Photochemical Denitrogenation Processes for Light Oils Effected by a Combination of UV Irradiation and Liquid−Liquid Extraction

Abstract

Denitrogenation processes for light oils, based on a combination of UV irradiation and liquid−liquid extraction, have been investigated. Two extraction systems, one oil/water and the other oil/acetonitrile, were used for the denitrogenation of three separate light oils, of differing nitrogen content and hydrocarbon composition. The denitrogenation results, obtained for three model nitrogen compounds (aniline, indole, and carbazole), were compared with those obtained for the actual light oils. In the oil/water system, the photodecomposition of carbazole was found to be strongly suppressed by the presence of double-ring aromatic hydrocarbons. This adverse effect, however, was reduced by the addition of hydrogen peroxide to the water phase, and in the presence of 30% hydrogen peroxide and 36 h of photoirradiation, the nitrogen content of the light oils was decreased successfully to <20% of the feed value. In the oil/acetonitrile system, the nitrogen-containing compounds in the light oils were extracted into the acetonitrile phase and were there photodecomposed effectively, even in the presence of double-ring aromatics. In this way and with 10 h of photoirradiation, the nitrogen content of the light oils was decreased successfully to <3% of the feed concentration. Both of the proposed processes, however, were found to have difficulty in the denitrogenation of highly substituted alkylcarbazole compounds. In both processes, desulfurization occurred simultaneously with denitrogenation, and the sulfur content of light oils was also decreased to <30% and 5% of the feed values, thus revealing that both of the proposed processes are satisfactory for application to the simultaneous denitrogenation and desulfurization of light oil feedstocks.