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A new model of the liquid/liquid equilibrium of butyric acid (BA) and water extraction from aqueous solutions to an organic solvent containing phosphonium ionic liquid and dodecane has been derived. It has seven fitting parameters and describes experimental data well. Reactive extraction with formation of the (p, 1) acid-IL complexes with p ≤ 11 acids on one hand and their aggregation by water bridges on the other hand refer to the dualistic character of the extraction process and the developed model. The values of two equilibrium constants characterizing the stability of hydrogen bonds between acid and IL anion are 3 and 2 orders of magnitude larger as compared with constants characterizing stability of acid−acid H-bonds. Water is extracted via two reactive mechanisms. The first is a competitive extraction of acid and water which results in the release of water from the solvent as the BA extraction proceeds. The second mechanism is coextraction of water with BA. At the acid loading of IL above 3, this mechanism dominates and the water loading increases linearly with the increasing acid loading. These mechanisms suggest that two types of water exist in the solvents with IL. Water associated directly to IL and hydration water associated with acid molecules in the complexes.

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Liquid-liquid equilibrium data of butyric acid in the systems water + solvent with tri-n-octylamine as extractant and n-alkanes as diluent, and water + pure n-alkanes are presented. The distribution coefficient is a linear function of the aqueous concentration of butyric acid for pure n-alkanes. For solvents containing trioctylamine, the dependence of the distribution coefficient of butyric acid goes through a maximum at a concentration of butyric acid of about 0.2 kmol‚m -3 . An overloading of the extractant reaching the value of almost 6 was observed. The loading is independent of the extractant concentration. The experimental data were interpreted by a chemical reaction mechanism and a related model in which the existence of (1,1) to (7,1) acid-amine complexes and a monomer and a dimer of butyric acid in the solvent was supposed. The equilibrium constants of formation of these complexes and the distribution of individual species in the solvent were estimated. This model fits experimental equilibrium data well. With increasing temperature, the value of the distribution coefficient of butyric acid decreases. Coextraction of water in the solvents is proportional to the concentration of butyric acid, and in the solvent with trioctylamine, it is 10 times higher than that in pure n-alkanes.

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Solvent properties of ionic liquids with trihexyltetradecylphosphonium cation and bis(2,4,4-trimethylpentyl)phosphinate anion (Cyphos IL-104) or chloride anion (Cyphos IL-101) were studied. IL-104 effectively extracted lactic acid (LA) with distribution coefficients above 40 at low acid concentrations. IL-104 extracted only undissociated acid (LAH) what supported the coordination mechanism of lactic acid extraction via H-bonding. In the extraction of lactic acid by phosphonium chloride (IL-101) an ion-exchange mechanism contributed remarkably to the extraction especially at basic pH where anionic form of this acid predominated. A high solubility of water in hydrophobic IL-104 up to 14.4 mass % was connected with the formation of reverse micelles. A dual mechanism of water extraction to phosphonium ionic liquids was identified, which consisted of water incorporation into reverse micelles and the inclusion of water into the hydrated complex of lactic acid with ionic liquid (IL). The extraction of lactic acid caused splitting of reverse micelles with liberation of water from the solvent. In the saturated solvent only hydration water remained in the complex of lactic acid with phosphonium ionic liquid, with the suggested structure (LAH)p(IL)(H2O)2, where the value of p ranged from 1 to 3.

Liquid-liquid equilibrium data of 5-methyl-2-pyrazinecarboxylic acid (MPCA) and H 2 SO 4 in water + organic solvent systems with the reactive extractant trioctylamine (TOA) are presented together with the model of equilibrium. Dissociation constants of both acids were also determined. The addition of 1 kmol • m -3 of Na 2 SO 4 decreased the pK a of MPCA and pK a2 of H 2 SO 4 from 3.09 to 2.87 and from 2.10 to 0.908, respectively. In the extraction of MPCA, the overloading of TOA indicated the formation of (p, 1) complexes (HMPCA) p TOA with p ) 1 to 3. The (1, 1) complex is more stable in n-alkanes with isodecanol. Other (p, 1) complexes are more stable in xylene. H 2 SO 4 with TOA in xylene form (r, q) complexes, (SO 4 2-) q-r (HSO 4 -) 2r-q (HTOA + ) q . At low H 2 SO 4 concentrations, a (1, 2) complex, TOA/sulfate, is formed. On increasing the acid concentration, the expected (1, 1) complex, TOA/hydrogen sulfate, aggregates, probably immediately, to complexes (2, 3) and (3, 3). When the ionic strength was increased by Na 2 SO 4 , the extraction of H 2 SO 4 was less effective. High water content of the solvent loaded with H 2 SO 4 with the stoichiometry (1, 2) suggests the formation of reverse micelles similarly as observed in ionic liquids.