Effects of sulphur on a Co/Mn-based catalyst for Fischer-Tropsch reactions

Abstract

The long term effect of up to 10 ppm H2S was studied for Fischer–Tropsch conversion of syngas by catalytic testing at 240 °C, 5 bar, H2/CO = 2.1 and GHSV = 2400 Nml/gcat h. Sulphur was dosed after ~ 300 or ~ 1000 h time on stream and the effect was monitored using on-line GC. The activity declined, and the effect correlated to the concentration of H2S in the feed. However, dosing after ~ 1000 h caused a stronger effect than dosing after ~ 300 h. The effects of sulphur are significant with respect to operational risks and mitigation but are substantially less severe than for a standard Co-based catalyst operated at 20 bar for wax production. The spent catalyst consisted of a mixture of cubic (Co, Mn)O, hexagonal Co, Co2C and sulphurous deposits; mainly MnSO4. It could not be concluded that sulphur had a direct effect on product selectivity, but it may have impacted water-gas-shift activity, and sudden changes in shift activity was found to correlate to changes in hydrocarbon selectivity.