Acoustic, volumetric and osmotic properties of binary mixtures containing the ionic liquid 1-butyl-3-methylimidazolium dicyanamide mixed with primary and secondary alcohols

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Abstract

In this paper, densities and speeds of sound for five binary systems {alcohol + 1-butyl-3-methylimidazolium dicyanamide} were measured from T = (293.15 to 323.15) K and atmospheric pressure. From these experimental data, apparent molar volume and apparent molar isentropic compression have been calculated and fitted to a Redlich–Meyer type equation. This fit was also used to calculate the apparent molar volume and apparent molar isentropic compression at infinite dilution for the studied binary mixtures. Moreover, the osmotic and activity coefficients and vapor pressures of these binary mixtures were also determined at T = 323.15 K using the vapor pressure osmometry technique. The experimental osmotic coefficients were correlated using the Extended Pitzer model of Archer. The mean molal activity coefficients and the excess Gibbs free energy for the studied mixtures were calculated from the parameters obtained in the correlation.

Highlights

► Physical and osmotic properties of binary mixtures {alcohol + [BMim][dca]} were measured. ► From experimental data, apparent molar properties and osmotic coefficients were calculated. ► The apparent properties were fitted using a Redlich–Meyer type equation. ► The osmotic coefficients were correlated using the Extended Pitzer and the MNRTL models.

Introduction

In the last years, ionic liquids (ILs) have become a new class of green benign solvents because of their unique properties such as low melting points, chemical and thermal stability, extensive liquid range, non-flammability, ability to dissolve a wide variety of materials, and their negligible vapor pressure, which allow their easy recovery.

In order to understand the role of these ionic compounds when they are mixed with other solvents, systematic studies of thermodynamic properties of mixtures containing ILs are very necessary. In this way, acoustic and volumetric data are of great importance in studying the intermolecular interactions between the IL and solvent and also for the development of thermodynamic models specific to these systems. Until now, several researchers have studied thermophysical properties of aqueous solutions of ILs, while accurate thermodynamic in non-aqueous solvents are very scarce for ionic liquids [1], [2], [3], [4], [5].

On the other hand, the osmotic and activity coefficients are useful to get a deeper knowledge about the nonideality of mixtures, especially about their thermodynamic behavior, and for testing the validity of usual thermodynamic tools. There are several methods to obtain these thermodynamic data, and despite the advantages of the vapor pressure osmometry (VPO) technique, such as its high accuracy, being less time-consuming than other techniques used for (vapor + liquid) equilibria, and the fact that small amounts are enough for the experiments, it is still scarcely used in the determination of coefficients of mixtures containing ionic liquids [4], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21].

In this work, densities and speeds of sound for the binary mixtures {1-propanol (1), or 2-propanol (1), or 1-butanol (1), or 2-butanol (1), or 1-pentanol (1) + 1-butyl-3-methylimidazolium dicyanamide (2)} were measured from T = (293.15 to 323.15) K and atmospheric pressure. From these experimental data, apparent molar volume and apparent molar isentropic compression were calculated and fitted to a Redlich–Meyer type equation [22], which was also used to calculate the apparent molar volume and apparent molar isentropic compression at infinite dilution. Moreover, osmotic and activity coefficients and vapor pressures of binary systems containing primary and secondary alcohols were determined at T = 323.15 K using the vapor pressure osmometry technique. The Extended Pitzer model modified by Archer [23], [24] was adopted to represent the experimental data. The parameters of the Extended Pitzer model modified by Archer were used to calculate the mean molal activity coefficients and the excess Gibbs free energy for the studied binary mixtures.

To our knowledge, no measurements of acoustical, volumetric or osmotic properties were previously published for the binary mixtures studied in this work, and only few papers containing data for the pure ionic liquid were found in the literature [25], [26].

Section snippets

Chemicals

The ionic liquid 1-butyl-3-methylimidazolium dicyanamide, [BMim][dca], was supplied by Iolitec GmbH (Germany) with a purity higher than 0.98 by mass. The water content, ww, and halide content, whalide, for this ionic liquid was certificated by the company and their values are ww = 1240 ppm and whalide < 700 ppm, respectively. In order to reduce the water content and volatile compounds to negligible values, prior to its use this compound was subjected to vacuum (p = 2 · 10−1 Pa) at moderate temperature (T = 

Apparent molar properties

Density and speed of sound values for the binary systems {1-propanol (1), or 2-propanol (1), or 1-butanol (1), or 2-butanol (1), or 1-pentanol (1) + [BMim][dca] (2)} from T = (293.15 to 323.15) K and atmospheric pressure are reported in table 2. At it can be observed, these physical properties increase by decreasing both temperature and alcohol compositions. A similar behavior was also found by other authors studying alcoholic solutions of other ILs [1], [2], [3], [4]. Moreover, comparing the

Conclusions

In this work, new data on density and speed of sound for {1-propanol, or 2-propanol, or 1-butanol, or 2-butanol, 1-pentanol + [BMim][dca]} binary systems were measured at different temperatures. From these experimental data, apparent molar volume and apparent molar isentropic compression were calculated and fitted to a Redlich–Meyer type equation, which was also used to calculate the apparent molar volume and apparent molar isentropic compression at infinite dilution for the studied binary

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). Noelia Calvar and Emilio J. González are thankful to FCT for awarding their postdoctoral grants (SFRH/BPD/37775/2007 and SFRH/BPD/70776/2010, respectively).

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