Membrane applications

Advantages to Membrane Separation This subsertion covers the commercially important membrane applications. AU except electrodialysis are pressure driven. All except pervaporation involve no phase change. All tend to be inherently low-energy consumers in the-oiy if not in practice. They operate by a different mechanism than do other separation methods, so they have a unique profile of strengths and weaknesses. In some cases they provide unusual sharpness of separation, but in most cases they perform a separation at lower cost, provide more valuable products, and do so with fewer undesirable side effects than older separations methods. The membrane interposes a new phase between feed and product. It controls the transfer of mass between feed and product. It is a kinetic, not an equihbrium process. In a separation, a membrane will be selective because it passes some components much more rapidly than others. Many membranes are veiy selective. Membrane separations are often simpler than the alternatives. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Brief Examples Microfiltration is the oldest and largest membrane field. It was important economically when other disciphnes were struggling for acceptance, yet because of its incredible diversity and lack of large apphcations, it is the most difficult to categorize. Nonetheless, it has had greater membrane sales than all other membrane applications combined throughout most of its histoiy. The early... 

Gas Dehydration Water is extremely permeable in polymer membranes. Dehydration of air and other gases is a growing membrane application. 

Mohr, C.M. Deeper, S.A. Engelgau, D.E. and Charboneau, B.L., Membrane Applications and Research in Food Processing, (Noyes Data Corporation, Park Ridge, NJ) p. 305 (1989). 

A number of studies have recently been devoted to membrane applications [8, 100-102], Yoshikawa and co-workers developed an imprinting technique by casting membranes from a mixture of a Merrifield resin containing a grafted tetrapeptide and of linear co-polymers of acrylonitrile and styrene in the presence of amino acid derivatives as templates [103], The membranes were cast from a tetrahydrofuran (THF) solution and the template, usually N-protected d- or 1-tryptophan, removed by washing in more polar nonsolvents for the polymer (Fig. 6-17). Membrane applications using free amino acids revealed that only the imprinted membranes showed detectable permeation. Enantioselective electrodialysis with a maximum selectivity factor of ca. 7 could be reached, although this factor depended inversely on the flux rate [7]. Also, the transport mechanism in imprinted membranes is still poorly understood. 

Other clinical studies have been focused on the artificial tympanic membrane application, ventilation mbes, an adhesion Barrier, elastic bioactive coatings on load-bearing dental and hip implants, and also for wound healing purposes. ... 

In this chapter, the focus is on how zeohte membranes can be appHed in the field of catalysis and to what extent this is successful. The latter is illustrated by reviewing some commonly studied zeohte membrane applications. Finally, the current hurdles that impede industrial application are discussed and some remarks... 

Fujikawa M, Ano R, Nakao K, Shimizu R and Akamatsu M. Relationships between structure and high-throughput screening permeability of diverse drugs with artificial membranes application to prediction of Caco-2 cell permeability. Bioorg Med Chem 2005 13 4721-32. 

Fig. 14 Water-soluble CCVJ, hydrophobic CCVJ farnesyl ester (FCVJ) for cell membrane applications [88], and hydrophilic CCVJ triethyleneglycol ester (CCVJ-TEG) [89]...

Prabhu, A.K. and S.T. Oyama, Highly hydrogen selective ceramic membranes Application to the transformation of greenhouse gases,. Membr. Sci, 176, 233-248, 2000. 

Van Koten and Frey used a hyperbranched poly(triallylsilane) as the support for palladium- pincer complexes.[63] The supported palladium-pincer complexes were applied in the catalytic aldol condensation of benzaldehyde and methyl isocyanate. Their activity was similar to that of single site Pd catalysts. According to the authors, the complex is suitable for continuous membrane applications, as demonstrated by their purification by means of dialysis. 

D. Schleuder, F. Hillenkamp, and K. Strupat. IR-MALDI-Mass Analysis of Electroblotted Proteins Directly from the Membrane Comparison of Different Membranes, Application to On-membrane Digestion, and Protein Identification by Database Searching. Anal. Chem., 71(1999) 3238-3247. 

Biosynthetic patterns, of macrolide antibiotics, 15 305-306 Biota, circulation of water with, 26 7-12 Biotechnological manufacturing, key characteristics of, ll 440t Biotechnological membrane applications, 15 848... 

The use of silicones in membrane applications is relatively new. It is, however, a rapidly growing area as evidenced by a number of original papers and reviews published recently. Pervaporation with the use of polymer membranes has been recognized as a versatile separation process in the chemical industry.458 A study of PDMS as an active layer in the composite pervaporation membranes for separation of alcohols and esters has been reported.459 Two-dimensional... 

An analysis of the individual PEM components offers evidence of almost unbroken R D see Fig. 13.10 (Jochem et al., 2007). The overall importance of the membrane is striking. Furthermore, the numbers of annual applications for bipolar plates (BPP) and the gas-diffusion layer (GDL) decrease after 2002, while the increase in membrane applications flattens out. This correlates with the equally lower number of fuel cell patents in the field of mobile applications. 

Other Domains of Membranes Application 3.1. Fuel Cells... 

Hubbell, W.L., 1990, Transbhayer couphng mechanism for the formation ofhpid asymmetry in biological membranes. Application to the photoreceptor disc membrane. Biophys. J. 57 ... 

Keizer, K. and A. J. Burggraaf. 1988. Porous ceramic materials in membrane applications. Science of Ceramics, ed. D. Taylor, 14 pp. 83-95. 

There are many different zeolite structures but only a few have been studied extensively for membrane applications. Table 10.1 lists some of these structures and their basic properties. One of the most critical selection criterion when choosing a zeolite for a particular application is the pore size exhibited by the material. Figure 10.1 compares the effective pore size of the different zeolitic materials with various molecule kinetic diameters. Because the pores of zeolites are not perfectly circular each zeolite type is represented by a shaded area that indicates the range of molecules that may stiU enter the pore network, even if they diffuse with difficulty. By far the most common membrane material studied is MFI-type zeolite (ZSM-5, Al-free siUcahte-l) due to ease of preparation, control of microstructure and versatility of applications [7]. 

Table 10.1 Summary of common zeolite structures used in membrane applications along with important properties and typical synthesis conditions. 

Xu P, Drewes JE, Bellona C, Amy G, Kim T-U, Adam M, Heberer T (2005) Rejection of emerging organic micropollutants in nanofiltration-reverse osmosis membrane applications. 

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

Polybenzazole block copolymers, (III), prepared by Martin et al. (2) were suitable in solid polymer electrolyte membrane applications as a solid polymer electrolyte doped membranes and in fuel cells derived from them. 

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