Gas-separation polysulfone

Hydrogen Hydrogen recovery was the first large commercial membrane gas separation. Polysulfone fiber membranes became available in 1980 at a time when H9 needs were rising, and these novel membranes qiiickly came to dominate the market. Applications include recovery of H9 from ammonia purge gas, and extraction of H9 from petroleum crackiug streams. Hydrogen once diverted to low-quahty fuel use is now recovered to become ammonia, or is used to desulfurize fuel, etc. H9 is the fast gas. 

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... 

The discussion directly following Eq (6) provides a simple, physically reasonable explanation for the preceding observations of marked concentration dependence of Deff(C) at relatively low concentrations. Clearly, at some point, the assumption of concentration independence of Dp and in Eq (6) will fail however, for our work with "conditioned" polymers at CO2 pressures below 300 psi, such effects appear to be negligible. Due to the concave shape of the sorption isotherm, even at a CO2 pressure of 10 atm, there will still be less than one CO2 molecule per twenty PET repeat units at 35°C. Stern (26) has described a generalized form of the dual mode transport model that permits handling situations in which non-constancy of Dp and Dh manifest themselves. It is reasonable to assume that the next generation of gas separation membrane polymers will be even more resistant to plasticization than polysulfone, and cellulose acetate, so the assumption of constancy of these transport parameters will be even more firmly justified. 

Membrane materials used are polysulfone, polystyrene, Teflon, and various rubbers. This type of separation possesses many advantages over other types of gas separation, e.g., mild operating conditions, lower energy consumption, low capital cost, and economic operation at both low and high flow rates. 

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. 

Sharpe, I. D., Ismail, A. F., and Shilton, S. J. (1999), A study of extrusion shear and forced convection residence time in the spinning of polysulfone hollow fiber membranes for gas separation, Sep. Purif. Technol, 17,101-109. 

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. 

Kesting RE, Fritzsche AK, Murphy MK, Cruse CA, Handermann AC, Malon RF, and Moore MD. The second-generation polysulfone gas-separation membrane. The use of Fewis acid Base complexes as transient templates to increase free volume. J. Appl. Pol. Sci. 1990 40 1557-1574. 

Monsanto s Prism permeators for gas separation also employ composite membranes. Polyamide coatings are not used for the composite membrane in the Prism module. The Prism membrane consists of a coating of silicone rubber applied from an organic solvent on a porous polysulfone substrate. The Prism membrane is another good example of a composite membrane where Structure Level IV is used to obtain good membrane properties (22). 

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. 

Typical data for asymmetric fibers for reverse osmosis applications are reported in Table 20.5-1. The ranges of these variables for as-spun and post reared cellulose acetate and polysulfone membranes currently used in gas separation are proprietary. Nevertheless, the surfnee porosity for such membranes is undoubtedly lower than for those described in Table 20,5-1, since, as indicated in Table 20,1-2, in their posttreated forms such membranes have seleclivities approaching the values or dense films. Porosities as high as those shown in Table 20.5-1 weuld produce unacceptably low seleclivities as a result of nondiscrirafimat pore flow,... 

Another industrial application of gas-separation membranes is the removal of carbon dioxide from natural gas. The CO2/CH4, selectivity is about 20 to 30 for polycarbonate, polysulfone, and cellulose acetate membranes at 35°C and 40 atm. A selectivity of over 60 can be obtained with Kapton , but this polymer is much less permeable than the others. Increasing the temperature raises the permeability of most polymers but generally causes a. slight decrease in selectivity. The operating temperature is chosen to be somewhat above the dew point of the residue gas. There is considerable COj absorbed in the membranes at high CO2 partial pressures, and the plasticization effect of CO2 increases the effective diffusion coefficients for all gases and makes the selectivity less than that based on pure-gas data. Methods of allowing for such nonlinear effects have been presented. ... 

In the field of gas separation a large number of materials can be used (polyolefins, polyamides (polvaramids), polyesters, polysulfones and. more specifically, polyvinyl-... 

A variety of polymers and copolymers are used for gas separation membranes. To be suitable for gas separation, the polymer must have good permeability and selectivity and the material must be capable of forming a strong, thin, defect-free membrane with good chemical and thermal stability. Commercial gas separation membranes are based on modified cellulose, treated polysulfone or a substituted polycarbonate polymer. Membranes... 

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