Measurements of activity coefficients at infinite dilution of aliphatic and aromatic hydrocarbons, alcohols, thiophene, tetrahydrofuran, MTBE, and water in ionic liquid [BMIM][SCN] using GLC

doi:10.1016/j.jct.2008.12.018

The Journal of Chemical Thermodynamics

Volume 41, Issue 5, May 2009, Pages 645-650

https://doi.org/10.1016/j.jct.2008.12.018 Get rights and content

Abstract

The activity coefficients at infinite dilution, $γ_{13}^{\infty}$ for 32 solutes: alkanes, alken-1-es, alkyn-1-es, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, tetrahydrofuran, tert-butyl methyl ether, and water in the ionic liquid 1-butyl-3-methylimidazolium thiocyanate [BMIM][SCN] were determined by gas-liquid chromatography at the temperatures from 298.15 K to 368.15 K. The values of the partial molar excess enthalpies at infinite dilution $Δ H_{1}^{E, \infty}$ were calculated from the experimental $γ_{13}^{\infty}$ values obtained over the temperature range. The selectivities for the hexane/benzene, cyclohexane/benzene, hexane/thiophene, and other separation problems were calculated from the $γ_{13}^{\infty}$ and compared to the other ionic liquids, N-methyl-2-pyrrolidinone, and sulfolane, taken from the recent literature. This work demonstrates that with chosen ionic liquid it is possible to separate different organic compounds with the highest selectivity, ever published.

Introduction

Ionic liquids (ILs), due to their unique properties such as wide liquid range, stability at high temperatures, no flammability, and negligible vapour pressure are the subject of an increasing number of investigations. These features ensure that ILs are good candidates for the separation processes and can successfully replace the conventional volatile, flammable, and toxic organic solvents. For ILs to be used effectively as solvents, it is essential to know how they interact with different solutes. Particularly, by varying the cation, anion, and/or substituent groups, the properties of ILs can be readily tuned to fit into specific requirements. The important measure of this property is given by the activity coefficient at infinite dilution, $γ_{13}^{\infty}$ , which describes the non-ideality for chosen species in a mixture {where 1 refers to the solute and 3 to the solvent (here IL)}. The primary appeal of ILs is based on their unique physical properties, including the ability to solvate a wide range of materials. The activity coefficient at infinite dilution, $γ_{13}^{\infty}$ , is especially important because it describes the extreme case in which only solute–solvent interactions contribute to non-ideality. Additionally, the values of $γ_{13}^{\infty}$ may have practical implications in chemical and industrial processes. Currently, a large number of experimental $γ_{13}^{\infty}$ data are available in the literature for imidazolium ionic liquids [1], [2], [3], [4], [5], [6], [7], [8], [9], [10].

Since the ILs have a negligible vapour pressure, the gas-liquid chromatography (GLC) is a suitable method for measuring the activity coefficients at infinite dilution $γ_{13}^{\infty}$ . From experimental values of $γ_{13}^{\infty}$ the selectivity at infinite dilution $S_{ij}^{\infty} = γ_{i 3}^{\infty} / γ_{j 3}^{\infty}$ and the capacity at infinite dilution $k_{j}^{\infty} = 1 / γ_{j 3}^{\infty}$ can be calculated for different separation problems as first information about two important components of the industrial mixture [11]. Experimental $γ_{13}^{\infty}$ values provide useful information about interaction between these two components (solvent (IL) and solute). However, the knowledge about $γ_{13}^{\infty}$ can only provides an idea of the system behaviour, not about the economics of a process which depend on many factors.

In most cases, a special technique based on the gas chromatographic determination of the solute retention time in a packed column filled with the IL as a stationary phase has been used [3], [5], [6], [8], [9], [10]. An alternative method is the “dilutor technique” [1], [2]. Values of $γ_{13}^{\infty}$ (where 1 refers to the solute = organic solvent, or water and 3 to the solvent = liquid phase ionic liquid) provide a useful tool for solvent selection in extractive distillation or solvent extraction processes. It is sufficient to know the separation factor of the components to be separated at infinite dilution in order to determine the applicability of a compound (a new IL) as a selective solvent.

In many publications, the activity coefficients at infinite dilution, $γ_{13}^{\infty}$ have been determined for alkanes, alk-1-enes, alk-1-ynes, cycloalkanes, aromatic hydrocarbons, carbon tetrachloride, and methanol in the IL at different temperatures. For example for 1-ethyl-3-methylimidazolium thiocyanate, [EMIM][SCN] for every hydrocarbon (alkane, cycloalkane, alk-1-ene, and alk-1-yne) the activity coefficient increases with an increase of the carbon chain/ring length [4]. Usually, the value of activity coefficient decreases when the interaction between the solvent and the IL increases. It can be seen from comparison of the activity coefficients, $γ_{13}^{\infty}$ for different aromatic hydrocarbons, or alcohols in ILs [3], [6], [9]. The value of the activity coefficient in water is the lowest in comparison with alcohols, or benzene [4]. The influence of the alkyl chain in the cation of IL for the bis {(trifluoromethyl)sulfonyl}imide anion, [Tf₂N]⁻ shows that for hexane, hex-1-ene, benzene, and cyclohexane the increase of the alkyl chain at the cation decreases the activity coefficient for every kind of hydrocarbon in the IL. It is found that the selectivities and capacities of different solutes are dependent on the opposite direction on the alkyl chain length of the cation of the IL. From the wide analysis of these two parameters, it was deduced that the best IL for the economic realization of the separation of aromatics and aliphatics is 1-butyl-3-methylimidazolium bis {(trifluoromethyl)sulfonyl}imide, [BMIM][Tf₂N] [9]. The partial molar excess enthalpies at infinite dilution values $Δ H_{1}^{E \infty}$ , were found to increase within the increasing carbon number of solute in each of the series: alkane, alk-1-ene, alk-1-yne, and cycloalkane [1], [3], [5], [6], [8], [9].

The selectivity $S_{ij}^{\infty}$ values for the separation of the {hexane (i) + benzene (j)} for example at T = 298.15 K using different IL compounds and some very polar solvents used in industry have values up to 95.4 for the [EMIM][SCN] [4]. The results demonstrate also a significant influence of the cation on the $S_{ij}^{\infty}$ values. For a given anion [Tf₂N]⁻, the values of $S_{ij}^{\infty}$ are much higher for the shorter alkyl chain at the imidazole ring. The results at T = 298.15 K for [MMIM]⁺, or [EMIM]⁺, or [BMIM]⁺ and [HMIM]⁺ are 30.8, or 24.5, or 16.7 or 12.4, respectively [1], [9]. It was shown earlier in many investigations that the selectivities of ILs in separating organic liquids are often higher than those for commonly used solvents, such as NMP, or (NMP + water). Comparing different results for many ILs, the selectivity $S_{ij}^{\infty}$ and capacity values for the separation of the {hexane (i) + benzene (j)} mixture have to be calculated; also the density, viscosity, toxicity, and cost for the investigated IL have to be discussed. The results presented show that the activity coefficients and intermolecular interactions of different solutes with the IL are very much dependent on the chemical structure of the IL.

Some ILs were found few years ago as good entrainers for the aliphatic/aromatic separation: 1-methyl-3-methylimidazolium methylsulphate, [MMIM][CH₃SO₄], or 1-ethyl-3-methyl ethylsulphate, [EMIM][C₂H₅SO₄], and 4-methyl-N-butylpyridinium salt, [MBPy][BF₄] have been chosen as the best ILs for the experiment [12]. It was shown that the [MBPy][BF₄] IL is the best for highest capacity and selectivity [12]. In conclusion, the examination has to be always done for selectivity together with capacity in a variety of solutes in ILs to provide a picture of interactions and costs.

This paper presents values of $γ_{13}^{\infty}$ for 32 solutes (alkanes, alken-1-es, alkyn-1-es, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, tetrahydrofuran, tert-butyl methyl ether, and water) in the ionic liquid [BMIM][SCN] over the temperature range from T = 298.15 K to T = 368.15 K. This particular ionic liquid was chosen after analysis of the influence of anion of IL on the selectivity and after very good results, obtained with [EMIM][SCN] [4].

Section snippets

Materials

The ionic liquid 1-butyl-3-methylimidazolium thiocyanate, [BMIM][SCN] had a purity of >0.98 mass fraction and was supplied by Fluka. Structure of investigated ionic liquid is presented below.

The ionic liquid was further purified by subjecting the liquid to a very low pressure of about 5 · 10⁻³ Pa at temperature about 343 K for approximately 5 h. This procedure removed any volatile chemicals and water from the ionic liquid. The solutes (alkanes, alken-1-es, alkyn-1-es, cycloalkanes, aromatic

Theoretical basis

The equation developed by Everett [16] and Cruickshank et al. [17] was used in this work to calculate the $γ_{13}^{\infty}$ of solutes in the ionic liquid $\ln γ_{13}^{\infty} = \ln (\frac{n_{3} RT}{V_{N} P_{1}^{*}}) - \frac{P_{1}^{*} (B_{11} - V_{1}^{*})}{RT} + \frac{P_{o} J_{2}^{3} (2 B_{12} - V_{1}^{\infty})}{RT} .$

In this work, subscript 1 refers to a solute, 2 refers to the carrier gas, and 3 refer to the solvent, [BMIM][SCN]. The n₃ is the number of moles of solvent on the column packing, R is the gas constant, T the column temperature, V_N denotes the net retention volume of the solute, $P_{1}^{*}$ the saturated vapour

Results and discussion

Table 1 lists the average values of $γ_{13}^{\infty}$ determined using the two columns packed with solvent over the temperature range from T = 298.15 K to T = 368.15 K and partial molar excess enthalpies at infinite dilution $Δ H_{1}^{E, \infty}$ determined from the Gibbs–Helmholtz equation: $\frac{\partial \ln γ_{i}^{\infty}}{\partial (1 / T)} = \frac{Δ H_{1}^{E, \infty}}{R} .$

The $Δ H_{1}^{E, \infty}$ is a basic thermodynamic function, calculated from the experimental results, which inform us about the fundamental interaction between solute and solvent. In general, within each of the series: alkane,

Conclusions

Activity coefficients at infinite dilution for various solutes in the ionic liquid [BMIM][SCN] were determined over the temperature range from T = 298.15 K to T = 368.15 K using the GLC method. It was found that the ionic liquid investigated shows definitely the highest selectivities at infinite dilution compared with any other ionic liquids measured to date and higher than the [EMIM][SCN], which are the typical entrainers such as NMP or sulfolane actually used in separation processes of aliphatic

Acknowledgment

Funding for this research was provided by the Ministry of Science and Higher Education in years 2008-2011(Grant N N209 096435).

References (29)

R. Kato et al.
Fluid Phase Equilib.
(2004)
U. Domańska et al.
J. Chem. Thermodyn.
(2008)
T.M. Letcher et al.
J. Chem. Thermodyn.
(2005)
F. Mutelet et al.
J. Chem. Thermodyn.
(2007)
F. Mutelet et al.
J. Chromatogr. A
(2006)
C.F. Poole
J. Chromatogr. A
(2004)
L. Alonso et al.
Fluid Phase Equilib.
(2008)
M. Krummen et al.
J. Chem. Eng. Data
(2002)
U. Domańska et al.
J. Phys. Chem. B
(2007)
T.M. Letcher et al.
J. Chem. Thermodyn.
(2005)

T.M. Letcher et al.

J. Chem. Eng. Data

(2005)

T.M. Letcher et al.

J. Chem. Eng. Data

(2003)

T.M. Letcher et al.

J. Chem. Eng. Data

(2003)

B. Kolbe et al.

Ber. Bunsen-Ges. Phys. Chem.

(1979)

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^☆: Presented at the 20th International Conference on Chemical Thermodynamics, Warsaw, Poland, 3–8 August 2008.

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Measurements of activity coefficients at infinite dilution of aliphatic and aromatic hydrocarbons, alcohols, thiophene, tetrahydrofuran, MTBE, and water in ionic liquid [BMIM][SCN] using GLC☆

Abstract

Introduction

Section snippets

Materials

Theoretical basis

Results and discussion

Conclusions

Acknowledgment

Fluid Phase Equilib.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chromatogr. A

J. Chromatogr. A

Fluid Phase Equilib.

J. Chem. Eng. Data

J. Phys. Chem. B

J. Chem. Thermodyn.

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Chem. Eng. Data

Ber. Bunsen-Ges. Phys. Chem.