Crosslinked polyamide composite membranes

To satisfy these requirements, numerous researches have been done for membrane materials, structure and fabrication technology. In-situ inter dal polycondensation method (Figure 2) was developed to obtain the high performance composite membrane. With this method, crosslinked polyamide composite membranes, which overcome these problems have been commercialized and become one of the major reverse osmosis membrane today. 

The combination of piperazine with trimesoyl chloride in composite membrane form was named NS-300. Trimesoyl chloride leads to a crosslinked polyamide structure. Apparently, however, considerable formation of hydrolyzed carboxylate groups also occurs. This is evidenced by the anion selectivity of the membrane, demonstrated by the sequential salt rejection data in Table 5.4 for a series of salts on test with a single set of membrane specimens. 

M. Kurihara, Y Himeshima, and T. Uemura, Crosslinked aromatic polyamide ultra-thin composite membrane from 1,3,5-Triaminobenzene, Proceedings of die 1990 InternatUmal Congress on Membranes and Membrane Processes, 1034 (1990). 

Kurihara, M., Uemura, T., Himeshima, Y., Ueno, K., and Bairinji, Y. (1994b). Development of crosslinked aromatic polyamide composite reverse osmosis membrane. Nippon Kagaku Kaishi 1994(2), 97-107. 

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... 

Some hydrolysis of the trimesoyl chloride takes place during membrane fabrication. ESCA studies indicated that approximately one-sixth of the carboxyl groups ere present as ionic carboxylate and five-sixths of the carboxyl groups are present as amides, leading to the above structure. The FT-30 barrier layer is insoluble in sulfuric acid and in all organic solvents, in agreement with the crosslinked nature indicated above. Its chemical structure is somewhat similar to the composition of the duPont Permasep B-9 hollow fiber polyamide, believed to be approximately as follows ... 

In reverse osmosis membranes, we tried to introduce high amide linkage into polyamide membrane to realize better salt rejection and better water flux. Consequently, crosslinked fully aromatic polyamide membrane from 1,3,5-Triaminobenzene has found to have excellent separation performance and durability. Moreover, based on "UTC-70", fully aromatic polyamide membrane from 1,3,5-Triaminobenzene commercialized by Toray, various types of membrane have developed to satisfy different requirements in wide ranges of application. In such membranes, controlling membrane performance is accomplished through composition of membrane materials, control of polycondensation reaction, physical treatment and chemical treatment, which are closely related to chemical and physical structures of membranes. 

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