Effect of Steam During Fischer–Tropsch Synthesis Using Biomass-Derived Syngas

The gasification of biomass is a promising technique to generate different forms of valuable alternative energy, including direct thermal energy and further conversion of synthesis gas to clean liquid fuels or chemicals via Fischer– Tropsch synthesis (FTS) [1–5]. The ideal H2/CO ratio for FTS is ~2/1 based on the stoichiometry. However, The H2/ CO for the synthesis gas obtained from biomass gasification is considerably lower, typically ~0.7/1. Elder et al. [6] studied the gasification of biomass using an air-blown pilot-scale gasification system at various conditions. Based on a ~17–30 kg h−1 wood chips feedstock, the unit produce 855 dm3 m−3 gas with the composition of 20 % carbon monoxide, 15.5 % hydrogen, 4 % methane, 10.7 % carbon dioxide and balance nitrogen [6], which is representative of syngas produced in these types of biomass gasifiers [7, 8]. This hydrogen-deficient type of syngas requires Fe and Rubased FTS catalyst to promote the water-gas-shift reaction. During FTS, the steam formed can react with CO to produce CO2 and hydrogen via the water gas shift reaction (H2O + CO → H2 + CO2), producing the required hydrogen Abstract Fischer–Tropsch synthesis (FTS) with biomass-derived syngas was performed using both iron-based 100Fe/6Cu/4K/25Al catalyst and ruthenium-based 5 % Ru/SiO2 catalyst. During FTS, different concentrations of steam were co-fed with the biomass-derived syngas to promote the water gas shift reaction and increase the H2/ CO ratio. On Fe-based catalysts the increase in steam concentration led to lower conversion, while deactivation is not observed on Ru-based catalysts. XRD of the spent iron-based catalyst showed the oxidation of iron carbides. Adding steam inhibited surface carbon deposition, as measured by temperature programmed hydrogenation. The iron carbide phase could be re-carburized by flowing CO. The addition of steam had different effects on these two catalysts. Fe-based catalyst showed significantly lower methane selectivity and greater C5+ hydrocarbon selectivity, while on the Ru-based catalyst, adding steam only showed slightly decreased methane selectivity.