Activity coefficients at infinite dilution of organic solutes in the ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] using gas–liquid chromatography

doi:10.1016/j.jct.2010.02.006

The Journal of Chemical Thermodynamics

Volume 42, Issue 6, June 2010, Pages 817-822

https://doi.org/10.1016/j.jct.2010.02.006 Get rights and content

Abstract

The activity coefficients at infinite dilution, $γ_{i}^{\infty}$ , for both polar and non-polar solutes in the ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] have been determined by gas–liquid chromatography at the temperatures from (303 to 343) K. The partial molar excess enthalpies at infinite dilution $H_{i}^{E, \infty}$ of the solutes in the ionic liquid were also calculated from the temperature dependence of the $γ_{i}^{\infty}$ values. The selectivity for the hexane/benzene and cyclohexane/benzene separation problems was calculated from experimental infinite dilution activity coefficient values and compared to the other ionic liquids, taken from the recent literature.

Introduction

Research of ionic liquids (ILs) is one of the most rapidly growing fields in the past years, much of which has the ultimate aim of large scale industrial application [1]. Due to their unique properties such as negligible vapour pressure at room temperature, stable liquid phase over a wide temperature range and stability at high temperatures, ionic liquids created interest to use them in synthesis and extraction processes for the reduction of the amount of volatile organic solvents (VOSs) used in industry. Activity coefficients at infinite dilution of a solute $i (γ_{i}^{\infty})$ provide a useful tool for solvent selection in extractive distillation or solvent extraction processes.

Since ILs have a negligible vapour pressure, the gas–liquid chromatography (GLC) using the ionic liquid as stationary phase, is the most suitable method for measuring activity coefficients at infinite dilution $γ_{i}^{\infty}$ . In the literature, there are a large number of studies on $γ_{i}^{\infty}$ for both polar and non-polar solutes in the di-substituted imidazolium based ILs which are considered to be a class of very promising extraction and separation reagents [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. In order to expand our knowledge about the nature of ILs, influence of the anion structure on the thermodynamic properties of the di-substituted imidazolium based ionic liquid with tetracyanoborate [TCB]⁻ anion was studied in this work. The 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB]⁻ is an ionic liquid of low viscosity (19.8 cP at T = 293 K) and high chemical and thermal stability [23]. The ILs containing the tetracyanoborate anion [TCB]⁻ are currently tested for their use in dye-sensitized solar cells (DSC) due to their unique properties including wide electrochemical window, very low viscosity, hydrophobicity and hydrolytic stability [24], [25].

This paper presents $γ_{i}^{\infty}$ values for 23 solutes (alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols) in the ionic liquid [EMIM][TCB] over the temperatures range from 303 K to 343 K. The partial molar excess enthalpies at infinite dilution, $H_{i}^{E, \infty}$ , of these solutes in the ionic liquid were also derived from the temperature dependence of the $γ_{i}^{\infty}$ values.

Section snippets

Materials

The hydrocarbons provided by Beijing Chemical Reagents Company were of analytical grade. Since the GLC process separated the solutes from any impurities, the solutes were used without further purification.

The 101 AW (the inert and white diatomite, 80/100 mesh) purchased from Shanghai Reagent Corporation was used as a solid support for the ionic liquid in the GC column. Before use, the support material was subjected to vacuum treatment with heating to remove traces of adsorbed moisture.

The ionic

Theoretical basis

The equation developed by Everett [28] and Cruickshank et al. [29] was used in this work to calculate the $γ_{i}^{\infty}$ of solutes in the ionic liquid $\ln γ_{13}^{\infty} = \ln (\frac{n_{3} RT}{V_{N} P_{1}^{*}}) - \frac{P_{1}^{*} (B_{11} - V_{1}^{*})}{RT} + \frac{P_{o} J (2 B_{12} - V_{1}^{\infty})}{RT},$ where V_N is the standardized retention volume of the solute; P_o is the outlet pressure; n₃ is the number of moles of the ionic liquid on the column packing; T is the column temperature; $P_{1}^{*}$ is the saturated vapour pressure of the solute at temperature T; B₁₁ is the second virial coefficient of the pure

Results and discussion

The values of $γ_{i}^{\infty}$ of different solutes (alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols) in [EMIM][TCB] obtained at several temperatures are listed in table 3. They have been approximated by the linear regression: $\ln γ_{i}^{\infty} = a + \frac{b}{T} .$ The coefficients a and b, the correlation coefficients R², and the values of $γ_{i}^{\infty}$ (T = 298.15 K) calculated with these coefficients are given in table 4. The quality of the linear regression was very good because most of the correlation

Conclusions

Activity coefficients at infinite dilution for 23 solutes (alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols) in the ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] were measured by gas–liquid chromatography over the temperature range from T = (303 to 343) K.

It was found that the IL investigated shows lower selectivity at infinite dilution than the ionic liquids with the same cation in the separation process of aliphatic compounds from aromatic

Acknowledgments

Funding for this research was provided by National Natural Science Foundation of China (NSFC No. 20901076) and the State Key Laboratory of Fine Chemicals (KF0811).

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The Journal of Chemical Thermodynamics

Activity coefficients at infinite dilution of organic solutes in the ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] using gas–liquid chromatography

Abstract

Introduction

Section snippets

Materials

Theoretical basis

Results and discussion

Conclusions

Acknowledgments

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Inorg. Chim. Acta

Chem. Soc. Rev.

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data