The effect of synthesis gas composition on the Fischer–Tropsch synthesis over Co/γ-Al2O3 and Co–Re/γ-Al2O3 catalysts

The Fischer–Tropsch synthesis over Co/γ-Al2O3 and Co–Re/γ-Al2O3 was investigated in a fixed-bed reactor at 20 bar and 483 K using feed gases with molar H2/CO ratios of 2.1, 1.5 and 1.0 simulating synthesis gas derived from biomass. With lower H2/CO ratios in the feed, the CO conversion and the CH4 selectivity decreased, while the C5+ selectivity and olefin/paraffin ratio for C2–C4 increased slightly. The water–gas shift activity was low for both catalysts, resulting in high molar usage ratios of H2/CO (close to 2.0), even at the lower inlet ratios (i.e. 1.5 and 1.0). For both catalysts, the drop in the production rate of hydrocarbons when shifting from an inlet ratio of 2.1 to 1.5 was significant mainly because the H2/CO usage ratio did not follow the change in the inlet ratio. The hydrocarbon selectivities were rather similar for inlet H2/CO ratios of 2.1 and 1.5, while significantly deviating from those for an inlet ratio of 1.0. With the studied catalysts, it is possible to utilize the advantages of an inlet ratio of 1.0 (higher selectivity to C5+, lower selectivity to CH4, no water–gas shifting of the bio-syngas needed prior to the FT reactor) if a low syngas conversion is accepted.