Insights on the chlorine resistance of polyester composite nanofiltration membranes

Abstract

The use of chlorine as a pretreatment of water treatment and desalination processes causes a loss in performance and lifespan of the membranes usually employed in these processes. Polyester (PE) membranes have been proposed as an alternative due to the absence of amidic hydrogen; however, fabricating PE composite membranes with equivalent performance and high tolerance towards chlorine has proven challenging. In this work, we evaluate the effects of monomer concentration and blends, proton scavenger, surfactant concentration, reaction time and temperature on interfacial polymerization (IP) of trimesoyl chloride and resorcinol. Reaction temperature was the most crucial factor to achieve a PE coating film with high crosslinking degree (XD), high divalent rejection and excellent chlorine tolerance. The resorcinol membrane showed a Na2SO4 rejection of >90 % before and after 6000 ppmh-Cl2 at pH 7. XPS analysis showed that chlorination of PE membranes resulted in loss of CC bonds and increase in C–C and C–O bonds. At high crosslinking degrees, the changes caused by chlorine were minimal. Based on the characterization and the performance of the chlorinated membranes, ring chlorination followed by ring hydrolysis is the proposed mechanism for degradation of lower XD membranes.