The Fischer-Tropsch synthesis is a chemical process that is a key step in the modern way production of synthetic fuels. Why do they say “synthesis” or “process” and avoid the word “reaction”? The names of scientists, in this case Franz Fischer and Hans Tropsch, usually refer to individual reactions. The fact is that there is no Fischer-Tropsch reaction as such. It is a set of processes. There are only three main reactions in this process, and there are at least eleven of them. In general, the Fischer-Tropsch synthesis is the conversion of so-called synthesis gas into a mixture of liquid hydrocarbons. Chemist Vladimir Mordkovich about methods for producing synthetic fuel, new types of catalysts and the Fischer-Tropsch reactor.
Vladimir Mordkovich - Doctor of Chemistry, Department of Physics and Chemistry of Nanostructures at Moscow Institute of Physics and Technology, Head of the Department of New Chemical Technologies and Nanomaterials at TISNUM, Scientific Director of Infra Technologies.
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Shale natural gas (English shale gas) - natural gas extracted from oil shale and consisting mainly of methane. Oil shale is a solid mineral of organic origin. Shales were mainly formed 450 million years ago at the bottom of the sea from plant and animal remains.
Alexandra Poshibaeva
Today, there are two main hypotheses for the formation of oil: inorganic (abiogenic) and organic (biogenic, and it is also called sedimentary-migration). Proponents of the inorganic concept believe that oil was formed from carbon and hydrogen by the Fischer-Tropsch process at great depths, at enormous pressures and temperatures above a thousand degrees. Normal alkanes can be formed from carbon, hydrogen in the presence of catalysts, but there are no such catalysts in nature. In addition, oils contain a huge amount of isoprenanes, cyclic biomarker hydrocarbons, 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 fossil fuel deposits last and what to do after their depletion? Like other minerals, we will have to develop raw materials with a lower content of a useful component. How to make oil, from what raw materials? Will it 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 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 how to obtain optical isomers of compounds based on aldehydes, finally carrying out an important reaction on which chemists have been working for many years. In the experiment, they combined two catalysts that work according to different principles. As a result of the joint action of these catalysts, two active organic molecules are formed, which are combined into the desired substance. Using this reaction as an example, the possibility of synthesizing a whole class of biologically important organic compounds is shown.
Elena Naimark
The followers of Stanley Miller, who performed famous experiments in the 1950s to simulate the synthesis of organic matter in the Earth's primary atmosphere, again turned to the results of old experiments. They studied the materials left over from those years. 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 seemed in the 50s. This result focuses the attention of modern researchers on the conditions of synthesis and accumulation of primary macromolecular organics: synthesis could be activated in the areas of eruptions, and volcanic ash and tuffs could become a reservoir of biological molecules.
Yu. M. Korolev
We asked Yu.M. Korolev - Leading Researcher of the Institute of Petrochemical Synthesis named after A.I. A.V. Topchiev. For more than thirty years he has been studying the X-ray phase composition of fossil hydrocarbon minerals and their transformation under the influence of time and temperature.
Rodkin M.V.
The dispute about the biogenic (organic) or abiogenic origin of oil is of particular interest to 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 that mimic the early stages of the formation of planetary systems, all kinds of carbohydrates are formed in water ice with an admixture of methanol and ammonia under the action 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 autocatalytic Butlerov reaction, although it does not require the presence of divalent metal ions.
Elena Naimark
The world of RNA was preceded by the time of prebiological synthesis, when molecules, one way or another 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 which was earlier, 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 the extraction of shale oil and gas. At the lecture, we will try to figure out what this technology is, what environmental problems are associated with it, and which ones 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 Germany, rich in coal, but poor in oil, the issue of the production of liquid fuel was acute. Since the invention of the process by the German researchers Franz Fischer and Hans Tropsch, many improvements and corrections 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 deprived of access to oil. The development of the GTL proceeded in stages, over generations. The first generation of GTL is responsible for the well-known German ersatz gasoline during the Great Patriotic War. The second developed in South Africa as a response to the international embargo. The third is in Western countries after the energy crisis of 1973. With each new generation of technology, capital costs decreased, the output 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. First, because of the presence of large gas fields in Siberia. The technology makes it possible to process gas directly on site and use existing oil pipelines for transportation, which is more cost-effective. Secondly, GTL makes it possible to utilize associated gases from oil fields, as well as refinery blow-off gases, which are usually burnt "on a candle". Thirdly, motor fuels obtained using this technology are superior to oil counterparts in terms of operational and environmental performance.
Oil is the only global raw material for the production of motor fuels and the most important for chemical synthesis. However, the situation is gradually changing. The depletion of world oil reserves forces us to turn to other sources of hydrocarbon raw materials, the most significant of which are coal and natural gas. Recoverable gas reserves in energy equivalent exceed oil reserves by 1.5 times, coal reserves - by more than 20 times. By expert opinion, by 2015 the share of oil in the global energy balance will be 38%, natural gas - 26%, coal - 25%.
The first stage in the conversion of natural gas and coal into chemical products and liquid fuels is their conversion into synthesis gas - a mixture of CO and H 2 . Further, the main directions of synthesis gas processing are as follows:
Synthesis of methanol;
. ammonia production;
. oxo-synthesis and formylation of aromatic compounds;
. carbonylation of methanol to acetic acid;
. carboxylation of olefins;
. Fischer-Tropsch synthesis (FT).
It should be noted that the production of synthesis gas (steam reforming or partial oxidation of methane, coal gasification) is the most expensive component of the entire production. Capital costs for the synthesis gas section in the construction of a plant for the production of methanol from natural gas or hydrocarbons using FT technology from coal are 60-70%.
The Fischer-Tropsch (FT) synthesis is a complex set of sequential and parallel transformations occurring on the surface of a heterogeneous catalyst. The main reactions are CO hydropolymerization with the formation of paraffins and olefins:
nCO + 2nH 2 CnH 2 n + H 2 O, nCO + (2n + 1) H2 n> CnH 2 n + 2 + H 2 O. In the presence of iron catalysts, significant amounts of oxygenates are also formed - alcohols, aldehydes, ketones and carboxylic acids . At elevated temperatures, in the presence of zeolite co-catalysts, aromatic compounds are formed. Side reactions - direct hydrogenation of CO into methane, disproportionation of CO (Bell-Boudoir reaction) and the reaction of water gas, which proceeds intensively on iron catalysts:
CO + 3H 2 - CH 4 + H 2 O,
2CO - C + CO 2, CO + H 2 O - CO 2 + H 2.
The maximum theoretically possible yield of hydrocarbons from 1 nm3 of synthesis gas with the composition CO:H2 = 1:2 is 208 g.
Under the conditions of FT synthesis, the thermodynamic probabilities of product formation are as follows:
Methane > alkanes > alkenes > O-containing;
. low molecular weight n-alkanes > high molecular weight n-alkanes;
- high molecular weight n-olefins > low molecular weight n-olefins.
In fact, the yield of methane on good FT synthesis catalysts does not exceed 8%. The molecular weight distribution is dictated by the polymerization kinetics (see below). Thus, the synthesis of FT is a kinetically controlled process, the composition of the final products is far from equilibrium.
Synthesis of FT is a highly exothermic process. The thermal effect of the CO hydropolymerization reaction is 165 kJ/mol CO, the thermal effect of direct hydrogenation is even higher - 215 kJ/mol. Withdrawal a large number heat during synthesis is the most important problem in the design of industrial plants for the synthesis of FT. The catalysts for the reaction are Group VIII metals. Ru, Fe, Co, Ni show the highest catalytic activity. Ruthenium is already active at 100°C; in its presence, paraffins of very high molecular weight (polymethylene) are formed at elevated pressure. However, this metal is too rare and expensive to be considered as an industrial catalyst. Nickel contacts at atmospheric pressure provide mainly direct hydrogenation of CO to methane. At elevated pressure, volatile Ni(CO) 4 is easily formed, so that the catalyst is washed out of the reactor. For these reasons, only iron and cobalt catalytic systems have been used commercially.
Cobalt catalysts were the first catalysts used in industry (in Germany and later in France and Japan in the 1930s and 1940s). Typical for their work are pressure 1-50 atm and temperature 180-250 °C. Under these conditions, mainly linear paraffins are formed. Cobalt has a significant hydrogenating activity, so part of CO inevitably turns into methane. This reaction accelerates sharply with increasing temperature, so cobalt catalysts cannot be used in the high temperature FT process. According to recent data, the specific activity of cobalt catalysts is higher than that of iron ones.
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 allow a wider range of products to be obtained: paraffins, lower α-olefins, alcohols. Under the conditions of FT synthesis, iron catalyzes the water gas reaction, which makes it possible to efficiently use the synthesis gas obtained from coal, in which the CO:H 2 ratio is below the stoichiometric 1:2. Iron catalysts have a lower hydrogen affinity than cobalt catalysts, so methanation is not a big problem for them. However, due to the same low hydrogenating activity, the surface of the iron contacts quickly carburizes, and their service life is several weeks. Cobalt contacts, on the contrary, are able to work without regeneration for a year or more. Another disadvantage of iron contacts is their inhibition by water. Since water is a product of synthesis, the kinetics of the process for iron catalysts is unfavorable, and the CO conversion per pass is low. For achievement high degree transformations, it is necessary to organize gas recycling.
Both iron and cobalt catalysts are extremely sensitive to sulfur poisoning. Therefore, synthesis gas must be pre-purified from sulfur, at least to a level of 2 mg/m 3 . Residual sulfur is adsorbed by the catalyst surface, so that, as a result, the products of FT synthesis practically do not contain it. This circumstance makes synthetic diesel fuel obtained by FT technology very attractive in view of today's stringent environmental requirements for transport.
In the synthesis of FT, a broad hydrocarbon fraction is formed (Fig. 1).
The distribution of products follows the kinetics of polymerization, and the proportion of individual hydrocarbons satisfies the Anderson-Schulz-Flory (ASF) distribution:
pn = p-(1 - α)2- α n-1, where n is the carbon number; α is the distribution parameter, which has the physical meaning of the ratio between the rate constants of chain growth and chain termination, or, in other words, the chain growth probability (Fig. 2). The value of α is determined by the nature of the catalyst, temperature and pressure of the process. For each class of products that are simultaneously formed at the same contact (paraffins, olefins, alcohols), the value of a can be different. Sometimes observed
The inclusion of lower olefins in the growing chain;
. cracking of higher paraffins;
- the presence on the surface of two or more types of polymerization centers, each of which provides its own value of α.
The distribution of ASF imposes a limitation on the selectivity of the process in relation to individual hydrocarbons and their narrow fractions. Thus, the yield of C5-C10 gasoline fraction cannot exceed 48%, C11-C18 diesel fraction - 30%. However, the selectivity towards solid paraffins increases monotonically with increasing α and asymptotically approaches 100% (Fig. 3). If the obtained paraffins are subjected to mild hydrocracking, the yield of the gas oil fraction can be increased to 60% on the reacted feedstock.
The present invention relates to a Fischer-Tropsch synthesis catalyst, a method for its production and a method for the synthesis of hydrocarbons. A supported Fischer-Tropsch synthesis catalyst is described, which includes a catalytic material, a promoter and a support material, wherein the catalytic material contains cobalt in an amount of at least 4% by weight of the catalyst and at least part of the cobalt has catalytic activity in the synthesis Fischer-Tropsch; the promoter contains nickel, and the amount of nickel present is less than the amount of cobalt; and the support material contains an oxide of a metal selected from either aluminum or titanium or zirconium. A method for producing a catalyst is described, in which the carrier is impregnated with cobalt and nickel compounds, and the impregnated composition is dried, calcined and activated. Also described is a method for the synthesis of hydrocarbons, in which the synthesis gas is in contact with the catalyst described above. EFFECT: increased activity, stability and selectivity of the catalyst. 3 n. and 31 z.p. f-ly, 2 tab., 3 ill.
Drawings to the RF patent 2389548
The field of technology to which the invention belongs
The present invention relates to Fischer-Tropsch synthesis and metal synthesis catalysts.
State of the art
In the Fischer-Tropsch process for converting synthesis gas to hydrocarbons, cobalt (Co) is the preferred active metal when the synthesis gas feedstock is natural gas. This conclusion is mainly justified by the low activity of Co in the conversion of water gas, otherwise it would lead to the conversion of part of the CO in the synthesis gas to carbon dioxide and hydrogen and, as a result, to the loss of part of the carbon in the feed.
Other known active metals in the Fischer-Tropsch synthesis are iron, ruthenium and nickel. Iron is often used, especially when the syngas feedstock is coal, because it needs its own activity in converting water gas in order to adjust the desired CO/H 2 ratio to around 2. Ruthenium is hampered by its high cost, while nickel excluded due to high selectivity to methane, thus leading to re-formation of gaseous feedstock. It is well known that nickel catalysts are used for methanation to remove traces of residual CO in the feedstock for ammonia synthesis.
Typically, the Fischer-Tropsch active metal is dispersed on a solid support. This carrier may be alumina, titanium dioxide or silicon dioxide, as well as many other oxides and mixed oxides, and the carrier may be chemically stabilized or treated different ways. Of particular interest is the high temperature treatment of alumina, which results in a catalyst with a high content of alpha alumina, and as a result, selectivity to higher hydrocarbons (C5+) is increased, as described in WO 02/47816 A1 (Statoil).
Catalyst preparation may include impregnation of the support using a chosen technique, or co-precipitation with components other than the cobalt precursor. Post-molding to the desired shape may also be part of this technique. In addition, the preparation of the catalyst usually includes steps such as drying, calcining and reduction in order to obtain an active catalyst. A number of other elements or compounds are often added during catalyst preparation. The latter may be referred to as builders, structural stability promoters, or promoters designed to improve the selectivity, activity, stability, or performance of the catalyst during regeneration. Some frequently investigated modifiers or promoters are thorium dioxide, zirconia, manganese, alkali metals, lanthanum oxide or a mixture of lanthanides, rhenium, ruthenium and platinum.
A number of alternative impregnation techniques are known in the art that use alternative solvents and chemicals, however, in the present invention, examples include a moisture capacity technique using aqueous solutions of cobalt nitrate (Co(NO 3 ) 2 ·6H 2 O) and possibly perrhenic acid (HReO 4) or ammonium perrhenate. Cobalt acetate(s), cobalt halide(s), cobalt carbonyl(s), cobalt oxalate(s), cobalt phosphate(s), cobalt organic compounds, ammonium perrhenate, rhenium halide(s), rhenium carbonyl (carbonyls), industrial solutions of metal salts, organic solvents, etc.
The moisture capacity technique provides that the metal-containing solution is mixed with a dry carrier until the pores are filled. The definition of the endpoint in this procedure may vary to some extent from laboratory to laboratory, such that the impregnated catalyst may have appearance completely dry matter or the appearance of a sticky substance such as snow. However, under no circumstances should any flowing liquid be present.
In addition, the impregnation technique can cover all available ways other than water capacity, such as precipitation, slurry impregnation with excess liquid, chemical vapor deposition, etc. It is well known that the impregnation method can affect the dispersion of the active metal (cobalt) and therefore the catalytic considered to be a structurally sensitive reaction, dispersion should not significantly affect selectivity. The impregnated catalyst is dried typically at 80-120°C in order to remove water from the pores of the catalyst and then calcined, typically at 200-450°C, e.g. 300°C for 2-16 hours.
Quantitative Analysis with a comparison of cobalt and nickel as the main metal in the Fischer-Tropsch synthesis was carried out in the work of H. Shultz, Topics in Catalysis, volume 26, 2003, pp. 73-85. Obviously, nickel has a higher hydrogenation activity than cobalt.
To the best of our knowledge, the use of nickel as a cobalt promoter has not been previously described, but EP-B-1058580 discloses the possibility of using nickel as a builder for supports such as alumina, titanium dioxide or magnesium oxide. It has been found that after calcination at temperatures up to 800°C to form a spinel compound, this modifying agent is able to suppress the solubility of the catalyst carrier in aqueous acid or neutral solutions. In the case where the builder is nickel, it is assumed that the spinel NiAl 2 O 4 is formed, which leads to a greater inertness of the support surface. However, no example was given of the effect of nickel as a modifying additive.
In addition, document EP-B-0296726 describes shaped alumina particles which are impregnated with a solution of nickel nitrate and then calcined at a temperature of about 1200° C. in order to form the spinel phase of nickel aluminate, which increases the strength of the particles. It is indicated that the heat treatment is carried out in an oxidizing environment in order to prevent the reduction of nickel to a metallic state, and therefore Ni is not used as a promoter. In addition, the resulting material is not used as a support for the Fischer-Tropsch catalyst, and there is no indication that cobalt is the active phase.
The main characteristics of a Fischer-Tropsch synthesis catalyst are activity, selectivity and stability. In addition, it is necessary to take into account the cost of the catalyst, both in terms of production costs and the cost of starting materials. The desired selectivity depends on which products are of interest for a given project, however, in the context of the present invention, the focus will be on the selectivity to the C5+ product, which is often used as an indicator of wax formation and, therefore, the potential for maximizing diesel production using hydroisomerization / paraffin cracking.
These characteristics are interrelated to some extent, for example, high activity can make it possible to lower the process temperature and thereby increase the selectivity for the C5+ product. The high stability over time means that the initial activity can be reduced, for example, by reducing the cobalt content or dispersing the cobalt.
Brief summary of the invention
According to the invention, a supported Fischer-Tropsch catalyst is provided which includes a catalytic material; a promoter and carrier material, wherein the catalytic material contains cobalt in an amount of at least 4% by weight of the catalyst, at least a portion of the cobalt has catalytic activity in the Fischer-Tropsch synthesis; the promoter contains nickel, and the amount of nickel present is less than the amount of cobalt; and the carrier material contains a metal oxide which is selected from either aluminum, or titanium, or zirconium.
Preferably, the support material consists of a metal oxide, which is selected from either aluminium, or titanium, or zirconium.
It is assumed that the carrier material contains an oxide of either aluminum, or titanium, or zirconium, optionally a combination of two or three oxides. However, titanium dioxide may include a small amount of alumina as a binder.
In addition, the metal oxide of the support material may include:
The metal oxide itself, i.e. the metal oxide and any small amount of other components that have inadvertently entered the metal oxide material as impurities or chemical residues from the production of the metal oxide material itself;
A metal oxide material that has been modified during catalyst preparation by the introduction of oxides of nickel, cobalt, or any of the promoter metals.
In the case of alumina as the support material, the term "alumina" is also intended to include a mixed alumina and silica, commonly known as "aluminosilicate", in which silica constitutes a minor part of the material.
In addition, the support material may include smaller amounts of catalytically inactive components, such as additives used to improve or maintain the mechanical strength of the catalyst particles. For example, alumina can be used as a binder in titanium dioxide based carriers. Preferably, the amount of such catalytically inactive components is less than 30% by weight, more preferably less than 20% by weight.
Preferably, the support material mainly consists of a metal oxide, which is selected from either aluminium, or titanium, or zirconium.
Some of the cobalt used in the preparation of the catalyst may be incorporated into the carrier as an oxide, optionally as a mixed oxide in combination with other metal oxides. The cobalt that is retained in the support is believed to have low catalytic activity in the Fischer-Tropsch synthesis (or no activity). Therefore, at least part of the cobalt must be present in the catalyst composition in such an amount and state (physical and chemical) that the catalyst composition becomes an effective catalyst for the conversion of synthesis gas to higher hydrocarbons (Fischer-Tropsch synthesis).
The support material may be alumina or titanium dioxide, preferably alpha or gamma alumina, most preferably alpha alumina. Optionally, the carrier material further comprises an oxide of a second metal selected from one or more of silicon, magnesium, cobalt, and nickel. The carrier may contain a spinel compound derived from alumina. Such a spinel compound may be nickel aluminate.
In addition, the catalyst may include other metal elements such as optional promoters or modifiers. Rhenium may be selected as an optional promoter. Preferably, the nickel is in the form of nickel oxide on the surface of the support. The amount of nickel may be less than 50 wt.%, preferably less than 30 wt.%, more preferably less than 15 wt.% relative to the amount of cobalt.
The cobalt or nickel can be incorporated into the metal oxide support as such, or as oxides mixed with other metal oxides in the support, such as alumina spinels. Oxides of such metals as silicon, aluminum and magnesium can play the role of binders for modifiers of basic metal oxide carriers.
In addition, the invention relates to a process for preparing the described catalyst composition, in which the carrier is impregnated with cobalt and nickel compounds, and the impregnated composition is dried, calcined and activated.
Preferably, the impregnated composition is calcined at temperatures less than 600°C, preferably in the range of 200-400°C. Preferably, the impregnated composition is calcined to such an extent that, in the final catalyst composition, less than 50% by weight, preferably less than 20% by weight, of the nickel added during the impregnation is converted to nickel spinel. Preferably, Ni(NO 3) 2 is chosen as the nickel compound during impregnation of the metal oxide support. Preferably, the impregnated and calcined composition is activated by reduction, preferably in an atmosphere containing a significant amount of hydrogen.
The present invention also relates to a process for the synthesis of hydrocarbons (Fischer-Tropsch), in which the synthesis gas is contacted with a catalyst according to the invention. Preferably, this process proceeds in three phases, where the reactants are gaseous, the product is at least partially liquid, and the catalyst is a solid. Preferably, the process takes place in a slurry bubble reactor column. Usually, H 2 and CO enter the suspension in the reactor, and the suspension contains a catalyst suspended in a liquid, which includes the interaction products of H 2 and CO, while the catalyst is maintained in suspension in the suspension, at least in part, due to gas bubbling supplied to the suspension.
Preferably, the process temperature is in the range of 190-250°C, for example 200-230°C. Preferably, the process pressure is in the range of 10-60 bar, for example 15 to 30 bar. Preferably, the ratio of H 2 /C in the gases entering the Fischer-Tropsch synthesis reactor is in the range from 1.1 to 2.2, for example from 1.5 to 1.95. Preferably, the reduced gas velocity in the reactor is in the range of 5 to 60 cm/s, for example 20 to 40 cm/s.
The synthetic product of the Fischer-Tropsch process is successively subjected to a post-treatment which may be selected from dewaxing, hydroisomerization, hydrocracking, and combinations thereof.
The present invention relates to the products of all methods and methods described here.
Surprisingly, it has been found that by adding nickel as a promoter to cobalt on the alumina surface, the activity, stability and/or selectivity of the catalyst increases depending on the composition and type of oxide support used. Nickel can be introduced by impregnation with an aqueous solution of Ni(NO 3) 2 or any other solution containing nickel, for example, in the form of a divalent ion or complex. Nickel can be in the same impregnating solution that contains cobalt and other optional promoters, or nickel is added in a separate impregnation step. After impregnation, the catalyst is dried and calcined at a relatively moderate temperature up to 600° C., typically 200-400° C., but in any case the formation of any appreciable amount of nickel spinel is avoided. The intent of this invention is that nickel, at least in part, will be reduced in a subsequent reduction step in order to play an active role as a cobalt promoter - catalyst for the Fischer-Tropsch synthesis. The amount of nickel that is needed to achieve the promoting effect and to optimize this effect will vary for different catalyst systems, depending on factors such as the amount of cobalt, type of support, type of other promoters (promoter) or modifiers (modifier) and the method of obtaining a catalyst .
In addition, the invention relates to a method for producing hydrocarbons, which consists in the fact that gaseous H 2 and CO are involved in the Fischer-Tropsch synthesis process in the presence of a catalyst, which is described above. The product of the Fischer-Tropsch synthesis is subsequently subjected to subsequent processing, which may include dewaxing, hydroisomerization, hydrocracking, washing, purification, fractionation, mixing, cracking, reforming, and combinations thereof.
The described Fischer-Tropsch synthesis catalyst is suitable for use in a three-phase reactor, especially in a bubble column. However, a further variant of the invention is to mold the catalyst into any suitable shape such as spheres, tablets or extrudates, with or without embeddings. In addition, additives or binders may be added, if necessary, during the molding process. Typically, such molded materials may have a size in the range of 1 to 20 mm and will be used in a fixed bed reactor or a compact three-phase reactor like an ebullating bed.
The Fischer-Tropsch synthesis operates with a synthesis gas containing hydrogen and CO in addition to inert or substantially inert components such as CO 2 , methane and/or nitrogen. In addition, significant amounts of steam and light hydrocarbons may be present, at least from the process itself, along with some olefinic and oxygenated by-products. The temperature of the process using a cobalt type catalyst and designed to produce mainly paraffin wax is in the range between 190 and 250°C, more typically between 200 and 230°C. The total pressure may be in the range of 10 to 50 bar, typically between 15 and 30 bar. The ratio of hydrogen and carbon monoxide consumed in this synthesis is approximately equal to 2. Therefore, the ratio of H 2 /CO in the feed will not differ greatly from the indicated value. However, it may be advantageous to use feeds with a reduced H 2 /CO ratio, for example between 1.5 and 1.95, in order to obtain increased selectivity for C5+ products.
The slurry bubble column may include some features within the reactor shell or may be connected as an external device. These features may include a gas distribution system, heat exchanger piping, a system for separating a liquid product from a slurry, and possibly forced circulation circulation pipes to enhance backmixing and equalize gradients in the reactor. The given gas flow rate per full reactor diameter is typically in the range of 10 to 60 cm/s, more typically 20 to 40 cm/s, thus providing agitated flow turbulent operation.
If necessary, the products can be condensed and separated using a system of tanks and separation columns, and mixed in order to obtain the desired products. Most of the long chain hydrocarbon product can be treated under a hydrogen atmosphere at elevated temperature and pressure in the presence of one or more catalysts to remove oxygenates and saturate olefins, crack the chain to the desired length, and isomerize substantially linear paraffins to branched paraffins. Typically, this treatment produces a synthetic diesel fuel or blended diesel fuel that does not contain aromatics or sulfur compounds, and in addition, this fuel has a very high cetane index (above 50 or even above 70) and the desired cloud point. Other products that may ultimately be produced include naphtha, especially petrochemical naphtha, base oil for lubricants and detergent synthesis components such as linear higher alpha olefins, along with liquefied petroleum gas (LPG) by-products. , alpha-olefins and oxygenated compounds.
Depending on the actual version technological process Fischer-Tropsch, different improved ones can be used in different ways. The high C5+ selectivity means that a large proportion of the desired synthetic oil or diesel fuel can be obtained from the fuel gas and that the amount of recycle streams in the plant can be reduced. This results in lower capital investment as well as lower raw material costs for these products, such as diesel fuel. The high stability and activity of the catalyst can lead to the development of smaller, more efficient reactors, as well as to a reduction in operating costs due to catalyst consumption. It should be expected that positive effect Nickel promotion of Fischer-Tropsch synthesis catalysts can be achieved in any type of reactor, such as fixed bed reactor, bubbled slurry column reactor, fluidized bed reactor, fluidized reactor, monolithic reactor, etc.
The present invention will now be illustrated by the following non-limiting examples.
Some tests in the fixed bed of activated catalysts were carried out in a laboratory plant with four reactors. Approximately 1 g of catalyst (controlled particle size fraction) is mixed with five times the volume of inert SiC particles. The reduction is carried out at a temperature of 350° C. in a reactor (in situ) using hydrogen as the reducing gas. The recovery phase lasts 16 hours. Under these conditions, a significant part of the available cobalt passes into the catalytically active state. Then carefully add a mixture of hydrogen and CO in a ratio of about 2:1. After 20 hours of operation in a mixture flow at 210° C. and a total pressure of 20 bar, the space velocity is adjusted to such an analysis that a CO conversion of between 45 and 50% is obtained after 90 hours. It is extremely important to compare the selectivity as well as the activity of catalysts at the same conversion value, since the concentration of water vapor generated by the reaction has a strong influence on the performance of the catalyst.
All catalysts used have a nominal cobalt content of 12% or 20 wt.% and 0.5 wt.% Re (or no rhenium), calculated assuming that cobalt and rhenium are completely reduced in the reduced catalysts. The actual metal content found by X-ray fluorescence (XRF) or inducible plasma (ICP) methods can differ up to ±10%, i.e. the cobalt content is between 18 and 22 wt.% of the total mass of the reduced catalyst at a nominal composition of 20 wt.% Co.
The data in Table 1 demonstrates that the addition of Ni to the cobalt or Co/Re catalyst significantly increases the activity. In addition, unexpectedly, it turned out that Ni can replace Re as a promoter. Even more surprisingly, the addition of Ni to the cobalt catalyst, either as a second promoter or instead of Re, did not reduce C 5 + selectivity, as might be expected since nickel is known to have a hydrogenating ability.
In addition, Ni has a stabilizing effect on the activity of the catalyst.
The results of typical tests for two classes of supports are summarized in Table 2. Note that alpha alumina as a catalyst support can be obtained from gamma alumina by high temperature treatment in the temperature range of 1000-1300°C.
A modified alpha alumina support containing a spinel compound can be prepared by impregnating gamma alumina or another high surface area alumina or alumina precursor with a divalent metal ion solution, followed by high temperature calcination. Said divalent metal may be a transition metal or an alkaline earth metal, nickel is preferred, and the subsequent calcination may be carried out in the temperature range from 1100 to 1250°C, for example at 1160°C.
The favorable effect of the nickel promoter on catalyst stability is seen for all three support materials used. The optimum nickel addition may vary for different catalyst systems, however, in most cases an addition in the range of 2-5% by weight appears to be sufficient. This will correspond to 10-50 wt.% nickel relative to cobalt, or preferably 10-30 wt.%.
In addition, these results demonstrate that a catalyst containing cobalt and nickel in equal amounts leads to a decrease in selectivity for C5+ products. This is not surprising since nickel is known to promote the formation of low molecular weight hydrocarbons, especially methane. Thus, when the amount of nickel exceeds the amount of cobalt, the favorable promotional effect of nickel is reduced, and its effect as a methane generation catalyst becomes more pronounced.
Experiments with industrial catalysts show a good effect on the stability of the catalyst containing only 10 wt.% Ni relative to Co. Additional tests of the catalyst with a ratio of Ni/Co=50/50 at.% showed the adverse effect of Ni due to a decrease in selectivity for C5+ hydrocarbons. This is to be expected since, at such high nickel concentrations, the properties of the Fischer-Tropsch synthesis catalyst are now determined by the activity of the nickel.
Figure 2 shows an additional example of a comparison of the catalyst 18-5A promoted with 5 wt.% Ni, with a standard catalyst 10-14A. Again, it has been demonstrated that the addition of nickel to the cobalt/rhenium impregnation solution appears to result in increased catalyst stability. The observed fluctuations in the curves in the range of 20-30 hours WRR are caused by adjusting the gas flow rate in order to match the conversion values.
An example of performance improvement for comparable catalysts 15-26A (squares) and 17-10A (diamonds) is shown in Figures 1a (top) and 1b (bottom). Obviously, catalyst 17-10A containing a nickel promoter has a significantly higher stability, approximately 3 times. Another remarkable effect was found when comparing the C5+ selectivity (in %) of the two catalysts, where nickel promotion gives an abnormal increase in selectivity in the first 100 hours and then levels off at a stable level. There is usually some decrease in selectivity over time.
CLAIM
1. A supported Fischer-Tropsch synthesis catalyst, which includes a catalytic material, a promoter and a support material, wherein the catalytic material contains cobalt in an amount of at least 4% by weight of the catalyst and at least part of the cobalt has a catalytic activity in Fischer-Tropsch synthesis; the promoter contains nickel, and the amount of nickel present is less than the amount of cobalt; and the carrier material contains an oxide of a metal selected from either aluminium, or titanium, or zirconium.
2. The catalyst according to claim 1, wherein the support material consists of a metal oxide selected from either aluminum or titanium or zirconium.
3. The catalyst according to claim 1 or 2, wherein the support material essentially consists of a metal oxide selected from either aluminum or titanium or zirconium.
4. The catalyst according to claim 1, wherein the support material is alpha or gamma alumina, preferably alpha alumina.
5. The catalyst of claim 1, wherein the carrier material further comprises a small amount (relative to the amount of alumina or titanium or zirconium) of a second metal oxide selected from one or more of silicon, aluminum, magnesium, cobalt and nickel.
6. The catalyst of claim 5, wherein the carrier material comprises an alumina-based spinel compound.
7. The catalyst of claim 6 wherein the spinel compound is nickel aluminate.
8. The catalyst of claim 1, which further includes other metal elements as optional promoters or modifiers.
9. The catalyst according to claim 8 which contains rhenium or manganese as an optional promoter.
10. The catalyst of claim 1 wherein the nickel is in the form of nickel oxide on the surface of the carrier.
11. The catalyst according to claim 1, wherein the amount of nickel is less than 50% by weight, based on the amount of cobalt.
12. The catalyst according to claim 11, wherein the amount of nickel is less than 30% by weight, relative to the amount of cobalt.
13. The catalyst according to claim 11, wherein the amount of nickel is less than 15% by weight relative to the amount of cobalt.
14. A process for the preparation of a catalyst according to any of the preceding claims 1 to 13, wherein the support is impregnated with cobalt and nickel compounds and the impregnated composition is dried, calcined and activated.
15. The method according to claim 14, wherein the impregnated carrier is calcined at a temperature below 600°C.
16. The method according to claim 15, wherein the calcination temperature is in the range of 200-400°C.
17. The process of claim 14, wherein the impregnated support is calcined to such an extent that less than 50% by weight of the nickel added during the impregnation is converted to nickel spinel in the final catalyst composition.
18. The process of claim 17 wherein the support is calcined to such an extent that less than 20 wt% nickel is converted in the final catalyst composition.
19. The method of claim 14, wherein Ni(NO 3 ) 2 is selected as the nickel source to impregnate the support.
20. The method of claim 14 wherein the impregnated and calcined support is activated by reduction, preferably in an atmosphere containing an effective concentration of hydrogen.
21. A process for the synthesis of hydrocarbons (Fischer-Tropsch), in which the synthesis gas is contacted with a catalyst according to any one of claims 1 to 13.
22. The process of claim 21, wherein the synthesis proceeds in three phases, wherein the reactants are gaseous, the product is at least partially a liquid, and the catalyst is a solid.
23. The method according to claim 21 or 22, wherein the synthesis takes place in a slurry bubble reactor column.
24. The method according to claim 21, in which H 2 and CO enter the suspension in the reactor, and the suspension contains a catalyst suspended in a liquid, which includes the interaction products of H 2 and CO, and the catalyst is maintained in suspension in a suspended state, at least in part by sparging the gas fed into the slurry.
25. The method according to claim 21, wherein the synthesis temperature is in the range of 190 to 250°C.
26. The method of claim 25 wherein the synthesis temperature is in the range of 200 to 230°C.
27. Process according to claim 21, wherein the synthesis pressure is in the range of 10 to 60 bar.
28. Process according to claim 27, wherein the synthesis pressure is in the range of 15 to 30 bar.
29. The process of claim 21, wherein the H 2 /CO ratio of the gas fed to the Fischer-Tropsch synthesis reactor is in the range of 1.1 to 2.2.
30. The method of claim 29 wherein the H 2 /CO ratio is in the range of 1.5 to 1.95.
31. The method of claim 21, wherein the reduced gas velocity in the reactor is in the range of 5 to 60 cm/s.
32. The method of claim 31, wherein the reduced gas velocity is in the range of 20 to 40 cm/s.
33. The method of claim 21, wherein the Fischer-Tropsch synthesis product is post-treated.
34. The process of claim 33, wherein the post-treatment is selected from dewaxing, hydroisomerization, hydrocracking, and combinations thereof.
The Fischer-Tropsch method for converting methane into heavier hydrocarbons was developed in 1923 and implemented in German industry in the 1940s.
Almost all aviation fuel in this country during the Second World War was produced using the Fischer-Tropsch synthesis from coal. Subsequently, this method of manufacturing motor fuels was abandoned, since the fuel obtained from oil refining, until recently, was more economically profitable.
When obtaining liquid fuel based on the Fischer-Tropsch synthesis, various carbon compounds (natural gas, hard and brown coal, heavy fractions of oil, wood waste) are converted into synthesis gas (a mixture of CO and H2), and then it is converted into synthetic "crude oil "- synth oil. This is a mixture of hydrocarbons, which, during subsequent processing, is divided into different kinds practically environmentally friendly fuel, free from impurities of sulfur and nitrogen compounds. It is enough to add 10% of artificial fuel to conventional diesel fuel so that the combustion products of diesel fuel begin to comply with environmental standards.
Even more efficient is the conversion of gas into expensive products of fine organic synthesis.
The conversion of gas to motor fuel can be generally represented as the conversion of methane into heavier hydrocarbons:
2nCH4 + 1/2nO2 = Cn H2n + nH2 O
It follows from the material balance of the gross reaction that the mass yield of the final product cannot exceed 89%.
The reaction is not directly feasible. Gas-to-liquid fuel conversion (CLF) goes through a series of technological stages(fig.17). At the same time, depending on what final product is to be obtained, one or another variant of the process is selected.
The Fischer-Tropsch synthesis can be considered as a reductive oligomerization of carbon monoxide, in which carbon-carbon bonds are formed, and in general view it is a complex combination of heterogeneous reactions, which can be represented by the total equations:
nCO + 2nH2 > (CH2)n + nH2O,
2nCO + nH2 > (CH2)n + nCO2 .
Rice. 17.
The reaction products are alkanes, alkenes and oxygen-containing compounds, that is, a complex mixture of products is formed, which is characteristic of the 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, the temperature, and the ratio of CO and H2 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 a hydrogenating activity, saturated hydrocarbons are predominantly formed.
At present, depending on the tasks set (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 are used as catalysts for the Fischer-Tropsch synthesis: iron - manganese, iron-molybdenum, etc.
In the 70 years since the discovery of synthesis, disputes over the reaction mechanism have not ceased. Three different mechanisms are currently being considered. The first mechanism, called the carbide mechanism, first proposed by Fischer and Tropsch and subsequently supported by other researchers, suggests the formation of C–C bonds as a result of the oligomerization of methylene fragments on the catalyst surface. At the first stage, CO is adsorbed and surface carbide is formed, and oxygen is converted into water or CO2:
At the second stage, the surface carbide is hydrogenated to form CHx 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 step 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 which condensation forms C–C bonds:
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 through the metal-carbon bond (the ability of CO to intercalate through the metal-alkyl bond was discussed above):
A fairly rich experimental material has been accumulated that testifies in favor of one or another variant of the mechanism, but it must be stated that at the present moment it is impossible to make an unambiguous 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 ongoing reactions.
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