Mechanistic investigations on the adsorption of organic sulfur compounds over solid adsorbents in the adsorptive desulfurization of transportation fuels

Adsorptive desulfurization is based on the ability of a solid adsorbent to selectively adsorb organic sulfur compounds from liquid transportation fuels. A study was conducted to examine if the direct S-M interaction of π-complex formation is involved in the adsorption of thiophenic sulfur compounds on the given adsorbent and to understand which type of interaction (direct S-M interaction or π-complex formation) is favorable for the selective adsorption of only sulfur compounds without adsorbing aromatics and olefins present in the fuel. A model fuel containing thiophene, tetrahydrothiophene, benzene, and 1,5-hexadiene was prepared and used as a feed. Adsorbents based on zeolites, mixed metal oxides, supported metal compounds, etc., were evaluated. Thiophene involved mainly π-complexation using delocalized electrons of the aromatic ring rather than a direct S-M bond with Ag-exchanged zeolite. The adsorption of aromatics and olefins along with sulfur compounds by π-complexation would deteriorate the quality of transportation fuels. Based on the results, better adsorbents selective for removing only sulfur compounds were selected for the adsorptive desulfurization of real gasoline, diesel, and jet fuel.