Desulfurization of transportation fuels by adsorption

This paper is a review on sorbents for desulfurization of transportation fuels (gasoline, diesel, and jet fuel). Since the π-complexation sorbents are the most promising, they are the focus of the discussion. During π-complexation, the thiophenic compounds can bind selectively to the sorbents, especially the substituted ones. The later remain highly unreacted in hydrodesulfurization (HDS) (i.e., "refractory" sulfur). Molecular orbital (MO) calculations and experiments have shown that these refractory compounds [(e.g., 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene (DMDBT)] bind strongly with the π-complexation sorbents because of a better electron donation/back-donation ability. The sorbents reviewed include Ag-Y, Cu(I)-Y, Ni(II)-Y, and Ni(II)-X zeolites prepared using various ion-exchange techniques. The techniques included vapor and solid-state ion exchanges, which are suitable for obtaining high loadings of transition metals. The best sorbent, Cu(I)-Y [vapor-phase ion-exchanged (VPIE)], is capable of producing almost 38 cm³ of desulfurized fuel per g of sorbent with a sulfur concentration of less than 0.2 ppmw. Using these π-complexation sorbents in layered bed matrices further increases the desulfurization capacity.