Structure and Reactivity of Brazilian Iron Ores as Low-Cost Oxygen Carriers for Chemical Looping Combustion

Chemical looping combustion (CLC) is one of the most efficient and advantageous CO2 capture technologies from an economic and energy point of view. An important key factor in this process is the oxygen carriers (OCs) used to transfer oxygen from the air to the fuel. In this work, three natural iron ores from Brazil were selected as interesting oxygen carriers for the CLC process due to their low cost and abundance in nature. Their chemical composition, redox properties, and structural evolution when submitted to a reactivity test in a thermobalance with 15% CH4 and H-2 were investigated. The OCs (ItaHP-MG, ItaHP-RN, and ItaLP-RN) revealed good resistance to fracture, and their reactivity increased after the first reaction cycle due to the occurrence of an activation process, leading to a gain in reactivity in the following cycles. The reactivity tests showed that for all OCs, the reactivity with hydrogen was higher when compared to methane, highlighting ItaHP-MG oxygen carrier with relevant rate index values for both fuels (9.60%/min and 3.55%/min for H-2 and CH4, respectively). However, OCs performed differently depending on the degree of use of the Fe2O3 phase. Interestingly, ItaHP-MG, with a high Fe2O3 content (96.5%), showed a regeneration of only 60%, while ItaLP-RN, whose Fe2O3 content is 41.5%, presented a degree of use above 85%. This effect is the result of preferential gas-solid interaction on the surface of the OC.