Elsevier

Fluid Phase Equilibria

Volume 378, 25 September 2014, Pages 102-106
Fluid Phase Equilibria

Ternary liquid–liquid equilibria of bis(trifluoromethylsulfonyl)-amide based ionic liquids + 2-propanol + di-iso-propyl ether

https://doi.org/10.1016/j.fluid.2014.06.028Get rights and content

Highlights

  • Ternary LLE for [NTf2] anion based ILs + 2-propanol + DiPE.

  • Influence of IL cation structure on S and β is discussed.

  • The highest selectivity for separation of 2-propanol/DiPE is observed for [COC2mMOR][NTf2].

Abstract

Ternary liquid–liquid equilibria for 3 systems containing ionic liquids 4-(2-methoxyethyl)-4-methylmorpholinium bis(trifluoromethylsulfonyl)-amide, 1-(2-methoxyethyl)-1-methylpiperidinium bis(trifluoromethylsulfonyl)-amide, 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)-amide) + 2-propanol + di-iso-propyl ether have been determined at T = 298.15 K. The solute distribution coefficient and the selectivity were calculated for all systems. The experimental results have been correlated using NRTL model. The influence of cation structure on selectivity and solute distribution ratio is discussed.

Introduction

Some ethers and alcohols form azeotropic mixtures [1]. The separation of such mixtures by rectification is impossible, therefore other method of separation should be used, for example liquid–liquid extraction, but in this case there is a need to choose of appropriate entrainer. A lot of works show that ionic liquids (ILs) can be successfully used in separation of azeotropic mixtures like thiophene/alkane [2], [3], [4], [5], [6], [7], aromatic/aliphatic hydrocarbons [2], [8], alcohols/alkanes [9], [10] as well as other mixtures [11], [12], [13]. Ionic liquids are non-volatile which makes them good entrainers in separation processes. To apply an ionic liquid as extractant in liquid–liquid extraction the measurements of ternary liquid–liquid equilibria is needed as well as calculations of selectivity and solute distribution ratio.

In this work the influence of the cation structure on the ternary liquid–liquid equilibria (LLE) of three ionic liquids based on bis(trifluoromethylsulfonyl)amide anion + 2-propanol + di-iso-propyl ether (DiPE) is presented. The list of ionic liquids is as follows: 4-(2-methoxyethyl)-4-methylmorpholinium bis(trifluoromethylsulfonyl)-amide, [COC2mMOR][NTf2], 1-(2-methoxyethyl)-1-methylpiperidinium bis(trifluoromethylsulfonyl)-amide, [COC2mPIP][NTf2], 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)-amide), [COC2mPYR][NTf2]. 2-Propanol and DiPE forms azeotropic mixture at 0.141 mass fraction of alcohol at T = 339.4 K [1].

There is no literature data on the ternary LLE for the systems ionic liquid + 2-propanol + DiPE therefore such studies are needed. This work is a continuation of our systematic study of the physicochemical properties of ionic liquids. In our previous works [6], [14], [15], [16], [17] the basic physicochemical properties of investigated ionic liquids were tested, such as: densities and viscosities as a function of temperature; decomposition temperatures; glass transition temperatures, and change of heat capacity at the glass transition temperatures [6] as well as activity coefficients at infinite dilution for organic solutes and water in the investigated ILs as a function of temperature [14], [15], [16] and ternary LLE at T = 298.15 K for systems IL + thiophene + heptane [17] and IL + methanol + heptane [6]. These ionic liquids exhibit a very good extraction property especially in the separation of methanol + heptane mixture and quite good extraction properties in the case of separation of thiophene + heptane system. Selectivity determined on the basis of the activity coefficients at infinite dilution are not high for investigated ILs and are as follows: 4.0, 2.7 and 2.8 (extrapolated values to T = 298.15 K) for [COC2mMOR][NTf2], [COC2mPIP][NTf2] and [COC2mPYR][NTf2], respectively [14], [15], [16]. On the basis of these data it can be expected that the extraction properties of investigated ILs for the system 2-propanol + DiPE will not be good, but it should be confirmed by measurements of ternary LLE.

Section snippets

Chemicals

The list of chemicals used in this study is presented in the Table 1 (including abbreviations of ILs). The structures, densities, viscosities, decomposition temperatures of investigated ionic liquids were presented in previous work [6], [14]. The ionic liquids were further purified by subjecting the liquid to a very low pressure of about 5 × 10−3 Pa at a temperature about 95 °C for ca. 5 h. This procedure removed any volatile chemicals and water from the ionic liquid. Analysis of the rest of

Modeling

The LLE was correlated with the NRTL model describing the excess Gibbs energy [18]. The NRTL nonrandom parameter α was set to a value of α = 0.3, which has given the best results of the correlation. The results of the correlation, values of the model parameters, and the corresponding standard deviations, σx defined as:σx=k=1Ni=13((xi,kIL,expxi,kIL,calc)2+(xi,kS,expxi,kS,calc)2)6Nwhere N is the number of tie lines, are given in Table 2. The results of the correlation are presented in Fig. 1,

Results and discussion

The compositions of the experimental tie-lines for the ternary systems IL + 2-propanol + di-iso-propyl ether at T = 298.15 K are reported in Table 3. The corresponding triangular diagrams with the experimental tie-lines for each system are shown in Fig. 1, Fig. 2, Fig. 3.

Values of selectivity S and solute distribution ratio β reported in Table 3 are calculated from experimental data according to equations:S=x2ILx3Sx2Sx3ILβ=x2ILx2Swhere x is the mole fraction, subscripts 2 and 3 refer to 2-propanol and

Conclusions

An experimental investigation on liquid–liquid equilibria of the ternary mixtures composed of tree ionic liquids based on bis(trifluoromethylsulfonyl)-amide anion + 2-propanol + di-iso-propyl ether has been carried out at T = 298.15 K. Obtained results indicate that the investigated ionic liquids could be used as entrainers in the separation of 2-propanol from di-iso-propyl ether but there are other ionic liquids, for which the selectivity calculated from the activity coefficients at infinite dilution

Acknowledgment

Author would like to thank to Warsaw University of Technology.

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