Reactivity of Al2O3- or SiO2-Supported Cu-, Mn-, and Co-based oxygen carriers for chemical looping air separation

The chemical looping air separation (CLAS) is a novel method for producing high-purity oxygen, which can be effectively integrated to oxy-fuel power plants. CuO/Cu2O, Mn2O3/Mn3O4, and Co3O4/CoO have been found to be the most thermodynamically suitable oxidation pairs for the CLAS process. In the current study, the reactivity and stability of these metal oxides were analyzed further. A total of six different oxygen carrier samples were prepared by the dry impregnation method on SiO2 and Al2O3 supports. Their redox behavior has been investigated in a thermogravimetric analyzer (TGA) at four different temperatures, i.e., 800, 850, 900, and 950 °C, where the temperature-programmed oxygen release and oxidation were applied for 5 continuous cycles using nitrogen and air, respectively. The results indicate that, although relatively all oxygen carriers exhibited good reactivity, CuO/Cu2O with SiO2 and Co3O4/CoO with Al2O3 were found to be most stable. Furthermore, oxygen transport capacity (OTC) (%) and rate of oxygen transport (ROT) (% min-1) were calculated. It was found that Cu oxide with SiO2 has the highest OTC of 4.77% as well as the highest ROT of 5.1 and 10.9% min-1 for oxygen release and oxidation, respectively, at 950 °C. The CuO/SiO2 oxygen carrier also exhibited better stability for the 41 continuous cycle test, with only 10.3% loss in OTC compared to 22.3% for Co3O4/Al2O3. The grain size growth was found to be the key cause in the loss of OTC. The oxygen concentration in the outlet stream for the CuO/SiO2 oxygen carrier was measured in packed-bed experiments at different temperatures. It was observed that the oxygen concentration at the outlet of the reactor was consistent with the equilibrium values at studied temperatures.