(Liquid + liquid) equilibria of the (water + butyric acid + dodecanol) ternary system

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Abstract

(Liquid + liquid) equilibrium (LLE) data for the (water + butyric acid + dodecanol) ternary system have been determined experimentally at T = (298.2, 308.2 and 318.2) K. Complete phase diagrams were obtained by determining binodal curves and tie lines. The reliability of the experimental tie lines was confirmed by using the Othmer–Tobias correlation. The UNIFAC method was used to predict the phase equilibrium in the ternary system using the interaction parameters determined from experimental data of CH3, CH2, COOH, OH and H2O functional groups. Distribution coefficients and separation factors were evaluated for the immiscibility region.

Introduction

The efficient separation of organic acids from aqueous solutions is an important problem in the chemical fermentation industry where many solvents have been tested to improve such recovery [1], [2], [3]. The LLE data of the related systems are needed for the design of an efficient and effective extraction system and numerous studies have been carried out to improve such techniques [4], [5], [6], [7], [8].

A detailed evaluation of solvents for the extraction of butyric acid is not available in the literature. Nevertheless, Zigová et al. carried out screening of 14 solvents for the extraction of butyric acid and a tertiary amine in different diluents, C8 to C18 alcohols, dibutyl ether, toluene, and vegetable oils, have been tested [9], [10], [11]. Recently, Kırbaşlar et al. [12], [13], [14] examined LLE data of three different ternary systems.

This study is part of a research programme on the recovery of butyric acid from dilute aqueous solutions using high-boiling solvents. In this paper, LLE results were presented for the (water + butyric acid + dodecanol) systems. The phase equilibrium data were predicted using the UNIFAC model of Fredenslund et al. [15], using UNIFAC-LLE prediction parameters published by Magnussen et al. [16].

Section snippets

Experimental

Butyric acid and dodecanol were purchased from Merck and were of >0.99 and >0.98 mass fraction purity, respectively. Butyric acid and dodecanol were used without further purification. The GC analysis did not detect any appreciable peaks of impurities. Deionised water was further distilled before use. Refractive indices were measured with an Abbé-Hilger refractometer; its stated accuracy is ±5 · 10−4. Densities were measured with an Anton Paar (Model 4500) density meter. Boiling point measurements

Results and discussion

The experimental tie lines of the (water + butyric acid + dodecanol) ternary system at each temperature are given in table 2. The experimental and predicted equilibrium data of the ternary system at T = 298.2 K are plotted in figure 1. As can be seen from figure 1, it was found that dodecanol was insoluble in water but miscible with butyric acid. Also, similar results were observed at T = 308.2 K and T = 318.2 K.

To measure the selectivity and extraction strength of the solvent to extract butyric acid, the

Conclusion

The LLE data of the (water + butyric acid + dodecanol) ternary system were determined experimentally at three temperatures. The temperature had practically no effect on the size of immiscibility region at the temperatures studied. The results showed that butyric acid was more readily soluble in solvent-rich phase than in the water-rich phase. It was apparent from the distribution and selectivity data that the separation of butyric acid from water by extraction with dodecanol was feasible. The

Acknowledgements

The author thanks to Sema Yuksel for helping experimental studies. This work was supported by The Research Fund of Istanbul University. Project number: T-35/23072003.

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