Elsevier

Fluid Phase Equilibria

Volume 332, 25 October 2012, Pages 151-158
Fluid Phase Equilibria

Experimental determination and correlation of tie line data for the system (water + butyric acid + methylcyclohexane) at four temperatures

https://doi.org/10.1016/j.fluid.2012.07.003Get rights and content

Abstract

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 measurements. 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 equations. 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.

Highlights

► Phase equilibria of water–BA–methylcyclohexane system were investigated. ► Experimental LLE data were correlated with NRTL and UNIQUAC models. ► Distribution coefficients and separation factors were evaluated.

Introduction

Liquid–liquid equilibrium (LLE) data for extraction of organic acids from water are important in evaluation of industrial extraction processes [1], [2], [3], [4], [5], [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], [8], [9], [10]. Particularly, separation of BA from the fermentation broths has been extensively investigated. 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 aqueous 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 aqueous solutions of the acid with heavy alcohols have been carried out by Kırbaşlar et al. [12], and Bilgin et al. [13], [14]. Kırbaşlar et al. [15], [16], [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 Çehreli and Gündogdu [18]. More LLE data for the relative systems 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 investigated LLE data of the systems consisting of BA, water, solvent with trioctylamine. Marták and Schlosser [22] have also studied the system (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 aqueous 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 data to establish the possibility of the use of this solvent for the separation of BA from water. The experimental data were correlated using the UNIQUAC and NRTL models [27], [28], [29]. The values for the interaction parameters were obtained and the calculated compositions compared with the experimental ones.

Section snippets

Materials

Butyric acid and methylcyclohexane with stated mass fraction purity higher than 0.99 were obtained from Merck. The organic chemicals were dried over molecular sieves (Merck 4 Å). Deionized and redistilled water was used throughout all the experiments. All materials were used as received without any further purification. The measured refractive index and density data of the chemicals used in this study along with the literature values are listed in Table 1.

Apparatus and procedure

The solubility data (binodal curves) for

Experimental solubility and tie line data

Equilibrium compositions on the binodal curve (in mass fraction) for the system (water + BA + MCH) at T = 298.2, 308.2, 318.2, and 328.2 K and atmospheric pressure are given in Table 3. The area of the two-phase region depends on the mutual solubilities of water and MCH. The same solubility data were plotted in Fig. 1 to show the effect of temperature on binary solubilities. As it can be seen, the temperature effect on the binodal curves and biphasic region of the ternary system is relatively evident

Conclusions

Experimental and correlated tie-line data for aqueous mixtures of BA with MCH were obtained at T = 298.2, 308.2, 318.2, and 328.2 K. The ternary system exhibits type-1 behavior of the LLE. The UNIQUAC and NRTL (α = 0.3 and regressed α) models were satisfactorily used to correlate the experimental data and to calculate the phase compositions of the mixtures studied. The corresponding optimized binary interaction parameters were also calculated. The obtained rmsd values indicate that both the models

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