Kinetics of oxidation of a reduced form of the Cu-based oxygen-carrier for use in chemical-looping combustion

Abstract

A co-precipitated mixture of CuO and Al2O3 is a good oxygen-carrier for chemical-looping combustion. The kinetics of regeneration of this reduced oxygen-carrier (355 - 500 μm) were measured from 300 to 750°C when reacting it with O2. Care was taken to ensure these measurements were not affected by interphase mass transfer. Efforts were also made to minimise sampling problems by using a rapid-response mass spectrometer for reactions lasting for 45 s or less; otherwise, a paramagnetic analyser for O2 was used, since the mass spectrometer drifted with time. The order of reaction with respect to O2 was found to be ∼ unity at 300 to 750°C. Below 600°C, the reduced oxygen-carrier was incompletely oxidised to a mixture of Cu2O and Al2O3. Above 600°C, regeneration was completely to CuO and Al2O3 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 + 1/2O2 → Cu2O, (1) Cu2O + 1/2O2 → 2CuO. (2) The activation energies and pre-exponential factors for both reactions were measured from initial rates. The kinetics in the first cycle of operations were found to be similar to those in the subsequent cycles.