Oxygen transport capacity and kinetic study of ilmenite ores for methane chemical-looping combustion

Highlights: • Achieved the highest ever oxygen transport capacity (14.2%) with natural ilmenite. • Phase transitions and morphology changes explained increased transport capacity. • Carbon deposition prevented by adjusting temperature and methane partial pressure. • Grain model and nonlinear regression used to accurately model reaction kinetics. -- Abstract: Reactivity and oxygen-transport capacity of Canadian and commercial ilmenite ores in the chemical-looping combustion of methane were investigated in a thermogravimetric analyzer (TGA). Oxygen carrier performance was evaluated over multiple cycles during which Canadian ilmenite oxygen transport capacity increased from 2.7% to 14.2% and the commercial sample maintained an approximately constant oxygen transport capacity at 4.5%. XRD and SEM results indicate that new phases were formed, and surface morphology was transformed significantly during cyclic operations. Studies on carbon deposition on the ilmenite surface indicate that lower methane partial pressure and reduction temperatures are favorable to effectively prevent this phenomenon. The kinetic grain model (GM) was found satisfactorily to fit reduction rate data obtained at atmospheric pressure. Intrinsic reaction rates and kinetic parameters were assessed, accordingly. Activation energy were estimated 106.7 ± 10.6 kJ/mol and 95.0 ± 8.5 kJ/mol for the Canadian and commercial samples, respectively.