Fischer-Tropsch synthesis (FTS) converts syngas (obtained from coal, biomass, natural gas or wastes) into hydrocarbons which can be transformed to clean fuels and chemicals. The products of FTS cover an extremely wide range including olefins, paraffins and oxygenates with carbon numbers extending from C1 to more than C100. The Anderson-Schulz-Flory (ASF) distribution model has been used consistently to describe the FTS product distribution. Nevertheless, observed deviations from the ideal ASF distribution plot are abnormally high yield of methane, low yield of C2, and sometimes a two-α ASF distribution. Mostly, the kinetic and mechanistic chain growth models are used to explain the FT product distribution, but none of these explanations has been sufficiently comprehensive to cover the full range of product distributions that have been obtained experimentally.
Relatively limited work has been done on the relationship between the FT product distribution and thermodynamics. The aim of current work is to develop and test a new quasi-equilibrium approach to the FTS product distribution. Aspen simulations conducted on FTS, in which the reaction conditions, such as reaction temperature, pressure, feeding different kinds of products (H2O, Olefins, Paraffins) as well as inert gas in the system, have been studied. We have compared the Aspen simulation results against the results obtained from FTS experiments using wide ranges of H2/CO/CO2 mixtures over both cobalt- and iron-based catalysts. The comparison revealed that most of the experimental results were quite close to those arrived at through Aspen thermodynamic simulations. It is therefore possible to use quasi-thermodynamic equilibrium to describe product distribution in FTS.