Mass-transfer effects on droplet phenomena and extraction column hydrodynamics revisited

The effect of solute mass transfer between the two liquid phases on the drop size distribution and holdup profiles of the dispersed phase in a multistage extraction column is experimentally investigated in this article. Experimental results of the drop size distribution, dispersed-phase volume fraction (holdup), and concentration profiles are obtained for both directions of mass transfer. The drop size distribution is measured by a photomicrographic technique, the holdup profile is measured by an ultrasonic technique, and the concentration profiles are measured by refraction index measurements. A strong influence of the mass-transfer direction on drop size and holdup has been found. The results are in qualitative agreement with the observations of other investigators. Mass transfer of butyric acid from toluene (dispersed) to water (continuous) produced larger drop sizes and lower values of the dispersed-phase holdup than for the equilibrated toluene-water system. For mass transfer of butyric acid from water (continuous) to toluene (dispersed) smaller drop sizes and higher holdup values are observed than for the equilibrated toluene-water system. This behavior significantly affects the performance of the extractor and indicates the necessity for more studies to determine the physics of the phenomenon and to model these processes appropriately.