Dependence of extraction equilibrium of monocarboxylic acid from aqueous solutions on the relative basicity of extractant

This paper describes monocarboxylic acid extraction from aqueous solution experiments, using five types of mixed solvents and 12 monocarboxylic acids. From the results of these experiments, a new mathematical model, including a new definition of extractantʹs basicity (pKa,BS), was developed and validated. Trioctylamine (TOA)/1-octanol, TOA/methyl iso-butyl ketone (MIBK), TOA/tetrachloromethane (CCl4), trialkylphosphine oxide (TRPO) /1-octanol and TRPO/ kerosene, were used as the extractant, and formic, acetic, propionic, butyric, valeric, caproic, monochloroacetic, dichloroacetic, trichloroacetic, glycolic, glyoxylic, and lactic acids, were used as the solutes extracted. The relative basicity of the extractant to the solute extracted (pKa,BS) was measured in different extractant concentrations. The experimental result confirms the mathematic model to predict the extraction equilibrium more accurately. pKa,BS can represent the complicated solvating power of the dilute to the association compound, and depends on the extractant concentration and the type of extractant, diluent and solute.