Transport of organic acids through polybenzimidazole based membranes by ‘Chemodialysis’

A method of ‘Chemodialysis’ (CD) involving polybenzimidazole (PBI) as a chemically active membrane material is demonstrated for carrying out selective separation of organic acids. PBI membranes possessing basic functionality selectively sorb acid, which is transported to the permeate side by concentration gradient. Transported acid is removed from the permeate side by using stripping agent. The sorption of non-acidic organic (glucose) and inorganic (NaCl) solutes being absent in PBI membranes, they were not transported on the permeate side. This offered high selectivity towards transporting acid. Three structurally different PBIs were evaluated as membrane materials for acid sorption and transport. Effects of variation in operational temperature, concentration and type of stripping solvent were evaluated. A single step process with appreciable acid transport rate coupled with very high selectivity convey promises of ‘Chemodialysis’ towards its applicability for the separation of organic acids from various industrial process streams (e.g. during production of organic acids by biological routes, which usually involve number of steps and extensive usage of chemicals for their recovery from fermentation broth). Moreover, this process holds additional benefit of low energy requirement, since it works with concentration gradient as the driving force and requires energy only for the circulation of solutions.