Kinetic analysis of the hydrodesulfurization of dibenzothiophene: Approach solution to the reaction network

The hydrodesulfurization of dibenzothiophene over CoMo/Al2O3 and MoS2 catalysts in a batch reactor at 340 degrees C and 3 MPa of hydrogen pressure was investigated. Overall, dibenzothiophene undergoes two parallel-sequential reactions: direct desulfurization leading to biphenyl and hydrogenation leading to the partially hydrogenated dibenzothiophene. The two intermediates are solely the sources to the formation of phenylcyclohexane. Improved kinetic analysis was performed in order to develop a more accurate expression to the contribution of the two routes in the hydrodesulfurization of dibenzothiophene. The apparent rate constants for direct desulfurization, k(1)(1), and hydrogenation, k(2)(2), pathways were estimated using a developed kinetic model where each intermediate is independently treated. The rates of the intermediate components (biphenyl and the partially hydrogenated dibenzothiophene) were found to be highly dependent on the subsequent sequential reactions. With this new model, it has been possible to assess accurately the magnitude of the extreme differences in the performance of the CoMo/Al2O3 and MoS2 catalysts. However, the model would as well be readily applicable to any hydrotreating catalysts. CoMo/Al2O3 catalyst showed high selectivity to the direct desulfurization pathway while the MoS2 catalyst exhibited considerable contribution from the hydrogenation pathway. The results show that the selectivity is more accurately expressed by the individual apparent rate constants rather than by the product distribution ratio.