Tropsch synthesis, Fischer

The Fisher-Tropsch plants build in Germany before World War II and during World War II produced about 16,000 barrels (1 barrel = 0.159 m3) per day of liquid fuels from coal, employing a Co catalyst in fixed-bed reactors [5], However, during the 1950s, the Fisher-Tropsch process turned out to be uneconomical as a consequence of the abundant supply of crude oil. Nevertheless, currently considerable attention is being paid to develop alternatives of the Fisher-Tropsch process to generate liquid fuels from natural gas, biomass, oil sands, oil shales, and coal [134], 

The Fisher-Tropsch catalytic process is carried out with a metallic catalyst [128], by a reductive oligomerization of carbon monoxide in the presence of hydrogen [135]  

In order to explain the mechanism of the Fisher-Tropsch reaction, some authors derived the Langmuir-Hinshelwood or Eley-Rideal types of rate expressions for the reactant consumption, where in the majority of cases the rate-determining step is supposed to be the formation of the building block or monomer, methylene [134], 

The methanol synthesis has a higher thermal efficiency (approximately 72%) [420] than the FT synthesis. CO2 is a reactant in the synthesis which gives room for a high carbon efficiency and less constraints on the syngas unit. 

It may be argued that energy efficiency is of less importance when natural gas is cheap, but high energy efficiency means small feed pretreat units and reduced requirements for utilities and hence less investments. Moreover, high efficiency means less CO2 production. Therefore, it is important that the s mgas composition is tuned (or adjusted for maximum conversion per pass) in the FT synthesis. 

Synthetic natural gas or substitute natural gas (SNG) can be manufactured by the methanation reaction [219] [423]. Reactions are seen in Table 2.16. 

For many years, methanation has been used as the final clean-up step in preparing synthesis gas for the ammonia s5mthesis (Section 2.5) and lately as one solution for cleaning hydrogen for PEM fuel cells. 

The methanation reactions are the reverse of the reactions for steam reforming. Nickel and other Group VIII metals are active. Both CO2 and CO are converted, meaning that the syngas should have a module M=3 (refer to Table 1.6). 

The Fischer-Tropsch (F-T) reaction, which is conducted as a solid-catalyzed gas-phase reaction, and which is commercially operated in several countries, is inevitably accompanied by local overheating of the catalyst surface as well as by the production of heavy wax (alkanes higher than C2o)- Local overheating of the catalyst may lead to catalyst deactivation and also to an increase in methane selectivity. Heavy wax may plug micropores of the catalyst and the catalyst bed itself, also resulting in catalyst deactivation. 

The slurry-phase F-T process, in which a slurry, composed of fine powdery catalyst and mineral oil, is used as the reaction medium, has been developed to overcome disadvantages of the gas-phase process [9]. However, the diffusion of synthesis gas into the micropores of the catalysts is so slow in the slurry phase that the overall reaction rate is markedly lower than that in the gas-phase reaction [10,11]. Further, the concentration of solid catalyst particles in the slurry medium is limited to low levels ( 20 wt%) in order to maintain slurry fluidity. Other disadvantages of the slurry reactors are the accumulation of high-molecular-weight products in the reactor during operation, and the in situ separation of fine catalyst particles from the heavy products. 

Fujimoto and Fan developed an F-T synthesis in the supercritical phase and compared its reaction performance to that in the liquid phase and the gas phase. The supercritical phase F-T reaction, as described here, shows unique characteristics such as rapid diffusion of reactant gas, effective removal of reaction heat, and in situ extraction of high-molecular-weight hydrocarbons (wax). 

Alumina-supported ruthenium catalysts were prepared by impregnating alumina (Aerosil, 200 m /g) with ruthenium chloride from its aqueous solution. The catalysts composition was Ru Al203 = 2 98 by weight. The catalyst precursors were dried overnight at 120°C in an air oven, and were then calcined at 450 °C for 2 h to form a supported metal oxide [12,13]. The catalysts were reduced in a hydrogen flow at 150°C and 300 °C for 1 h each, and at 400 °C for 2 h in series and then passivated. They were reduced again at 400 °C for 2 h in situ before the catalytic reaction. 

Silica-supported cobalt catalysts were prepared from cobalt nitrate (Co(N03)2), lanthanum nitrate (La(N03)3) and commercially available silica gel (Fuji Davison, ID gel, 270 m /g) using conventional methods of impregnation [14]. The composition of the catalyst was Co La Si02 = 20 6 87 by weight. The catalyst precursor was dried in air at 120°C and then calcined at 450 °C for 3 h to form supported metal oxides. It was then exposed to hydrogen at 400 °C for 12 h. The mean pore diameter of the catalyst was 8.7 nm. 

This is a catal3dic process leading to the formation of higher hydrocarbons (and/or alcohols) from CO and H2 closely related to methanol synthesis. Earlier isotopic studies were reviewed by Eidus.l A very detailed paper by Raje and Davis summarised tracer studies up to 1995.I ) Some important milestones will only be surveyed here and a few more recent results will be added. 

The possible steps of Fischer-Tropsch (FT) reaction and its catalysts (Fe, Co, Ru, Ni) represent a very complicated systemThe catalysts usually need a formation or self-organisation , meaning that the full activity will only be reached after a certain period. This means that for Fe-based catalysts, a part of the initial Fe oxide is transformed into iron carbide. This was investigated as early as 1948 by the tracer method.A fused iron catalyst was carbided with The synthesis product from CO/H2 = 1 1 reactant contained 10-15% labelled molecules, almost independently of the reaction conditions, even in repeated runs, indicating the minor role of carbide incorporation into hydrocarbons. The formation of a Fe-Al-Cu catalyst at 523 K and various H2/CO ratios required 100 to 2000 minutes. The yield of retained carbon decreased gradually, while the FT yield increased more abruptly after this period. [ 1 

Techniques described in the previous sections should be combined with the tracer studies of Fischer-Tropsch reaction. One has to add a labelled 

More detailed schemes have been presented in Refs. 86, 91 and 92. 

Radiotracers contributed to clarify that the chain initiation is different on Fe and Co or Ni catalysts. This question was first studied by using 

The first study that utilized syngas (CO + H2) with Ni/kieselgur catalysts, producing higher-chain hydrocarbons at atmospheric pressures was discovered by Franz Fischer in 1925. However, Fischer discovered that a mixture of cobalt and chromium oxides was more active. From these discoveries, several developments were made, such as design and construction of GTL plants, seeking the development of more efficient processes. The success of the innovation process in GTL technology has a very important impact potential for biomass. 

Currently, there are three large industrial complexes one factory Shell Company in Malaysia a series of plants operated by Sasol and one factory of PetroSA, both in South. The first one, despite the small scale of 15,000 barrels per day, it is economically viable because their production is destined for food-grade paraffin. In South Africa, the PetroSA industrial plant has a capacity of 36,000 barrels per day, while the two Sasol plants produce more than 100,000 barrels per day (bpd). 

The shipping cost is much lower than that of natural gas. It has calorific (kcal N m ) about one thousand times lower than oil, which not only cause high costs for transportation, but also requires specific assets (pipelines or LNG tankers) for their exploitation. 

The products produced by GTL plants have important environmental benefits compared to traditional products because they are produced from a relatively cleaner fuel natural gas. 

The theoretical ratio of H2/CO used in the reaction is approximately 2 1. However, in addition to the Fischer-Tropsch (Equation 23.17), we have the steam reforming reaction in parallel (Equation 23.18). 

A silicon-chip-based reactor was applied for the Fischer-Tropsch synthesis using an iron catalyst [77]. The chips had outer dimensions of 1 X3cm with channel dimensions of 5 or 100 pm width at 50-100 pm depth. The reaction was carried out at a H2/CO ratio of 3, and flow rates of 0.4 std. cm min between 200 and 250 °C. Conversions between 50 and 70% were found after 12 h activation of the catalyst under reaction conditions. 

In this chapter, the various characteristics of MSR for fluid-solid reactions are presented. It is clear that microreactors are mostly suitable for reactions that have fast intrinsic kinetics and require rapid transport, are carried out at high temperatures and pressures, and, therefore, ensure inherent safety. Effective exploitation of the full chemical potential of catalysts through high rates of heat and mass transfer provides an excellent means for identifying novel synthesis routes that are both economically attractive and environmentally benign. 

The time available for chemical transformation in the MSR is very short because of their small size, which results in low hold-ups, on one hand, but necessitates highly efficient mass/heat transfer, on the other. The amount of power dissipation for multiphase reactions per unit of interfacial area is very low, leading to significant reductions in the energy consumption. 

Nevertheless, there are several constraints hampering the use of microstruc-tured devices for fluid-solid reactions. In the catalytic reactions, the performance is very adversely affected by catalyst deactivation. Effective in situ catalyst regeneration thus becomes necessary, as the simple catalyst change practiced in conventional reactors is usually no longer an option. The thickness of the catalytic wall is often greater than the internal diameter of the channel and, therefore, may impede heat transfer for highly exothermic reactions leading to nonisothermal behavior. 

Reactions involving highly viscous materials or suspended particles are difficult to carry out in the microreactor. 

Franz Fischer (1877-1947) a German chemist who together with Hans Tropsch discovered in the 1920 the Fischer-Tropsch synthesis. He also worked with Wilhelm Ostivald and Emil Fischer, in 1914, he became Director of the Kaiser Wilhelm Institute for Coal Research. 

Hans Tropsch (1889-1935) A German chemist born in German Bohemia (now Czech Republic). From 1920 until 1928 he worked ai the Kaiser Wilhelm Institute for Coal Research both with Franz Fischer and Otto Roelen. in 1928 he became professor at the Institute for Coal Research in Prague. From 1931 until 1935, he worked in the United States at the Armour Institute of Technology in Chicago. Owing to an illness he returned to Germany in 1935, where he died shortly after his arrival. 

There is at present much interest in the use of solid ruthenium catalysts for Fischer-Tropsch synthesis.24 It has been found that the maximum chain growth in the synthesis reaction is strongly affected by the size of the ruthenium particles. The smaller the particles, the lower the molecular weight of the products. Specifically it has been found that the maximum petroleum production should result if the crystallite size can be controlled in the range of 3-4 nm. 

The catalytic hydrogenation of carbon monoxide resulting in the formation of paraffin-olefin mixtures of different C-numbers is what is called the Fischer-Tropsch synthesis. The product spectrum depends on the operating conditions and the catalysts applied and on the partial pressures of CO and H2 in the synthesis gas  

The resulting hydrocarbons are characterized by the strong arrangement of the C-atoms used as a raw material in the petrochemical industry or for the production of synthetic hydrocarbons [13]. 

Until now the Fischer-Tropsch technology has never been able to compete economically with conventional fuel and was limited to very isolated cases. Recent process innovations, however, give hope to a comeback for the exploitation of untapped gas fields in remote regions as an alternative to LNG processing. Shell and Sasol are currently the only companies to operate Fischer-Tropsch plants on a commercial basis. 

A significant application of hydrogen with a large-scale technological importance is in the food industry the hardening of fats and oils by catalytic hydrogenation for the purpose of extended durability. The process takes place at pressures of 20 - 40 MPa and at temperatures of 200 - 400 °C. 

One of the most important, and perhaps the best studied, applications of three-phase fluidization is for the hydrogenation of carbon monoxide by the Fischer-Tropsch (F-T) process in the liquid phase. In this process, synthesis gas of relatively low hydrogen to carbon monoxide ratio (0.6 0.7) is bubbled through a slurry of precipitated catalyst suspended in a heavy oil medium. The F-T synthesis forms saturated and unsaturated hydrocarbon compounds ranging from methane to high-melting paraffin waxes (MW 20,000) via the following two-step reaction  

The overall reaction of the desired hydrocarbon synthesis is thus 

Selectivity to desired products including light hydrocarbons, gasoline, or diesel fuel depends upon the catalyst employed, the reactor temperature, and the type of process employed. Products of the F-T synthesis are suitable for further chemical processing because of their predominantly straight chain structure and the position of the double bond at the end of the chain. By-products formed on a lesser scale include alcohols, ketones, acids, esters, and aromatics. 

Transport properties and reaction engineering aspects of F-T synthesis have been the subject of comprehensive reviews, e.g., Kolbel and Ralek (1980), Anderson (1984), and Saxena et al. (1986). Readers are referred to these references for details on the F-T synthesis and the extensive literature listings contained in them. 

Another current development in the use of F-T chemistry in a three-phase slurry reactor is Exxon s Advanced Gas Conversion or AGC-21 technology (Eidt et al., 1994 Everett et al., 1995). The slurry reactor is the second stage of a three-step process to convert natural gas into a highly paraffinic water-clear hydrocarbon liquid. The AGC-21 technology, as in the Sasol process, is being developed to utilize the large reserves of natural gas that are too remote for economical transportation via pipelines. The converted liquid from the three-step process, which is free of sulfur, nitrogen, nickel, vanadium, asphaltenes, polycyclic aromatics, and salt, can be shipped in conventional oil tankers and utilized by most refineries or petrochemical facilities. 

FIGURE 3.1 Variation of crude oil price. (Reproduced from U.S. Energy Information Administration Website. Independent Statistics Analysis, http //www.eia.gov/dnav/pet/hist/ LeafHandler.ashx n=PET s=RBRTE f=D, Accessed Sept. 2013.) 

TABLE 3 A U.S. Department of Energy Estimate of World Fossil Fuel Reserves  

The interest in coal conversion processes, however, is increasing due to the order of magnitude higher price for the petroleum crude as compared to the pre-1970s prices. 

The current (2013) high prices of oil and the fact that no major fields have been discovered make the coal (or inexpensive hydrocarbons) to oil alternative commercially attractive for countries that have far greater coal reserves than petroleum crude. This can also be judged from the fact that the number of research publications dealing with Fischer-Tropsch process in 2009 was approximately three times those in 1998 (Zhang et al. 2010). 

The overall coal to oil conversion occurs in three stages (1) mining of coal, (2) preparation of synthesis gas, and (3) the Fischer-Tropsch synthesis along with downstream processing. According to Dry (1990), the second and third stages contribute 23 and 30% of the total capital investment, respectively. 

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A number of chemical products are derived from Sasol s synthetic fuel operations based on the Fischer-Tropsch synthesis including paraffin waxes from the Arge process and several polar and nonpolar hydrocarbon mixtures from the Synthol process. Products suitable for use as hot melt adhesives, PVC lubricants, cormgated cardboard coating emulsions, and poHshes have been developed from Arge waxes. Wax blends containing medium and hard wax fractions are useful for making candles, and over 20,000 t/yr of wax are sold for this appHcation. 

The second reaction is called the Fischer-Tropsch synthesis of hydrocarbons. Depending on the conditions and catalysts, a wide range of hydrocarbons from very light materials up to heavy waxes can be produced. Catalysts for the Fischer-Tropsch reaction iaclude iron, cobalt, nickel, and mthenium. Reaction temperatures range from about 150 to 350°C reaction pressures range from 0.1 to tens of MPa (1 to several hundred atm) (77). The Fischer-Tropsch process was developed iadustriaHy under the designation of the Synthol process by the M. W. Kellogg Co. from 1940 to 1960 (83). 

Heat Release and Reactor Stability. Highly exothermic reactions, such as with phthaHc anhydride manufacture or Fischer-Tropsch synthesis, compounded with the low thermal conductivity of catalyst peUets, make fixed-bed reactors vulnerable to temperature excursions and mnaways. The larger fixed-bed reactors are more difficult to control and thus may limit the reactions to jacketed bundles of tubes with diameters under - 5 cm. The concerns may even be sufficiently large to favor the more complex but back-mixed slurry reactors. 

Fischer-Tropsch Waxes. Polymethylene wax [8002-74-2] production is based on the Fischer-Tropsch synthesis, which is basicaHy the polymerisation of carbon monoxide under high pressure and over special catalysts to produce hydrocarbons (see Fuels, synthetic-liquid fuels). 

The first demonstration of catalytic conversion of synthesis gas to hydrocarbons was accompHshed ia 1902 usiag a nickel catalyst (42). The fundamental research and process development on the catalytic reduction of carbon monoxide was carried out by Fischer, Tropsch, and Pichler (43). Whereas the chemistry of the Fischer-Tropsch synthesis is complex, generalized stoichiometric relationships are often used to represent the fundamental aspects ... 

Fig. 11. Optimum pressure/temperature ranges for Fischer-Tropsch synthesis processes showiag the various catalysts ia parentheses. To convert MPa to...

General References Dry, The Fischer-Tropsch Synthesis, Catalysis Sci-... 

Fischer-Tropsch Synthesis The best-known technology for producing hydrocarbons from synthesis gas is the Fischer-Tropsch synthesis. This technology was first demonstrated in Germany in 1902 by Sabatier and Senderens when they hydrogenated carbon monoxide (CO) to methane, using a nickel catalyst. In 1926 Fischer and Tropsch were awarded a patent for the discovery of a catalytic technique to convert synthesis gas to liquid hydrocarbons similar to petroleum. 

Other reactions may also occur during the Fischer-Tropsch synthesis, depending on the catalyst employed and the conditions used Water-gas shift ... 

The indirect liquefaction basehne design is for a plant of similar size. Unhke the direct hquefaction basehne, the design focuses on producing refined transportation fuels by use of Sheh gasification technology. Table 27-17 shows that the crude oil equivalent price is approximately 216/m ( 34/bbl). Additional technological advances in the production of synthesis gas, the Fischer-Tropsch synthesis, and product refining have the potential to reduce the cost to 171/m ( 27/bbl) (1993 US dollars), as shown in the second column of Table 27-17. 

As an example of the chemical signihcance of the process technology, the products of die Fischer-Tropsch synthesis, in which a signihcant amount of gas phase polymerization occurs vary markedly from hxed bed operation to the fluidized bed. The hxed bed product contains a higher proportion of straight chain hydrocarbons, and the huidized bed produces a larger proportion of branched chain compounds. 

J.R. Anderson and M. Boudait (eds), Catalysis, Science and Technology, Several volumes. Springer Verlag, Berlin TP156 C35 C375 Volume 1 M.E. Diy, The Fischer-Tropsch synthesis, pp. 160-255. 

Hot (230-240°F) potassium carbonate treating was patented in Germany in 1904 and perfected into modem commercial requirements by the U.S. Bureau of Mines. The U.S. Bureau of Mines was working on Fischer-Tropsch synthesis gas at the time. Potassium carbonate treating requires high partial pressures of CO2. It therefore cannot successfully treat gas containing only H2S. ... 

Masters, Adv. Organometallic Chem. 17, 61-103 (1979). R. B. Anderson, The Fischer-Tropsch Synthesis, Academic Press, London, 1984, 320 pp. 

Diy, M. E. (1990). Fischer-Tropsch Synthesis over Iron Catalysts, Spring 1990 A.I.Ch.E. Meeting, Orlando, Florida. March 18-22, 1990. 

During the late seventies and early eighties, when oil prices rose after the 1973 war, extensive research was done to change coal to liquid hydrocarbons. However, coal-derived hydrocarbons were more expensive than crude oils. Another way to use coal is through gasification to a fuel gas mixture of CO and H2 (medium Btu gas). This gas mixture could be used as a fuel or as a synthesis gas mixture for the production of fuels and chemicals via a Fischer Tropsch synthesis route. This process is... 

Synthesis gas consists of a nonhydrocarhon mixture (H2,CO) ohtain-ahle from more than one source. It is included in this chapter and is further noted in Chapter 5 in relation to methane as a major feedstock for this mixture. This chapter discusses the use of synthesis gas obtained from coal gasification and from different petroleum sources for producing gaseous as well as liquid hydrocarbons (Fischer Tropsch synthesis). 

Hydrocarbons from Synthesis Gas (Fischer Tropsch Synthesis, FTS)... 

Fischer Tropsch synthesis is catalyzed by a variety of transition metals such as iron, nickel, and cobalt. Iron is the preferred catalyst due to its higher activity and lower cost. Nickel produces large amounts of methane, while cobalt has a lower reaction rate and lower selectivity than iron. By comparing cobalt and iron catalysts, it was found that cobalt promotes more middle-distillate products. In FTS, cobalt produces... 

Dry, M. E., The Fischer Tropsch Synthesis, in Catalysis Science and Technology, edited hy J. R. Anderson and M. Boudart, Springer Verlag, 1981. 

Rober, M. Fischer-Tropsch Synthesis in Catalysis in Cj Chemistry, edited by W. Keim, D. Reidel Publishing Company, Dordrecht, The Netherlands, 1983, pp. 41-87. 

Many chemicals are produced from synthesis gas. This is a consequence of the high reactivity associated with hydrogen and carhon monoxide gases, the two constituents of synthesis gas. The reactivity of this mixture was demonstrated during World War II, when it was used to produce alternative hydrocarbon fuels using Fischer Tropsch technology. The synthesis gas mixture was produced then hy gasifying coal. Fischer Tropsch synthesis of hydrocarbons is discussed in Chapter 4. 

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