Salt Effect in Vapor—Liquid Equilibrium at Fixed Liquid Composition

Abstract

The effect of salt concentration on equilibrium vapor composition at atmospheric pressure was studied in four ethanol-water-salt systems at the boiling point, with mixed--solvent composition held constant. The salts investigated were potassium iodide, ammonium bromide, sodium acetate, and potassium acetate. As expected, the two inorganic salts were in good agreement with the Furter equation. In the case of the two salts of organic acids the agreement became less and less valid as salt concentration increased. The failure of the equation with the two acetate salts was attributed to the presence of significant organic ion-alcohol interaction, a situation which does not normally become significant with inorganic ions in aqueous alcohol solution except at high alcohol concentrations. '-phe original equation for salt effect in vapor-liquid equilibrium, proposed by Furter in 1958 (1,2), predicts the effect of a salt dissolved in a mixed solvent on vapor-liquid equilibrium when the composition of the solvent is held constant: In («./«) -fc*.(1)In the equation, equilibrium vapor composition expressed in the form of an improvement factor, aja, is related to salt concentration % in the liquid phase by the salt effect parameter, k. According to the theoretical 1 Current address:

Thermodynamic representation of phase equilibria of mixed‐solvent electrolyte systems

“…While Eq. 1 is attractive because of its simplicity, the salt effect parameter has been shown to be dependent on salt and solvent compositions and the range of applicability is limited (Meranda and Furter, 1972;Burns and Furter, 1979). Ohe (1976) proposed a model in which the salt forms a preferential solvate with one of the solvents in a two-solvent system.…”

Comparative work about UNIFAC based models for hydroalcoholic systems with electrolytes

“…Table 2 presents an outline of the selected data. There were 138 experimental points for water + ethanol + KAc and 87 points for water + ethanol + CaCl2 system in published research (CIPARIS, 1966;BURNS and FURTER, 1979;MERANDA and FURTER, 1966;SCHMITT, 1975;NISHI, 1975;HASHITANI et al, 1968). Data were disregarded when the molar fraction of solvents in free salt basis was equal to zero.…”

“…This paper presents a comparative work between four models (KIKIC et al, 1991;ACHARD et al, 1994;YAN et al, 1999;AZNAR and TELLES, 2001) based on the UNIFAC model to calculate activity coefficient. The assessment was carried out concerning deviations between calculated and experimental data (CIPARIS, 1966;BURNS and FURTER, 1979;MERANDA and FURTER, 1966;SCHMITT, 1975;NISHI, 1975;HASHITANI et al, 1968) of water + ethanol + salt (KAc and CaCl2) systems.…”

Thermodynamic Modeling of Vapor−Liquid Equilibria in Mixed Aqueous−Organic Systems with Salts

“…However, it was later shown that k may depend on the nature of the salt and on solvent composition. It was also shown that the range of applicability of eq 1 is limited (Meranda and Furter, 1972;Burns and Furter, 1979). Ohe (1976) proposed a model in which the salt forms a preferential solvate with one of the solvents in a twosolvent system.…”