Thermodynamic properties at infinite dilution of deep eutectic solvents with organic solutes at different temperatures

Abstract

Many industrial processes in the chemical industry require surge amounts of energy to separate organic mixtures. While numerous separating substances used for this purpose are volatile and have closely related boiling points to the mixtures, they are environmentally harmful. As a result, new separation substances in the space of these solvents should be researched. The latest group of solvents known as deep eutectic solvents (DESs), classified as Type (III), were studied in the space of conventional organic solvents, which are currently used in industrial processes for extraction or separation purposes. In the forecast, deep eutectic solvents have gained significant interest as part of the low melting temperature solvents with many other attractive and unique properties. This includes their physical, thermophysical, and thermodynamic properties. These properties were investigated in this study in order to better understand the intermolecular interactions of 1-ethyl-1-methylpyrrolidinium bromide + glycerol [(EMPYR) Br + Gly] or 1-ethyl1-methylpyrrolidinium bromide + ethylene glycol [(EMPYR) Br + EG], with methanol or ethanol. Hence, the first section of the study investigated the physical properties, including density and sound velocity, of deep eutectic solvents and their binary mixtures, as a function of temperature. The obtained physical properties were used to compute the thermophysical properties, i.e., excess molar volume (Vm E ), intermolecular free length (Lf), variation in isentropic compressibility (∆Ks), and isentropic compressibility (Ks ), to advance the study of the intermolecular interactions of the selected deep eutectic solvents and their binary mixtures. Furthermore, the second section of this study investigated the infinite dilution activity coefficients of five different deep eutectic solvents, including (1) 1-ethyl-1-methylpyrrolidinium bromide + glycerol [(EMPYR) Br + Gly], (2) 1-ethyl-1-methylpyrrolidinium bromide + ethylene glycol [(EMPYR) Br + EG], (3) 1-ethyl-1-methylpyrrolidinium bromide + 1-pentanediol [(EMPYR) Br + 1.5-PDO], (4) 1-ethyl-1-methylpyrrolidinium bromide + 1-hexanediol [(EMPYR) Br + 1.6- HDO], and (5) trihexyltetradecylphosphonium decanoate + ethylene glycol [(THTDP) Dc + EG], with various solutes at different temperatures. The obtained infinite dilution activity coefficients (γ13 ∞ ) were utilized to compute the other thermodynamic properties, viz., enthalpy (∆H1 E,∞), entropy (∆S1 E,∞), and Gibbs free energy (∆G1 E,∞) as well as the selectivity (Sij ∞) and capacity (kj ∞), of the selected organic solutes. The separation was possible with the investigated solvents. As is known, the accurate and precise analysis of the thermodynamic properties of liquid substances such as deep eutectic solvents is of significant interest to the chemical industry as it would help ascertain the implementation of these solvents on a large scale for industrial separation processes.