On the influence of some strong electrolytes on the partitioning of acetic acid to aqueous/organic two-phase systems in the presence of tri-n-octylamine: Part I: Methyl isobutyl ketone as organic solvent

The recovery of carboxylic acids from aqueous phases is often achieved by reactive extraction with water-insoluble amines which are dissolved in an organic solvent. The basic design of such downstream processes requires a thermodynamic framework for the encountered liquid–liquid equilibrium. The thermodynamic framework should be able to describe the rather uncommon and surprising effects that comparatively small amounts of strong electrolytes might have. Such strong electrolytes can either reduce or increase the affinity of a carboxylic acid for the organic phase in particular at low aqueous phase concentrations of the carboxylic acids. That behavior was explained in previous investigations with citric acid as a model compound for a carboxylic acid and modeled by combining the dissociation/protonation equilibrium in the aqueous phase with the formation of organic phase complexes of (amine + acid(s) + water). In the present investigation this work is extended to acetic acid as another example for a carboxylic acid. New experimental results are reported for the influence of sodium chloride, sodium nitrate, sodium sulfate, sodium citrate and hydrochloric acid on the partitioning of acetic acid to coexisting aqueous/organic liquid phases of the system (water + methyl isobutyl ketone (organic solvent) + tri-n-octylamine (chemical extractant)) at 25 °C. The phase behavior is described by an extension of the previously published thermodynamic framework that is able to describe/predict the influence of a strong electrolyte on the partitioning of acetic acid.