Fluid Phase Equilibria 332 (2012) 151–158 Contents lists available at SciVerse ScienceDirect Fluid Phase Equilibria jou rnal h omepage: www.elsevier.com/locate/fluid Experimental determination and correlation of tie line data for the system (water + butyric acid + methylcyclohexane) at four temperatures H. Ghanadzadeh b , A. Ghanadzadeh a,∗ , M. Janbaz a , S. Shekarsaraee a a Department of Chemistry, University of Guilan, 41335 Rasht, Iran b Department of Chemical Engineering, University of Guilan, Rasht, Iran a r t i c l e i n f o Article history: Received 21 March 2012 Received in revised form 27 June 2012 Accepted 4 July 2012 Available online 14 July 2012 Keywords: LLE data Ternary mixture NRTL model UNIQUAC model LSER approach a b s t r a c t This study demonstrates the experimental solubility and tie line data for (water + butyric acid + methylcyclohexane) system at temperatures of 298.2, 308.2, 318.2, and 328.2 K and atmospheric pressure. The cloud-point titration method was used to determine solubility data (binodal curves). The tie line data were determined by acidimetric titration, the Karl–Fischer technique, and refractive index mea- surements. The investigated ternary system exhibits type-1 behavior of liquid–liquid equilibrium. The thermodynamic models UNIQUAC and NRTL were used to correlate the experimental tie-line data. The consistency of the tie-line data was determined through the Othmer Tobias and Hand correlation equa- tions. Distribution coefficients and separation factors were calculated over the immiscibility regions. A comparison of the extracting capability of the solvent at different temperatures was made with respect to separation factors. The Katritzky multiparameter scale was applied to correlate distribution coefficients and separation factors in this ternary system. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Liquid–liquid equilibrium (LLE) data for extraction of organic acids from water are important in evaluation of industrial extrac- tion processes [1–6]. The precise LLE data are always needed for efficient separation operations, which can be obtained from direct measurements. Butyric acid (BA) is one of the important carboxylic acid, which has many uses in different industries. In addition, to its traditional uses, the importance of this acid is quickly increasing in many other fields. BA is a clear, colorless liquid with an unpleasant and vomit-like odor melting at 265.2 K. It can be produced by chemical synthetic or fermentation methods [7–10]. Particularly, separation of BA from the fermentation broths has been extensively inves- tigated. However, the extraction of this acid from dilute aqueous solutions is an important problem. In the past, several authors have reported equilibrium data for the aqueous solutions of BA with various organic solvents. Mainly, heavy alcohols, esters, aliphatic amines, and hydrocarbons have been used and the phase equilibrium data of the related systems are presented in the literature. In earlier report, LLE data of the aque- ous mixtures of BA with a hydrocarbon (toluene) at a wide range of temperature have been measured and predicted by Badakhshan et al. [11]. Determination and correlation of equilibrium data for the ∗ Corresponding author. Tel.: +98 1313233262; fax: +98 1313233262. E-mail address: aggilani@guilan.ac.ir (A. Ghanadzadeh). aqueous solutions of the acid with heavy alcohols have been car- ried out by Kırbas ¸ lar et al. [12], and Bilgin et al. [13,14]. Kırbas ¸ lar et al. [15–17] have also presented important equilibrium data for systems consisting of water, BA, and esters. Some important LLE data on ternary aqueous mixtures including BA have been reported by C ¸ ehreli and Gündogdu [18]. More LLE data for the relative sys- tems have been reported by Uslu et al. [19]. In some reports, an aliphatic amine (trioctylamine) was used as extractant in various diluents. Schlosser et al. [20] and Qin et al. [21] have investi- gated LLE data of the systems consisting of BA, water, solvent with trioctylamine. Marták and Schlosser [22] have also studied the sys- tem (water + BA + phosphonium ionic liquid). The LLE data for the quaternary system including o-xylene, water, BA, and 1-butanol have been reported by Park et al. [23]. In recent effort to improve BA extraction, a cycloalkane and its relative ketone were used as organic solvents. Ghanadzadeh et al. [24,25] recently reported the LLE results for the aqueous mixtures of BA with cyclohexane and cyclohexanone at various temperatures. In this research, methylcyclohexane (MCH) was tested as organic solvent for recovery of BA from water. This solvent has already been used as an extractant in the determination of LLE data for the ternary aqueous mixtures of propionic acid [26]. The focus of this study is placed on the phase behavior of LLE for the aque- ous mixtures of BA with MCH. In order to investigate the change of equilibrium characteristics, four different temperatures were selected. At each temperature, T = 298.2, 308.2, 318.2 and 328.2 K, the phase compositions were measured. Distribution coefficients (D) and separation factors (S) were determined from the tie-line 0378-3812/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2012.07.003