Mechanistic Features of Oxidative Desulfurization Using Sono-Fenton–Peracetic Acid (Ultrasound/Fe²⁺–CH₃COOH–H₂O₂) System

Abstract

This article attempts to identify the links between the chemistry of oxidative desulfurization and cavitation physics for an ultrasound-assisted oxidative desulfurization (UAOD) process using Fenton–peracetic acid as the oxidant. The model system employed was dibenzothiophene (as a model sulfur compound) and toluene (as a model gasoline/diesel). Experiments were performed to assess the role of each component of the oxidant in the chemistry of the process. H₂O₂ was found to be the key component of the oxidant that balances between several competing pathways and reactions in overall oxidative desulfurization process. Addition of Fe²⁺ to peracetic acid has a beneficial effect, whereas excess H₂O₂ has an adverse effect on the process. This article also highlights the physical and mechanistic features of the UAOD process. Transient cavitation is revealed to play a negative role in the desulfurization process, whereas ultrasound has a positive effect. The former effect is a consequence of the scavenging of HO₂^• radicals in the aqueous phase by radicals generated by cavitation bubbles, whereas the latter effect is attributed to the generation of a fine emulsion between the oxidant and toluene phases as a result of strong micromixing generated by ultrasound. The results of this study clearly point out that less scavenging and effective interphase transfer of HO₂^• radicals are more crucial to the utilization of HO₂^• radicals for desulfurization than mere generation