Amine Extraction of Hydroxycarboxylic Acids. 3. Effect of Modifiers on Citric Acid Extraction

The extraction equilibrium in the systems aqueous solution of a hydroxycarboxylic acid−solution of trialkylamine in an organic diluent can be largely modified by the nature of the diluent. Binary diluents composed of a neutral paraffinic solvent and an active modifier can be used to adjust the desired equilibrium behavior of a particular system. In the present work the equilibria in the systems aqueous solutions of citric acid−solutions of trialkylamine in binary diluents have been measured. Chloroform or methyl isobutyl ketone has been used as modifiers and n-heptane as neutral diluent. Besides these two data systems earlier data for the system with 1-octanol as modifier are also considered. Different mathematical models for correlating these data are proposed comprising specific effects of formation of various acid−amine complexes and nonspecific effects of interactions among the components of the organic phase. The optimum parameter values of the individual models are presented, and the goodness of fit...