Photochemical desulfurization and denitrogenation process for vacuum gas oil using an organic two-phase extraction system

The simultaneous removal of sulfur- and nitrogen-containing compounds from vacuum gas oil (VCO), based on the combination of UV irradiation and liquid-liquid extraction using an oil/acetonitrile two-phase system, has been investigated. Detailed desulfurization and denitrogenation reactivities for the various compounds in VGO have also been studied by means of field ionization mass spectrometry (FI-MS) and gas chromatography with atomic emission detection (GC-AED), respectively. When VGO and acetonitrile are mixed and photoirradiated, the sulfur and nitrogen compounds in the VGO are distributed into the acetonitrile phase and photodecomposed there to form highly polarized compounds, which do not distribute into the lower-polarity VGO. The successive removal of these compounds from VGO to acetonitrile can therefore be carried out under moderate conditions, such that the sulfur and nitrogen contents for the VGO are decreased simultaneously to less than 1% of the feed values. FI-MS and GC-AED analyses reveal that dinaphthothiophenes, tetrahydrodinaphthothiophenes, tetrahydrodibenzothiophenes, and carbazoles, having large carbon numbers of the alkyl substituents, are the most difficult compounds to remove by the present photochemical organic two-phase extraction process. The removal efficiencies for sulfur and nitrogen compounds obtained from VGO were compared with the results obtained for light oil feedstocks, and the applicability of the present process to the refining of VGO was examined. From a consideration of the above results, a fully organized overall refining process for petroleum-derived middle and heavy feedstocks has been developed.