Iron-Based Fischer-Tropsch Catalysts

A key factor controlling the quality of the precipitate is the uniformity of mixing of reactants, which influences the chemical and physical properties of the 

Because of its versatility coprecipitation will remain a major route to high-metal catalysts in the future. A challenge will be to reduce the environmental impact by minimizing water consumption and by reducing the amount of salt-containing effluents in addition to improving the catalysts by an improved quality of mixing. 

The author thanks S. Axon, J. Casci and A. Zwijnenburg for suggestions and comments and Johnson Matthey for permission to publish. 

Andrew, S.P.S. (1976) in Preparation of Catalysts I, Scientific Bases for the Preparation of Heterogeneous Catalysts (eds B. Ddmon, P.A. Jacobs and 

(1996) Catalyst Handbook, Manson Publishing Ltd, London. 

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At this point, the system was tested with catalyst for activation and FTS, in the hopes that the seal leak rates would be impeded by the presence of small catalyst particles. The FTFE 20-B catalyst (L-3950) (Fe, 50.2% Cu, 4.2% K, 1.5% and Si, 2.4%) was utilized. This is part of the batch used for LaPorte FTS run II.20 The catalyst was activated at 543 K with CO at a space velocity (SV) of 9 sl/h/g catalyst for 48 h. A total of 1,100 g of catalyst was taken and 7.9 L of C30 oil was used as the start-up solvent. At the end of the activation period, an attempt was made for Fischer-Tropsch synthesis at 503 K, 175 psig, syngas SV = 9 sl/h/g catalyst, and H2/CO = 0.7. However, the catalyst was found to be completely inactive for Fischer-Tropsch synthesis. Potential reasons for catalyst poisoning under present experimental conditions were investigated. Sulfur and fluorine are known to poison iron-based Fischer-Tropsch catalysts.21,22 Since the stator of the pump is... 

In many respects the SMDS process (Figure 18.8) precipitated a change in the Fischer-Tropsch community with respect to the preferred catalyst for Fischer-Tropsch synthesis and the approach to product workup. It is therefore instructive to understand why Shell moved away from iron-based Fischer-Tropsch catalysts (and as a consequence also high-temperature synthesis) and opted for a Co-LTFT process with an uncomplicated refinery design that does not produce... 

The two important discoveries in the search for iron-based Fischer-Tropsch catalysts were (a) the finding that the addition of alkali yielded significant improvements in the activity and selectivity (to liquid products) of iron catalysts (15), and (b) the development of the medium-pressure synthesis (16). In 1943 a pilot plant was constructed at Schwarz-Leide in Germany for the comparative testing of iron-based catalysts. However, the outcome of World War II curtailed its activities. After 1945 many of the plants were destroyed and, for those remaining, recommencement of operation was forbidden for several years. Of the three plants restarted, the last at Bergkamen was closed in 1962. 

Deactivation rates and aged catalyst properties have been investigated as a function of time on stream for iron-based Fischer-Tropsch catalysts in the presence/absence of potassium and/or silicon. There is a synergism in activity maintenance with the addition of both potassium and silicon to an iron catalyst. The addition of silicon appears to stabilize the surface area of the catalyst. Catalysts containing only iron or added silicon with or without potassium consist mainly of iron oxide at the end of the run. However, iron carbides are the dominant phase of the iron catalyst with added potassium alone. Catalyst surface areas increase slightly during synthesis. The bulk phase of the catalyst does not correlate to the catalyst activity. The partial pressure of water in the reactor is lower for potassium-containing catalysts and is not a reliable predictor of catalyst deactivation rate. 

The aim of this work was to apply combined temperature-programmed reduction (TPR)/x-ray absorption fine-structure (XAFS) spectroscopy to provide clear evidence regarding the manner in which common promoters (e.g., Cu and alkali, like K) operate during the activation of iron-based Fischer-Tropsch synthesis catalysts. In addition, it was of interest to compare results obtained by EXAFS with earlier ones obtained by Mossbauer spectroscopy to shed light on the possible types of iron carbides formed. To that end, model spectra were generated based on the existing crystallography literature for four carbide compounds of... 

Li, S., Li, A., Krishnamoorthy, S., and Iglesia, E. 2001. Effects of Zn, Cu, and K promoters on the structure and on the reduction, carburization, and catalytic behavior of iron-based Fischer-Tropsch synthesis catalysts. Catal. Lett. 77 197-205. 

Iron-based Fischer-Tropsch synthesis (FTS) catalysts are preferred for synthesis gas with a low H2/CO ratio (e.g., 0.7) because of their excellent activity for the water-gas shift reaction, lower cost, lower methane selectivity, high olefin... 

Mn-promoted Fe-based Fischer-Tropsch Catalysts. 4.1.1 Unsupported Fe-Mn Fischer-Tropsch Catalysts. Iron-based F-T catalysts possess both hydrogenation and WGS activity, imposing a flexible option as a working catalyst for typically coal-derived CO-rich syngas conversion. Iron-based catalysts often contain small amounts of K and some other metals/metal oxides as promoters to improve their activity and selectivity. Mn has been widely used as one of the promoters for unsuppported Fe-based F T catalysts, particularly in promoting the production of C2 C4 olefins. ... 

Study of Deactivation of Iron-Based Fischer-Tropsch Synthesis Catalysts... 

Iron-based Fischer-Tropsch (FT) catalysts undergo a series of phase transformations during activation and use (1). Activation with carbon monoxide or syngas typically results in the conversion of Fe O to Fe O and ultimately to one or more iron carbides (2). During FT synthesis, iron carbides can be oxidized to Fe O if the or COj/CO ratios are high... 

J. B. Butt, Carbide phases on iron-based Fischer-Tropsch synthesis catalysts— part II some reaction studies, Catalysis Letters, vol. 7, no. 1—4, pp. 83—105,... 

T. Li, Y. Yang, C. Zhang, et al., Effect of manganese on an iron-based Fischer-Tropsch synthesis catalyst prepared from ferrous sulfate, Fuel, vol. 86, no. 7-8, pp. 921-928, 2007. 

De Haan, R., Joorst, G., Mokoena, E., Nicolaides, C.P., 2007. Non-sullided nickel supported on sihcated alumina as catalyst for the hydrocracking of n-hexadecane and of iron-based Fischer—Tropsch wax. Apphed Catalysis A 327, 247—254. 

The data available for heterogeneous Fischer-Tropsch catalysts indicate that with cobalt-based catalysts the rate of the water gas-shift reaction is very slow under the synthesis conditions (5). Thus, water is formed together with the hydrocarbon products [Eq. (14)]. The iron-based catalysts show some shift activity, but even with these catalysts, considerable quantities of water are produced. 

Very recently Geus and co-workers [44, 45] have applied another method based on chemical complexes. This is the complex cyanide method to prepare both monocomponent (Fe or Co) and multicomponent Fischer-Tropsch catalysts. A large range of insoluble complex cyanides are known in which many metals can be combined, e.g. iron(n) hexacyanide and iron(m) hexacyanide can be combined with iron ions, but also with nickel, cobalt, copper, and zinc ions. Soluble complex ions of molybdenum(iv) which can produce insoluble complexes with metal cations are also known. Deposition precipitation (Section A.2.2.1.5) can be performed by injection of a solution of a soluble cyanide complex of one of the desired metals into a suspension of a suitable support in a solution of a simple salt of the other desired metal. By adjusting the cation composition of the simple salt solution, with a same cyanide, it is possible to adjust the composition of the precursor from a monometallic oxide (the case when the metallic cation is identical to that contained in the complex) to oxides containing one or several foreign elements. 

Assuming that olefin intermediates are produced on the surface of the Fischer-Tropsch catalyst, similar mechanisms for chain growth have been suggested. Alcoholic intermediates also have been proposed based on the isotope-labeling studies of Emmett et al. on iron surfaces. The understanding and control of the insertion reaction appears to be the key for controlling the product distribution. Clearly the mechanism of this reaction will be subjected to close scrutiny in the near future. 

Fischer-Tropsch catalysts are sensitive to poisoning by sulfur-containing compounds. The sensitivity of the catalyst to sulfnr is greater for cobalt-based catalysts than for their iron connterparts. 

Sasol Fischer-Tropsch Process. 1-Propanol is one of the products from Sasol s Fischer-Tropsch process (7). Coal (qv) is gasified ia Lurgi reactors to produce synthesis gas (H2/CO). After separation from gas Hquids and purification, the synthesis gas is fed iato the Sasol Synthol plant where it is entrained with a powdered iron-based catalyst within the fluid-bed reactors. The exothermic Fischer-Tropsch reaction produces a mixture of hydrocarbons (qv) and oxygenates. The condensation products from the process consist of hydrocarbon Hquids and an aqueous stream that contains a mixture of ketones (qv) and alcohols. The ketones and alcohols are recovered and most of the alcohols are used for the blending of high octane gasoline. Some of the alcohol streams are further purified by distillation to yield pure 1-propanol and ethanol ia a multiunit plant, which has a total capacity of 25,000-30,000 t/yr (see Coal conversion processes, gasification). 

Fischer Tropsch technology is best exemplified by the SASOL projects in South Africa. After coal is gasified to a synthesis gas mixture, it is purified in a rectisol unit. The purified gas mixture is reacted in a synthol unit over an iron-based catalyst. The main products are gasoline, diesel fuel, and jet fuels. By-products are ethylene, propylene, alpha olefins, sulfur, phenol, and ammonia which are used for the production of downstream chemicals. 

Rao, V. U. S., Stiegel, G. J., Cinquegrane, G. J., and Srivastava, R. D. 1992. Iron-based catalysts for slurry-phase Fischer-Tropsch process Technology review. Fuel Process. Technol. 30 83-107. 

Ngantsoue-Hoc, W., Zhang, Y., O Brien, R.J., Luo, M., and Davis, B.H. 2002. Fischer-Tropsch synthesis Activity and selectivity for Group I alkali promoted iron-based catalysts. Appl. Catal. 236 77-89. 

A continuous cross-flow filtration process has been utilized to investigate the effectiveness in the separation of nano sized (3-5 nm) iron-based catalyst particles from simulated Fischer-Tropsch (FT) catalyst/wax slurry in a pilot-scale slurry bubble column reactor (SBCR). A prototype stainless steel cross-flow filtration module (nominal pore opening of 0.1 pm) was used. A series of cross-flow filtration experiments were initiated to study the effect of mono-olefins and aliphatic alcohol on the filtration flux and membrane performance. 1-hexadecene and 1-dodecanol were doped into activated iron catalyst slurry (with Polywax 500 and 655 as simulated FT wax) to evaluate the effect of their presence on filtration performance. The 1-hexadecene concentrations were varied from 5 to 25 wt% and 1-dodecanol concentrations were varied from 6 to 17 wt% to simulate a range of FT reactor slurries reported in literature. The addition of 1-dodecanol was found to decrease the permeation rate, while the addition of 1-hexadecene was found to have an insignificant or no effect on the permeation rate. 

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