Evaluation of Oxidative Desulfurization and Solvent Extraction of Model Sulfur Compounds, Present in Petroleum Middle Distillates, with Infrared and Nuclear Magnetic Resonance Spectroscopy

Abstract

Oxidative desulfurization has attracted considerable attention, since it can remove the refractory sulfur compounds under relatively mild conditions. The types of the sulfur compounds and the composition of the distillate affect the efficiency of the method. The composition of a distillate determines its properties and its performance characteristics, but it is too complex to model it exactly. In the present study, simple surrogate blends of eight model sulfur compounds in the range of petroleum middle distillates were created and oxidized, using the hydrogen peroxide-acetic acid system, at reaction temperatures of 50 and 70 °C. The total sulfur content was constant at 1% w/w. The organic phase of the oxidized products was extracted with acetonitrile and methanol. The sulfur content was determined using X-ray fluorescence and the mass yield was calculated. Liquid phase infrared spectra were obtained during the oxidation and the extractive desulfurization processes. The solid sediments that were precipitated in specific cases were identified using solid-state infrared and proton nuclear magnetic resonance. The influence of temperature upon the formation of sulfoxides or sulfones during the oxidative desulfurization of the sulfur compounds was studied in detail. The oxidation temperature of 70 °C was shown to be suitable for the completion of the oxidative desulfurization while both extraction solvents were efficient in the removal of the sulfur compounds.