Reactive Extraction of Citric Acid Using Different Extractants: Equilibrium, Kinetics and Modeling

Recovery of citric acid from biotechnologically produced low concentration aqueous solution has attracted several separation techniques for the downstream processing. Amongst them, reactive extraction is a convenient, cheap, and effective method. Three different extractants are used in this study, namely tri-n-butyl phosphate (TBP), tri-n-octylamine (TOA), and Aliquat 336 (A336), all diluted in methyl-iso-butyl ketone (MIBK). The isothermal batch experiments were performed for the equilibrium and kinetic studies at T = 300.15 +/- 1 K. Around 92 % extraction efficiency (E %) was obtained using 20 % (v/v) TOA in MIBK. Based on the overloading of amine (Z > 0.5), (2: 1) acid: extractant complex in TOA+MIBK phase was proposed. Kinetics of extraction of citric acid (0.2-0.8 kmol m(-3)) was also performed in a Lewis-type stirred cell, using TOA in MIBK. The extraction reaction was occurring in the diffusion film. The second order rate constant was calculated as k(2) = 0.0351 m(3) kmol(-1) s(-1). The extraction parameters were estimated by differential evolution optimization technique. Optimal value of equilibrium constant, K-E, was found to be 3.6. 10(-3) (m(3) kmol(-1))(2), for the reactive extraction of citric acid using 20 % TOA in MIBK, and was found in close agreement with experimental values.