Intensification of Liquid-Liquid Extraction in a Microreactor Equipped with Low and High-Frequency Ultrasound Waves: A Numerical Study

The aim of this study is the numerical investigation of liquid-liquid extraction inside a spiral T-microreactor integrated with ultrasonic waves. The influence of low-frequency ultrasound (20.3, 42.3, and 61.61 kHz) and high-frequency one (1.7 MHz) on extraction efficiency is evaluated by CFD modeling. The organic-aqueous phase flow patterns inside the microreactor are graphically analyzed. The organic phase is regarded as a dispersed phase and the aqueous phase as a continuous fluid using the two-phase VOF. In addition, the SIMPLE algorithm is used for pressure and velocity coupling. The results obtained from the CFD simulation of aqueous-organic phase flow patterns are compared with the experimental results. The application of both types of ultrasounds showed a higher extraction efficiency compared to the condition of not applying it. The decreasing trend for extraction efficiency and ultrasound effect was observed for increasing flow rate. The extraction efficiency is less affected by increasing the power of low-frequency ultrasound up to the range of 600 mV, after which a sharp increase is observed up to 840 mV. In addition, in the range above 600 mV, the increase in extraction efficiency can be attributed to the formation of emulsion, which leads to a higher surface per unit volume and higher extraction efficiency. The results indicated that for low-frequency ultrasound, 20.3 kHz resulted in higher extraction efficiency rather than the other one. Comparing the extraction efficiency for applying high (1.7 MHz) and low-frequency ultrasound (20.3, 42.3, and 61.61 kHz) showed that 1.7 MHz has a considerable positive effect on its increase. Indeed, 1.7 MHz ultrasound resulted in the highest extraction efficiency compared to low frequencies, due to the ability of high-frequency ultrasound to induce micro-jets and micro-streams into the microreactor.