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 degrees C when O/C ratio is 1:1. Furthermore, the maximum syngas yield (CO + H-2) reached 129.20 mL/g of Fe2O3/CaSO4-Al2O3 at the gasification temperature of 950 degrees C. Results showed that the optimum operating conditions are steam rate of 0.06 mL/min at 950 degrees 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.