Activity coefficients at infinite dilution measurements for organic solutes in the ionic liquid 1-butyl-3-methyl-imidazolium 2-(2-methoxyethoxy) ethyl sulfate using g.l.c. at T = (298.15, 303.15, and 308.15) K

https://doi.org/10.1016/j.jct.2005.01.015Get rights and content

Abstract

The activity coefficients at infinite dilution, γ13 (where 1 refers to the solute and 3 to the solvent), for both polar and non-polar solutes in the ionic liquid 1-butyl-3-methyl-imidazolium 2-(2-methoxyethoxy) ethyl sulfate have been determined by gas-liquid chromatography. The interaction at the gas-liquid interface between the solutes and the solvent was examined by varying solvent liquid loading on the column. Corrected retention values, taking carrier gas and solute imperfections into account, were determined and used to calculate the activity coefficients at infinite dilution. In this work the activity coefficients at infinite dilution for various solutes (alkanes, alk-1-enes, alk-1-ynes, cycloalkanes, aromatic hydrocarbons, carbon tetrachloride and methanol) in the ionic liquid were measured at three temperatures T = (298.15, 303.15, and 308.15) K. This investigation is related to our previous work on the measurement of γ13 in the ionic liquid solvents: 1-methyl-3-octyl-imidazolium chloride or 1-hexyl-3-methyl-imidazolium tetrafluoroborate or 1-hexyl-3-methyl-imidazolium hexafluorophosphate or 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) imide.The results have again been used to predict the solvent potential for the hexane/benzene separation from calculated selectivity values. The results are compared to γ13 for similar systems found in the literature in an attempt to understand the effect the nature of the cation and anion has, on solute–solvent interactions.

The partial molar excess enthalpies at infinite dilution values, ΔH1E, were calculated from the experimental γ13 values obtained over the temperature range.

Introduction

Activity coefficients at infinite dilution, γ13 (where 1 refers to the solute and 3 to the solvent), provide a useful tool for solvent selection in extractive distillation or solvent extraction processes. It is sufficient to know the separation factor at infinite dilution, of the components to be separated, in order to determine the applicability of a compound (in this work, a new ionic liquid) as a selective solvent. This work is a continuation of our investigation on ionic liquids to determine activity coefficients at infinite dilution. Our group has previously measured the γ13 for organic volatile solutes in the ionic solvents: 1-methyl-3-octyl-imidazolium chloride [1], 1-hexyl-3-methyl-imidazolium tetrafluoroborate [2], 1-hexyl-3-methyl-imidazolium hexafluorophosphate [3] and 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) imide [4].

Ionic liquids (ILs) are under intense investigation, especially as replacement solvents for reaction and separations, since they exhibit negligible vapor pressure and would not, therefore, contribute to air pollution. ILs are salts that are liquid at low temperatures, which can be as low as room temperature [5].

The activity coefficients at infinite dilution, γ13, have been determined for alkanes, alk-1-enes, alk-1-ynes, cycloalkanes, aromatic hydrocarbons, carbon tetrachloride and methanol in the ionic liquid 1-butyl-3-methyl-imidazolium 2-(2-methoxyethoxy) ethyl sulfate, [BMIM][MDEGSO4], using gas-liquid chromatography at the temperatures T = (298.15, 303.15, and 308.15) K. The formula of anion of 1-butyl-3-methyl-imidazolium 2-(2-methoxyethoxy) ethyl sulfate is:[BMIM][CH3(OCH2CH2)2OSO3]The selectivity Sij is the ratio of activity coefficients at infinite dilution and is given by the equation Sij=γi3/γj3, where i and j refer to the liquids to be separated and in this work refer to hexane and benzene, respectively. The selectivity value is used to determine the potential of the ionic solvent for extractive distillation in the separation of aromatic compounds from aliphatic compounds [6].

Gas-liquid chromatography is a well-established and accurate method that is used to obtain γ13 [7], [8]. The partial molar excess enthalpies at infinite dilution values, ΔH1E, were also calculated from the γ13 values obtained over the temperature range.

Section snippets

Materials or chemicals

The ionic liquid ECOENG™41M, [BMIM][MDEGSO4], had a purity of >0.98 mass fraction and was supplied by Solvent Innovation. The ionic liquid was further purified by subjecting the liquid to a very low pressure of about 5 × 10−3 Pa at room temperature for approximately 30 min. This procedure removed any volatile chemicals and water from the ionic liquid. A Karl–Fischer titration method using methanol showed that the water concentration in the ionic liquid was less than 0.001 mass percent. The solutes:

Theory

The equation developed by Everett [11] and Cruickshank et al. [12]lnγ13=lnn3RTVNP1-(B11-V1)P1RT+(2B12-V1)PoJ23RTwas used in this work to calculate the γ13 of solutes in the ionic liquid. The VN denotes the net retention volume of the solute, Po the outlet pressure, PoJ23 the mean column pressure, n3 the number of moles of solvent on the column packing, the column temperature T, P1 the saturated vapor pressure of the solute at temperature T, B11 the second virial coefficient of pure

Results and discussion

Table 3 lists the average γ13 values for the varying amounts of solvent on the solid packing at T = (298.15, 303.15, and 308.15) K. The γ13 value for the n-alkanes, alk-1-enes, alk-1-ynes and cycloalkanes increases with an increase in carbon number. FIGURE 1, FIGURE 2, FIGURE 3 show the natural logarithm of the activity coefficients in the ionic liquid as a function of the inverse absolute temperature for four alkanes, three alkynes and three cycloalkanes, respectively. For the small temperature

Acknowledgments

The authors thank the FRD (South Africa) and KBN (Poland) for financial support for this work according to Polish–South African agreement of co-operation.

References (20)

  • J.W. Bayles et al.

    J. Chem. Thermodyn.

    (1993)
  • T.M. Letcher et al.

    J. Chem. Thermodyn.

    (1995)
  • A. Heintz et al.

    J. Chem. Thermodyn.

    (2002)
  • D. Warren et al.

    J. Chem. Thermodyn.

    (2003)
  • T.M. Letcher et al.

    J. Chem. Eng. Data

    (2003)
  • T.M. Letcher et al.

    J. Chem. Eng. Data

    (2003)
  • N. Deenadayalu et al.

    J. Chem. Eng. Data

    (2005)
  • K.R. Seddon

    Kinet. Catal.

    (1996)
  • D. Tiegs, J. Gmehling, A. Medina, M. Soares, J. Bastos, P. Alessi, I. Kikic, Activity Coefficients at Infinte Dilution,...
  • C.L. Young et al.

    Physicochemical measurements by gas chromatography

    (1979)
There are more references available in the full text version of this article.

Cited by (71)

  • Determination of physicochemical properties of ionic liquids by gas chromatography

    2021, Journal of Chromatography A
    Citation Excerpt :

    The experimental procedure employed by these authors has changed little in contemporary studies. Infinite dilution activity coefficients for ionic liquids have been determined by gas chromatography at temperatures within the range 25°C < T < 105°C, support loadings typically from 30 to 60 % (w/w), and on columns generally ≤ 1 m, Table 3 [27,35-38,47,50,56,67-71,78-236]. Columns of different length and phase loading are used to accommodate the wide range of retention times and to evaluate the repeatability of the measurements.

  • MOSCED parameters for 1-n-alkyl-3-methylimidazolium-based ionic liquids: Application to limiting activity coefficients and intuitive entrainer selection for extractive distillation processes

    2019, Journal of Molecular Liquids
    Citation Excerpt :

    It is therefore important that the reference data set be screened for suspect data points prior to the regression. To accomplish this, we used the compiled reference data set of Paduszyński [68] that was screened for suspect data when parameterizing his machine learning based models for limiting activity coefficients of nonelectrolytes in ILs [44,58,59,64,69-112]. Additionally, in the present study, we are restricted to solutes for which MOSCED parameters currently exist.

View all citing articles on Scopus
View full text