Mechanistic Features of Ultrasound-Assisted Oxidative Desulfurization of Liquid Fuels

A new technology for the removal of sulfur compounds from liquid fuels is oxidative desulfurization. Although several studies have reported the enhancement effect of ultrasound irradiation on oxidative desulfurization, the exact mechanism underlying this enhancement is not known yet. In this study, we have addressed this issue with dual approach of coupling experiments with mathematical model for cavitation. Results of this study have given interesting revelation of interaction between mechanism of ultrasound, cavitation, and oxidation system. Isolation of cavitation phenomenon helps to increase the extent of oxidation. This effect is attributed to formation of hydrogen and carbon monoxide during transient collapse of cavitation bubbles due to thermal dissociation of hexane vapor entrapped in the bubble, which hamper the action of O species generated from the oxidation system. Transient cavitation itself does not give rise to radical formation, because of rather low temperature peaks reached during collapse. Therefore, cavitation does not enhance the oxidation process, but in fact, has an adverse effect on it. Current study has established that the beneficial effect of ultrasound on oxidative desulfurization system is merely of a physical nature (i.e., emulsification due to intense micromixing), with no involvement of a sonochemical effect.