Gallic Acid Separation by DES-Based Aqueous Biphasic Systems: Experimental, ePC-SAFT, and Classical Thermodynamic Study

Gallic acid (GA) is considered a representative polyphenol derived from natural sources. The partitioning behavior of GA can reveal how the polyphenol compounds in fruit residue would separate in techniques such as aqueous biphasic systems (ABS). In recent years, modern ABSs have used deep eutectic solvents (DES) that known as green solvents. In this work, aqueous biphasic systems (ABS) have been utilized to study the partitioning of GA. This study investigates the liquid–liquid equilibria (LLE) of ABS composed of DES and a solution of inorganic salts (K2HPO4 and K3PO4) at a temperature of 298.15 K and atmospheric pressure. The DES used consists of choline chloride (ChCl) as the hydrogen bond acceptor and 1,4-butanediol as the hydrogen bond donor in a 1:3 molar ratio. LLE tie-lines were determined and analyzed, and the partitioning coefficients of GA (KGA) and its extraction efficiency (EGA%) were calculated for each tie-line. The partition coefficient of GA was consistently greater than 1 across all samples, with maximum values of 2.95 and 2.74 for K2HPO4 and K3PO4, respectively. The thermodynamic behavior of the pseudoternary system (salt, DES, and water) was examined using electrolyte solution models by incorporating extended NRTL, extended UNIQUAC, and ePC-SAFT models. Comparisons of the RMSD indicated that these models show good agreement with the experimental data when regressing the binary interaction parameters in the ternary system. These binary interaction parameters were then used to predict additional tie-lines and the continuation of the binodal curves with good accuracy. Based on the predicted tie-lines, the partitioning behavior of GA was regressed, and the highest predicted value of KGA, 3.44, was achieved using an ABS with weight fractions of 0.35 DES, 0.3 K3PO4, and 0.35 water in feed. The RMSD values for ternary systems containing K3PO4 were 0.0086 for the extended NRTL model, 0.0219 for the extended UNIQUAC model, and 0.0506 for the ePC-SAFT model.