Ultrasound-assisted oxidative desulfurization of fuel using butyl triphenyl phosphonium chloride as a promising catalyst

Abstract

The traditional hydrodesulfurization process has severe disadvantages, such as operating at a higher temperature and pressure and the inability to remove refractive sulfur compounds (S-compounds). To overcome these difficulties, the present study reports the synthesis and characterization of ionic liquid (IL), butyl triphenyl phosphonium chloride ([BTPP]Cl) and its application to the S-removal of model fuel (MF) using ultrasound-assisted oxidative desulfurization (UAODS). Ultrasound irradiation enhances the desulfurization efficiency by eliminating resistance to mass transfer between the organic and aqueous phases. The application of ultrasound generates more active free radicals which help in the conversion of S-compounds to their respective sulfones. MF contains dibenzothiophene (DBT) in n-octane (500 ppm), where 78.45% removal of DBT was achieved under optimized conditions of mass ratio of IL to MF:1/1, mole ratio of oxidant to sulfur:20/1, 50 °C, and 30 min under the application of sonication. Moreover, [BTPP]Cl could be regenerated and recycled for six consecutive cycles. The driving force behind the higher desulfurization performance using [BTPP]Cl was supposed to be the interactions between the IL and DBT. Various S-compounds such as thiophene (T), benzothiophene (BT), and 3-methyl thiophene (3-MT) were also studied for their UAODS reactivity. Thus, [BTPP]Cl proved to be a potential catalyst for application in the UAODS of a fuel, and the process can be employed for industrial application.