Supports porous polysulfone

PA-300, NS-lOO, which are crossllnked polyamide derivatives -ultrathln film depositions on porous polysulfone supports) are accurately represented by this scheme. In comparing the Loeb-Sourirajan type of membrane to the composite membrane, one may be puzzled by the function of the gel layer shown in the scheme. 

Considerable activity has been generated on composite reverse osmosis membranes by Japanese researchers. Patent applications were recently published, for example, covering research at Teijin Ltd. on interfacially formed membranes prepared from polydiallylamines (17) and from amine adducts of trls-(glycidyl) isocyanurate (18). Both types of membranes were formed on micro-porous polysulfone supports. Kurihara and coworkers have developed a composite membrane, designated PEC-1000, which is formed by an... 

The poly(ether/amide) thin film composite membrane (PA-100) was developed by Riley et al., and is similar to the NS-101 membranes in structure and fabrication method 101 102). The membrane was prepared by depositing a thin layer of an aqueous solution of the adduct of polyepichlorohydrin with ethylenediamine, in place of an aqueous polyethyleneimine solution on the finely porous surface of a polysulfone support membrane and subsequently contacting the poly(ether/amide) layer with a water immiscible solution of isophthaloyl chloride. Water fluxes of 1400 16001/m2 xday and salt rejection greater than 98% have been attained with a 0.5% sodium chloride feed at an applied pressure of 28 kg/cm2. Limitations of this membrane include its poor chemical stability, temperature limitations, and associated flux decline due to compaction. 

In composite RO membranes, the selective top layer and the porous support layer are usually made of different polymeric materials. The selective top layer is formed on the porous support in a second step, typically by an interfacial polymerization reaction. For example, a commercially available thin film composite RO membrane is made by coating a porous polysulfone support with a polyamide thin film formed by the interfacial reaction of m-phenylenediamine and 1,3,5-benzenetricarbonyl trichloride. Details regarding membrane structures can be found elsewhere in the... 

Figure 5 Cross-section of double-layered composite membrane the top layer. A, Is a dense poly(l,6-dlmethy 1-1,4-pheny lene oxide), the Intermediate layer, B, Is made of poly(dl-methyl siloxane) and the support, C, Is a porous 150 m polysulfone support. The membrane displays a separation factor of 4.1 toward an O /No air mixture and over 5 X 10"...

High performance thin-film composite membranes for reverse osmosis applications were fabricated by coating solutions of a highly chlorine-tolerant disulfonated PAES [92,93]. As base monomers, 4,4 -dichlorodiphenyl sulfone and 4,4 -biphenol are used. 4,4 -dichlorodiphenyl sulfone is then directly sulfonated to get a disulfonated monomer, 3,3 -disutfonate-4,4 -dichlorodiphenyl sulfone. These monomers can be directly copolymerized on a commercially available porous polysulfone support. 

Two polyamide/polysulfone composite membranes, a commercial membrane (C-PA) and an experimental one (PAO) are studied in this Chapter. The polysulfone support of sample C-PA is the porous P-PS membrane previously studied. The roughness of both polyamide membranes is higher than that of other studied membranes, being the experimental composite membrane more than three times rougher than the commercial one (Ra(C-PA) = 25.0 nm and Ra(PAO) = 81.7 nm obtained from 15 jm AFM images), as can be observed in Figme 9 AFM images. 

A thin polymer him can be formed in situ on the surface of a porous substrate membrane by an interfacial polycondensation process. A classical example of this method was described by Rozelle et al. in detail for the formation of the North Star NS-100 membrane 30]. According to their description, the polysulfone support films are placed, shiny surface upwards, into a 0.67% aqueous polyethyicnimine (PEI) solution in an aluminum tray. After 1 min, the PEI solution is poured off, and the tray held in a vertical position for 1 min to allow the excess solution to drain from the surface of the him. Then the wet surface is contacted with a 0.5% solution of toluene 2,4-diisocyanate (TDI) for 1 min at room temperature. After draining the excess TDI solution, the u y is placed horizontally at 11S C for 10 min. After the heat curing, the composite membrane is easily peeled off from the aluminum surface. 

Viji unya also studied the effect of some diol isomers as the liquid fillers in mixed-matrix membranes for gas separation. They incorporated 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and 2,3-butanediol liquid fillers into silicone rubber coating on top of the porous polysulfone support membrane. Similar to PEG liquid filler, it was found that 1,2-butanediol and 2,3-butanediol could improve propylene over propane selectivity. However, the selectivity of propylene over propane was not enhanced when 1,3-butanediol and 1,4-butanediol were added to silicone rubber. In PEG, the hydroxyl group is attached to each carbon atom on carbon backbones. A portion of 1,2- and 2,3-butanediol molecules are similar to PEG in which the hydroxyl groups are attached to the adjacent carbon atoms. In contrast, the hydroxyl groups in 1,3- and 1,4-butanediol molecules are not attached to the adjacent carbon atoms. Therefore, it was proposed that the position of hydroxyl groups of the butanediols plays an important role for the improvement of propylene over propane selectivity. 

In some other successful examples, zeolite nanoparticles have been incorporated into a polymer matrix to form a thin-film nanocomposite RO membrane and to create a preferential flow path for water molecules, leading to enhanced water transport through the membrane [64,65]. Use of zeolite in the development of TFN for RO was first reported by Hoek and co-workers [66]. Similarly, Jeong et al. [64] prepared a thin-film RO nanocomposite membrane by interfacial in situ polymerization on porous polysulfone support, in which NaA zeolite nanoparticles were incorporated into a thin PA film. Introduction of zeolite nanoparticles into a conventional PA RO thin film has enhanced flux to more than double of the conventional membrane with a salt rejection of 99.7%, which is attributed to the smoother and more hydrophilic negatively charged surface. Silica nanoparticles of various sizes have also been incorporated into a PA polymer matrix for RO desalination [67]. Presence of silica nanoparticles was found to remarkably modify the PA network structure, and subsequently the pore structure and transport properties with only 1-2 wt% of silica, a membrane was fabricated with significantly enhanced flux and salt rejection. 

The most widely used chemically modified PPO in the development of thin film composite membranes is sulfonated polyphenylene oxide (SPPO). The polymer in the acid form as well as salt form has been used by Bikson to produce multilayer composite membranes. These types of membranes have been described to have at least two chemically distinct layers deposited on a porous substrate in a single coating step process. The outer layer forms a protective defect-sealing surface whereas the inner layer is the selective SPPO layer. This layer is adjacent to the porous support membrane. The two top layers are formed simultaneously on top of porous polysulfone support hollow fibers. A coating solution of SPPO in the lithium salt form (SPPO-Li ) and amine functional silicone fluid was coated on top of the polysulfone fibers. These coated fibers were used to construct a hollow fiber separator permeator. 

Fig. 10. Composite hoUow-fiber membranes (a) polysulfone boUow fiber coated witb fiiran resin. A and B denote fiiran resin surface and porous support, respectively (b) cross section of composite boUow fiber (PEI/TDI coated on polysulfone matrix). C, D, and E denote tightly cross-linked surface, "gutter" gel layer, and porous support, respectively. Both fibers were developed for reverse osmosis appHcation (15).

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. 

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. 

These types of separators consist of a solid matrix and a liquid phase, which is retained in the microporous structure by capillary forces. To be effective for batteries, the liquid in the microporous separator, which generally contains an organic phase, must be insoluble in the electrolyte, chemically stable, and still provide adequate ionic conductivity. Several types of polymers, such as polypropylene, polysulfone, poly(tetrafluoroethylene), and cellulose acetate, have been used for porous substrates for supported-liquid membranes. The PVdF coated polyolefin-based microporous membranes used in gel—polymer lithium-ion battery fall into this category. Gel polymer... 

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. 

The porous support layer is a skinless microgel with approximately 0.1 pM pores and, in most cases, consists of polysulfone. 

In addition to the usual vinyl monomers, most organic compounds having adequate vapor pressure could be used to deposit a barrier layer on porous supports. Additional copolymers could be formed by inclusion of nitrogen in the reactant gases. The supports used included Millipore filters, porous polysulfone films and porous glass tubes. Examples were presented of plasma formed membranes with 99 percent salt rejection, 38 gfd flux (63.3 L/sq m/hr) and low flux decline in seawater tests. A recent report by Heffernan et al describes gas phase deposition of membranes on hollow fibers (30). 

---