Effect of silica on iron-based Fischer-Tropsch catalysts

Abstract

The effect of silica addition via coprecipitation and as a binder to a doubly promoted Fischer-Tropsch (F-T) synthesis iron catalyst (100 Fe/5 Cu/4.2 K) was studied. The catalysts (nominally 50 μm particles) were prepared by coprecipitation, followed by binder addition and spray drying at 250 °C in a 1 m diameter, 2 m tall spray dryer. The binder silica content was varied from 0 to 20 wt%. A catalyst with 12 wt% binder silica was found to have the highest attrition resistance. F-T reaction studies over 100 hours in a fixed-bed reactor showed that this catalyst maintained around 95% CO conversion with a methane selectivity of less than 7 wt% and a C5+ selectivity of greater than 73 wt%. The effect of adding precipitated silica from 0 to 20 parts by weight (pbw) to this catalyst (containing 12 wt% binder silica) was also studied. Addition of precipitated silica was found to be detrimental to attrition resistance and resulted in increased methane and reduced wax formation.