Abstract: To study the structural variation of coke on residue HDCCR catalysts with time-on-stream, the spent catalysts tested at different times on a bench-scale continuous stirred tank reactor were analyzed. The spent catalysts were successively dissolved in steps with n-heptane and toluene to obtain toluene-soluble soft coke and hard coke deposited on catalysts. Then the structures of the two types of coke were analyzed respectively. The variation of sulfur content and carbon residue of hydrotreatedresidue was investigated, and it was concluded that the catalytic performance tended to decrease as the reaction proceeded. TG-MS, 13CNMR and Raman spectroscopywere used to investigate the structural changes of hard coke, it revealed that the aromaticity and graphitization of the hard coke did not significantly increase at the time-on-stream from 0 to 60 min. However, when the time-on-stream was increased to 240 min, the proportion of aromatic carbon in the hard coke increased, and the graphitization of coke enhanced. Combined with the results of FT-ICR MS of toluene-soluble soft coke at different time-on-stream, the increase in condensed aromatics in the toluene-soluble soft coke performed on 60 min suggests that the coke precursors have already dehydrogenatedandcondensated in the early stage, whereas the formed coke is still soluble in toluene. In the advanced stage of the residue hydrotreating reaction, owing to the limitation of the catalytic capacity, the dehydrogenation-condensation reaction was intensified, which contributed to the further increase in coke aromaticity, hard coke which is difficult to remove even further reducing the catalytic activity.

Key words: heavy oil hydrotreating, catalyst, coke, aromaticity, toluene-soluble soft coke