Membrane micro-porous

The membrane (Micro Porous Glass=MPG, Ise Industry Production Si02 70-80, AI2O3 4-6, BO3 10-12 wt.%) used in this study was 10 mm OD, 8 mm ID and 50 mm length with the pore diameter of 0.34 micron meters. For the immobilization of the catalyst in the membrane pores, Ag and Re were separately supported. A silver ketenide was formed in the membrane pores by the reaction of the two solutions, a mixed solution of acetic anhydride (3.0 g) and pyridine (50 cm ), at room temperature for 12 hr... 

In supported liquid membranes, a chiral liquid is immobilized in the pores of a membrane by capillary and interfacial tension forces. The immobilized film can keep apart two miscible liquids that do not wet the porous membrane. Vaidya et al. [10] reported the effects of membrane type (structure and wettability) on the stability of solvents in the pores of the membrane. Examples of chiral separation by a supported liquid membrane are extraction of chiral ammonium cations by a supported (micro-porous polypropylene film) membrane [11] and the enantiomeric separation of propranolol (2) and bupranolol (3) by a nitrate membrane with a A/ -hexadecyl-L-hydroxy proline carrier [12]. 

The membrane is usually dense but sometimes micro-porous. If the external resistances to mass transfer are neglected in Figure 10.10, then pFj = p F l and pi, = p P i and Equation 10.20 can be written in terms of the volumetric flux as ... 

Generally, a distinction can be made between membrane bioreactors based on cells performing a desired conversion and processes based on enzymes. In ceU-based processes, bacteria, plant and mammalian cells are used for the production of (fine) chemicals, pharmaceuticals and food additives or for the treatment of waste streams. Enzyme-based membrane bioreactors are typically used for the degradation of natural polymeric materials Hke starch, cellulose or proteins or for the resolution of optically active components in the pharmaceutical, agrochemical, food and chemical industry [50, 51]. In general, only ultrafiltration (UF) or microfiltration (MF)-based processes have been reported and little is known on the application of reverse osmosis (RO) or nanofiltration (NF) in membrane bioreactors. Additionally, membrane contactor systems have been developed, based on micro-porous polyolefin or teflon membranes [52-55]. 

Considerable activity has been generated on composite reverse osmosis membranes by Japanese researchers. Patent applications were recently published, for example, covering research at Teijin Ltd. on interfacially formed membranes prepared from polydiallylamines (17) and from amine adducts of trls-(glycidyl) isocyanurate (18). Both types of membranes were formed on micro-porous polysulfone supports. Kurihara and coworkers have developed a composite membrane, designated PEC-1000, which is formed by an... 

A cumulative success of artificial ion-channel functions by simple molecules may disclose a wide gate for the design of ion channels and possible applications to ionics devices. Incorporation of these channels into bilayer lipid membrane systems may trigger the developments towards ionics devices. The conventional BLM system, however, is not very stable, one major drawback for the practical applications, and some stabilization methods, such as impregnating the material in micro-porous polycarbonate or polyester filters, are required. On the other hand,... 

Figure 2.37 Permeability coefficients as a function of the gas kinetic diameter in micro-porous silica hollow fine fibers [58]. Reprinted from J. Membr. Sci. 75, A.B. Shelekhin, A.G. Dixon and Y.H. Ma, Adsorption, Permeation, and Diffusion of Gases in Microporous Membranes, 233, Copyright 1992, with permission from Elsevier...

In this chapter membrane preparation techniques are organized by membrane structure isotropic membranes, anisotropic membranes, ceramic and metal membranes, and liquid membranes. Isotropic membranes have a uniform composition and structure throughout such membranes can be porous or dense. Anisotropic (or asymmetric) membranes, on the other hand, consist of a number of layers each with different structures and permeabilities. A typical anisotropic membrane has a relatively dense, thin surface layer supported on an open, much thicker micro-porous substrate. The surface layer performs the separation and is the principal barrier to flow through the membrane. The open support layer provides mechanical strength. Ceramic and metal membranes can be either isotropic or anisotropic. 

J.J. Kim, T.S. lang, Y.D. Kwon, U.Y. Kim and S.S. Kim, Structural Study of Micro-porous Polypropylene Hollow Fiber Membranes Made by the Melt-Spinning and Cold-Stretching Method, J. Membr. Sci. 93, 209 (1994). 

Membrane contactors are typically shell-and-tube devices containing micro-porous capillary hollow fiber membranes. The membrane pores are sufficiently small that capillary forces prevent direct mixing of the phases on either side of the membrane. The membrane contactor shown in Figure 13.8 separates a liquid and a gas phase this is a liquid/gas contactor [18]. Membrane contactors... 

Bessarabov s devices use composite membranes consisting of a thin silicone rubber polymer layer coated onto a microporous poly(vinylidene fluoride) support layer. These membranes have high fluxes and minimal selectivities for the hydrocarbon gases, but the dense silicone layer provides a more positive barrier to bleed-through of liquid than do capillary effects with simple micro-porous membranes. 

The third main class of separation methods, the use of micro-porous and non-porous membranes as semi-permeable barriers (see Figure 2c) is rapidly gaining popularity in industrial separation processes for application to difficult and highly selective separations. Membranes are usually fabricated from natural fibres, synthetic polymers, ceramics or metals, but they may also consist of liquid films. Solid membranes are fabricated into flat sheets, tubes, hollow fibres or spiral-wound sheets. For the micro-porous membranes, separation is effected by differing rates of diffusion through the pores, while for non-porous membranes, separation occurs because of differences in both the solubility in the membrane and the rate of diffusion through the membrane. Table 2 is a compilation of the more common industrial separation operations based on the use of a barrier. A more comprehensive table is given by Seader and Henley.1... 

Two membrane types that operate on different principles have been used in commercially available membrane separators microporous membranes and selectively permeable, nonporous polyimide or Nafion membranes. The micro-porous Teflon PTFE membrane can be used to remove water vapor or organic solvent vapor. Any gaseous component, including volatile analytes such as Hg, is partially or extensively removed. The sweep gas flow rate is typically similar to the sample carrier gas flow rate. 

R.J.R. Uhlhom, M.H.B.J. Huis in t Veld, K. Keizer and A.J. Burggraaf, High Permselectivities of Micro-porous Silica-Modified y-Alumina Membranes , J. Mater. Sci. Lett., 8 1135-38 (1989). 

The first membrane reactor studies made use of dense metallic membranes, but due to certain limitations of these dense materials (sec below) and due to the rapid progress in the development of (micro)porous... 

Microporous and, particularly, ultramicropous membranes are more difficult to characterize. Different procedures based on the low-pressure part of the N2 adsorption isotherm have been proposed [36], but they often require knowledge of the shape of the pores and of gas-surface interaction parameters which are not always available. Small angle X-ray scattering (SAXS) is another technique which is well suited to micro-porous powders, but difficult to execute in the case of composite layers, as in microporous membranes. Xenon-129 NMR has recently been proposed [37] for the characterization of amorphous silica used in the preparation of microporous membranes, but the method requires further improvement. Methods based on permeability measurements appear to be limited by the lack of understanding of the mass transport mechanisms in (ultra)microporous systems. 

Chemical damage occurs when a contaminant in the feed water is incompatible with the polymer comprising the membrane, the micro-porous support, or the fabric support. Besides oxidizers that degrade the crosslinking of a thin-film membrane, there are a variety of chemicals that swell or dissolve the polysulfone microporous support, including the following compounds. 

Honeycomb multichannel ceramic membranes on micro-porous cordierite support... 

In this paper, we report the use of several micro-porous synthetic membranes to prepare contaminated peptides and proteins for MALDl-TOF analysis. By spotting contaminated samples directly onto activated synthetic membranes, impurities such as salts, glycerol, and detergents can be washed from the sample, while biopolymers remain intact. Following addition of matrix, samples can be desorbed and ionized... 

In this controlled-release ocular insert, the drug reservoir is a thin disc of pilocarpine-alginate complex sandwiched between two transparent discs of micro-porous membrane fabricated from ethylene-vinyl acetate copolymer (Fig. 5). The microporous membranes permit the tear fluid to penetrate into the drug... 

Fig. 23 Schematic illustration of a pH-activated drug-delivery system and the pH-dependent formation of micro-porous membrane in the intestinal tract.

J. G. Wijmans, J. P. B. Baaij, and C. A. Smolders, The mechanism of formation of micro-porous or skinned membranes produced by immersion precipitation. Journal of Membrane Science 14, 263-274 (1983). 

Tsuru, T., Yamaguchi, K., Yoshioka, T., and Asaeda, M. Methane steam reforming by micro-porous catalytic membrane reactors. AIChE Journal, 2004, 50 (11), 2794. 

In general, membrane-supported liquid-liquid extraction is offered as a micro-porous hollow fibre module (Fig. 2.23). The membrane contactor contains thousands of micro-porous hollow fibres knitted into an array that is wound around a distribution tube with a central baffle. The hollow fibres are arranged in a uniform open packing allowing the utilisation of the total membrane surface area. The liquid flows over the shellside (outside of the hollow fibre), is introduced through the distribution tube and moves radially across the array of hollow fibres and then around the baffle and is carried out by the collection tube. 

Basic adsorption isotherms have been described in this chapter. For micro-porous membranes, the use of the DR equation to describe micropore filling has been shown to be quite adequate. Techniques for the determination of surface area and pore size distribution have ben presented. The use of potential functions for the determination of pore size distribution in microporous materials has been described. Although the potential function techniques give consistent and satisfactory results, caution must be exerted in using these techniques for the calculation of the pore size distribution, due to the uncertainty involved in the values of the parameters used in the calculation and the simplifying assumptions employed in the derivation of the model equations. 

The most demanding support requirements are those for ultra thin micro-porous gas separation membranes, which are currently being developed in several research organisations worldwide including ECN (Petten, the Netherlands). In principle, a mesoporous Knudsen or UP membrane can serve as support for these membranes if the defect density in the substrate surface, i.e. the mesoporous layer, is low enough. Indeed, the quality of the Knudsen or UF membrane as support for a microporous gas separation membrane should be higher than is usually needed for the UF or Knudsen function [4]. This means that not every mesoporous ceramic membrane is a suitable support for micro-porous or dense amorphous gas separation membranes. 

The synthesis of nanophase ceramics is one of these concepts, it allows micro-porous ceramic materials with ceramic grains in the nanometer range to be obtained. Research in the field of nanophase materials is very active. A number of results on the control of microstructure and temperature stability of metal oxide ceramics can be applied to membrane preparation. Works carried out on non-oxide ceramics such as silicon carbide, silicon oxinitride or aluminum nitride should be regarded in order to extend the domain of available membrane materials. 

For membranes implemented in the second reactor only the results of micro-porous membranes will be discussed in detail, because palladium membranes gave almost the same results and the performance is better than that of Knudsen diffusion membranes. The yield and selectivities have been calculated at different permeate pressures and are plotted in Fig. 14.11. The results for the conventional reactor are obtained without a membrane implemented in the process. 

R364 W. Heink, J. Karger and S. Vasenkov, Application of Pulsed Field Gradient NMR to Characterize the Transport Properties of Micro-porous Membranes , Membr. Sci. Technol Ser., 2000,6, 97 R365 P. J. F. Henderson, C. K. Hoyle and A. Ward, Expression, Purification and Properties of Multidrug Efflux Proteins , Biochem. Soc. Trans., 2000,28, 513... 

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