Deep Hydrodesulfurization of Light Gas Oil. 1. Kinetics and Mechanisms of Dibenzothiophene Hydrodesulfurization

Abstract

Hydrodesulfurization (HDS) of light gas oil was investigated using sulfided Co−Mo/Al2O3 catalyst. The behavior of dibenzothiophene, monomethyldibenzothiophenes (C1-DBTs) and dimethyldibenzothiophenes (C2-DBTs) in HDS was traced under the following conditions: temperature, 280−400 °C; LHSV, 2−10 h-1; and gas/oil, 1000 and 125 NL (L-(NTP))/L. The HDS of these compounds was treated as a pseudo-first-order reaction. The ratio of the rate constants of 4-methyldibenzothiophene (4-MDBT) and DBT to that of 4,6-dimethyldibenzothiophene (4,6-DMDBT) diminished relative to those of the model reactions. The activation energies of DBTs increased in the order DBT < 4-MDBT < 4,6-DMDBT, while the differences between values diminished relative to those of HDS reactions using a single component among DBT, 4-MDBT, and 4,6-DMDBT. The retarding effect of H2S on HDS decreased in the order DBT > 4-MDBT, and further, 4,6-DMDBT was not inhibited. The results indicated that the selectivity for biphenyls in the HDS of DBT was higher than in the HDS of 4-MDBT or 4,6-DMDBT and that DBT and 4-MDBT were adsorbed by the catalyst more weakly than 4,6-DMDBT. An aromatic hydrocarbon of larger ring number has a stronger retarding effect on the HDS rate. The addition of phenanthrene decreased the HDS rate of DBTs in the order DBT > 4-MDBT > 4,6-DMDBT, while 1-methylnaphthalene did not affect the HDS rate. The effect of phenanthrene on the HDS rate appeared to be related to the differences in the adsorption ability of DBTs. To the contrary, the addition of acridine decreased HDS rate in the order 4,6-DMDBT > 4-MDBT > DBT. The results indicate that the retarding effect of acridine is different from that of phenanthrene.