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.
Owing to its biological and chemical applications, the separation of protocatechuic acid, a polyphenol compound, is of interest to researchers. Extraction studies with initial acid concentration (0.001-0.01 kmol m À3 ) using aminic extractant tri-n-octyl amine (TOA) (0.2287 kmol m À3 -1.1436 kmol m À3 ) in diluent octanol at diverse temperature ranges from 288 K -313 K was done. Parameters like loading ratio, distribution coefficient, equilibrium complexation constant, diffusion coefficient, number of stages necessary for protocatechuic acid counter-current extraction were obtained; this information is useful in designing a process for the in situ separation of the acid from the fermentation broth as well as from the waste streams. The increase in temperature distribution coefficient was found to increase up to the temperature of 303 K and was found to decrease with a further rise in temperature. The entropy and enthalpy values for the reaction at different temperatures were obtained. The highest extraction of 91.1 % and distribution coefficient of 1.14 were obtained at 313 K for an acid concentration of 0.01 kmol m À3, and TOA concentration of 1.1436 kmol m À3 and 4 stages are required for counter-current extraction process for acquiring the required separation efficiency. Development of 1:1 complex of protocatechuic acid and TOA take place as concluded from the values of the loading ratio.
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