Spray-dried Fe Fischer-Tropsch (FT) catalysts can be prepared that have sufficient attrition resistance for use in slurry bubble column reactors without sacrifice of their activities and selectivities. Earlier studies from our group have shown that the type (binder or binder-andprecipitated) and concentration of silica incorporated into Fe spray-dried Fischer-Tropsch (FT) catalysts have significant impacts on catalyst attrition and that attrition resistance is strongly dependent on particle density. Although the use of a refractory oxide such as SiO 2 is necessary to produce and maintain the high active surface area of a catalyst, the use of high concentrations of binder or binder-and-precipitated SiO 2 results in poorer attrition resistance. This paper reports on the effect of precipitated silica by itself on the attrition resistance of Fe FT catalysts produced by spray drying. Earlier work by others suggested that the use of precipitated SiO 2 alone produced less than adequate attrition-resistant Fe catalysts. However, our previous results hinted at the possibility for the preparation of attrition-resistant catalysts using smaller concentrations of precipitated SiO 2 . Spray-dried Fe catalysts were prepared having a composition of 100 Fe/5 Cu/ 4.2 K but with varying amounts of precipitated SiO 2 . The results show that the use of small amounts of precipitated SiO 2 alone in spray-dried Fe catalysts can result in good attrition resistance. All catalysts investigated with SiO 2 weight percentages e12 produced fines less than 10 wt % during the jet cup attrition test, making them suitable for long-term use in a slurry bubble column reactor. Thus, concentration rather than type of SiO 2 incorporated into the catalyst has a more critical impact on the catalyst attrition resistance of spray-dried Fe catalysts. Lower amounts of SiO 2 added to a catalyst give higher particle densities and, therefore, higher attrition resistances. To produce a suitable SBCR catalyst, however, the amount of SiO 2 added has to be optimized to provide adequate surface area, particle density, and attrition resistance.
Attrition properties of two spray-dried iron Fischer−Tropsch (F−T) catalysts with compositions 100:5:4.2:11 Fe/Cu/K/(P)SiO2 (catalyst P; P = precipitated) and 100:5:4.2:1.1 Fe/Cu/K/(B)SiO2 (catalyst B; B = binder) were studied under reactive conditions in a stirred-tank slurry reactor (STSR) by determining particle size distribution and morphology before and after reaction tests. Catalyst P experienced a large reduction in Sauter mean diameter (87%) after 380 h of testing in the STSR, which is attributed to its morphology (large number of irregularly shaped particles). Low attrition strength of this catalyst was also evident from considerable generation of fine particles (<10 μm) during the STSR test (62.5% increase in fraction of fines). Catalyst B, consisting of largely spherical particles, experienced a smaller reduction in Sauter mean diameter (39.9%) and generation of fine particles was much smaller (3.7%). These two catalysts had excellent selectivity characteristics (low methane and high C5 + yields), but their productivity and stability (deactivation rate) need to be improved.
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