Abstract

The first half of this dissertation reports the development of supported Fe FT catalysts including the effects of various, carefully chosen preparation methods on the performance of alumina-supported iron/copper/potassium (FeCuK/Al2O3); it was determined that non-aqueous slurry impregnation and co-impregnation yielded catalysts with activities as high as any reported in the literature. Furthermore, the effects of support properties including pore size, hydroxyl group concentration, and support stabilizer were investigated for FeCuK/Al2O3 catalysts containing 20 or 40% Fe. For the first time, we report the performance of a supported Fe FT catalyst that is not only more active and stable than any supported Fe catalyst previously reported, but also has activity equivalent to that of the most active, unsupported catalysts. More importantly, the catalyst is extremely stable as evidenced by the fact that after 700 h on stream, its activity and productivity are still increasing. These catalyst properties result from the use of a novel γ-alumina support material doped with silica and pretreated at 1100°C. This unique support has a high pore volume, large pore diameter, and unusually high thermal stability. The ability to pretreat this support at 1100°C enables preparation of a material having a low number of acid sites and weak metal oxide-support interactions, all desirable properties for an FT catalyst. The second half of this dissertation investigates the effects of operating conditions including the partial pressures of CO and H2 and temperature on the deactivation by carbon of 25 wt% Co/ 0.25 wt% Pt/Al2O3 catalyst. It also reports the kinetics of the main FT reaction on this catalyst. As temperature increases, the H2 and CO orders for the main reaction (in the absence of deactivation) become more positive and more negative, respectively. A new mechanism was proposed to account for the inhibition effect of CO at high reaction temperatures, which includes H-assisted dissociation of CO to C* and OH*. Further, twelve samples of the CoPt/Al2O3 catalyst were tested over a period of 800 hours and XCO < 24%, each at a different set of CO and H2 partial pressures and temperature (220-250°C). At reaction temperature of 230°C, increasing PCO or PH2 increases the deactivation rate; possibly due to formation of polymeric carbons. The H2 and CO partial pressure orders for the deactivation rate at 230°C were found to be 1.12 and 1.43, respectively using a generalized-power-law-expression (GPLE) with limiting activity of 0.7 and 1st order deactivation. For a H2/CO of 2 (PH2 = 10 bar and PCO = 5 bar) the deactivation rate increases as process temperature increases from 220 to 250°C with an activation energy of 81 kJ/mol. However, at higher CO partial pressure (PCO = 10 bar) the deactivation rate for the Co catalyst of this study decreases with increasing temperature; this can possibly be attributed to the formation of more active cobalt sites at higher temperatures due to surface reconstruction.

Degree

PhD

College and Department

Ira A. Fulton College of Engineering and Technology; Chemical Engineering

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2014-11-01

Document Type

Dissertation

Handle

http://hdl.lib.byu.edu/1877/etd7314

Keywords

Fischer-Tropsch, supported iron, silica-stabilized alumina, cobalt catalyst, deactivation by carbon, kinetics

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