Reactive extraction of organic acids by supercritical CO2

Reactive extraction of citric acid and acetic acid from their aqueous solutions by supercritical (SC) CO2 was studied. Since organic acids are polar compounds which can hardly be extracted by SC CO2, reactants which increase the solubility of the acid by a chemical reaction are used. Alamine 336 and Hostarex A 327 were used as reactants and oleyl alcohol was selected as an active diluent, i.e., a solvent containing functional groups that interact strongly with the acid-amine complex. For this purpose, the solubilities of synthetic citric and acetic acid solutions, amines and acid-amine complexes in SC CO2 were examined. The extraction experiments were carried out at 313 K, 100 atm and 5 ml/min CO2 feed rate in a system which is continuous in terms of CO2. The solubilities of the acids in SC CO2 were very low; however, the solubilities of the amines in SC CO2 were higher than those of the acids. The acid-amine complexes were extracted more than the amines and the acids alone under the given conditions. Among the tertiary amines studied, Alamine 336 indicates better results than Hostarex A 327 for the extraction of both acids.