Separation of Protocatechuic Acid Using Di-(2-ethylhexyl)phosphoric Acid in Isobutyl Acetate, Toluene, and Petroleum Ether

Protocatechuic acid has potential pharmacological significance, like antioxidant, antibacterial, and anticancer activity. The extraction of carboxylic acids from dilute aqueous phase is a topic of current interest to researchers. The present equilibrium study deals with the reactive extraction of protocatechuic acid from an aqueous solution by using di-(2-ethylhexyl)phosphoric acid (D2EHPA) in diluents, such as isobutyl acetate (IBA), toluene, and petroleum ether at isothermal conditions (298 +/- 1 K). The physical extraction of protocatechuic acid with pure diluents is also carried out. The difference between the physical extraction and the reactive extraction was studied. The effects of acid concentration (0.001-0.01 mol.kg(-1)), extractant concentration (0.3445-3.1010 mol.kg(-1)), and type of diluent on the recovery of protocatechuic acid from aqueous solution were determined. K-D values were obtained in the ranges of 1.14-4.03, 0.12-0.67, and 0.08-0.48 for D2EHPA in isobutyl acetate, toluene, and petroleum ether, respectively. A maximum K-D was obtained as 4.03 using 3.101 mol-kg(-1) D2EHPA (in IBA), while 80.11% of the initial protocatechuic acid was extracted. The D2EHPA IBA system was found to provide the highest distribution coefficient of the three diluents tested. The extraction equilibrium complexation constant, K-E, was obtained in the ranges of 5.56-1.17, 0.82-0.20, and 0.49-0.14 for D2EHPA in isobutyl acetate, toluene, and petroleum ether, respectively. The feasibility of the extraction process was evaluated by calculating the minimum solvent to feed ratio and the number of theoretical stages of the extraction column. The number of theoretical stages for the D2EHPA-IBA system was calculated to be 3, and it was 1 for the D2EHPA - toluene and D2EHPA-petroleum ether systems.