Chemical looping combustion of ultra low concentration of methane with Fe₂O₃/Al₂O₃ and CuO/SiO₂

This study examines the performance of two metal oxide species in oxidizing ultra low concentration of methane (below 1% in volume). The focus on low methane concentrations are driven by its practical importance in applications such as abatement of ventilation air methane (VAM) in mining operations. Two mixed metal oxides, Fe₂O₃/Al₂O₃ and CuO/SiO₂, were selected as oxygen carriers and prepared using dry impregnation method. The metal oxide loading contents are found to be 45 wt% and 48 wt%, respectively. The redox reactivity of the selected oxygen carriers were studied at various methane concentrations (i.e., 0.1%, 0.5% and 1% in volume) and temperatures between 873 K and 1073 K using a thermogravimetric analyzer. At low methane concentrations and low temperatures (below 1073 K) the conversion of Fe₂O₃ to Fe₃O₄ showed higher reduction reactivity than the reduction of CuO to Cu. The redox reactivity of Fe₂O₃/Al₂O₃ was also found to be quite stable even after 60 redox cycles at 1073 K. The respective weight percentages for oxidation and reduction were found to be 100% and 96.67%, corresponding to a full oxidized state Fe₂O₃ and a reduced state between Fe₃O₄ and FeO respectively. Moreover, the results for the global reactivity of reduction and oxidation (calculated at X = 0.5) showed that the reduction rates were temperature and concentration dependent, varying from 0.14%/s to 2.2%/s over the range of temperatures and methane concentrations of interest. The oxidation rates were much higher than their reduction counterpart. The values varied from 8.95%/s at 873 K to 10.65% at 1073 K