Influences of reaction and thermal conditions on microstructural evolutions of ilmenite oxygen carriers for chemical looping combustion

Ilmenite ore has been widely accepted to be a cost-effective oxygen carrier (OC) of Chemical Looping Combustion (CLC) for CO₂ capture. The focus of this study is to investigate into the influences of chemical impact, thermal variation and ageing effect on microstructure and performance evolutions of ilmenite OCs. Iron element migration, crystallinity and morphology alterations, and irreversible change of chemical composition were identified to be the major aspects responsible for gradual microstructural evolutions of Ilmenite OCs. Iron element migration from bulk materials to particle surface, occurring during the oxidation step of redox cycles, was of temperature- and O₂ concentration- dependences. A schematic diagram was developed to explain the pathways of irreversible iron migration and alteration of chemical composition in redox cycle reactions. By lowering phase interaction between Fe₂TiO₅ and TiO₂, the cycled thermal shock (due to reaction and processing in CLC) promotes the iron element concentration on OC particle surface and the ilmenite OC reactivity. Long-term ageing at elevated temperature, as one of typical severe conditions in CLC, exhibits activation effects for ilmenite OCs, even though it causes increased crystallinity, denser particle structure and redistribution of Fe₂TiO₅-TiO₂ phase