Fischer-Tropsch iron catalysts

Fig. 38. Thermomagnetic curve for Fischer-Tropsch iron catalyst, / original, II...

Chen W, Fan Z, Pan X, Bao X. Effect of confinement in carbon nanombes on the activity of Fischer-Tropsch iron catalyst. J Am Chem Soc 2008 130 9414-9. 

Temperature-programmed reduction combined with x-ray absorption fine-structure (XAFS) spectroscopy provided clear evidence that the doping of Fischer-Tropsch synthesis catalysts with Cu and alkali (e.g., K) promotes the carburization rate relative to the undoped catalyst. Since XAFS provides information about the local atomic environment, it can be a powerful tool to aid in catalyst characterization. While XAFS should probably not be used exclusively to characterize the types of iron carbide present in catalysts, it may be, as this example shows, a useful complement to verify results from Mossbauer spectroscopy and other temperature-programmed methods. The EXAFS results suggest that either the Hagg or s-carbides were formed during the reduction process over the cementite form. There appears to be a correlation between the a-value of the product distribution and the carburization 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. 

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. 

The various factors that can contribute to deactivation of iron Fischer-Tropsch (FT) catalysts include transformation of the active phase into an inactive constituent, poisoning by carbonaceous species and heteroatoms, and loss of active phase surface area. Progress in elucidating the causes of deactivation is hampered by the inability to conclusively identify the active phase in iron FT catalysts. In recent work involving doubly promoted, unsupported iron catalysts, the sequence of phase transformations shown in Figure 1 that take the catalyst from its as-prepared hematite phase to iron carbide [1,2] was postulated. 

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... 

These results make it clear that relating the catalyst composition to the catalytic activity of an iron Fischer-Tropsch synthesis catalyst will be a demanding task. It appears that the carbide phase is more active than the oxide phase. Furthermore, the data for the promoted and unpromoted show that the initial activity of the x-Fe5C2 phase is as great as the e or e -carbide (Fe2C to Fe2 2C) phases. The present data do not allow us to decide whether it is the presence of potassium or the stability of the iron carbide phases that allows the e or e -carbide (Fe2C to Fe2.2C) phases to remain as the conversion declines to a low level while the x-FesC2 oxidizes as the conversion decreases. 

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. 

C.-H. Zhang, Y. Yang, B.-T. Teng, et al., Study of an iron-manganese Fischer-Tropsch synthesis catalyst promoted with copper, Journal of Catalysis, vol. 237, no. 2, pp. 405-415, 2006. 

Fischer-Tropsch Process. The Hterature on the hydrogenation of carbon monoxide dates back to 1902 when the synthesis of methane from synthesis gas over a nickel catalyst was reported (17). In 1923, F. Fischer and H. Tropsch reported the formation of a mixture of organic compounds they called synthol by reaction of synthesis gas over alkalized iron turnings at 10—15 MPa (99—150 atm) and 400—450°C (18). This mixture contained mostly oxygenated compounds, but also contained a small amount of alkanes and alkenes. Further study of the reaction at 0.7 MPa (6.9 atm) revealed that low pressure favored olefinic and paraffinic hydrocarbons and minimized oxygenates, but at this pressure the reaction rate was very low. Because of their pioneering work on catalytic hydrocarbon synthesis, this class of reactions became known as the Fischer-Tropsch (FT) synthesis. 

In the early 1920s Badische Arulin- und Soda-Fabrik aimounced the specific catalytic conversion of carbon monoxide and hydrogen at 20—30 MPa (200—300 atm) and 300—400°C to methanol (12,13), a process subsequendy widely industrialized. At the same time Fischer and Tropsch aimounced the Synth in e process (14,15), in which an iron catalyst effects the reaction of carbon monoxide and hydrogen to produce a mixture of alcohols, aldehydes (qv), ketones (qv), and fatty acids at atmospheric pressure. 

M. E. Dry, "Fischer-Tropsch SyntEesis Over Iron Catalysts," paper presented at 1990 SpringyTLChP National Meetings Orlando, Fla., Mar. 18—22, 1990. 

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). 

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). 

Hardness on the Mohs scale is often above 8 and sometimes approaches 10 (diamond). These properties commend nitrides for use as crucibles, high-temperature reaction vessels, thermocouple sheaths and related applications. Several metal nitrides are also used as heterogeneous catalysts, notably the iron nitrides in the Fischer-Tropsch hydriding of carbonyls. Few chemical reactions of metal nitrides have been studied the most characteristic (often extremely slow but occasionally rapid) is hydrolysis to give ammonia or nitrogen ... 

Shortly after World War I, Badische Amlin patented the catalytic conversion of synthesis gas to methanol, and Fischer and Tropsch (F-T) announced a rival process in which an iron catalyst converted synthesis gas into a mixture of oxygenated hydrocarbons. Later,... 

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

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... 

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