Nanofiltration polysulfone

An excellent review of composite RO and nanofiltration (NE) membranes is available (8). These thin-fHm, composite membranes consist of a thin polymer barrier layer formed on one or more porous support layers, which is almost always a different polymer from the surface layer. The surface layer determines the flux and separation characteristics of the membrane. The porous backing serves only as a support for the barrier layer and so has almost no effect on membrane transport properties. The barrier layer is extremely thin, thus allowing high water fluxes. The most important thin-fHm composite membranes are made by interfacial polymerization, a process in which a highly porous membrane, usually polysulfone, is coated with an aqueous solution of a polymer or monomer and then reacts with a cross-linking agent in a water-kniniscible solvent. 

Chloride, sulfate, and other anions may affect the removal of arsenic by nanofiltration. The effects often depend on the composition of the nanofilter. Specifically, increasing NaCl concentrations actually improves arsenic removals with polyamide thin-film composite filters. On the other hand, NaCl solutions may interfere with the removal of arsenic with sulfonated polysulfone thin-film composite nanofilters (Shih,... 

Figure 5.8 Membranes based on sulfonated polysulfone and substituted poly(vinyl alcohol) are produced by Hydranautics (Nitto) for nanofiltration applications...

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). 

FIGURE 42.4 Chemical stmctures of polymers for nanofiltration (a) cellulose triacetate, (b) aromatic polyamide, (c) polyvinyl alcohol, and (d) polysulfone. 

Porous membranes can be made of polymers (polysulfones, polyacrylonitrile, polypropylene, silicones, perfluoropolymers, polyimides, polyamides, etc.), ceramics (alumina, silica, titania, zirconia, zeolites, etc.) or microporous carbons. Dense organic membranes are commonly used for molecular-scale separations involving gas and vapor mixtures, whereas the mean pore sizes of porous membranes is chosen considering the size of the species to be separated. Current membrane processes include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), gas and vapor separation (GS), and pervaporation (PV). Figure 1 indicates the types and sizes of species typically separated by these different separation processes. 

Peyravi, M., Rahimpour, A., and Jahanshahi, M. 2012. Thin film composite membranes with modified polysulfone supports for organic solvent nanofiltration. Journal of Membrane Science 423 24 225-237. 

Maurya, S. K., Parashuram, K., Singh, P. S., Ray, P, and Reddy, A. V. R. 2012. Preparation of polysulfone-polyamide thin film composite hollow fiber nanofiltration membranes and their performance in the treatment of aqueous dye solutions. Desalination 304 11-19. 

Miao, J., Chen, G., Gao, C., and Dong, S. 2008. Preparation and characterization of Al, O-carboxymethyl chitosan/ Polysulfone composite nanofiltration membrane cross-linked with epichlorohydrin. Desalination 233 147-156. 

Use of nanofiltration for non-aqueous separations is limited by membrane compatibility - a common material in composite nanofiltration membranes used for aqueous separations is polysulfone which possesses limited solvent resistance [134]. However, during the past two decades a number of materials have emerged with improved solvent resistance that have enabled a broad range of organic solvent nanofiltration (OSN) applications. These materials include polydimethylsiloxane, polyphenylene oxide, polyacrylic acid, polyimides, polyurethanes, and a limited number of ceramics. Commercial products are offered by Koch Membrane Systems, W.R. Grace, SolSep, and Hermsdorfer Institut fur Technische Keramik (HITK) [135]. 

GE-Osmonics (part of GE Water Technologies) commercializes the Desal 5 nanofiltration membranes, used for removal of hardness and other contaminants, alcohol recovery from aqueous solution and removal of salt from salt whey. The membrane has 4 layers, a polyester nonwoven, an asymmetric micro-porous polysulfone and two proprietary thin films, which might be based on sulfonated polysulfone and polypiperazineamide [34]. A comparison between DesaF 5 and NF270 for nanofiltration has been reported by [44] (Tab. 4.3). 

Nanofiltration membranes can also be obtained by coating ultrafiltration membranes with different polymer solutions. Nitto Denko commercializes NTR-729 HF, a low-pressure spiral element also suitable for nanofiltration of salt and low molecular weight organic compounds. The membrane has a polysulfone porous support coated with a thin layer of polyvinyl alcohol. Analogous procedures have been reported in the Hterature. Membranes with cutoffs between 800 and 4500 g/mol and water permeabihties of up to 10 1/h m bar... 

Sulfonated polysulfone seems to also play an important role in nanofiltration and reverse osmosis membranes commercialized by Desal. According to Petersen [34] the Desal-5 membrane appears to consist of three layers a microporous polysulfone, a sulfonated overlay and a top ultrathin layer based on polypipera-zineamide. 

Another method of preparing nanofiltration membranes is to dip-coat a thin layer of sulfonated poly(phenylene oxide) (SPPO) [17], sulfonated polysulfone (SPS) [18], or carboxylated polysulfone [19] on a porous substrate membrane. The sulfonic acid groups in SPPO and SPS also become negatively charged with -SO3 groups upon dissociation. Sulfonic acid is a stronger acid than carboxylic acid. 

Zhang et al. prepared TFC membranes for nanofiltration by interfacial polymerization of piperazine and trimesoyl chloride on top of polysulfone UF membranes with molecular weight cutoff (MWCO) values of 60 000 Da and water permeabilities of 100-150 Lm h bar [28]. Figure 4.12 shows the SEM picture of the sur-... 

Du, R.H. and Zhao, J.S. 2004. Properties of poly (A,A-dimethylaminoethyl methacrylate)/ polysulfone positively charged composite nanofiltration membrane.. 7. Memh. Sci. 239 83-188. 

Nanohybrid materials have been furthermore used for ultra-/nanofiltration applications. Nanofiltration is a pressure-driven membrane separation process and can be used for the production of drinking water as well as for the treatment of process and waste waters. Some apphcations are desalination of brackish water, water softening, removal of micropollutants, and retention of dyes. Ultrafiltration membranes based on polysulfones filled with zirconia nanoparticles are usually prepared via a phase-inversion technique and have been used since 1990 [328]. Various studies were done in order to assess the effect of the addition of Zr02 to polysulfone-based ultrafiltration membranes [329] and the influence of filler loading on the compaction and filtration properties of membranes. The results indicate that the elastic strain of the nanohybrid membranes decreases and the time-dependent strain... 

In principle, for separation of salt from concentrated brine solutions, desahnation techniques common for seawater are suitable. Koyuncu et al. (2004) reported studies on reactive dye/sodium chloride separation using nanofiltration membranes made from polysulfone-polyamide. The emphasis of this research, however, was more directed towards the quality of the purified water than on reclamation of salt or dye. Wenzel et al. (1996) suggested re-use of the bath of a reactive dyeing process containing all auxiliaries after the hydrolyzed reactive dye has been removed by adsorption on activated carbon. The dyes were degraded in an anaerobic digester. 

Membranes with diverse structures (porous, dense and composites) and from different materials (regenerated cellulose, polysulfone, polyamide/polysulfone) currently used in filtration processes (Ultrafiltration, Nanofiltration and Reverse Osmosis) and other separation applications were studied. 

Aromatic tri-functional acid and amine monomers are used to obtain reticulated polyamides, which have better mechanical and chemical stability and, for that reason, they are preferred for nanofiltration and reverse osmosis membrane materials. In these membranes, a thin polyamide layer (less than l jm thickness) is fabricated by interfacial polymerization on the top of a porous support (normally an ultrafiltration polysulfone membrane), which usually presents a non-woven reinforcement for mechanical stability as can be seen in Figure 8. Despite its small thickness, the polyamide dense layer is the main regulator of the rejection/transport of water and ions across the membrane. 

A commercial composite polyamide/polysulfone membrane for nanofiltration... 

Impedance plots for the other studied membranes (composite polyamide/ polysulfone nanofiltration NF45 and RgC regenerated cellulose) are shown in Figures 9.16 and 9.17 respectively, and differences in the IS curves and equivalent circuits associated with both kinds of membranes are related to their different structures ... 

Adams FV. Polysulfone/p-cyclodextrin polyurethane mixed-matrix composite nanofiltration membrane for water treatment. PhD Thesis, University of Johannesburg 2013. 

Figure 32.1 Chemical structures of (a) polysulfone and (b) polyethersulfone and FTIR-ATR spectra of the commercial nanofiltration membranes NF45, NF270, and NTR7450. The spectra reveal that the membranes contain a polysulfone layer (Puro et al., 2006, with permission of IChemE s journals).

Rajesh, S., S. SenthUkumar, A. Jayalakshmi, M. T. Nirmala, A. F. Ismail, and D. Mohan. 2013. Preparation and performance evaluation of poly (amide-imide) and TiOj nanoparticles impregnated polysulfone nanofiltration membranes in the removal of humic substances. Colloids Surf. A Physicochem. Eng. Asp. 418 92-104. 

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