Properties Analysis of Spent Catalyst for Fixed-Bed Residue Hydrotreating Unit: Composition of Deposited Elements Along Catalyst Bed

Element compositions of spent catalyst from a commercial fixed-bed residue hydrotreating unit of Petro-China were analyzed in order to investigate the reasons for the catalyst deactivation. The spent catalysts were sampled from different axial position of the reactor. Depositions of C, H, S, N, Ni and V on the spent catalysts were studied. No necessary relation was observed for the contents of various deposited elements along the bed at the end of a run. The deposition amount of elements was mainly related to local reaction conditions and catalyst loading states in the fixed-bed. The catalysts with high metal depositions have low contents of coke, high contents of sulfur and high H/C, which indicates that residue hydrotreating is an autocatalytic process. Metal sulfides deposited on catalysts have a hydrogenation activity in residue hydrotreating. The coke on residue hydrotreating catalysts mainly comes from some specific condensed ring structures containing nitrogen existed in asphaltene which is difficult to hydrotreat. Key words: Spent catalyst; Residue hydrotreating; Deposited elements; Composition