Mechanistic insights of CO2-coke reaction during the regeneration step of the fluid cracking catalyst

The regeneration of a coked fluid catalytic cracking (FCC) catalyst under O2/He and CO2/He atmospheres from room temperature up to 1000 °C was studied using online mass spectroscopy. The catalyst was also thermally treated at temperatures between 300 °C and 500 °C in order to promote coke modification. It was verified that the amount of aliphatic carbon decreased for higher temperatures. These treatments have a more significant impact on the coke-CO2 reaction than on the coke-O2 reaction. The former reaction was the focus of the present investigation and the results were compared to the latter reaction. CO2 preferentially reacts in the beginning of coke burning and a remarkable decrease of CO2 activity is observed with the calcinated coked catalyst. Regeneration under 13CO2/He at constant temperatures between 600 °C and 940 °C revealed a first-order kinetics for the coke-CO2 reaction. The CO2 molecule reacts dissociatively introducing oxygenated functionality into the coke. These species are decomposed at high temperature forming CO and no water is observed during the CO2-coke reaction.

Coked FCC catalyst modified with pre-calcination treatment were burned under O2/He and CO2/He atmosphere. CO2 preferentially reacts in the beginning of coke burning and a remarkable decreasing of CO2 activity is observed with pre-calcination coked catalyst. Regeneration under 13CO2/He revealed a first kinetics order for coke-CO2 reaction. The CO2 molecule react dissociatively introducing oxygenated functionality in the coke. Figure optionsDownload as PowerPoint slide