Unexpected increase in C5Â + selectivity at temperature rise in high pressure Fischer-Tropsch synthesis over Co-Al2O3/SiO2 catalyst

The effect of process variables on selectivity of Fischer-Tropsch synthesis (FTS) over Co/SiO2 catalyst was studied in a fixed-bed reactor operating in gas recycle mode. The unusual increase in C5 + selectivity with temperature was found in FTS at 6 MPa. Whereas at a moderate pressure (2 MPa) the catalyst response on temperature was typical for FTS, i.e. increase in activity concurrent with decrease of C5 + selectivity, at high pressure the C5 + selectivity grew up in parallel with catalyst activity. Selectivity to C35 + hydrocarbons was in order of magnitude greater in the FTS at 6 MPa compared to 2 MPa.