Chlorine tolerant, multilayer reverse-osmosis membranes with high permeate flux and high salt rejection

Abstract

A new class of high molecular weight polyethersulfone ionomers is described in which the ionic content can be varied, at will, over a very wide and fully controllable range. A novel type of coating process enables these materials to be deposited from alcohol-type solvents as cohesive but very thin (50–250 nm) films on porous support membranes, giving high-flux membranes (3.3–5.0 L m−2 h−1 bar−1) with very good, though not outstanding, salt rejection (typically 92–96%). A secondary layer of formaldehyde–cross-linked polyvinyl alcohol can be deposited from aqueous solution on the surface of the ionomer membrane, and this layer increases salt rejection to greater than 99% without serious loss of water permeability. The final multilayer membrane shows excellent chlorine tolerance in reverse-osmosis operation.