Kinetics of the Oxidation of a Co-precipitated Mixture of Cu and Al2O3 by O2 for Chemical-Looping Combustion

A co-precipitated mixture of CuO and Al2O3 is a good oxygen carrier for chemical-looping combustion in, e.g., CuO + CO -> Cu + CO2. The kinetics of regeneration of this reduced oxygen carrier (particle size of 355-500 mu m) by O-2 were measured from 300 to 750 degrees C. Care was taken to ensure that these measurements were not affected by interphase mass transfer or mixing of gases in the bed and sampling system. The order of reaction with respect to O-2 was found to be approximately unity, and the rates of regeneration in subsequent cycles could be approximated by those in the first. Below 600 degrees C, oxidation of the reduced oxygen carrier was incomplete. Above 600 degrees C, oxidation was complete to CuO and was controlled to a considerable extent by external mass transfer. At these higher temperatures, regeneration involved a shrinking core mechanism and the two consecutive steps: 2Cu + 1/2O(2) -> Cu2O, Delta H-1073 K(0) = -167.3 kJ/mol (1) Cu2O + 1/2O(2) -> 2CuO, Delta H-1073 K(0) = -131.5 kJ/mol (2) At 900 degrees C, the fully oxidized carrier decomposed to Cu2O and O-2.