Hydrocarbon selectivity model for the slurry phase Fischer–Tropsch synthesis on precipitated iron catalysts

Abstract

A new hydrocarbon product distribution model for Fischer–Tropsch-synthesis (FTS) reaction has been developed. The model is based on the assumption that there are two types of active sites on the catalyst surface: type-1, where growth of hydrocarbon intermediates occurs, and type-2, where reversible readsorption of 1-olefins occurs. The readsorbed 1-olefins form alkyl intermediates, C n H 2 n+1 , on the surface, which in turn can participate in several reactions: chain growth propagation, hydrogenation to n-paraffins, and dehydrogenation to 2-olefins. Chain growth is considered on the basis of methylene monomer (CH 2) insertion mechanism. Steady-state mass balances for adsorbed intermediates C 1–C 50 and equations for the product formation rates were derived. The model has been tested using results from experiments conducted over long periods of time under industrially relevant conditions in a slurry reactor. The model predictions provide information on hydrocarbon product distribution, 2-olefin content and total olefin content as a function of carbon number. The curved line for the distribution of paraffins and olefins can be fitted well with the proposed hydrocarbon selectivity model, over the entire range (C 1–C 50) of carbon numbers. The kinetic model proposed in this paper can be used for interpretation of experimental data, comparison of performance of different catalysts, and reactor modelling and simulation studies.