Investigation on the oxygen-carrying performance and reaction kinetics of CaMnxFe1−xO3−δ perovskites prepared from red mud

Abstract

In this study, two Ca/Mn/Fe perovskite oxygen carriers (i.e., CaMn0.5Fe0.5O3−δ and CaMn0.75Fe0.25O3−δ, respectively) were prepared using red mud and two pure reagents to recycle the red mud for the chemical looping combustion of biomass. The oxygen uncoupling (OU) capacity and redox cycle characteristics of perovskites were examined by thermogravimetric analysis (TGA) under a gaseous (H2, O2, N2) environment. With the same Mn/Fe mole ratio, reagent-based perovskites exhibited a higher total oxygen transport capacity, while perovskites derived from red mud exhibited a better cycling stability. The addition of red mud did not affect the reactivity of perovskites. The curves of conversion level vs time revealed that two control mechanisms are involved in the reaction between oxygen carriers and gaseous compounds. That is, the oxidation kinetics of perovskite oxygen carriers were mainly controlled by a chemical reaction, while the reduction kinetics were controlled by a chemical reaction at a low conversion level, and with the increase in the reduction degree, gas diffusion through the solid product layer was enhanced. In addition, kinetic parameters of OU and redox were obtained, and the grain model was considered to be suitable to describe reduction and oxidation reactions.