Combined Cu/Mn Oxides as an Oxygen Carrier in Chemical Looping with Oxygen Uncoupling (CLOU)

Abstract

This study investigates the O 2 uncoupling properties of five different oxygen carrier particles, consisting of combined oxides of CuO and Mn 3 O 4 . The oxygen carriers were produced by freeze granulation followed by calcination at 950 °C for 6 h. Particles with 5, 10, 20, 31, and 61 wt % CuO were examined in both an inert (pure N 2 ) atmosphere and in the presence of solid fuel (wood char) at 750 °C. At this relatively low temperature during fluidization with N 2, the samples were capable of releasing gas-phase O 2 in concentrations up to 1%. During reduction with wood char in 15 g of oxygen carriers, some materials could release gaseous O 2 equal to 1.4% of their total mass. When the crushing strength and attrition index were measured with a customized jet cup, the mechanical stability of these samples was compared. These measurements showed that, in general, samples with a higher CuO content were more mechanically stable. On the basis of XRD analysis of the oxygen carriers, the major phase transitions were Mn 2 O 3 ↔ Mn 3 O 4 and combined spinel (Cu,Mn) 3 O 4 ↔ CuMnO 2 . These transitions both provide a considerable amount of O 2 . It is concluded that the Cu–Mn–O system has considerable potential to be used as a oxygen carrier in chemical-looping applications at lower temperatures, perhaps interesting for biofuel combustion.