Comprehensive Study of Fe2O3/Al2O3 Reduction with Ultralow Concentration Methane under Conditions Pertinent to Chemical Looping Combustion

An experimental study was conducted to identify the most suitable alumina-supported iron-based oxygen carrier for the abatement of ultralow concentration methane using a chemical looping approach. This was done by evaluating the performance characteristics such as reactivity, cyclic stability, and gas conversion. The experiments were carried out in a thermogravimetric analyzer and a fixed bed reactor setup under the desired conditions. Thermodynamics analysis was carried out using the commercially available software ASPENPLUS. The analysis suggested that the favorable iron-based oxygen carriers were those with the weight content of Fe2O3 less than 50 wt %. Three Fe2O3/Al2O3 samples were therefore prepared with the metal oxide contents in the range of 10-45 wt %, i.e., Fe10Al, Fe25Al, and Fe45Al. The thermogravimetric analysis experimental results showed that the reduction reactivity and stability were improved with the addition of support material compared with unsupported Fe2O3. Moreover, the reduction reactivity varied with the solid conversion range and the weight content of the parent material. For full reduction of Fe2O3 to Fe3O4, the sample Fe10Al showed the highest reduction reactivity. However, in terms of the rate of oxygen transport (which considers the combined effects of the oxygen transfer capacity and reactivity), the highest value was achieved by the Fe45Al sample. The gas conversion of CH4 to CO2 was also quite dependent on the weight content of Fe2O3. Essentially, Fe45Al delivered the longest duration on high-level conversion (i.e., complete conversion of CH4 to CO2). In summary, Fe45Al was found to be the most suitable oxygen carrier candidate in this application. The effect of operational parameters was further examined with various reaction temperatures (873-1073 K), methane concentrations (0.1-1.5 vol %), and CO2 compositions (0-50 vol %).