Fischer–Tropsch synthesis product selectivity over an industrial iron-based catalyst: Effect of process conditions

•Methane selectivity decreases with decrease in temperature and H2/CO feed ratio.•Space velocity and pressure have a small effect on hydrocarbon product distribution.•Oxygenates participate in secondary reactions.•Olefin content decreases with increase in residence time and H2/CO feed ratio.

The effect of process conditions on product selectivity of Fischer–Tropsch synthesis (FTS) over industrial iron-based catalyst (100 Fe/5 Cu/4.2 K/25 SiO2) was studied in a 1-L stirred tank slurry reactor. Experiments were performed over a range of different reaction conditions, including three temperatures (T = 493, 513 and 533 K), four pressures (P = 0.8, 1.5, 2.25 and 2.5 MPa), two synthesis gas feed molar ratios (H2/CO = 0.67 and 2) and gas space velocity from 0.52 to 23.5 Ndm3/g-Fe/h. The effect of process conditions on reaction pathways of FTS and secondary 1-olefin reactions was analyzed by comparing product selectivities, chain growth probabilities and ratios of main products (n-paraffin, 1- and 2-olefin). Reduction of methane production and increase of C5+ products was achieved by decreasing temperature, inlet H2/CO ratio and/or increasing pressure. Overall selectivity toward methane and C5+ did not show significant changes with variations in residence time. All of the product selectivity variations were shown to be related to changes in chain length dependent growth probabilities.

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