Spray-dried iron Fischer-Tropsch catalysts. 2. Effect of carburization on catalyst attrition resistance

Spray drying has been recently used by this research team in the preparatio n of Fe Fischer-Tropsch catalysts with higher attrition resistance for use in slurry bubble column reactors. In the first paper in this series, the ef fects of the type, concentration, and network structure of SiO2 on the attr ition resistance of two series of spray-dried Fe catalysts in their calcine d state were explored and the dependence of catalyst attrition resistance o n catalyst particle density was discussed. As a continuation of our previou s effort, the effect of carburization on catalyst attrition resistance was studied and is presented in this paper. After carburization, the majority c omponent of the catalysts, hematite (Fe2O3), was converted to iron carbides , mostly X-carbide (Fe2C5). Breakage of individual catalyst particles and f ines formation, which can be considered as evidence of chemical attrition, was only observed during carburization of the catalyst with low SiO2 concen tration <9 wt %. With an increase in the total concentration of SiO2, such chemical attrition during the Fe phase change appeared to be eliminated or negligible except for the breakup of large agglomerates during carburizatio n. There were, generally, significant decreases in the Brunauer-Emmett-Tell er surface areas and average particle sizes of the catalysts upon carburiza tion. Surprisingly, carburization of these Fe catalysts did not weaken the particle structures with regards to physical attrition. In fact, depending on catalyst composition, the overall attrition resistances of the carburize d catalysts measured using a jet cup system were similar to or better than those of the same catalysts in their calcined form. However, any seeming im provement in attrition resistance is suggested to be related mainly to the increase in catalyst particle density (related to catalyst inner structure) after carburization.