Membrane materials from

Palmer and Samuelson (1924) were the first to report the isolation and partial characterization of membrane material from milk lipid globules. The methods they used are similar to those used for this isolation today. Brunner (1974), who himself was instrumental in development of isolation methods (Brunner et al. 1953), provided a detailed review of the history of isolation methods. In this section we will summarize the currently used methods and indicate their advantages and disadvantages. 

McPherson, A. V., Dash, M. C. and Kitchen, B. J. 1984A. Isolation of bovine milk fat globule membrane material from cream without prior removal of caseins and whey proteins. J. Dairy Res. 51, 113-121. 

FIGURE 11.3 Gel-layer formation on surface of an ultrafiltration membrane made from (I) hydrophobic and (II) hydrophilic material. C, solute concentration Ci < C2 < C3, 1 adsorption layer, 2 gel-polarization layer, 3 membrane material. (From Cherkasov, A.N., Tsareva, S.V., and Polotsky, A.E., J. Membr. Sci., 104, 157, 1995.)... 

Actual and projected sales for inorganic membrane materials. From Crull [1]... 

FIGURE 8.1 Permeabilities for carbon dioxide passing through several membrane materials. (From Fair, J. R. Chem. Proc. 52 (10) 81 (1989). With permission.)... 

Synthesize membrane materials from thio-acids final product may be a glass, glass/ceramic, or ceramic structure with stable sulfur-hydrogen groups. 

Manufacturing processes are a second area for innovation. Scale-up of new membrane materials from the lab to pilot scale is a nontrivial task. Robust coating processes, flexible packaging, and more effective quality control tools could all improve the manufacturing yields and costs associated with membrane systems. This could have an immediate impact in areas where membranes are a technically viable solution, but are not currently economically competitive with alternate separation technologies. 

D. Grandine, II (Millipore) Processes of making a porous membrane material from polyvinylidene fluoride, and products. US Patent 4203848, May 1980. 

This chapter covers multi-step work of tailoring C02-selective membrane material, from new copolymers designs to tailor-made copolymer/PEG blends, moreover thin film composite membrane performance are also discussed. The relationships between gas transport properties, structure, morphology and physical properties are analyzed. The performance at different operating conditions and with mixed gases is monitored as well in order to have a guideUne for scaling up the membranes. The benefits of these membranes are the simplicity of preparation, low cost and resistance toward acid gas treatment. 

Figure 9.2 Floating roofs and flexible membranes can be used to prevent the release of material. (From Smith and Petela, The Chemical Engineer, no. 517, 9 April, 1992 reproduced by permission of the Institution of Chemical Engineers.)...

Validation Considerations. Mechanisms other then size exclusion maybe operative ia the removal of vimses from biological fluids. Thus vims removal must be vaUdated within the parameters set forth for the production process and usiag membrane material representative of the product line of the filter. 

Ceramic, Metal, and Liquid Membranes. The discussion so far implies that membrane materials are organic polymers and, in fact, the vast majority of membranes used commercially are polymer based. However, interest in membranes formed from less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafHtration and microfiltration appHcations, for which solvent resistance and thermal stabHity are required. Dense metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported or emulsified Hquid films are being developed for coupled and facHitated transport processes. 

FoUowiag Monsanto s success, several companies produced membrane systems to treat natural gas streams, particularly the separation of carbon dioxide from methane. The goal is to produce a stream containing less than 2% carbon dioxide to be sent to the national pipeline and a permeate enriched ia carbon dioxide to be flared or reinjected into the ground. CeUulose acetate is the most widely used membrane material for this separation, but because its carbon dioxide—methane selectivity is only 15—20, two-stage systems are often required to achieve a sufficient separation. The membrane process is generally best suited to relatively small streams, but the economics have slowly improved over the years and more than 100 natural gas treatment plants have been installed. 

Many terms have been used to describe the contents of a microcapsule active agent, actives, core material, fill, internal phase (IP), nucleus, and payload. Many terms have also been used to describe the material from which the capsule is formed carrier, coating, membrane, shell, or wall. In this article the material being encapsulated is called the core material the material from which the capsule is formed is called the shell material. 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Ultrafiltration separations range from ca 1 to 100 nm. Above ca 50 nm, the process is often known as microfiltration. Transport through ultrafiltration and microfiltration membranes is described by pore-flow models. Below ca 2 nm, interactions between the membrane material and the solute and solvent become significant. That process, called reverse osmosis or hyperfiltration, is best described by solution—diffusion mechanisms. 

Silver—Zinc Separators. The basic separator material is a regenerated cellulose (unplastici2ed cellophane) which acts as a semipermeable membrane aHowiag ionic conduction through the separator and preventing the migration of active materials from one electrode to the other. 

Second, most membrane materials adsorb proteins. Worse, the adsorption is membrane-material specific and is dependent on concentration, pH, ionic strength, temperature, and so on. Adsorption has two consequences it changes the membrane pore size because solutes are adsorbed near and in membrane pores and it removes protein from the permeate by adsorption in addition to that removed by sieving. Porter (op. cit., p. 160) gives an illustrative table for adsorption of Cytochrome C on materials used for UF membranes, with values ranging from 1 to 25 percent. Because of the adsorption effects, membranes are characterized only when clean. Fouling has a dramatic effect on membrane retention, as is explained in its own section below. 

Misunderstandings arise when membrane users assume that MWCO means what it seems to say. The definition implies that a 50 kD membrane will separate a 25 kD material from a 75 kD material. The rule of thumb is that the molecular mass must differ by a factor of ten for a good separation. Special techniques are used to permit the separation of proteins with much smaller mass ratio. 

Cellulose acetate is a common membrane material, but others include nylon and aromatic polyamides. The mechanism at the membrane surface involves the influent water and impurities attempting to pass through the pressurized side, but only pure water and certain impurities soluble in the membrane emerge from the opposite side. 

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