Characterization of a sol-gel derived CuO/CuAl2O4 oxygen carrier for chemical looping combustion (CLC) of gaseous fuels: relevance of gas-solid and oxygen uncoupling reactions

摘要

A new sol–gel CuO/CuAl2O4 material was characterized in a thermogravimetric analyzer (TGA) for chemical looping combustion (CLC) with gaseous fuels, including the relevance of the oxygen uncoupling mechanism in oxygen transference was considered. This material possesses high reactivity and oxygen transport capacity, which combines the best features of the previously reported impregnated and spray-dried materials. During the cycles with N2 and air, CuO was fully decomposed into Cu2O in N2 and then regenerated to CuO in air, similarly to chemical looping with oxygen uncoupling (CLOU) for solid fuels. Decomposition of CuAl2O4 to CuAlO2 was quite slow, and the followed regeneration cannot be accomplished. Subsequently, the adequate and stable reaction rates of this material were examined in high numbers of cycles (>50 cycles) with gaseous fuels. The material undergone such cycles with gaseous fuels was then subjected to cycles with N2 and air. Segregation of CuO from Al2O3 in the CuAl2O4 was observed during gaseous fuels combustion, which produced more available oxygen for CLOU than the initial material. Finally, the relative importance of gas–solid reactions in CLC against oxygen uncoupling in CLOU was examined with the appearance of gaseous fuel.