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 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-and-precipitated) 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 SiO2 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 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 work by others suggested that the use of precipitated SiO2 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 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 small amounts of precipitated SiO2 alone in spray-dried Fe catalysts can result in good attrition resistance. All catalysts investigated with SiO2 weight percentages less than or equal to 12 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 SiO2 incorporated into the catalyst has a more critical impact on the catalyst attrition resistance of spray-dried Fe catalysts. Lower amounts of SiO2 added to a catalyst give higher particle densities and, therefore, higher attrition resistances. To produce a suitable SBCR catalyst, however, the amount of SiO2 added has to be optimized to provide adequate surface area, particle density, and attrition resistance.