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

Abstract

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 k2 = 0.0351 m3 kmol–1 s–1. The extraction parameters were estimated by differential evolution optimization technique. Optimal value of equilibrium constant, KE, was found to be 3.6 · 10–3 (m3 kmol–1)2, for the reactive extraction of citric acid using 20 % TOA in MIBK, and was found in close agreement with experimental values.

Keywords

• reactive extraction
• citric acid
• differential evolution
• modeling
• equilibrium
• kinetics