Vapour pressures and osmotic coefficients of binary mixtures containing alcohol and pyrrolidinium-based ionic liquids

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Highlights

Abstract

The osmotic and activity coefficients and vapour pressures of mixtures containing primary (1-propanol, 1-butanol and 1-pentanol) and secondary (2-propanol and 2-butanol) alcohols with pyrrolidinium-based ionic liquids (1-butyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide, C4MpyrNTf2, and 1-butyl-1-methyl pyrrolidinium trifluoromethanesulfonate, C4MpyrTFO) have been experimentally determined at T = 323.15 K. For the experimental measurements, the vapour pressure osmometry technique has been used. The results on the influence of the structure of the alcohol and of the anion of the ionic liquid on the determined properties have been discussed and compared with literature data. For the correlation of the osmotic coefficients obtained, the Extended Pitzer model of Archer and the Modified Non-Random Two Liquids model were applied. The mean molal activity coefficients and the excess Gibbs energy for the studied mixtures were calculated from the parameters obtained in the correlation.

Introduction

The vapour pressure osmometry technique (VPO) is usually used for the characterisation of diverse mixtures [1], [2], [3], [4] or for the determination of the molar mass of polymers [5], [6], [7]. The main advantages of this technique are, among others, its high accuracy, the fact that it is less time-consuming than other techniques and that it is enough a small amount of sample to perform the experiment. These advantages led some researchers to apply this technique for the characterisation of systems containing ionic liquids (ILs) [8], [9], [10], [11], [12], [13], [14], [15], [16]. The osmotic and activity coefficients, as well as the vapour pressures of mixtures composed by organic solvents and ILs are important to understand the non-ideality and thermodynamic behaviour of these systems.

In this work, osmotic and activity coefficients and vapour pressures of binary mixtures containing 1-propanol or 2-propanol with 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, C4MpyrNTf2, and 1-propanol or 2-propanol or 1-butanol or 2-butanol or 1-pentanol with 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, C4MpyrTFO, have been experimentally determined at T = 323.15 K using the VPO technique. These data have been compared with those taken from the literature [17], [18], [19] with the corresponding imidazolium and pyridinium-based liquids in order to analyse the influence of the cation of the ionic liquid on the behaviour of the mixtures.

The results obtained have been correlated using the ion-interaction Extended Pitzer model of Archer [20], [21], and the local composition model Modified Non-Random Two Liquid (MNRTL) [22]. Besides, from the parameters obtained, the mean molal activity coefficients and the excess Gibbs energy for the binary mixtures studied have been also calculated.

Section snippets

Chemicals

The suppliers and purities of the chemical used in this work are presented in table 1. Before the experimental measurements, the ionic liquids were subjected to vacuum (p = 2 · 10−1 Pa) at moderate temperature (T = 323.15 K) to reduce the content of volatile compounds and water. Besides, ionic liquids were stored in bottles under an argon atmosphere to preserve their purity. All the alcohols were degassed ultrasonically and dried over molecular sieves type 4 · 10−10 m, supplied by Aldrich, and kept in an

Results and discussion

The osmotic coefficients of the binary mixtures containing 1-propanol or 2-propanol with C4MpyrNTf2, and 1-propanol or 2-propanol or 1-butanol or 2-butanol or 1-pentanol with C4MpyrTFO were experimentally determined in the molality range (0.05 to 3.30 mol · kg−1) at T = 323.15 K.

From the measured output ΔR, the osmotic coefficients can be determined using the next relation:νϕm=kΔRwhere ν is the number of ions into which the electrolyte dissociates (ν = 2 in case of these ionic liquids), and k is the

Conclusions

The osmotic and activity coefficients together with the vapour pressures for the binary mixtures containing the pyrrolidinium-based ionic liquids 1-butyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide, C4MpyrNTf2 with 1-propanol, or 2-propanol, and 1-butyl-1-methyl pyrrolidinium trifluoromethanesulfonate, C4MpyrTFO with 1-propanol or 2-propanol or 1-butanol or 2-butanol or 1-pentanol were determined at T = 323.15 K using the VPO technique.

From the results obtained, it can be deduced that

Acknowledgements

This work was 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) and by the FSE. Noelia Calvar is thankful to FCT for awarding her postdoctoral grant (SFRH/BPD/37775/2007).

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