Activity coefficients at infinite dilution measurements for organic solutes in the ionic liquid N-butyl-4-methylpyridinium tosylate using GLC at T = (328.15, 333.15, 338.15, and 343.15) K

doi:10.1016/j.fluid.2008.10.008

Fluid Phase Equilibria

Volume 276, Issue 1, 15 February 2009, Pages 31-36

https://doi.org/10.1016/j.fluid.2008.10.008 Get rights and content

Abstract

Activity coefficients at infinite dilution for 19 solutes: alkanes, cycloalkanes, alk-1-enes, alk-1-ynes, benzene and alcohols in the ionic liquid N-butyl-4-methylpyridinium tosylate ([BMPy][TOS]) were determined by gas–liquid chromatography at four temperatures T = (328.15, 333.15, 338.15, and 343.15) K. The partial molar excess enthalpy values at infinite dilution $Δ H_{1}^{E, \infty}$ were calculated from the experimental gamma infinity values obtained over the temperature range. The selectivity for the hexane/benzene and cyclohexane/benzene separations was calculated from the gamma infinity values and compared to the literature values for other ionic liquids, NMP and sulfolane.

Introduction

Recent work has shown that some room-temperature ionic liquids (ILs) have the potential to be good solvents for separating organic liquids using solvent extraction or extractive distillation processes [1], [2], [3], [4], [5], [6], [7]. Some ILs have also been shown to have great potential as media for chemical reactions. One of the many appealing properties of ILs, that makes them so attractive in replacing many organic solvents currently used in industry, is their very low vapour pressure which eliminates volatilization and air pollution problems. It is however the thermodynamic information, which reflects how the different solutes interact with these solvents, that is crucial in assessing their usefulness and allows one to predict better and more efficient ILs.

This work is a continuation of our investigation into the solvent properties of ILs through the determination of activity coefficients at infinite dilution, $γ_{13}^{\infty}$ , using gas–liquid chromatography [6], [7], [8], [9], [10], [11], [12], [13], [14]. Our previous work includes measurements of $γ_{13}^{\infty}$ for organic solutes in the ILs: 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) [6], 1-ethyl-3-methyl trifluoroacetate (EMIM][TFA]) [7], 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIM][Tf₂N]) [8], 1-butyl-3-methylimidazolium 2-(2-methoxyethoxy)-ethyl sulfate ([BMIM][MDEGSO₄]) [9], and 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM][BF₄]) [15]. In our work we have calculated the selectivities and capacities at infinite dilution for many different separation problems, directly from experimental $γ_{13}^{\infty}$ values. Our results are important in expanding the knowledge about the nature of ILs, in assisting in the systematic study of their physicochemical properties and in extending the applications of thermodynamic models such as UNIFAC [16].

Ionic liquids which have been shown to have potentially excellent entrainer properties for the separation of aliphatic from aromatic hydrocarbons by extractive distillation or extraction are 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO₄]), ethyl(2-hydroxyethyl)dimethylammonium bis{(trifluomethyl)sulfonyl}imide (C₂Tf₂N), or [EMIM][SCN], or [BMIM][MDEGSO₄], or 4-methyl-N-butylpyridinium tetrafluoroborate ([BMPy][BF₄]), or N-methylpyridinium bis{(trifluomethyl)sulfonyl}imide [EPy][Nf₂T] [1], [2], [3], [4], [6], [9], [17], [18], [19]. Generally, the selectivity for the separation of aromatic hydrocarbons/aliphatic hydrocarbons decreases with increasing length of the alkyl chain on the imidazolium, or ammonium cation, or anion of the IL.

A short analysis of the presented results, showed that the IL composed of the [BMPy]⁺ cation [2] and an aromatic based anion, such as the tosylate anion [TOS]⁻ (increasing the solubility of benzene in the IL) can be an effective solvent for the separation of aromatic/aliphatic hydrocarbons [20]. This paper presents $γ_{13}^{\infty}$ values for 19 solutes (alkanes, cycloalkanes, alk-1-enes, alk-1-ynes, benzene and alcohols) in the ionic liquid N-butyl-4-methylpyridinium tosylate, [BMPy][TOS] at four temperatures T = (328.15, 333.15, 338.15, and 343.15) K.

Section snippets

Materials or chemicals

The IL investigated here, N-butyl-4-methylpyridinium tosylate, [BMPy][TOS] was synthesized for us on request by io-li-tec, Germany, and was reported to have a purity of >98 mass percent. Unfortunately, this IL is solid up to the temperature 315.52 K. The structure of investigated ionic liquid is presented below.

The ionic liquid was purified by subjecting the liquid to a very low pressure of about 5 × 10⁻³ Pa at about 343 K for approximately 5 h. Next IL is during 5–8 h together with the Chromosorb at

Theoretical basis

The equation developed by Everett [24] and Cruickshank et al. [25] was used in this work to calculate the $γ_{13}^{\infty}$ of solutes in the ionic liquid: $\ln γ_{13}^{\infty} = \ln (\frac{n_{3} R T}{V_{N} P_{1}^{*}}) - \frac{P_{1}^{*} (B_{11} - V_{1}^{*})}{R T} + \frac{P_{o} J_{2}^{3} (2 B_{12} - V_{1}^{\infty})}{R T}$ V_N denotes the net retention volume of the solute, P_o the outlet pressure, $P_{o} J_{2}^{3}$ the mean column pressure, n₃ the number of moles of solvent on the column packing, T the column temperature, $P_{1}^{*}$ the saturated vapour pressure of the solute at temperature T, B₁₁ the second virial coefficient of the pure

Results and discussion

Table 3 lists the average $γ_{13}^{\infty}$ values for two different amounts of solvent on the column packing (26.52% and 31.07%) in the temperature range from 328.15 to 343.15 K.

The values of $γ_{13}^{\infty}$ for alkanes, cycloalkanes, alk-1-enes, alk-1-ynes, benzene and alcohols increase with increasing solute alkyl chain. This behaviour is typical for all the ILs we have tested. The activity coefficient values for the different high column packings were very similar (see Table 3) and indicate that gas–liquid

Conclusions

Activity coefficients at infinite dilution for various solutes in the ionic liquid [BMPy][TOS] were measured in the temperature range from 328.15 to 343.15 K using the GLC method. The $γ_{13}^{\infty}$ values obtained were used to determine the potential application of this IL as a selective solvent for separation processes. We found that this IL had a higher selectivity in separating aliphatic hydrocarbons from aromatic hydrocarbons, than did sulfolane [35], commercially used entrainer. The selectivity of

Acknowledgements

Founding for this research was provided by the Polish Ministry of Education and Sciences for the Joint Project of Polish-South African Scientific and Technological International Cooperation.

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Activity coefficients at infinite dilution measurements for organic solutes in the ionic liquid N-butyl-4-methylpyridinium tosylate using GLC at T = (328.15, 333.15, 338.15, and 343.15) K

Abstract

Introduction

Section snippets

Materials or chemicals

Theoretical basis

Results and discussion

Conclusions

Acknowledgements

Fluid Phase Equilib.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Fluid Phase Equilib.

J. Chem. Thermodyn.

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Chromatogr. A

Fuel Process. Technol.

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Phys. Chem. B

J. Phys. Chem. B

J. Chem. Eng. Data

J. Chem. Eng. Data