Multichannel ceramic membranes

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

Due to their high stiffness and brittleness, it is not possible to extend to ceramic membranes geometries applicable with organic membranes like spirals, which give rise to high surface volume ratios. The ceramic membranes used for tangential filtration are nsually multichannel tubes or, in some applications, honeycomb monoliths. A very attractive type of membrane is the ceramic hollow fiber with an external diameter of less than 1 mm and ceramic walls with a thickness of a... 

Although some ceramic membrane elements are proposed with a flat geometry, most of them exhibit a cylindrical shape for a multichannel element (Figure 6.1). The reason for that is the much better mechanical properties obtained for cylindrical-shaped ceramics and the easier sealing of the elements compared to flat shapes. 

FIGURE 6.1 Schematic representation of the multichannel structure of a ceramic membrane element. 

Originally, multichannel ceramic membranes have been produced at the industrial scale by SCT-Exekia and Orehs in France with commercial elements registered, respectively, as Membralox and Kerasep. The membrane filtration area in this case can reach 0.35 m /element depending on channel diameter and the number of channels per element. FILTANIUM elements, representative of flower-like geometries, have been produced more recently by TAMI industries in France (Figure 6.3). These elements with a cross-section diameter of either 10 or 25 mm exhibit a number of channels that vary from 3 to 39 and a membrane filtration area of 0.5 m for the largest elements. The increase in membrane surface compared to equivalent cylindrical-shaped channels can be estimated at 30%. 

Behind the general parameters (viscosity, transmembrane pressure, temperature, flow velocity) which can influence cross-flow filtration with ceramic membranes two aspects must be considered to be more specific of this sort of membrane. One is related to the geometry (tubular multichannel or honeycomb) found for the major part of commercially available membranes, the other is the amphoteric behaviour of metal oxides used in the preparation of these ceramic membranes. 

As previously mentioned, most of ceramic membrane elements are produced under cylindrical shapes, that is, tube, multichannel, and monolith elements. Membrane modules are composed of one or more of these filtration elements, inserted in stainless steel housing (Figure 9.15). Plastic housings are also used, but stainless steel is often preferred to fully exploit specific properties of inorganic membranes, in particular, their ability to work in tough chemical and... 

Commercialized ceramic membranes can be of different configurations, from disc/fiat-sheet to multichannel tubes. The membrane microstructure is always very similar, that is, a thin separation layer made of finer particles supported onto a more porous multilayer substrate with a gradient pore structure, as shown in Figure 10.1. The only layer involved in separation is normally the thinnest layer with the finest pore size. The thickest layer, which consists of big particles for low resistance to permeates, provides the mechanical strength, whereas the layers in between are needed for a uniform formation of the top separation layer. Normally, different techniques are used for each individual layer, which results in soaring expenditures with the number of layers involved. 

Membralox Ceramic Multichannel Membrane Modules, Technical Brochure, Alcoa/SCT, Aluminum Company of America, Pittsburgh, Pa., 1987. 

In the early 1980s, former employees of Euroceral founded a small company located near Montpellier in France known as Ceram-Filtre. The rather less well-known Ceram-Filtre membranes comprise a multichannel support with 19 channels of 4 mm diameter and a microfiltration membrane made of an oxide. 

In the second half of the 1980s, an increasing number of companies entered the field of inorganic membranes, the most significant ones being ceramic companies such as NGK of Japan which also developed a multichannel membrane element (19 channels, 3 mm diameter), Nippon Cement and Toto also from Japan and very recently Coming who also developed a multichannel membrane structure. 

Adamson, A. W. 1982. Physical Chemistry of Surfaces. 4th ed. John Wiley Sons, New York. Alcoa. 1987. Mcmbralox ceramic multichannel membrane modules. Product brochure. 

U. S. Filter Membralox Products Group 181 Thom Hill Road Warrendale, PA 15086 USA Membralox tubular and multichannel ceramic MF, UF and NF membranes. Ceraflo MF membranes. 

Most inorganic membrane supports exhibit a tubular shape. This is a well-adapted geometry for cross-flow filtration in which the feed stream is circulated across the surface of the membrane and the permeated flux passes through the membrane in a perpendicular direction. Stainless steel, carbon, and ceramic are the most frequently used materials in the preparation of supports. As shown in Fig. 2, tubes or multichannel substrates can act as membrane supports. A well-designed support must be mechanically strong, and its resistance to fluid flow must be very low. Aiming at enhancing flux performances, multilayered substrates have been prepared that exhibit an asymmetric structure... 

Figure 7-15, Multichannel geometry of a, ceramic macroporous membrane coated at the surface of an alumina support by the slip-casting method.

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