Plasma Polymerization in Composite Membrane Fabrication

Plasma polymerization has been explored in considerable detail as a potential route to composite reverse osmosis membranes. Yasuda has written an excellent review covering the fundamentals and progress of plasma polymerization through 1974.88 Advances since then have not been particularly promising from a commercial standpoint, with the exception of the Solrox membrane (see below). 

Early work by Buck and Davar89 examined the plasma polymerization of several monomer systems. Best results in terms of reverse osmosis performance were achieved with vinylene carbonate/acrylonitrile and vinyl acetate/acrylo-nitrile. 

Wydeven and his coworkers examined the plasma polymerization of several amine monomers and obtained the best reverse osmosis membranes using allyl-amine.90/91 Reverse osmosis performances of 98 to 99% salt rejection and 4 to 8 gfd flux were achieved at test conditions of 1.0% sodium chloride, 600 psi, 20 C. ESCA spectra showed the nitrogen groups in the plasma-formed polymer to be nitrile or imine groups, but not amine groups. Oxygen was also present in the ESCA analysis. Elemental analysis showed a membrane stoichiometry of C3H 3 8N 0.9O0.1. 

Yasuda obtained membranes with good reverse osmosis properties by polymerizing gas plasma mixtures of acetylene/water/nitrogen and acetylene/wa-ter/carbon monoxide.92 9J Elemental analysis of the acetylene/water/nitrogen membrane was not given, but it was likely approximately equivalent to the allyl-amine-derived composition. Yasuda has observed membrane performance levels as high as 99% salt rejection and 38 gfd, tested on 3.5% sodium chloride at 1,500 psi. 

To date, no commercial examples of these membrane compositions have appeared in the marketplace. 

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