Fischer–Tropsch synthesis and water gas shift kinetics for a precipitated iron catalyst

Abstract

A large number of kinetic data points (83 sets) was obtained over a wide range of CO conversion (7–90%), pressure (1.3–2.5MPa) and H2/CO ratio (0.67–1.5) with an iron catalyst (100 Fe/5.1 Si/1.25K). The kinetics of the catalyst in the low (XCO<70%) and high conversion (XCO>70%) regions were studied separately. Twenty six Fischer–Tropsch synthesis (FTS) and water gas shift (WGS) kinetic models were tested and discriminated. Water and CO2 inhibition was evaluated. While all thirteen FTS models gave a satisfactory fit, the new FTS models that included CO2 inhibition surpassed the others. Water inhibition of the FTS rate was insignificant over both low and high conversion ranges. For the WGS kinetics of the iron catalyst, a newly constructed empirical model and one from the literature provided the best fits of the WGS rates, while nine mechanistic models and one power law WGS model were unable to satisfactorily fit the WGS kinetic data. Water did not significantly limit the WGS rate and CO2 only inhibited the rate at high CO conversions. The equations obtained for the low and high CO conversion ranges varied greatly. The errors for the models for 85% of the FTS and WGS data points were less than 10%, and the errors of the remaining points fell in the range of 10–15%.