PVT properties for binary ionic liquids of 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide with anisole or acetophenone at pressures up to 50 MPa

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Abstract

Densities of pure 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide, [C3mpip][NTf2], and its mixtures with anisole or acetophenone were measured with a high-pressure densimeter at temperatures from 298.15 K to 348.15 K and pressures up to 50 MPa. The Tait equation was employed to represent pressure effect on the isothermal densities. The experimental results reveal that the excess volumes of (anisole + [C3mpip][NTf2]) and (acetophenone + [C3mpip][NTf2]) are all negative over the entire experimental conditions. In addition to an empirical generalized equation, the density data were also correlated quantitatively with the Flory–Orwoll–Vrij (FOV) and the Schotte equations of state.

Highlights

► The densities were measured with a high-pressure densimeter. ► The systems are ionic liquid [C3mpip][NTf2] with anisole or acetophenone. ► The densities data fitted accurately to the Tait equation. ► The excess volumes are all negative over the entire experimental conditions. ► The FOV and Schotte equations of state are correlated well the density data.

Introduction

In the last decade, room-temperature ionic liquids (RTILs) have received wide attention to be used as green solvents, reaction media, heat transfer agents, lubricants, plasticizers, or catalysts, due to their unique physical properties such as extremely low volatility, non-flammability, high thermal stability, etc. [1], [2], [3], [4], [5], [6], [7], [8]. Numerous thermodynamic data of ionic liquids and their mixtures are available in public databanks, such as Ionic Liquids Database – (ILThermo) NIST Standard Reference Database #147 (http://ilthermo.boulder.nist.gov/ILThermo/mainmenu.uix). Among various thermodynamic properties, pressure–volume–temperature (PVT or density) data are fundamentally important in the development of thermodynamic models for the systems containing ionic liquids. For instance, the PVT data of pure components can be used for determining the fluid-specific parameters of thermodynamic models and those of mixtures for determining the binary interaction parameters. The volumetric data also provide useful supporting evidences to reveal the molecular interactions between the constituent components.

Among several other ionic liquids, 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide, ([C3mpip][NTf2]), a carbon dioxide-philic agent, is considered as a potential candidate for carbon dioxide capture. The PVT properties of pure ionic liquid [C3mpip][NTf2] have been measured at temperature (293.15 to 393.15) K and pressure (0.1 to 35) MPa [9] and used to determine the characteristic parameters of the modified cell model equation of state [10]. In the present study, density data were measured with a high-pressure vibrating tube densimeter for two binary systems of (anisole + [C3mpip][NTf2]) and (acetophenone + [C3mpip][NTf2]) at temperatures from 298.15 K to 348.15 K over pressures from 0.1 MPa to 50 MPa. The presence of anisole and acetophenone was expected to reduce the viscosity of the absorbents. To the best of our knowledge, the PVT data of these two binary systems are not available in public literature. The Tait equation was used to represent the pressure effect on the isothermal densities for these two binary systems. The excess volumes were calculated from the experimental PVT data and a Redlich–Kister type equation was adopted to express the excess volumes in terms of composition. Moreover, the new PVT data were correlated with the Flory–Orwoll–Vrij (FOV) [11] and the Schotte [12] equations of state over the entire experimental conditions.

Section snippets

Experimental

Anisole and acetophenone were purchased from Acros Organics (Germany) with purity level of 0.99 in mass fraction. Ionic liquid, [1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonil)imide] or [C3mpip][NTf2] (CAS 608140-12-1) was purchased from Ionic Liquids Technologies GmbH (IoLiTec, Germany) with purity 0.99 in mass fraction. According to the producer note, the water content is less than 50 ppm. The trace amount of water in the chemicals was removed with molecular sieves. The ionic

Results and discussion

The densities of pure anisole, acetophenone, [C3mpip][NTf2] and the binary mixtures of (anisole + [C3mpip][NTf2]) and (acetophenone + [C3mpip][NTf2]) were measured at T = (298.15, 318.15, and 348.15) K over pressures range from (0.1 to 50) MPa. Table 2 compares the experimental results with the literature values for pure components where the literature densities of [C3mpip][NTf2] at T = 298.15 K and 318.15 K were estimated from the smoothed data of Gardas et al. [9]. The tabulated values also include the

Correlation of specific volume with equations of state (EOS)

The Flory–Orwoll–Vrij (FOV) [11] and the Schotte [12] EOS were used to correlate the experimental specific volumes. These two EOS are defined as follows.

The FOV EOS:PV¯/T¯=V¯1/3(V¯-1/3-1)-1-(TV¯)-1.The Schotte EOS:PV¯/T¯=(RT/PMV)(1-V¯-1/3)+(V¯1/3-1)-1-(TV¯)-1,where M is the molar mass, P¯=P/P,V¯=V/V, and T¯=T/T. The fluid-specific model parameters P, V, and T represent characteristics pressure, specific volume and temperature, respectively, which were determined by fitting the EOS to

Conclusions

The PVT properties have been measured for two ionic liquid-containing binary systems, (anisole + [C3mpip][NTf2]) and (acetophenone + [C3mpip][NTf2]), at temperatures from 298.15 K to 348.15 K and pressures up to 50 MPa. The Tait equation represented accurately the pressure effect on the densities of the pure liquids and their mixtures at given temperature and composition. The empirical generalized model, using only two characteristic parameters, correlated quantitatively the PVT data of each binary

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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