Reaction characteristics and lattice oxygen transformation mechanism of semi-coke chemical looping gasification with Fe₂O₃/CaSO₄–Al₂O₃ oxygen carrier

Chemical looping gasification (CLG) provides a potential way for clean utilization of solid fuels with the innate CO₂ separation and capture. Selection of suitable oxygen carrier and operating conditions in reactor are the key for fuels conversion. In this work, Fe₂O₃–Al₂O₃, CaSO₄–Al₂O₃ and Fe₂O₃/CaSO₄–Al₂O₃ oxygen carriers (OCs) were synthesized by impregnation method and innovatively applied in semi-coke chemical looping gasification (SCCLG) for syngas production. The reaction conditions (oxygen carrier types, temperature, steam addition amount) of oxygen carrier for syngas production were tested in a thermogravimetric analyzer (TGA) and a fixed-bed reactor. The experimental results showed that syngas yield of SCCLG with Fe₂O₃/CaSO₄–Al₂O₃ is more than that with Fe₂O₃–Al₂O₃ or CaSO₄–Al₂O₃ OC at 1000 °C when O/C ratio is 1:1. Furthermore, the maximum syngas yield (CO + H₂) reached 129.20 mL/g of Fe₂O₃/CaSO₄–Al₂O₃ at the gasification temperature of 950 °C. Results showed that the optimum operating conditions are steam rate of 0.06 mL/min at 950 °C with O/C of 1:1. Finally, the reaction mechanism of SCCLG was proposed based on experimental methods combing with advanced analytical testing and density functional theory (DFT) calculations results, and it reveals that OC in SCCLG underwent the reduction processes of Fe₂O₃/CaSO₄–Al₂O₃ to CaFeSO/CaO–Al₂O₃ and then to Fe/CaS–Al₂O₃, which can efficiently improve the sulfur escape of CaSO₄ OC. The present study provides an efficient way for conversion and utilization of fossil fuels in energy and chemical industry fields.