Effect of Lactate-Based Protic Ionic Liquids on the Thermodynamic and Transport Properties of Aqueous Lithium Bromide Solutions at Different Temperatures

In recent years, there has been a growing interest in the utilization of protic ionic liquids (PILs) as a type of environmentally sustainable green solvent in various applications, including absorption refrigeration systems that involve lithium bromide. To gain a comprehensive understanding of the thermophysical properties of lithium bromide in water and aqueous solutions containing three different protic ionic liquids (PILs) composed of the cations 2-hydroxyethylammonium, bis­(2-hydroxyethyl)­ammonium, and tris­(2-hydroxyethyl)­ammonium, in combination with the lactate anion, a thorough investigation was conducted using ultrasonic, volumetric, and viscometric methods. The analysis of these thermophysical properties is crucial, as it allows for the examination of the underlying forces at play within the liquid mixtures. In this particular study, key thermophysical parameters, such as apparent molar volume, apparent molar isentropic compressibility, and viscosity coefficients, were investigated for both lithium bromide in water and its aqueous solutions containing PILs. The findings revealed a significant influence of solute–solvent interactions in the studied systems, which were observed to intensify with increasing concentrations of PILs. These outcomes are discussed in relation to hydrophilic–hydrophilic and ion–hydrophilic interactions, along with an analysis of the associated thermodynamic parameters. The cosphere overlap model was employed to interpret the positive transfer values observed in the experimental data.