Optimization of ultrasound-assisted oxidative desulfurization of model sulfur compounds using commercial ferrate (VI)

• Use of commercial ferrate shows high sulfur removal in untreated diesel oil.
• Utilized Box-Behnken method to determine optimum parameters.
• High removal of benzothiophene and dibenzothiophene under oxidative desulfurization.

In this study, ultrasound-assisted oxidative desulfurization of benzothiophene and dibenzothiophene using ferrate and a phase transfer agent was investigated. The effects of ferrate concentration (100–300 ppm), phase transfer agent (100–300 mg), ultrasonication time (10–30 min), and organic to aqueous phase ratio (10:30–30:10) on sulfur reduction were examined. A Box-Behnken design was utilized to evaluate the effects of various parameters and determine optimum conditions in desulfurization. The level of significance of each parameter and their interaction were analyzed using the analysis of variance. Results showed the optimal conditions for benzothiophene to be 16.4 min, 122.1 mg PTA, 29.7 mL:10.3 mL and 204.8 ppm ferrate. Meanwhile, optimum desulfurization conditions for dibenzothiophene could be attained at 29.5 min, 111.6 mg PTA, 16.2 mL:23.8 mL and 245.3 ppm ferrate. Moreover, sulfur removal of 85.7% and 91.0% in diesel oil was achieved for benzothiophene and dibenzothiophene using the optimized conditions.