Distribution of citric, acetic and oxalic acids between water and organic solutions of tri-n-octylamine

Phase equilibria governing the reactive extraction of citric acid from aqueous solution into solutions of tri-n-octylamine in the single solvents toluene, chloroform and methyl isobutyl ketone are investigated. In addition to batch extraction experiments, infrared spectroscopic measurements were performed. These spectroscopic investigations yield information about the stoichiometry of complex formation. All measurements were carried out at 298.15 K. A model for the liquid-liquid equilibrium which takes into account chemical reactions as well as physical interactions in both phases is used to correlate the experimental data. In comparison with earlier work, the model was extended to include the partitioning of the amine as well as its influence on the aqueous phase pH. The model reliably describes the partitioning of acid, water and organic compounds into the coexisting phases. New model parameters are also presented in order to complement recent publications on the partitioning of other single carboxylic acids (acetic and oxalic acids) into the same water/organic solvent systems. (C) 1997 Elsevier Science B.V.