A novel desulfurization process for light oils has been investigated, based on the precipitation of S-alkylsulfonium salts produced by the reaction of sulfur-containing compounds with alkylating agents (CH 3 I and AgBF 4 ). Dibenzothiophenes (DBTs) and benzothiophenes (BTs), present in the light oils, were methylated by the addition of the alkylating agents, in the presence of dichrolomethane, to be removed as precipitates under moderate conditions. A semiempirical molecular orbital (MO) calculation shows that the desulfurization reactivity for both DBTs and BTs increases with increasing electron density on the sulfur atom, lying parallel to the plane of the molecules, and that the desulfurization activity for BTs decreases with electron density (bond order) on the unsaturated bond in the thiophene ring. The desulfurization of light oil, containing a high amount of aromatic hydrocarbons, was relatively difficult, because the methylation of aromatics occurs competitively with the S-methylation reaction. Desulfurization was, however, accelerated by an increase in the quantity of the alkylating agents added, such that the sulfur content of the light oils was decreased successfully to less than 0.005 wt %. The resulting light oil products confirm that the proposed process is satisfactory for application to the deep desulfurization of light oils. The desulfurization reactivity of the individual sulfur-containing compounds in light oils was found to depend on the aromatic content of the light oils. This is because the S-methylsulfonium salts are converted to parent sulfur-containing compounds by reaction with aromatic hydrocarbons.

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A novel deep desulfurization process for light oils, based on visible light-induced electron-transfer oxidation using 9,10-dicyanoanthracene (DCA) in an organic two-phase liquid−liquid extraction system, has been investigated. Sulfur-containing compounds, when dissolved in acetonitrile, are successfully oxidized by photoirradiation at wavelengths of λ > 400 nm in the presence of DCA, to form highly polarized compounds, which do not distribute into the nonpolar light oil. When light oil and acetonitrile are mixed and are photoirradiated with DCA, the sulfur-containing compounds are extracted successively and are photooxidized in the acetonitrile phase. In this way, a deep desulfurization is achieved:  the sulfur content in light oil being reduced from 0.18 wt % to less than 0.005 wt %. The DCA and the aromatic hydrocarbons in the acetonitrile are able to be recovered by the addition of water, followed by extraction with n-hexane. The DCA distributed into the light oil is strongly adsorbed by silica gel and can then be desorbed into the acetonitrile aqueous solution to be reused for further desulfurization. An overall desulfurization procedure is developed, with the data obtained showing that the proposed process is satisfactory for application to the deep desulfurization for light oil.

A desulfurization process, based on photoinduced electron-transfer oxidation using 9,10-dicyanoanthracene (DCA) and organic two-phase extraction, has been applied to the desulfurization of catalytic-cracked gasoline (CCG). Sulfur-containing compounds (thiol, disulfide, and thiophenes), in acetonitrile solution, are photooxidized by photoirradiation, at wavelengths of λ > 400 nm in the presence of DCA, to form highly polarized compounds (sulfoxide, sulfone, and sulfate anion), and these compounds do not distribute into the CCG. Thus, when CCG and acetonitrile solution are mixed and are photoirradiated with DCA, the sulfur-containing compounds are extracted into the acetonitrile phase and are photooxidized, thus providing the successive removal of sulfur from CCG to acetonitrile under moderate conditions. In this way, the sulfur content of CCG is reduced successfully from 100 ppm to less than 30 ppm. The large quantity of olefins contained in the CCG is minimally photooxidized, owing to their small fluorescence quenching rate with DCA, and thus the desulfurized CCG has the same high octane number as that of the feed CCG.

A desulfurization process, based on the formation and subsequent precipitation of S-alkylsulfonium salts using alkylating agents (CH 3 I and AgBF 4 ), has been applied to the desulfurization of catalytic-cracked gasoline (CCG). The desulfurization reactivity of each sulfur compound (thiol, disulfide, benzothiophene, tetrahydrothiophene, and thiophenes) in n-decane solution, as a model gasoline, was compared with that obtained from actual CCG. The sulfur compounds in CCG are methylated by the addition of the alkylating agents under moderate conditions and are removed as the precipitates of the corresponding S-alkylsulfonium salts. By employing this new process, the sulfur content of the CCG was decreased from 100 ppm to less than 30 ppm. The benzothiophene in CCG was found to be the most difficult compound to desulfurize, whereas the thiophenes were the most difficult compounds for the model gasoline. Although the olefin concentration was decreased significantly following desulfurization, the resulting CCG demonstrated as high an octane number as the feed CCG. The results thus suggest that the proposed process is satisfactory for application to the desulfurization of CCG.