Celanese Gmbh

Howard J Davis

Norman W Thomas

A preformed polybenzimidazole semipermeable membrane (e.g., a film or hollow filament) is chemically modified in accordance with the present invention. Imidazole groups of the polybenzimidazole membrane are cross-linked by reaction with a strong polybasic acid or its acid chloride (as defined). During the reaction the polybasic acid is dissolved in a relatively mild acid medium (e.g., glacial acetic acid) which serves to decrease the basicity of the imidazole groups and to promote the desired cross-linking reaction. The resulting cross-linked membrane is tougher than the untreated membrane and may be more readily handled without deleterious results. Also, the resulting cross-linked polybenzimidazole membrane no longer is soluble in N,N-dimethylacetamide, and exhibits improved service characteristics such as improved compaction resistance during prolonged usage at high pressure. The product of the present invention is particularly suited for use in separations from acid waste streams. Cross-linked polybenzimidazole membranes capable of reverse osmosis separations, ion exchange separations, and ultrafiltration separations may be formed in accordance with the present process.

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Warren, NJ, United States of America

Howard J Davis