(211b) Models for Infinite Dilution Activity Coefficients in Ternary Liquid Systems

The objective of this research was to study the change in partition coefficient with concentration of solute in a liquid system consisting of two relatively immiscible solvents. This would require a consistency between data for infinite dilution partition coefficients and ternary LLE data at finite concentrations of the solute. Moreover an attempt would be made to model the infinite dilution and finite concentration behavior of these systems by a single thermodynamic model. During the course of our work, we found 35 ternary systems in the literature for which the infinite dilution partition coefficients and the ternary LLE data could not be predicted accurately by the currently available liquid state models.

Ternary liquid-liquid equilibrium data for hexane+1-butanol+water, carbon tetrachloride +propanoic acid+water, and water+propanoic acid+hexane were measured from very low concentrations of the solute to finite concentrations at 25 C. The measured partition coefficients showed good agreement with the literature values. UNIQUAC and modified UNIQUAC activity coefficient models were used to represent the data. The results showed large errors, exhibiting the inability of these models to correlate the data. Attempts are being made to apply some modified versions of quasi-chemical activity coefficient models to these systems.