Polyamide composite membranes

PA membrane surface Polymeric support Fabric backing 

There have been several improvements made to polyamide, composite membranes that have enhanced their performance. Perhaps the most 

Membrane Type Homogenous asymmetric, thin-film composite 

Low-pressure membranes have also been developed. These membranes offer high flux at low temperatures and pressure albeit with some reduction in rejection (the permeability of polyamide membranes is a function of temperature, with lower water temperatures generally requiring higher operating pressures to maintain productivity—see Chapter 9.2). These low-pressure membranes allow for operation at low temperature at lower pressure than non low-pressure membranes. 

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All oxidants used must be removed in the final stage of the pretreatment process, as they are known to damage most polymer membranes used for desalination. In particular, chlorine is known to be harmful to commonly used thin-film composite polyamide membranes. 

Cellulose acetate and linear aromatic polyamide membranes were the industry standard until 1972, when John Cadotte, then at North Star Research, prepared the first interfacial composite polyamide membrane.8 This new membrane exhibited both higher throughput and rejection of solutes at lower operating pressure than the here-to-date cellulose acetate and linear aromatic polyamide membranes. Later, Cadotte developed a fully aromatic interfacial composite membrane based on the reaction of phenylene diamine and trimesoyl chloride. This membrane became the new industry standard and is known today as FT30, and it is the basis for the majority... 

Nanofiltration (NF) is a pressure-driven membrane separation technology used to separate ions from solution. Nanofiltration membranes were widely available beginning in the 1980 s. This technology uses microporous membranes with pore sizes ranging from about 0.001 to 0.01 microns. Nanofiltration is closely related to RO in that both technologies are used to separate ions from solution. Both NF and RO primarily use thin-film composite, polyamide membranes with a thin polyamide skin atop a polysulfone support (see Chapter 4.2.2). 

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... 

The initial studies by Cadotte on interfacially formed composite polyamide membranes indicated that monomeric amines behaved poorly in this membrane fabrication approach. This is illustrated in the data listed in Table 5.2, taken from the first public report on the NS-100 membrane.22 Only the polymeric amine polyethylenimine showed development of high rejection membranes at that time. For several years, it was thought that polymeric amine was required to achieve formation of a film that would span the pores in the surface of the microporous polysulfone sheet and resist blowout under pressure However, in 1976, Cadotte and coworkers reported that a monomeric amiri piperazine, could be interfacially reacted with isophthaloyl chloride to give a polyamide barrier layer with salt rejections of 90 to 98% in simulated seawater tests at 1,500 psi.4s This improved membrane formation was achieved through optimization of the interfacial reaction conditions (reactant concentrations, acid acceptors, surfactants). Improved technique after several years of experience in interfacial membrane formation was probably also a factor. 

Figure 5.11 SEM photographs of the surface texture of composite polyamide membranes from aliphatic and aromatic amines (a) uncoated microporous poly-sulfone (b) polyamide from polyethylenimine and trimesoyl chloride (c) tri-ethylenetetramine and trimesoyl chloride (d) 1,3-benzenediamine and trimesoyl chloride (e) 2,4-toluenediamine and trimesoyl chloride (f) 4-methoxy-1,3-benzenediamine and trimesoyl chloride. Note the smooth surface for aliphatic amine-based interfacial trimesamides and the coarse ridge-and-valley structure for aromatic amine-based interfacial trimesamides.

In the patent by Kurihara, Uemura and Okada,38 combinations of a polymeric amine with a monomeric amine were used to produce composite polyamide membranes having high salt rejections. The membranes were described as having a bilayer polyamide barrier film a surface polyamide zone rich in monomeric amine, and a subsurface polyamide zone incorporating both monomeric and polymeric amine. This patent disclosure demonstrated an understanding of the mechanism of interfacial polyamide barrier layer formation. 

Liu, M., Wu, D., Yu, S., and Gao, C. 2009. Influence of the polyacyl chloride structure on the reverse osmosis performance, surface properties and chlorine stability of the thin-fihn composite polyamide membranes. Journal of Membrane Science 326 205-214. 

Abu Tarboush, B. J., Rana, D., Matsuura, T, Arafat, H. A., and Narbaitz, R. M. 2008. Preparation of thin film composite polyamide membranes for desalination using novel hydrophilic surface modifying macromolecules. Journal of Membrane Science 325 166-175. 

Although the hydrophobic surface of nylon membranes may be improved by hydrolysis or chemical modification, composite polyamide membranes are preferred in chromatographic applications. Klein et al. [42] prepared polyamide microporous membranes by modification of terminal amino groups. Covalent binding of a polyhydroxyl-containing material to the polyamide membrane increases the density... 

Z.V.P. Murthy, S.K. Gupta, Sodium cyanide separation and parameter estimation for reverse osmosis thin-film composite polyamide membrane,... 

Zhou, Y., Yu, S., Gao, C. and Feng, X. 2009. Surface modification of thin composite polyamide membranes by electrostatic self-deposition of polycations for improved fouling resistance. Sep. Purif. Technol. 66 287-294. 

Vertssimo, S., Peinemami, K.V. and Bordado, J. 2006. Influence of the diamine structure on the nanofiltration performance, surface morphology and surface charge of the composite polyamide membranes. ZMemfeSci. 279 266-275. 

One of the more interesting fronts of development includes the search for improved membrane materials. While no new polymeric RO membranes have been introduced commercially over the last 20 to 30 years, there have been developments in performance (see Figure 1.5). These improvements in performance were achieved via modifications to the membrane itself (surface modifications made possible due to more advanced membrane characterization techniques) and closer tolerances in the interfacial polymerization reaction to make the membrane, and enhancements of the module design. Membranes with these improvements are commercially available today. While work is continuing with modifications to the current thin-film composite polyamide membranes, researchers are looking toward additional materials that might be suitable for use as RO membranes. 

Thin film composite polyamide membranes are used for reverse osmosis and nanofiltration... 

S.Y. Lee, H.J. Kim, R. Patel, S.J. Im, J.H. Kim, B.R. Min, Silver nanoparticles immobilized on thin film composite polyamide membrane Characterization, nanofiltration, antifouhng properties. Polymers for Advanced Technologies 18 (2007) 562-568. 

B.J. Abu Tarboush, D. Rana, T. Matsuura, H.A. Arafat, R.M. Narbaitz, Fbeparation of thin-fibn-composite polyamide membranes for desalination using novel hydrophilic surface modifying macromolecules, J Memb Sci, 325 (2008) 166-175. 

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