Modification of traditionally impregnated Fe2O3/Al2O3 oxygen carriers by ultrasonic method and their performance in chemical looping combustion

The selection of high-performance oxygen carriers has always been a major focus of attention and considered to be a determining factor in chemical-looping combustion (CLC). The traditional impregnation method by agitator for material synthesis usually causes a long crystallization time, uncontrollable crystalline size formation, and insufficient penetration and dispersion of the active component into the binder. The physical incorporation of ultrasound technology into the impregnation process is considered an effective method in the material synthesis field. In this study, the modification of a traditionally impregnated Fe2O3/Al2O3 oxygen carrier by ultrasonic method and its performance in the CLC process with methane as fuel were investigated to clarify the ultrasonic effect on the physicochemical properties of the Fe2O3/Al2O3 oxygen carrier. The characterization and optimization of an ultrasonic-assisted Fe2O3/Al2O3 oxygen carrier by varying the ultrasonic time and ultrasonic power were especially in focus. The results confirmed a significant improvement in the physical properties of the Fe2O3/Al2O3 oxygen carrier and its reactivity performance by ultrasonic modification. Ultrasound effectively promoted the penetration and dispersion of Fe2O3 into the pores and on the surface of Al2O3 powder, resulting in a great reduction in crystalline size. Higher methane conversion was obtained by an ultrasonic-assisted Fe2O3/Al2O3 oxygen carrier. The optimal ultrasonic parameters determined by orthogonal experimental design (OED) method and characterization analyses were 30 min of ultrasonic time and 500 W of ultrasonic power. Cyclic tests showed that the CO2 yield and CH4 conversion increased slightly from around 28% to 34% and 70% to 76%, respectively. Characterization indicated that the pore structural properties of reduced UI-20Fe/Al-30-300 samples were improved at typical cycles, resulting in more CH4 converted. Overall, ultrasound technology is a promising way to promote the physicochemical properties of oxygen carriers in the CLC process. (c) 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.