Optimisation of syngas production from a novel two-step chemical looping reforming process using Fe-dolomite as oxygen carriers

Abstract

The production of syngas from hydrogen carbon feedstocks such as natural gas and biomass is of high importance to the chemical industry. In conventional chemical looping steam reforming(CLSR), the composition of the syngas produced is limited by the chemical equilibrium of the water-gas-shift reaction. In this study, we demonstrate that a two-step chemical looping reforming (TS-CLR) process is capable of alleviating the equilibrium limit to produce syngas of higher CO and H2 contents. For example, the total mole fraction of H2 and CO in the syngas produced from the conventional CLSR of toluene at 900 °C is limited to below 89.4 vol% (dry basis), whereas TS-CLR could produce syngas with >94 vol% of CO and H2 under the same condintions. The TS-CLR process is best carried out in a bed of Fe-dolomite oxygen carriers with a Ca:Fe ratio of 1:1 (denoted as C1F1). Compared to the pure Ca2Fe2O5 and Fe2O3/Al2O3 oxygen carriers, the C1F1 affords improvements in syngas yield, carbon conversion and syngas purity. The superior performance of C1F1 is attributed to the promotion of the lattice oxygen activities of Ca2Fe2O5 by MgO, as well as its excellent phase reversibility over redox cycles.