Investigation of the reduction kinetics of high loaded CuO-based materials suitable for the Ca/Cu looping process

In this work, the reduction reactions of highly loaded CuO-based materials with H2, CO and CH4, have been investigated. The oxygen transport capacity of the materials was barely affected (i.e. losses around 5%) along 100 reduction/oxidation cycles at 1123 K tested in TGA. The experimental results suggested that a shrinking core model (SCM) with chemical reaction control is able to predict the reduction conversion of highly loaded CuO-based materials in powder and pellet form, and the kinetic parameters were accordingly determined to this model. The activation energy values obtained for the materials supported over Al2O3 and MgAl2O4 are in the range of 10 kJ mol−1 for H2, 25 kJ mol−1 for CO and 60 kJ mol−1 for CH4, in agreement with results published in the literature, indicating that using Al2O3 or MgAl2O4 as support has not a significant effect on the reactivity. It has been found that internal diffusion plays a role for the highly loaded CuO-based in pellet form when supported over MgAl2O4 and when using CO and CH4 as reducing agents. Mixtures of reducing gases have been also tested in the TGA for a pellet using Al2O3 as support and the experimental results have been successfully fitted using the kinetic parameters previously determined. Finally, a simplified energy balance for the reactions involved in the reduction/calcination stage of the Ca/Cu process has been performed to determine operational conditions in which the reaction fronts for both reactions proceed together in the reactor. The results indicate that the materials tested present suitable reaction kinetics to sustain the reduction/calcination stage.