THERMODYNAMICS AND CHEMICAL ENGINEERING DATA Chinese Journal of Chemical Engineering, 19(4) 565 569 (2011) Salt Effect on the Liquid-Liquid Equilibrium of (Water + Propionic Acid + Cyclohexanol) System at T  (298.2, 303.2, and 308.2) K Bahram Ghalami-Choobar * , Ali Ghanadzadeh and Shahram Kousarimehr Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box: 19141, Rasht, Iran Abstract Effects of salt and temperature on the liquid phase equilibrium of the (water + propionic acid + cyclo- hexanol) system were investigated. The liquid-liquid equilibrium data in the presence of KCl for various salt ionic strength of 0.5, 1.0, 1.5, 2.0, and 2.5 mol·dm 3 and in absence of the salt at T  (298.2, 303.2, and 308.2) K were determined. The experimental results were correlated based on the Othmer-Tobias equation and Pitzer ion-interaction model. Thermodynamic properties such as distribution coefficients and activity coefficients of propionic acid in water + cyclohexanol were determined. In addition, the separation factor, S, of the chosen solvent was obtained for the investigated system. Keywords liquid-liquid equilibrium, salt effect, propionic acid, distribution coefficient 1 INTRODUCTION Separation of carboxylic acids from dilute aque- ous solutions is an important operation in many indus- trial processes [1]. Propionic acid is one of the impor- tant carboxylic acid widely used as mold inhibitor in baking and esterifying agent in the production of thermoplastics and in the manufacture of flavors and perfume bases [2, 3]. Liquid-liquid extraction is one of the practical separation processes. Liquid-liquid ex- traction using aqueous two-phase systems (ATPS) has been demonstrated to be a highly efficient separation technique for small organic species [4, 5]. The addition of a salt or a non-volatile solute in a solvent mixture and temperature can significantly change two-phase equilibrium composition. Adding salt to an aqueous solution of an organic acid can result in either a de- crease (salting out) or an increase (salting in) in solu- bility of the organic acid. The concentration of a component in a liquid-liquid system increases if the component is salted-in and decreases if it is salted out of the liquid phase [6 8]. This salt effect has been ad- vantageously used in distillation, separation and sol- vent extraction. The salt effect is also important in biological separation processes such as purification of proteins, enzymes, nucleic acids, and others [9]. In recent years, the liquid-liquid equilibrium (LLE) [10] and salt effect on the liquid-liquid equilib- rium systems [11, 12] have been studied. The LLE data of (water + propionic acid + solvents) ternary systems are important in chemical industry. Propionic acid obtains by chemical reactions or by fermentation with bacteria of the genus propionibacterium. Several sol- vents have been tested to improve the recovery of propionic acid from aqueous solutions [13 16]. How- ever, salt effect on the thermodynamic data of our inves- tigated system (water + propionic acid + cyclohexanol) has not been reported in literature. In this work, effects of salt and temperature on the liquid-liquid equilibrium data of water + propionic acid + cyclohexanol system were investigated. To obtain LLE data, the most common methods include titration, Karl-Fisher titration and gas chro- matograghy methods. In this work, the experimental measurements were performed with the potetiometric titration and Karl-Fisher methods. The experimental results were correlated based on the Othmer-Tobias equation and the Pitzer ion-interaction model, in which a small number of adjustable parameters were applied. The Pitzer parameters represent the measure of the interactions between ions and solvent molecules. In addition, separation factor value, S, of the chosen solvent was evaluated for the investigated system. 2 EXPERIMENTAL 2.1 Materials Propionic acid, cyclohexanol, and potassium chloride were purchased from Merck. The mass frac- tion purities of the compounds were 0.99, 0.99, and 0.995, respectively. The chemicals were used without further purification. Double distilled water was used throughout all experiments. 2.2 Apparatus and procedure A 0.02 dm 3 of aqueous solution of potassium chloride, for adjusting the ionic strength at the desired value, was shaken with 0.02 dm 3 of cyclohexanol and the known amount of propionic acid at constant tem- perature T  (298.2, 303.2, and 308.2) K and then were stirred vigorously for at least 2 h, then it was settled down for 4 h. All these procedures were completed in a double-wall container thermostated with water from a Model GFL circulation system. After that propionic acid concentration in each phase was determined by Received 2010-08-01, accepted 2011-04-27. * To whom correspondence should be addressed. E-mail: B-Ghalami@guilan.ac.ir