Alternative membranes

Ion exchange, in contrast, creates an effluent that contains between two and five times the mass of inorganic material removed from the product water. Coagulation with aluminum or iron salts creates a sludge, which creates a disposal problem. Green pressure, especially in Switzerland and mid-west USA, which lie in the middle of large land masses, has started to force industrialists to install alternative membrane processes to avoid these discharges. 

There is ongoing work to investigate alternative membranes that not only exhibit durability and high performance, but also can be manufactured inexpensively at high volume. Work at Ballard Advanced Materials Corporation has concentrated on developing low-cost membranes using trifluorostyrene and substituted trifluorostyrene copolymeric compositions (17). 

Gumbleton M, Abulrob AG, Campbell L. Caveolae an alternative membrane transport compartment. Pharm Res 2000 17(9) 1035-1048. 

There are a number of critical variables in the design of successful electric membrane equipment. Among these are the properties and cost of the membranes, the design and cost of the spacers, the size, cost, and construction of the alternating membrane-spacer-assembly—called the membrane stack—and the current density at which the unit is operated. 

Ravetch JV, Perussia B. Alternative membrane forms of Fc gamma RIII(CD16) on human natural killer cells and neutrophils. Cell type-specific expression of two genes that differ in single nucleotide substitutions. J Exp Med 1989 170(2) 481-97. 

Xuezhong Du etal., 2001, Performances of proton exchange membrane fuel cells with alternate membranes. Physical Chemistry Chemical Physics, 3, 3175-3179. 

Ear less is known about the process of flavivirus assembly. Electron microscopy has shown that immature virions can be found in the lumen of the endoplasmic reticulum (Murphy, 1980). The nucleocapsid core is not assembled free in the cytoplasm rather, its assembly appears to take place on the cytoplasmic face of membranes with which prM and E proteins are associated (Khromykh et al., 2001). The carboxy-terminal signal sequence of the precursor to the capsid protein is thought to anchor that protein to the membrane (Amberg et al., 1994). This should allow interactions to occur between the capsid protein and the envelope proteins, which are also anchored to the membrane but reside in the lumen of the endoplasmic reticulum or vesicles. The capsid protein also contains a conserved stretch of hydrophobic residues located roughly in the middle of the protein that has been suggested to serve as an additional or alternative membrane anchor (Markoff et al., 1997). 

In a more complete membrane process optimization or cost comparison of alternative membrane processes, the cost associated with any loss of the valuable gas component(s) needs to be considered as another operating expense just like any other utility expense. For example, in the case of the removal of carbon dioxide from natural gas (methane), there will be some amount of methane in the permeate (albeit in a small quantity) due to imperfect rejection of methane by the membrane. Since methane is, in this case, the desirable product component, its presence in the permeate represents a loss or an expense. The value of the loss should be included in any cost comparison. 

D.S. Watkins, K. Dirks, and D. Epp. 33rd International Power Sources Symposium, The Electrochemical Society. Pennington, NJ, 1988. M. Wakizoe, O.A. Velev, and S. Srinivasan. Analysis of proton-exchange membrane fuel-cell performance with alternate membranes. Electrochimica Acta 40, 335-344 1995. 

Development of Alternative Membranes. Nafion membranes show considerable promise with respect to their performance characteristics, low resistivity and long-term stability. However, the present cost (about 30/ft ) of Nafion membranes is rather expensive for the SPE cell to be cost-effective for industrial and utility applications. TJje ultimate goal is to reduce the membrane cost to about 3/ft. Alternative membranes have been evaluated for use in the SPE cell. Only fluorocarbon membranes have been considered in this application (10), since the cell environment is corrosive, and cell tempperature is high (from 80°C to 150°C). <, 3, 3 - trifluorostyrene-sulfonic acid... 

A recent study has shown that (58) membranes with carboxylic acid groups cannot be used without alkaline supporting electrolyte because of low swelling and poor conductivity in pure water. It is clear that the alternate membrane for the SPE cell should be a perfluorinated sulfonic acid membrane. To date (1981), Nafion still retains its uniqueness for this electrochemical application. 

Alternatively, membrane filtration can be used to separate soluble metal complexes, containing polymer-attached ligands, from reactants and products [43]. A major advantage of using soluble polymer-enlarged catalysts in conjunction with membrane separation is that it is readily amenable to continuous operation. A novel example of this concept is the use of dendritic ligands [44] in combination with membrane filtration. 

There are several potential routes to the preparation of composite reverse osmosis membranes, whereby the ultrathin semipermeable film is formed or deposited on the microporous sublayer.1 2 The film can be formed elsewhere, then laminated to the microporous support, as was done in the earliest work on this membrane approach. Or it can be formed in place by plasma polymerization techniques. Alternatively, membrane polymer solution or polymer-forming reactants can be applied in a dipcoating process, then dried or cured in place. The most attractive approach from a commercial standpoint, however, has been the formation of the semipermeable membrane layer in situ by a classic "non-stirred" interfacial reaction method. Several examples of membranes made by this last approach have reached commercial status. 

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