Abstract: Heteroatom composition of coke deposited on catalytic cracking catalyst and flue gas were analyzed under different process conditions. According to density functional theory, the most stable configurations of typical nitrogen and sulfur compounds in carbon deposits were obtained by using Gaussian 09 software at B3LYP/def2-TZVP level, the Laplacian bond level was used as the criterion, and the conversion mechanism of heteroatom in carbon deposits was studied. The results showed that the nitrogen-containing compounds in coke deposited on catalyst were mainly pyridine, pyrrole and quaternary ammonium compounds, and the sulfur-containing compounds were mainly thiophene compounds. In the initial stage of catalyst regeneration, nitrogen-containing compounds escaped in the form of :NH and .CN were mainly converted into NH₃ and HCN, sulfur-containing compounds escaped in the form of .HS and :S were mainly converted into H₂S and COS, and NH₃, HCN, H₂S and COS were finally converted into NO_x and SO_x respectively. The simulation results were consistent with the flue gas composition under different regeneration process conditions.

Key words: catalytic cracking catalyst, carbon deposit, radical, Laplacian bond order, transformation mechanism