Characterization and Modeling of the Liquid Phase of Deep Eutectic Solvents Based on Fatty Acids/Alcohols and Choline Chloride

Abstract

The solid−liquid equilibria phase diagrams of eight eutectic systems formed by choline chloride and fatty acids, or fatty alcohols, were measured to characterize the nonideality of the liquid phase of these systems, commonly reported in the literature as examples of type III deep eutectic solvents (DESs), and to evaluate the best modeling approaches to their description. Most of these systems are shown to present only slight deviations from ideal behavior, resulting from a fine balance of the hydrogen bonding between the hydroxyl/carboxylic groups with the chloride anion and the interactions present in the pure compounds. The phase diagrams measured were modeled with an associative equation of state (EoS) and a g E model. As an EoS, the perturbed-chain statistical associating fluid theory (PC-SAFT) was used, and this model was able to accurately describe the experimental data and to provide reliable estimates of the eutectic points using just a single binary temperature-dependent interaction parameter that often correlates with the acid/alcohol chain length. The performance of PC-SAFT was further compared with the g E model, a non-random two-liquid model (NRTL), and was found to provide a better description of the experimental data, especially for the more nonideal systems. Ultimately, the data gathered, and the molecular modeling, allowed the discussion of the behavior of fatty acids or fatty alcohols as hydrogen bond donors in choline chloride-based DESs.

The Role of Polyfunctionality in the Formation of [Ch]Cl-Carboxylic Acid-Based Deep Eutectic Solvents

“…These results suggest that additional functional groups in the HBD's structure may play a vital role for inducing a higher nonideality in [Ch]Cl-based DESs. This assumption is supported by our previous work, 12 on mixtures of [Ch]Cl with monocarboxylic acids; these were shown to have a nearly ideal behavior, exhibiting very small deviations Table S1) while the solid lines depict the PC-SAFT results using the parameters from Table 2 and Table 4, and the dashed lines represent the ideal-mixture behavior. Considering the nonideality of the systems investigated here, PC-SAFT was used to model the experimental phase diagrams and, as depicted in Figure 3, an accurate description of the experimental data was obtained by using up to two temperature independent binary interaction parameters (k ij and k ij_eps ) ( Table 4).…”

“…ARD values for melting temperature obtained between experimental data and ideal-mixture behavior as well as between experimental data and PC-SAFT modeling using the parameters in Table 2 and Table 4. 12 mainly determined by the melting temperatures of the pure acids. In contrast, the eutectic temperatures assessed with PC-SAFT suggest that T E might result from a combined effect of the acid bulk size, the number of functional groups within the HBD, and the molecular interactions between acid molecules.…”

Insights into the Nature of Eutectic and Deep Eutectic Mixtures

“…Based on the new proposed definition, to properly label a eutectic mixture as simple, or deep, the SLE phase diagram must be available, and the melting properties of the pure compounds must be known in order to draw the ideal solubility curve. Concerning these two aspects, in the following sections we explore the results over a series of different mixtures and compounds as well as modeling approaches helping to better establish the eutectic coordinates and the liquid phase non-idealities [18,19].…”

Using COSMO-RS to design choline chloride pharmaceutical eutectic solvents

“…Instead, only the data closer to the eutectic point were regressed. The systems choline chloride/octadecanoic acid [54] and choline chloride/ [N 2222 ]Cl [55]are displayed in Fig. 3 to exemplify both situations.…”