Demonstrating the applicability of chemical looping combustion for the regeneration of fluid catalytic cracking catalysts

Abstract

Fluid Catalytic Cracking (FCC) units are responsible for roughly 25% of CO2 emissions from oil refineries, which themselves account for 4–6% of total global CO2 emissions. Although post- and oxy-combustion technologies have been proposed for CO2 capture in FCC, Chemical Looping Combustion (CLC) may also be a potential approach that has lower energy consumption. An equilibrium catalyst (ECat) was first modified with oxidised oxygen carriers (CuO, Co3O4, Mn2O3) using wet-impregnation, and their reduced states (Cu, CoO, Mn3O4, MnO) were generated by hydrogen reduction. To demonstrate that the impregnated reduced oxygen carriers had no significant negative effects on cracking, the prepared catalysts were used to crack n-hexadecane using the standard FCC microactivity test (ASTM D3907-13). The CLC behaviour of coke deposited on the reduced oxygen carrier impregnated ECats, was investigated with the stoichiometrically required amount of oxidised oxygen carrier impregnated ECat in lab scale fixed-bed and fluidised-bed reactors equipped with an online mass spectrometer to monitor CO2 release. Although the conversion and liquid to gas ratio were largely unaffected, coke selectivity did increase with the impregnation of reduced oxygen carriers. However, this increase is mostly attributed to solvent extractable coke. It is possible to reach about 90 vol% combustion efficiency of the coke deposited on ECat using mechanically mixed with CuO and Mn2O3, but the regeneration temperature required, 800 °C, is considerably higher than that under typical regenerator conditions of 650–750 °C for 30–60 min. However, relatively high combustion efficiencies of greater than 94 vol% of the coke deposited on reduced Cu and Mn3O4 impregnated ECat were achieved with the stoichiometrically required amount of CuO and Mn2O3 impregnated ECat at 750 °C for 45 min., close to conventional FCC regenerator conditions.