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

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.