Kinetics of the chemical looping oxidation of CO by a co-precipitated mixture of CuO and Al2O3

The rates of oxidation of CO to CO2 by particles of a co-precipitated mixture of CuO and Al2O3 (355-500 mu m) have been measured in a fluidised bed; these measurements were not affected by interphase mass transfer or the deposition of carbon. Efforts were made to minimise sampling problems by using a rapid-response mass spectrometer to analyse the gases from the hotter beds or those fluidised by gases with high [CO]. However, the base-line of the mass spectrometer drifted with time. so an infra-red analyser measured [CO2] and [CO] in the off-gases from cooler beds, in which CO was oxidised to CO2 more slowly. These techniques enabled rates of reaction to be measured front 250 to 900 degrees C; the order of reaction in CO was always close to unity. It was established that above 500 degrees C, the oxidation of CO by particles of CuO was controlled mainly by external mass transfer. At similar to 250 degrees C, it appears that CO reacts directly with solid CuO in: CuO + CO -> Cu + CO2. (1) However, above similar to 700 degrees C, CuO particles seem to react by the shrinking core mechanism, predominantly involving the two consecutive steps: 2CuO + CO -> Cu2O + CO2, (3) Cu2O + CO -> 2Cu + CO2. (4) The activation energies and pre-exponential factors for reactions 1 and 4 were measured. (c) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.