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

Abstract

Reverse osmosis and nanofiltration membranes are susceptible to biofouling, in particular when treating municipal wastewater, and chlorine compounds are widely used to successfully control the bacteria that causing biofouling. However, chlorine-containing disinfectants chemically degrade current commercial RO and NF membranes, especially the polyamide (PA)-thin film composite membranes that dominate the current market. The low chlorine tolerance of conventional PA membranes leads to irreversible damage to membrane performance due to chlorine attack beginning at the amide nitrogen in PA membranes. This presentation presents the synthesis and characterization of a systematic series of highly chlorine-tolerant, sulfonated copolymer membranes, for use as desalination membranes, based on chemistry that is entirely different from the conventional post-polymerization sulfonation technique. Using direct copolymerization of sulfonated and other monomers, reproducible sulfonated copolymer membranes can be prepared as various polymer structures and compositions at different sulfonation levels. This synthesis method overcomes the problems of conventional sulfonation technology such as molecular weight reduction during sulfonation. This study will discuss the preparation and evaluation of several families of sulfonated copolymers such as random or segmented multiblock copolymers in terms of fundamental desalination characteristics (e.g., water permeability (or permeance), salt permeability, and salt rejection). In addition, thin-film composite membranes were prepared via brush coating of dilute sulfonated polymer solutions on commercial microporous polysulfone membrane. These sulfonated copolymers or their thin-film composite membranes exhibit high water permeability (or permeance) and good salt rejection. To delineate structure-property relations for these materials, solubility and diffusivity of water and salt (e.g., NaCl) were also evaluated for a series of sulfonated copolymers with various sulfonation levels in acid or salt forms. These intrinsic properties were compared with those of commonly used cellulose acetate and polyamide membranes in the literature. This fundamental and systematic study of structure-property relations regarding newly synthesized sulfonated copolymer membranes provides guidelines regarding material selection for new desalination membranes.