Fluid Phase Equilibria 370 (2014) 19–23 Contents lists available at ScienceDirect Fluid Phase Equilibria jou rn al h om epage: www.elsevier.com/locate/fluid (Liquid + liquid) equilibria of the (water + carboxylic acid + dibasic esters mixture (DBE-2)) ternary systems Erol ˙ Ince ∗ , Yavuz Selim As ¸ c ¸ ı Istanbul University, Engineering Faculty, Chemical Engineering Department, 34320 ˙ Istanbul, Turkey a r t i c l e i n f o Article history: Received 3 January 2014 Received in revised form 27 February 2014 Accepted 1 March 2014 Available online 12 March 2014 Keywords: (Liquid + liquid) equilibria Carboxylic acids Dibasic esters mixture UNIFAC Modified UNIFAC a b s t r a c t (Liquid + liquid) equilibrium (LLE) data for the {water + carboxylic acid + dibasic esters mixture (dimethyl adipate + dimethyl glutarate)} system were determined experimentally at T = 298.2 K for each acid. In this work, we studied formic acid, acetic acid and propionic acid. All the phase diagrams were obtained by determining solubility curve and tie-line data. The reliability of the experimental tie-line data was confirmed by using the Othmer–Tobias correlation. The UNIFAC and modified UNIFAC models were used to predict the phase equilibrium in the system determined from experimental data using the interac- tion parameters between CH 2 , CH 3 , HCOOH, COOH, CH 3 COO, and H 2 O functional groups. Distribution coefficients and separation factors were evaluated for the immiscibility region. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Organic acids can be extensively used in many important fields ranging from pharmaceutical, food, and textile to petrochemical industries. Carboxylic acids, including acetic, propionic, and formic acids are among the most used organic chemicals. It is well-known that the ideal way to produce carboxylic acids, and also other compounds having sufficient acidic properties, is the fermentation processes that have already been proven to be environmentally friendly and renewable resources. One of the most common problems of fermentation in the production of these car- boxylic acids is their low concentration which is present in dilute form (<10% (V)). For separation of organic acids from fermenta- tion broth, a lot of methods have been investigated [1–9]. The separation of carboxylic acid and water by distillation is very diffi- cult, requiring a column with many stages and a high reflux ratio, thus incurring high running costs. Because of the lower energy cost (liquid + liquid) extraction is an alternative method to distil- lation. At the same time (liquid + liquid) extraction is a well-known technique to separate the carboxylic acid from aqueous solutions and many solvents have been tried to improve such recovery [10]. In the search for more benign solvents as potential replacements for chlorocarbons or aromatic hydrocarbons and as new solvents for separations, we have studied the dibasic esters, which have ∗ Corresponding author. Tel.: +90 212 473 70 70; fax: +90 212 473 71 80. E-mail address: erolince@istanbul.edu.tr (E. ˙ Ince). excellent properties for industrial applications. They are environ- mentally friendly and have low cost, low toxicity, great stability, and rather high boiling temperatures, while their viscosity and den- sity are close to those of water. Despite extensive literature reports on liquid–liquid equilibria and phase diagrams, liquid–liquid equi- librium data have rarely been published for the dibasic esters mixture systems of interest. However the liquid–liquid equilibria of the some dibasic esters have been studied by ˙ Ince [11–15]. The real behavior of fluid mixtures can be calculated with the help of activity coefficients. The correct description of the dependence on temperature, pressure and composition in mul- ticomponent systems requires reliable thermodynamic models, which allow the calculation of these properties from available experimental data. The UNIFAC model was developed by Mag- nussen et al. [16]. The UNIFAC model for the estimation of activity coefficients works on the concept that a liquid mixture may be considered a solution of structural units from which the molecules are formed rather than a solution of the molecules themselves. It has the advantage of being able to form a very large number of molecules from a relatively small set of structural units. The struc- tural units in the calculation method are called subgroups. The mole fractions, X E i and X R i of LLE phases can be calculated using the following equation: ( i X i ) E = ( i X i ) R (1) where E is the extract (solvent) phase; R is the raffinate (aqueous) phase;  is the activity coefficient of the component i. http://dx.doi.org/10.1016/j.fluid.2014.03.002 0378-3812/© 2014 Elsevier B.V. All rights reserved.