Optimization of ultrasound-assisted oxidative desulfurization of benzothiophene using co-precipitated phosphotungstic acid and tetrabutylammonium chloride

The consumption of fuel oil has continuously increased due to industrialization. Sulfur emissions brought by fuel combustion present threats to the environment and human health. To comply with stringent regulations set by government agencies for sulfur limits in fuel oils, desulfurization methods are employed by industries. Ultrasound-assisted oxidative desulfurization (UAOD) is an emerging method to remove refractory sulfur compounds such as benzothiophene (BT) in fuel oils. In this study, a novel composite catalyst was synthesized with the aim of combining the properties of phosphotungstic acid (HPW) and tetrabutylammonium chloride (TBAC) for the conversion of BT under UAOD. The effects of BT concentration (100–500 ppm), catalyst dosage (0.1–0.2 g), reaction time (10–30 min), and H 2 O 2 :BT oil ratio (0.5–1.5) were examined. Increased oxidation efficiency was observed for low levels of BT concentration and H 2 O 2 :BT oil ratio together with high levels of catalyst dosage and reaction time. The parametric effects of catalyst dosage, reaction time, and H 2 O 2 :BT oil ratio were found to be highly significant with p -value of <0.0001. The quadratic effect of H 2 O 2 :BT oil ratio was also significant with p -value of 0.0033. Optimum parameter levels were obtained using Response Surface Methodology-Box Behnken design (RSM-BBD). An average of 81.49 % as the optimum oxidation efficiency was obtained under optimum parameter levels of 189.27 ppm BT concentration, 0.16 g of catalyst, 26.64 min, and 0.51 H 2 O 2 :BT oil ratio. These results indicate the applicability of the composite catalyst in the removal of BT using UAOD.