Study On Ultrasound-assisted Oxidative Desulfurization Catalyzed By Phosphotungstic Acid/Activated Carbon

Recently, hydrogen peroxide oxidative desulfurization has been widely studied,due to their mild reaction conditions, economical and environmental friendly oxidantas well as good performance in the removal of benzothiophenes anddibenzothiophenes. However, as the hydrogen peroxide system is composed ofimmiscible oil-water two phase, low mass transfer rate between the two phase resultsin a long reaction time and the excess consumption of hydrogen peroxide. The studyon ultrasound-assisted oxidative desulfurization has shown that ultrasound canfaciliate the formation of emulsification between the oil-water two phase, which couldgreatly boost the process of oxidative desulfurization. But the catalysts used in theultrasound-assisted oxidative desulfurization system reported in literature are allhomogenous catalysts, which are difficult in seperation and recycle. So thedevelopment of solid catalyst used under ultrasound irradiation is quite important forthe industrial application of oxidative desulfurization.In this study, phosphotungstic acid/activated carbon catalysts were prepared andused in the developing and optimizing the ultrasound-supported solid catalyst-H2O2oxidative desulfurization process. The catalysts were characterized by XRD, FT-IR,and N2physisorption, in order to understand the disperse state of phosphotungsticacid on activated carbon. Experiments were done to choose the optimal catalyst usedin ultrasound assisted oxidative desulfurization. The results shown thatphosphotungstic acid was highly dispersed and kept intact on activated carbon. Theconcurrence of phosphotungstic acid and activated carbon played a synergistic effecton the oxidation of dibenzothiophene. After supported phosphotungstic acid onactivated carbon, DBT conversion was greatly increased. The catalytic reactivity ofphosphotungstic acid/activated carbon catalyst increased with a reduction in particlesize and an increase in phosphotungstic acid loading amount. Besides, it was proposedthat phosphotungstic acid/activated carbon catalyst with10%of phosphotungstic acidwas the best candidate for ultrsound oxidative desulfurization.Then different technological parameters on the effect of ultrasound-supportedsolid catalyst-H2O2system have been studied, such as catalyst dose, ultrasound power,reaction temperature and the amount of oxidant. Meanwhile, the stability and thereusability of phosphotungstic acid/activated carbon catalyst have been also tested. The results shown that there was an optimum amount about the addition of solidcatalyst under ultrasound irradiation. DBT conversion increased with an increase inultrasound power, reaction temperature and the amount of oxidant. After reuse forthree times, DBT conversion catalyzed by phosphotungstic acid/activated carboncatalyst was still higher than that catalyzed by the mixture of phosphotungstic acidand activated carbon, and phosphotungstic acid/activated carbon catalyst can keep itsstability under ultrasoud irradiation. The results can not only provide some bases forthe subsequent optimization of ultrasound-supported solid catalyst-H2O2oxidativedesulfurization process and its industrial applications, but also can offer a referece forthe design of ultrasound reactor.