Preparation of attrition-resistant spray-dried Fe Fischer-Tropsch catalysts using precipitated SiO2

Spray-dried Fe Fischer-Tropsch (FT) catalysts can be prepared that have suf ficient attrition resistance for use in slurry bubble column reactors witho ut sacrifice of their activities and selectivities. Earlier studies from ou r group have shown that the type (binder or binder-and-precipitated) and co ncentration of silica incorporated into Fe spray-dried Fischer-Tropsch (FT) catalysts have significant impacts on catalyst attrition and that attritio n resistance is strongly dependent on particle density. Although the use of a refractory oxide such as SiO2 is necessary to produce and maintain the h igh active surface area of a catalyst, the use of high concentrations of bi nder or binder-and-precipitated SiO2 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 w ork by others suggested that the use of precipitated SiO2 alone produced le ss than adequate attrition-resistant Fe catalysts. However, our previous re sults hinted at the possibility for the preparation of attrition-resistant catalysts using smaller concentrations of precipitated SiO2. Spray-dried Fe catalysts were prepared having a composition of 100 Fe/5 Cu/4.2 K but with varying amounts of precipitated SiO2. The results show that the use of sma ll amounts of precipitated SiO2 alone in spray-dried Fe catalysts can resul t in good attrition resistance. All catalysts investigated with SiO2 weight percentages less than or equal to 12 produced fines less than 10 wt % duri ng the jet cup attrition test, making them suitable for long-term use in a slurry bubble column reactor. Thus, concentration rather than type Of SiO2 incorporated into the catalyst has a more critical impact on the catalyst a ttrition resistance of spray-dried Fe catalysts. Lower amounts of SiO2 adde d to a catalyst give higher particle densities and, therefore, higher attri tion resistances. To produce a suitable SBCR catalyst, however, the amount of SiO2 added has to be optimized to provide adequate surface area, particl e density, and attrition resistance.