Excess molar volume and excess Gibbs energy of activation for viscous flow for the binary mixtures of N-ethylpyridinium dicyanamide [C2py][DCA] with alcohols

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Highlights

  • The density and viscosity for binary mixtures of [C2py][DCA]+alcohols were measured over the whole composition.

  • A new concept – the relative viscosity of mixture, ηr = η/(x1η1 + x2η2), is put forward.

  • A correct equation of ΔG≠E was derived in terms of ηr and the values of ΔG≠E for these mixtures were calculated.

  • A new method for estimating the viscosity, η, of the mixture is proposed.

Abstract

The density and viscosity of multicomponent solutions play an important role in industrial areas concerning mass and heat transfer, as well as fluid flow. To expand the potential application of ILs, it is important to know the physicochemical properties of ILs with solvents for ILs’ widely used. The density and viscosity for binary mixtures of ionic liquid (IL) [C2py][DCA] with ethanol, 1-propanol and 2-propanol were measured across the entire range of mole fraction (x1 = 0.0000–1.0000) at T = (288.15–318.15) K. The excess molar volumes, VE, were calculated and well fitted by Redlich–Kister equation. The obtained VE are negative values over the whole composition range and it means that there is greater interaction between the ions and the alcohol molecules. The values of Δη have been applied to description of the viscosity deviation of the mixtures from the ideal one, but the equation of excess Gibbs energy of activation for viscous flow, ΔG≠E, for mixture cannot be derived from Δη. And more serious is that an incorrect equation of ΔG≠E is widely used in the literature. In view of this situation, we put forward a new concept – the relative viscosity of mixture, ηr. On a basis of the new concept, a correct equation of ΔG≠E is obtained. The values of ηr and ΔG≠E of mixtures [C2py][DCA]+alcohol over the whole composition range were calculated. The values of ηr are less than one and ΔG≠E are negative so that this result means that the interaction among ions becomes weaker due to ion solvation. The ΔG≠E values of the mixtures [C2py][DCA]+alcohol were well fitted by the Redlich–Kister equation. Using the Redlich–Kister’s parameters, the values of viscosity for mixtures [C2py][DCA]+alcohols were estimated and the estimated η(est.) is in good agreement with the experimental η. In order to test the reliability of the method proposed in this work, we also deal with the data of mixtures for [HDBU]IM + H2O, [BDBU]IM + H2O and [Mim]Ac + Alcohols in the literatures. The results also prove that this method is reasonable.

Introduction

Ionic liquids (ILs) are composed of organic cations and inorganic or organic anions, which have melting points below 373 K. ILs are solvents with possible applications in several fields in many fields such as chemical fields [1], [2], pharmaceutical science [3] and electrochemistry [4] because of their peculiar properties such as non-volatility, non-flammability and high thermal conductivity [5]. In the past few years, much work focus on physic-chemical properties of pure ILs. To expand the potential application of ILs, study on mixture systems about ionic liquids have attracted more and more attention from industry and academic community. Fletcher et al. suggested that mixing different ILs in appropriate proportions may have better properties than those of the pure compounds [6]. For example, the presence of water and other solvents in ILs will influence on their thermophysical properties such as catalytic performance [7] and enhancement of CO2 capture [8]. Hence, the knowledge of mixtures of ILs and other solvents is essential from both the scientific and the utilitarian point of view. To the best of our knowledge, densities and viscosity for mixtures of [C2py][DCA] with ethanol, 1-propanol and 2-propanol have not been reported in the literature. As our continuous work [9], [10], [11], the followings were reported in this work: (1) Density and viscosity for binary mixtures [C2py][DCA] with ethanol, 1-propanol and 2-propanol were measured over the entire composition range at T = (288.15–318.15) K interval 5 K and the excess molar volumes VE were calculated and discussed; (2) A new concept – the relative viscosity of mixture, ηr, was put forward and a new equation of excess Gibbs energy, ΔG≠E, of activation for viscous flow of mixture was derived on the basis of the new concept; (3) The values of ΔG≠E of mixtures {[C2py][DCA]+alcohol} were calculated by the equation of ΔG≠E and fitted by Redlich–Kister equation; (4) In terms of Redlich–Kister parameters, the values of ΔG≠E of mixtures {[C2py][DCA]+alcohol} were estimated; (5) In order to prove the reliability of the equation of ΔG≠E derived on the new concept, the data of mixtures {[HDBU]IM + H2O}, {[BDBU]IM + H2O} [12] and {[Mim]Ac + alcohols} [13] in the literature were processed by the method proposed in this work.

Section snippets

Chemicals

Distilled deionized water with a conductance of (0.8–1.2) × 104S·m−1 was used in all experiments. The sources and purities of all other chemicals are listed in Table S1 in Supporting Information. The actual degree of purified pyridine, 1-bromoethane and ethyl acetate was evaluated by using gas chromatography analysis (an Aglient GC-6820 equipped with an FID detector). The values obtained by this test were: 0.999 for purified for pyridine, 0.999 for purified 1-bromoethane and 0.999 for ethyl

Results and discussion

The density and viscosity of alcohols (ethanol, 1-propanol and 2-propanol) were measured in this work at T = (288.15–318.15) K and p = 0.1 MPa and compared with those in the literature [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34] in Table S2. The percent absolute relative deviations (ARD%) are calculated by the following equation [35], [36]:ARD%=|Plit-Pexp|Plit×100%where Pexpt represents density or viscosity of

Conclusions

The density and viscosity for binary mixtures of [C2py][DCA] with ethanol, 1-propanol and 2-propanol were measured over the whole composition range at T = (288.15–318.15) K. The excess molar volumes, VE, were calculated and well fitted by a Redlich–Kister equation. The calculated values of VE are negative indicates a stronger interaction between the ion and the alcohol molecule in the mixtures. The VE values are quite related to the alcohol chain length, which increases with the increasing alcohol

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21673107) and Liaoning Excellent Talents in University (LR2015025), Peoples Republic of China.

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