The influence of ultrasonic waves on hydrodynamics and mass transfer of circulating drops in liquid–liquid extraction process was studied. The recommended chemical systems of toluene–acetic acid–water with mass transfer resistance mainly in the organic phase, and cumene–isobutyric acid–water in the aqueous phase were used. An extraction column, equipped with an ultrasonic emitter of 35.40 kHz real frequency and 0.37 mW/cm2 intensity, was employed. The ultrasound properties were measured using the hydrophone standard method. Drops terminal velocity was comparable with the Grace model. In mass transfer study, significant enhancement was revealed in overall mass transfer coefficient for different drop sizes and for the both mass transfer directions by using ultrasonic waves. The average and maximum enhancements were, respectively, 20.8 and 31.7% for toluene–acetic acid–water, and 40.3 and 55.1% for cumene–isobutyric acid–water. Small drops exhibited a higher enhancement percentage. Regarding the mass transfer direction, the system of cumene–isobutyric acid–water with continuous to dispersed phase direction, was benefited more as the consequence of creating effective agitation in continuous phase than in dispersed phase.
