Assessment of limitations and potentials for improvement in deep desulfurization through detailed kinetic analysis of mechanistic pathways

Utilizing an improved method for the assignment of the rate constants to the complicated network of reaction pathways in the hydrodesulfurization (HDS) of polyaromatic sulfur compounds (PASCs), new understanding has been obtained concerning the intrinsic Limitations to achieving the new distillate fuels standards. Establishing the relative rates for hydrogenation of the parent sulfur compound and its desulfurized products, and considering thermodynamic limitations on hydrogenated intermediates are critical to these improved kinetics. With this new approach, it has been possible to more accurately assess the differences in performance of different catalysts such as Co-MoSx/Al2O3, Ni-MoSx/Al2O3 and analogous catalysts supported on carbons, the basic causes of selectivity change with temperature, and the mechanistic consequences of inhibitors on the HDS product distributions. Ni promoted catalysts were found to possess much higher hydrogenation activities than comparable Co promoted catalysts. Carbon supported catalysts appear to have potential for HDS at high temperatures. Inhibition by H2S affects both hydrogenation and direct sulfur extraction HDS routes, but, secondary hydrogenation of desulfurized aromatic products was found to be the most sensitive to inhibition. Naphthalene inhibits all hydrogenation reactions but has little effect on direct HDS. (C) 1998 Elsevier Science B.V. All rights reserved.