Development of a New Chlorine and Biofouling Resistant Polyamide Membrane

Abstract : Report developed under SBIR contract topic A01-029. A new polyamide (PA) reverse osmosis (RO) composite membrane has been prepared, based on the reaction of highly purified cis, trans, cis, trans 1,2,3,4-cyclopentanetetracarboxylic acid chloride with m-phenylenediamine (MPD). The new membrane has demonstrated the ability to withstand high concentrations of chlorine in immersion tests without detrimental effects. The contact time was 30,000 mg/L-hr, or 6.8 years of exposure at the 0.5 mg/L level. In long-term RO field tests using flat sheet membrane test cells with 0.5 mg/L chlorinated feed water the membranes showed slow deterioration particularly after system shutdowns (depressurizations). Nevertheless, the new membrane compared favorably with conventional PA membranes based on trimesoyl chloride and MPD. Degradation of the new PA composite membrane was not restricted to the PA desalination barrier. The chemical composition of the porous supporting membrane, delamination of the PA film from the support, and the presence of heavy metals in the feed have been shown to be contributing factors. Gradual biological degradation of PA membrane has not been ruled out. All PA composite membranes supported on porous polysulfone (PS) deteriorated more rapidly in immersion experiments compared to the same PA membranes supported on polyetherimide membranes. Ring chlorination of PS in the presence of chlorine may be a possible mechanism leading to PA composite membrane deterioration. Today, all commercial PA composite RO membranes are made with PS supporting membranes. Further development studies are required.