Novel hydrophilic nylon 6,6 microfiltration membrane supported thin film composite membranes for engineered osmosis

Previous investigations of engineered osmosis (EO) concluded that hydrophobic support layers of thin film composite membrane causes severe internal concentration polarization due to incomplete wetting. Incomplete wetting reduces the effective porosity of the support, inhibiting mass transport and thus water flux. In this study, novel thin film composite membranes were developed which consist of a poly(piperazinamide) or polyamide selective layer formed by interfacial polymerization on top of a nylon 6,6 microfiltration membrane support. This intrinsically hydrophilic support was used to increase the “wetted porosity” and to mitigate internal concentration polarization. Reverse osmosis tests showed that the permselectivity of our best poly(piperazinamide) and polyamide thin film composite membranes approached those of a commercial nanofiltration and a commercial reverse osmosis membrane, respectively. The osmotic flux performance of the new polyamide thin film composite membrane showed matched water flux, 10 fold lower salt flux and 8–28 fold lower specific salt flux than the standard commercial cellulose triacetate forward osmosis membrane from Hydration Technology Innovations™. The relatively good performance in osmotic flux tests of our thin film composite membranes was directly related to the high permselectivity of the selective layers coupled with the hydrophilicity of the nylon 6,6 support. These results suggest that these nylon 6,6 supported thin film composite membranes may enable applications like forward osmosis or pressure retarded osmosis.