Polybenzimidazole thin film composite membranes

Abstract

A composite permselective membrane comprises an ultrathin semipermeable layer comprising a polybenzimidazole polymer in occluding contact with at least one surface of a microporous polymer support layer. Such membranes provide better combinations of flux and rejection rates in reverse osmosis processes than do conventional semipermeable membranes of polybenzimidazole polymer alone. In an embodiment, a composite permselective membrane is prepared by casting an ultrathin semipermeable layer of the polybenzimidazole polymer on a microporous polymer support layer. The semipermeable layer is preferably subjected to a drying step to evaporate part of the polybenzimidazole polymer solvent, then contacted with a coagulating bath. In some cases, the properties of the composite permselective membrane can be improved by annealing by contacting with an annealing liquid at an elevated temperature, the annealing liquid being selected from the group consisting of aqueous and non-aqueous solutions of liquid organic compounds which are solvents or non-solvents for the polybenzimidazole, and neat liquid organic compounds which are nonsolvents for said polybenzimidazole polymer.