Review in desulfurization of liquid fuels: Microwave and ultrasound oxidative-assisted techniques

Desulfurization removes sulfur compounds from fuel to prevent harmful SOx emissions. The limitations of hydrodesulfurization (HDS) in eliminating refractory sulfur (RS) compounds, along with strict fuel sulfur regulations, have driven research into advanced methods. Oxidative desulfurization (ODS) has emerged as a promising alternative, effectively reducing sulfur content in gasoline and diesel under mild conditions while ensuring compliance with environmental standards. Due to the ability to eliminate RS compounds under mild circumstances and its favorable operating conditions, ODS is suggested as a suitable alternative or complement to HDS. Different approaches can be integrated with ODS to enhance its efficacy, such as ultrasound-assisted, plasma-assisted, microwave-assisted, hydrodynamic cavitation-assisted, photocatalytic, electrochemical oxidative, magnetic field-assisted, and bio-oxidative desulfurization. The present study initially surveys an overview of the developed desulfurization technologies to generate ultra-low-sulfur fuels. The latest advances in microwave-assisted (MODS) and ultrasound-assisted oxidative desulfurization (UODS) were reviewed. Additionally, the benefits and limitations of each approach for desulfurizing liquid fuels have been studied. Finally, all factors that affect these techniques and their mechanism were discussed. This review aims to give critical references and prospective suggestions for advancing desulfurization technologies using MODS and UODS.