Fischer–Tropsch process

is a molecule that illustrates the kind of reduced carbon species speculated to occur in the Fischer–Tropsch process. The Fischer–Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally having the formula (CnH2n+2). The more useful reactions produce alkanes as follows: : (2n + 1) H2 + n CO → CnH2n+2 + n H2O where n is typically 10–20, resulting mostly in the formation of higher alkanes. The formation of methane (n = 1) is unwanted. Most of the alkanes produced tend to be straight-chain, suitable as diesel fuel. In addition to alkane formation, competing reactions give small amounts of alkenes, as well as alcohols and other oxygenated hydrocarbons. Fischer–Tropsch intermediates and elemental reactions Converting a mixture of H2 and CO into aliphatic products is a multi-step reaction with several intermediate compounds. The growth of the hydrocarbon chain may be visualized as involving a repeated sequence in which hydrogen atoms are added to carbon and oxygen, the C–O bond is split and a new C–C bond is formed. For one –CH2– group produced by CO + 2 H2 → (CH2) + H2O, several reactions are necessary: • Associative adsorption of CO • Splitting of the C–O bond • Dissociative adsorption of 2 H2 • Transfer of 2 H to the oxygen to yield H2O • Desorption of H2O • Transfer of 2 H to the carbon to yield CH2 The conversion of CO to alkanes involves hydrogenation of CO, the hydrogenolysis (cleavage with H2) of C–O bonds, and the formation of C–C bonds. Such reactions are assumed to proceed via initial formation of surface-bound metal carbonyls. The CO ligand is speculated to undergo dissociation, possibly into oxide and carbide ligands. Other potential intermediates are various C1 fragments including formyl (CHO), hydroxycarbene (HCOH), hydroxymethyl (CH2OH), methyl (CH3), methylene (CH2), methylidyne (CH), and hydroxymethylidyne (COH). Furthermore, and critical to the production of liquid fuels, are reactions that form C–C bonds, such as migratory insertion. Many related stoichiometric reactions have been simulated on discrete metal clusters, but homogeneous Fischer–Tropsch catalysts are of no commercial importance. Addition of isotopically labelled alcohol to the feed stream results in incorporation of alcohols into product. This observation establishes the facility of C–O bond scission. Using 14C-labelled ethylene and propene over cobalt catalysts results in incorporation of these olefins into the growing chain. Chain growth reaction thus appears to involve both 'olefin insertion' as well as 'CO-insertion'. :8 CO + 17 H2 -> C8H18 + 8 H2O == Feedstocks: carbon dioxide ==

Carbon dioxide has emerged as an important carbon source for replacement of chemicals and fuels derived from fossil fuels. Based on the pioneering work of Sasol in South Africa using gasification to produce Syngas, an entire slate of downstream chemicals and fuels can manufactured. Fischer-Tropsch using high-temperature iron-based catalysts yields a wide array of short-chain paraffins, olefins, and aromatics. Low-temperature cobalt-based catalysts produce a majority of longer-chain n-paraffin species, mainly as liquids and waxes. These can be processed into a multitude of products such as zero-sulfur sustainable aviation fuel, diesel, base oils, and naphtha feedstock that can be catalytically reformed for BTX production of polymer precursors. By substituting carbon dioxide as the carbon source, entire fossil fuel supply chains can be replaced with Fischer-Tropsch products. Production of a Syngas feedstock made from carbon dioxide can use the following catalyzed chemical reactions: • Reverse Water Gas Shift reaction: CO2 + H2 -> CO + H2O • Dry Methane Reforming: CO2 + CH4 -> 2 CO + 2 H2 The reverse water gas shift reaction uses carbon dioxide and an excess of hydrogen such as from water electrolysis (green hydrogen) to yield a Syngas mixture of carbon monoxide (CO) and hydrogen (H2) with the desired H2:CO Syngas ratio for a downstream Fischer-Tropsch catalyst; a commercial catalytic process that has been pioneered by Dimensional Energy. Dry methane reforming utilizes CO and methane (CH4) to yield a 1:1 H2-to-CO Syngas mixture that can be augmented with an external source of hydrogen or by the water-gas shift reaction to achieve the desired Syngas ratio. Commercial dry methane Reforming catalysts are available from HYCO1 and BASF. Carbon dioxide is not a typical direct feedstock for FT catalysis. Hydrogen and carbon dioxide react over a cobalt-based catalyst, producing methane. With iron-based catalysts unsaturated short-chain hydrocarbons are also produced. Upon introduction to the catalyst's support, ceria functions as a reverse water-gas shift catalyst, further increasing the yield of the reaction. The short-chain hydrocarbons were upgraded to liquid fuels over solid acid catalysts, such as zeolites. ==Feedstocks: gasification==

Fischer–Tropsch plants associated with biomass or coal or related solid feedstocks (sources of carbon) must first convert the solid fuel into gases. These gases include CO, H2, and alkanes. This conversion is called gasification. Synthesis gas ("syngas") obtained from biomass/coal gasification is a mixture of hydrogen and carbon monoxide. The H2:CO ratio is adjusted using the water-gas shift reaction. Coal-based FT plants produce varying amounts of CO2, depending upon the energy source of the gasification process. However, most coal-based plants rely on the feed coal to supply all the energy requirements of the process. Feedstocks: GTL Carbon monoxide for FT catalysis is derived from hydrocarbons. In gas to liquids (GTL) technology, the hydrocarbons are low molecular weight materials that often would be discarded or flared. Stranded gas provides relatively cheap gas. For GTL to be commercially viable, gas must remain relatively cheaper than oil. Several reactions are required to obtain the gaseous reactants required for FT catalysis. First, reactant gases entering a reactor must be desulfurized. Otherwise, sulfur-containing impurities deactivate ("poison") the catalysts required for FT reactions. Product distribution In general the product distribution of hydrocarbons formed during the Fischer–Tropsch process follows an Anderson–Schulz–Flory distribution, which can be expressed as: : = (1 − α)2αn−1 where Wn is the weight fraction of hydrocarbons containing n carbon atoms, and α is the chain growth probability or the probability that a molecule will continue reacting to form a longer chain. In general, α is largely determined by the catalyst and the specific process conditions. Examination of the above equation reveals that methane will always be the largest single product so long as α is less than 0.5; however, by increasing α close to one, the total amount of methane formed can be minimized compared to the sum of all of the various long-chained products. Increasing α increases the formation of long-chained hydrocarbons. The very long-chained hydrocarbons are waxes, which are solid at room temperature. Therefore, for production of liquid transportation fuels it may be necessary to crack some of the FT products. In order to avoid this, some researchers have proposed using zeolites or other catalyst substrates with fixed sized pores that can restrict the formation of hydrocarbons longer than some characteristic size (usually n < 10). This way they can drive the reaction so as to minimize methane formation without producing many long-chained hydrocarbons. Such efforts have had only limited success. ==Catalysts==

Four metals are active as catalysts for the Fischer–Tropsch process: iron, cobalt, nickel, and ruthenium. Since FT process typically transforms inexpensive precursors into complex mixtures that require further refining, FT catalysts are based on inexpensive metals, especially iron and cobalt. An important figure in recent Fischer-Tropsch catalyst development has been Dr. Rafael Espinoza, who has developed both iron-based and cobalt-based catalysts starting with Sasol followed by ConocoPhillips, and lastly with Dimensional Energy. His continued developments and optimizations provided key improvements for the active catalyst and ceramic support structure. Promoters and supports In addition to the active metal (usually Fe or Co), two other components comprise the catalyst: promoters and the catalyst support. Promoters are additives that enhance the behavior of the catalyst. For F-T catalysts, typical promoters including potassium and copper, which are usually added as salts. The choice of promoters depends on the primary metal, iron vs cobalt. Iron catalysts need alkali promotion to attain high activity and stability (e.g. 0.5 wt% ). Potassium-doped α-Fe2O3 are synthesized under variable calcination temperatures (400–800 °C). Addition of Cu for reduction promotion, addition of , for structural promotion and maybe some manganese can be applied for selectivity control (e.g. high olefinicity). The choice of promoters depends on the primary metal, i.e., iron vs cobalt. 3 and C4 alkenes have been oligomerized at Sasol. However, recovering the olefins for use as chemicals in, e.g., polymerization processes is advantageous. The second direction of iron catalyst development has aimed at highest catalyst activity to be used at low reaction temperature where most of the hydrocarbon product is in the liquid phase under reaction conditions. The main product fraction then is a paraffin wax, which is refined to marketable wax materials at Sasol; however, it also can be very selectively hydrocracked to a high quality diesel fuel. Thus, iron catalysts are very flexible.--> ==History==

The F-T process attracted attention as a means of Nazi Germany to produce liquid hydrocarbons. The original process was developed by Franz Fischer and Hans Tropsch, working at the Kaiser-Wilhelm-Institut for Chemistry in 1926. They filed a number of patents, e.g., , applied 1926, published 1930. It was commercialized by Brabag in Germany in 1936. Being petroleum-poor but coal-rich, Germany used the process during World War II to produce ersatz (replacement) fuels. FT production accounted for an estimated 9% of German war production of fuels and 25% of the automobile fuel. Many refinements and adjustments have been made to the process since Fischer and Tropsch's time. The United States Bureau of Mines, in a program initiated by the Synthetic Liquid Fuels Act, employed seven Operation Paperclip synthetic fuel scientists in a Fischer–Tropsch plant in Louisiana, Missouri in 1946. In Britain, Alfred August Aicher obtained several patents for improvements to the process in the 1930s and 1940s. Aicher's company was named Synthetic Oils Ltd (not related to a company of the same name in Canada). Around the 1930s and 1940s, Arthur Imhausen developed and implemented an industrial process for producing edible fats from these synthetic oils through oxidation. The products were fractionally distilled and the edible fats were obtained from the - fraction which were reacted with glycerol such as that synthesized from propylene. The process required at least 60 kg of coal per kg of synthetic butter. ==Commercialization==

Sasol in South Africa. It uses coal liquefaction to produce petroleum-like synthetic crude oil from coal. The world's largest scale implementation of Fischer–Tropsch technology is a series of plants operated by Sasol in South Africa, a country with large coal reserves, but little oil. With a capacity of 165000 Bpd at its Secunda CTL plant. The first commercial plant opened in 1952. Sasol uses coal and natural gas as feedstocks and produces a variety of synthetic petroleum products, including most of the country's diesel fuel. Dimensional Energy Using a pathway originating from carbon dioxide, Dimensional Energy has designed, built, and operated two Fischer Tropsch demo/pilot plants in Tucson, AZ, USA and Richmond, BC, Canada. PetroSA PetroSA, another South African company, operates a refinery with a 36,000 barrels a day plant that completed semi-commercial demonstration in 2011, paving the way to begin commercial preparation. The technology can be used to convert natural gas, biomass or coal into synthetic fuels. Shell middle distillate synthesis One of the largest implementations of Fischer–Tropsch technology is in Bintulu, Malaysia. This Shell facility converts natural gas into low-sulfur Diesel fuels and food-grade wax. The scale is . Arcadia eFuels Texas based Arcadia eFuels in conjunction with Sasol and Topsoe is constructing a sustainable aviation fuel plant in Vordingborg, Denmark that will use Fischer-Tropsch process to convert syngas derived from water electrolysis and carbon capture into an e-diesel fuel for aviation. The plant will begin production in 2028 with additional plants in development in Teesside, United Kingdom and the United States. Velocys Velocys operated a demonstration plant with Envia in Oklahoma City during 2017 and 2018. The Joint Venture was closed down and reactors returned to Velocys after the site was sold to another joint venture partner for $4.15 million. The company's Fischer-Tropsch reactors were used by TOYO Engineering Corporation to produce sustainable aviation fuel (SAF) from woodchips at its demonstration plant in Nagoya, Japan in 2020. The produced fuel was used in flight JL 515 from Tokyo to Sapporo on June 17, 2021, marking the first time aviation fuel derived from gasified woodchips and synthesized into SAF was used in a commercial flight. SGCE Starting as a biomass technology licensor In Summer of 2012 SGC Energia (SGCE) successfully commissioned a pilot multi tubular Fischer–Tropsch process unit and associated product upgrading units at the Pasadena, Texas Technology Center. The technology center focused on the development and operations of their XTLH solution which optimized processing of low value carbon waste streams into advanced fuels and wax products. This unit also serves as an operations training environment for the 1100 BPD Juniper GTL facility constructed in Westlake LA. UPM (Finland) In October 2006, Finnish paper and pulp manufacturer UPM announced its plans to produce biodiesel by the Fischer–Tropsch process alongside the manufacturing processes at its European paper and pulp plants, using waste biomass resulting from paper and pulp manufacturing processes as source material. Uzbekistan GTL , Tashkent Rentech A demonstration-scale Fischer–Tropsch plant was built and operated by Rentech, Inc., in partnership with ClearFuels, a company specializing in biomass gasification. Located in Commerce City CO, the facility produces about of fuels from natural gas. Commercial-scale facilities were planned for Rialto, California; Natchez, Mississippi; Port St. Joe, Florida; and White River, Ontario. Rentech closed down their pilot plant in 2013, and abandoned work on their FT process as well as the proposed commercial facilities. INFRA GTL Technology , TX In 2010, INFRA built a compact Pilot Plant for conversion of natural gas into synthetic oil. The plant modeled the full cycle of the GTL chemical process including the intake of pipeline gas, sulfur removal, steam methane reforming, syngas conditioning, and Fischer–Tropsch synthesis. In 2013 the first pilot plant was acquired by VNIIGAZ Gazprom LLC. In 2014 INFRA commissioned and operated on a continuous basis a new, larger scale full cycle Pilot Plant. It represents the second generation of INFRA's testing facility and is differentiated by a high degree of automation and extensive data gathering system. In 2015, INFRA built its own catalyst factory in Troitsk (Moscow, Russia). The catalyst factory has a capacity of over 15 tons per year, and produces the unique proprietary Fischer–Tropsch catalysts developed by the company's R&D division. In 2016, INFRA designed and built a modular, transportable GTL (gas-to-liquid) M100 plant for processing natural and associated gas into synthetic crude oil in Wharton TX. The M100 plant is operating as a technology demonstration unit, R&D platform for catalyst refinement, and economic model to scale the Infra GTL process into larger and more efficient plants. BP-JM FT CANS technology British Petroleum and Johnson Matthey co-licence a modified tubular fixed-bed FT technology called "FT CANS". The technology allows gas flow through the catalyst, followed by high-velocity annular heat transfer down the outside of the tube. This allows the use of very small catalyst particles with the benefits of a fixed bed. The technology was first demonstrated at the Fulcrum Sierra site in Nevada, USA. Other In the United States and India, some coal-producing states have invested in Fischer–Tropsch plants. In Pennsylvania, Waste Management and Processors, Inc. was funded by the state to implement FT technology licensed from Shell and Sasol to convert so-called waste coal (leftovers from the mining process) into low-sulfur diesel fuel. ==Research developments==

Choren Industries has built a plant in Germany that converts biomass to syngas and fuels using the Shell FT process structure. The company went bankrupt in 2011 due to impracticalities in the process. Biomass gasification (BG) and Fischer–Tropsch (FT) synthesis can in principle be combined to produce renewable transportation fuels (biofuels). In partnership with Sunfire, Audi produces E-diesel in small scale with two steps, the second one being FT. U.S. Air Force testing Syntroleum, formerly a publicly traded United States company, has produced over of diesel and jet fuel from the Fischer–Tropsch process using natural gas at its demonstration plant near Tulsa, Oklahoma. Using natural gas as a feedstock, the ultra-clean, low sulfur fuel has been tested extensively by the United States Department of Energy and the United States Department of Transportation. Syntroleum worked to develop a synthetic jet fuel blend that will help the Air Force to reduce its dependence on imported petroleum. The Air Force, which is the United States military's largest user of fuel, began exploring alternative fuel sources in 1999. On December 15, 2006, a B-52 took off from Edwards Air Force Base, California for the first time powered solely by a 50–50 blend of JP-8 and Syntroleum's FT fuel. The seven-hour flight test was considered a success. The goal of the flight test program is to qualify the fuel blend for fleet use on the service's B-52s, and then flight test and qualification on other aircraft. The test program concluded in 2007. This program was part of the Department of Defense Assured Fuel Initiative, an effort to develop secure domestic sources for the military energy needs. The Pentagon had hoped to reduce its use of crude oil from foreign producers and obtain about half of its aviation fuel from alternative sources by 2016. More recently in 2021, another batch of synthetic jet fuel was manufactured for the Air Force by Twelve and Emerging Fuels Technology - the latter being Syntroleum's successor company which was established by the founders and management team of Syntroleum and having bought its laboratory in Tulsa. == Process efficiency ==

Using conventional FT technology the process ranges in carbon efficiency from 25 to 50 percent and a thermal efficiency of about 50% for CTL facilities idealised at 60% with GTL facilities at about 60% efficiency idealised to 80% efficiency. ==Fischer–Tropsch in nature==

A Fischer–Tropsch-type process has also been suggested to have produced a few of the building blocks of DNA and RNA within asteroids. Similarly, the hypothetical abiogenic petroleum formation requires some naturally occurring FT-like processes. Biological Fischer-Tropsch-type chemistry can be carried out by the enzyme nitrogenase at ambient conditions. == See also ==