Studies of the mechanism of thiophene hydrodesulfurization: Conversion of 2,3- and 2,5-dihydrothiophene and model organometallic compounds

Catalytic hydrodesulfurization (HDS), the process by which organically bound sulfur is removed from crude oils, is one of the largest-scale chemical processes practiced in the world. Thiophene is typical of the organosulfur compounds found in petroleum, and considerable effort has been directed toward investigating the mechanism for thiophene hydrodesulfurization. Recently, the authors have reported new kinetic information involving the HDS of thiophene, 2,3- and 2,5- dihydrothiophenes, and tetrahydrothiophene. These studies were performed with both Re/{gamma}-Al{sub 2}O{sub 3} and Mo/{gamma}-Al{sub 2}O{sub 3} catalysts using a flow microreactor system; in particular, rhenium studies provided new information data concerning reaction intermediates. They have also been able to prepare and characterize thiophene-related organometallic compounds which serve as plausible models for bonding and conversion on catalytic surfaces. The combination of these studies has led to new insights concerning alternate mechanistic pathways for thiophene HDS. This comprehensive mechanism, which is based on kinetic studies using model HDS catalysts and on the synthesis and characterization of relevant transition metal complexes, is offered as a plausible route for thiophene HDS.