Correlation and prediction of liquid-liquid distribution coefficients in aqueous systems using a modified Wilson model

Abstract

A modified Wilson model is tested for its ability to correlate and predict distribution coefficients in two representative systems: 1-butanol-water and cyclohexanewater. The model is fitted to ternary equilibrium data for various solutes in these systems using a procedure involving minimization of the least-squares distance between calculated and experimental logarithmic distribution ratios. In addition, benzene-water, hexane-water, and cyclohexane-water distribution coefficients for infinitely diluted liquid solutes are predicted using only binary system information. All computations involve using both van der Waals and molar volumes as structural parameters to account for the geometry of the molecules studied. Satisfactory representations of experimental distribution ratios and fairly accurate distribution coefficients at infinite dilution are obtained for both systems. However, in a number of cyclohexane-water systems, miscibilities of constituent binary mixtures are poorly predicted from ternary system information when van der Waals volumes are used. Replacement of van der Waals volumes by molar volumes has little influence on the fit, but significant improvement is observed for the prediction of both binary miscibility properties and for distribution coefficients at infinite dilution in all the solvent-water systems considered.