnetic resonance (NMR) spectrum is determined by the process of free induction decay. This decay is approximately exponential, so the line shape is Lorentzian. This follows because the Fourier transform of an exponential function in the time domain is a Lorentzian in the frequency domain. In NMR spectroscopy the lifetime of the excited states is relatively long, so the lines are very sharp, producing high-resolution spectra | https://en.wikipedia.org/wiki?curid=39260084 |
Spectral line shape alter the relaxation time, and hence spectral line shape, of those protons that are in water molecules that are transiently attached to the paramagnetic atoms, resulting contrast enhancement of the MRI image. This allows better visualisation of some brain tumours. Some spectroscopic curves can be approximated by the sum of a set of component curves. For example, when Beer's law applies, the measured intensity, "I", at wavelength λ, is a linear combination of the intensity due to the individual components, "k", at concentration, "c". ε is an extinction coefficient. In such cases the curve of experimental data may be decomposed into sum of component curves in a process of curve fitting. This process is also widely called deconvolution. Curve deconvolution and curve fitting are a completely different mathematical procedures. Curve fitting can be used in two distinct ways. Spectroscopic curves can be subjected to numerical differentiation. When the data points in a curve are equidistant from each other the Savitzky–Golay convolution method may be used. The best convolution function to use depends primarily on the signal-to-noise-ratio of the data. The first derivative (slope, formula_19) of all single line shapes is zero at the position of maximum height. This is also true of the third derivative; odd derivatives can be used to locate the position of a peak maximum. The second derivatives, formula_20, of both Gaussian and Lorentzian functions have a reduced half-width | https://en.wikipedia.org/wiki?curid=39260084 |
Spectral line shape This can be used to apparently improve spectral resolution. The diagram shows the second derivative of the black curve in the diagram above it. Whereas the smaller component produces a shoulder in the spectrum, it appears as a separate peak in the 2nd. derivative. Fourth derivatives, formula_21, can also be used, when the signal-to-noise-ratio in the spectrum is sufficiently high. Deconvolution can be used to apparently improve spectral resolution. In the case of NMR spectra, the process is relatively straight forward, because the line shapes are Lorentzian, and the convolution of a Lorentzian with another Lorentzian is also Lorentzian. The Fourier transform of a Lorentzian is an exponential. In the co-domain (time) of the spectroscopic domain (frequency) convolution becomes multiplication. Therefore, a convolution of the sum of two Lorentzians becomes a multiplication of two exponentials in the co-domain. Since, in FT-NMR, the measurements are made in the time domain division of the data by an exponential is equivalent to deconvolution in the frequency domain. A suitable choice of exponential results in a reduction of the half-width of a line in the frequency domain. This technique has been rendered all but obsolete by advances in NMR technology. A similar process has been applied for resolution enhancement of other types of spectra, with the disadvantage that the spectrum must be first Fourier transformed and then transformed back after the deconvoluting function has been applied in the spectrum's co-domain. | https://en.wikipedia.org/wiki?curid=39260084 |
C22H25NO2 The molecular formula CHNO may refer to: | https://en.wikipedia.org/wiki?curid=39261491 |
Liver support system A liver support system is a therapeutic device to assist in performing the functions of the liver in persons with liver damage. The primary functions of the liver include removing toxic substances from the blood, manufacturing blood proteins, storing energy in the form of glycogen, and secreting bile. The hepatocytes that perform these tasks can be killed or impaired by disease, resulting in hepatic insufficiency. A sudden onset of life-threatening hepatic insufficiency is known as acute liver failure (ALF). In hyperacute and acute liver failure the clinical picture develops rapidly with progressive encephalopathy and multiorgan dysfunction such as hyperdynamic circulation, coagulopathy, acute kidney injury and respiratory insufficiency, severe metabolic alterations and cerebral edema that can lead to brain death. In these cases the mortality without liver transplantation (LTx) ranges between 40-80%. LTx is the only effective treatment for these patients although it requires a precise indication and timing to achieve good results. Nevertheless, due to the scarcity of organs to carry out liver transplantations, it is estimated that one third of patients with ALF die while waiting to be transplanted. On the other hand, a patient with a chronic hepatic disease can suffer an acute decompensation of liver function following a precipitating event such as variceal bleeding, sepsis and excessive alcohol intake among others that can lead to a condition referred to as acute-on-chronic liver failure (ACLF) | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Both types of hepatic insufficiency, ALF and ACLF, can potentially be reversible and liver functionality can return to a level similar to that prior to the insult or precipitating event. LTx is the only treatment that has shown an improvement in the prognosis and survival with most severe cases of ALF. Nevertheless, cost and donor scarcity have prompted researchers to look for new supportive treatments that can act as “bridge” to the transplant procedure. By stabilizing the patient's clinical state, or by creating the right conditions that could allow the recovery of native liver functions, both detoxification and synthesis can improve, after an episode of ALF or ACLF. Basically, three different types of supportive therapies have been developed: bio-artificial, artificial and hybrid liver support systems (Table 2). Bio-artificial liver support systems are experimental extracorporeal devices that use living cell lines to provide detoxification and synthesis support to the failing liver. Bio-artificial liver (BAL) Hepatassist 2000 uses porcine hepatocytes whereas ELAD system employs hepatocytes derived from human hepatoblastoma C3A cell lines. Both techniques can produce, in fulminant hepatic failure (FHF), an improvement of hepatic encephalopathy grade and biochemical parameters | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Nevertheless, they are therapies with high complexity that require a complex logistic approach for implementation; a very high cost and possible inducement of important side effects such as immunological issues (porcine endogenous retrovirus transmission), infectious complications and tumor transmigration have been documented. Other biological hepatic systems are Bioartificial Liver Support (BLSS) and Radial Flow Bioreactor (RFB). Detoxification capacity of these systems is poor and therefore they must be used combined with other systems to mitigate this deficiency. Today its use is limited to centers with high experience in their application. Artificial liver support systems are aimed to temporally replace native liver detoxification functions and they use albumin as scavenger molecule to clear the toxins involved in the physiopathology of the failing liver. Most of the toxins that accumulate in the plasma of patients with liver insufficiency are protein bound, and therefore conventional renal dialysis techniques, such as hemofiltration, hemodialysis or hemodiafiltration are not able to adequately eliminate them. Between the different albumin dialysis modalities, single pass albumin dialysis (SPAD) has shown some positive results at a very high cost; it has been proposed that lowering the concentration of albumin in the dialysate does not seem to affect the detoxification capability of the procedure. Nevertheless, the most widely used systems today are based on hemodialysis and adsorption | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system These systems use conventional dialysis methods with an albumin containing dialysate that is later regenerated by means of adsorption columns, filled with activated charcoal and ion exchange resins. At present, there are two artificial extracorporeal liver support systems: the Molecular Adsorbents Recirculating System (MARS) from Gambro and Fractionated Plasma Separation and Adsorption (FPSA), commercialised as Prometheus (PROM) from Fresenius Medical Care. Of the two therapies, MARS is the most frequently studied, and clinically used system to date. MARS was developed by a group of researchers at the University of Rostock (Germany), in 1993 and later commercialized for its clinical use in 1999. The system is able to replace the detoxification function of the liver while minimizing the inconvenience and drawbacks of previously used devices. "In vivo" preliminary investigations indicated the ability of the system to effectively remove bilirubin, biliary salts, free fatty acids and tryptophan while important physiological proteins such as albumin, alpha-1-glicoproteine, alpha 1 antitrypsin, alpha-2-macroglobulin, transferrin, globulin tyrosine, and hormonal systems are unaffected. Also, MARS therapy in conjunction with CRRT/HDF can help clear cytokines acting as inflammatory and immunological mediators in hepatocellular damage, and therefore can create the right environment to favour hepatocellular regeneration and recovery of native liver function | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system MARS is an extracorporeal hemodialysis system composed of three different circuits: blood, albumin and low-flux dialysis. The blood circuit uses a double lumen catheter and a conventional hemodialysis device to pump the patient's blood into the MARS FLUX, a biocompatible polysulfone high-flux dialyser. With a membrane surface area of 2.1 m, 100 nm of thickness and a cut-off of 50 KDa, the MARSFLUX is essential to retaining the albumin in the dialysate. Blood is dialysed against a human serum albumin (HSA) dialysate solution that allows blood detoxification of both water-soluble and protein-bound toxins, by means of the presence of albumin in the dialysate (albumin dialysis). The albumin dialysate is then regenerated in a close loop in the MARS circuit by passing through the fibres of the low-flux diaFLUX filter, to clear water-soluble toxins and provide electrolyte/acid-base balance, by a standard dialysis fluid. Next, the albumin dialysate passes through two different adsorption columns; protein-bound substances are removed by the diaMARS AC250, containing activated charcoal and anionic substances are removed by the diaMARS IE250, filled with cholestyramine, an anion-exchange resin. The albumin solution is then ready to initiate another detoxifying cycle of the patient's blood that can be sustained until both adsorption columns are saturated, eliminating the need to continuously infuse albumin into the system during treatment (Fig. 1) | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system A systematic review of the literature from 1999 to June 2011 was performed in the following databases: The LiverNet is a database dedicated to the liver diseases treated with the support of extracorporeal therapies. To date, the most currently used system is the Molecular Adsorbent Recirculating System (MARS), which is based on the selective removal of albumin bound molecules and toxins from the blood in patients with acute and acute-on-chronic liver failure. The purpose is to register prospectively all patients treated worldwide with the MARS system in order to: The liverNet is an eCRF database (www.livernet.net) using a SAS platform that allows major advantages for the centres including the automatic calculations of most liver rand ICU scoring systems, instant queries online, instant export of all patients included in the database of each centre to an Excel file for direct statistical analysis and finally instant online statistical analysis of selective data decided by the scientific committee. Therefore, the LiverNet is an important tool to progress in the knowledge of liver support therapies. Hepatic encephalopathy (HE) represents one of the more serious extrahepatic complications associated with liver dysfunction. Neuro-psychiatric manifestations of HE affect consciousness and behaviour | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Evidence suggests that HE develops as some neurotoxins and neuro active substances, produced after hepatocellular breakdown, accumulates in the brain as a consequence of a portosystemic shunt and the limited detoxification capability of the liver. Substances involved are ammonia, manganese, aromatic aminoacids, mercaptans, phenols, medium chain fatty acids, bilirubin, endogenous benzodiazepines, etc. The relationship between ammonia neurotoxicity and HE was first described in animal studies by Pavlov et al. Subsequently, several studies in either animals or humans have confirmed that, a ratio in ammonia concentration higher than 2 mM between the brain and blood stream, causes HE, and even a comatose state when the value is greater than 5 mM. Some investigators have also reported a decrease in serum ammonia following a MARS treatment (Table 3). Manganese and copper serum levels are increased in patients with either acute or acute on chronic liver failure. Nevertheless, only in those patients with chronic hepatic dysfunction, a bilateral magnetic resonance alteration on Globos Pallidus is observed, probably because this type of patients selectively shows higher cerebral membrane permeability. Imbalance between aromatic and branched chain aminoacids (Fischer index), traditionally involved in HE genesis, can be normalized following a MARS treatment. The effects are noticeable even after 3 hours of treatment and this reduction in the Fisher index is accompanied with an improvement in the HE. Novelli G "et al | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system " published their three years experience on MARS analyzing the impact of the treatment in the cerebral level for 63 patients reporting an improvement in Glasgow Coma Score (GCS) for all observed in all patients. In the last 22 patients, cerebral perfusion pressure was monitored by Doppler (mean flow velocity in middle cerebral artery), establishing a clear relationship between a clinical improvement (especially neurological) and an improvement in arterial cerebral perfusion. This study confirms other results showing similar increments in cerebral perfusion in patients treated with MARS. More recently, several studies have shown a significant improvement of HE in patients treated with MARS. In the studies by Heemann "et al." and Sen "et al." an improvement in HE was considered when encephalopathy grade was reduced by one or more grades vs. basal values; for Hassenein et al., in their randomized controlled trial, improvement was considered when a decrease of two grades was observed. In the latter, 70 patients with acute on chronic liver failure and encephalopathy grade III and IV were included. Likewise, Kramer et al. estimated an HE improvement when an improvement in peak N70 latency in electroencephalograms was observed. Sen "et al."44 observed a significant reduction in Child-Pugh Score (p<0,01) at 7 days following a MARS treatment, without any significant change in the controls | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Nevertheless, when they looked at the Model for End-Stage Liver Disease Score (MELD), a significant reduction in both groups, MARS and controls, was recorded (p<0,01 y p<0,05, respectively). Likewise, in several case series, an improvement in HE grade with MARS therapy is also reported. Hemodynamic instability is often associated with acute liver insufficiency, as a consequence of endogenous accumulation of vasoactive agents in the blood. This is characterized by a systemic vasodilatation, a decrease of systemic vascular resistance, arterial hypotension, and an increase of cardiac output that gives rise to a hyperdynamic circulation. During MARS therapy, systemic vascular resistance index and mean arterial pressure have been shown to increase and show improvement. Schmidt et al. reported the treatment of 8 patients, diagnosed with acute hepatic failure, that were treated with MARS for 6 hours, and were compared with a control group of 5 patients to whom ice pads were applied to match the heat loss produced in the treatment group during the extracorporeal therapy. They analyzed hemodynamic parameters in both groups hourly. In the MARS group, a statistically significant increase of 46% on systemic vascular resistance was observed (1215 ± 437 to 1778 ± 710 dinas x s x cm x m) compared with a 6% increase in the controls. Mean arterial pressure also increased (69 ± 5 to 83 ± 11 mmHg, p< 0.0001) in the MARS group, whereas no difference was observed in the controls | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Cardiac output and heart rate also decreased in the MARS group as a consequence of an improvement in the hyperdynamic circulation. Therefore, it was shown that a statistically significant improvement was obtained with MARS when compared with the SMT. Catalina et al. have also evaluated systemic and hepatic hemodynamic changes produced by MARS therapy. In 4 patients with acute decompensation of chronic liver disease, they observed after MARS therapy, an attenuation of hyperdynamic circulation and a reduction in the portal pressure gradient was measured. Results are summarized in table 4. There are other studies also worth mentioning with similar results: Heemann "et al". and Parés "et al". among others. Dethloff T "et al". concluded that there is a statistically significant improvement favourable to MARS in comparison with Prometheus system (Table 5). Hepatorenal syndrome is one of the more serious complications in patients with an acute decompensation of cirrhosis and increased portal hypertension. It is characterized by hemodynamic changes in splanchnic, systemic and renal circulation. Splanchnic vasodilatation triggers the production of endogenous vasoactive substances that produce renal vasoconstriction and low glomerular filtration rate, leading to oliguria with a concomitant reduction in creatinine clearance. Renal insufficiency is always progressive with a very poor prognosis, with survival at 1 and 2 months of 20 and 10% respectively | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Pierre Versin is one of the pioneers in the study of hepatorenal syndrome in patients with liver impairment. Great efforts have been made trying to improve the prognosis of this type of patient; however, few have solved the problem. Orthotopic liver transplantation is the only treatment that has shown to improve acute and chronic complications derived from severe liver insufficiency. Today it is possible to combine albumin dialysis with continuous veno-venous hemodialfiltration, which provides a greater expectation for these patients by optimization of their clinical status. MARS treatment lowers serum urea and creatinine levels improving their clearance, and even favors resolution of hepatorenal syndrome. Results are confirmed in a randomized controlled trial published by Mitzner "et al". in which 13 patients diagnosed with hepatorenal syndrome type I were treated with MARS therapy. Mean survival was 25,2±34,6 days in the MARS group compared to 4,6±1,8 days observed in the controls in whom hemodiafiltration and standard care (SMT) was applied. This resulted in a statistically significance difference in survival at 7 and 30 days (p<0.05). Authors concluded that MARS therapy, applied to liver failure patients (Child-Pugh C and UNOS 2A scores) who develop hepatorenal syndrome type I, prolonged survival compared to patients treated with SMT | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Although mechanisms explaining previous findings are not yet fully understood, it has been reported that there was a decrease in plasma rennin concentrations in patients diagnosed with acute on chronic liver failure with renal impairment that were treated with MARS. Likewise, other studies have suggested some efficacy for MARS in the treatment of hepatorenal syndrome. However, other references have been published that do not show efficacy in the treatment of these types of patients with MARS therapy. Khuroo "et al". published a metaanalysis based in 4 small RCT's and 2 non RCT's in patients diagnosed with ACLF, concluding that MARS therapy would not bring any significant increment on survival compared with SMT. Another observational study in 6 patients with cirrhosis, refractory ascitis and hepatorenal syndrome type I, not responding to vasoconstrictor therapy, showed no impact on hemodynamics following MARS therapy; however authors concluded that MARS therapy could effectively serve as bridge to liver transplantation. Total bilirubin was the only parameter analyzed in all trials that was always reduced in the groups of patients treated with MARS; Banayosy "et al". measured bilirubin levels 14 days after since MARS therapy was terminated and observed a consistent, significant decrease not only for bilirubin but also for creatinine and urea (Table 6). Impact of MARS therapy on plasma biliary acids levels was evaluated in 3 studies. In the study from Stadbauer "et al" | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system , that was specifically addressing the topic, it is reported that MARS and Prometheus systems lower to the same extent biliary acids plasma concentration. Heemann "et al". and Laleman "et al". have also published a significant improvement for these organic ions. Pruritus is one of the most common clinical manifestations in cholestasis liver diseases and one of the most distressing symptoms in patients with chronic liver disease caused by viral hepatitis C. Many hypothesis have been formulated to explain physio pathogenesis of such manifestation, including incremental plasma concentration of biliary acids, abnormalities in the bile ducts, increased central neurotransmitters coupling opioid receptors, etc... Despite the number of historical drugs used, individually or combined (exchange resins, hidrophilic biliary acids, antihistamines, antibiotics, anticonvulsants, opioid antagonists), there are reported cases of intractable or refractory pruritus with a dramatic reduction in patients’ quality of life (i.e. sleep disorders, depression, suicide attempts...). Intractable pruritus can be an indication for liver transplantation. The MARS indication for intractable pruritus is therapeutically an option that has shown to be beneficial for patients in desperate cases, although at high cost. In several studies, it was confirmed that after MARS treatments, patients remain free from pruritus for a period of time ranging from 6 to 9 months | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Nevertheless, some authors have concluded that besides the good results found in the literature, application of MARS therapy in refractory pruritus requires larger evidence. Pharmacokinetics and pharmacodynamics for a majority of drugs can be significantly be modified with liver failure, affecting the therapeutic approach and potential toxicity of the drugs. In these type of patients, Child-Pugh score represents a poor prognostic factor to assess the metabolic capacity of the failing liver. In patients with hepatic failure, drugs that are only metabolized in the liver, accumulate in the plasma right after they are administered, and therefore it is needed to modify drug dosing in both, concentration and time intervals, to lower the risk of toxicity. It is also necessary to adjust the dosing for those drugs that are exclusively metabolized by the liver, and have low affinity for proteins and high distribution volume, such as fluoroquinolones (Levofloxacin and Ciprofloxacin). Extracorporeal detoxification with albumin dialysis increases the clearance of drugs that are bound to plasmatic proteins (Table 7). In the meta-analysis published by Khuroo "et al". which included 4 randomized trials an improvement in survival for the patients with liver failure treated with MARS, compared with SMT, was not observed. However, neither in the extracorporeal liver support systems review by the Cochrane (published in 2004), nor the meta-analysis by Kjaergard "et al" | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system was a significance difference in survival found for patients diagnosed with ALF treated with extracorporeal liver support systems. Nevertheless, these reviews included all kind of liver support systems and used a heterogeneous type of publication ( abstracts, clinical trials, cohort, etc.). There is literature showing favorable results in survival for patients diagnosed with ALF, and treated with MARS., In a randomized controlled trial, Salibà "et al". studied the impact on survival of MARS therapy for patients with ALF, waiting on the liver transplant list. Forty-nine patients received SMT and 53 were treated with MARS. They observed that patients that received 3 or more MARS sessions showed a statistically significance increase in transplant-free survival compared with the others patients of the study. Notably, 75% of the patients underwent liver transplantation in the first 24 hours after inclusion in the waiting list, and besides the short exposure to MARS therapy, some patients showed a better survival trend compared to controls, when they were treated with MARS prior to the transplant. In a case-controlled study by Montejo "et al". it was reported that MARS treatment do not decrease mortality directly; however, the treatment contributed to significantly improve survival in patients that were transplanted. In studies by Mitzner "et al". and Heemann "et al". they were able to show a significance statistical difference in 30-day survival for patients in the MARS group. However, El Banayosy "et al" | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system and Hassanein "et al". noticed a non significant improvement in survival, probably because of the short number of patients included in the trials. In the majority of available MARS studies published with patients diagnosed with ALF, either transplanted or not, survival was greater in the MARS group with some variations according to the type of trial, ranging from 20-30%, and 60-80%. Data is summarized in Tables 8, 9 and 10. <br> <br> For patients diagnosed with acute on chronic liver failure and treated with MARS therapy, clinical trial results showed a not statistically significant reduction in mortality (odds ratio [OR] =0,78; confident interval [CI] =95%: 0,58 – 1,03; p= 0,1059, Figure 3) <br>A non-statistically significant reduction of mortality was shown in patients with ALF treated with MARS (OR = 0,75 [CI= 95%, 0,42 – 1,35]; p= 0,3427). (Figure 4) <br>Combined results yielded a non-significant reduction on mortality in patients treated with MARS therapy. However, the low number of patients included in each of the studies may be responsible for not being able to achieve enough statistical power to show differences between both treatment groups. Moreover, heterogeneity for the number of MARS sessions and severity of liver disease of the patients included, make it very difficult for the evaluation of MARS impact on survival. Recently, a meta-analysis on survival in patients treated with an extra-hepatic therapy has been published | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Searching strategies yielded 74 clinical trials: 17 randomized controlled trials, 5 case control and 52 cohort studies. Eight studies were included in the meta-analysis: three addressing acute liver failure, one with MARS therapy and five addressing acute on chronic, being four MARS related. Authors concluded that extra-hepatic detoxifying systems improve survival for acute liver insufficiency, whereas results for acute decompensation of chronic liver diseases suggested a non significant survival benefit. Also, due to an increased demand for liver transplantation together with an augmented risk of liver failure following large resections, development of detoxifying extrahepatic systems are necessary. Safety, defined as presence of adverse events, is evaluated in few trials. Adverse events in patients receiving MARS therapy are similar to those in the controls with the exception of thrombocytopenia and hemorrhage that seems to occur more frequently with the MARS system. Heemann et al. reported two adverse events most probably MARS related: fever and sepsis, presumably originated at the catheter. In the study by Hassanein "et al.", two patients in the MARS group abandoned the study owing to hemodynamic instability, three patients required larger than average platelets transfusion and three more patients presented gastrointestinal bleeding. Laleman "et al" | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system detected one patient with thrombocytopenia in both the MARS and Prometheus treatment groups, and an additional patient with clotting of the dialysis circuit and hypotension, only in the Prometheus group. Kramer "et al". (Biologic-DT) wrote about 3 cases with disseminated intravascular coagulation in the interventional group, two of them with fatal outcomes. Mitzner "et al". described, among patients treated with MARS, a thrombocytopenia case and a second patient with chronic hepatitis B, who underwent TIPS placement on day 44 after randomization and died on day 105 of multiorgan failure, as a consequence of complications related to the TIPS procedure. Montejo "et al". showed that MARS is an easy technique, without serious adverse events related to the procedure, and also easy to implement in ICU settings that are used to renal extracorporeal therapies. The MARS International Registry, with data from more than 500 patients (although sponsored by the manufacturer), shows that the adverse effects observed are similar to the control group. However, in these severely ill patients it is difficult to distinguish between complications of the disease itself and side effects attributable to the technique. Only three Studies addressing cost-effectivenenss of MARS therapy have been found. Hassanein et al. analysed costs of randomized patients with ACLF receiving MARS therapy or standard medical care. They used the study published in 2001 by Kim et al | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system describing the impact of complications in hospitalization costs in patients diagnosed with alcoholic liver failure. Cost of 11 patients treated with standard medical care (SMT) were compared to those that received MARS, in addition to SMT (12 patients). In the MARS group, there was less in-hospital mortality and complications related to the disease, with a remarkable reduction in cost which compensated the MARS related expenditure (Table 11). There were 5 survivors in the control group, with a cost per patient of $35.904, whereas in the MARS group, 11 patients out of 12 survived with a cost per patient of $32.036 which represents a $4000 savings per patient in favors of the MARS group. Hessel et al. published a 3-year follow-up of a cohort of 79 patients with ACLF, of whom 33 received MARS treatments and 46 received SMT. Survival was 67% for the MARS group and 63% for the controls, that was reduced to 58 and 35% respectively at one year follow-up, and then 52 and 17% at three years. Hospitalization costs for the MARS treated group were greater than that for the controls (€31.539 vs. €7.543) and similarly direct cost at 3-year follow-up (€8.493 vs. €5.194). Nevertheless, after adjusting mortality rate, the annual cost per patient was €12.092 for controls and €5.827 for MARS group; also in the latter, they found an incremental cost-effectiveness ratio of 31.448 € per life-year gained (LYG) and an incremental costs per QALY gained of 47171 € | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Two years later, same authors published the results of 149 patients diagnosed with ACLF. There were 67 patients (44,9%) treated with MARS and 82 patients (55,1%) were allocated to receive SMT. Mean survival time was 692 days in the MARS group (33% at 3 years) and 453 days in the controls (15% at 3 years); the results were significant (p=0,022). Differences in average cost was €19.853 (95% IC: 13.308-25.429): 35.639 € for MARS patients and 15.804 € for the control group. Incremental cost per LYG was 29.985 € (95% IC: 9.441-321.761) and €43.040 (95% IC: 13.551-461.856) per quality-adjusted life years (QALY). Liver support systems, such as MARS, are very important to stabilize patients with acute or acute on chronic liver failure and avoid organ dysfunction, as well as a bridge-to-transplant. Although initial in-hospital costs are high, they are worth for the favorable outcome. Etiology: Goals of MARS Therapy MARS Therapy Indication Treatment Schedule: Etiology: Goals of MARS Therapy MARS Therapy Indication Treatment Schedule: Etiology: Goals of MARS Therapy MARS Therapy Indication Treatment Schedule: Etiology: Goals of MARS Therapy MARS Therapy Indication Treatment Schedule: Etiology: Goals of MARS Therapy MARS Therapy Indication Treatment Schedule: Same contraindications as with any other extracorporeal treatment may be applied to MARS therapy | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system Blood Flow The trend is to use high flow rates, although it is determined by the technical specifications of the combined machine and catheters’ size Intermittent treatments: Continuous treatments: Dyalisate Flow Rate Intermittent treatments: Continuous treatments: Replacement Flow Rate Heparin Anticoagulation Similarly to CVVHD, it depends of previous patient's coagulation status. In many cases it will not be needed, unless the patient presents a PTT inferior to 160 seconds. In patients with normal values, a bolus of 5000 to 10000 IU of heparin could be administered at the commencement of the treatment, followed by a continuous perfusion, to keep PTT in ratios from 1,5 to 2,5 or 160 to 180 seconds. Monitoring A biochemical analysis is recommended (liver and kidney profile, ionic, glucose) together with a hemogram at the end of first session and before starting the following one. Coagulation analysis must be also performed before starting the session to adjusting heparin dose. In case that medication susceptible to be eliminated by MARS is being administered, it is also recommended to monitor their levels in blood End of the Session and both catheter's lumens heparinized Federal Drug Administration (FDA) cleared, in a document dated on May 27, 2005, MARS therapy for the treatment of drug overdose and poisoning. The only requirement is that the drug or poison must be susceptible to be dialysed and removed by activated charcoal or anionic exchange resins | https://en.wikipedia.org/wiki?curid=39261916 |
Liver support system More recently, on December 17, 2012, MARS therapy has been cleared by the FDA for the treatment of hepatic encephalopathy due to a decompensation of a chronic liver disease Clinical trials conducted with MARS treatment in HE patients having a decompensation of chronic liver disease demonstrated a transient effect from MARS treatments to significantly decrease their hepatic encephalopathy scores by at least 2 grades compared to standard medical therapy (SMT). The MARS is not indicated as a bridge to liver transplant. Safety and efficacy has not been demonstrated in controlled, randomized clinical trials. The effectiveness of the MARS device in patients that are sedated could not be established in clinical studies and therefore cannot be predicted in sedated patients | https://en.wikipedia.org/wiki?curid=39261916 |
Darken's equations In 1948, Lawrence Stamper Darken published an article entitled "Diffusion, Mobility and Their Interrelation through Free Energy in Binary Metallic Systems", in which he derived two equations describing solid-state diffusion in binary solutions. Specifically, the equations Darken created relate “binary chemical diffusion coefficient to the intrinsic and self diffusion coefficients”. The equations apply to cases when a solid solution's two interdiffusing components do not have the same coefficient of diffusion. The result of this article had a large impact on the understanding of solid state diffusion and as a result the equations have come to be known as “Darken’s equations”. Darken's first equation is Darken's first equation is used to calculate marker velocity, given here as formula_2, in respect to a binary system where the different components have their own corresponding diffusion coefficients, "D" and "D", as was discussed in the Kirkendall experiment. The marker velocity is in terms of length per unit time and the diffusion coefficients are in terms of length squared per unit time. The variables "N" and "N" represent the atom fraction of the corresponding component. In addition, the variable "x" is the distance term. It is important to note that this equation only holds in situations where the total concentration remains constant | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations For a binary system this is defined by "C" + "C" = "C", where "C" is the overall concentration of the system that remains constant, and "C" and "C" are the corresponding component's concentration. This is equivalent to saying that the partial molar volumes of the two components are constant and equal. In addition, the ends of the system need to be fixed in position for the equation to hold. These constraints will be further analyzed in the derivation. Darken's second equation is Darken's second equation is used to calculate the chemical diffusion coefficient (also known as the inter-diffusion coefficient), formula_4, for a binary solution. The variables "N" and "D" are the same as previously stated for Darken's first equation. In addition, the variable "a" is the activity coefficient for the component one. Similar to the first equation, this equation only holds in situations when the total concentration remains constant. To derive these equations Darken mainly references Kirkendall and Smigelskas’s experiment, and W. A. Johnson’s experiment, along with other findings within the metallurgical community. In deriving the first equation, Darken referenced Simgelskas and Kirkendall's experiment, which tested the mechanisms and rates of diffusion and gave rise to the concept now known as the Kirkendall effect. For the experiment, inert molybdenum wires were placed at the interface between copper and brass components, and the motion of the markers was monitored | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations The experiment supported the concept that a concentration gradient in a binary alloy would result in the different components having different velocities in the solid solution. The experiment showed that in brass zinc had a faster relative velocity than copper, since the molybdenum wires moved farther into the brass. In establishing the coordinate axes to evaluate the derivation, Darken refers back to Smigelskas and Kirkendall’s experiment which the inert wires were designated as the origin. In respect to the derivation of the second equation, Darken referenced W. A. Johnson’s experiment on a gold–silver system, which was performed to determine the chemical diffusivity. In this experiment radioactive gold and silver isotopes were used to measure the diffusivity of gold and silver, because it was assumed that the radioactive isotopes have relatively the same mobility as the non-radioactive elements. If the gold–silver solution is assumed to behave ideally, it would be expected the diffusivities would also be equivalent. Therefore, the overall diffusion coefficient of the system would be the average of each components diffusivity; however, this was found not to be true. This finding led Darken to analyze Johnson's experiment and derive the equation for chemical diffusivity of binary solutions. As stated previously, Darken's first equation allows the calculation of the marker velocity formula_2 in respect to a binary system where the two components have different diffusion coefficients | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations For this equation to be applicable, the analyzed system must have a constant concentration and can be modeled by the Boltzmann–Matano solution. For the derivation, a hypothetical case is considered where two homogeneous binary alloy rods of two different compositions are in contact. The sides are protected, so that all of the diffusion occurs parallel to the length of the rod. In establishing the coordinate axes to evaluate the derivation, Darken sets the x-axis to be fixed at the far ends of the rods, and the origin at the initial position of the interface between the two rods. In addition this choice of a coordinate system allows the derivation to be simplified, whereas Smigelskas and Kirkendall's coordinate system was considered to be the non-optimal choice for this particular calculation as can be seen in the following section. At the initial planar interface between the rods, it is considered that there are infinitely small inert markers placed in a plane which is perpendicular to the length of the rods. Here, inert markers are defined to be a group of particles that are of a different elemental make-up from either of the diffusing components and move in the same fashion. For this derivation, the inert markers are assumed to be following the motion of the crystal lattice. The motion relative to the marker is associated with diffusion, formula_6, while the motion of the markers is associated with advection, formula_7 | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations Fick’s first law, the previous equation stated for diffusion, describes the entirety of the system for only small distances from the origin, since at large distances advection needs to be accounted for. This results in the total rate of transport for the system being influenced by both factors, diffusion and advection. The derivation starts with Fick's first law using a uniform distance axis "y" as the coordinate system and having the origin fixed to the location of the markers. It is assumed that the markers move relative to the diffusion of one component and into one of the two initial rods, as was chosen in Kirkendall's experiment. In the following equation, which represents Fick's first law for one of the two components, "D" is the diffusion coefficient of component one, and "C" is the concentration of component one: This coordinate system only works for short range from the origin because of the assumption that marker movement is indicative of diffusion alone, which is not true for long distances from the origin as stated before. The coordinate system is transformed using a Galilean transformation, "y" = "x" − ν"t", where "x" is the new coordinate system that is fixed to the ends of the two rods, ν is the marker velocity measured with respect to the "x" axis. The variable "t", time, is assumed to be constant, so that the partial derivative of "C" with respect to "y" is equal to the partial of "C" with respect to "x" | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations This transformation then yields The above equation, in terms of the variable "x", only takes into account diffusion, so the term for the motion of the markers must also be included, since the frame of reference is no longer moving with the marker particles. In the equation below, formula_2 is the velocity of the markers. Taking the above equation and then equating it to the accumulation rate in a volume results in the following equation. This result is similar to Fick's second law, but with an additional advection term: The same equation can be written for the other component, designated as component two: Using the assumption that "C", the total concentration, is constant, "C" and "C" can be related in the following expression: The above equation can then be used to combine the expressions for formula_15 and formula_16 to yield Since "C" is constant, the above equation can be written as The above equation states that formula_19 is constant because the derivative of a constant is equal to zero. Therefore, by integrating the above equation it is transforms to formula_20, where formula_21 is an integration constant. At relative infinite distances from the initial interface, the concentration gradients of each of the components and the marker velocity can be assumed to be equal to zero. Based on this condition and the choice for the coordinate axis, where the "x" axis fixed at the far ends of the rods, "I" is equal zero | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations These conditions then allow the equation to be rearranged to give Since "C" is assumed to be constant, formula_23. Rewriting this equation in terms of atom fraction formula_24 and formula_25 yields Referring back to the derivation for Darken's first equation, formula_2 is written as Inserting this value for formula_2 in formula_30 gives As stated before, formula_23, which gives Rewriting this equation in terms of atom fraction formula_24 and formula_25 yields By using formula_37 and solving to the form formula_38, it is found that Integrating the above gives the final equation: This equation is only applicable for binary systems that follow the equations of state and the Gibbs–Duhem equation. This equation, as well as Darken's first law, formula_41, gives a complete description of an ideal binary diffusion system. This derivation was the approach taken by Darken in his original 1948, though shorter methods can be used to attain the same result. Darken's second equation relates the chemical diffusion coefficient, formula_42, of a binary system to the atomic fractions of the two components. Similar to the first equation, this equation is applicable when the system does not undergo a volume change. This equation also only applies to multicomponent systems, including binary systems, that obey the equations of state and the Gibbs–Duhem equations. To derive Darken's second equation the gradient in Gibb's chemical potential is analyzed | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations The gradient in potential energy, denoted by F, is the force which causes atoms to diffuse. To begin, the flux "J" is equated to the product of the differential of the gradient and the mobility "B", which is defined as the diffusing atom's velocity per unit of applied force. In addition, "N" is Avogadro's number, and "C" is the concentration of diffusing component two. This yields which can be equated to the expression for Fick's first law: so that the expression can be written as After some rearrangement of variables the expression can be written for "D", the diffusivity of component two: Assuming that atomic volume is constant, so "C" = "C" + "C", Using a definition activity, formula_48, where "R" is the gas constant, and "T" is the temperature, to rewrite the equation in terms of activity gives The above equation can be rewritten in terms of the activity coefficient γ, which is defined in terms of activity by the equation formula_50. This yields The same equation can also be written for the diffusivity of component one, formula_52, and combining the equations for "D" and "D" gives the final equation: Darken’s equations can be applied to almost any scenario involving the diffusion of two different components that have different diffusion coefficients. This holds true except in situations where there is an accompanying volume change in the material because this violates one of Darken’s critical assumptions that atomic volume is constant | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations More complicated equations than presented must be used in cases where there is convection. One application in which Darken’s equations play an instrumental role is in analyzing the process of diffusion bonding. Diffusion bonding is used widely in manufacturing to connect two materials without using adhesives or welding techniques. Diffusion bonding works because atoms from both materials diffuse into the other material, resulting in a bond that is formed between the two materials. The diffusion of atoms between the two materials is achieved by placing the materials in contact with each other at high pressure and temperature, while not exceeding the melting temperature of either material. Darken’s equations, particularly Darken’s second equation, come into play when determining the diffusion coefficients for the two materials in the diffusion couple. Knowing the diffusion coefficients is necessary for predicting the flux of atoms between the two materials, which can then be used in numerical models of the diffusion bonding process, as, for example, was looked at in the paper by Orhan, Aksoy, and Eroglu when creating a model to determine the amount of time required to create a diffusion bond. In a similar manner, Darken’s equations were used in a paper by Watanabe et al., on the nickel-aluminum system, to verify the interdiffusion coefficients that were calculated for nickel aluminum alloys. Application of Darken’s first equation has important implications for analyzing the structural integrity of materials | https://en.wikipedia.org/wiki?curid=39262593 |
Darken's equations Darken’s first equation, formula_54, can be rewritten in terms of vacancy flux, formula_55. Use of Darken’s equation in this form has important implications for determining the flux of vacancies into a material undergoing diffusion bonding, which, due to the Kirkendall effect, could lead to porosity in the material and have an adverse effect on its strength. This is particularly important in materials such as aluminum nickel superalloys that are used in jet engines, where the structural integrity of the materials is extremely important. Porosity formation, known as Kirkendall porosity, in these nickel-aluminum superalloys have been observed when diffusion bonding has been used. It is important then to use Darken’s findings to predict this porosity formation. | https://en.wikipedia.org/wiki?curid=39262593 |
Syngas to gasoline plus (STG+) is a thermochemical process to convert natural gas, other gaseous hydrocarbons or gasified biomass into drop-in fuels, such as gasoline, diesel fuel or jet fuel, and organic solvents. This process follows four principal steps in one continuous integrated loop, comprising four fixed bed reactors in a series in which a syngas is converted to synthetic fuels. The steps for producing high-octane synthetic gasoline are as follows: The STG+ process uses standard catalysts similar to those used in other gas to liquids technologies, specifically in methanol to gasoline processes. Methanol to gasoline processes favor molecular size- and shape-selective zeolite catalysts, and the STG+ process also utilizes commercially available shape-selective catalysts, such as ZSM-5. According to Primus Green Energy, the STG+ process converts natural gas into 90+-octane gasoline at approximately . The energy content of gasoline is , making this process about 60% efficient, with a 40% loss of energy. As is the case with other gas to liquids processes, STG+ utilizes syngas produced via other technologies as a feedstock. This syngas can be produced through several commercially available technologies and from a wide variety of feedstocks, including natural gas, biomass and municipal solid waste. Natural gas and other methane-rich gases, including those produced from municipal waste, are converted into syngas through methane reforming technologies such as steam methane reforming and auto-thermal reforming | https://en.wikipedia.org/wiki?curid=39274704 |
Syngas to gasoline plus Biomass gasification technologies are less established, though several systems being developed utilize fixed bed or fluidized bed reactors. Other technologies for syngas to liquid fuels synthesis include the Fischer-Tropsch process and the methanol to gasoline processes. Research conducted at Princeton University indicates that methanol to gasoline processes are consistently more cost-effective, both in capital cost and overall cost, than the Fischer-Tropsch process at small, medium and large scales. Preliminary studies suggest that the STG+ process is more energetically efficient and the highest yielding methanol to gasoline process. The primary difference between the Fischer-Tropsch process and methanol to gasoline processes such as STG+ are the catalysts used, product types and economics. Generally, the Fischer-Tropsch process favors unselective cobalt and iron catalysts, while methanol to gasoline technologies favor molecular size- and shape-selective zeolites. In terms of product types, Fischer-Tropsch production has been limited to linear paraffins, such as synthetic crude oil, whereas methanol to gasoline processes can produce aromatics, such as xylene and toluene, and naphthenes and iso-paraffins, such as drop-in gasoline and jet fuel. The main product of the Fischer-Tropsch process, synthetic crude oil, requires additional refining to produce fuel products such as diesel fuel or gasoline | https://en.wikipedia.org/wiki?curid=39274704 |
Syngas to gasoline plus This refining typically adds additional costs, causing some industry leaders to label the economics of commercial-scale Fischer-Tropsch processes as challenging. The STG+ technology offers several differentiators that distinguish it from other methanol to gasoline processes. These differences include product flexibility, durene reduction, environmental footprint and capital cost. Traditional methanol to gasoline technologies produce diesel, gasoline or liquefied petroleum gas. STG+ produces gasoline, diesel, jet fuel and aromatics, depending on the catalysts used. The STG+ technology also incorporates durene reduction into its core process, meaning that the entire fuel production process requires only two steps: syngas production and gas to liquids synthesis. Other methanol to gasoline processes do not incorporate durene reduction into the core process, and they require the implementation of an additional refining step. Due to the additional number of reactors, traditional methanol to gasoline processes include inefficiencies such as the additional cost and energy loss of condensing and evaporating the methanol prior to feeding it to the durene reduction unit. These inefficiencies can lead to a greater capital cost and environmental footprint than methanol to gasoline processes that use fewer reactors, such as STG+. The STG+ process eliminates multiple condensation and evaporation, and the process converts syngas to liquid transportation fuels directly without producing intermediate liquids | https://en.wikipedia.org/wiki?curid=39274704 |
Syngas to gasoline plus This eliminates the need for storage of two products, including pressure storage for liquefied petroleum gas and storage of liquid methanol. Simplifying a gas to liquids process by combining multiple steps into fewer reactors leads to increased yield and efficiency, enabling less expensive facilities that are more easily scaled. The STG+ technology is currently operating at pre-commercial scale in Hillsborough, New Jersey at a plant owned by alternative fuels company Primus Green Energy. The plant produces approximately 100,000 gallons of high-quality, drop-in gasoline per year directly from natural gas. Further, the company announced the findings of an independent engineer’s report prepared by E3 Consulting, which found that STG+ system and catalyst performance exceeded expectations during plant operation. The pre-commercial demonstration plant has also achieved 720 hours of continuous operation. Primus Green Energy has announced plans to break ground on its first commercial STG+ plant in the second half of 2014, and the company has announced that this plant is expected to produce approximately 27.8 million gallons of fuel annually. In early 2014, the U.S. Patent and Trademark Office (USPTO) allowed Primus Green Energy’s patent covering its single-loop STG+ technology. | https://en.wikipedia.org/wiki?curid=39274704 |
Faraday Medal (electrochemistry) The Faraday Medal is awarded by the Electrochemistry Group of the Royal Society of Chemistry. Since 1977, it honours distinguished mid-career electrochemists working outside of the United Kingdom and the Republic of Ireland for their research advancements. The laureates are: | https://en.wikipedia.org/wiki?curid=39283803 |
Charles Goodyear Medal The is the highest honor conferred by the American Chemical Society, Rubber Division. Established in 1941, the award is named after Charles Goodyear, the discoverer of vulcanization, and consists of a gold medal, a framed certificate and prize money. The medal honors individuals for "outstanding invention, innovation, or development which has resulted in a significant change or contribution to the nature of the rubber industry". Awardees give a lecture at an ACS Rubber Division meeting, and publish a review of their work in the society's scientific journal "Rubber Chemistry and Technology". | https://en.wikipedia.org/wiki?curid=39286085 |
Arsonic acid is the simplest of the arsonic acids. It is a hypothetical compound, although the tautomeric arsenious acid (As(OH)) is well established. In contrast to the instability of HAsO(OH), the phosphorus compound with analogous stoichiometry exists as the tetrahedral tautomer. Similarly, organic derivatives such as phenylarsonic acid are tetrahedral with pentavalent central atom. There are similar acids that are the same except for having different pnictogens. The phosphorus equivalent is phosphonic acid. | https://en.wikipedia.org/wiki?curid=39289972 |
Tetramethyluric acid may refer to: | https://en.wikipedia.org/wiki?curid=39292209 |
C9H12N4O3 The molecular formula CHNO may refer to: | https://en.wikipedia.org/wiki?curid=39292230 |
C18H16O4 The molecular formula CHO may refer to: | https://en.wikipedia.org/wiki?curid=39292725 |
Compounds of fluorine Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding (a weaker bridging link to certain nonmetals). Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements (but not all) the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others (elements in certain groups) the highest oxidation states of oxides and fluorides are always equal. While an individual fluorine atom has one unpaired electron, molecular fluorine (F) has all the electrons paired. This makes it diamagnetic (slightly repelled by magnets) with the magnetic susceptibility of −1.2×10 (SI), which is close to theoretical predictions. In contrast, the diatomic molecules of the neighboring element oxygen, with two unpaired electrons per molecule, are paramagnetic (attracted to magnets) | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine The fluorine–fluorine bond of the difluorine molecule is relatively weak when compared to the bonds of heavier dihalogen molecules. The bond energy is significantly weaker than those of Cl or Br molecules and similar to the easily cleaved oxygen–oxygen bonds of peroxides or nitrogen–nitrogen bonds of hydrazines. The covalent radius of fluorine of about 71 picometers found in F molecules is significantly larger than that in other compounds because of this weak bonding between the two fluorine atoms. This is a result of the relatively large electron and internuclear repulsions, combined with a relatively small overlap of bonding orbitals arising due to the small size of the atoms. The F molecule is commonly described as having exactly one bond (in other words, a bond order of 1) provided by one p electron per atom, as are other halogen X molecules. However, the heavier halogens' p electron orbitals partly mix with those of d orbitals, which results in an increased effective bond order; for example, chlorine has a bond order of 1.12. Fluorine's electrons cannot exhibit this d character since there are no such d orbitals close in energy to fluorine's valence orbitals. This also helps explain why bonding in F is weaker than in Cl. Reactions with elemental fluorine are often sudden or explosive. Many substances that are generally regarded as unreactive, such as powdered steel, glass fragments, and asbestos fibers, are readily consumed by cold fluorine gas | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine Wood and even water burn with flames when subjected to a jet of fluorine, without the need for a spark. Reactions of elemental fluorine with metals require different conditions that depend on the metal. Often, the metal (such as aluminium, iron, or copper) must be powdered because many metals passivate by forming protective layers of the metal fluoride that resist further fluoridation. The alkali metals react with fluorine with a bang (small explosion), while the alkaline earth metals react not quite as aggressively. The noble metals ruthenium, rhodium, palladium, platinum, and gold react least readily, requiring pure fluorine gas at 300–450 °C (575–850 °F). Fluorine reacts explosively with hydrogen in a manner similar to that of alkali metals. The halogens react readily with fluorine gas as does the heavy noble gas radon. The lighter noble gases xenon and krypton can be made to react with fluorine under special conditions, while argon will undergo chemical transformations only with hydrogen fluoride. Nitrogen, with its very stable triple bonds, requires electric discharge and high temperatures to combine with fluorine directly. Fluorine reacts with ammonia to form nitrogen and hydrogen fluoride . Fluorine's chemistry is dominated by its strong tendency to gain an electron. It is the most electronegative element and elemental fluorine is a strong oxidant. The removal of an electron from a fluorine atom requires so much energy that no known reagents are known to oxidize fluorine to any positive oxidation state | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine Therefore, fluorine's only common oxidation state is −1. It differs from this value in elemental fluorine, where the atoms are bonded to each other and thus at oxidation state 0, and a few polyatomic ions: the very unstable anions and with intermediate oxidation states exist at very low temperatures, decomposing at around 40 K. Also, the cation and a few related species have been predicted to be stable. Fluorine forms compounds with all elements except neon and helium. In particular, it forms binary compounds, named fluorides, with all said elements except argon. All of the elements up to einsteinium, element 99, have been checked except for astatine and francium, and fluorine is also known to form compounds with mendelevium, element 101, rutherfordium, element 104, and seaborgium, element 106. As a result of its small size and high negative charge density, the fluoride anion is the "hardest" base (i.e., of low polarizability). Because of this, fluorides in real salt crystals often have higher effective charges than oxides of the same metal, even though oxygen's formal charge is twice as great as fluorine's. As a part of a molecule, it is a part with great inductive effect. In the latter case, it significantly increases the acidity of a molecule: the anion formed after giving the proton off becomes stable as a result. Consider acetic acid and its mono-, di-, and trifluoroacetic derivatives and their pK values (4.74, 2.66, 1.24, and 0 | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine 23); in other words, the trifluoro derative is 33,800 times stronger an acid than acetic. Fluorine is a principal component of the strongest known charge-neutral acid, . There is evidence for an even stronger acid, , but it has not proved isolable. In a molecule that is composed of a central atoms and fluorines attached to it, the intermolecular bonding is not very strong. Moreover, the dense negative balls that fluorines are repel each other. Therefore, the intermolecular bonding strength falls further down, a result of which is the low melting point of high fluorides. Fluorine combines with hydrogen to make a compound (HF) called hydrogen fluoride or, especially in the context of water solutions, hydrofluoric acid. The H-F bond type is one of the few capable of hydrogen bonding (creating extra clustering associations with similar molecules). This influences various peculiar aspects of hydrogen fluoride's properties. In some ways the substance behaves more like water, also very prone to hydrogen bonding, than one of the other hydrogen halides, such as HCl. Hydrogen bonding amongst HF molecules gives rise to high viscosity in the liquid phase and lower than expected pressure in the gas phase. Hydrogen fluoride does not boil until 20 °C in contrast to the heavier hydrogen halides which boil between −85 °C and −35 °C (−120 °F and –30 °F). HF is miscible with water (will dissolve in any proportion), while the other hydrogen halides have large solubility gaps with water | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine Hydrogen fluoride and water also form several compounds in the solid state, most notably a 1:1 compound that does not melt until −40 °C (−40 °F), which is 44 degrees Celsius (79 degrees Fahrenheit) above the melting point of pure HF. Unlike other hydrohalic acids, such as hydrochloric acid, hydrogen fluoride is only a weak acid in water solution, with acid dissociation constant (pK) equal to 3.19. HF's weakness as an aqueous acid is paradoxical considering how polar the HF bond is, much more so than the bond in HCl, HBr, or HI. The explanation for the behavior is complicated, having to do with various cluster-forming tendencies of HF, water, and fluoride ion, as well as thermodynamic issues. At great concentrations, a property called homoconjugation is revealed. HF begins to accept fluoride ions, forming the polyatomic ions (such as bifluoride, ) and protons, thus greatly increasing the acidity of the compound. Hydrofluoric acid is also the strongest of the hydrohalic acids in acetic acid and similar solvents. Its hidden acidity potential is also revealed by the fact it protonates acids like hydrochloric, sulfuric, or nitric. Despite its weakness, hydrofluoric acid is very corrosive, even attacking glass (hydrated only). Dry hydrogen fluoride dissolves low-valent metal fluorides readily. Several molecular fluorides also dissolve in HF. Many proteins and carbohydrates can be dissolved in dry HF and can be recovered from it. Most non-fluoride inorganic chemicals react with HF rather than dissolving | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine Metal fluorides are rather dissimilar from other metal halides, adopting distinctive structures. In many respects, metal fluorides are more similar to oxides, often having similar bonding and crystal structures. Owing to its high electronegativity, fluorine stabilizes metals in higher oxidation states with high M:halide ratios. Numerous charge-neutral penta- and hexafluorides are known, whereas analogous chlorides and bromides are rarer. The molecular binary fluorides are often volatile, either as solids liquids, or gases at room temperature. The solubility of fluorides varies greatly but tends to decrease as the charge on the metal ion increases. Dissolved fluorides produce basic solutions. The alkali metals form monofluorides. All are soluble and have the sodium chloride (rock salt) structure, Because the fluoride anion is basic, many alkali metal fluorides form bifluorides with the formula MHF. Among other monofluorides, only silver(I) and thallium(I) fluorides are well-characterized. Both are very soluble, unlike the other halides of those metals. Unlike the monofluorides, the difluorides may be either soluble or insoluble. Several transition metal difluorides, such as those of copper(II) and nickel(II), are soluble. The alkaline earth metals form difluorides that are insoluble. In contrast, the alkaline earth chlorides are readily soluble. Many of the difluorides adopt the fluorite structure, named after calcium fluoride (and also adopted by several metal dioxides such as CeO, UO, ThO, etc | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine ), which surrounds each metal cation with 8 fluorides. Some difluorides adopt the rutile structure, named after a form of titanium dioxide and adopted by several other metal dioxides also. The structure is tetragonal and puts metal atoms in octahedral coordination. Beryllium difluoride is different from the other difluorides. In general, beryllium has a tendency to bond covalently, much more so than the other alkaline earths and its fluoride is partially covalent (although still more ionic than its other halides). BeF has many similarities to SiO (quartz) a mostly covalently bonded network solid. BeF has tetrahedrally coordinated metal and forms glasses (is difficult to crystallize). When crystalline, beryllium fluoride has the same room temperature crystal structure as quartz and shares many higher temperatures structures also. Beryllium difluoride is very soluble in water, unlike the other alkaline earths. (Although they are strongly ionic, they do not dissolve because of the especially strong lattice energy of the fluorite structure.) However, BeF has much lower electrical conductivity when in solution or when molten than would be expected if it were ionic. Many metals form trifluorides, such as iron, bismuth, the rare-earth elements, and the metals in the aluminium and scandium columns of the periodic table. The trifluorides of many rare earths, as well as bismuth, have the YF structure. Trifluorides of plutonium, samarium (at high temperature), and lanthanum adopt the LaF structure | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine Iron and gallium trifluorides have the FeF structure, which is similar to rhenium trioxide. Only ScF is cubic (ReO) at ambient temperature; this material also has the unusual property of negative thermal expansion, meaning it shrinks on heating, over a quite broad temperature range. Gold trifluoride adopts a structure of linked –AuF– squares that align in a helix (spiral chain). In contrast to gold's distinctly ionic trifluoride, its trichloride and tribromide are volatile dimeric molecules. Aluminium trifluoride is a high melting point solid which is a monomer in the gas phase, while its other trihalides are low-melting, volatile molecules or linear polymeric chains that form dimers as gases phase. No trifluoride is soluble in water, but several are soluble in other solvents. The tetrafluorides show a mixture of ionic and covalent bonding. Zirconium, hafnium, plus many of the actinides form tetrafluorides with an ionic structure that puts the metal cation in an 8-coordinate square antiprism. Melting points are around 1000 °C. Titanium and tin tetrafluorides are polymeric, with melting points below 400 °C. (In contrast, their tetrachlorides are molecular and liquids at room temperature.) Vanadium tetrafluoride has a similar structure to tin's and disproportionates at 100–120 °C to the trifluoride and the pentafluoride. The tetrafluorides of iridium, platinum, palladium, and rhodium all share the same structure which was not known until 1975 | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine They have octahedrally coordinated metal atoms with four of the fluorines shared and two unshared. The melting points, where known, are below 300 °C. Manganese tetrafluoride is an unstable solid that decomposes even at room temperature. Only one of the two allotropes, α-MnF, is understood. In this compound, manganese forms –MnF– octahedra which share bridging fluorines to make –MnF– rings which are then further connected three dimensionally. Metal penta- and higher fluorides are all molecular and hence at least somewhat volatile. Vanadium, niobium, and tantalum form pentafluorides as their highest charge-neutral fluoride. Vanadium pentafluoride is the only non-volatile high-charged metal fluoride, with vanadium being centers of –VF– octahedra. The niobium and tantalum pentafluorides, have the same tetrahedra in their structures, with the difference being the formation of the tetra- (rather than poly-) meric molecules. Bismuth's highest fluoride is a volatile penta species that is a powerful fluorinating agent. In the solid state, it is polymeric, consisting of linear chains of octahedra, sharing axial fluorides. In combination with alkali metals, pentavalent bismuth can form hexafluorobismuthate, [BiF], upon reaction with a fluoride donor, either strong (such as NaF) or not (such as XeF). Many metals that form hexafluorides also can form pentafluorides. For instance, uranium, which has a well-known hexafluoride, also forms two different pentafluoride structures | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine The room-temperature (alpha) form has the same linear chain structure as bismuth pentafluoride. As a molecular (gas) species, UF has a square pyramidal structure. The metals that make well-characterized hexafluorides include nine metals in the center of the periodic table (molybdenum, technetium, ruthenium, rhodium, tungsten, rhenium, osmium, iridium, and platinum) along with elements 92–94: uranium, neptunium, and plutonium. At room temperature, tungsten hexafluoride is a gas. Molybdenum hexafluoride and rhenium hexafluoride are liquids. The rest are volatile solids. Metal hexafluorides are oxidants because of their tendency to release fluorines: for example, platinum hexafluoride was the first compound to oxidize molecular oxygen and xenon. Polonium also forms a hexafluoride, but it is understudied. Rhenium is the only metal known to bond with seven fluorides, which is the record for number of charged ligands for a charge-neutral metal compound.Rhenium heptafluoride adopts a pentagonal bipyramid molecular geometry. Calculations shows that the currently unknown but perhaps possible iridium heptafluoride (report of synthesis is being prepared), technetium heptafluoride, and osmium heptafluoride will also have this structure). Osmium octafluoride was first reported in 1913, but in 1958 that compound was shown to be actually osmium hexafluoride. A 1993 theoretical study predicted very weak bonds in osmium octafluoride and said that it would be difficult to ever detect experimentally | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine The study predicted that, if made, OsF would have Os–F bonds of two different lengths. The nonmetal binary fluorides are volatile compounds. They show a great difference between period 2 and other fluorides. For instance, period 2 elements elements fluorides never exceed the octet in their atoms. (Boron is an exception due to its specific position in the periodic table.) Lower-period elements, however, may form hypervalent molecules, such as phosphorus pentafluoride or sulfur hexafluoride. The reactivity of such species varies greatly—sulfur hexafluoride is inert, while chlorine trifluoride is extremely reactive—but there are some trends based on periodic table locations. Boron trifluoride is a planar molecule. It has only six electrons around the central boron atom (and thus an incomplete octet), but it readily accepts a Lewis base, forming adducts with lone-pair-containing molecules or ions such as ammonia or another fluoride ion which can donate two more electrons to complete the octet. Boron monofluoride is an unstable molecule with an unusual (higher than single) bond to fluorine. The bond order has been described as 1.4 (intermediate between a single and double bond). It is isoelectronic with N. Silicon tetrafluoride, similar to carbon tetrafluoride and germanium tetrafluoride, adopts a molecular tetrahedral structure. SiF is stable against heating or electric spark, but reacts with water (even moist air), metals, and alkalies, thus demonstrating weak acidic character | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine Reactions with organomagnesium compounds, alcohols, amines, and ammonia yield adduction compounds. Fluorosilicic acid, a derivative of SiF, is a strong acid in aqueous solution (the anhydrous form does not exist). Pnictogens (nitrogen's periodic table column) show very similar trends in reactivity and acidity of the highest fluorides (pentafluorides) and most common ones (trifluorides), with the said property increasing down the group: NF is stable against hydrolysis, PF hydrolyzes very slowly in moist air, while AsF completely hydrolyzes. SbF hydrolyzes only partially because of the increasing ionic character of the bond to fluorine. The compounds are weak Lewis bases, with NF again being an exception. The pentafluorides of phosphorus and arsenic are much more reactive than their trifluorides; antimony pentafluoride is such a strong acid that it holds the title of the strongest Lewis acid. Nitrogen is not known to form a pentafluoride, although the tetrafluoroammonium cation () features nitrogen in the formal oxidation state of +5. Nitrogen monofluoride is a metastable species that has been observed in laser studies. It is isoelectronic with O and, unusually, like BF, has a higher bond order than single-bonded fluorine. The chalcogens (oxygen's periodic table column) are somewhat similar: The tetrafluorides are thermally unstable and hydrolyze, and are also ready to use their lone pair to form adducts to other (acidic) fluorides. Sulfur and selenium tetrafluorides are molecular while TeF is a polymer | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine The hexafluorides are the result of direct fluorination of the elements (compare: other hexahalides of these elements do not even exist). They increase in reactivity with atomic number: SF is extremely inert, SeF is less noble (for example, reacts with ammonia at 200 °C (400 °F)), and TeF easily hydrolyzes to give an oxoacid. Oxygen's highest fluoride is oxygen difluoride, but fluorine can theoretically (as of 2012) oxidize it to a uniquely high oxidation state of +4 in the fluorocation: . In addition, several chalcogen fluorides occur which have more than one chalcogen (OF, SF, etc.). The well-characterized heavier halogens (chlorine, bromine, and iodine) all form mono-, tri-, and pentafluorides: XF, XF, and XF. Of the neutral +7 species, only iodine heptafluoride is known. While chlorine and bromine heptafluorides are not known, the corresponding cations and , extremely strong oxidizers, are. Astatine is not well-studied, and although there is a report of a non-volatile astatine monofluoride, its existence is debated. Many of the halogen fluorides are powerful fluorinators. Chlorine trifluoride is particularly noteworthy—readily fluorinating asbestos and refractory oxides—and may be even more reactive than chlorine pentafluoride. Used industrially, ClF requires special precautions similar to those for fluorine gas because of its corrosiveness and hazards to humans. Several important inorganic acids contain fluorine. They are generally very strong because of the high electronegativity of fluorine | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine One such acid, fluoroantimonic acid (HSbF), is the strongest charge-neutral acid known. The dispersion of the charge on the anion affects the acidity of the solvated proton (in form of ): The compound has an extremely low pK of −28 and is 10 quadrillion (10) times stronger than pure sulfuric acid. Fluoroantimonic acid is so strong that it protonates otherwise inert compounds like hydrocarbons. Hungarian-American chemist George Olah received the 1994 Nobel Prize in chemistry for investigating such reactions. The noble gases are generally non-reactive because they have filled electronic shells. Until the 1960s, no chemical bond with a noble gas was known. In 1962, Neil Bartlett found that platinum hexafluoride reacts with xenon. He called the compound he prepared xenon hexafluoroplatinate, but since then the product has been revealed to be mixture, perhaps monofluoroxenyl(II) pentafluoroplatinate, [XeF][PtF], monofluoroxenyl(II) undecafluorodiplatinate, [XeF][PtF], and trifluorodixenyl(II) hexafluoroplatinate, [XeF][PtF]. Bartlett's fluorination of xenon has been highly praised. Later in 1962, xenon was found to react directly with fluorine to form the di- and tetrafluorides. Since then, other noble gas fluorides have been reported. The binary compounds xenon include xenon difluoride, xenon tetrafluoride, and xenon hexafluoride. Xenon forms several oxyfluorides, such as xenon oxydifluoride, XeOF, by hydrolysis of xenon tetrafluoride. Its lighter neighbor, krypton also forms well-characterized compounds, e.g | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine , krypton difluoride. Krypton tetrafluoride was reported in 1963, but was subsequently shown to be a mistaken identification; the compound seems to be very hard to synthesize now (although even the hexafluoride may exist). In accordance with the periodic trends, radon is more reactive toward fluorine. Radon difluoride has been claimed. The lighter noble gases (helium through argon) do not form stable binary fluorides. Elements frequently have their highest oxidation state in the form of a binary fluoride. Several elements show their highest oxidation state only in a few compounds, one of which is the fluoride; and some elements' highest known oxidation state is seen exclusively in a fluoride. For groups 1–5, 10, 13–16, the highest oxidation states of oxides and fluorides are always equal. Differences are only seen in chromium, groups 7–9, copper, mercury, and the noble gases. Fluorination allows some elements to achieve relatively low highest oxidation states that are otherwise hard to achieve. For example, no binary oxide is known for krypton, but krypton difluoride is well-studied. At the same time, for some other elements, certain very high oxidation states are known only for the oxygen-based species, not the fluorine-based ones. For the previously mentioned volatile oxides, there are no corresponding hepta- or octafluorides. (For example, ruthenium octafluoride is unlikely to be ever synthesized, while ruthenium tetroxide has even found an industrial use | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine ) The main problem that prevents fluorine from forming the highest states in covalent hepta- and octafluorides is that it is hard to attach such a large number of ligands around a single atom; the number of ligands is halved in analogous oxides. However, octafluoride anions, such as the octafluoroiodate (), octafluorozirconate (), and octafluoroxenate () anions are well-known. The highest oxidation states may be uncommon to everyday life, or even industrial usage. For example, the synthesis of mercury tetrafluoride, the first compound to achieve an oxidation state above +2 for a group 12 element, breaking the filled 5d-shell, again showing the significance of the relativistic effects on the heavy elements, and fueling the debate over whether mercury, cadmium, and zinc are transition metals, occurred at cryogenic temperatures and the compound decomposes at the temperatures of solid nitrogen. More unstable still, the only cobalt(V) species, the cation, has only been observed in gas phase (with no interactions with other atoms, thus no shown stability in any chemical environment). The reason why such unstable species exist is complicated, yet can be summarized as follows on the example of the hypothesized molecule: According to the modern calculations, five fluorine atoms and one nitrogen atoms can theoretically arrange themselves in different ways, such as and , and , , etc. The + system is of the smallest energy (most stable) | https://en.wikipedia.org/wiki?curid=39292926 |
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