Fischer–Tropsch synthesis: activation of low-alpha potassium promoted iron catalysts

The purpose of this study is to investigate the influence of activation gas type (CO, syngas and H2), activation temperature and pressure on FTS activity and selectivity. A series of Fischer–Tropsch synthesis (FTS) reactions in a continuously stirred tank reactor (CSTR) for 400–1000 h were carried using a Fe/K/Si=100/1.25/5.1 (atomic ratio) catalyst. The highest CO conversion was obtained for a CO activated catalyst while hydrogen activation yielded the lowest, regardless of the activation temperature. A higher activation temperature yielded a higher peak CO conversion during the induction period. FTS activity for syngas pretreatment showed a dependency on the activation pressure. In addition to the FTS activity, CO activation showed the best overall hydrocarbon productivity. The lowest hydrocarbon production rate was obtained with the H2 activated catalyst. Carbon monoxide activation also yielded the lowest methane selectivity and activation temperature did not affect the CH4 selectivity in the range of 230–270 °C. Activation temperature had little effect on the formation of olefin (C2–C20) and the olefin fraction decreased in the order of H2>syngas>CO activation. The induction period was present following each of the three pretreatments: CO, H2, or syngas with the same H2/CO ratio as used during the synthesis period.