Eutectic Mixtures Based on Polyalcohols as Sustainable Solvents: Screening and Characterization

Abstract

Despite some promising potential applications of eutectic systems containing choline chloride and a polyalcohol, a detailed investigation of the thermodynamic behavior of these systems is still missing. In this work, the solid-liquid equilibria phase diagrams of binary systems containing choline chloride, and one from six different polyalcohols (ethylene glycol, 1,3-propanediol, glycerol, meso-erythritol, xylitol and sorbitol), were measured in the full composition. Excepting the mixtures with glycerol or ethylene glycol a quasi-ideal behavior in the [Ch]Cl solubility curve is observed. In the polyalcohol solubility curve, the mixtures present small negative deviations from ideality, excepting[Ch]Cl+ethylene glycol, which is slightly positive. The solid−liquid phase diagrams show a large liquidus composition window, and not a fixed stoichiometry for the eutectic points, where the mixtures can be used as solvents close, or below, room temperature. Aiming at their application, viscosities and densities were measured at the eutectic point in the temperature range from 278.15 to 373.15 K. All systems present densities and viscosities higher than water, which are directly related to the strong interactions between the components. Solvatochromic parameters were measured to characterize the solvents and they show how to achieve solvent tunability by varying the polyalcohol mole fraction.

Is ethaline a deep eutectic solvent?

“…1, which reveals several interesting features of the {ChCl + EG} system. We first note, that the solidus temperatures of this work (average: T eut = (244 AE 1) K) agree well with those of Silva et al, 15 (243 AE 1) K. However, the corresponding liquidus temperatures, T i , deviate for x ChCl 4 0.18. Here our values are in reasonable agreement with data of Crespo et al 16 Accordingly, the present liquidus temperatures suggest an eutectic composition of x eut ChCl E 0.17, whereas that of ref.…”

“…13,14 Surprisingly, the liquid-solid transformation-a key property for applications-of {ChCl + EG} mixtures, including ethaline, is not well defined. In particular, for ChCl mole fractions 0.15 t x ChCl t 0.7 reported melting-point data 3,15,16 scatter considerably (Fig. 1).…”

“…S1 of the ESI, † suggesting that the assumed composition, x eut ChCl , of the eutectic point is incorrect and/or that its melting point, T eut , is very sensitive to small amounts of water. Accordingly, it appeared worthwhile to record phase transition data for a {ChCl + EG} 15 (blue, J, water content: o600 ppm for ChCl and o150 ppm for EG) and Crespo et al 16 (blue ~; digitized from their Fig. 2).…”

Solid-liquid phase behavior of eutectic solvents containing sugar alcohols

“…More specifically, the experimental activity coefficients for the system ChCl + mannitol are uncommon; in the large series of binary systems containing ChCl already studied only a few present positive deviations from ideality in the ChCl side, which might be related to the to changes in the crystalline form of ChCl or the formation of some intermediate compound. However, the results are comparable with those for mixtures of [Ch]Cl with meso-erythritol, xylitol, sorbitol previously studied by us [21], where the polyalcohol exhibited negative deviations from ideality.…”

“…In previous works [10,20,21], we have characterized the solidliquid equilibria (SLE) of several eutectic mixtures composed of sugar alcohols, combined with quaternary ammonium salts. Although commonly reported as DES, the results demonstrated that most of these systems do not show significant deviations from the ideal-mixture behavior and, consequently, exhibit low melting temperature depressions.…”