Hydrodesulfurization of catalytic cracked gasoline. 3. Selective catalytic cracked gasoline hydrodesulfurization on the Co-Mo/γ-Al2O3 catalyst modified by coking pretreatment

The interaction of olefins with the hydrodesulfurization (HDS) catalyst surface was studied by the time course of catalytic cracked gasoline (CCG) HDS on the Co-Mo/γ-Al2O3 catalyst. Olefin hydrogenation activity was decreased drastically in the beginning 30 h. After 75 h of time on stream, to wash the catalyst surface, toluene was flown into the reactor at room temperature and this toluene wash recovered some olefin hydrogenation activity. The oligomers of CCG olefins were found in the effluent of toluene wash. It was suggested that oligomerized and polymerized olefin (coke) selectively deactivated the olefin hydrogenation active site. The possibility of improving the HDS selectivity of Co-Mo/γ-Al2O3 by carbonaceous deposit was investigated for HDS reactions of CCG and model compounds. The catalyst with coking pretreatment after sulfiding showed the higher CCG HDS selectivity than that of the catalyst without coking pretreatment. Thiophene HDS in the presence of diisobutylene or 1-octene was also carried out, and the relative deactivation by the coking pretreatment was in the following order, isoolefin hydrogenation>thiophene HDS>n-olefin hydrogenation. The improvement of CCG HDS selectivity by the coking pretreatment was considered to be caused by the selective deactivation of isoolefin hydrogenation active site.