Removal of Dibenzothiophenes from Fuels by Oxy-desulfurization

Abstract

Removal of sulfur species from fuels is an increasingly critical environmental issue. Hydrodesulfurization (HDS) removes sulfur compounds, such as mercaptans and sulfides, from hydrocarbons; however, some sulfur-containing compounds are very difficult to remove and need deep desulfurization processes. In this study, another approach is explored, where dibenzothiophene can be removed from the HDS products by a liquid-phase process. Four different sulfur removal approaches are tested: oxidation, extraction, consecutive oxidation and extraction, and simultaneous oxidation and extraction. A detailed parametric experimental study was performed to select the best technique for the specified purpose of this investigation. n-Octane doped with dibenzothiophenes is used as a model fuel, which is extracted by polar solvents [N-methyl-2-pyrolidone (NMP), dimethyl formamide (DMF), and acetonitrile (ACN)]. These solvents are found to have a moderate capability of removing sulfur species. Applying oxidation in the liquid phase resulted in partial removal of the sulfur content, but most of the sulfur components are not removed from the fuel phase. However, applying both oxidation and extraction steps (either consecutively or simultaneously) resulted in dissolution of sulfur production in the solvent phase. NMP was found to be the best solvent (among the tested ones in this investigation) for the removal of oxidized sulfur species. This is related to the high capability of NMP (polar solvent) for the removal of oxidized (polar) sulfur species (sulfones).