Liquid phase equilibria of (water + propionic acid + oleyl alcohol) ternary system at several temperatures
Introduction
The separation of carboxylic acids from aqueous fermentation media by solvent extraction has been an actual research area. A large amount of investigation has been carried out in recent years on the (liquid–liquid) equilibrium (LLE) measurements of ternary systems, in order to understand and provide further information about the phase behaviour of such systems [1], [2], [3], [4], [5], [6], [7].
Propionic acid is a widely used carboxylic acid in pharmaceutical industry as a cellulosic solvent and can be used to provide propionates as fungicides. It is also used in the electroplating industry, and to prepare perfume esters [8]. Recently, there has been increasing interest in producing propionic acid from whey lactose using Propionibacterium [9], [10]. Fermented whey has been shown to be a natural ‘fungistatic’ agent when incorporated in bread or other bakery products. It can replace chemical preservatives and is of substantial commercial importance in the sale of ‘natural’ bakery products. The Na+, Ca2+ and K+ salts of propionic acid have also been listed as preservatives which are of the category known as generally recognized as safe (GRAS) food additives [11]. Since, the liquid extraction of propionic acid from aqueous solution is industrially and scientifically important, various organic solvents have been investigated and reported for propionic acid extraction [12], [13], [14], [15]. Oleyl alcohol used in this study may be considered also as a suitable solvent for extraction of propionic acid from water, having low vapour pressure, capability to form two phases at reasonable temperatures and rapid phase separation (low density and high viscosity).
The aim of this work is to present the phase behaviour of LLE for (water + propionic acid + oleyl alcohol) ternary system at 298.15, 308.15 and 318.15 K and atmospheric pressure, for which no such data were available in the literature. The tie-lines were also predicted using the UNIFAC method (a group contribution method) developed by Fredenslund et al. [16], and compared with the experimental data.
Section snippets
Experimental
Propionic 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. Densities of the chemicals were measured by a densimeter (Anton Paar, DMA 4500) with a resolution accuracy of 1 × 10−5 g/cm3. Refractive indexes were determined with a refractive index unit (Anton Paar, RXA 170) integrated to the densimeter also in 1 × 10−5 precision.
Results and discussion
The experimental tie-line compositions of the equilibrium phases at 298.15, 308.15 and 318.15 K were given in Table 2, for which xi1 and xi3 refer to the mole fractions of the ith component in the aqueous and solvent phases, respectively. It was found that oleyl alcohol was very little soluble in water but miscible with propionic acid. The experimental and predicted tie-lines and binodal curves for the system at each temperature were plotted in Fig. 1, Fig. 2, Fig. 3. The plait point values of
Conclusion
The LLE data of the ternary mixtures water + propionic acid + oleyl alcohol were presented at 298.15, 308.15 and 318.15 K. The UNIFAC model was used to calculate the phase compositions of the mixtures. It was observed that the UNIFAC predictions do not fit the experimental results quantitatively, but it agrees qualitatively. The temperature had practically no effect on the size of immiscibility region at the temperatures studied. It is shown that propionic acid is more soluble in solvent phase than
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