Reduction and oxidation kinetics of Mn3O4/Mg–ZrO2 oxygen carrier particles for chemical-looping combustion

The kinetics of reduction with methane and oxidation with oxygen of Mn3O4 supported on Mg–ZrO2 prepared by freeze granulation has been investigated. The reactivity experiments were performed in a thermogravimetric analyzer (TGA) using different reacting gas concentrations and temperatures in the range of 1073–1223 K. The oxygen carrier particles showed high reactivity during both reduction and oxidation at all investigated temperatures. An empirical reaction model, which assumes a linear relation between time and conversion, was used to determine the kinetic parameters for reduction and oxidation, with chemical reaction being the main resistance to the reaction. The order of reaction found was 1 with respect to CH4 and 0.65 with respect to O2. The activation energy for the reduction reaction was 119 and 19kJmol-1 for the oxidation reaction. The reactivity data and kinetic parameters were used to estimate the solid inventory in the air and fuel reactor of a CLC system. The optimum solid inventory obtained was 135kgMWf-1 at a value of ΔXs=0.4ΔXs=0.4. At these conditions, the recirculation rate of oxygen carrier between air and fuel reactor was 7.1kgs-1 per MW of fuel, which could be accomplished in an industrial reactor. The high reactivity of the Mn3O4/Mg–ZrO2 with both methane and oxygen showed that this is a very promising oxygen carrier for CLC.