Isobaric vapor–liquid equilibria for ethanol–water system containing different ionic liquids at atmospheric pressure

doi:10.1016/j.fluid.2006.01.023

Fluid Phase Equilibria

Volume 242, Issue 2, 25 April 2006, Pages 147-153

https://doi.org/10.1016/j.fluid.2006.01.023 Get rights and content

Abstract

Isobaric vapor–liquid equilibrium (VLE) data for ethanol–water systems containing ionic liquids (ILs) 1-methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) at atmospheric pressure (101.32 kPa) were measured with a circulation still. The results showed that the VLE of ethanol–water systems in the presence of different ILs was obviously different from that of the IL-free system. All ILs studied showed a salting-out effect, which gave rise to a change of the relative volatility of ethanol, and even to an elimination of the azeotropic point. It was found that the salting-out effect followed the order of [BMIM][Cl] > [BMIM][Br] > [BMIM][PF₆] and [MMIM][DMP] > [EMIM][DEP], which was ascribed to the preferential solvation ability of the ions resulting from the dissociation of the IL.

Introduction

Special distillation, e.g. extractive distillation or salt distillation, is widely used in industry for separating azeotropic or close-boiling binary mixtures [1], [2]. In the special distillation, a third component, namely the entrainer, is added to the liquid mixture to alter the relative volatility and make the separation viable. In the salt distillation process, calcium chloride and potassium acetate are commonly used entrainers, however, which may erode the sieve plate, precipitate and build up in the tower due to their causticity and limited solubility. As a molten salt at room temperature, IL might be used as a suitable solvent and salt in the special distillation process, and might be superior to the commonly used entrainer due to its non-volatility, less causticity and good performance in improving the separation efficiency. Furthermore, thermodynamic data for IL-containing systems are essential for a better understanding of thermodynamic behaviors of such systems, for separation design purpose and for the development of thermodynamic models. Although some thermodynamic data for IL-containing systems have been reported, for example, LLE data [3], [4], [5], [6], [7], [8], VLE data [8], [9], [10], GLE data [11], [12] and infinite activity coefficients of some organic solvents [13], [14], [15], [16], [17], [18], the isobaric VLE data for such systems are extremely scarce.

In this work, isobaric VLE data for ethanol–water systems containing ILs [MMIM][DMP], [EMIM][DEP], [BMIM][Cl], [BMIM][Br] and [BMIM] [PF₆] were presented at atmospheric pressure (101.32 kPa), and the effect of ILs on the VLE of ethanol–water system was discussed briefly. The structures of the ILs investigated in this work were shown as follows:

Section snippets

Materials

The chemical reagents used were ethanol, cyclohexane, redistilled water and ILs. AR grade ethanol and cyclohexane with purity of 99.7% were purchased from Beijing Red Star Reagents Company, China. The purity of reagents was checked by a gas chromatography (GC2010, Japan). Based on the literature method [19], [20], the ILs used were prepared and purified in the laboratory, and the purity was more than 98% in terms of NMR analysis. Furthermore, all ILs were purified by vacuum evaporation to

Reliability assessment of the set-up

In order to check the reliability of the experimental set-up, isobaric VLE data for ethanol–cyclohexane system at atmospheric pressure (101.32 kPa) were measured and compared with the literature data [23] as shown in Fig. 2. It can be seen from Fig. 2 that the VLE data measured was in good agreement with the literature data [23]. Hence the set-up can be used to investigate the effect of IL on the VLE of ethanol–water system at atmospheric pressure (101.32 kPa). The experimental isobaric VLE data

Conclusions

Isobaric VLE data for ethanol–water systems containing ILs [MMIM][DMP], [EMIM][DEP], [BMIM][Br], [BMIM][Cl] and [BMIM][PF₆] were measured at atmospheric pressure (101.32 kPa). The results indicated that all ILs studied showed a salting-out effect, which leaded to an enhancement of relative volatility of ethanol and even to an elimination of the azeotropic phenomenon at specific IL content. For the systems studied, the salting-out effect follows the order of [BMIM][Cl] > [BMIM][Br] > [BMIM][PF₆], and

Acknowledgement

The authors are grateful to the financial support from National Science Foundation of China (20376004) that allows the authors to accomplish the research presented herein.

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Isobaric vapor–liquid equilibria for ethanol–water system containing different ionic liquids at atmospheric pressure

Abstract

Introduction

Section snippets

Materials

Reliability assessment of the set-up

Conclusions

Acknowledgement

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Chem. Thermodyn.

J. Mol. Catal. A: Chem.

Fluid Phase Equilib.

Fluid Phase Equilib.

Chem. Eng. Prog.

Can. J. Chem. Eng.

Chem. Commun.

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data