Prediction of Overall Mass Transfer Coefficients in a Hanson Mixer-Settler Using Effective Diffusivity

Abstract

The volumetric overall mass transfer coefficients of a pilot scale Hanson mixer-settler extraction column with seven stages have been measured using toluene/acetone/water and n-butyl acetate/acetone/water systems. The effects of operational variables such as agitation speed, phase ratio, and throughput on volumetric overall mass transfer coefficient have been investigated and found to be significant. By using the interfacial area, the dispersed phase overall mass transfer coefficients are determined from the volumetric coefficients. Comparison between theoretical models and experimental results of overall mass transfer coefficient shows that these models do not have enough accuracy for design. In the present work, effective diffusivity is substituted for molecular diffusivity in the Grober equation for prediction of dispersed phase overall mass transfer coefficients. The enhancement factor is determined experimentally and therefrom an empirical correlation is proposed for prediction of effective diffusivity as a function of the Reynolds number, Eotvos number and dispersed phase holdup. Dispersed phase overall mass transfer coefficients predicted by the presented model are in good agreement with experimental results.