Ternary liquid–liquid equilibrium data for the (water + butyric acid + n-hexane or n-hexanol) systems at T = (298.2, 308.2, and 318.2) K

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Abstract

In this study, liquid–liquid equilibrium (LLE) values for the (water + butyric acid + n-hexane) and (water + butyric acid + n-hexanol) ternary systems were experimentally obtained at T = (298.2, 308.2, and 318.2) K and atmospheric pressure for the first time. The cloud point method was used to determine the solubility data. The concentration of each phase was determined by acidimetric titration, the Karl-Fischer technique, and refractive index measurements. Both the ternary systems exhibit type-1 behaviour of LLE. The experimental tie-line data were correlated using the UNIQUAC and NRTL models. The Othmer–Tobias and the Hand correlation equations were used to check the consistency of the obtained tie-line data for each system. Distribution coefficients and separation factors were calculated over the immiscibility regions. Finally, the Katritzky LSER multi-parameter equation was used to correlate the separation factors.

Graphical abstract

Phase diagram for the {(water + BA + n-hexane (○) or n-hexanol (Δ)} at T = 298.2 K.

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Highlights

Liquid phase equilibria of (water + BA + n-hexane or n-hexanol) were studied. ► Experimental LLE data were correlated with NRTL and UNIQUAC models. ► Distribution coefficients and separation factors were calculated. ► The Katritzky LSER equation was used to correlate the separation factors.

Introduction

Butyric acid (BA) is a short chain carboxylic acid that has many important applications in various industries. BA is a colourless liquid and has an unpleasant smell. It is soluble in water and many organic solvents. This acid has important applications in chemical, beverage, food, cosmetic and pharmaceutical industries [1]. Both the chemical and fermentation processes have been used for BA production [2]. Nevertheless, the chemical synthesis is the method used mainly for the industrial scale production of BA. It is largely produced from petrochemical resources due to cost considerations [3]. However, there is a great interest in the BA production from microbial fermentation due to increasing ecological concerns. For BA bio-production, various fermentation routes (using various organisms) have been investigated from biomass [4], [5], [6]. The next stage is the use of separation process such as solvent extraction for recovery of the acid from fermentation broth [7]. Thus, from an industrial point of view, separation of this acid from aqueous solutions is an important issue.

Until now, extraction and liquid–liquid equilibrium (LLE) measurements for systems containing carboxylic acid mainly BA have been carried out by many investigators [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. One of the earliest reports of LLE for the ternary system consisting of BA is that of Leung and Badakhshan [19]. As far as the authors are aware, heavy alcohols [20], [21], [22], esters [23], [24], [25], [26], [27], [28] amines [29], [30], nitriles [31], and ketones [32] have mainly been used as extractants in the LLE measurements. We have recently reported LLE data for the aqueous solutions of BA with various organic solvents (mainly hydrocarbons) [33], [34], [35]. As a continuation of the previous works, we present the solubility and tie-line data for the ternary systems consisting of water, BA and organic solvents at T = (298.2, 308.2, and 318.2) K. In this study, n-hexane and n-hexanol were selected as organic solvents (extractants). n-Hexane (an aliphatic hydrocarbon) is a colourless liquid and is almost insoluble in water (i.e. 0.0095 g · dm−3). n-Hexanol (a straight primary alcohol) is slightly soluble in water but miscible in most organic solvents (5.9 g · dm−3).

To the best of our knowledge, the LLE data of the (water + BA + n-hexane or n-hexanol) ternary systems have not been reported in the available literature. For a comparison of the extracting capabilities of the solvents for the separation of the acid from water, the distribution coefficients and separation factors were experimentally determined. In this work, three different temperatures were chosen in order to observe the change of equilibrium phase compositions. Experimental tie-line data were correlated using the universal quasi chemical (UNIQUAC) method of Abrams and Prausnitz [36] and the non-random two-liquid (NRTL) model of Renon and Prausnitz [37], [38], [39]. The values for the UNIQUAC and NRTL interaction parameters were obtained. In order to evaluate the extracting capability of the selected solvents for the separation of the acid from water, distribution coefficients and separation factors were experimentally determined from the tie-line data.

Section snippets

Material

The chemicals; 1-hexane and butyric acid (BA) with stated mass fraction purities higher than 0.99 were purchased from Merck. 1-hexanol (mass fraction purity > 0.98) was purchased from Scharlau. The stated purity of the materials was checked on the basis of their refractive indices. Deionized and redistilled water with an electrical conductivity less than 5 μS · cm−1 at T = 298.2 K was used throughout all experiments. All materials were used as received without any further purification. The provenance

Experimental solubility and tie line data

Solubility and equilibrium tie-line data for the (water + butyric acid + n-hexane or n-hexanol) ternary systems were measured at T = (298.2, 308.2, and 318.2) K and atmospheric pressure. The measured solubility data for the ternary systems at each temperature are given in table 3. The tie-line data for these ternary systems were obtained experimentally at atmospheric pressure and within the temperature range of (298.2 to 318.2) K with intervals of 10 K. The experimental LLE data for the ternary systems

Conclusions

The LLE data for the (water + butyric acid + n-hexane or n-hexanol) ternary systems were obtained at T = (298.2, 308.2, and 318.2) K. Both the ternary systems exhibit type-1 behaviour of the LLE, where the only one liquid pair (water + solvent) is partially miscible. The UNIQUAC and NRTL (α = 0.3) thermodynamic models were acceptably used to correlate the experimental LLE data and to calculate the phase compositions of the studied systems. From the experimental tie-line data, the corresponding binary

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