Dynamic Simulation of Alternate Flow Liquid-Liquid Extraction Tower

Abstract

An extraction tower for which liquids were fed alternately in square wave form was dynamically simulated by simplified mathematical models. The assumptions employed for the simplifications were discussed by comparing experimental responses with computed responses of the models. Fixing flow rates, step response curves were recorded for relatively high concentration inputs at various initial concentrations of both light and heavy phases. Ternary system used in this experiment was Toluene-acetic acid-water system, the distribution coefficient of which heavily depended on the equilibrium concentration. A model assuming pseudo-steady state for dispersed phase was ensured to be sufficient for the dynamic simulation of the tower, when the mean residence time (Holdup/Volume flow rate) of continuous phase was 20 times greater than that of dispersed phase. This made it possible to treat the tower as a series of concentrated constant system. The assumption of averaging the square wave flow rates was also sure to hold in our experimental conditions. A nonlinear model having an adjustable over-all mass transfer capacity coefficient, which was assumed to be function of distribution coefficient, was able to describe the tower dynamics within detectable errors, even, though the distribution equilibrium showed high nonlinearity.