Kinetic Analyses and Inhibition by Naphthalene and H₂S in Hydrodesulfurization of 4,6-Dimethyldibenzothiophene (4,6-DMDBT) over CoMo-Based Carbon Catalyst

Abstract

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 °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.

APPLICATION OF NEW ZRO2-SBA-15 MATERIALS AS CATALYTIC SUPPORTS: STUDY OF INTRINSIC ACTIVITY OF MO CATALYSTS IN DEEP HDS

“…It is generally accepted that the HDS of 4,6-DMDBT follows a pseudo-first-order kinetics (Farag, 1999). This also seems to be true for all our catalysts.…”

Kinetics of Hydrodesulfurization of Dibenzothiophene on Sulfided Commercial Co-Mo/γ-Al2O3 Catalyst

“…2). This indicates a pseudofirst order kinetic similar to earlier reports (Wang, et al 2004;Farag et al 1999;Singhal, et al 1982). However, at a low temperature, DBT adsorption may be important despite the low concentration that was employed.…”

“…It has also been shown that the relative significance of hydrogenolysis and hydrogenation routes depended on Co/Mo ratios (Wang, et al 2004). Furthermore, the two routes could also be substantially affected by the presence of Naphthalene or hydrogen sulfide for the HDS of DBT or 4,6-dimethyldibenzothiophene (Farag, et al 1999).…”

Fuel Formulation Studies

“…benzothiophenes with no substituents in 2-or 7-position 2. dibenzothiophenes with no substituents in the 4-or 6-position 3. dibenzothiophenes with one substituent in the 4-position 4. dibenzothiophenes with two substituents in the 4-and 6-positions For these distillates to meet the mandated sulfur specifications, all compounds in groups 1, 2, and 3 will have to be completely desulfurized, and at least half of those in the least-reactive fourth group will also have to be converted. Several studies using different types of catalysts and operating conditions have identified 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as the most refractory sulfur compounds which will have to be eliminated to achieve deep desulfurization [49,50,[63][64][65][66][67][68][69][70].…”