Strong anion exchange recovery of aqueous dicarboxylates: Extraction and sorption equilibrium comparison

Ion-exchange can be used for primary recovery of aqueous dicarboxylic acids at neutral pH, where there is almost complete acid dissociation. The equilibria of anion exchange of aqueous dicarboxylate anions (fumarate, itaconate, malate and succinate) with anions (Cl− and OH−) bound to quaternary ammonium compounds (Aliquat extractant and Dowex sorbent) were quantified. All equilibria could be described by the same model. The four dicarboxylates behaved similarly, and were exchanged by two Cl− or OH− anions. Sorption gave a much better exchange than extraction and OH− gave a much better exchange than Cl−. In batch equilibrium experiments most Cl− is not exchanged by dicarboxylate, pointing at the importance of column operation.