AMINE EXTRACTION OF HYDROXYCARBOXYLIC ACIDS .1. EXTRACTION OF CITRIC-ACID WITH 1-OCTANOL N-HEPTANE SOLUTIONS OF TRIALKYLAMINE

Extraction of citric acid from aqueous solutions with TAA, a mixture of tertiary aliphatic amines, dissolved in 1-octanol/n-heptane mixtures, and coextraction of water have been studied as a function of acid, amine, and octanol concentrations at different temperatures. Using a "chemical modeling" approach, two complexes [acid.amine.h11H2O and acid.(amine)2.h12H2O] have been assumed to exist in the organic phase, and the corresponding equilibrium constants, apparent enthalpies, and entropies of complex formation have been evaluated. The overall equilibrium constants, beta'11 and beta'12, and hydration numbers, h11 and h12, have been correlated with the concentration of amine and with various properties of the mixed solvents. The solubility of water in acid-free organic phase has been found to be the best fitting parameter. According to IR spectra, the amine-acid interaction is represented by an equilibrium between the extreme types of an H-bond ("neutral" O-H...NR3 and ionic O-...H-+NR3). A mathematical model of acid extraction and water coextraction has been formulated.