Thermophysical and Thermodynamic Properties of 1-Butyl-3-methylimidazolium Tetrafluoroborate and 1-Butyl-3-methylimidazolium Hexafluorophosphate over an Extended Pressure Range

Abstract

The current study focuses on 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF 4 ], and 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF 6 ]. The objective is to study the influence of pressure as well as that of the anion on several properties of this type of ionic liquid. The speed of sound and densities in pure ionic liquids (ILs) as a function of temperature and pressure have been determined. Several other thermodynamic properties such as compressibilities, expansivities, and heat capacities have been obtained. To the best of our knowledge, this research comprises both the first speed of sound data and the first evaluation of heat capacities at high pressures for ILs. Speed of sound measurements have been carried out in broad ranges of temperature (283 < T/K < 323) and pressure (0.1 < p/MPa < 150), sometimes inside the metastable liquid region using a nonintrusive microcell. The T-P melting line of [bmim][PF 6 ] has also been determined by an acoustic method. Density measurements have been performed for broad ranges of temperature (298 < T/K < 333) and pressure (0.1 < p/MPa < 60) using a vibrating tube densimeter. The pressure dependence of the heat capacities, which is generally mild, is found to be highly dependent on the curvature of the temperature dependence of the density.

Structural organization and phase behaviour of 1-butyl-3-methylimidazolium hexafluorophosphate: an high pressure Raman spectroscopy study

“…The range up to 100 1C was explored and at that temperature the L-S2 equilibrium pressure was found to be 465 MPa. A comparison between our present equilibrium data and the data reported by de Azevedo et al, 18 and Li et al 19,20 shows that S2 corresponds to the same crystalline phase whose melting point had been previously investigated. Such a comparison is presented in Fig.…”

“…Together with the mentioned work from de Azevedo, 18 we just became aware that also Yoshimura and coworkers did not observe crystallization events in [bmim] [BF 4 ]. 38 After acceptance of the manuscript, we became aware of the very recent work from Takekiyo and coworkers reporting on the detection of one crystalline phase for [bmim] [PF 6 ] under high pressure conditions.…”

“…The equilibrium between the liquid and S2 phases is described using a blue continuous line. This is obtained by linear fit of the data from studies of de Azevedo et al 18 (full black squares), Sawamura et al The open red circle refers to our previous characterization of the equilibrium between S1 and S2 at ambient pressure 35 and the similar result from…”

“…17 Thermophysical and thermodynamic properties of both [bmim] [PF 6 ] and [bmim] [BF 4 ] under pressure have been studied, including speed of sound and density determinations. 18 The latter report also provided information on the high pressure-high temperature phase diagram of [ 6 ]), at pressures up to 1 GPa, providing a description for the phase diagram of this salt and highlighting the existence of one crystalline phase over this pressure range. 19 More recently the same group presented new results based on an extensive high pressure Raman spectroscopy investigation on [bmim] [PF 6 ] up to 2 GPa, focusing on the in situ crystallization of this ionic liquid.…”

Scaling Model of Low-Temperature Transport Properties for Molecular and Ionic Liquids

“…Two individual coefficients of linear equations (11)- (12) determined for each respective property 0 ( , 0 ), 0 ( , 0 ), 0 ( , 0 ) from the experimental data [11][12][13][14][15][16][17][18][19] are reported in Table 1 for Ar, N 2 , C 2 H 4 , and C 2 H 6 and the set of seven ILs. For the latter the working temperature range [290, 370 K] of a stable liquid without its upper limit (it is unknown, as a rule) was considered.…”