Fischer–Tropsch process
   HOME

TheInfoList



OR:

The Fischer–Tropsch process is a collection of
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...
s that converts a mixture of
carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
and
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
, known as
syngas Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principly used for producing ammonia or methanol. Syngas is combustible and can be used as ...
, into liquid
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s. These reactions occur in the presence of metal
catalysts Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
, typically at temperatures of and pressures of one to several tens of atmospheres. The process was first developed by Franz Fischer and
Hans Tropsch Hans Tropsch (October 7, 1889 – October 8, 1935) was a chemist responsible, along with Franz Fischer, for the development of the Fischer–Tropsch process. Life Tropsch was born in Plan bei Marienbad, Sudet-German Bohemia at that time part o ...
at the
Kaiser Wilhelm Institute for Coal Research The Max-Planck-Institut für Kohlenforschung (german: Max-Planck-Institut für Kohlenforschung) is an institute located in Mülheim an der Ruhr, Germany specializing in chemical research on catalysis. It is one of the 86 institutes in the Max Pla ...
in
Mülheim an der Ruhr Mülheim, officially Mülheim an der Ruhr () and also described as ''"City on the River"'', is a city in North Rhine-Westphalia in Germany. It is located in the Ruhr Area between Duisburg, Essen, Oberhausen and Ratingen. It is home to many compa ...
, Germany, in 1925. As a premier example of C1 chemistry, the Fischer–Tropsch process is an important reaction in both
coal liquefaction Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. This process is often known as "Coal to X" or "Carbon to X", where X can be many different hydrocarbon-based products. However, the most c ...
and
gas to liquids Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies ...
technology for producing liquid hydrocarbons. In the usual implementation, carbon monoxide and hydrogen, the feedstocks for FT, are produced from
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
,
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon d ...
, or
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
in a process known as
gasification Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...
. The process then converts these gases into synthetic lubrication oil and
synthetic fuel Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by refo ...
. This process has received intermittent attention as a source of low-sulfur diesel fuel and to address the supply or cost of petroleum-derived hydrocarbons. It is now receiving much renewed attention as a means of producing carbon-neutral liquid hydrocarbon fuels from atmospheric CO2 and hydrogen.


Reaction mechanism

The Fischer–Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally having the formula (C''n''H2''n''+2). The more useful reactions produce
alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in wh ...
s as follows: : (2''n'' + 1) H2 + ''n'' CO → C''n''H2''n''+2 + ''n'' H2O where ''n'' is typically 10–20. The formation of methane (''n'' = 1) is unwanted. Most of the alkanes produced tend to be straight-chain, suitable as
diesel fuel Diesel fuel , also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and ...
. In addition to alkane formation, competing reactions give small amounts of
alkenes In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, a ...
, as well as
alcohols In chemistry, an alcohol is a type of organic compound that carries at least one hydroxyl () functional group bound to a saturated carbon atom. The term ''alcohol'' originally referred to the primary alcohol ethanol (ethyl alcohol), which is ...
and other oxygenated hydrocarbons. The reaction is a highly
exothermic reaction In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change Δ''H''⚬ is negative." Exothermic reactions usually release heat. The term is often confused with exergonic reaction, which IUPAC defines ...
due to a standard
reaction enthalpy The standard enthalpy of reaction (denoted \Delta_ H^\ominus or \Delta H_^\ominus) for a chemical reaction is the difference between total reactant and total product molar enthalpies, calculated for substances in their standard states. This can in ...
(ΔH) of −165 kJ/mol CO combined.


Fischer–Tropsch intermediates and elemental reactions

Converting a mixture of H2 and CO into
aliphatic In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane ...
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 Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
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 carbonyl Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe c ...
s. The CO
ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...
is speculated to undergo dissociation, possibly into oxide and
carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of t ...
ligands. Other potential intermediates are various C1 fragments including formyl (CHO), hydroxycarbene (HCOH), hydroxymethyl (CH2OH),
methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ...
(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 In organometallic chemistry, a migratory insertion is a type of reaction wherein two ligands on a metal complex combine. It is a subset of reactions that very closely resembles the insertion reactions, and both are differentiated by the mechanis ...
. Many related stoichiometric reactions have been simulated on discrete metal clusters, but homogeneous Fischer–Tropsch catalysts are poorly developed and 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 Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...
and
propene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petrol ...
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’. :8CO + 17H2 -> C8H18 + 8H2O


Feedstocks: gasification

Fischer–Tropsch plants associated with coal or related solid feedstocks (sources of carbon) must first convert the solid fuel into gaseous reactants, ''i.e.'', CO, H2, and alkanes. This conversion is called
gasification Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...
and the product is called
synthesis gas Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principly used for producing ammonia or methanol. Syngas is combustible and can be used ...
("syngas"). Synthesis gas obtained from coal gasification tends to have a H2:CO ratio of ~0.7 compared to the ideal ratio of ~2. This ratio is adjusted via the
water-gas shift reaction Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer okewith air and gasifying it with steam". The caloric yield of this is about 10% of a modern syngas plant. F ...
. 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 Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies ...
(GTL) technology, the hydrocarbons are low molecular weight materials that often would be discarded or flared. Stranded gas provides relatively cheap gas. GTL is viable provided gas remains relatively cheaper than oil. Several reactions are required to obtain the gaseous reactants required for FT
catalysis Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
. First, reactant gases entering a reactor must be desulfurized. Otherwise, sulfur-containing impurities deactivate ("
poison Poison is a chemical substance that has a detrimental effect to life. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figuratively, with a broa ...
") the
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s required for FT reactions. Several reactions are employed to adjust the H2:CO ratio. Most important is the
water-gas shift reaction Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer okewith air and gasifying it with steam". The caloric yield of this is about 10% of a modern syngas plant. F ...
, which provides a source of
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
at the expense of carbon monoxide: :H2O + CO -> H2 + CO2 For FT plants that use
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
as the
feedstock A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials that are feedstock for future finished products. As feeds ...
, another important reaction is
dry reforming Carbon dioxide reforming (also known as dry reforming) is a method of producing synthesis gas (mixtures of hydrogen and carbon monoxide) from the reaction of carbon dioxide with hydrocarbons such as methane with the aid of noble metal catalysts (typ ...
, which converts the methane into CO and H2: : CH4 + CO2 -> 2CO + 2H2


Process conditions

Generally, the Fischer–Tropsch process is operated in the temperature range of . Higher temperatures lead to faster reactions and higher conversion rates but also tend to favor methane production. For this reason, the temperature is usually maintained at the low to middle part of the range. Increasing the pressure leads to higher conversion rates and also favors formation of long-chained
alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in wh ...
s, both of which are desirable. Typical pressures range from one to several tens of atmospheres. Even higher pressures would be favorable, but the benefits may not justify the additional costs of high-pressure equipment, and higher pressures can lead to catalyst deactivation via coke formation. A variety of synthesis-gas compositions can be used. For cobalt-based catalysts the optimal H2:CO ratio is around 1.8–2.1. Iron-based catalysts can tolerate lower ratios, due to intrinsic
water-gas shift reaction Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer okewith air and gasifying it with steam". The caloric yield of this is about 10% of a modern syngas plant. F ...
activity of the
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
catalyst. This reactivity can be important for synthesis gas derived from coal or biomass, which tend to have relatively low H2:CO ratios (< 1).


Design of the Fischer–Tropsch process reactor

Efficient removal of heat from the reactor is the basic need of FT reactors since these reactions are characterized by high exothermicity. Four types of reactors are discussed:


Multi tubular fixed-bed reactor

:This type of reactor contains a number of tubes with small diameter. These tubes contain catalyst and are surrounded by cooling water which removes the heat of reaction. A fixed-bed reactor is suitable for operation at low temperatures and has an upper temperature limit of 257 °C (530 K). Excess temperature leads to carbon deposition and hence blockage of the reactor. Since large amounts of the products formed are in liquid state, this type of reactor can also be referred to as a trickle flow reactor system.


Entrained flow reactor

:An important requirement of the reactor for the Fischer–Tropsch process is to remove the heat of the reaction. This type of reactor contains two banks of heat exchangers which remove heat; the remainder of which is removed by the products and recycled in the system. The formation of heavy waxes should be avoided, since they condense on the catalyst and form agglomerations. This leads to fluidization. Hence, risers are operated over 297 °C (570 K).


Slurry reactors

:Heat removal is done by internal cooling coils. The synthesis gas is bubbled through the waxy products and finely-divided catalyst which is suspended in the liquid medium. This also provides agitation of the contents of the reactor. The catalyst particle size reduces diffusional heat and mass transfer limitations. A lower temperature in the reactor leads to a more viscous product and a higher temperature (> 297 °C, 570 K) gives an undesirable product spectrum. Also, separation of the product from the catalyst is a problem.


Fluid-bed and circulating catalyst (riser) reactors

:These are used for high-temperature FT synthesis (nearly 340 °C) to produce low-molecular-weight unsaturated hydrocarbons on alkalized fused iron catalysts. The fluid-bed technology (as adapted from the catalytic cracking of heavy petroleum distillates) was introduced by Hydrocarbon Research in 1946–50 and named the 'Hydrocol' process. A large scale Fischer–Tropsch Hydrocol plant (350,000 tons per annum) operated during 1951–57 in Brownsville, Texas. Due to technical problems, and impractical economics due to increasing petroleum availability, this development was discontinued. Fluid-bed FT synthesis has recently been very successfully reinvestigated by Sasol. One reactor with a capacity of 500,000 tons per annum is now in operation and even larger ones are being built (nearly 850,000 tons per annum). The process is now used mainly for C2 and C7 alkene production. This new development can be regarded as an important progress in FT technology. A high-temperature process with a circulating iron catalyst ('circulating fluid bed', 'riser reactor', 'entrained catalyst process') was introduced by the Kellogg Company and a respective plant built at Sasol in 1956. It was improved by Sasol for successful operation. At Secunda, South Africa, Sasol operated 16 advanced reactors of this type with a capacity of approximately 330,000 tons per annum each. Now the circulating catalyst process is being replaced by the superior Sasol-advanced fluid-bed technology. Early experiments with cobalt catalyst particles suspended in oil have been performed by Fischer. The bubble column reactor with a powdered iron slurry catalyst and a CO-rich syngas was particularly developed to pilot plant scale by Kölbel at the Rheinpreuben Company in 1953. Recently (since 1990) low-temperature FT slurry processes are under investigation for the use of iron and cobalt catalysts, particularly for the production of a hydrocarbon wax, or to be hydrocracked and isomerised to produce diesel fuel, by Exxon and Sasol. Today slurry-phase (bubble column) low-temperature FT synthesis is regarded by many authors as the most efficient process for clean diesel production. This technology is also under development by the Statoil Company (Norway) for use on a vessel to convert associated gas at offshore oil fields into a hydrocarbon liquid.


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'')2''α''''n''−1 where ''W''''n'' 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

A variety of
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s can be used for the Fischer–Tropsch process, the most common are the
transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...
s
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
,
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
, and
ruthenium Ruthenium is a chemical element with the symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most other chemical ...
.
Nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
can also be used, but tends to favor methane formation (“
methanation Methanation is the conversion of carbon monoxide and carbon dioxide (COx) to methane (CH4) through hydrogenation. The methanation reactions of COx were first discovered by Sabatier and Senderens in 1902. CO''x'' methanation has many practical ap ...
”).


Cobalt

Cobalt-based catalysts are highly active, although iron may be more suitable for certain applications. Cobalt catalysts are more active for FT synthesis when the feedstock is natural gas. Natural gas has a high hydrogen to carbon ratio, so the water-gas shift is not needed for cobalt catalysts. Iron catalysts are preferred for lower quality feedstocks such as coal or biomass. Synthesis gases derived from these hydrogen-poor feedstocks has a low-hydrogen-content and require the water-gas shift reaction. Unlike the other metals used for this process (Co, Ni, Ru), which remain in the metallic state during synthesis, iron catalysts tend to form a number of phases, including various oxides and
carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of t ...
s during the reaction. Control of these phase transformations can be important in maintaining catalytic activity and preventing breakdown of the catalyst particles. 144px, Methylidyne­tricobalt­nonacarbonyl is a molecule that illustrates the kind of reduced carbon species speculated to occur in the Fischer–Tropsch process. In addition to the active metal the catalysts typically contain a number of "promoters," including potassium and copper. Group 1 alkali metals, including potassium, are a poison for cobalt catalysts but are promoters for iron catalysts. Catalysts are supported on high-surface-area binders/supports such as
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
, alumina, or
zeolites Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These p ...
. Promoters also have an important influence on activity. Alkali metal oxides and copper are common promoters, but the formulation depends on the primary metal, iron vs cobalt. Alkali oxides on cobalt catalysts generally cause activity to drop severely even with very low alkali loadings. C≥5 and CO2 selectivity increase while methane and C2–C4 selectivity decrease. In addition, the alkene to alkane ratio increases. FT catalysts are sensitive to poisoning by sulfur-containing compounds. Cobalt-based catalysts are more sensitive than their iron counterparts.


Iron

Fischer–Tropsch iron catalysts need alkali promotion to attain high activity and stability (e.g. 0.5 wt% ). 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 working catalyst is only obtained when—after reduction with hydrogen—in the initial period of synthesis several iron carbide phases and elemental carbon are formed whereas iron oxides are still present in addition to some metallic iron. With iron catalysts two directions of selectivity have been pursued. One direction has aimed at a low-molecular-weight olefinic hydrocarbon mixture to be produced in an entrained phase or fluid bed process (Sasol–Synthol process). Due to the relatively high reaction temperature (approx. 340 °C), the average molecular weight of the product is so low that no liquid product phase occurs under reaction conditions. The catalyst particles moving around in the reactor are small (particle diameter 100 µm) and carbon deposition on the catalyst does not disturb reactor operation. Thus a low catalyst porosity with small pore diameters as obtained from fused magnetite (plus promoters) after reduction with hydrogen is appropriate. For maximising the overall gasoline yield, C3 and C4 alkenes have been oligomerized at Sasol. However, recovering the olefins for use as chemicals in, e.g., polymerization processes is advantageous today. 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. Typically, such catalysts are obtained through precipitation from nitrate solutions. A high content of a carrier provides mechanical strength and wide pores for easy mass transfer of the reactants in the liquid product filling the pores. 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.


Ruthenium

Ruthenium Ruthenium is a chemical element with the symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most other chemical ...
is the most active of the Fischer–Tropsch catalysts. It works at the lowest reaction temperatures, and it produces the highest molecular weight hydrocarbons. It acts as a catalyst as the pure metal, without any promoters, thus providing the simplest catalytic system of FT synthesis, where mechanistic conclusions should be the easiest—e.g., much easier than with iron as the catalyst. Like with nickel, the selectivity changes to mainly methane at elevated temperature. Its high price and limited world resources exclude industrial application. Systematic studies with ruthenium catalysts should contribute substantially to the further exploration of the fundamentals of FT synthesis. There is an interesting question to consider: what features have the metals nickel, iron, cobalt, and ruthenium in common to let them—and only them—be FT catalysts, converting the CO/H2 mixture to aliphatic (long chain) hydrocarbons in a ‘one step reaction’. The term ‘one step reaction’ means that reaction intermediates are not desorbed from the catalyst surface. In particular, it is amazing that the much carbided alkalized iron catalyst gives a similar reaction as the just metallic ruthenium catalyst.


HTFT and LTFT

High-Temperature Fischer–Tropsch (or HTFT) is operated at temperatures of 330–350 °C and uses an iron-based catalyst. This process was used extensively by
Sasol Sasol Limited is an integrated energy and chemical company based in Sandton, South Africa. The company was formed in 1950 in Sasolburg, South Africa and built on processes that were first developed by German chemists and engineers in the early ...
in their
coal-to-liquid Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. This process is often known as "Coal to X" or "Carbon to X", where X can be many different hydrocarbon-based products. However, the most c ...
plants (CTL). Low-Temperature Fischer–Tropsch (LTFT) is operated at lower temperatures and uses an iron or cobalt-based catalyst. This process is best known for being used in the first integrated GTL-plant operated and built by
Shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
in
Bintulu Bintulu is a coastal town on the island of Borneo in the central region of Sarawak, Malaysia. Bintulu is located 610 kilometres (380 mi) northeast of Kuching, 216 kilometres (134 mi) northeast of Sibu, and 200 kilometres (120 mi) ...
, Malaysia.


History

Since the invention of the original process by Franz Fischer and Hans Tropsch, working at the Kaiser-Wilhelm-Institut for Chemistry in 1926, many refinements and adjustments were made. Fischer and Tropsch filed a number of patents, ''e.g.'', , applied 1926, published 1930. It was commercialized by
Brabag Brabag (Braunkohle Benzin AG) was a German firm, planned in 1933 and operating from 1934 until 1945, that distilled synthetic aviation fuel, diesel fuel, gasoline, lubricants, and paraffin wax from lignite. It was an industrial cartel firm closely ...
in Germany in 1936. Being petroleum-poor but coal-rich, Germany used the process during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
to produce ''
ersatz An ersatz good () is a substitute good, especially one that is considered inferior to the good it replaces. It has particular connotations of wartime usage. Etymology ''Ersatz'' is a German word literally meaning ''substitute'' or ''replacement ...
'' (replacement) fuels. FT production accounted for an estimated 9% of German war production of fuels and 25% of the automobile fuel. The
United States Bureau of Mines For most of the 20th century, the United States Bureau of Mines (USBM) was the primary United States government agency conducting scientific research and disseminating information on the extraction, processing, use, and conservation of mineral ...
, in a program initiated by the Synthetic Liquid Fuels Act, employed seven
Operation Paperclip Operation Paperclip was a secret United States intelligence program in which more than 1,600 German scientists, engineers, and technicians were taken from the former Nazi Germany to the U.S. for government employment after the end of World War ...
synthetic fuel Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by refo ...
scientists in a Fischer–Tropsch plant in
Louisiana, Missouri Louisiana is a city in Pike County, Missouri, United States. The population was 3,364 at the 2010 census. Louisiana is located in northeast Missouri, on the Mississippi River, south of Hannibal. Louisiana is located at the junction of State Rout ...
in 1946. In Britain, Alfred August Aicher obtained several
patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...
s 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 Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
. The products were fractionally distilled and the edible fats were obtained from the - fraction which were reacted with
glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
such as that synthesized from propylene. "Coal butter" margarine made from synthetic oils was found to be nutritious and of agreeable taste, and it was incorporated into diets contributing as much as 700 calories per day. The process required at least 60 kg of coal per kg of synthetic butter.


Commercialization


Ras Laffan, Qatar

The LTFT facility Pearl GTL at
Ras Laffan Ras Laffan Industrial City ( ar, راس لفان, Ra’s Lafān) is an industrial hub located north of Doha, Qatar. It is administrated by QatarEnergy. Ras Laffan Industrial City is Qatar's main site for production of liquefied natural gas and ...
, Qatar, is the second largest FT plant in the world after Sasol's Secunda plant in South Africa. It uses cobalt catalysts at 230 °C, converting natural gas to petroleum liquids at a rate of , with additional production of of oil equivalent in
natural gas liquids Natural-gas condensate, also called natural gas liquids, is a low-density mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields. Some gas species within the raw natu ...
and
ethane Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
. Another plant in Ras Laffan, called Oryx GTL, has been commissioned in 2007 with a capacity of . The plant utilizes the Sasol slurry phase distillate process, which uses a cobalt catalyst. Oryx GTL is a joint venture between QatarEnergy and
Sasol Sasol Limited is an integrated energy and chemical company based in Sandton, South Africa. The company was formed in 1950 in Sasolburg, South Africa and built on processes that were first developed by German chemists and engineers in the early ...
.


Sasol

The world's largest scale implementation of Fischer–Tropsch technology is a series of plants operated by
Sasol Sasol Limited is an integrated energy and chemical company based in Sandton, South Africa. The company was formed in 1950 in Sasolburg, South Africa and built on processes that were first developed by German chemists and engineers in the early ...
in
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
, a country with large coal reserves, but little oil. With a capacity of 165 000 Bpd at its Secunda plant. The first commercial plant opened in 1952. Sasol uses coal and now natural gas as feedstocks and produces a variety of synthetic petroleum products, including most of the country's
diesel fuel Diesel fuel , also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and ...
.


PetroSA

PetroSA PetroSA (The Petroleum, Oil and Gas Corporation of South Africa ( SOC) Ltd.) is the national oil company (NOC) of South Africa. Its main activities are the extraction of natural gas from offshore fields about 89 km from Mossel Bay, the prod ...
, 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 Bintulu is a coastal town on the island of Borneo in the central region of Sarawak, Malaysia. Bintulu is located 610 kilometres (380 mi) northeast of Kuching, 216 kilometres (134 mi) northeast of Sibu, and 200 kilometres (120 mi) ...
, Malaysia. This
Shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
facility converts
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon d ...
into low-
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
Diesel fuel Diesel fuel , also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and ...
s and food-grade wax. The scale is .


Velocys

Construction is underway for Velocys' commercial reference plant incorporating its microchannel Fischer–Tropsch technology; ENVIA Energy's Oklahoma City GTL project being built adjacent to Waste Management's East Oak landfill site. The project is being financed by a joint venture between Waste Management, NRG Energy, Ventech and Velocys. The feedstock for this plant will be a combination of
landfill gas Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane ...
and pipeline natural gas.


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, Tx 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 Finnish may refer to: * Something or someone from, or related to Finland * Culture of Finland * Finnish people or Finns, the primary ethnic group in Finland * Finnish language, the national language of the Finnish people * Finnish cuisine See also ...
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 Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
resulting from paper and pulp manufacturing processes as source material.


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, Colorado, the facility produces about of fuels from natural gas. Commercial-scale facilities were planned for
Rialto, California Rialto is a city in San Bernardino County, California, United States, 56 miles east of Los Angeles, near the Cajon Pass, Interstate 15, Interstate 10, State Route 210 and Metrolink routes. Its population was 104,026 as of the 2020 Census ...
;
Natchez, Mississippi Natchez ( ) is the county seat of and only city in Adams County, Mississippi, United States. Natchez has a total population of 14,520 (as of the 2020 census). Located on the Mississippi River across from Vidalia in Concordia Parish, Louisiana, ...
;
Port St. Joe, Florida Port St. Joe is a city located at the intersection of U.S. Highway 98 and State Road 71 and the county seat of Gulf County, Florida. As of the 2020 census,the population was 3,357. This was a decline from 3,644 as of the 2000 census. His ...
; and
White River, Ontario White River is a township located in Northern Ontario, Canada, along Highway 17 of the Trans-Canada Highway. It was originally a rail town on the Canadian Pacific Railway in 1885. Its main employers are Albert Bazzoni Ltd., A&W Restaurant, Tri ...
. 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

In 2010, INFRA built a compact Pilo
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 (Texas, USA). 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.


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 Coal refuse (also described as coal waste, rock, slag, coal tailings, waste material, rock bank, culm, boney, or gob) is the material left over from coal mining, usually as tailings piles or spoil tips. For every tonne of hard coal generated by mi ...
(leftovers from the mining process) into low-sulfur diesel fuel.


Research developments

Choren Industries has built a plant in
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
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 Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...
(BG) and Fischer–Tropsch (FT) synthesis can in principle be combined to produce renewable transportation fuels (
biofuel Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration ...
s).


Audi

In partnership with Sunfire,
Audi Audi AG () is a German automotive manufacturer of luxury vehicles headquartered in Ingolstadt, Bavaria, Germany. As a subsidiary of its parent company, the Volkswagen Group, Audi produces vehicles in nine production facilities worldwide. ...
produces E-diesel in small scale with two steps, the second one being FT.


U.S. Air Force certification

Syntroleum Syntroleum Corporation was a United States company engaged in development and commercialization of proprietary gas to liquids (GTL) and coal to liquids (CTL) processes known jointly as the Syntroleum Process. Renewable Energy Group acquired the ...
, a publicly traded United States company, has produced over of diesel and jet fuel from the Fischer–Tropsch process using natural gas and coal at its demonstration plant near
Tulsa, Oklahoma Tulsa () is the second-largest city in the state of Oklahoma and 47th-most populous city in the United States. The population was 413,066 as of the 2020 census. It is the principal municipality of the Tulsa Metropolitan Area, a region wit ...
. Syntroleum is working to commercialize its licensed Fischer–Tropsch technology via coal-to-liquid plants in the United States, China, and Germany, as well as gas-to-liquid plants internationally. Using natural gas as a feedstock, the ultra-clean, low sulfur fuel has been tested extensively by the
United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United States ...
(DOE) and the
United States Department of Transportation The United States Department of Transportation (USDOT or DOT) is one of the executive departments of the U.S. federal government. It is headed by the secretary of transportation, who reports directly to the President of the United States and ...
(DOT). Most recently, Syntroleum has been working with the
United States Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Si ...
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 The Boeing B-52 Stratofortress is an American long-range, subsonic, jet-powered strategic bomber. The B-52 was designed and built by Boeing, which has continued to provide support and upgrades. It has been operated by the United States Air ...
took off from
Edwards Air Force Base Edwards Air Force Base (AFB) is a United States Air Force installation in California. Most of the base sits in Kern County, but its eastern end is in San Bernardino County and a southern arm is in Los Angeles County. The hub of the base is ...
,
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
for the first time powered solely by a 50–50 blend of
JP-8 JP-8, or JP8 (for "Jet Propellant 8") is a jet fuel, specified and used widely by the US military. It is specified by MIL-DTL-83133 and British Defence Standard 91-87, and similar to commercial aviation's Jet A-1, but with the addition of corrosi ...
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 is part of the
Department of Defense Department of Defence or Department of Defense may refer to: Current departments of defence * Department of Defence (Australia) * Department of National Defence (Canada) * Department of Defence (Ireland) * Department of National Defense (Philipp ...
Assured Fuel Initiative, an effort to develop secure domestic sources for the military energy needs. The Pentagon hopes to reduce its use of crude oil from foreign producers and obtain about half of its aviation fuel from alternative sources by 2016. With the B-52 now approved to use the FT blend, the
C-17 Globemaster III The McDonnell Douglas/Boeing C-17 Globemaster III is a large military transport aircraft that was developed for the United States Air Force (USAF) from the 1980s to the early 1990s by McDonnell Douglas. The C-17 carries forward the name of t ...
, the
B-1B The Rockwell B-1 Lancer is a supersonic variable-sweep wing, heavy bomber used by the United States Air Force. It is commonly called the "Bone" (from "B-One"). It is one of three strategic bombers serving in the U.S. Air Force fleet along w ...
, and eventually every
airframe The mechanical structure of an aircraft is known as the airframe. This structure is typically considered to include the fuselage, undercarriage, empennage and wings, and excludes the propulsion system. Airframe design is a field of aerospa ...
in its inventory to use the fuel by 2011.


Carbon dioxide reuse

Carbon dioxide is not a typical 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
zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These p ...
s.


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 An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
. Similarly, the hypothetical
abiogenic petroleum The abiogenic petroleum origin is a fringe science which proposes that most of earth's petroleum and natural gas deposits were formed inorganically. Mainstream theories about the formation of hydrocarbons on earth point to an origin from the decompo ...
formation requires some naturally occurring FT-like processes.


See also

* * * * , a generic term for this type of process * * * * * *


References


Further reading

* * * *


External links


Fischer–Tropsch archives

Fischer–Tropsch fuels from coal and biomass

Abiogenic gas debate (AAPG Explorer Nov. 2002)

Gas origin theories to be studied (AAPG Explorer Nov. 2002)


* '' ttps://web.archive.org/web/20051106005801/http://www.fischer-tropsch.org/primary_documents/patents/GB/gb309002.pdf Process of synthesis of liquid hydrocarbons' – Great Britain patent GB309002 –
Hermann Plauson Hermann Plauson was an Estonian professor, engineer and inventor. Plauson investigated, among other things, the production of power based on atmospheric electricity. Biography Plauson was the director of the Fischer–Tropsch "'' Otto Traun R ...
*
Clean diesel from coal
' by Kevin Bullis *
Implementing the “Hydrogen Economy” with Synfuels (pdf)
'
Carbon-to-liquids research

Effect of alkali metals on cobalt catalysts
{{DEFAULTSORT:Fischer-Tropsch Process Biofuels technology Catalysis Coal Organometallic chemistry Petroleum production Synthetic fuel technologies German inventions 1925 in science 1925 in Germany Organic redox reactions Name reactions