Evaluation of Cu-based oxygen carrier for chemical looping air separation in a fixed-bed reactor

• Steam used as carrier gas is demonstrated by thermodynamics.
• Both the reduction and oxidation included quick and slow stages.
• Experimental results demonstrate CLAS can be achieved in fixed-beds.
• Nucleation and nuclei growth model can describe the reduction and oxidation well.
• Stable property of Cu4Mg6 oxygen carrier in multi-cycles test is obtained.

Chemical looping air separation (CLAS) is a novel technology to separate oxygen from air. In CLAS process, oxygen carrier releases oxygen in steam atmosphere and the reduced oxygen carrier is regenerated in air atmosphere. The performance of oxygen carrier is essential to CLAS technology. In this study, the feasibility of CuO in steam atmosphere was evaluated by thermodynamics. Steam is not involved in any reaction. The production of oxygen is achieved by the decomposition of CuO to Cu2O and the optional reduction temperatures should be 850–1050 °C. In order to inhibit the agglomeration of copper oxides, oxygen carriers were prepared with 60 wt.% SiO2, TiO2, ZrO2 and MgAl2O4 as support materials. The oxygen release and absorb rates of the four oxygen carriers were determined under reduction temperatures of 950, 975 and 1000 °C and oxidation temperatures of 800, 850, 900 °C in a fixed-bed reactor. Both the reduction and oxidation include quick and slow reaction stages. The reduction rate increases and the oxidation rate decreases with the investigated temperature increasing. The reduction and oxidation macro-kinetic models of the four oxygen carriers were established based on the reactivity data. Binders have great effect on reduction kinetic parameters. The Cu4Mg6 oxygen carrier has the highest reduction and oxidation rates. The stability of Cu4Mg6 was investigated by multi-cycles test. The oxygen release and absorb rates keep stable in each cycle. The chemical and physical characteristics of the oxygen carriers prepared and reacted were also measured. The chemical phases are only copper oxides and binder. The surface area becomes larger after cycles. There is no obvious agglomeration observed after multi-cycles test.