Chemical Looping Combustion Process Using Supported Copper Oxide Oxygen Carriers
Creators: name: Daneshmandjahromi, Sanaz
Publisher: name: Graduate Studies
Year: 2024
Subjects: subject: CCUS
subject: Carbon capture
subject: CCS
subject: Chemical looping combustion
subject: global warming
subject: carbon dioxide
subject: CuO oxygen carrier
subject: support
subject: nanomaterial
subject: mesoporous
subject: kinetics
subject: modified grain model
subject: Engineering--Environmental
subject: Engineering--Chemical

description: Chemical looping combustion (CLC) is an innovative and environmentally promising technology for efficient and low-emission combustion of fossil fuels. Unlike conventional combustion processes, CLC operates by utilizing metal oxide particles as oxygen carriers (OCs) to facilitate the combustion of fuel while preventing the mixing of air and fuel, thereby minimizing the formation of nitrogen oxides (NOx) and enabling carbon capture. This unique approach makes CLC an attractive solution for mitigating greenhouse gas emissions from power plants and industrial processes. The oxygen carrier is a pivotal component of the CLC process. Therefore, the development of a highly stable oxygen carrier is of utmost importance for the commercialization of the CLC process. To this end, this thesis investigates the fabrication of synthetic oxygen carriers for the CLC process considering the activity and stability of the OCs in cyclic operation. In this study, CuO was selected as the oxygen carrier because it is relatively cheap, abundant, and highly reactive. The effect of support type and the CuO loading were investigated to optimize the physical properties of the prepared oxygen carriers and their performance in the CLC process. Silica, zirconia, and alumina supports were synthesized by the aerogel method, and CuO was impregnated on the surface of them. Results indicated that zirconia aerogel support exhibited the highest reactivity for methane combustion, and γ-alumina aerogel support displayed the least favorable performance, primarily due to the interaction between copper and alumina and the formation of coke. In order to prevent the interaction between CuO and Al2O3, a new method was employed to synthesize α-Alumina with a significantly increased surface area. It was observed that the alumina support transformed into α-Alumina in the temperature range of 1000-1200 °C, resulting in a surface area between 100-160 m2/g. OCs showed high activity during reduction and oxidation reactions and the conversion was complete after a few minutes because the interaction between CuO and Alumina was prevented. Yolk-shell structured γ-alumina support was also prepared in order to prevent the formation of spinel. It was found that the CuO-impregnated yolk-shell oxygen carrier showed the highest oxygen transport capacity and the highest resistance to coke formation compared to the core-shell and γ-alumina support because the presence of homogeneous coating of zirconia prevented the interaction between alumina and copper oxide and avoided the formation of coke. The effect of the immobilization of the CuO in the structure of the support was investigated in the CLC process. CuO nanoparticles, ranging from 20% to 60% in weight, were encapsulated within the nanochannels of silica and zirconia using a sol-gel technique. The findings suggested that a loading of up to 60 wt.% of CuO on the zirconia support could be achieved without any loss of the OC’s activity and stability. Silica-supported OCs exhibited lower oxygen transport capacity than the anticipated theoretical values. This reduction was a result of both CuO decomposing into Cu2O during the reduction process and the fusion and collapse of mesoporous silica. The kinetics of redox steps in the CLC process were investigated using a modified grain model considering grain size distribution in the OC particles based on their pore size distribution profile and the “pore to sphere” factor.