Long-lasting investigation of the Cu-based oxygen carrier particles in chemical looping air separation

Abstract

Chemical looping air separation can produce oxygen with features of operation-simple, cost-effective, and energy-effective. The stability of oxygen carrier is significant for the long-term operation of the system. Adding inert binders is one of the effective ways to improve the stabilities of oxygen carrier particles. In this paper, SiO2, ZrO2, TiO2 and MgAl2O4 were selected as inert binders to prepare Cu-based oxygen carriers and the adding ratios were 40 wt%, 50 wt% and 60 wt% respectively. The stabilities of the oxygen carriers were investigated in a packed-bed facility. Crystalline phases, surface area, crushing strength and surface morphology of the fresh and cycled oxygen carriers were measured to analyze the deactivation reasons for specific oxygen carriers. Zener pinning theory was also introduced to explain the effect of inert binders. Results of multi-cycles tests show that there is a poor stability of Cu/Ti oxygen carrier even though the adding ratio of TiO2 is as high as 60 wt%. The oxygen carrier with 50 wt% MgAl2O4 as binder presents high stability. However, the stability of Cu60Mg40 oxygen carrier decreases with proceeding of the cycles. When the SiO2 or ZrO2 adding ratio is as high as 60 wt%, the reactivity of Cu40Si60 or Cu40Zr60 oxygen carrier keeps stable under multi-cycling. The sticking together of particles caused by the crystal migration and growth is the main reason of the deactivation of specific oxygen carrier. Inert binders play important roles in preventing the agglomeration of oxygen carrier particles. However, the high binder adding ratio could decrease the oxygen transfer rate. The optimum adding ratios of SiO2, ZrO2 and MgAl2O4 in the oxygen carriers are determined as 60 wt%, 60 wt% and 50 wt% respectively.