Separation mechanisms of citric and itaconic acids by water-immiscible amines

Abstract

The selective separation of citric and itaconic acids by amine extractants was studied. The stoichiometry of the carboxylate:amine complexes was established by various independent experimental techniques. Loading and distribution curves as well as FT-IR and fluorescence spectra were recorded. Tri-n-octyl amine in 1-octanol was selective for the stronger carboxylate, citrate. Acid-base coupled extractants composed of di-(2-ethylhexyl) phosphoric acid and methyltriocyl ammonium cation in dichloromethane formed reverse micelles with uncharged surfaces. This extractant was selective for the more hydrophobic itaconate, which is located in the apolar envelope of the reverse micelle. Citrate was located in the aqueous inner core bound to the ammonium cation. The roles of amine salt, the diluent and of water-immiscible additives on the selectivity of the extraction are discussed.