A microdroplet-based continuous countercurrent extraction process with a high phase ratio (60-110) is proposed in this work. A countercurrent extraction apparatus containing a cross-flow T-junction microdisperser and a milli-scale column was established, and phenol extracted from water and transferred to n-octanol was used as the model system. The diameters of the microdroplets formed by the microdisperser were studied, and these ranged from 160 to 220 mu m with a uniform diameter distribution and a relative standard deviation of < 15%. The holdups of the two phases in the countercurrent column were investigated, and a prediction model was established. The effects of the experimental parameters, namely, the circulation ratio, flow rate, phase ratio, and column length, on the extraction efficiency, volumetric mass transfer coefficient (K(o)a), and theoretical stage were studied. The value of K(o)a ranged from 0.087 to 0.352 s(-1) within the scope of the experiment, and the theoretical stage value of 2 was achieved with a column height of only 25 cm under certain conditions, indicating a higher mass transfer efficiency compared with traditional devices. The mechanism of mass transfer intensification was discussed and identified to be dependent on the microscale diameter and uniform diameter distribution of the droplets.
