A desulfurization and denitrogenation process for light oils has been investigated based on the chemical oxidation of sulfur-and nitrogen-containing compounds using hydrogen peroxide and acetic acid as oxidizing agent. Sulfur and nitrogen compounds, when dissolved in n-tetradecane and xylene, were oxidized under moderate conditions and were removed successfully. By use of this basic process, although nitrogen content of actual light oils was reduced to <22% of the corresponding feed values, sulfur content failed to be reduced to the required deep desulfurization level (0.05 wt %). This is because the alkyl-substituted sulfones, produced during the oxidation of sulfur compounds, remain in the resulting light oils, owing to their high hydrophobicity. These, however, may be removed from the light oils by subsequent extraction, using an acetonitrile/ water azeotropic mixture, such that the sulfur contents of the light oils were decreased to <0.05 wt %, while maintaining a high oil recovery yield.

The denitrogenation behavior of light oils, when occurring during a novel desulfurization process based on alkylation and a subsequent precipitation method, using the alkylating agents (CH3I and AgBF4), has been investigated. Denitrogenation results, obtained for three model nitrogen compounds (aniline, indole, and carbazole) in a xylene solution, were compared with the results for three light oils, of differing nitrogen, sulfur, and aromatic concentration. The nitrogen compounds in the light oils were found to be N-methylated by reaction with the alkylating agents, such that they were removed as precipitates under moderate conditions. By use of this process, the nitrogen contents of all of the light oils were reduced successfully to less than 20% of the corresponding feed concentration, thus demonstrating that the present process is satisfactory for the simultaneous denitrogenation of light oils combined with desulfurization. Although the denitrogenation of aniline and indole compounds from the light oils proceeded effectively, carbazoles and especially those having a large carbon number of alkyl substituents were difficult to be denitrogenized by the present process. This is because the electron density on the nitrogen atom decreases with increasing carbon number of the alkyl substituents on the molecule of the carbazoles.

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.

The denitrogenation behavior of several model nitrogen compounds has been investigated during a novel desulfurization and simultaneous denitrogenation process based on alkylation using CH3I and AgBF4 (alkylating agents) and subsequent precipitation of the resulting materials. The denitrogenation reactivities obtained for basic nitrogen compounds (aniline, pyridine, quinoline, and acridine) dissolved in xylene solution were compared to those for neutral compounds (pyrrole, indole, and carbazole). The basic compounds and carbazole were removed from xylene by reaction with the alkylating agents as precipitates of the corresponding N-methylated tetrafluoroborates, whereas pyrrole and indole produced insoluble polymerized materials on their unsaturated bonds. It was found that the denitrogenation reactivities lie in the order pyridine > aniline > acridine > quinoline for basic compounds and pyrrole > indole > carbazole for neutral compounds. Semiempirical MO calculations show that the reactivities of the basic compounds depend on the electron density on the π orbital for the nitrogen atom lying perpendicular to the plane of the molecules.

Photochemical production and recovery process of biphenyls from the desulfurization products, obtained by oxidative desulfurization (ODS) of light oils, has been investigated. The S-oxidized dibenzothiophenes (DBT sulfones), when dissolved in 2-propanol, were converted successfully into the corresponding biphenyls by photoirradiation at wavelengths of λ > 280 nm using a highpressure mercury lamp, under conditions of nitrogen atmosphere and at room temperature. The present photochemical process was found to be also effective for the production of biphenyls from the DBT sulfones present in the desulfurization products of low-aromatic-content light oils. The quantitative recovery of biphenyls from the resulting 2-propanol solution was carried out successfully by adsorption using neutral aluminum oxide and subsequent elution with dichloromethane/n-hexane (20/80 v/v) mixture.