Elsevier

Thermochimica Acta

Volume 540, 20 July 2012, Pages 116-122
Thermochimica Acta

Binodal curves and tie line data of the water–propionic acid–iso-butyl acetate at T = (298.2, 308.2, 318.2, and 328.2) K

https://doi.org/10.1016/j.tca.2012.04.020Get rights and content

Abstract

Experimental liquid–liquid equilibrium (LLE) data for the system of (water + propionic acid + iso-butyl acetate) were obtained at T = (298.2, 303.2, 308.2, and 313.2) K and atmospheric pressure. This ternary system exhibits type-1 behavior of LLE. The experimental tie-line data were correlated using the UNIQUAC and NRTL models. The reliability of the experimental tie-line data was determined by applying the Othmer–Tobias and Hand correlations. Distribution coefficients and separation factors were calculated over the immiscibility regions. The influence of temperature on the equilibrium characteristics and separation factor was found to be minor at the temperatures studied. The average rmsd values between the observed and calculated mass fractions were 0.92% and 0.98% for the UNIQUAC and NRTL models, respectively. The thermodynamic models showed good agreement to the experimental results.

Highlights

► Liquid equilibrium data of (water + PA + IBA) system were measured. ► Experimental LLE data were correlated with NRTL and UNIQUAC models. ► Distribution coefficients and separation factors were evaluated.

Introduction

Liquid phase equilibrium data for extraction of carboxylic acids from water are important in estimation of industrial solvent extraction units [1], [2], [3], [4]. The LLE data are always required for efficient separation operations, which can be obtained from direct measurements.

Propionic acid (PA) is one of the important carboxylic acid, which has many scientific and industrial applications. It is a clear, corrosive liquid with a pungent odor melting at 252.2 K. PA can be produced by chemical synthetic or fermentation methods. Therefore, the extraction of this acid from water is an important problem. Several important investigations have been carried out on the extraction and equilibrium measurements of the acid from aqueous solutions.

In the past, several authors have reported LLE data for the aqueous solutions of PA with various organic solvents [5], [6], [7]. Many solvents have been tested, and the phase equilibrium data of the related systems are presented in the literature. Mainly, heavy alcohols [8], ketones [9], esters [10], ethers [11] and hydrocarbons [12] have been used for extraction of PA from aqueous solutions. One of the earliest publications of liquid phase equilibria for aqueous solutions of PA with solvent was that of Radecki et al. [13]. They have reported the partition coefficients for PA between the aqueous and organic phases. In later papers, important equilibrium data of the acid have been reported by Badakhshan et al. [14], and Arce et al. [15], [16]. They have used hydrocarbons and ketones as organic solvents for extraction of PA from water, respectively. More LLE data for aqueous solutions of PA with ketones have been reported by Taghikhani et al. [17], and Özmen [18], Çehreli et al. [19], and Uslu and Inci [20].

The determination and correlation of LLE data for the aqueous solution of the acid with heavy alcohols have been carried out by Radwan and Al-Muhtaseb [21], and Kirbaslar et al. [22]. Senol [23], [24], [25] have also studied the systems (water + carboxylic acid + methylcyclohexanol or 1-octanol) at 293.15 K. The equilibrium data of system (water + PA + oleyl alcohol) have been presented by Bilgin and Arısoy [26]. In some reports halogenated hydrocarbons was used as organic solvents [1]. Mohsen-Nia et al. [27] have investigated LLE data of the system (water + PA + dichloromethane). There are also some reports indicated that esters and or dibasic esters can be used as organic solvents for extraction of PA from water. Some important LLE data on relative systems have been reported by Kirbaslar et al. [28], [29], and Özmen et al. [30], [31], and Çehreli et al. [32]. Nitriles have also been tried and tested to improve the extraction of this acid from water. Letcher et al. [33], [34] have studied the systems (water + carboxylic acid + benzonitrile or butanenitrile).

The author of this work with co-workers recently reported the LLE results for the aqueous mixtures of PA with organic solvents. The organic solvents were 2-ethyl-1-hexanol [35] and hydrocarbons (cyclohexane, methylcyclohexane, and toluene) [36]. In this research, iso-butyl acetate (IBA) was chosen as organic solvent for recovery of PA from water. In order to investigate the change of equilibrium characteristics, four different temperatures were selected. At each temperature, T = (298.2, 303.2, 308.2 and 313.2) K, the phase compositions were measured.

Distribution coefficients and separation factors were calculated from the tie-line data to establish the possibility of the use of this solvent for the separation of PA from water. The experimental data were correlated using the UNIQUAC and NRTL models [37], [38]. The values for the binary interaction parameters were obtained for these equilibrium models. In general, both the correlation models are appropriate for the LLE correlation of the investigated system.

Section snippets

Materials

Propionic acid and iso-butyl acetate with stated mass fraction purity higher than 0.99 were obtained from Merck. Deionized and redistilled water was used throughout all the experiments. The stated purity of the materials was checked on the basis of their refractive indices and densities. All materials were used as received without any further purification.

Apparatus and procedure

The solubility curves for the ternary mixtures were determined by the cloud point method in an equilibrium glass cell. The binary mixtures of

Results and discussion

The experimental LLE data for the (water + PA + iso-butyl acetate) ternary system were measured at T = (298.2, 303.2, 308.2 and 313.2) K. The experimental values for the ternary system at each temperature are listed in Table 3. The LLE diagrams at various temperatures for the investigated system are plotted in Fig. 1, Fig. 2, Fig. 3, Fig. 4. Because (PA + water) and (PA + iso-butyl acetate) are two liquid pairs that are completely miscible and the only liquid pair (water + iso-butyl acetate) is partially

Conclusions

The LLE data for the ternary system of (water + PA + iso-butyl acetate) were experimentally 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) 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. Both the models give good results for the investigated system.

The

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