Osmotic coefficients and apparent molar volumes of 1-hexyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid in alcohols

https://doi.org/10.1016/j.jct.2013.09.041Get rights and content

Highlights

Abstract

In this work, density for the binary mixtures of 1-hexyl-3-methylimidazolium trifluoromethanesulfonate in alcohols (1-propanol, or 2-propanol, or 1-butanol, or 2-butanol, or 1-pentanol) was measured at T = 323.15 K and atmospheric pressure. From this property, the corresponding apparent molar volumes were calculated and fitted to a Redlich–Meyer type equation. For these mixtures, the osmotic and activity coefficients, and vapor pressures of these binary systems were also determined at the same temperature using the vapor pressure osmometry technique. The experimental osmotic coefficients were modeled by the Extended Pitzer model of Archer. The parameters obtained in this correlation were used to calculate the mean molal activity coefficients and the excess Gibbs free energy for the studied mixtures.

Introduction

Ionic liquids (ILs) are salts with a melting point lower than 100 °C. As it is known, these solvents have interesting properties, which make them attractive for a number of applications. Some of these properties are their negligible vapor pressure, their non-flammability, their chemical stability and their excellent solubility for organic and inorganic compounds. Due to their relative novelty, there is still a lack of experimental data, especially concerning physical properties and phase behavior, which becomes vital for the application of ILs in industrial processes or for developing thermodynamic models.

Studies of thermodynamic properties of mixtures containing ILs mixed with other compounds are crucial because they provide useful information to understand the behavior of these liquid salts in common solvents. As example, density and derived properties are usually required to develop specific thermodynamic models and they are also of great relevance in assessing intermolecular interactions between the ionic liquid and the solvent. The calculation of osmotic and activity coefficients allows to analyze the nonideality of mixtures, studying their thermodynamics, and to test the usually used thermodynamic tools. To date, most of the works are based on the study of physical properties of ILs in water, while the studies of non-aqueous mixtures containing ILs are still not abundant [1], [2], [3], [4], [5].

This paper is an extension of our studies on volumetric and osmotic properties of ILs in alcohols [6], [7]. In this work, densities for the binary mixtures {1-propanol (1), or 2-propanol (1), or 1-butanol (1), or 2-butanol (1), or 1-pentanol (1) + 1-hexyl-3-methylimidazolium trifluoromethanesulfonate (2)} are reported at T = 323.15 K and atmospheric pressure. From these data, the corresponding apparent molar volumes were obtained and fitted to a Redlich–Meyer type equation [8]. On the other hand, a vapor pressure osmometry technique was used to obtain osmotic and activity coefficients and vapor pressures of the above mentioned binary mixtures. The Extended Pitzer model modified by Archer [9], [10] was used for modeling the experimental data. Finally, the mean molal activity coefficients and the excess Gibbs free energy for the studied binary mixtures were calculated from the obtained parameters.

The ionic liquid studied in this work was selected in order to compare the experimental results obtained here with those previously published for the binary mixtures of 1-butyl-3-methylimidazolium trifluoromethanesulfonate in alcohols [7]. The comparison of these results allows evaluating the effect of the alkyl chain length of the cation on the properties reported in this work.

To our knowledge, some papers containing physical property data for the pure ionic liquid were previously published [11], [12], [13]; nevertheless, the experimental data reported in this work were not previously determined.

Section snippets

Chemicals

The ionic liquid 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, [HMim][TfO], was supplied by Iolitec GmbH (Germany) with a purity higher than 0.990 by mass. Prior to its use, this compound was dried under vacuum (p = 2 · 10−1 Pa; T = 323.15 K). The water content, ww, for the dried ionic liquid was 520 ppm.

Alcohols were purchased in specialized companies. They were ultrasonically degassed and dried over molecular sieves type 4 · 10−10 m, supplied by Aldrich, and kept in bottles under inert

Apparent molar volume

In this work, densities, ρ, for the binary systems of [HMim][TfO] in alcohols (1-propanol (1), or 2-propanol (1), or 1-butanol (1), or 2-butanol (1), or 1-pentanol (1)) were measured at T = 323.15 K and atmospheric pressure. The experimental data, which are reported in table 2, show that this physical property increases with molality, following a similar behavior to that presented by alcoholic solutions of “classical” electrolytes [17], [18]. Moreover, density data decrease in the order: 1-pentanol

Conclusions

In this study, densities and apparent molar volumes for mixtures containing [HMim][TfO] ionic liquid and alcohols (1-propanol, or 2-propanol, or 1-butanol, or 2-butanol, 1-pentanol) are reported at T = 323.15 K. A Redlich–Meyer type equation was applied to fit the apparent molar volumes. Then, the corresponding apparent molar volumes at infinite dilution were also calculated.

The obtained results show that apparent molar volume for [HMim][TfO] in primary and secondary alcohols increases with

Acknowledgements

This work is partially supported by project PEst-C/EQB/LA0020/2011, financed by FEDER through COMPETE – Programa Operacional Factores de Competitividade and Fundação para a Ciência e a Tecnologia – FCT (Portugal). Emilio J. González and Noelia Calvar are thankful to FCT for awarding their postdoctoral grants (SFRH/BPD/70776/2010 and SFRH/BPD/37775/2007, respectively).

References (33)

  • R. Sadeghi et al.

    J. Chem. Thermodyn.

    (2009)
  • M.T. Zafarani-Moattar et al.

    J. Chem. Thermodyn.

    (2005)
  • A.V. Orchillés et al.

    J. Chem. Thermodyn.

    (2006)
  • N. Calvar et al.

    J. Chem. Thermodyn.

    (2012)
  • E.J. González et al.

    J. Chem. Thermodyn.

    (2013)
  • S. Nebig et al.

    Fluid Phase Equilib.

    (2010)
  • B. González et al.

    J. Chem. Thermodyn.

    (2008)
  • M.T. Zafarani-Moattar et al.

    J. Chem. Thermodyn.

    (2007)
  • J. Wawer et al.

    J. Chem. Thermodyn.

    (2008)
  • N. Calvar et al.

    J. Chem. Thermodyn.

    (2010)
  • E. Gómez et al.

    J. Chem. Thermodyn.

    (2011)
  • N. Calvar et al.

    Fluid Phase Equilib.

    (2012)
  • N. Calvar et al.

    J. Chem. Thermodyn.

    (2011)
  • N. Calvar et al.

    J. Chem. Thermodyn.

    (2009)
  • N. Calvar et al.

    J. Chem. Thermodyn.

    (2009)
  • H. Shekaari et al.

    J. Chem. Thermodyn.

    (2009)
  • Cited by (14)

    • Equilibrium in electrolyte systems

      2018, Thermodynamics of Phase Equilibria in Food Engineering
    • (Vapor + liquid) equilibria of alcohol + 1-methyl-1-propylpiperidinium triflate ionic liquid: VPO measurements and modeling

      2016, Journal of Chemical Thermodynamics
      Citation Excerpt :

      It has been proven that it can also be useful for the determination of thermophysical properties of ionic liquids [6–9]. Some studies have been published in the literature, where VPO is used for osmotic and activity coefficients determination with alcohols [10–13]. The VPO technique has many advantages as high accuracy, lower cost, small sample volume, ability to work with viscous substances [14].

    • Conductometric and spectroscopic studies of cetyltrimethylammonium bromide in aqueous solutions of imidazolium based ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate

      2015, Journal of Molecular Liquids
      Citation Excerpt :

      The anions are usually halides, PF6−, BF4− and SCN−. Several studies have been done on imidazolium based ILs with different anions like BF4− [19–21], PF6− [22–24], Cl− [25,26], Br− [27–29], DCA− [30], [CF3SO3]− [31,32] and [SCN]− [33]. The aggregation behavior of surfactant molecules in ILs is of great interest both from environmental and academic points of view.

    View all citing articles on Scopus
    View full text