New catalysts for deep hydrotreatment of diesel fuel -: Kinetics of 4,6-dimethyldibenzothiophene hydrodesulfurization over alumina-supported molybdenum carbide

Hydrodesulfurization (HDS) of 4,6-dimethyidibenzothiophene was investigated as a probe for the deep HDS of diesel fuel over alumina-supported molybdenum carbide catalysts. The reaction was carried out at 613 K under 4 MPa total pressure in a fixed-bed reactor, without sulfur addition to the liquid feed, H2S being generated by the transformation of the reactant. The reaction proceeds by two parallel routes leading either to 3,3'-dimethylbiphenyl by a direct desulfurization (DDS) pathway or to 3-(3'-methylcyclohexyl)toluene through a preliminary hydrogenation (HYD) pathway. Kinetic data can be divided into two ranges depending on the contact time. For contact times from 0 to 0.4 s (conversion < 45%), the HDS of 4,6-dimethyldibenzothiophene was found to be zeroth-order with respect to the reactant. Therefore, constant reaction rates can be measured for the two routes, the DDS pathway being the more important (r(HYD)/r(DDS) = 0.7). All data can be interpreted in terms of kinetic coupling of the two catalytic DDS and HYD cycles through a common intermediate species. For contact times higher than 0.4 s the kinetics are more complex. (C) 2002 Elsevier Science B.V. All rights reserved.