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The chemical looping process is a promising approach for carbon capture. Oxygen carriers play the crucial role of carrying oxygen between oxidation and reduction reactors. In this study, iron-based composites, added with alumina and zirconia, were used as the oxygen carriers. The feasibility study of these composites for chemical looping applications was then evaluated by measuring their properties, including mechanical properties, relative density, microstructures, crystal structure, and their capacity of oxygen. The results suggest that the addition of zirconia led the decrease of the bulk relative density and thus had a negative effect to both crush strength and attrition. Crush strength declined from 57 kgf to 26 kgf when using zirconia, replacing alumina, in an iron-based composite as the inner material. In addition, the phases in oxidizing and reducing reaction were also revealed. The formation of the spinel phase (FeAl2O4) was the major factor that altered the capacity of oxygen. It inhibited Fe2O3’s ability to be completely reduced to Fe and thus decrease the capacity of oxygen. The value was therefore decreased from 9.7% to 6.2% after 50 redox cycles in alumina addition composite. On the other hand, for the zirconia addition, all of the Fe2O3 could transform to Fe, which provided 8.5% of oxygen capacity after 50 redox cycles. A dense layer which was identified as the Fe2O3 in the bulk surface was observed in the samples reacted with 50 redox cycles. The proposed mechanism of the formation of Fe2O3 layer and its corresponding kinetic analysis was also revealed in this study. |
