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