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Novel non-trimesoyl chloride based polyamide membrane with significantly reduced Ca2+ surface deposition density

Yuan, Bingbing, Li, Pengfei, Sun, Honghong, Zhao, Shengchao, Li, Peng, Sun, Haixiang, Niu, Q. Jason
Journal of membrane science 2019
acidity, alginates, artificial membranes, benzoic acid, calcium, carboxylic acids, cleaning, deprotonation, desalination, fouling, longevity, market share, models, nanosheets, organochlorine compounds, polyamides, water treatment
Polyamide membranes based on trimesoyl chloride (TMC) have captured the majority of the market share for desalination in water treatment. The TMC based membrane is prone to form calcium bridges with the organic foulants due to the relatively strong deprotonation ability of the benzoic acid generated from the incomplete reaction of the acyl chloride monomers. The foulants are thus rapidly deposited on the surface of the TMC based membrane, which results in the deterioration of water production and decrease of membrane lifespan. Herein, we have fabricated a polyamide membrane based on novel trimesoyl-[4,4-dimethyl-5(4H)-azlactone] (TMDMA) monomer instead of TMC monomer. Since the carboxylic groups of the prepared TMDMA polyamide nanofilm are not directly connected to the phenyl ring, the acidity coefficient (pKa) value is higher and, consequently, deprotonation ability is expected to be weaker. To confirm this theory, we have conducted the fouling experiment on TMDMA based membrane with alginate as a model foulant and compared that with TMC based polyamide membranes. A lower flux decline (33%) and higher cleaning efficiency (90.72%) are observed for the TMDMA polyamide membrane, while the flux decline and cleaning efficiency for the TMC based polyamide membrane are 52% and 49.52% respectively. Furthermore, the average Ca2+ density of the TMDMA polyamide membrane surface before and after cleaning are 81.52 mg m−2 and 21.61 mg m−2 respectively, which are lower than that of the TMC based polyamide membrane surface. Thus, it is clearly showing that the surface of the TMDMA polyamide membrane is not prone to form calcium bridges with foulants due to the weaker complexation between Ca2+ and the carboxylic acid groups.