Red Mud as Oxygen Carrier for Chemical Looping Combustion of Methane: Reactivity and Cyclic Performance

Chemical looping combustion(CLC) is a novel combustion technology with inherent CO2 separation from the carbon-based fuels. The development of low. cost oxygen carrier (OC) with high reactivity and good recycl ability is the key factor for the application of CLC technology. Red mud, a byproduct from the alumina production, can be considered as an ideal candidate as a cheap OC due to the high content of iron oxide and high specific surface area. In this study, the red mud was proposed as an oxygen carrier for chemical looping combustion of methane, and the effects of calcination temperature and reaction temperature on the reactivity and cyclic performance of this OC was investigated. The physicochemical properties of the red mud were characterized by XRF, XRD, TG-DSC, BET and H-2-TPR technologies. It was found that high calcination temperature result in the decrease of the OC reactivity but improve the thermal stability due to the formation of composite salts (e.g., Na6Al4Si4O17 and Ca2Al2SiO7) via the reactions between alkali. metal oxide (Na2O) or alkaline. earth. metal oxide (CaO) and the inert materials (Al2O3 and SiO2). Among the different red mud OCs (e.g., 800-RM, 850-RM, 900-RM and 950-RM, which were obtained after calcination at 800, 850, 900 and 950 degrees C, respectively), the 900-RM sample shows the highest CH4 conversion (71%) and CO2 selectivity (79%) during the performance testing, indicating high activity for methane oxidation. This phenomenon suggests that 900 degrees C is the most suitable calcination temperature. No obvious changes on the reactivity and phase structure of the red mud was observed after 30 redox cycles, which indicates that the calcined red mud OC owns excellentredox stability for CLC of methane.