Kinetic analyses and inhibition by naphthalene and H2S in hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) over CoMo-based carbon catalyst

Hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) in decane has been investigated over a Co-Mo/C catalyst, using a magnetically stirred autoclave reactor. The hydrodesulfurization reaction was found to be pseudo-first order with respect to 4,6- DMDBT. Direct desulfurization was detected to be Arrhenius-dependent with an activation energy of 35.7 kcal/mol, while hydrogenation pathway showed a maxima at 340 degrees C. The activation energy of hydrogenation in the Arrhenius-dependent region was calculated to be 17.9 kcal/mol, as hydrogenation is thermodynamically limited at high temperature. The reaction of hydrodesulfurization appears to proceed via two different partially dependent routes, hydrogenation and desulfurization, over the present catalyst. Hydrogenation of 3,3'-dimethylbiphenyl at different temperatures was also measured to identify the rates of the step involved in the hydrodesulfurization network of 4,6-DMDBT. Attention was particularly paid to the effects of naphthalene and H2S on the two different reaction pathways to propose the mechanism of their inhibition. Two different catalytic active sites, one for hydrogenation and the other for both hydrogenation and direct desulfurization, are discussed to be present.