Elsevier

Fluid Phase Equilibria

Volume 303, Issue 2, 25 April 2011, Pages 168-173
Fluid Phase Equilibria

Phase equilibria of (water–carboxylic acid–diethyl maleate) ternary liquid systems at 298.15 K

https://doi.org/10.1016/j.fluid.2011.01.020Get rights and content

Abstract

Liquid–liquid equilibrium (LLE) data for the ternary systems of (water–formic acid–diethyl maleate), (water–acetic acid–diethyl maleate), (water–propionic acid–diethyl maleate), (water–butyric acid–diethyl maleate), and (water–valeric acid–diethyl maleate) were investigated at 298.15 K and atmospheric pressure. Complete phase diagrams were obtained by determining solubility and the tie-line data. The tie-line data were compared with the results predicted by the UNIFAC and the modified UNIFAC (Dortmund) methods and correlated by means of UNIQUAC model. The reliability of the experimental tie-line data was confirmed by using the Othmer–Tobias correlation. Distribution coefficients and selectivity were evaluated for the immiscibility region.

Research highlights

LLE data of water–carboxylic acid–diethyl maleate were presented at 298.15 K. ► Tie-line data were compared with data obtained from UNIFAC, mod. UNIFAC, UNIQUAC. ► Distribution coefficients were evaluated for the immiscibility region. ► Diethyl maleate can be used as a adequate solvent for carboxylic acid extraction.

Introduction

Carboxylic acids are widely used in the food, pharmaceutical and chemical industries, and mostly produced in bioengineering processes where they have to be recovered from aqueous solutions. Several separation methods have been employed to remove carboxylic acids [1] and liquid extraction is one of these. Since, the liquid extraction of carboxylic acids from aqueous solutions is industrially and scientifically important, the precise LLE data of a liquid mixture composed of (water–carboxylic acid–solvent) are required. Various organic solvents for extraction of dilute carboxylic acids from water have been tested and reported in the literature [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47].

The solvent selection is of prime importance for successful separation by liquid–liquid extraction, and much of the process research is directed toward the evaluation of potential solvents. The desired properties of solvents are a high distribution coefficient, good selectivity toward solute and little or no miscibility with feed solution. Other factors affecting solvent selection are boiling point, density, interfacial tension, viscosity, corrosiveness, flammability, toxicity, stability, compatibility with product, availability and cost. Diethyl maleate, used in this study as a solvent, has many of these properties.

This study is a part of a research program on the recovery of carboxylic acids from dilute aqueous solutions using organic solvents. In this paper, we report the LLE results for the ternary system (water–carboxylic acid–diethyl maleate), for which no such data were available. LLE for (water–carboxylic acid–diethyl maleate) mixtures have been determined for each of the C1 (formic acid), C2 (acetic acid), C3 (propionic acid), C4 (butyric acid), and C5 (valeric acid) carboxylic acids at 298.15 K. Complete phase diagrams were obtained by solubility and tie-line data simultaneously for each acid. The tie-line data were compared with the results predicted by the UNIFAC [48] and the modified UNIFAC (Dortmund) [49] methods and correlated by means of UNIQUAC model [50].

Section snippets

Chemicals

The chemicals, formic acid (Merck, >98%), acetic acid (Merck, >99%), propionic acid (Merck, >99%), butyric acid (Merck, ≥99%), valeric acid (Merck, >99%), and diethyl maleate (Merck, ∼95%) were used without further purification. Deionised and redistilled water was used throughout all experiments. The purity of the chemicals was checked on the basis of their densities and refractive indexes at 293 ± 0.2 K. Refractive indexes and densities were measured with Anton Paar densimeter (Model DMA 4500)

Results and discussion

The compositions of mixtures on the binodal curve, as well as the mutual binary solubilities for the systems [water (1)–formic acid (2)–diethyl maleate (3)], [water (1)–acetic acid (2)–diethyl maleate (3)], [water (1)–propionic acid (2)–diethyl maleat (3)], [water (1)–butyric acid (2)–diethyl maleat (3)], and [water (1)–valeric acid (2)–diethyl maleat (3)] at 298.15 K were given in Table 2 in which xi denotes mole fraction of the ith component. Table 3 tabulates the experimental tie-line

Conclusion

The LLE data for the ternary systems of (water–formic acid–diethyl maleate), (water–acetic acid–diethyl maleate), (water–propionic acid–diethyl maleate), (water–butyric acid–diethyl maleate), and (water–valeric acid–diethyl maleate) were investigated at 298.15 K and atmospheric pressure.

Separation factors found to be greater than 1, varying between 2.08 and 8.68 for formic acid, 2.92 and 11.48 for acetic acid, 5.19 and 30.66 for propionic acid, 16.11 and 97.88 for butyric acid, and 128.84 and

Acknowledgement

The authors thanks to Prof. J. Gmehling for the opportunity of using Dortmund Data Bank.

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