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Reactive extraction of citric acid from dilute aqueous solutions was studied using three different extractants, namely tri-n-butylphosphate (TBP), tri-n-octylamine (TOA), and Aliquat 336 (A336), dissolved in three different diluents: butyl acetate, decanol, and benzene. The isothermal batch equilibrium experiments were carried out at T = 300.15 ± 1 K. The extraction was interpreted in terms of the distribution coefficient (K D ). Maximum extraction efficiency (E = 95.5%) was obtained at 20% (v/v) TOA in butyl acetate with complexation constant K E2 = 1039.7 (kg mol −1 ) 2 for the (2:1) complex. In addition to having a higher loading ratio (Z > 0.5), the overloading of amine(TOA) in the case of the citric acid + TOA + decanol system was also confirmed by spectroscopic (FTIR) analysis. The linear solvation energy relationship model was successfully applied to predict the distribution coefficient. The complex stoichiometry was also optimized using differential evolution. A close resemblance was observed between experimental and model values.

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In the present study, the reactive extraction of levulinic acid (4-oxopentanoic acid) was investigated by using Aliquat 336 in various organic solvents [benzene, dichloromethane (DCM), dodecane, methyl isobutyl ketone (MIBK), 1-octanol] from dilute aqueous solution. Equilibrium data obtained at 298 K and 101.325 kPa were used to determine the values of distribution coefficient (K D), degree of extraction (E%), loading factor (Z), and complexation constants (K E). Among the diluents tested, DCM gave the highest extraction efficiency. Using 0.5454 mol·kg–1 of Aliquat 336 in DCM, K D and E% were obtained as 2.082 and 67.55%, respectively, at 0.2795 mol·kg–1 initial acid concentration in the aqueous solution. Z values were found to be between 0.033 and 1.628 depending on the nature of the diluent used and Aliquat 336 concentration in the organic phase. Using mass action law modeling, the stoichiometry of the extraction reaction was determined. It was observed that mostly 1:1, 2:1, and 3:1 types of complexes were formed. The results inferred that the polarity and the molecular size of the solvent were the important critical factors which decide the solubilization of the solvates in the organic phase. DCM was found to be the most appropriate solvent among tested ones for the reactive extraction of levulinic acid. The feasibility of the extraction process was also assessed by calculating the minimum solvent (extractant + diluent) to feed ratio and the number of theoretical stages required for the recovery of levulinic acid in the extraction column.

Pyruvic acid is extensively utilized in the chemical, pharmaceutical, and agrochemical industries. Novel biotechnological routes to pyruvic acid production receiving great attention and recent focus of research are toward its separation from fermentation broth or recovery from waste streams. Based on reversible complexation, extraction equilibria of the system (water + pyruvic acid + extractant/diluents) were measured at T = 308.2 K using various concentrations of pyruvic acid (0.1 kmol·m–3 to 0.5 kmol·m–3) and extractant (tri-n-butyl phosphate, TBP) (0.36 kmol·m–3 to 2.56 kmol·m–3) in different diluents (n-heptane, toluene, and methyl-iso-butyl ketone, MIBK). Different physiochemical properties such as dipole moment and E T parameter have been used for comparison. Results are given in terms of various parameters such as distribution coefficient, equilibrium complexation constant, loading ratio and extraction efficiency. Using expressions derived for extraction equilibria, equilibrium complexation constants (K E) were evaluated to be 0.369 m3·kmol–1, 0.482 m3·kmol–1, and 0.578 m3·kmol–1 for n-heptane, toluene, and MIBK, respectively, whereas solvation number of TBP (m) was estimated to be one for all the three diluents. Only (1:1) complex was proposed for all the three diluents with no overloading (Z < 0.5) in any case. Higher chemical extraction was observed in inactive diluents: n-heptane and toluene.