Other Interfacial Membranes Based on Polymeric Amines

OTHER INTERFACIAL MEMBRANES BASED ON POLYMERIC AMINES 

Various polyamines have been synthesized and evaluated in the fabrication of the NS-100 type of membrane. These various compositions are described in the patent literature. Some of these efforts have involved polymeric amines containing only secondary amino groups to reach a goal of improved chlorine resistance. Whether any of them have reached commercial status cannot be determined because of the current trend to avoid publication of the compositions of new commercial reverse osmosis membranes. 

Kurihara and coworkers at Toray Industries prepared several aminated derivatives of polyepichlorohydrin, then formed composite polyamide membranes by interfacial reaction with isophthaloyl chloride.38 Polyepichlorohydrin was converted to polyepiiodohydrin, then reacted with either4-(aminomethyl)piperidine, 3-(methylamino)hexahydroazepine, or 3-(amino)hexahydroazepine. Also, poly-epiaminohydrin was prepared by reduction of the azide derivative of polyepiiodohydrin. Best salt rejections were obtained if the polymeric amine formulation contained a substantial proportion of the monomeric amines as coreactants in the interfacial reaction. In tests on 3.5% sodium chloride at 800 psi and 25 C, salt rejections of 99.5% at fluxes of 8 to 9 gfd were characteristic. A three-zone barrier layer was produced, consisting of a heat-crosslinked polyamine gel (as in NS-100), a polyamide layer incorporating both the polymeric 

Kawaguchi and coworkers at Teijin have prepared a series of polymers based on poly(diallyl amine), its copolymer with sulfur dioxide, and various terpolymers.39 The chemistry of this polymer synthesis is shown below. The patent description shows the diallylamine polymers to be polypiperidine (six-membered ring) derivatives, but there are a number of publications that show this monomer to produce preferably polypyrrolidine (five-membered ring) structures  

These polymers were then interfacially reacted with di- and trifunctional aromatic acyl halides to give polyamides. Because the only reactive amine groups in these polymers were of the secondary amine type, such polymers should be chlorine-resistant. Dynamic chlorine tests (5 ppm, pH 6.0 to 6.5, 0.5% NaCI, 600 psi, 25°C) of 40 to 80 hours duration appeared to uphold this inference. 

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