Deterioration Mechanism of a Tertiary Polyamide Reverse Osmosis Membrane by Hypochlorite

A tertiary polyamide membrane was synthesized using N,N′-dimethyl-m-phenylenediamine. The durability of this membrane to chlorination by hypochlorite treatment followed by sodium hydroxide treatment was examined, and then deterioration mechanisms were proposed. The tertiary polyamide membrane demons...

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Bibliographic Details
Published in:Environmental science & technology 2019-08, Vol.53 (15), p.9109-9117
Main Authors: Hashiba, Koki, Nakai, Satoshi, Ohno, Masaki, Nishijima, Wataru, Gotoh, Takehiko, Iizawa, Takashi
Format: Article
Language:English
Subjects:
Benzene
Chlorination
Chlorine
Cleavage
Collapse
Deterioration
Durability
Hydrocarbons
Hypochlorous acid
Infrared spectroscopy
Nitrogen
pH effects
Phenylenediamine
Polyamide resins
Polyamides
Reverse osmosis
Salt rejection
Sodium
Sodium hydroxide
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Summary:A tertiary polyamide membrane was synthesized using N,N′-dimethyl-m-phenylenediamine. The durability of this membrane to chlorination by hypochlorite treatment followed by sodium hydroxide treatment was examined, and then deterioration mechanisms were proposed. The tertiary polyamide membrane demonstrated better durability to free chlorine than a conventional secondary polyamide one; however, the former was deteriorated by hypochlorite for 24 h at 2000 ppm of free chlorine below pH 7.5. The salt rejection and permeation performance of the membrane were almost unchanged, and the least chlorination of the active layer occurred during hypochlorite treatment at pH 10. These results indicated that hypochlorous acid rather than hypochlorite ion was the free chlorine species that induced membrane deterioration. The deterioration became severe as chlorination progressed, resulting in collapse of the active layer below pH 7.5. Chlorination and hydrolysis of the model tertiary amide N-methylbenzanilide and Fourier transfer infrared spectroscopy of a deteriorated membrane showed that chlorination of the tertiary polyamide occurred via direct chlorination of the benzene bound to the amidic nitrogen. Silver ion probing of the deteriorated membrane revealed that amide bond scission occurred in the active layer, which might be related to the electron deficiency of the amidic nitrogen caused by chlorination of its benzene ring.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.9b00663