Fe2O3-Al2O3 oxygen carrier materials for chemical looping combustion, a redox thermodynamic and thermogravimetric evaluation in the presence of H2S

Alumina-supported Fe2O3 oxygen carrier material (OCM) system is among the most promising OCM systems for solid and gaseous fuel CLC. This work utilizes a comprehensive thermogravimetric and thermodynamic equilibrium approach to redox and CLOU performance, oxygen transfer capacity, reduction rate and sulfur tolerance of the Fe2O3 impregnated on Al2O3 OCM. Thermodynamic evaluations reveal that the beneficial composition range lies in a wide range of 7.5-34% molar Fe2O3 ratios. This is the range at which aluminum-rich corundum phase, i.e., (Al, Fe)(2)O-3, remains stable throughout the oxidizing to very reducing oxygen partial pressures in fuel reactor. The experimental system in this study contains 20mass% Fe2O3, i.e., X-Fe=13.8% molar which lies well within this interval. Deep redox cycle experiments confirm the thermodynamic modeling and during the long residence time of this experiment, the sample is almost fully reduced and exhibits its thermodynamic redox oxygen capacity of close to 1.5mass%. Extension of the deep redox cycles to 15 cycles induces no performance deterioration in terms of capacity, rate of reduction or morphological failure. The redox experiment under sour reducing gas indicates no H2S poisoning for the 20mass% Fe2O3 supported on Al2O3 OCM. The findings that this system is not affected with the H2S content of the gas, and the prediction of the SO2 release from the fuel reactor is in good agreement with our recent reactor testing findings available in the literature.