Prediction of vapor-liquid equilibria for acetic acid aqueous solutions containing salt

Abstract

A calculation method to predict the salt effect on the vapor-liquid equilibria of acetic acid aqueous solutions is proposed. In the developed method, the nonidealities of the liquid phase are considered by employing the vapor pressure models of electrolyte solutions (Shiah and Tseng, Fluid Phase Equilibria, 90 (1994) 75–85; Jaques and Furter, AIChE J., 18 (1972) 343–346) to describe the ion-ion and ion-solvent interactions and the Tan's modified Wilson or NRTL model (Tan, Chem. Eng. Res. Des., 65 (1987) 355–366; Tan, Trans. Ind. Eng. Chem., 68 (1990) 93–103)) to describe the solvent-solvent interactions. The chemical theory model is applied to the vapor phase to describe the deviations from ideal gas behavior caused by dimerization of acetic acid. The data required by this method are the equilibrium constant of dimerization in the vapor phase, the vapor pressure of aqueous electrolyte solutions and the solvent-solvent interaction parameters in the liquid phase activity coefficient model. No ternary parameter is required. The proposed method has been used to predict the VLE of five saltacetic acidwater systems for salt concentrations varying from zero to saturation. The calculated results agree well with the experimental ones reported in literatures, with the overall absolute deviations of vapor phase compositions being 1.00% if the modified Wilson model is employed, and 1.64% if the modified NRTL model is used to describe the solvent-solvent interactions. For the bubble point temperatures, the overall mean deviations are 0.99 K if modified Wilson model is used and 1.34K if modified NRTL model is used.