Evaluation of Novel Ceria-Supported Metal Oxides As Oxygen Carriers for Chemical-Looping Combustion
Journal article, 2012
Oxygen carrier particles consisting of 60 wt % copper, iron, or manganese oxide supported on 40 wt % ceria (CeO2) or gadolinia doped-ceria (Ce0.9Gd0.1O1.9) have been manufactured and examined as oxygen carrier materials for chemical-looping combustion (CLC). Unlike conventional support materials, such as alumina (Al2O3), these ceria-based support materials are active under prevailing conditions in the fuel reactor and have the ability to participate in redox reactions. The oxygen carrier materials were synthesized via extrusion and were examined by successive oxidation and reduction cycles in a bench-scale fluidized bed reactor made of quartz. The experiments were conducted at 900 and 925 degrees C for copper-based materials, and at 950 degrees C for iron- and manganese-based materials. Methane or syngas (50% CO and 50% H-2) using a flow rate of 900 mL/min for Cu-based materials and 450 mL/min for Mn- and Fe-based materials was used as the fuel. For all experiments, 15 g of oxygen carrier was used. The oxidation was performed with a gas mixture of 5% O-2 and 95% N-2. The results show that CeO2 and Ce0.9Gd0.1O1.9 are viable support materials for the oxides of copper and iron. Moreover, the active particles supported on Ce0.9Gd0.1O1.9 were more reactive compared to those supported on CeO2. CH4 was completely converted to CO2 and H2O by CuO supported on Ce0.9Gd0.1O1.9, while the conversion of CH4 for Fe2O3 supported on Ce0.9Gd0.1O1.9 was as high as 90%. Ceria-supported Mn3O4 particles showed poor performance when CH4 was used as fuel. Syngas was fully converted to CO2 and H2O by all the oxygen carriers synthesized and examined in this work. The ability of CuO and Mn2O3 to release O-2 in gas phase when fluidized in inert background was also investigated; in the case of copper oxide, substantial oxygen release was observed. Analysis of fresh and used particles by X-ray diffractometry did not reveal the formation of any unexpected phases. All particles showed good fluidization properties with low attrition and little tendency toward agglomeration.