Separation and Characterization of Sulfoxides in Crude Oils

A good understanding of the chemical composition of organic sulfur compounds (OSCs) in petroleum is necessary to develop suitable hydrogenation catalysts and optimize desulfurization refining processes. In this study, sulfur species in crude oils derived from different geological sources were characterized by electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The O 1 S 1 class species (with one oxygen and one sulfur atom in the molecule) strongly responded in positive-ion ESI MS and were considered as sulfoxides. These compounds were separated into polar fractions by chromatographic separation and reduced by LiAlH 4 to obtain corresponding sulfur compounds. The O 1 S 1 class species were confirmed as sulfoxides, which have similar distribution in carbon number and double bond equivalent (DBE) to sulfides in the oils. However, the molecular composition of sulfoxides in different crude oils was largely different. Polar sulfur compounds amount to a considerable proportion (>27%) of total sulfur for all investigated crude oils, while sulfoxides occupied just a small proportion (0.08–5.9% of total sulfur for the investigated oils) of the polar sulfur compounds. Other polar sulfur compounds were found resistant to hydrodesulfurization and should be explored in the following studies.