APPLICATION OF ELECTROLYTE THEORY TO EXTRACTIVE SEPARATIONS USING HYDROTROPES

The use of polar hydrotropes in extractive distillation and in liquid- liquid extraction has been extensively reported in the literature. In this article, the effect of hydrotropes on increasing the effectivenes s of separation is explained in terms of the effect of the dipole-indu ced dipole and the ion-induced dipole interactions on the activity coe fficients of the neutral solutes in the aqueous phase. The self-consis tent local composition theory is used to correlate quantitatively the observed behavior in systems involving liquid-liquid equilibria. The t heory yields composition-dependent expressions for the effect of each independent pair interaction on the activity coefficient of a neutral solute in the aqueous phase. The ratio of the activity coefficients of the two solutes is of interest in this context. The resulting express ion for the separation factor is elegant and admits simple physical in terpretation. The essential features of hydrotrope-assisted extraction are correctly described by the theory. The ability of the theory to c orrelate data is demonstrated for two systems.