Liquid–liquid equilibria of water/acetic acid/1-butanol system — effects of sodium (potassium) chloride and correlations

Sodium and potassium chloride were experimentally shown to be effective in modifying the liquid–liquid equilibrium (LLE) of water/acetic acid/1-butanol system in favour of the solvent extraction of acetic acid from an aqueous solution with 1-butanol, particularly at high salt concentrations. Both the salts enlarged the area of the two-phase region; decreased the mutual solubilities of water and marginally decreased the concentrations of 1-butanol and acetic acid in the aqueous phase while significantly increased the concentrations of the same components in the organic phase. These effects essentially increased the heterogeneity of the system, which is an important consideration in designing a solvent extraction process. The equilibrium data were well correlated by Eisen–Joffe equation with respect to the overall molar ratio of salt to water in the liquid phases. By expressing the salt–solvent interaction parameters as a third order polynomial of salt concentration in the liquid phase, Tanʹs modified NRTL model [T.C. Tan, Trans. Inst. Chem. Eng., Part A 68 (1990) 93–103.] for solvent mixtures containing salts or dissolved non-volatile solutes was able to provide good correlation of the present LLE data. Using the regressed salt concentration coefficients for the salt–solvent interaction parameters and the solvent–solvent interaction parameters obtained from the same system without salt, the calculated phase equilibria compared satisfactorily well with the experimental data.