Thermodynamic properties of phosphonium-based ionic liquid mixtures at different temperatures

Abstract

Ionic Liquids (ILs) are relatively newly formed types of solvents. As part of ongoing research, research groups and industries are focusing on solvents classified as ionic liquids, which have a low melting point,and they have been given great attention focusing on their thermophysical properties and applications. In order to utilize or industrially exploit these types of solvents, the understanding of intermolecular interactions and properties of pure liquids and their mixtures is important. Thermophysical properties of ionic liquid mixtures, especially density, viscosity and speed of sound are measured as a function of temperature. Accurate analysis on thermophysical properties of ionic liquids is more of paramount interest as they indicate the transformation of ionic liquids from small laboratory level to large-scale industrial implementation.In this study, new data for the binary mixtures containing {trihexyltetradecylphosphonium chloride ([P+14, 6, 6, 6] [Cl-]) IL and propanoic acid (PA)} and {1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]) + benzaldehyde or ethyl acetoacetate} were investigated under atmospheric pressure (p equivalent to 0.1 MPa) and at temperatures (293.15 to 313.15) K. Densities (ρ),viscosities (𝜂) as well as speeds of sound (𝑢)were measured over the whole range of mole fraction (𝑥𝑖= 0 to 1). The computed excess properties which includes excess molar volumes(𝑉mE), apparent molar volume (𝑉𝜙),intermolecular free length (Lf), isentropic compressibility(𝑘𝑠), deviations in viscosity (Δ𝜂), apparent molar isentropic compressibility (𝐾𝜙) and deviation in isentropic compressibility(Δ𝑘𝑠)were computed from the experimentally determined data of densities, viscosities and speeds of sound. In addition, measurements of activity coefficients at infinite dilution forvolatile organic compounds (alkenes, alcohols, alkanes, cycloalkanes, aromatic hydrocarbons, thiophene, ketones, acetonitrile, water and tetrahydrofuran) in the IL [trihexyltetradecylphosphonium-bis-(2, 4,4-trimethylpentyl)-phosphinate and trihexyltetradecylphosphonium chloride] were conducted at different temperatures.The obtained results and derived properties have been elucidated in terms of the interactions taking place among the solvent systems.