Polysulfone membrane support

Geong and coworkers reported a new concept for the formation of zeolite/ polymer mixed-matrix reverse osmosis (RO) membranes by interfacial polymerization of mixed-matrix thin films in situ on porous polysulfone (PSF) supports [83]. The mixed-matrix films comprise NaA zeoHte nanoparticles dispersed within 50-200 nm polyamide films. It was found that the surface of the mixed-matrix films was smoother, more hydrophilic and more negatively charged than the surface of the neat polyamide RO membranes. These NaA/polyamide mixed-matrix membranes were tested for a water desalination application. It was demonstrated that the pure water permeability of the mixed-matrix membranes at the highest nanoparticle loadings was nearly doubled over that of the polyamide membranes with equivalent solute rejections. The authors also proved that the micropores of the NaA zeolites played an active role in water permeation and solute rejection. 

Two different RO membrane types were evaluated in this study. The first was a standard cellulose acetate based asymmetric membrane. The second type, a proprietary cross-linked polyamine thin-film composite membrane supported on polysulfone backing, was selected to represent potentially improved (especially for organic rejection) membranes. Manufacturer specifications for these membranes are provided in Table III. Important considerations in the selection of both membranes were commercial availability, high rejection (sodium chloride), and purported tolerance for levels of chlorine typically found in drinking water supplies. Other membrane types having excellent potential for organic recovery were not evaluated either because they were not commercially... 

An interesting group of composite membranes with very good properties is produced by condensation of furfuryl alcohol with sulfuric acid. The first membrane of this type was made by Cadotte at North Star Research and was known as the NS200 membrane [32], These membranes are not made by the interfacial composite process rather a polysulfone microporous support membrane is contacted first with an aqueous solution of furfuryl alcohol and then with sulfuric acid. The coated support is then heated to 140 °C. The furfuryl alcohol forms a polymerized, crosslinked layer on the polysulfone support the membrane is completely black. The chemistry of condensation and reaction is complex, but a possible polymerization scheme is shown in Figure 5.10. 

Exposure of a thin-film composite membrane to a variety of organic compounds can result in swelling or dissolution of the polysulfone microporous support layer.13 Suspect chemicals include ... 

Chemical damage occurs when a contaminant in the feed water is incompatible with the polymer comprising the membrane, the micro-porous support, or the fabric support. Besides oxidizers that degrade the crosslinking of a thin-film membrane, there are a variety of chemicals that swell or dissolve the polysulfone microporous support, including the following compounds. 

A third class of solute-wall interactions is the sample adsorption to the accumulation wall which may become particularly problematic in Fl-FFF since the accumulation wall consists of a membrane. The severity of adsorption differs significantly among the limited number of membranes that have been used in Fl-FFF, so that as additional membranes are explored, one can expect improvements. A number of membranes has been tested for use for Fl-FFF with respect to sample adsorption including polypropylene, polysulfone, several supported regenerated celluloses and their derivatives and polycarbonate membranes [166]. The extent of sample adsorption obtained with the wrong membrane material is demonstrated in Fig. 33. 

Coating of ultrafiltration/microfiltration membrane supports such as polyvinylidene fluoride (PVDF) or polysulfone (PSF) with solutions of polymers such as poly(ether-hlocfc-amide) [51]. 

PSF membrane supported by polysulfone hollow fibers. PA membrane suiqiorted by polyamide hollow fibers. 

One of the most important degradation mechanisms of SLM is an emulsification ofthe membrane phase due to lateral shear forces. Therefore, formation of barrier layers on the membrane surface by physical deposition [98] or by interfacial polymerization could prevent instability [99, 100]. A polysulfone support with N-methylpyiTolidone as a solvent was coated by a poly(ether ketone) layer as the outside layer and gave a specific composite membrane support. Such composite hoUow-fiber membranes showed significant improvement in stabUity in copper ions permeation. 

Several polymers have been used as porous supports. One of the earliest composite membrane systems was a porous support formed from cellulose nitrate-cellulose acetate with a membrane barrier layer of cellulose triacetate. While this membrane successfully desalted seawater, it was fragile and expensive. To a large degree, present day commercially available composite membranes use a polysulfone porous support. 

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... 

Mohammad et al. [29] fabricated NF composite membranes by the interfacial polymerization technique and studied the membrane s surface by AFM. The membrane support was prepared from a dope containing polysulfone (PSf) (P1835-BP Amoco) and poly(vinylpyrrolidone) (PVP) (Fluka) with JV-methyl-2-pyrrolidone (NMP) as the solvent. The top active layer was obtained through interfacial polymerization between trimesoyl chloride (TMC) in hexane and the aqueous phase containing bisphenol A (BPA). Table 5.9 shows the summary of the membrane preparation conditions. The first three membranes identified as PT-30, PT-45, and PT-60 differ in the period of interfacial reaction. The other three membranes identified as PC-05, PC-1, and PC-2 differ in terms of the concentration of BPA in the aqueous phase. The pore sizes determined by AFM and also calculated using the Donnan-steric-... 

Ariza et al. studied the surfaces of three different types of membranes by AFM (six membranes in total). Two of them were polysulfone membranes one was a supported ultrafiltration commercial membrane (PSf), and the other was a symmetric experimental membrane (PSC, polysulfone composite) [43[. Two were composite RO polyamide/polysulfone membranes one was a commercial membrane supplied by FilmTec called NF45, and the other was a laboratory-made membrane called BO, both having polyamide as the active layer. The final two were experimentally activated membranes called DPA-2 and DTA-2, obtained by adding a given amount of di-2-ethylhexylphosphoric acid (DEHPA) and di-2-ethylhexylthiophosphoric acid (DTPA), respectively, to BO as carriers when the polyamide skin layer was formed... 

Polysulfone is used in apphcations requiring good high-temperature resistance such as coffee carafes, piping, sterilizing equipment, and microwave oven cookware. The good hydrolytic stability of polysulfone is important in these applications. Polysulfone is also used in electrical applications for connectors, switches, and circuit boards and in reverse osmosis apphcations as a membrane support. ... 

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. 

Supported Liquid Membranes. Supported liquid membranes (SLMs) consist of a hydrophobic, porous plastic sheet or hollow fiber (usually polypropylene or polysulfone). The pores are filled with an organic solvent in which the carrier is dissolved. This membrane separates the aqueous source and receiving phases (Figure 8c). The liquid-containing pores allow transport of the target species via the dissolved carrier, while the plastic sheet offers support for the liquid membrane. Pore sizes generally range from 0.02 to 1.0 pm. 

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