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 hydrodesulfuriz ation (HDS) of polyaromatic sulfur compounds (PASCs), new understandin g has been obtained concerning the intrinsic Limitations to achieving the new distillate fuels standards. Establishing the relative rates fo r hydrogenation of the parent sulfur compound and its desulfurized pro ducts, and considering thermodynamic limitations on hydrogenated inter mediates are critical to these improved kinetics. With this new approa ch, it has been possible to more accurately assess the differences in performance of different catalysts such as Co-MoSx/Al2O3, Ni-MoSx/Al2O 3 and analogous catalysts supported on carbons, the basic causes of se lectivity change with temperature, and the mechanistic consequences of inhibitors on the HDS product distributions. Ni promoted catalysts we re found to possess much higher hydrogenation activities than comparab le Co promoted catalysts. Carbon supported catalysts appear to have po tential for HDS at high temperatures. Inhibition by H2S affects both h ydrogenation and direct sulfur extraction HDS routes, but, secondary h ydrogenation of desulfurized aromatic products was found to be the mos t sensitive to inhibition. Naphthalene inhibits all hydrogenation reac tions but has little effect on direct HDS. (C) 1998 Elsevier Science B .V. All rights reserved.