Mechanism of Halogen Attack on Composite Reverse-Osmosis Membranes, Phase 2

摘要

To identify the mechanisms of chlorine interactions with reverse-osmosis (RO)membranes and determine the relative importance of these mechanisms in causing flux decline in membranes, researchers studied highly crosslinked polyamide membranes made by an interfacial-polymerization technique. Results of the program indicate that the flux decline is due to a decrease in water sorption by the membrane polymer caused by uptake of chlorine into the polymer. Three methods of chlorine uptake were identified: (1) N-chlorination of secondary polyamides, (2) N-chlorination of residual amine groups in the polymer, and (3) sorption of chlorine into the membrane polymer. The first of these has the most effect on membrane performance. Membranes made from tertiary polyamides (not subject to N-chlorination) can maintain high fluxes when exposed to chlorine, but do not reject salt well enough to allow their use as seawater-desalination membranes.