Distribution between C2 and C3 in low temperature Fischer-Tropsch synthesis over a TiO2-supported cobalt catalyst

Deviation of C-2 (including olefin and paraffin) in the Anderson-Schulz-Flory (ASF) distribution in Fischer-Tropsch synthesis (FTS) has been observed consistently but relatively few studies have focused on this. Explanations for C-2 deviation have been proposed by previous researchers in the literature and secondary reactions of ethene are believed as the cause for the deviation. However, the ratio particularly between C-2 and C-3 olefins and other neighbouring olefins has not yet been thoroughly investigated and this might lead eventually to insights in the mechanism of Fischer-Tropsch synthesis. FTS experimental runs were conducted in a tubular fixed bed reactor on a TiO2-supported cobalt catalyst. The reaction conditions were varied including the H-2/C-O ratio in the feed, the reaction temperature, and the space velocity (SV) of the feed gas. The decrease of the reaction rate caused by a lack of H-2 when the H-2/CO ratio was low is discussed. The olefin/paraffin (O/P) ratios obtained at different temperatures and SVs are presented as they relate to the three H-2/CO ratios. We then focus on the distribution of C-2 and C-3 under varied reaction conditions, including temperature, SV, and H-2/CO ratio, and characterize the relationship between C-2 and C-3 in terms of both the olefins and the total amounts of them. Experimental data derived from other reactor types, continuous stirred tank reactor (CSTR) and batch reactor with the same catalysts, have also been included in the investigation of C-2 and C-3 distribution. The ratio between C-2 and C-3 olefins is a linear function of CO conversion only in spite of the fact that the data is for different feed flowrates and compositions, operating temperatures and different reactors. However the ratio for the total C-2 to total C-3 was different for different H-2/CO feed ratios, but for a fixed H-2/CO ratio was a linear function of temperature only. (C) 2015 Elsevier B.V. All rights reserved.