Ceramic membranes micropores

R.S.A. de Lange, J.H.A. Hekkink, K. Keizer and A.J. Burggraaf, Permeation and Separation Studies on Microporous Sol-Gel Modified Ceramic Membranes , Microporous Mater., 4 169-86 (1995). 

Caro, J. Noack, M. Kolsch, P. Chemically modified ceramic membranes. Microporous Mesoporous Mater 1998, 22, 321-332. 

De Lange, R. S. A., Hekkink, J. H. A., Keizer, K. and Burggraaf, A. J. (1995b) Permeation and separation studies on microporous sol-gel modified ceramic membranes. Microporous Materials, 4,169-186. 

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. 

Surface media Captures particles on the upstream surface with efficiencies in excess of depth media, sometimes close to 100% with minimal or no off-loading. Commonly rated according to the smallest particle the media can repeatedly capture. Examples of surface media include ceramic media, microporous membranes, synthetic woven screening media and in certain cases, wire cloth. The media characteristically has a narrow pore size distribution. 

The only ceramic membranes of which results are published, are tubular microporous silica membranes provided by ECN (Petten, The Netherlands).[10] The membrane consists of several support layers of a- and y-alumina, and the selective top layer at the outer wall of the tube is made of amorphous silica (Figure 4.10).[24] The pore size lies between 0.5 and 0.8 nm. The membranes were used in homogeneous catalysis in supercritical carbon dioxide (see paragraph 4.6.1). No details about solvent and temperature influences are given but it is expected that these are less important than in the case of polymeric membranes. 

Membrane materials have to withstand a pressure difference and relatively high temperatures (500 °C and up). Microporous ceramic membranes have been... 

A common method to slip-cast ceramic membranes is to start with a colloidal suspension or polymeric solution as described in the previous section. This is called a slip . The porous support system is dipped in the slip and the dispersion medium (in most cases water or alcohol-water mixtures) is forced into the pores of the support by a pressure drop (APJ created by capillary action of the microporous support. At the interface the solid particles are retained and concentrated at the entrance of pores to form a gel layer as in the case of sol-gel processes. It is important that formation of the gel layer starts... 

Bhavc, R. R., J. Gillot and P. K. T. Liu. 1989. High temperature gas separations for coal offgas cleanup with microporous ceramic membranes. Paper 124f read at AIChE Annual Meeting, 5-10 November 1989, San Francisco. 

Uhlhom, R. J. R., M. H. B. J. Huis in t Veld, K. Keizer and A. J. Burggraaf. 1989a. Theory and experiments on transport of condensable gases in microporous ceramic membrane systems. Proc. 1st Inti Cong, Inorganic Membrane, 3-6 July, 323-328, Montpellier. 

V. Schroder, O. Behrend, and H. Schubert Effect of Dynamic Interfacial Tension on the Emulsification Process Using Microporous Ceramic Membranes. J. Colloid Interface Sci. 202, 334 (1998). 

V. Schroder and H. Schubert Emulsification Using Microporous Ceramic Membranes. In Proceedings of the First European Congress on Chemical Engineering (ECCE 1) 2491, Florence Italy (1997). 

During the last few years, ceramic- and zeolite-based membranes have begun to be used for a few commercial separations. These membranes are all multilayer composite structures formed by coating a thin selective ceramic or zeolite layer onto a microporous ceramic support. Ceramic membranes are prepared by the sol-gel technique described in Chapter 3 zeolite membranes are prepared by direct crystallization, in which the thin zeolite layer is crystallized at high pressure and temperature directly onto the microporous support [24,25],... 

The sol-gel process involves the transition of a system from a liquid "sol" (mostly colloidal) into a solid "gel" phase (11). By applying this methodology, it is possible to fabricate ceramic or glass materials in a wide variety of forms ultrafine or spherical-shaped powders, thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic ceramics and glasses, or extremely porous aerogel materials. 

This chapter is split in two parts. The first part will briefly treat the preparation of flat ceramic membrane supports by colloidal processing. In our laboratory, these supports are used to study stability and gas separation properties of microporous silica membranes because they are easy to prepare and demand less complex testing equipment. 

Schroder, V., Behrend, O., and Schubert, H. (1998a). Effect of dynamic interfacial tension on the emulsification process using microporous, ceramic membranes. J. Coll. Interf. Sci. 202, 334-340. 

Ceramic membranes are quite important since microporous ceramics are the principal barrier in UFe separation. Similar devices are used for microfiltration membranes and to a lesser extent for ultrafiltration. Homogeneous films are transformed into microporous devices by irradiation followed by selective leaching of the radiation damaged tracks, by stretching (Cortex is one welldmown example), or by electrochemical attack on aluminum. A few membranes are made by selective leaching of one component from a solid, as in membranes derived from glass or by selective extraction of polymer blends. 

L.V.C. Rees and L. Song in Recent Advances in Gas Separationby Microporous Ceramic Membranes p. 139-186, N.K. Kanellopoulos ed., Elsevier, Amsterdam (2000). 

T. liyama, T. Ohkubo, K. Kaneko, In Recent Advances in Gas Separation by Microporous Ceramic Membranes, Ed. N.K. Kanellopouos, Elsevier, pp.35-66 (2000). 

The methods of preparing inorganic membranes with tortuous pores vary enormously. Some use rigid dense solids as the templates for creating porous structures while many others involve the deposition of one or more layers of smaller pores on a premanufactured microporous support with larger pores. Since ceramic membranes have been studied, produced and commercialized more extensively than any other inorganic membrane materials, more references will be made to the ceramic systems. 

While dip coating and spin coating are used most often for making microporous ceramic membranes, the filtration technique for forming dynamic membranes can also be used [Okubo et al., 1991]. The filtration method is particularly suitable when the support does not have enough pore volume to supply sufficient slip particles at the support surface to form a layer of membrane. 

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