Barrier Polymers for High-Selectivity, Reverse-Osmosis Membranes

A new class of RO membrane is proposed that would exhibit unprecedented selectivity against organic compounds. Such membranes would be useful in water-recycle applications in space, as they would lead to exceedingly high water purity. As envisioned, the membranes would behave as "barriers" to organic molecules but still would allow water to pass. Two key innovations are required. The first is the use of "plasma polymerization" to produce a thin film of highly branched, tightly crosslinked material. The intermolecular spaces in these materials are such that water molecules are small enough to fit through, but moderately sized organic molecules such as phenol, benzene, urea, and ethanol are not. These materials have shown the potential of having selectivities greater than 10,000 for water over organic molecules, compared with maximum selectivities of 50 for conventional membrane materials. The second innovation is the use of a new membrane structure that eliminates problems with the inherent brittleness of the highly selective plasma-polymer material. In the Phase I program we will make these barrier membranes and then subject them to an organic "challenge" test to demonstrate that they are indeed barrier membranes. Work in Phase II would address fabrication scale-up and modularization of these membranes.