Fischer–Tropsch Reactions and Product Distribution Suits for Downstream

Abstract

Generic models for the mean carbon number n̄, H/C ratio β and chain growth probability α, as a function of C5+ selectivity for Fischer–Tropsch reactions, have been developed based on gas analysis data and product mass. These models allow predicting the parameters when detailed compositions of oil and wax are unavailable. Meanwhile, the distribution of individual 2–5 methyl paraffins of iron and cobalt catalysts containing K, Zr and Pt promoters or poisoned by COS and HBr were studied. The chain-length-dependent formation of methyl paraffins was demonstrated on both iron and cobalt catalysts. The fraction of the methyl paraffins produced on an active iron catalyst (15–22%) was 5–7 times higher than that of a cobalt catalyst (1–3%). Ethylidene (CH2CH–M) was proposed as one possible iso-chain growth monomer, based on the higher fraction of 3-methyl product. The effects of the promoters and the poisons on the formation of iso-paraffins and 1-olefin were complicated. K (Fe), Zr and S (Co) improved the formation of 1-olefins and suppressed the formation of iso-paraffins, partly due to the electronic effect (back-donation) of the promoters. Pt inhibited the formation of both 1-olefins and iso-paraffins on a cobalt catalyst. Adding HBr was found to promote the formation of iso-paraffins on an iron catalyst.