Deep Eutectic Solvents as Azeotrope Breakers: Liquid-Liquid Extraction and COSMO-RS Prediction

The efficient and sustainable separation of azeotropic mixtures remains a challenge in chemical engineering. In this work, the performance of benign solvents, namely deep eutectic solvents (DES), in the separation of aromatic-aliphatic hydrocarbon azeotropic mixtures via liquid-liquid extraction (LLE) was evaluated. The DES studied in this work were based on different ammonium salts (cholinium chloride, [Ch]Cl, benzylcholinium chloride, [BzCh]Cl, and tetrabutylammonium chloride, [N₄₄₄₄]Cl) as hydrogen bond acceptor (HBA) and one organic acid (levulinic acid, LevA) as hydrogen bond donor (HBD), always in the mole ratio of 1 HBA:2 HBD. The thermophysical properties, namely density and viscosity, of the three used DES were measured in the temperature range T = (293.15 up to 353.15) K and at atmospheric pressure. The phase equilibria diagrams of all ternary systems were determined at T = 298.15 K and at atmospheric pressure using ¹H NMR spectroscopy. The results showed that the introduction of a more hydrophobic HBA in the DES promotes the improvement of the distribution coefficient, while playing with the aromaticity of the DES leads to higher selectivity. In addition, the performance of the predictive conductor-like screening model for real solvent (COSMO-RS) model in the description of these systems was also evaluated. COSMO-RS is capable of quantitatively predicting the phase behavior and tie-lines for ternary mixtures containing DES as well as of estimating the trend of distribution ratio and selectivity.