Transforming sulfur paste into sulfuric acid through chemical looping combustion of sulfur with Fe-based oxygen carriers: Thermodynamics, conversion, and mechanisms analysis

•Sulfur conversion with active particles in a way of gas–solid reaction is first investigated.•Three low-cost Fe-based oxygen carriers are used for chemical looping.•Thermodynamic analysis, experiments, reaction kinetics and DFT calculation are used.•The reaction pathway of S2 oxidization on Fe2O3 (0001) surface is firstly proposed. Chemical looping combustion (CLC) of elemental sulfur presents a promising approach for enhancing SO2 concentration and reducing NOx emissions in the sulfuric acid industry. This process replaces gaseous oxygen from air with lattice oxygen from solid oxygen carriers to oxidize sulfur for SO2 production. However, the interaction mechanism of the gas–solid reactions between oxygen carrier particles and gaseous sulfur remains unclear. The present work investigated the reaction behavior of sulfur paste, a by-product of the coal chemical industry, with three types of Fe-based materials including natural iron ore, red mud and synthesized Fe-based composite as oxygen carriers respectively. Thermodynamic analysis was used to simulate the sulfur conversion behavior, and validated through temperature-dependent experiments and reaction kinetic models. Additionally, density functional theory (DFT) and first-principles calculations were utilized to explore the interaction mechanisms between S2 molecules and Fe2O3 surfaces at the microscopic level.The results confirmed that Fe2O3 can react with S to generate SO2 without thermodynamic limitation. Reaction kinetics for the three oxygen carriers with S can be well described by existing models, with Fe-Al oxygen carrier exhibiting the highest reactivity. The measurement results of the reacted oxygen carriers demonstrated their sulfur-resistance ability. The decisive step of the reaction is the formation of the O-S-O structure, and the formation of one SO2 molecule requires overcoming a reaction energy barrier of 208.68 kJ/mol.