PVT properties of binary mixtures of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with anisole or acetophenone at elevated pressures

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Highlights

  • The densities were measured with a high-pressure densimeter.

  • The systems are ionic liquid [C4mim][NTf2] with anisole or acetophenone.

  • The densities data fitted accurately to the Tait equation.

  • The excess volumes are all negative over most experimental conditions.

  • The FOV and the Schotte equations of state are correlated well the excess volumes.

Abstract

The isothermal densities of pure ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C4mim][NTf2], and its mixtures with anisole or acetophenone were measured by using a vibrating tube densimeter over temperatures ranging from (298.15 to 348.15) K and pressures from (0.1 to 50) MPa. The Tait equation was used to correlate the density data and accurately represents densities varying with pressure at given temperature and composition. The excess volumes were calculated from the experimental data and found that those are all negative, except for (acetophenone + [C4mim][NTf2]) at 298.15 K with containing acetophenone of 0.1 in mole fraction. The modified Redlich–Kister was applied to correlate the excess volumes. The Flory–Orwoll–Vrij (FOV) and the Schotte equations of state were also employed to correlate the density data over entire experimental conditions.

Introduction

The wide range of combinations between anion and cation allow a great variety of ionic liquids (ILs) applications [1]. The numerous ILs applications appear due to their unique physical properties such as negligible volatility, non-flammability, high thermal conductivity, chemical and physical stability, and high potential for recycling [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. We need the knowledge of a broad set of properties as a function of temperature and pressure to characterize the ionic liquid thermophysically [10]. Furthermore, thermodynamic and transport properties are necessary for optimal design of chemical and separation processes [2]. Pressure–volume–temperature (PVT or density) data can provide valuable information for development of thermodynamic models, especially for the systems containing ionic liquids or polymeric materials.

The compound 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C4mim][NTf2], is considered as a potential candidate for carbon dioxide capture. The PVT properties of the pure ionic liquid [C4mim][NTf2] have been measured at temperatures from (293.15 to 328.20) K and pressures (0.1 to 59) MPa [10] and have been predicted with the knowledge of viscosity at temperatures (273.15 to 353.15) K and pressures (0.1 to 300) MPa [11]. In the present study, density values were measured with a high-pressure vibrating tube densimeter for two binary systems of (anisole + [C4mim][NTf2]) and (acetophenone + [C4mim][NTf2]) at temperatures from (298.15 to 348.15) K over pressures from (0.1 to 50) MPa. The use of anisole or acetophenone was expected to reduce the viscosity of ionic liquid. Previously reported data are not available for these binary systems investigated.

The experimental densities were correlated with the Tait equation to represent the pressure effect on the isothermal densities. A modified Redlich–Kister equation was used to express the excess volumes in terms of composition. The volumetric data reveal the molecular interactions between the components. The Flory–Orwoll–Vrij (FOV) [12] and the Schotte [13] equations of state correlated the new PVT data over the entire experimental condition.

Section snippets

Experimental

The material description is given in table 1. Ionic liquid, [1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide] or [C4mim][NTf2] (CAS 174899-83-3) was purchased from Ionic Liquids Technologies GmbH (IoLiTec, Germany) with purity 0.99 in mass fraction. Anisole and acetophenone were purchased from Acros Organics (Germany) with purity level of 0.99 in mass fraction. The amount of water in the chemicals was removed by using molecular sieves. The ionic liquid was degassed by vacuuming

Results and discussion

The densities of pure ionic liquid [C4mim][NTf2] and the binary mixtures of (anisole + [C4mim][NTf2]) and (acetophenone + [C4mim][NTf2]) were measured at T = (298.15, 318.15, and 348.15) K over the pressures range from (0.1 to 50) MPa. The densities of pure anisole and acetophenone are mentioned elsewhere [20] with the same experimental condition. High pressure density data for [C4mim][NTf2] are already available in the literature but only at temperature up to T = 328.20 K [10] and another one uses a

Conclusions

The measured PVT properties of (anisole + [C4mim][NTf2]) and (acetophenone + [C4mim][NTf2]) mixtures accurately correlated with the Tait equation and show the pressure effect on the densities of the pure ionic liquid and it mixtures at temperatures from (298.15 to 348.15) K and pressures up to 50 MPa. The excess volumes are negative over almost the entire range of experimental measurement and correlated well with the modified Redlich–Kister model. The PVT data were correlated quantitatively for

Acknowledgements

The authors are grateful for financing provided by the National Science Council, Taiwan, through Grant No. NSC99-2214-E-011-079-MY3. The authors also thank Dr. Ho-mu Lin for valuable discussions.

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