Desalination Membranes Based on Sulfonated Poly(arylene ether sulfone) Random Copolymers

Abstract

The current commercially available membranes for water desalination by reverse osmosis are derived from two basic classes of polymers: cellulose acetate and crosslinked aromatic polyamides. Cellulose acetate membranes are susceptible to microbiological attack, compaction at higher temperatures and pressures, and their operation is limited to a relatively narrow pH range. The polyamide membranes show improved transport properties at given applied pressure and stability over a wider range of pH compared to cellulose acetate membranes. However, these polyamide membranes suffer from poor resistance to continual exposure to oxidizing agents such as chlorine in desalination applications. To overcome these problems, we have synthesized and characterized a new generation of desalination membranes for water purification, based on chemistry that is entirely different from conventional post-polymerization sulfonation technology. As a result, reproducible sulfonated poly(arylene ether sulfone) copolymer membranes have been prepared for desalination. This family of copolymers has been studied for use as proton exchange membranes, while no report has been issued on its water desalination properties. A key technical feature of these new membranes is their high tolerance chlorine in feed water and their excellent reproducibility in fabrication. Our main approach to optimizing polymer design is to use random, cross-linked, block, and blends based on disulfonated copolymers to achieve high water permeability and high salt rejection simultaneously. In this study on random copolymers, we vary the sulfonation level and investigate the solubility, diffusivity and permeability of the desalination membranes towards water and sodium chloride. At a high level of salt rejection, the membranes achieve high water permeability. In addition, the intrinsic properties of polymeric membranes to separate water and salt are being considered in terms of water permeability and salt permeability, and we are using this framework to establish guidelines for material selection and design for desalination membranes.