Modified NRTL model for predicting the effect of dissolved solute on the vapour-liquid equilibrium of solvent mixtures

Abstract

The NRTL model is extended to include solute-solvents mixture by considering the contribution of the solute-solvent interaction to the excess Gibbs free energy of mixing in terms of the local mole fraction of the dissolved solute solvated in an environment of each of the solvent components. The solute-solvent interaction parameters can be calculated from the bubble points of the individual solvent components containing the same concentration of the dissolved solute as the mixture. Comparing the 854 predicted vapour compositions and bubble points with the experimental values of the 75 solute-solvents mixtures at different values of the nonrandomness factor associated with the solute-solvent interaction, it can be inferred that the local mole fraction of the solute solvated by a given solvent component is directly proportional to the composition of the solvent component on the solute-free basis. On this basis, the predictive accuracy in terms of the mean ratio and difference between predicted and experimental vapour composition is 0.980 and -0.003 respectively, which are comparable with those obtained from an earlier model, based on the Wilson's concept of local volume fraction. The present model is compatible with phase instability, a feature which is not shown by the previous model based on the local volume fraction concept.