Gallic Acid Separation\nby DES-Based Aqueous Biphasic\nSystems: Experimental, ePC-SAFT, and Classical Thermodynamic Study

Gallic acid (GA) is considered a representative polyphenol\nderived\nfrom natural sources. The partitioning behavior of GA can reveal how\nthe polyphenol compounds in fruit residue would separate in techniques\nsuch as aqueous biphasic systems (ABS). In recent years, modern ABSs\nhave used deep eutectic solvents (DES) that known as green solvents.\nIn this work, aqueous biphasic systems (ABS) have been utilized to\nstudy the partitioning of GA. This study investigates the liquid–liquid\nequilibria (LLE) of ABS composed of DES and a solution of inorganic\nsalts (K<sub>2</sub>HPO<sub>4</sub> and K<sub>3</sub>PO<sub>4</sub>) at a temperature of 298.15 K and atmospheric pressure. The DES\nused consists of choline chloride (ChCl) as the hydrogen bond acceptor\nand 1,4-butanediol as the hydrogen bond donor in a 1:3 molar ratio.\nLLE tie-lines were determined and analyzed, and the partitioning coefficients\nof GA (<i>K</i><sub>GA</sub>) and its extraction efficiency\n(<i>E</i><sub>GA</sub>%) were calculated for each tie-line.\nThe partition coefficient of GA was consistently greater than 1 across\nall samples, with maximum values of 2.95 and 2.74 for K<sub>2</sub>HPO<sub>4</sub> and K<sub>3</sub>PO<sub>4</sub>, respectively. The\nthermodynamic behavior of the pseudoternary system (salt, DES, and\nwater) was examined using electrolyte solution models by incorporating\nextended NRTL, extended UNIQUAC, and ePC-SAFT models. Comparisons\nof the RMSD indicated that these models show good agreement with the\nexperimental data when regressing the binary interaction parameters\nin the ternary system. These binary interaction parameters were then\nused to predict additional tie-lines and the continuation of the binodal\ncurves with good accuracy. Based on the predicted tie-lines, the partitioning\nbehavior of GA was regressed, and the highest predicted value of <i>K</i><sub>GA</sub>, 3.44, was achieved using an ABS with weight\nfractions of 0.35 DES, 0.3 K<sub>3</sub>PO<sub>4</sub>, and 0.35 water\nin feed. The RMSD values for ternary systems containing K<sub>3</sub>PO<sub>4</sub> were 0.0086 for the extended NRTL model, 0.0219 for\nthe extended UNIQUAC model, and 0.0506 for the ePC-SAFT model.