Comparison of preparation methods for iron-alumina oxygen carrier and its reduction kinetics with hydrogen in chemical looping combustion

Seven preparation methods, namely sol-gel, co-precipitation, hydrothermal synthesis, low heating solid-state reaction, freeze granulation, combustion synthesis, and mechanical mixing, were used to synthesize Fe2O3/Al2O3 oxygen carrier for chemical looping combustion. A comprehensive physicochemical characterization (i.e. productivity, crushing strength, crystalline characteristics, microstructure, and chemical reactivity with hydrogen) was carried out, and the effects of preparation methods and processes on the oxygen carrier performance were explored. Taking into consideration various physicochemical indices, the sol-gel method and the freeze granulation method were preferred for oxygen carrier preparation. Following that, a critical chemical reaction in in situ gasification chemical looping combustion, the reduction reaction between oxygen carrier and hydrogen, was clarified in terms of reaction kinetics through the non-isothermal kinetics analysis and the double extrapolation method. Temperature programmed reduction experiments of the sol-gel-derived Fe2O3/Al2O3 particle and hydrogen were performed using a chemisorption analyzer. The reduction mechanisms and kinetics parameters for the two-stage reaction (reduced from Fe2O3 to Fe3O4 and then from Fe3O4 to FeAl2O4) were determined. In the first stage, the reduction reaction is described by the surface reaction model with an order of 2; on the other hand, the conversion from Fe3O4 to FeAl2O4 is dominated by the nucleation and nuclei growth process. (C) 2014 Curtin University of Technology and John Wiley & Sons, Ltd.