Do-it-yourself fisher tropsch process. Catalyst for the Fischer-Tropsch process (variants) and method for its preparation. Ideas about key reactions in catalysis

Fischer-Tropsch synthesis is a chemical process that is a key step in the most modern method for producing synthetic fuels. Why do they say “synthesis” or “process” and avoid the word “reaction”? Individual reactions are usually named after scientists, in this case Franz Fischer and Hans Tropsch. The fact is that there is no Fischer-Tropsch reaction as such. This is a complex of processes. There are only three main reactions in this process, and there are at least eleven of them. In general, Fischer-Tropsch synthesis is the conversion of so-called synthesis gas into a mixture of liquid hydrocarbons. Chemist Vladimir Mordkovich on methods for producing synthetic fuel, new types of catalysts and the Fischer-Tropsch reactor.

Vladimir Mordkovich - Doctor of Chemical Sciences, Department of Physics and Chemistry of Nanostructures at MIPT, Head of the Department of New Chemical Technologies and Nanomaterials at TISNUM, Scientific Director of the Infra Technologies company.

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Shale natural gas (eng. shale gas) is natural gas extracted from oil shale and consisting primarily of methane. Oil shale is a solid mineral of organic origin. Shales were mainly formed 450 million years ago on the seabed from plant and animal remains.

Alexandra Poshibaeva

Today there are two main hypotheses for the formation of oil: inorganic (abiogenic) and organic (biogenic, also called sedimentary-migration). Proponents of the inorganic concept believe that oil was formed from carbon and hydrogen through the Fischer-Tropsch process at great depths, at enormous pressures and temperatures above a thousand degrees. Normal alkanes can be formed from carbon and hydrogen in the presence of catalysts, but such catalysts do not exist in nature. In addition, oils contain a huge amount of isoprenanes, cyclic hydrocarbons-biomarkers, which cannot be formed by the Fischer-Tropsch process. Chemist Alexandra Poshibaeva talks about the search for new oil deposits, the inorganic theory of its origin and the role of prokaryotes and eukaryotes in the formation of hydrocarbons.

Andrey Bychkov

Hydrocarbons today are the energy basis of our civilization. But how long will the fossil fuel deposits last and what to do after they are depleted? Like other minerals, we will have to develop raw materials with a lower content of useful components. How to make oil, from what raw materials? Will this be beneficial? Already today we have a lot of experimental data. The lecture will discuss questions about the processes of oil formation in nature and show new experimental results. Andrey Yurievich Bychkov, Doctor of Geological and Mineralogical Sciences, Professor of the Russian Academy of Sciences, Professor of the Department of Geochemistry at Moscow State University, will tell you about all this.

Elena Naimark

American scientists have learned to obtain optical isomers of aldehyde-based compounds, finally carrying out an important reaction that chemists have been working on for many years. In the experiment, they combined two catalysts operating on different principles. As a result of the combined action of these catalysts, two active organic molecules are formed, which combine to form the desired substance. Using this reaction as an example, the possibility of synthesizing a whole class of biologically important organic compounds is demonstrated.

Elena Naimark

The followers of Stanley Miller, who carried out famous experiments in the 50s to simulate the synthesis of organic matter in the primary atmosphere of the Earth, again turned to the results of old experiments. They examined the materials remaining from those years using the latest methods. It turned out that in experiments that simulated volcanic emissions of a vapor-gas mixture, a wide range of amino acids and other organic compounds were synthesized. Their diversity turned out to be greater than it was imagined in the 50s. This result focuses the attention of modern researchers on the conditions of synthesis and accumulation of primary high-molecular organics: synthesis could be activated in areas of eruptions, and volcanic ash and tuffs could become a reservoir of biological molecules.

Korolev Yu. M.

We asked Yu.M. to tell us how scientists are trying to unravel the mystery of the origin of oil, or more precisely, petroleum hydrocarbons. Korolev - leading researcher at the Institute of Petrochemical Synthesis named after. A.V. Topchieva. He has been studying the X-ray phase composition of fossil hydrocarbon minerals and their transformation under the influence of time and temperature for more than thirty years.

Rodkin M.V.

The debate about the biogenic (organic) or abiogenic origin of oil is especially interesting for the Russian reader. Firstly, hydrocarbon raw materials are one of the main sources of income in the country’s budget, and secondly, Russian scientists are recognized leaders in many areas in this old, but still not closed scientific dispute.

Alexander Markov

A variety of organic substances have been discovered in space, but little is known about the mechanisms of their formation. Astrophysicists and chemists from France, Denmark and Mexico have experimentally shown that under conditions simulating the early stages of the formation of planetary systems, all kinds of carbohydrates are formed in water ice mixed with methanol and ammonia under the influence of ultraviolet radiation, including ribose, the most important component of RNA. The authors suggest that the chemical process leading to the synthesis of these carbohydrates is similar to the Butlerov autocatalytic reaction, although it does not require the presence of divalent metal ions.

Elena Naimark

The world of RNA was preceded by a time of prebiological synthesis, when molecules necessary for replication were born - nucleotides, proteins, lipids. Previously, chemists considered the processes of their synthesis separately. Now, in the laboratory of John Sutherland, a path has been found that leads to the synthesis of a large set of biological molecules at once. There is no need to guess what came first, RNA or proteins - they were probably synthesized simultaneously in a single cascade of chemical reactions; at the beginning it appears hydrogen cyanide and hydrogen sulfide with metal catalysts. The authors called this network of reactions cyanosulfide protometabolism. With the release of a new study, we can talk about a turning point in the science of the origin of life.

Dmitry Grishchenko

Much and often is written about shale oil and gas production. At the lecture we will try to figure out what this technology is, what environmental problems are associated with it, and which are just a figment of the imagination of journalists and environmentalists.

Fischer-Tropsch synthesis

The technology for producing synthetic fuel from hydrocarbon gas GTL (gas-to-liquid, i.e. “gas-to-liquid”) began to develop in the 20s of the last century thanks to the invention of the Fischer-Tropsch synthesis reaction. At that time, in coal-rich but oil-poor Germany, the issue of liquid fuel production was acute. Since the invention of the process by German researchers Franz Fischer and Hans Tropsch, many improvements and revisions have been made, and the name "Fischer-Tropsch" is now applied to a large number of similar processes. GTL technology, as such, is almost a hundred years old, and it has been developing for many years as a forced alternative to oil production for countries without access to oil. The development of GTL proceeded in stages, over generations. The first generation of GTL is responsible for the German ersatz gasoline that was widely known during the Great Patriotic War. The second developed in South Africa as a response to the international embargo. Third - in Western countries after the energy crisis of 1973. With each new generation of technology, capital costs decreased, the yield of motor fuel per ton of raw materials increased, and by-products became less and less.

The development of technology for processing natural gas into synthetic oil is especially important for Russia for several reasons. Firstly, due to the presence of large gas deposits in Siberia. The technology makes it possible to process gas directly on site and use existing oil pipelines for transportation, which is more economically profitable. Secondly, GTL makes it possible to utilize associated gases from oil fields, as well as refinery blow-off gases, which are usually burned “on a candle”. Thirdly, motor fuels obtained using this technology are superior to petroleum analogues in terms of operational and environmental indicators.

From solid hydrocarbons (usually coal):

C + H 2 O → C O + H 2 (\displaystyle (\mathsf (C+H_(2)O\rightarrow CO+H_(2))))

To do this, superheated water vapor was blown through a layer of hot coal. The product was so-called water gas - a mixture of carbon monoxide (carbon monoxide) and hydrogen. The Fischer-Tropsch process is further described by the following chemical equation:

C O + 2 H 2 → - C H 2 - + H 2 O (\displaystyle (\mathsf (CO+2H_(2)\rightarrow (\text(-))CH_(2)(\text(-))+H_( 2)O))) 2 C O + H 2 → - C H 2 - + C O 2 (\displaystyle (\mathsf (2CO+H_(2)\rightarrow (\text(-))CH_(2)(\text(-))+CO_(2 ))))

The mixture of carbon monoxide and hydrogen is called synthesis gas, or syngas, and the term "water gas" is also used.

The mixture of resulting hydrocarbons is purified to obtain the target product - synthetic gasoline. The production of heavier fuels by the Fischer-Tropsch method is not economically profitable due to the rapid poisoning of the catalyst.

After the war, captured German scientists participated in Operation Paperclip, continuing to work on synthetic fuels for the United States Bureau of Mines.

For the first time, the synthesis of hydrocarbons from a mixture of CO and H 2 was carried out at the beginning of the 20th century: methane was synthesized by Sabatier and Sanderens, ethylene was synthesized by E.I. Orlov. In 1913 the company BASF acquired a patent for the production of mixtures of hydrocarbons and alcohols from synthesis gas over alkalized Co-Os catalysts (later this direction resulted in the creation of a process for the synthesis of methanol). In 1923, German chemists F. Fischer and H. Tropsch, employees of the company Ruhrchemie, reported the production of oxygen-containing products from synthesis gas over Fe catalysts, and in 1926 - hydrocarbons. The first industrial reactor was launched in Germany in 1935, using a Co-Th precipitated catalyst. In the 30s and 40s. Based on Fischer-Tropsch technology, the production of synthetic gasoline (Kogazin-I, or syntin) with an octane number of 40–55, a synthetic high-quality diesel fraction (Kogazin-II) with a cetane number of 75–100, and solid paraffin was established. The raw material for the process was coal, from which synthesis gas was obtained through gasification, and from it hydrocarbons. By 1945, there were 15 Fischer-Tropsch synthesis plants in the world (in Germany, the USA, China and Japan) with a total capacity of about 1 million tons of hydrocarbons per year. They produced mainly synthetic motor fuels and lubricating oils.

In the years after World War II, Fischer-Tropsch synthesis received a lot of attention around the world because it was believed that oil reserves were running out and a replacement needed to be found. In 1950, a plant was launched in Brownsville (Texas) with a capacity of 360 thousand tons/year. In 1955, a South African company Sasol built its own production, which still exists and develops today. Since 1952, a plant with a capacity of about 50 thousand tons/year has been operating in Novocherkassk, using equipment exported from Germany. The raw material was first coal from the Donetsk basin, and then natural gas. The German Co-Th catalyst was eventually replaced by the original Co-Zr. The plant was equipped with a precision distillation column so that the plant's product range included individual hydrocarbons of high purity, including odd carbon number α-olefins. The installation operated at the Novocherkassk Synthetic Products Plant until the 90s. twentieth century and was stopped for economic reasons.

All these enterprises largely borrowed the experience of German chemists and engineers accumulated in the 30s and 40s.

The discovery of vast oil deposits in Arabia, the North Sea, Nigeria, and Alaska sharply reduced interest in Fischer-Tropsch synthesis. Almost all existing factories were closed, the only large production remaining in South Africa. Activity in this area resumed by the 1990s.

In 1990 the company Exxon launched a pilot plant for 8 thousand tons/year with a Co catalyst. In 1992, a South African company Mossgas built a plant with a capacity of 900 thousand tons/year. Unlike technology Sasol, natural gas from an offshore field was used as a raw material. In 1993 the company Shell launched a plant in Bintulu (Malaysia) with a capacity of 500 thousand tons/year, using a Co-Zr catalyst and original “middle distillate” technology. The raw material is synthesis gas obtained by partial oxidation of local natural gas. Currently Shell is building a plant using the same technology, but with an order of magnitude greater capacity in Qatar. Companies also have their own projects in the field of Fischer-Tropsch synthesis of varying degrees of development Chevron, Conoco, , ENI , Statoil, Rentech, Syntroleum and etc.

Scientific basis of the process

Fischer-Tropsch synthesis can be thought of as a reductive oligomerization of carbon monoxide:

n C O + (2 n + 1) H 2 → C n H 2 n + 2 + n H 2 O (\displaystyle (\mathsf (nCO+(2n+1)H_(2)\rightarrow C_(n)H_(2n +2)+nH_(2)O))) n C O + 2 n H 2 → C n H 2 n + n H 2 O (\displaystyle (\mathsf (nCO+2nH_(2)\rightarrow C_(n)H_(2n)+nH_(2)O)))

Typical process conditions are: pressure from 1 atm (for Co catalysts) to 30 atm, temperature 190–240 °C (low-temperature synthesis option, for Co and Fe catalysts) or 320–350 °C (high-temperature option, for Fe).

The mechanism of the reaction, despite decades of study, remains unclear in detail. However, this poor knowledge of reactions is typical for heterogeneous catalysis.

Thermodynamic laws for Fischer-Tropsch synthesis products are as follows.

1. It is possible to form hydrocarbons of any molecular weight, type and structure from CO and H 2 except acetylene, the formation of which is energetically unfavorable.
2. The probability of hydrocarbon formation decreases in the order: methane > other alkanes > alkenes. The probability of forming normal alkanes decreases and normal alkenes increases with increasing chain length.
3. An increase in the total pressure in the system promotes the formation of heavier products, and an increase in the partial pressure of hydrogen in the synthesis gas favors the formation of alkanes.

The actual composition of the products of hydrocarbon synthesis from CO and H 2 differs significantly from the equilibrium one. In most cases, the distribution of products by molecular weight under stationary conditions is described by the formula p(n) = n(1-α)²α n-1, where p(n) is the mass fraction of hydrocarbon with carbon number n, α = k 1 /(k 1 +k 2), k 1, k 2 - rate constants for chain growth and termination, respectively. This is the so-called Anderson-Schultz-Flory distribution (ASF distribution). Methane (n=1) is always present in greater quantities than predicted by the ASF distribution, since it is formed independently by direct hydrogenation reaction. The value of α decreases with increasing temperature and, as a rule, increases with increasing pressure. If the reaction produces products of different homologous series (paraffins, olefins, alcohols), then the distribution for each of them may have its own α value. The distribution of ASF imposes restrictions on the maximum selectivity for any hydrocarbon or narrow fraction. This is the second problem after the problem of reaction heat removal in Fischer-Tropsch synthesis.

Syntheses based on carbon monoxide and hydrogen

Process	Catalyst	Catalyst carrier	Temperature, °C	Pressure, MPa	Product
Methane synthesis	Ni	ThO 2 or MgO	250౼500	0,1	Methane
Synthesis of higher hydrocarbons	Co,Ni	ThO 2 , MgO, ZrO 2	150౼200	0.1౼1	A mixture of paraffins and olefins with a carbon chain length of C1౼C100
Synthesis of higher hydrocarbons and oxygen-containing compounds	Fe	Cu, NaOH (KOH), Al 2 O 3, SiO 2	200౼230	0.1౼3	Mainly paraffins and olefins mixed with oxygen-containing compounds
Synthesis of paraffins	Co	TiO 2 , ZrO 2 , ThO 2 , MgO	190౼200	1	Mainly hard paraffins with a melting point of 70-98°C
	Ru	MgO	180౼200	10౼100	High molecular weight paraffins
Isosynthesis	ZrO 2, ThO 2, Al 2 O 3	K2CO3	400౼450	10	Paraffins and olefins are predominantly of isoconstruction
	ThO 2	౼	350౼500	10౼100	Isoparaffins and aromatic hydrocarbons
Methanol synthesis	ZnO, Cr 2 O 3, CuO	౼	200౼400	5౼30	Methanol
Synthesis of higher alcohols	Fe, Fe-Cr, Zn-Cr	Al 2 O 3 , NaOH	180౼220,	1౼3, 15౼25	Methanol and higher alcohols

Usage

Currently, two companies are commercializing their technologies based on the Fischer-Tropsch process. Shell in Bintulu uses natural gas as a feedstock and produces predominantly low sulfur diesel fuel. In 1955 in Sasolburg (South Africa) the company Sasol commissioned the first plant for the production of liquid fuel from coal using the Fischer-Tropsch method. Coal comes directly from coal mines through a conveyor to produce synthesis gas. Then the Sasol-2 and Sasol-3 plants were built. The process was used to meet energy needs during isolation under the apartheid regime. Attention to this process has renewed in the search for ways to produce low-sulfur diesel fuels to reduce the environmental damage caused by diesel engines. Currently, South Africa produces 5౼6 million tons of hydrocarbons per year using this method. However, the process is unprofitable and is subsidized by the state as a national treasure. Production in South Africa is focused not so much on the production of motor fuel, but on the production of individual more valuable fractions, for example, lower olefins.

Small American company Rentech is currently focused on converting nitrogen fertilizer plants from using natural gas as feedstock to using coal or coke and liquid hydrocarbons as a by-product.

Choren in Germany and Changing World Technologies (CWT) built factories using the Fischer-Tropsch process or similar.

The Fischer-Tropsch process is a mature technology already in use on a large scale, although its adoption is hampered by high capital costs, high operating and maintenance costs and relatively low crude oil prices. In particular, the use of natural gas as a feedstock becomes expedient when “stranded gas” is used, i.e. natural gas sources located far from the main cities, which are impractical to operate with conventional gas pipelines and LNG technology.

There are large reserves of coal that can be used as a source of fuel as oil reserves are depleted. Since coal is available in huge quantities around the world, this technology can be used temporarily if conventional oil becomes more expensive. The combination of biomass gasification and Fischer-Tropsch synthesis is a promising way to produce renewable or green automotive fuels. Synthetic fuel made from coal is competitive when oil prices are above $40. per barrel The capital investments that need to be made range from 7 to 9 billion dollars. for 80 thousand barrels. capacity for the production of synthetic fuel from coal. For comparison, similar oil refining capacities cost about $2 billion.

At the beginning of 2006, projects for the construction of 9 indirect coal liquefaction plants with a total capacity of 90–250 thousand barrels were considered in the United States. in a day.

China plans to invest $15 billion. until 2010౼2015 in the construction of plants for the production of synthetic fuel from coal. The National Development and Reform Commission (NDRC) said that the total capacity of coal liquefaction plants will reach 16 million tons of synthetic fuel per year, which is 5% of oil consumption in 2005 and 10% of oil imports.

In 2015, the INFRA Group, which developed and patented a new generation of technology for the production of liquid synthetic fuels based on the Fischer-Tropsch synthesis process from natural or associated gas (GTL), biomass and coal (XTL), commissioned a catalyst factory. The production facility, with a capacity of 15 tons per year, produces a patented catalyst for the Fischer-Tropsch synthesis reaction, developed by company specialists. The task of the factory is to produce catalysts for GTL INFRA plants, as well as to develop processes for the production of new modifications of the catalyst on an industrial scale. In 2016, INFRA designed and built a modular, transportable GTL (gas-to-liquids) plant for processing natural and associated gas into synthetic oil M100 in Wharton (Texas, USA). The company's plans include commercial operation of the plant and sale of synthetic oil. At the request of an oil and gas company, the INFRA group began designing a GTL plant, which is planned to be located in the Nenets Autonomous Okrug. The plant, with a capacity of 20 thousand petroleum products per year, will produce winter diesel fuel and high-octane gasoline from natural gas from the Vasylkivskoye gas condensate field. The implementation of the gas processing plant construction plan using INFRA's advanced GTL technology will provide the market of the Nenets Autonomous Okrug with high-quality commercial fuel - diesel and gasoline - and significantly reduce the cost of purchasing expensive northern supplies. The development of a feasibility study for construction was carried out in 2017, the design will be completed in 2019. (see http://ru.infratechnology.com/info/).

Technologies for processing coal into liquid fuel raise many questions from environmentalists. The most serious problem is carbon dioxide emissions. Recent work from the National Renewable Energy Laboratory has shown that full-cycle greenhouse gas emissions for coal-derived synthetic fuels are about twice as high as their gasoline-based equivalents. Emissions of other pollutants have also increased greatly, although many of them can be collected during production. Carbon burial has been proposed as a way to reduce carbon monoxide emissions. Upload C O 2 (\displaystyle CO_(2)) into oil reservoirs will increase oil production and increase the service life of fields by 20-25 years, however, the use of this technology is possible only with stable oil prices above 50-55 dollars. per barrel An important problem in the production of synthetic fuels is the high water consumption, the level of which is from 5 to 7 gallons for every gallon of fuel produced.

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The article is devoted to the use of synthesis gas as an alternative feedstock to oil for the production of artificial liquid fuels, hydrocarbons (Fischer-Tropsch synthesis) and aldehydes (hydroformylation or oxo-synthesis). The mechanisms of the reactions under consideration are discussed.

INTRODUCTION

History knows many examples when, due to urgent need, new original approaches to solving long-existing vital problems were born. Thus, in pre-war Germany, deprived of access to oil sources, a severe shortage of fuel necessary for the functioning of powerful military equipment was brewing. Having significant reserves of fossil coal, Germany was forced to look for ways to convert it into liquid fuel. This problem was successfully solved by the efforts of excellent chemists, of whom above all should be mentioned Franz Fischer, director of the Kaiser Wilhelm Institute for Coal Research.

In 1926, the work of F. Fischer and G. Tropsch “On the direct synthesis of petroleum hydrocarbons at ordinary pressure” was published, in which it was reported that when carbon monoxide is reduced with hydrogen at atmospheric pressure in the presence of various catalysts (iron - zinc oxide or cobalt - oxide chromium) at 270°C, liquid and even solid homologues of methane are obtained.

This is how the famous synthesis of hydrocarbons from carbon monoxide and hydrogen arose, since then called the Fischer-Tropsch synthesis. A mixture of CO and H 2 in various proportions, called synthesis gas, can easily be obtained from coal or any other carbon-containing raw material.

It should be noted that by the time the Fischer-Tropsch synthesis was developed, there was another method for producing liquid fuel - not from synthesis gas, but directly from coal by direct hydrogenation. The German chemist F. Bergius also achieved significant success in this area, who in 1911 obtained gasoline from coal. To be fair, we emphasize that the Fischer-Tropsch synthesis did not arise out of nowhere - by that time there were scientific prerequisites that were based on the achievements of organic chemistry and heterogeneous catalysis. Back in 1902, P. Sabatier and J. Sanderan first obtained methane from CO and H 2. In 1908, E. Orlov discovered that when carbon monoxide and hydrogen are passed over a catalyst consisting of nickel and palladium supported on coal, ethylene is formed.

The artificial liquid fuel industry achieved its greatest growth during the Second World War. Suffice it to say that synthetic fuel almost completely covered Germany’s needs for aviation gasoline. After 1945, due to the rapid development of oil production and the fall in oil prices, the need to synthesize liquid fuels from CO and H 2 disappeared. The petrochemical boom has arrived. However, in 1973, the oil crisis broke out - the oil-producing countries of OPEC (Organization of Petroleum Exporting Countries) sharply increased prices for crude oil, and the world community was forced to realize the real threat of depletion of cheap and accessible oil resources in the foreseeable future. The energy shock of the 70s revived the interest of scientists and industrialists in the use of raw materials alternative to oil, and here the first place undoubtedly belongs to coal. The world's coal reserves are huge; according to various estimates, they are more than 50 times greater than oil resources, and they can last for hundreds of years. There is no doubt that in the foreseeable future the use of synthesis gas will play a key role not only and not so much for the production of “coal” fuels (here it is still difficult to compete with oil fuels), but primarily for the purposes of organic synthesis. Currently, gasoline, gas oil and paraffins are produced on an industrial scale using the Fischer-Tropsch method only in South Africa. Sasol installations produce about 5 million tons of liquid hydrocarbons per year.

A reflection of the intensification of research on syntheses based on CO and H 2 is a sharp increase in publications devoted to the chemistry of one-carbon molecules (the so-called C 1 chemistry). Since 1984, the international journal "C1-Molecule Chemistry" began to be published. Thus, we are witnessing an upcoming renaissance in the history of coal chemistry. Let's consider some ways of converting synthesis gas, leading to the production of both hydrocarbons and some valuable oxygen-containing compounds. The most important role in CO transformations belongs to heterogeneous and homogeneous catalysis.

PRODUCTION OF SYNTHESIS GAS

The first method of producing synthesis gas was the gasification of coal, which was carried out back in the 30s of the 19th century in England with the aim of producing flammable gases: hydrogen, methane, carbon monoxide. This process was widely used in many countries until the mid-1950s, and was then replaced by methods based on the use of natural gas and oil. However, due to the reduction of oil resources, the importance of the gasification process began to increase again.

Currently, there are three main industrial methods for producing synthesis gas.

1. Gasification of coal. The process is based on the interaction of coal with water vapor:

C + H 2 O = H 2 + CO.

This reaction is endothermic, the equilibrium shifts to the right at temperatures of 900-1000°C. Technological processes have been developed that use steam-oxygen blasting, in which, along with the mentioned reaction, an exothermic reaction of coal combustion occurs, providing the required heat balance:

C + 1/2O 2 = CO.

2. Methane conversion. The reaction between methane and water vapor is carried out in the presence of nickel catalysts (Ni-Al 2 O 3) at elevated temperatures (800-900°C) and pressure:

CH 4 + H 2 O = CO + 3H 2.

Any hydrocarbon raw material can be used as a raw material instead of methane.

3. Partial oxidation of hydrocarbons. The process consists of incomplete thermal oxidation of hydrocarbons at temperatures above 1300°C:

C n H 2n+2 + 1/2nO 2 = nCO + (n + 1)H 2 .

The method is applicable to any hydrocarbon feedstock, but the most commonly used in industry is the high-boiling fraction of oil - fuel oil.

The CO:H 2 ratio significantly depends on the method used for producing synthesis gas. With coal gasification and partial oxidation, this ratio is close to 1: 1, while with methane conversion, the CO: H 2 ratio is 1: 3. Projects for underground gasification, that is, gasification of coal directly in the seam, are currently being developed. It is interesting that this idea was expressed by D.I. Mendeleev more than 100 years ago. In the future, synthesis gas will be produced by gasification not only of coal, but also of other carbon sources, including urban and agricultural waste.

CARBON MONOXIDE, METAL CARBONYLS AND THE 18 ELECTRON RULE

Numerous syntheses based on carbon monoxide and hydrogen are of enormous practical and theoretical interest, since they make it possible to obtain valuable organic compounds from two simple substances. And here the decisive role is played by catalysis by transition metals, which are capable of activating inert molecules CO and H 2 . Activation of molecules is their transfer to a more reactive state. It should be especially noted that in the transformations of synthesis gas, a new type of catalysis has been widely developed - catalysis by transition metal complexes or metal complex catalysis (see article by O.N. Temkin).

Is the CO molecule really that inert? The idea of ​​the inertness of carbon monoxide is conditional. Back in 1890, Mond obtained from metallic nickel and carbon monoxide the first carbonyl compound of a metal, a volatile liquid with a boiling point of 43°C - Ni(CO) 4 . The history of this discovery, which can be attributed to chance, is interesting. Mond, studying the causes of rapid corrosion of nickel reactors in the production of soda from NaCl, ammonia and CO 2, found that the cause of corrosion was the presence of carbon monoxide impurities in CO 2, which reacted with nickel to form tetracarbonyl Ni(CO) 4. This discovery allowed Mond to further develop methods for purifying nickel through the production of volatile nickel carbonyl and its subsequent thermal decomposition back to nickel and CO. 25 years later, iron carbonyl - Fe(CO) 5 - was also accidentally discovered. When a long-forgotten steel cylinder containing CO was opened at BASF, a yellow liquid was found at the bottom - iron pentacarbonyl, which was gradually formed as a result of the reaction of metallic iron with CO under elevated pressure. Since metal carbonyls are very toxic compounds, at first the attitude of chemists towards them was very cool, but later amazing properties were discovered, including catalytic ones, which determined their widespread use, especially in the chemistry of carbon monoxide. Note that many metals in a finely dispersed state can directly react with carbon monoxide, but only nickel and iron carbonyls are obtained in this way. Carbonyls of other metals are obtained by reducing their compounds in the presence of CO at high pressures.

The composition of transition metal carbonyl complexes can be predicted based on the 18 electron rule, according to which the complex will be stable if the sum of the valence electrons of the metal and the electrons provided by the ligand, in our case CO, is equal to 18, since in this case the electronic configuration corresponds to the stable configuration of the noble atoms gases (krypton).

The carbon monoxide molecule has lone pairs of electrons, and a pair of electrons on the carbon can be provided to form a donor-acceptor bond with the metal. As an example, consider the structure of iron and nickel carbonyls Fe(CO) 5 and Ni(CO) 4. The iron and nickel atoms have 8 and 10 valence electrons, respectively, and to fill the electron shell of the atom to the configuration of the noble gas atom krypton, 10 and 8 electrons are missing, and therefore, when carbonyls are formed, the iron atom must be provided with electron pairs by five CO molecules, and the nickel atom - four .

Transition metals having an odd number of valence electrons form binuclear carbonyl complexes. Thus, for cobalt, which has nine valence electrons, nine electrons are missing from a stable electronic configuration. Mononuclear complexes, by accepting four pairs from CO molecules, will have unpaired electrons, and such particles of a radical nature interact with each other to form a metal-metal bond, and as a result, a dimeric complex Co 2 (CO) 8 is formed.

The interaction or coordination of carbon monoxide with a metal leads to a redistribution of electron density not only on CO, but also on the metal, which significantly affects the reactivity of the carbonyl complex. The most common is the so-called linear type of coordination of CO:

In this case, not only the s-interaction occurs due to a free pair of carbon electrons, but also the p-interaction due to the transfer of electrons from the d-orbital of the metal to the energetically accessible vacant orbitals of carbon:

VIEWS ABOUT KEY REACTIONS IN CATALYSIS

Let us note several important key reactions in metal complex catalysis. These are primarily oxidative addition and reductive elimination reactions. Oxidative addition is the addition of neutral AB molecules, such as H2 or halogen, to the metal center of the complex. In this case, the metal is oxidized, which is accompanied by an increase in its coordination number:

where L is the ligand. This addition is accompanied by cleavage of the A-B bond.

The reaction of oxidative addition of a hydrogen molecule, as a result of which its activation occurs, is very important. The reaction of oxidative addition of hydrogen to a square planar complex of monovalent iridium, discovered by Vasco and Dilucio, became widely known. As a result, the oxidation state of iridium increases from I to III:

The reaction opposite to oxidative addition is called reductive elimination, in which the oxidation number and coordination number of the metal are reduced by two.

Let us also note the reaction of migration introduction, which consists in the introduction of unsaturated compounds through the metal-carbon and metal-hydrogen bonds. The CO introduction reaction is key for many processes involving synthesis gas:

The introduction of olefin is the most important reaction among the catalytic transformations of olefins: hydrogenation, hydroformylation, etc.

FISCHER-TROPSCH SYNTHESIS

Fischer-Tropsch synthesis can be considered as a reductive oligomerization reaction of carbon monoxide in which carbon-carbon bonds are formed, and in general it is a complex combination of a number of heterogeneous reactions that can be represented by the summary equations:

nCO + 2nH 2 = (CH 2) n + nH 2 O,
2nCO + nH 2 = (CH 2) n + nCO 2.

The reaction products are alkanes, alkenes and oxygen-containing compounds, that is, a complex mixture of products is formed, characteristic of a polymerization reaction. The primary products of the Fischer-Tropsch synthesis are a- and b-olefins, which are converted to alkanes as a result of subsequent hydrogenation. The nature of the catalyst used, temperature, and the ratio of CO and H 2 significantly affect the distribution of products. Thus, when using iron catalysts, the proportion of olefins is high, while in the case of cobalt catalysts, which have hydrogenating activity, saturated hydrocarbons are predominantly formed.

Currently, as catalysts for Fischer-Tropsch synthesis, depending on the objectives (increasing the yield of gasoline fraction, increasing the yield of lower olefins, etc.), both highly dispersed iron catalysts supported on oxides of aluminum, silicon and magnesium, and bimetallic catalysts: iron - manganese, iron-molybdenum, etc.

In the 70 years since the discovery of the synthesis, controversy over the reaction mechanism has not subsided. Three different mechanisms are currently being considered. The first mechanism, called the carbide mechanism, first proposed by Fischer and Tropsch and later supported by other researchers, involves the formation of C-C bonds as a result of the oligomerization of methylene fragments on the surface of the catalyst. At the first stage, CO is adsorbed and surface carbide is formed, and oxygen is converted into water or CO 2:

In the second stage, the surface carbide is hydrogenated to form CH x fragments (x = 1-3):

Chain elongation occurs as a result of the reaction of surface methyl and methylene, and then the chain grows through the introduction of methylene groups:

The chain termination stage occurs as a result of desorption of the alkene from the catalyst surface:

The second mechanism, called hydroxycarbene, also involves the hydrogenation of CO coordinated on the metal with the formation of surface hydroxycarbene fragments, as a result of the condensation of which the formation of C-C bonds occurs:

The third mechanism, which can be called the insertion mechanism, involves the formation of C-C bonds as a result of the introduction of CO into the metal-carbon bond (the ability of CO to insert into the metal-alkyl bond was discussed above):

Quite a wealth of experimental material has been accumulated, indicating in favor of one or another version of the mechanism, but it must be stated that at the present time it is impossible to make a clear choice between them. It can be assumed that due to the great importance of the Fischer-Tropsch synthesis, research in this direction will continue intensively and we will witness new views on the mechanisms of the reactions occurring.

HYDROFORMYLATION OF OLEFINS

One of the most important examples of industrial processes involving synthesis gas is the hydroformylation reaction (oxo-synthesis). In 1938, Rehlen, while studying the mechanism of the Fischer-Tropsch synthesis, discovered this remarkable reaction, the importance of which is difficult to overestimate. In this process, alkenes, in the presence of catalysts, mainly cobalt or rhodium, at pressures above 100 atm and temperatures of 140-180°C, interact with synthesis gas and are converted into aldehydes - the most important intermediates in the production of alcohols, carboxylic acids, amines, polyhydric alcohols and etc. As a result of the hydroformylation reaction, straight and branched chain aldehydes are obtained, containing one carbon atom more than in the original molecule:

The most valuable are the normal aldehydes, while the iso aldehydes can be considered as undesirable by-products. World production of aldehydes by the hydroformylation process reaches 7 million tons per year, with about half being n-butyraldehyde, from which n-butyl alcohol is obtained. Aldol condensation followed by hydrogenation produces 2-ethylhexanol, used for the production of polyvinyl chloride plasticizers.

Cobalt carbonyls are most widely used as hydroformylation catalysts; recently, the use of rhodium catalysts has been described, which allow the process to be carried out under milder conditions.

The mechanism of hydroformylation is based on a combination of the fundamental processes described above: coordination and incorporation of olefins and CO, oxidative addition and reductive elimination. As an example, let us consider the mechanism of hydroformylation of ethylene using a catalyst - octacarbonyl dicobalt Co 2 (CO) 8. It has been shown that hydroformylation itself is catalyzed by soluble cobalt hydrocarbonyl HCo(CO)4, into which Co2(CO)8 is converted under the action of hydrogen:

Co 2 (CO) 8 + H 2 = 2HCo(CO) 4

As a result of the dissociation HCo(CO) 4 = HCo(CO) 3 + CO, a coordinatively unsaturated intermediate HCo(CO) 3 is formed, on which ethylene is coordinated. Next, ethylene is introduced into the Co-H bond and an ethyl cobalt complex is formed, then coordination and introduction of CO occurs through the Co-C bond with the formation of an acyl cobalt complex. Oxidative addition of hydrogen to cobalt and subsequent reductive elimination leads to the aldehyde, the catalyst is regenerated and the process continues. The mechanism of hydroformylation can be visualized as a catalytic cycle:

PROSPECTS FOR THE SYNTHESIS OF OXYGEN-CONTAINING COMPOUNDS

The process of producing methanol, the most important product of the chemical industry, from synthesis gas, mastered in the 1920s, is of great importance. At the same time, the direct synthesis of other oxygen-containing compounds from synthesis gas also seems very attractive. The use of synthesis gas is described for the production of alcohols of composition C 1 -C 4 (lower alcohols), from which lower olefins are then obtained by dehydration. In the 70s, catalysts of complex composition were proposed, consisting of oxides of copper, cobalt, chromium, vanadium, manganese and alkali metal salts, which made it possible to obtain alcohols of normal structure of composition C 1 -C 4 from synthesis gas at a temperature of 250°C and pressure of only 6 atm:

The literature describes the formation of a wide variety of oxygen-containing compounds from synthesis gas, for example: acetaldehyde, acetic acid, ethylene glycol, etc.

All these reactions seem quite real. Unfortunately, these methods currently cannot compete with already developed industrial processes, since they occur under very harsh conditions and with little selectivity. It can be hoped that the search for new effective methods for the industrial use of synthesis gas will continue intensively, and there is no doubt that this area has a great future.

LITERATURE

1. Catalysis in C 1 -chemistry / Ed. L. Kaima. L.: Chemistry, 1987. 296 p.

2. Karakhanov E.A. What is petrochemistry // Soros Educational Journal. 1996. No. 2. p. 65-73.

3. Kharitonov Yu.Ya. Complex compounds // Ibid. No. 1. c. 48-56.

4. Temkin O.N. Catalytic chemistry // Ibid. c. 57-65

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ABSTRACT

Fischer-Tropsch process

Introduction

hydrocarbon catalyst process

History knows many examples when, due to urgent need, new original approaches to solving long-existing vital problems were born. Thus, in pre-war Germany, deprived of access to oil sources, a severe shortage of fuel necessary for the functioning of powerful military equipment was brewing. Having significant reserves of fossil coal, Germany was forced to look for ways to convert it into liquid fuel. This problem was successfully solved by the efforts of excellent chemists, of whom, first of all, we should mention Franz Fischer, director of the Kaiser Wilhelm Institute for Coal Research.

In 1926, the work of Franz Fischer and Hans Tropsch “On the direct synthesis of petroleum hydrocarbons at ordinary pressure” was published. It reported that when hydrogen reduces carbon monoxide at atmospheric pressure in the presence of various catalysts (iron-zinc oxide or cobalt-chromium oxide) at 270°C, liquid and even solid homologues of methane are obtained.

This is how the famous synthesis of hydrocarbons from carbon monoxide and hydrogen arose, since then called the Fischer-Tropsch synthesis (FT). A mixture of CO and H 2 in various proportions, called synthesis gas, can be obtained either from coal or from any other carbon-containing raw material. Since the invention of the process by German researchers, many improvements and revisions have been made, and the name "Fischer-Tropsch" is now applied to a large number of similar processes.

To be fair, it should be noted that the Fischer-Tropsch synthesis did not arise out of nowhere - by that time there were scientific prerequisites that were based on the achievements of organic chemistry and heterogeneous catalysis. Back in 1902, P. Sabatier and J. Sanderan first obtained methane from CO and H 2. In 1908, E. Orlov discovered that when carbon monoxide and hydrogen are passed over a catalyst consisting of nickel and palladium supported on coal, ethylene is formed.

The first industrial reactor was launched in Germany in 1935, using a Co-Th precipitated catalyst. In the 1930-40s, based on Fischer-Tropsch technology, the production of synthetic gasoline (Kogazin-I, or syntin) with an octane number of 40h55, synthetic high-quality diesel fraction (Kogazin-II) with a cetane number of 75h100 and solid paraffin was launched. The raw material for the process was coal, from which synthesis gas was obtained through gasification, and from it hydrocarbons. The artificial liquid fuel industry achieved its greatest growth during the Second World War. By 1945, there were 15 Fischer-Tropsch synthesis plants in the world (in Germany, the USA, China and Japan) with a total capacity of about 1 million tons of hydrocarbons per year. They produced mainly synthetic motor fuels and lubricating oils. In Germany, synthetic fuel almost completely covered the needs of the German army for aviation gasoline. Annual production of synthetic fuels in this country has reached more than 124,000 barrels per day, i.e. about 6.5 million tons in 1944.

After 1945, due to the rapid development of oil production and the fall in oil prices, the need to synthesize liquid fuels from CO and H 2 disappeared. The petrochemical boom has arrived. However, in 1973, the oil crisis broke out - the oil-producing countries of OPEC (Organization of Petroleum Exporting Countries) sharply increased prices for crude oil, and the world community was forced to realize the real threat of depletion of cheap and accessible oil resources in the foreseeable future. The energy shock of the 70s revived the interest of scientists and industrialists in the use of raw materials alternative to oil, and here the first place undoubtedly belongs to coal. The world's coal reserves are enormous; according to various estimates, they are more than 50 times greater than oil resources, and they can last for hundreds of years.

In addition, the world has a significant number of sources of hydrocarbon gases (both direct natural gas deposits and associated petroleum gas), which for one reason or another are not used for economic reasons (considerable distance from consumers and, as a consequence, high transportation costs in a gaseous state). However, the world's hydrocarbon reserves are depleting, energy needs are growing, and under these conditions the wasteful use of hydrocarbons is unacceptable, as evidenced by the steady increase in world oil prices since the beginning of the 21st century.

Under these conditions, the Fischer-Tropsch synthesis again becomes relevant.

1. Chemistry of the process

1.1 Basic reactions of hydrocarbon formation

The total reactions of the synthesis of hydrocarbons from carbon and hydrogen oxides, depending on the catalyst and process conditions, can be represented by different equations, but they all boil down to two main ones. The first main reaction is the Fischer-Tropsch synthesis itself:

(1)

The second main reaction is the equilibrium of water gas. This process occurs especially easily on iron catalysts as a secondary one:

(2)

Taking this secondary reaction into account for FT synthesis on iron catalysts, the overall equation is obtained:

(3)

Reactions (1) and (3) with stoichiometric, exhaustive conversion make it possible to obtain a maximum yield of 208.5 g of hydrocarbons per 1 m 3 of a CO + H 2 mixture with the formation of only olefins.

Reaction (2) can be suppressed by low temperatures, short contact times, circulation of synthesis gas and removal of water from the cycle gas, so that synthesis can proceed partly according to equation (1) with the formation of water and partly according to equation (3) with the formation of CO 2 .

From equation (1) with double conversion according to equation (2), the overall equation for the synthesis of hydrocarbons from CO and H 2 O according to Kölbel-Engelhardt is obtained:

(4)

The stoichiometric yield is 208.5 g [-CH 2 -] per 1 m 3 of CO + H 2 mixture.

The formation of hydrocarbons from CO 2 and H 2 is due to equation (1) and the reverse reaction (2):

(5)

Stoichiometric yield is 156.25 g [-CH 2 -] per 1 m 3 of CO 2 + H 2 mixture.

In general, the equations look like this:

For the synthesis of paraffins

(6)

(7)

(8)

(9)

For olefin synthesis

(10)

(11)

(12)

(13)

1.2 Adverse reactions

Undesirable reactions should be considered hydrogenation of CO into methane, decomposition of CO and oxidation of the metal with water or carbon dioxide.

Methane is formed in the presence of cobalt and nickel catalysts:

(14)

The stoichiometric yield is 178.6 g of CH 4 per 1 m 3 of a CO + H 2 mixture. The water formed in this case is then converted (especially on iron catalysts) in the presence of CO into a mixture of CO 2 + H 2, therefore the total reaction of methane formation is different:

(15)

The stoichiometric yield is 178.6 g of CH 4 per 1 m 3 of a CO + H 2 mixture. At temperatures above 300°C, methane is also formed during the hydrogenation of CO 2 according to the overall equation:

(16)

The stoichiometric yield is 142.9 g of CH 4 per 1 m 3 of the CO 2 + H 2 mixture. The synthesis process is complicated by the formation of carbon according to the Boudoir reaction:

(17)

FT synthesis can be directed towards the predominant formation of alcohols or aldehydes, which are formed as by-products during the synthesis of hydrocarbons. The basic equations in the case of alcohols are as follows

(18)

(19)

(20)

and aldehydes are formed like this:

(21)

(22)

Equations for other products formed in small quantities (ketones, carboxylic acids, esters) are omitted.

1.3 Reaction mechanism

Hydrogenation of carbon monoxide in the FT process is a complex of complex, parallel and sequential reactions. The first stage is the simultaneous chemisorption of carbon monoxide and hydrogen on the catalyst. In this case, carbon monoxide combines with a carbon atom with a metal, as a result of which the C-O bond is weakened and the interaction of CO and hydrogen is facilitated with the formation of a primary complex. The growth of the hydrocarbon chain (“beginning of the chain”) begins from this complex. As a result of further stepwise addition of a surface compound bearing one carbon atom, the carbon chain lengthens (“chain growth”). Chain growth ends as a result of desorption, hydrogenation, or interaction of the growing chain with synthesis products (“chain termination”).

The main products of these reactions are saturated and unsaturated hydrocarbons of the aliphatic series, and the by-products are alcohols, aldehydes and ketones. Reactive compounds (unsaturated hydrocarbons, aldehydes, alcohols, etc.) can be incorporated into growing chains during subsequent reactions or form a surface complex that gives rise to a chain. Subsequent reactions between the resulting products lead to acids, esters, etc. Dehydrocyclization reactions occurring at higher synthesis temperatures lead to aromatic hydrocarbons. One should also not exclude the occurrence of cracking or hydrocracking of higher boiling hydrocarbons that were initially formed and desorbed from the catalyst if they are again adsorbed on it.

The mechanism of the reaction, despite decades of study, remains unclear in detail. However, this situation is typical for heterogeneous catalysis. The most recognized mechanism is with growth at the end of the chain. Molecules or atoms that pass into an excited state during the simultaneous chemisorption of carbon monoxide and hydrogen on the catalyst react to form an enol primary complex (Scheme A 1), which also gives rise to a chain. Chain growth (Scheme A 2) begins with the elimination of an H 2 O molecule from two primary complexes (with the formation of a C-C bond) and the abstraction of a C atom from a metal atom as a result of hydrogenation. The resulting C 2 complex, attaching one primary complex, releases an H 2 O molecule and, as a result of hydrogenation, is freed from the metal. Thus, through condensation and hydrogenation, the chain grows stepwise for each subsequent C-atom. The beginning of the chain can be depicted as follows:

Scheme A 1

The growth of the chain at the outermost C-atoms goes like this:

Scheme A 2

and so on until:

Another possibility is that initially the Me-C bond in the primary adsorption complex is partially hydrogenated, and then the resulting compound condenses with the primary complex, which leads to chain growth according to scheme (A 3) or according to scheme (A 4) and as a result, secondary methyl branched adsorption complex:

Scheme A 3

Scheme A 4

Desorption of the primary adsorption complex, which always contains a hydroxy group, leads to aldehydes, and in subsequent reactions to alcohols, acids and esters:

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Hydrocarbons can be formed as a result of dehydration or splitting of adsorption complexes:

Scheme A 5

Alcohols and aldehydes can also start the chain after their adsorption on the catalyst in phenolic form

or olefins, which are likely bound in enol form on the catalyst after reaction with water.

Polymerization of CH 2 groups is considered as another possibility for chain growth. When the primary complex is hydrogenated, HO-CH 2 - and CH 2 -surface complexes are formed:

Scheme B

The hydrogenated surface complex interacts with a similar complex with the elimination of water (B 1):

Scheme B 1

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In the same way, the resulting surface complexes can interact with the primary, non-hydrogenated complex (with the formation of a C 2 -addition complex according to scheme B 2) or react with the complex after its hydrogenation (according to scheme B 1):

Scheme B 2

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The chain can also grow by polymerization of the initially formed CH 2 groups according to scheme B (with a change in charge to Me):

Scheme B

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The contribution of polymerization to the chain growth process depends on the ratio of the rates of condensation and polymerization.

2. Catalysts

FT synthesis begins with the simultaneous chemisorption of CO and H 2 on metal atoms. Transition metals with 3d and 4f electrons or their interstitial compounds (carbides, nitrides, etc.) are especially suitable for the formation of such a chemisorption bond. Group VIII metals serve as catalysts: Ru is the most active, then Co, Fe, Ni. To increase the surface area, they are often applied to porous supports such as silica gel and alumina. Only Fe and Co have found application in industry. Ruthenium is too expensive, and its reserves on Earth are too small to be used as a catalyst in large-scale processes. On nickel catalysts at atmospheric pressure, mainly methane is formed, but with increasing pressure, nickel forms volatile carbonyl and is washed out of the reactor.

Cobalt catalysts were the first catalysts used industrially (in Germany and later in France and Japan in the 1930s and 1940s). Typical pressures for their operation are 1-50 atm and temperatures of 180-250°C. Under these conditions, mainly linear paraffins are formed. Cobalt has significant hydrogenating activity, so part of the CO inevitably turns into methane. This reaction accelerates sharply with increasing temperature, so cobalt catalysts cannot be used in the high temperature FT process.

Iron catalysts have been used in FT synthesis plants in South Africa since the mid-1950s. Compared to cobalt, they are much cheaper, operate in a wider temperature range (200-360°C), and make it possible to obtain a wider range of products: paraffins, lower b-olefins, alcohols. Under the conditions of FT synthesis, iron catalyzes the reaction of water gas, which makes it possible to effectively use synthesis gas obtained from coal, in which the CO: H 2 ratio is lower than the stoichiometric 1: 2. Iron catalysts have a lower affinity for hydrogen compared to cobalt catalysts, so methanation does not is a big problem for them. However, due to the same low hydrogenating activity, the surface of iron contacts quickly becomes carbonized. Cobalt contacts can work much longer without regeneration. Another disadvantage of iron contacts is their inhibition by water. Since water is a synthesis product, the CO conversion in one pass is low. To achieve a high degree of conversion, it is necessary to organize gas recycle.

Both iron and cobalt catalysts are extremely sensitive to sulfur poisoning. Therefore, the synthesis gas must first be purified from sulfur, at least to a level of 2 mg/m3. Residual sulfur is adsorbed by the surface of the catalyst, so that, as a result, the FT synthesis products practically do not contain it. This circumstance makes synthetic diesel fuel obtained using FT technology very attractive in view of modern strict environmental requirements for transport.

When freshly prepared iron group catalysts are exposed to various agents, the composition and structure of the catalysts changes, and phases appear that are actually active in FT synthesis. While the number of such phases in the case of cobalt and nickel is relatively small, for iron there are many of them, so the catalytic system becomes more complex. Iron forms interstitial compounds of various compositions with carbon or other metalloids (nitrogen, boron, etc.), without losing the “metallic” character necessary for PT synthesis.

Many studies have confirmed that iron catalysts change in phase composition, oxidation state, and interstitial carbon structures during FT synthesis. At the beginning of synthesis, the iron of the reduced catalyst transforms into Fe 2 C carbide (Hagg's carbide). At the same time, but more slowly, Fe 3 O 4 oxide is formed, the proportion of which (based on the original iron) is constantly increasing, while the content of Fe 2 C carbide varies little depending on operating time and temperature. The free carbon content increases with increasing synthesis time. Under operating conditions, the phase composition of the catalyst is in equilibrium with the composition of the reaction mixture and only to a small extent depends on the method of its preparation or pre-treatment (reduction, carbidation).

Bartholomew's work shows that on Co- and Ni-catalysts, CO is hydrogenated into methane along two routes, each of which is associated with certain areas on the surface. A.L. Lapidus and co-workers put forward a two-center model of the Co catalyst for the synthesis of FT. According to these ideas, the centers of the first type are crystallites of metallic Co. CO is adsorbed dissociatively on them and then hydrogenated into methane. At these same centers, a CO disproportionation reaction occurs, leading to carbonization of the catalyst. Centers of the second type represent the boundary between metallic Co and the oxide phase on the surface of the catalyst. They are responsible for the growth of the hydrocarbon chain. Carbon monoxide is adsorbed on CoO in a weakly bound associative form, then moves to the carrier, where it forms surface complexes of the CH x O type with hydrogen. These complexes interact with each other, forming polymer structures on the surface. Their hydrogenation with CoO produces hydrocarbons.

Two types of CO adsorption on the surface are detected by the spectrum of temperature-programmed desorption (TPD) of CO, in which the centers of the first type correspond to a peak with T max in the region of 250-350°C, and the centers of the second type - T max< 250°C. По соотношению площадей пиков можно судить о доле каждого из типов центров и, соответственно, предсказывать каталитическое действие контакта.

Experiments have shown a good correlation between the yield of hydrocarbons and the number of weakly bound CO adsorption sites on the contact surface.

The oxide phase of Co-catalysts is usually formed during their preliminary heat treatment (calcination and/or reduction) due to the interaction of the oxide carrier (SiO 2, Al 2 O 3, etc.), cobalt oxide and promoter. Catalysts that do not contain an oxide phase are not capable of catalyzing the formation of liquid hydrocarbons from CO and H 2 because they do not have polymerization centers on their surface.

Thus, the oxide phase of FT synthesis catalysts plays a decisive role in the formation of liquid hydrocarbons, and to create effective catalysts for this process, special attention must be paid to the selection of the carrier and preliminary heat treatment of the catalyst. By influencing the active part of the catalyst by preliminary heat treatment, which leads to increased interaction of the active phase with the carrier, or by introducing modifying oxide additives into the catalyst, it is possible to enhance the polymerization properties of the catalyst and, therefore, increase the selectivity of the reaction with respect to the formation of liquid hydrocarbons.

Based on the principle of action, promoters are divided into two groups - structural and energetic.

Hardly reducible oxides of heavy metals, such as Al 2 O 3, ThO 2, MgO and CaO, are used as structural promoters. They promote the formation of a developed catalyst surface and prevent recrystallization of the catalytically active phase. A similar function is also performed by carriers - kieselguhr, dolomite, silicon dioxide (in the form of freshly precipitated hydroxide gel or potassium silicate).

Energy promoters, which are also called chemical, electronic or activating additives, according to the electronic mechanism of the reaction, increase its speed and affect selectivity. Chemically active structural promoters can also act as energy promoters. Energy promoters (especially alkalis) also significantly affect the texture of the catalyst (surface, pore distribution).

Alkali metal carbonates are most often used as energy promoters for iron catalysts (regardless of the production method). Iron catalysts produced by different methods have different optimal concentrations of alkaline additives. Precipitated catalysts should not contain more than 1% K 2 CO 3 (calculated as Fe); for certain precipitated catalysts, the optimum is 0.2% K 2 CO 3 (a deviation of 0.1% significantly affects activity and selectivity). Is there an optimal concentration for fused catalysts? 0.5% K 2 O.

Promoters that determine both structural and energetic effects include copper. Copper facilitates the reduction of iron, and this process, depending on the amount of copper, can occur at a temperature lower (up to 150°C) than without the additive. Further, this additive, when drying iron hydroxide (II and III), promotes its oxidation to Fe 2 O 3. Copper favors the formation of iron-carbon compounds and, together with alkali, accelerates the reduction of iron and the formation of carbide and carbon. Copper does not affect the selectivity of FT synthesis.

3. Factors influencing the process

3.1 Quality of raw materials

The yield and composition of FT synthesis products largely depends on the CO:H 2 ratio in the initial synthesis gas. This ratio, in turn, significantly depends on the method used for producing synthesis gas. Currently, there are three main industrial methods for obtaining the latter.

1. Gasification of coal. The process is based on the interaction of coal with water vapor:

This reaction is endothermic, the equilibrium shifts to the right at temperatures of 900–1000°C. Technological processes have been developed that use steam-oxygen blasting, in which, along with the mentioned reaction, an exothermic reaction of coal combustion occurs, providing the required heat balance:

2. Methane conversion. The reaction between methane and water vapor is carried out in the presence of nickel catalysts (Ni/Al 2 O 3) at elevated temperatures (800-900ºC) and pressure:

Any hydrocarbon raw material can be used as a raw material instead of methane.

3. Partial oxidation of hydrocarbons. The process consists of incomplete thermal oxidation of hydrocarbons at temperatures above 1300°C:

The method is also applicable to any hydrocarbon feedstock.

During coal gasification and partial oxidation, the CO:H2 ratio is close to 1:1, while during methane conversion it is 1:3.

In general, the following patterns can be noted:

- in the case of an initial mixture enriched with hydrogen, paraffins are preferably obtained, and the thermodynamic probability of their formation decreases in the order methane > low molecular weight n-alkanes > high molecular weight n-alkanes;

- synthesis gas with a high content of carbon monoxide leads to the formation of olefins and aldehydes, and also promotes carbon deposition. The probability of alkene formation decreases in the order high molecular weight n-olefins > low molecular weight n-olefins.

3.2 Temperature

FT synthesis is a highly exothermic reaction. The heat generated is up to 25% of the calorific value of synthesis gas. The rate of synthesis and, at the same time, the yield of product per unit volume of catalyst per unit time increase with increasing temperature. However, the rate of adverse reactions also increases. Therefore, the upper temperature of FT synthesis is limited primarily by undesirable methane and coke formation. A particularly strong increase in methane yield with increasing temperature is observed for Co catalysts.

As a rule, the process is carried out at a temperature of 190–240°C (low temperature option, for Co and Fe catalysts) or 300–350°C (high temperature option, for Fe catalysts).

3.3 Pressure

Just as with increasing temperature, the rate of reactions also increases with increasing pressure. In addition, increasing the pressure in the system promotes the formation of heavier products. Typical pressure values ​​for industrial processes are 0.1 h5 MPa. Since increased pressure makes it possible to increase synthesis productivity, for economic efficiency the process is carried out at a pressure of 1.2–4 MPa.

The combined influence of temperature and pressure, as well as the nature of the catalyst on the yield of various products, satisfies the Anderson-Schultz-Flory (ASF) distribution, described by the formula

where P n is the mass fraction of hydrocarbon with carbon number n;

b=k 1 /(k 1 +k 2), k 1, k 2 - rate constants for growth and chain termination, respectively.

Methane (n=1) is always present in greater quantities than predicted by the ASF distribution, since it is formed independently by direct hydrogenation reaction. The value of b decreases with increasing temperature and, as a rule, increases with increasing pressure. If the reaction produces products of different homologous series (paraffins, olefins, alcohols), then the distribution for each of them may have its own value b. ASF distribution imposes restrictions on maximum selectivity for any hydrocarbon or narrows.

Graphically, the distribution of ASF is presented in Figure 1.

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3.4 Volume velocity

Increasing the space velocity (or decreasing the contact time) of a gas does not favor reactions occurring at a lower rate. These include reactions occurring on the surface of the catalyst - the elimination of oxygen, the hydrogenation of olefins and the growth of the carbon chain. Therefore, with a decrease in the average contact time in the synthesis products, the amount of alcohols, olefins and short-chain compounds (gaseous hydrocarbons and hydrocarbons from the boiling range of the gasoline fraction) increases.

4. Varieties of technological schemes

The main technical problem of Fischer-Tropsch synthesis is the need to remove large amounts of heat released as a result of highly exothermic chemical reactions. The design of the reactor is also largely determined by the type of products for which it is intended. There are several types of reactor designs for FT synthesis, which determine one or another technological scheme of the process.

4.1 Scheme with a multi-tube reactor and a stationary catalyst bed

In such reactors, a low-temperature process occurs in the gas phase. The design of a multi-tube reactor is shown in Figure 2.

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Multi-tube reactors are easy to operate, do not create problems with catalyst separation, and can be used to obtain products of any composition. However, they have a number of disadvantages: difficulty in manufacturing, high metal consumption, complexity of the catalyst overload procedure, significant pressure drop along the length, diffuse restrictions on large catalyst grains, and relatively low heat removal.

One of the possible technological schemes for high-performance FT synthesis in a multi-tubular reactor is presented in Figure 3.

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Technological parameters are presented in Table 1, the composition of the resulting products is in Table 2.

Table 1 - Operating conditions for industrial gas-phase Fischer-Tropsch synthesis plants on a stationary catalyst bed

Table 2 - Typical composition of hydrocarbons obtained in industrial Fischer-Tropsch syntheses on a stationary catalyst bed

Characteristic	Meaning
Product composition (average data), wt.%
hydrocarbons:
Degree of conversion of CO + H 2 mixture, %
Yield of hydrocarbons C 2+, g per 1 m 3 of CO + H 2 mixture

4.2 Scheme with a fluidized catalyst bed

Fluidized bed reactors provide good heat removal and an isothermal process. Diffuse restrictions in them are minimal due to the high linear gas velocity and the use of a finely dispersed catalyst. However, such reactors are difficult to bring into operating mode. The problem is separating the catalyst from the products. Individual nodes are subject to severe erosion. The fundamental limitation of fluidized bed reactors is the inability to produce heavy paraffins in them. Figure 4 shows a flow diagram of FT synthesis in a reactor with a fluidized bed of catalyst.

Figure 4. Schematic of the Fischer-Tropsch process in a fluidized bed reactor:

1, 3 - heaters; 2 - synthesis gas generator; 4 - heat exchangers; 5 - washing column; 6 - reactor; 7 - cyclone; 8 - separator.

Technological parameters of the process when working according to the scheme under consideration are presented in Table 3, the composition of the resulting products is in Table 4.

Table 3 - Operating conditions of an industrial Fischer-Tropsch synthesis plant in a reactor with a fluidized bed of catalyst

Table 4 - Typical composition of hydrocarbons produced in a fluidized bed reactor

4.3 Scheme with circulating suspended powder catalyst

This scheme also applies to the high-temperature F-T process. The technological flow diagram of the Fischer-Tropsch process in a stream of suspended powder catalyst is shown in Figure 5.

Figure 5. Scheme of FT synthesis in a flow of suspended powder catalyst:

1 - oven; 2 - reactor; 3 - refrigerators; 4 - separator column for oil washing; 5 - capacitor; 6 - separation column; 7 - column for washing the resulting gasoline; 8 - column for gas washing.

Technological parameters of the synthesis in the case of carrying out the process in a stream of suspended powder catalyst are presented in Table 5, the composition of the resulting products is in Table 6.

Table 5 - Operating conditions for industrial Fischer-Tropsch synthesis plants in a stream of suspended powder catalyst

Table 6 - Typical composition of hydrocarbons produced in a Fischer-Tropsch synthesis unit in a suspended powder catalyst stream

4.4 Scheme with a bubbling (slurry) reactor

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The bubbling type reactor, also called bubble (slurry), is considered the most effective for the synthesis of FT. In this apparatus, synthesis gas passes from bottom to top through a layer of high-boiling solvent in which a fine catalyst is suspended. Similar to fluidized bed reactors, the bubble reactor provides efficient mass transfer and heat removal. At the same time, it is possible to obtain heavy products in it, as in a tubular apparatus. Figure 6 shows a diagram of the operation of such a reactor.

The process flow diagram using a bubble reactor is shown in Figure 7.

Figure 7. Scheme of FT synthesis in a bubble reactor:

1 - compressor; 2 - flow meters; 3 - diaphragms; 4 - samplers; 5 - reactor: 6 - steam collector; 7 - heat exchanger; 8 - food containers; 9 - separation tanks; 10 - pumps; 11 - refrigerator; 12 - installation for CO 2 release; 13 - filter; 14 - apparatus for preparing a catalyst suspension; 15 - centrifuge; 16 - oil container.

Using the example of this scheme, one can note the great technological flexibility of the FT synthesis, when by varying the quality of raw materials and technological indicators it is possible to obtain a product of the required fractional composition (Table 7).

Table 7 - Composition of products under various modes of FT synthesis in a bubble reactor

Indicators	Getting different products
	with low mol. mass	with an average mol. mass	with high mol. mass
Yield of total product C 3+, g per 1 m 3 of CO + H 2 mixture

The values ​​of technological parameters for the scheme under consideration are given in Table 8.

Table 8 - Operating conditions for industrial Fischer-Tropsch synthesis plants with a bubble reactor

Parameter	Meaning
Pressure, MPa
Temperature, °C
Ratio of H 2: CO in the source gas
Volumetric velocity, h -1
Conversion rate CO CO + H 2 mixtures, %	89h92
Yield of hydrocarbons C 1+, g per 1 m 3 of CO + H 2 mixture

To obtain low molecular weight hydrocarbons, higher temperatures and volumetric velocities, but lower pressures, are used. If high molecular weight paraffins are required, then these parameters are changed accordingly.

5. Modern production

Relatively low world oil prices, fluctuating slightly around $20 (in terms of the value of the 2008 US dollar) after the Second World War until the 70s of the 20th century, for a long time made the construction of large production facilities based on Fischer-Tropsch synthesis unprofitable. Large-scale production of synthetic hydrocarbons from synthesis gas existed and developed only in South Africa, however, this was not due to economic benefits, but to the political and economic isolation of the country under the apartheid regime. And currently, the plants of Sasol (South African Coal, Oil and Gas Corporation) remain among the most productive in the world.

In modern conditions, enterprises using the FT process are able to operate profitably at an oil price of more than $40 per barrel. If the technological scheme provides for the capture and storage or utilization of carbon dioxide generated during synthesis, this figure increases to $50h55. Since world oil prices have not fallen below these levels since 2003, the construction of large enterprises for the production of synthetic hydrocarbons from synthesis gas was not long in coming. Notably, most of the projects are located in Qatar, which is rich in natural gas.

The largest GTL (Gas to liquid) enterprises operating and under construction, based on the synthesis of FT, are described below.

5.1 Sasol 1, 2, 3. PetroSA

The South African company Sasol has accumulated extensive experience in the industrial application of FT synthesis. The first pilot plant, Sasol 1, was launched in 1955, the raw material for which is synthesis gas obtained by coal gasification. Due to the trade embargo against South Africa in the 50s - 80s of the 20th century, two larger production facilities were commissioned in 1980 and 1984 to provide the country with energy resources - Sasol 2 and Sasol 3.

In addition, Sasol is the licensor of the GTL process for the South African state oil company PetroSA. Her business, also known as Mossgas, has been in business since 1992. The feedstock is natural gas produced offshore.

Over many years of operation of Sasol's production facilities, the company's engineers sought to improve the synthesis technology; all four types of reactors described in section 4 were tested, starting with multi-tube reactors operating at atmospheric and later at elevated pressure, and ending with bubble reactors.

Sasol companies supply the market with both motor fuels and petrochemical feedstocks (olefins, alcohols, aldehydes, ketones and acids, as well as phenol, cresols, ammonia and sulfur).

5.2 Oryx

This enterprise was put into operation in 2007 in Qatar. The licensor was jointly Sasol and Chevron, forming an international joint venture, Sasol Chevron Limited.

The source natural gas is subjected to steam reforming, after which the resulting synthesis gas is fed into a bubble reactor, where low-temperature FT synthesis takes place. Synthesis products undergo hydrotreating and hydrocracking.

Commercial products are clean diesel fuel (less than 5 ppm sulfur, less than 1% aromatics, cetane number about 70), as well as naphtha, used as a feedstock for pyrolysis.

5.3 SMDS

Shell commissioned its Shell MDS (Middle Distillate Synthesis) plant in Malaysia in 1993. The process is based on a modern modification of the FT process. Synthesis gas for carrying out the FT reaction is obtained by partial oxidation of natural gas. The process is carried out in multi-tube reactors filled with a high-performance catalyst. The synthesis products (mainly high-molecular alkanes) undergo hydrocracking and hydroisomerization.

Production is aimed at producing high-quality synthetic diesel fuel and kerosene, as well as paraffins.

5.4 Pearl

The Pearl facility includes the world's largest GTL production facility, established by Shell in partnership with Qatar Petroleum. The first stage of the complex was launched in May 2011, reaching full capacity is planned for 2012. The technological process, in general, is a development of the technologies used in the SMDS plant. The chain of processes is identical: natural gas extracted from offshore fields undergoes partial oxidation to produce a mixture of H 2 and CO; The synthesis gas is then converted in multi-tube reactors (24 units) into long-chain paraffins. The latter, as a result of hydrocracking and separation, produce commercial products: motor fuels, naphtha (raw materials for petrochemicals), as well as base lubricating oils and paraffins as by-products.

5.5 Escravos

This GTL project, located in Nigeria, was originally developed jointly by Sasol and Chevron Corporation, as was Oryx. However, due to significantly increased costs of implementing the project, Sasol abandoned it. The plant is currently being built with the participation of Chevron Nigeria Limited and the Nigerian National Petroleum Company. Commissioning of the plant is scheduled for 2013. The feedstock is natural gas. The FT synthesis itself will be carried out in bubble reactors. A distinctive feature of the technological scheme is the use of Chevron's proprietary ISOCRACKING process, thanks to which synthetic paraffins - products of FT synthesis - are cracked to light and medium distillates and refined.

Commercial products are motor fuels (primarily diesel), naphtha, as well as oxygen-containing products - methanol and dimethyl ether.

Table 9 summarizes general information about the synthetic hydrocarbon production processes described above.

Table 9 - Current GTL capacities in the world

Company	Technology Developer	Location	Capacity, barrels/day
		Sasolburg, South Africa
		Secunda, South Africa
Petro S.A. (formerly Mossgas)		Mossel Bay, South Africa
		Bintulu, Malaysia
		Escravos, Nigeria	34000 (project)
		Ras Laffan, Qatar
		Ras Laffan, Qatar

In addition, the construction of FT synthesis plants in Algeria (up to 33 thousand barrels per day) and Iran (up to 120 thousand barrels per day) is promising.

There is information about the joint development of Sasol and the Norwegian Statoil of plants located on offshore platforms or even floating plants for processing natural and associated gas into liquid hydrocarbons. However, nothing is known about the implementation of this project.

A basic design has been developed and further negotiations are underway on the construction of a GTL plant in Uzbekistan. It is planned to process methane produced by the Shurtan gas chemical complex using technology from Sasol and Petronas.

The companies ExxonMobil, Syntroleum, ConocoPhillips are engaged in research in the field of GTL processes, however, these companies so far have at their disposal only pilot plants used for research purposes.

Conclusion

Fischer-Tropsch synthesis makes it possible to obtain high-quality motor fuels and valuable raw materials from natural fossil fuels, currently used primarily as fuel for thermal and power plants (coal, natural gas) or even flared or emitted into the atmosphere (associated petroleum gas). for subsequent chemical synthesis. The development of Shell's technologies takes the first path, while Sasol's processes combine both directions. Figure 8 shows possible options for processing the primary products of FT synthesis.

Figure 8. Directions for processing synthetic hydrocarbons.

The quality of diesel fuel obtained in the FT process using Sasol Chevron technology is presented in Table 10.

Table 10 - Characteristics of synthetic diesel fuel

Characteristic	Synthetic diesel fuel	Standard requirements
Density at 15°C, kg/m 3
Boiling point of 95% fraction, °C
Kinematic viscosity at 40°C, mm 2 /s
Flash point, °C
Cetane number
Cloud point

Successful or unsuccessful experience in operating modern GTL production facilities, primarily Pearl - the most modern and largest GTL enterprise - will likely determine the future development of technology and plants using the FT process. GTL technology, in addition to unstable oil prices, has other significant problems.

The first of them is very high capital intensity. According to calculations, investments in a plant with a capacity of 80 thousand barrels of synthetic hydrocarbons per day, the feedstock for which is coal, range from $7 billion to $9 billion. For comparison, a refinery with the same productivity will cost $2 billion. Most of the capital costs (60-70 %) falls on the synthesis gas production complex. Real figures confirm the calculations: the costs of the Escravos GTL being built in Nigeria rose from the planned $1.7 billion to $5.9 billion. The construction of the Pearl GTL cost Shell $18-19 billion. Implementation of a grandiose project in Qatar to build a GTL plant with a capacity of 154 thousand . barrels per day of synthetic hydrocarbons was rejected by the developer Exxon Mobil. It was planned to invest $7 billion in the project, which clearly would not have been enough. However, the company explained the abandonment of the project by a "reallocation of resources" in favor of the construction of the Barzan gas processing plant, also located in Qatar.

Another significant problem is the impact on the environment. As shown in Section 1, the FT process produces carbon dioxide, which is a greenhouse gas. CO 2 emissions are believed to be the cause of global climate change, and the amount of carbon dioxide emitted is limited by greenhouse gas emission quotas. In the production-refining-consumption chain, carbon dioxide emissions for synthetic motor fuels are approximately twice as high as those for petroleum fuels. There are various technologies for recycling carbon dioxide (from storage in underground reservoirs to injection into a gas or oil-bearing formation), but they significantly increase the cost of already expensive GTL projects. However, it is worth noting that other harmful emissions from direct combustion of synthetic fuels in internal combustion engines are 10-50% lower than for oil fuels (Table 11).

Table 11 - Harmful emissions from the combustion of synthetic and traditional diesel fuel

An environmental problem may include the need for a large amount of water to carry out gasification of coal, if the latter is used as a feedstock. Often the climate in countries rich in coal but poor in oil is arid. However, at the second stage of GTL production - the actual synthesis of FT - water is a by-product, which, after purification, can be used in the technological process. This technique is used at the Pearl plant. Since water is not needed to produce synthesis gas at this plant, it is used to generate high-pressure steam when cooling FT reactors. The resulting water vapor drives compressors and electric generators.

The GTL market is a growing market. The main factors driving this market are the urgent need to monetize large reserves of natural gas, associated petroleum gas and gas from coal deposits that are difficult to utilize by other means (pipeline transport or liquefaction) against the backdrop of an ever-increasing global demand for liquid hydrocarbons and increasingly stringent requirements for the environmental characteristics of hydrocarbon fuels . The development of GTL technologies is a good market opportunity for those countries and companies that have large reserves of natural or associated gas and coal. GTL production may not compete, but complement such areas in the industry as LNG (Liquefied natural gas), production of environmentally friendly fuels, and high-quality base oils.

List of sources used

1. Chemicals from coal. Per. with him. /Ed. I.V. Kalechitsa - M.: Chemistry, 1980. - 616 p., ill.

2. Karakhanov E.A. Synthesis gas as an alternative to oil. II. Methanol and syntheses based on it // Soros educational journal. - 1997. - No. 12. - P. 68.

3. The Early Days of Coal Research [Electronic resource]. - Access mode: http://www.fe.doe.gov/aboutus/history/syntheticfuels_history.html

4. Fischer-Tropsch process [Electronic resource]. - Access mode: http://ru.wikipedia.org/wiki/Fisher_Process_-_Tropsch

5. Review of Fischer-Tropsch synthesis catalysts [Electronic resource]. - Access mode: http://www.newchemistry.ru/letter.php? n_id=7026&cat_id=5&page_id=1

6. Dry M.E. Applied Catalysis A: General. - 2004. - No. 276, - R. 1.

7. 11. Storch G., Golambik N., Golambik R. Synthesis of hydrocarbons from carbon monoxide and hydrogen. - M.: I.L., 1954. - P. 257.

8. Lee W.H., Bartolomew C.H.J. Catal. - 1989. - No. 120. - R. 256.

9. Wisam Al-Shalchi. Gas to liquids technology (GTL). - Baghdad - 2006.

10. Oil [Electronic resource]. - Access mode: http://ru.wikipedia.org/wiki/Oil

11. Matthew Dalton. Big Coal Tries to Recruit Military to Kindle a Market. // The Wall Street Journal. - 2007. - Sept. eleven.

12. Explore Sasol - Sasol history [Electronic resource]. - Access mode: http://www.sasol.com/sasol_internet/frontend/navigation.jsp? navid=700006&rootid=2

13. The PetroSA GTL Refinery & LTFT Technology Development [Electronic resource]. - Access mode: http://www.petrosa.co.za/

14. Oryx GTL [Electronic resource]. - Access mode: http://www.oryxgtl.com/Englishv3/index.html

15. Shell MDS Technology and Process [Electronic resource]. - Access mode: http://www.shell.com.my/home/content/mys/products_services/solutions_for_businesses/smds/process_technology/

16. Inside Shell's Bintulu GTL Plant [Electronic resource]. - Access mode: http://www.consumerenergyreport.com/2010/11/14/inside-shells-bintulu-gtl-plant/

17. First cargo of Pearl GTL products ship from Qatar [Electronic resource]. - Access mode: http://www.shell.com/home/content/media/news_and_media_releases/2011/first_cargo_pearl_13062011.html

18. Gas-to-liquids (GTL) processes [Electronic resource]. - Access mode: http://www.shell.com/home/content/innovation/meeting_demand/natural_gas/gtl/process/

19. Escravos Gas-to-Liquids Project, Niger Delta [Electronic resource]. - Access mode: http://www.hydrocarbons-technology.com/projects/escravos/

20. GTL market review [Electronic resource]. - Access mode: http://www.newchemistry.ru/letter.php? n_id=5331

21. Uzbekistan is developing cooperation with the companies Sasol and Petronas [Electronic resource]. - Access mode: http://www.anons.uz/article/politics/5042/

22. Pearl GTL [Electronic resource]. - Access mode: http://www.rupec.ru/blogs/? ID=3048

23. Exxon Mobil, Qatar Unplug GTL Project [Electronic resource]. - Access mode: http://www.imakenews.com/lng/e_article000760746.cfm? x=b96T25P, bd1Rfpn

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