Synthetic Oxygen Carriers for Chemical Looping Applications

Chemical looping combustion and/or chemical looping with oxygen uncoupling are promising combustion technologies that utilize oxygen carriers to burn fuels, producing a flue gas stream primarily composed of CO2 and steam. However, commercializing these processes faces a significant obstacle requiring the development of appropriate oxygen carriers with specific properties. Another emerging energy-efficient approach for oxygen generation is Chemical looping air separation, providing an alternative to energy-intensive oxygen production technologies. Yet, further research is required to optimize and scale up this relatively new technology. Therefore, this thesis aims to investigate synthetic materials and develop mixed oxygen carriers with enhanced properties for chemical looping combustion and chemical looping with oxygen uncoupling. Additionally, it targets to comprehensively study a benchmark material for chemical looping air separation, outlining the optimized process conditions. In this work, tungsten oxide was employed to modify Ni-based carriers through impregnation and coprecipitation methods. Impregnated materials exhibited lower carbon formation and greater stability. Therefore, impregnation procedure was utilized to optimize metal loadings, resulting in improved oxygen capacity and elimination of carbon formation. Specifically, the sample composed of 60 wt.% NiO, 25wt.% WO3 balanced ZrO2 achieved an oxygen capacity of 15.6% without carbon formation. Moreover, CuO-WO3/ZrO2 carriers were prepared through coimpregnation and sequential impregnation techniques and tested for chemical looping with oxygen uncoupling. The WO3 modification enhanced the transport capacity due to the formation of different Cu-W intermediate phases in both samples. However, the coimpregnated carrier released higher oxygen amounts. Furthermore, a Cu-based oxygen carrier for chemical looping air separation was investigated through thermodynamic analysis, kinetic modeling, and fluidized bed simulation. The study indicated that operating the reactors under a bubbling fluidization regime and the reducer at 1000 °C and the oxidizer at 800 °C yielded the highest oxygen flowrate. Overall, this thesis contributes to the advancement of chemical looping technologies by developing novel oxygen carriers and optimizing process conditions for chemical looping air separation. The findings presented here pave the way for the future commercialization and implementation of these promising technologies, offering energy-efficient solutions for oxygen production and reducing carbon emissions