Poisoning effect of nitrogen compounds on the performance of CoMoS/Al_2O_3 catalyst in the hydrodesulfurization of dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene

摘要

The poisoning effect of carbazole and quinoline on the performance of sulfided CoMo/Al_2O-3 in the hydrodesulfurization (HDS) of dibenzothiophene (DBT),4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT)has been examined.The HDS of 4-MDBT or 4,6--DMDBT is retarded by the presence of the nitrogen compounds in the reaction has been examined. The HDS of 4--MDBT or 4,6-DMDBT is retarded by the presence of the nitrogen compound in the reaction stream even it low concentrations, e.g.50 ppm, while the HDS of DBT remains nearly unaffected by these compounds unless the concentrations are high , in excess of 500 ppm. The nitrogen compounds suppress the ring-hydrogenation step (HYD) more that the direct desulfurization step (DDS) in the HDS of DBT , while an opposite trend is observed in the HDS of 4-MDBT or 4,6-DMDBT, i.e.DDS is suppressed to a greater extent that HYD. tHE Nitrogen nitrogen compounds poison acidic sites on the catalyst, as confirmed by the reduced amounds of pyridine adsorbed and by the suppressed isomerization of 2,2'-dimethylbiphenyl on the poisoned catalyst.Quinoline exhibits a stronger poisoning effect that carbazole. The HDS of the three DBT compounds studied in this work are suppressed to different extents by the nitrogen compounds because the extent of steric hindrance to the C-S-C bond by methyl groups attached to the ring structure is different depending on the BDT compounds