Extraction Mechanism and Behavior of Malic Acid with Tri‐octylamine (TOA)

Abstract

Liquid–liquid equilibria of malic acid with tri‐octylamine (TOA) as extractant and 1‐octanol, methyl isobutyl ketone (MIBK) and chloroform as the diluents were investigated, and Fourier transform infrared spectrometer (FTIR) spectrum of the organic phase samples loaded with malic acid were taken to obtain the stoichiometry of complex. The extraction behavior depends on the concentration of malic acid in the equilibrium aqueous phase, species of diluent, and TOA concentrations in the organic phase. A large degree of extraction in protonated diluent appeared at low equilibrium malic acid concentration in the aqueous phase, while the sequence was as MIBK > 1‐octanol > chloroform at high equilibrium malic acid concentration. It has the same sequence as the degree of extraction at overloading region. Malic acid is bonded to TOA in three forms of (1,2), (1,1), and (2,1), and for the complex (1,2), one carboxyl on malic acid was bonded to TOA with ion‐pair association and another with hydrogen bond. By using mass action law, and taking some assumptions, an expression of extraction equilibrium was derived, and the apparent extraction equilibrium constants were evaluated. The predict equilibrium data agreed well with the experimental values.

Keywords:

• TOA
• Malic acid
• Extraction equilibrium
• Ion‐pair association
• Hydrogen bond association

Acknowledgment

Financial support of this work was provided by the National Natural Science Foundation of China, Grant No. 29836130.