Modified product selectivity in Fischer-Tropsch synthesis by catalyst pre-treatment

Abstract

Fischer-Tropsch Synthesis (FTS) yields a spectrum of products with carbon lengths of 1 to upwards of 100 units. In order to make use of the full spectrum of hydrocarbon fractions, particularly the heavier units, secondary processing is required. Modifying the FTS product distribution and catalyst activity in order to decrease the amount of long chain hydrocarbons (C25+) may allow significant simplification of FTS based processes. To this end we report the results of in-situ pre-treatment of alumina supported cobalt catalysts (Co/Ru/La – Al2O3) with acetylene in a fixed-bed reactor. It is postulated that acetylene dissociation and dehydrogenation resulted in the generation of carbidic and CxHy species on the catalyst surface. The formation of these carbonaceous species on different active sites of the catalyst surface following pre-treatment also significantly altered the FTS product distribution by affecting the extent and pathway of 1-olefin secondary reactions. It is thought that these changes resulted from decreased incorporation of 1-olefins in further chain growth and a decrease in secondary hydrogenation rate. The amount of heavy hydrocarbons (waxes) produced was reduced by more than two-fold.