New Material Membranes and the Holy Grail: Chlorine Stable Reverse Osmosis Membranes

The increasing urgency of the water scarcity disaster that the world faces is broadening the application of new membrane technologies to more challenging water sources, but the notable absence of new membrane materials and products is limiting the success of those efforts. The polyamide thin film composite (PA-TFC) membrane originally developed by Filmtec, and commercialized by DOW, has grown to dominate the market for reverse osmosis (RO) membranes to an extent that it is essentially the only product type available in the market. Cellulose acetate RO membranes are still sparingly available but there are very limited suppliers and they can be difficult to secure. For all intents and purposes, innovative separations or concentrations using RO must rely on the PA-TFC membranes for developing commercial operations. The lack of polymer diversity in commercial RO membranes severely limits opportunities for new separations to those where the commercial membranes are chemically and thermally compatible. Scientists and innovators in the RO space have expressed the need for new material membranes that can withstand, among other things, oxidants such as free chlorine that can be used to disinfect water by eliminating microbial growth and biofouling. The phrase “chlorine tolerant membranes are the holy grail” is well known in the industry, demonstrating the universal interest in this type of product. Cellulose acetate membranes are known to have some resistance to free chlorine but their performance with respect to salt rejection, flux, and compaction resistance is poor compared to the PA-TFC membranes. Surprisingly, no chlorine tolerant true competitor to the PA-TFC membrane has been commercialized yet. To produce a high-performance chlorine tolerant RO membrane, the challenge is two-fold. First a new polymer material must be identified with the appropriate characteristics for oxidant resistance, high water permeability, and low salt permeability. Second, a scalable manufacturing method must be developed to produce an extremely thin non-porous film that can withstand manufacturing stresses and high-pressure operations.

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