Fischer–Tropsch synthesis: accounting for chain-length related phenomena Original Research Article

The attempts to explain the deviations from Anderson–Schulz–Flory (ASF) distribution, the strong dependency of olefin content on molecular size, and the negative deviations from a constant molar activity for an initiator in Fischer–Tropsch synthesis (FTS) have led to a two-active-site model, models related to olefin readsorption, and the vapor–liquid equilibrium based explainations. However, none of these theories is able to adequately explain all of these chain-length related problems. Based on the studies of accumulated products in FTS reactions conducted in a continuously stirred autoclave reactor, we proposed that the apparent products of the FTS reaction is a mixture of freshly produced FTS products (Φ) and the products left in the reactor (Δ), Sn = Δn + Φn. Using this concept, all of the chain-length related problems were accounted for. Based on the results of calculations, we predict that the correct α-value of hydrocarbons greater than C8 will be smaller than currently reported value, that the paraffin to olefin ratios will be much smaller than the values reported, and that the product distribution and the paraffin to olefin ratios of a FTS reaction may depend on the molecular size but to a much lesser degree than claimed. According to our model, we conclude that in order to obtain the correct product distribution and the paraffin to olefin ratio of a FTS reaction, it is necessary to find a way to evaluate or eliminate the term Δ, which requires conducting FTS research in a different way.