Development of Fe-based oxygen carrier using spent FCC catalyst as support for high temperature chemical looping combustion

Chemical looping combustion is based on the transfer of oxygen from air to fuel by means of an oxygen carrier using a metal oxide. This study investigated the development of an oxygen carrier by adding iron to a spent commercial fluid catalytic cracking catalyst (Fe/FCC) and comparing to Fe/Al2O3, and Fe/SiO2 oxygen carriers that may be suitable for the high-temperature (1100 degrees C) process. The FCC material was chosen as a low-cost oxygen carrier. The FCC support strongly modified the reduction behavior of the Fe-based carrier as compared to the Fe/Al2O3 and Fe/SiO2 carriers. Multicycle studies with CH4 revealed the FCC support impacted the CO2 selectivity (13.5%) at 1100 degrees C to produce more gaseous CO as compared to the 900 degrees C (89.7%) due to the formation of FeAl2O3 and Fe2SiO4 phases when the Fe2O3 was reduced at 1100 degrees C. The FeAl2O3 and Fe2SiO4 phases also considerably slowed the CO2 formation rate on the Fe/FCC oxygen carrier at 1100 degrees C as compared to the 900 degrees C reaction tests. The higher-temperature (1100 degrees C) decreased the oxygen transfer capacity of the Fe/FCC carrier, did not significantly increase the capacity of either the Fe/SiO2 and Fe/Al2O3 carriers. These results suggest that high-temperatures (1100 degrees C) may lead to carrier transformations through sintering and agglomeration that significantly reduce the kinetics and performance of the oxygen carrier. This research suggests at higher temperatures, shorter reduction times may be necessary to prevent the formation of these phases and the subsequent deactivation of the carrier for total oxidation.