Highly efficient deep desulfurization of fuels by chemical oxidation

Abstract

This paper describes the oxidation of several model S-containing molecules with hydrogen peroxide in a two liquid–liquid (L–L) phase system with a phase transfer catalyst under atmospheric pressure in the 333–353 K temperature range. The influence of the reaction temperature, the nature of the substrate, the solvent, the molar ratio of the oxidant (H₂O₂) and the S-containing molecule were examined. The reaction rates of the oxidative desulfurization (ODS) reaction were found to increase with the temperature, and with the molar ratio of H₂O₂ and the S-containing molecule. The potential of this methodology is illustrated by the complete S-removal from a 5.0 wt% dibenzothiophene mixture at 353 K, under excess of H₂O₂ oxidant in less than three hours of reaction. In addition, the ODS reaction was strongly enhanced when the water solvent was replaced by acetonitrile. The very high ODS reaction rate observed with the acetonitrile solvent could be explained in terms of the much higher solubility of the sulfone reaction product in this solvent and also by its very low surface tension, which facilitates the transfer of products and reagents at the polar–apolar interface. Finally, the very mild sulfoxidation reaction was applied to a kerosene fraction. The results revealed that S-levels below 25 ppm are achieved at 353 K upon using a H₂O₂ ∶ substrate molar ratio of 2.5 ∶ 1.