Drop size distribution and holdup profiles in a multistage extraction column

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Abstract
A population‐balance‐equation model is employed for the analysis of liquid‐liquid extraction columns. This model considers drop breakage, coalescence, and exit phenomena for the drop phase caused by drop‐drop and drop‐continuous phase interactions. Drop breakage and coalescence rates are employed from a previous study on liquid dispersions in stirred‐tank contactors. A drop exit frequency is developed based on a stochastic modeling approach. The model is tested by drop size distribution and dispersed‐phase volume fraction (holdup) data obtained for a multistage column contactor of pilot‐plant scale. Steady‐state drop size distribution and transient holdup measurements are obtained by a photomicrographic technique and an ultrasonic technique, respectively. The model can predict flooding of the column. The effect of mass transfer on the hydrodynamic parameters of the contactor is also examined. The population‐balance‐equation model can be used for the control of extraction columns and can be extended to include mass‐transfer calculations for the prediction of extraction efficiency.