Ultrasonic process intensification during the preparation of dimethyl carbonate based on the alcoholysis of ethylene carbonate and the kinetic behavior of dimethyl carbonate

Abstract

The use of ultrasonic process intensification in the preparation of dimethyl carbonate (DMC) by alcoholysis of ethylene carbonate can make up for several disadvantages of heterogeneous catalysis, such as low conversion and long reaction time. In this study, alcoholysis with methanol and ethylene carbonate as raw materials and KF/MgO as a catalyst was enhanced by ultrasonic technology. It was calculated that the theoretical value of the heat of reaction was −19.46 kJ mol⁻¹ and the experimental value was close to 7.15 kJ mol⁻¹. The alcoholysis of ethylene carbonate was an exothermic reaction. An essential finding is that ultrasound can accelerate the reaction rate of alcoholysis of ethylene carbonate and improve the reaction efficiency. When the reaction temperature was 60 °C, the time for the reaction to stabilize was shortened from 50 min to 30 min. When the reaction time was 30 minutes, the conversion of ethylene carbonate under ultrasonic conditions was 79.0%, which was 6.0% higher than the conversion under mechanical stirring. According to the reaction kinetic equation, the activation energy of the alcoholysis of ethylene carbonate was 15.04 kJ mol⁻¹ and the conversion under different reaction conditions was predicted. The catalyst used for the ultrasonic process intensification had obvious pitting on the surface after repeated use. This result may be attributed to the local high temperature, high pressure and the microjet created by the collapse of cavitation bubble cores, which provide a new physical and chemical environment for chemical reactions. The high-speed microjet formed by the collapse of cavitation bubbles repeatedly impacts the surface of the catalyst, causing cavitation erosion on the surface of the catalyst. The fluid shock waves and high-speed microjets formed by the asymmetric collapse of the cavitation bubbles can induce a dispersion effect to make the cavitation field distribution uniform, which can effectively promote the mixing and mass transfer between the KF/MgO catalyst and the reactants, and accelerate the reaction process.