Thermophysical Properties and Water Saturation of [PF₆]-Based Ionic Liquids

Abstract

In this work, mutual solubilities of two [PF6]-based ionic liquids (ILs) with water and their thermophysical properties, namely, melting properties of pure ILs and densities and viscosities of both pure and water-saturated ILs, were determined. The selected ILs comprise 1-methyl-3-propylimidazolium and 1-methyl-3-propylpyridinium cations combined with the anion hexafluorophosphate. Mutual solubilities with water were measured in the temperature range from (288.15 to 318.15) K. From the experimental solubility data dependence on temperature, the molar thermodynamic functions of solution, such as Gibbs energy, enthalpy, and entropy of the ILs in water were further derived. In addition, a simulation study based on the COSMO-RS methodology was carried out. For both pure ILs and water-equilibrated samples, densities and viscosities were determined in the temperature interval between (303.15 and 373.15) K. The isobaric thermal expansion coefficients for pure and water-saturated ILs were calculated based on the density dependence on temperature.

Thermophysical properties of pure and water-saturated tetradecyltrihexylphosphonium-based ionic liquids

“…The IL and water phases were initially vigorously agitated and then allowed to reach saturation equilibrium and complete phase separation, during a period of at least 48 h. This period proved, in previous works [7,[26][27][28][29], to be the minimum time required to guarantee a complete separation of the two phases and that no further variations in water mole fractions occurred for longer periods. It is safe to admit that after 48 h the saturation values were achieved.…”

“…Most of the authors focused their studies on the physical properties of imidazolium- [4,25,30,31] and pyridinium-based ILs [8,32], while few researches have centered their attention in phosphonium-based ILs [12, [33][34][35][36][37][38]. Furthermore, few works investigated the influence of water in the physical properties of ILs [4,7,8,25] and, to the best of our knowledge, none has extended these studies to the phosphonium cation family of ILs.…”

“…Most of the studies concerning the measurement of thermophysical properties of ILs have been focused on imidazolium-and pyridinium-based ILs [3][4][5][6][7][8][9]. However, compared with those nitrogen-based ILs, phosphonium-based salts are less toxic, thermally more stable, readily available in bulk quantities and less expensive [10][11][12].…”

Surface tension and refractive index of pure and water-saturated tetradecyltrihexylphosphonium-based ionic liquids

“…Ionic liquids are a group of molten salts usually composed of inorganic or organic anions, and relatively large organic cations, which do not form an ordered crystal and, consequently, they remain liquid at or near room temperature [1][2][3][4]. Besides the overexplored imidazolium-based ionic liquids [5][6][7][8][9][10][11], new families of ionic liquids attracted increasing interest in the past few years. Among them, studies considering piperidinium-, pyrrolidinium-, pyridinium- [12,13], cholinium- [14,15] and guanidinium-based [16] cations have emerged in literature.…”

Separation of the ethanol/water azeotropic mixture using ionic liquids and deep eutectic solvents

“…ILs are molten salts, consisting of large asymmetric organic cations and organic or inorganic anions. The low symmetry, high vibrational freedom and charge delocalization of the ions composing an IL reduce the stability of the crystalline phases, and thus their melting temperatures [8]. Many areas of application for ILs, except for use as entrainers, have been studied [9][10][11].…”