(Liquid + liquid) equilibria for the ternary (water + acetic acid + toluene) system at different temperatures: Experimental data and correlation

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Abstract

(Liquid + liquid) equilibrium (LLE) of the ternary (water + acetic acid + toluene) system was investigated at temperatures of (288.2, 298.2, and 313.2) K, under atmospheric pressure. This chemical system is frequently used in liquid–liquid extraction investigations. The results show that the distribution coefficient of acetic acid between organic and aqueous phases rises with increasing temperature, but the separation factor decreases within the temperature range covered. Meanwhile, a maximum extraction factor (about 100) was achieved for the solute aqueous phase mass fraction around 0.27 at T = 288.2 K. The tie line data for this system were sufficiently correlated by Othmer–Tobias and Hand equations. The experimental results were used to obtain binary interaction parameters as predicted by the non-random two liquid (NRTL) and universal quasi chemical (UNIQUAC) equation models using the Aspen Plus simulator. Root mean square deviation (RMSD) values as low as 0.0119 and 0.0139 were obtained for these models, respectively; indicating excellent correlation results for the provided experimental solubility data.

Highlights

► Solute distribution coefficient rises with temperature; however, mildly at low dosages. ► Solute extraction factor decreases with temperature, favoring extraction efficiency. ► A maximum separation is achieved at solute aqueous phase mass fraction of about 0.27. ► Both well known NRTL and UNIQUAC models predict the experimental data nicely.

Introduction

Separation of carboxylic acids from aqueous solutions resulting from fermentation processes or synthetic methods is an important process that has many supplications from different industries. Accordingly, the recovery of acetic acid from aqueous solutions has been investigated extensively [1], [2], [3], [4] due to its wide consumption.

Many solvents have been tried to improve the recovery of organic acids from dilute solutions. There are practical concerns when choosing extraction solvents, toluene can be considered as a suitable solvent for extraction of carboxylic acids from water, having low vapour pressure, capability to form two phases, and rapid phase separation due to its low density (0.8669 kg · m−3 at T = 298.2 K) and low viscosity (5.90 · 10−4 Pa · s at T = 298.2 K) [5], [6].

In extraction process, exact liquid–liquid equilibrium data and accurate modelling are demanded. Activity coefficient models, such as the non-random two liquid (NRTL) [7] and the universal quasi chemical (UNIQUAC) [8] models have been frequently used for the predicting different (liquid + liquid) systems. The binary interaction parameters of models have been obtained by regression with experimental data.

It is noteworthy that previous LLE data for the extraction of acetic acid from water using toluene solvent have been reported in two articles. In 1973, Dakshinamurty et al. [9] just reported the experimental data for this system at temperatures of (303.2, 313.2, and 333.2) K, and in 1985 Badakhshan et al. [10] compared experimental data with the predicted values by the universal functional activity coefficient (UNIFAC) model at temperatures of (278.2, 283.2, 293.2, 303.2, and 323.2) K. Considering wide use of this system in liquid–liquid extraction investigations [4], [11], the objective of this research is to provide a new series of LLE data for the ternary {water (1) + acetic acid (2) + toluene (3)} system at three specified temperatures of (288.2, 298.2, and 313.2) K. Then NRTL and UNIQUAC models are examined for regression of experimental data and obtaining binary interaction parameters, using Aspen Plus simulator. Also, distribution coefficient and separation factor for acetic acid were determined at different temperatures for the purpose of process design and simulation applications. No attempt has been made so far, for correlating LLE data of this system with NRTL and UNIQUAC models.

Section snippets

Materials

All materials were purchased from Merck Company. Toluene and acetic acid were with mass fraction purities >0.995 and were used without further purification. Standard 0.1 mol · dm−3 (±0.2%) sodium hydroxide solutions were used for titration. Deionized water with ionic conductivity <0.08 μS · cm−1 was produced from a deionizer (Hastaran Teb. Co.) and used in all experiments. Table 1 summarizes relevant information on sample material purities.

Apparatuses

The two phase (liquid + liquid) equilibrium was established in

Tie-lines, distribution coefficients and separation factor

The experimental tie line data for the {water (1) + acetic acid (2) + toluene (3)} ternary system at different used temperatures are presented in table 2. Results at T = 313.2 K in this work were compared to the published data by Dakshinamurty et al. [9]. Difference between these two data sources (solute weight fraction in the organic phase) varied from 12 to 24%. The lower difference is for lower solute concentration. The procedure used in this work is based on utilizing the results of the direct

Conclusions

The LLE for the ternary systems of (water + acetic acid + toluene) was studied at temperatures of (288.2, 298.2, and 313.2) K and under atmospheric pressure.

The efficiency of the extraction of acetic acid from water by toluene was evaluated by the criteria of the distribution coefficient and separation factor. It was revealed that the acetic acid distribution coefficient was increased, while, the separation factor decreased with temperature. Meanwhile, a maximum extraction factor (about 100) is

Acknowledgement

We express thanks to the university authorities for providing the financial support to carry out this work.

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