Polysulfone asymmetric

These solvents include tetrahydrofuran (THF), 1,4-dioxane, chloroform, dichioromethane, and chloroben2ene. The relatively broad solubiHty characteristics of PSF have been key in the development of solution-based hoUow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Hollow-fibermembranes). The solvent Hst for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crysta11i2ation in many solvents. When the PES stmcture contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (Amoco Corp.) polyethersulfone, solution stabiHtyis much improved over that of PES homopolymer. 

Membrane most UF membranes are polysulfone. Asymmetric microporous with thin skin... 

Membrane Most UF membranes are polysulfone asymmetric microporous with thin skin 0.1 to 1 [rm supported on a porous layer 50 to 250 jrm. Pore size 0.001-0.2 [rm. This is too porous for RO. Pore size prevents concentration polarization (limiting RO) but performance is limited by gel polarization with 0.2-0.4. Xgei = 0.25-0.35 for macromolecules = 0.75 for colloids. Need to have membrane life > 1 year. 

Solubility of the three commercial polysulfones follows the order PSF > PES > PPSF. At room temperature, all three of these polysulfones as well as the vast majority of other aromatic sulfone-based polymers can be readily dissolved in a handful of highly polar solvents to form stable solutions. These powerful solvents include NMP, DMAc, pyridine, and aniline. 1,1,2-Trichloroethane and 1,1,2,2-tetrachloroethane are also suitable solvents but are less desirable because of their potentially harmful health effects. In addition to being soluble in the aforementioned list, PSF is also readily soluble in a host of less polar solvents by virtue of its lower solubility parameter. These solvents include tetrahydrofuran (THF), 1,4 dioxane, chloroform, dichloromethane, and chlorobenzene. The relatively broad solubility characteristics of PSF have been key in the development of solution-based hollow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Membrane Technology). The solvent list for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crystallization in many solvents. When the PES structure contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (British Petroleum) polyethersulfone, solution stability is much improved over that of PES homopolymer. 

Interfdci l Composite Membra.nes, A method of making asymmetric membranes involving interfacial polymerization was developed in the 1960s. This technique was used to produce reverse osmosis membranes with dramatically improved salt rejections and water fluxes compared to those prepared by the Loeb-Sourirajan process (28). In the interfacial polymerization method, an aqueous solution of a reactive prepolymer, such as polyamine, is first deposited in the pores of a microporous support membrane, typically a polysulfone ultrafUtration membrane. The amine-loaded support is then immersed in a water-immiscible solvent solution containing a reactant, for example, a diacid chloride in hexane. The amine and acid chloride then react at the interface of the two solutions to form a densely cross-linked, extremely thin membrane layer. This preparation method is shown schematically in Figure 15. The first membrane made was based on polyethylenimine cross-linked with toluene-2,4-diisocyanate (28). The process was later refined at FilmTec Corporation (29,30) and at UOP (31) in the United States, and at Nitto (32) in Japan. 

One unique appHcation area for PSF is in membrane separation uses. Asymmetric PSF membranes are used in ultrafiltration, reverse osmosis, and ambulatory hemodialysis (artificial kidney) units. Gas-separation membrane technology was developed in the 1970s based on a polysulfone coating appHed to a hoUow-fiber support. The PRISM (Monsanto) gas-separation system based on this concept has been a significant breakthrough in gas-separation... 

Cellulose acetate, the earhest reverse osmosis membrane, is still widely used. Asymmetric polyamide and thin-film composites of polyamide and several other polymers have also made gains in recent years whereas polysulfone is the most practical membrane material in ultrafiltration appHcations. 

In 1966, Cadotte developed a method for casting mlcroporous support film from polysulfone, polycarbonate, and polyphenylene oxide plastics ( ). Of these, polysulfone (Union Carbide Corporation, Udel P-3500) proved to have the best combination of compaction resistance and surface microporosity. Use of the mlcroporous sheet as a support for ultrathin cellulose acetate membranes produced fluxes of 10 to 15 gfd, an increase of about five-fold over that of the original mlcroporous asymmetric cellulose acetate support. Since that time, mlcroporous polysulfone has been widely adopted as the material of choice for the support film in composite membranes, while finding use itself in many ultrafiltration processes. 

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... 

In 1996, a paper was published which was dedicated to selecting suitable membranes for separations in organic solvents [466]. Membranes tested in an asymmetrical channel included polysulfone MWCO 20,000 g/mol, regenerated cellulose MWCO 20,000 g/mol, PTFE pore size 0.02 mm, polyaramide MWCO 50,000 g/mol, poly(vinylidene fluoride) MWCO 50,000 g/mol, poly(phenylene oxide) MWCO 20,000 g/mol and a DDS fluoro polymer MWCO 30,000 g/mol. The first membrane was tested with water, the others with THF or a THF/ace-tonitrile mixture. Numerous problems occurred with the different membranes. The best membrane for THF was found to be the DDS fluoro polymer membrane. 

Pinnau, I., and Koros, W. (1991), Structures and gas separation property asymmetric polysulfone membranes made by dry, wet, and dry/wet phase-inversion, J. Appl. Polym. Sci., 43,1491-1502. 

Ismail, A. F., Ng, B. C., and Abdul Rahman, W. A. W. (2003), Effects of shear rate and forced convection residence time on asymmetric polysulfone membranes structure and gas separation performance, Sep. Purif. Technol, 33,255-272. 

The spiral wound membranes tested for extraction of impurity-free NaSCN from aqueous process solution were polyamide (PA-300), CTA-700, PERMA-400, and PERMA-250. PA-300 was prepared by interfacial polymerization technique, while the PERMA membranes were prepared by coating a novel proprietary copolymer onto a microporous polysulfone substrate followed by cross-linking of the top layer. Thus, the morphology of these membranes was TFC. CTA-700 was asymmetric in nature and was prepared by solution casting and phase inversion method. 

Almost all RO membranes are made of polymers, cellulosic acetate and matic polyamide types, and are rated at 96-99% NaCl rejection. RO membranes are generally of two types, asymmetric or skinned membranes and thin film composite membranes. The support material is commonly polysulfones, while the thin film is made from various types of polyamines and polyureas. 

Polysulfone hollow fibers are usually asymmetric in cross-section, with either an internal skin (for use in blood filtration) or an external skin (for use in gas separation). The ability to form asymmetric structures with divergent permeabilities attributable to the skin and supporting structures makes glassy polymers, such as the polysulfones, attractive for use in the development of separation devices. In contrast to membranes having a uniform cross-section, these asymmetric structures permit much higher filtration rates with equivalent sieving spectra. 

Henis and asymmetric polysulfone hollow high H /CO selectivity of 33 with a low- ... 

Figure 1 Asymmetric macrovold-free polysulfone hollow fiber [The fiber was spun with bore off-center to detect irregularities In the substructure ( 5)].

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