Preparation of thin-film composite polyamide reverse osmosis membranes

Thin-Film Composite (TFC) polyamide membranes in spiral wound configuration are widely used in seawater desalting plants worldwide because of their superior solute-rejecting properties and attractive water permeation rates. TFC polyamide membranes are three layered membranes, prepared in two stages wherein conventional phase separation and interfacial polymerisation techniques are combined to give an ultra-thin separation barrier deposited over a fabric-supported macroporous membrane. Preparation of composite polyamide membranes in commercial dimensions requires control of chemical, mechanical and environmental factors to insure uniform reproducible membranes of desired performance characteristics. The specification of raw materials, choice of solvents/reactive chemicals and their purity requirements, and ambient humidity during membrane preparation require careful monitoring and control. The Desalination Division of BARC is presently engaged in the scaling-up of TFC polyamide membrane preparations for reverse osmosis applications. The various critical parameters requiring attention to achieve high solute separation are outlined in this paper.