Deep Hydrodesulfurization of Light Gas Oil. (Part 2). Effect of Hydrogen Sulfide on Hydrodesulfurization of Dibenzothiophenes Included in Hydrotreated Light Gas Oil.

Abstract

Sulfided Co-Mo/Al2O3 catalyst was used to investigate the hydrodesulfurization (HDS) of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) included in hydrotreated light gas oil (H-LGO) of less than 0.168wt% of sulfur-content. The behavior of DBT, 4-MDBT, and 4, 6-DMDBT in HDS was traced under the following conditions: temperature 290-370°C, LHSV 2-10h-1, and Gas/Oil 125Nl/l. The HDS of these compounds was treated as a pseudo-first-order reaction with respect to their concentrations. The ratio between HDS rate constants of various DBTs in H-LGO was substantially larger than that between the comparable constants in straight-run LGO (SR-LGO). Activation energies of the HDS of DBTs increased in the order DBT<4-MDBT<4, 6-DMDBT, while the differences between the activation energies were larger for H-LGO HDS than for SR-LGO HDS. It thus appeared that H-LGO HDS formed a lesser quantity of H2S than did SR-LGO HDS. The retarding effect of H2S on HDS was investigated by using polysulfide, which easily formed H2S under HDS conditions. The retarding effect of H2S on HDS decreased in the order DBT>4-MDBT, while the HDS of 4, 6-DMDBT was not retarded. These results could be explained by assuming a competitive adsorption between DBTs and H2S.