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/gamma-Al(2)O(3) and Co-Re/gamma-Al(2)O(3) was investigated in a fixed-bed reactor at 20 bar and 483K using feed gases with molar H(2)/CO ratios of 2.1, 1.5 and 1.0 simulating synthesis gas derived from biomass. With lower H(2)/CO ratios in the feed, the CO conversion and the CH(4) selectivity decreased, while the C(5+) selectivity and olefin/paraffin ratio for C(2)-C(4) increased slightly. The water-gas shift activity was low for both catalysts, resulting in high molar usage ratios of H(2)/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 H(2)/CO usage ratio did not follow the change in the inlet ratio. The hydrocarbon selectivities were rather similar for inlet H(2)/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 C(5+), lower selectivity to CH(4), no water-gas shifting of the bio-syngas needed prior to the FT reactor) if a low syngas conversion is accepted.