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

A new hydrocarbon product distribution model for Fischer-Tropsch-synthesis (FTS) reaction has been developed. The model is based on the assumption tha t there are two types of active sites on the catalyst surface: type-1, wher e growth of hydrocarbon intermediates occurs, and type-2, where reversible readsorption of 1-olefins occurs. The readsorbed 1-olefins form alkyl inter mediates, CnH2n+1, on the surface, which in turn can participate in several reactions: chain growth propagation, hydrogenation to n-paraffins, and deh ydrogenation to 2-olefins. Chain growth is considered on the basis of methy lene monomer (CH2) insertion mechanism. Steady-state mass balances for adso rbed intermediates C-1-C-50 and equations for the product formation rates w ere derived. The model has been tested using results from experiments condu cted over long periods of time under industrially relevant conditions in a slurry reactor. The model predictions provide information on hydrocarbon pr oduct distribution, 2-olefin content and total olefin content as a function of carbon number. The curved line for the distribution of paraffins and ol efins can be fitted well with the proposed hydrocarbon selectivity model, o ver the entire range (C-1-C-50) of carbon numbers. The kinetic model propos ed in this paper can be used for interpretation of experimental data, compa rison of performance of different catalysts, and reactor modelling and simu lation studies. (C) 2001 Elsevier Science Ltd. All rights reserved.