Water and Salt Transport Behavior through Hydrophilic-Hydrophobic Copolymer Membranes and Their Relations to Reverse Osmosis Membrane Performance

摘要

Sulfonated copolymers are one of the most attractive areas of research due to their versatile applications. More recently, sulfonated polymers have received significant attention related to their use as fuel cell membranes. Sulfonated polymers have also been considered as interesting membrane materials for ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). These materials exhibit good resistance properties to bio-, protein-, and oily water-fouling due to their hydrophilic nature and negative surface charge. They also exhibit high tolerance to chlorine, which is a problem with current commercial polyamide RO membranes. However, in previous work, the widespread use of sulfonated polymer membranes was hindered by the fact that they were prepared using post-polymerization sulfonation employing very strong sulfonating agents (i.e., chlorosulfuric acid and sulfuric acid). These sulfonation techniques resulted in undesirable chain scission, branching and crosslinking. That is, their stability and performance characteristics as membranes for water purification were not sufficient for commercial practice. Fortunately, a promising development in this area has been achieved via the synthesis of tailor-made sulfonated copolymer membranes via direct copolymerization of disulfonated monomer. These sulfonated copolymer membranes can be reproducibly prepared with different morphologies, and they exhibit excellent hydrolytic and thermo-oxidative stability. Therefore, in the present study, these sulfonated copolymers have been highlighted as potential membranes for RO. The current work includes studies of antifouling properties and chemical stability against free chlorine attack, as well as fundamental RO separation performance (e.g., water permeability and salt rejection at various operating conditions (i.e., feed concentration, feed pressure, and feed flow-rate)). Intrinsic properties of the membranes, such as salt partition coefficient and diffusivity, will be discussed as will the tradeoff relationship between water flux and salt rejections in this family of materials.