Elsevier

Fluid Phase Equilibria

Volume 298, Issue 2, 25 November 2010, Pages 287-292
Fluid Phase Equilibria

Gas-liquid chromatography measurements of activity coefficients at infinite dilution of hydrocarbons and alkanols in 1-alkyl-3-methylimidazolium bis(oxalato)borate

https://doi.org/10.1016/j.fluid.2010.08.016Get rights and content

Abstract

The activity coefficients at infinite dilution, γi for various solutes: alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols in the ionic liquids 1-butyl-3-methylimidazolium bis(oxalato)borate [BMIM][BOB] and 1-hexyl-3-methyl-imidazolium bis(oxalato)borate [HMIM][BOB] have been determined by gas-liquid chromatography at the temperatures ranging from 308 to 348 K. The partial molar excess enthalpies at infinite dilution HiE, of the solutes in the ionic liquids were also derived from the temperature dependence of the γi values. The selectivities for the hexane/benzene, cyclohexane/benzene and hexane/hexene separation problems were calculated from experimental infinite dilution activity coefficient values and compared to the other ionic liquids, taken from the recent literatures.

Introduction

This work is a continuation of our investigations on the determination of activity coefficients at infinite dilution for many organic solutes in ionic liquids using gas-liquid chromatography. Our previous work includes measurements of γi for organic solutes in the ionic liquids (ILs): 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [EMIM][FAP] [1] and 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] [2]. Due to their unique properties such as no flammability, wide liquid range, stability at high temperatures, and negligible vapor pressure, so not surprisingly, one of the most significant applications for ionic liquids is using them as solvents for clean liquid–liquid extraction replacement for conventional volatile, flammable and toxic organic solvents [3], [4]. Activity coefficients at infinite dilution of a solute i (γi) is a suitable and widely accepted approach for quantify the volatility of the solute as well as to provide information on the intermolecular energy between solvent and solute [5], [6]. Since ILs have a negligible vapor pressure, the gas-liquid chromatography (GLC) using the ionic liquid as stationary phase has been proven to be a good method for measuring activity coefficients at infinite dilution γi.

Until now, there are so many publications about the ILs based on some common anions, such as bis(trifluoromethanesulfonyl)imide[NTf2] [7], [8], [9], [10], [11], [12], [13], tetrafluoroborate [BF4] [14], [15], [16], [17], hexafluorophosphate [PF6] [18] and trifluoromethanesulfonate [CF3SO3] [19], [20], [21]. In order to expand our knowledge about the nature of ILs, influence of the anion structure on the thermodynamic properties of the disubstituted imidazolium based ionic liquid with bis(oxalato)borate [BOB] anion was studied in this work. For this study, activity coefficients at infinite dilution, γi values for 23 solutes: alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols in the ionic liquids 1-butyl-3-methylimidazolium bis(oxalato)borate [BMIM][BOB] and 1-hexyl-3-methyl-imidazolium bis(oxalato)borate [HMIM][BOB] have been determined over the temperatures range from (308 to 348) K. The partial molar excess enthalpies at infinite dilution, HiE,, of these solutes in the ionic liquids were also derived from the temperature dependence of the γi values. This work also intends to provide information about the slight modification in the length of these substituents and its influence on the value of γi and selectivity of ionic liquids based on the bis(oxalato)borate anion.

Section snippets

Materials

1-Alkyl-3-methylimidazolium bis(oxalato)borate (R = butyl, hexyl) were synthesized from 1-alkyl-3-methylimidazolium bromide (R = butyl, hexyl) with lithium bis(oxalato)borate (LiBOB) according to the procedures [22]. A silver nitrate test was performed on the RTIL and indicated that a less than 50 ppm of bromide ion impurity existed in the RTIL. The ionic liquids were purified and dried under high vacuum at 343 K for 24 h to remove organic solvents and water, and its structure was confirmed by 1H NMR,

Theoretical basis

The equation developed by Everett [24] and Cruickshank et al. [25] was used in this work to calculate the γi of solutes in the ionic liquid:lnγ13=lnn3RTVNP1*P1*(B11V1*)RT+PoJ(2B12V1)RTVN is the standardized retention volume of the solute, Po is the outlet pressure, n3 is the number of moles of the ionic liquid on the column packing, T is the column temperature, P1* is the saturated vapor pressure of the solute at temperature T, B11 is the second virial coefficient of the pure solute, V1*

Results and discussion

Table 1, Table 2 list the values of γi of different solutes (alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols) in the ionic liquids [BMIM][BOB] and [HMIM][BOB] in the temperature range from 308 to 348 K and partial molar excess enthalpies at infinite dilution HiE,, determined from the Gibbs–Helmholtz equation:lnγi(1/T)=HiE,R

Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8 show the natural logarithm of the activity coefficients in the ionic

Conclusions

Activity coefficients at infinite dilution for various solutes (alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols) in the ionic liquids 1-butyl-3-methylimidazolium bis(oxalato)borate [BMIM][BOB] and 1-hexyl-3-methyl-imidazolium bis(oxalato)borate [HMIM][BOB] were measured in the temperature range from 308 K to 348 K using GLC method. These results show the influence of the cation's and anion's alkyl chain length on the γi and Sij values. For the separation of

Acknowledgments

Funding for this research was provided by National Natural Science Foundation of China (NSFC No. 20901076), Knowledge Innovation Program of the Chinese Academy of Sciences, DICP (Grant No. K2009D03), and State Key Laboratory of Fine Chemicals (KF0811).

References (35)

  • P.-F. Yan et al.

    J. Chem. Thermodyn.

    (2010)
  • V. Dohnal et al.

    Fluid Phase Equilib.

    (1991)
  • T.M. Letcher et al.

    J. Chem. Thermodyn.

    (1976)
  • N.V. Gwala et al.

    J. Chem. Thermodyn.

    (2010)
  • U. Domanska et al.

    Fluid Phase Equilib.

    (2009)
  • U. Domanska et al.

    J. Chem. Thermodyn.

    (2009)
  • U. Domanska et al.

    J. Chem. Thermodyn.

    (2008)
  • P.-F. Yan et al.

    J. Chem. Eng. Data

    (2010)
  • J.G. Huddleston et al.

    Chem. Commun.

    (1998)
  • A.G. Fadeev et al.

    Chem. Commun

    (2001)
  • A.-L. Revelli et al.

    J. Chem. Eng. Data

    (2009)
  • T.M. Letcher et al.

    J. Chem. Eng. Data

    (2008)
  • J. Zhang et al.

    J. Chem. Eng. Data

    (2007)
  • A. Heintz et al.

    J. Chem. Eng. Data

    (2006)
  • A. Heintz et al.

    J. Chem. Eng. Data

    (2005)
  • A. Heintz et al.

    J. Chem. Eng. Data

    (2005)
  • Q. Zhou et al.

    J. Chem. Eng. Data

    (2006)
  • Cited by (0)

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