Phase equilibria of liquid (water + butyric acid + oleyl alcohol) ternary system

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Abstract

(Liquid + liquid) equilibrium (LLE) data for the ternary system of (water + butyric acid + oleyl alcohol) at T = (298.15, 308.15, and 318.15) K are reported. Complete phase diagrams were obtained by determining solubility and the tie-line data. The reliability of the experimental tie lines was confirmed by using Othmer–Tobias correlation. The UNIFAC method was used to predict the phase equilibrium data. The phase diagrams for the ternary mixtures including both the experimental and correlated tie lines are presented. Distribution coefficients and separation factors were evaluated for the immiscibility region. A comparison of the solvent extracting capability was made with respect to distribution coefficients, separation factors, and solvent-free selectivity bases for T = (298.15, 308.15, and 318.15) K. It is concluded that oleyl alcohol may serve as an adequate solvent to extract butyric acid from its dilute aqueous solutions.

Introduction

Solvent extraction techniques employed in downstream separations or integrated with fermentation of organic acids are of economic importance in the chemical industry. (Liquid + liquid) equilibrium (LLE) data of the related systems are needed for the design of an efficient and productive extraction system and many studies have been carried out to improve such techniques [1], [2], [3], [4], [5]. Butyric acid is a widely used carboxylic acid in the food, perfumes, pharmaceutical, polymer, leather and paint industry. The use of butyric acid or its esters as additives, particularly in the food or cosmetic industries, makes its origin important since consumers have preferences for natural products. In recent years, some studies have been performed to evaluate and offer a solvent for the separation of butyric acid from water. Zigová et al. carried out screening of 14 solvents for the extraction of butyric acid and a tertiary amine (Hostarex A327) in different diluents, C8 to C18 alcohols, dibutyl ether, toluene, and vegetable oils (rape seed and sunflower oil) [6], [7], [8]. Recently, LLE data of three different systems including butyric acid have been examined [9], [10], [11].

Oleyl alcohol may be considered as a suitable solvent for extraction of butyric acid from water, having low vapour pressure, capability to form two phases at reasonable temperatures and rapid phase separation (low density and high viscosity). As a continuation of the previous studies on the recovery of butyric acid from dilute aqueous solutions using organic solvents [9], [10], the present work aims to produce new (liquid + liquid) equilibrium (LLE) data for the extraction of butyric acid from water. In this paper, the LLE results of the (water + butyric acid + oleyl alcohol) ternary system at T = (298.15, 308.15, and 318.15) K are reported, for which no such data are available in the literature. The tie lines are also predicted using the UNIFAC method developed by Fredenslund et al. [12], and compared with the experimental data.

The mole fractions, XiE and XiR, of (liquid + liquid) equilibrium phases can be calculated using the following equation:γiEXiE=γiRXiR,where E refers to the extract (solvent) phase; R the raffinate (aqueous) phase; γ the activity coefficient of the i component; and i is the component number.

Section snippets

Experimental

Butyric acid and oleyl alcohol were purchased from Merck and were of 0.99 and ∼0.85 mass fraction purity, respectively. They were used without further purification. Deionised and redistilled water was used throughout all experiments. Refractive indexes were measured with Abbé–Hilger refractometer; its stated accuracy is ±5 · 10−4. Densities were measured with Anton Paar densimeter (Model 4500) in ±10−4 precision. Boiling point measurements were performed by using a Fischer boiling point

Results and discussion

The experimental tie-line data of (water + butyric acid + oleyl alcohol) ternaries at T = (298.15, 308.15, and 318.15) K are given in table 2. It was found that oleyl alcohol was slightly soluble in water, but miscible with butyric acid. The experimental and predicted tie lines and binodal curves for the system at each temperature are plotted in FIGURE 1, FIGURE 2, FIGURE 3, in which the concentrations are given in mass fractions.

To show the selectivity and extraction strength of the solvent to

Conclusion

The LLE data of the ternary mixtures (water + butyric acid + oleyl alcohol) are presented at T = (298.15, 308.15, and 318.15) K. The UNIFAC model was used to calculate the phase compositions of the mixtures. It was found that the UNIFAC predictions do not fit the results quantitatively, but they are in harmony qualitatively. The temperature had practically no effect on the size of immiscibility region at the temperatures studied. It is shown that butyric acid is more soluble in the solvent phase than

Acknowledgement

The author is grateful to Ciğdem Arısoy for helping experimental studies.

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