Multichannel monolithic elements

The permeate is continuously removed through the membrane from the entrance to the exit of the flow channel of the membrane (in frame-and-plaie, tubular or multichannel monolithic elements) as the process stream flows across the membrane surface. Consequently the tangential velocity decreases along the length of the membrane. The velocity at the entrance, however, normally differs from that at the exit only by a small amount since in one pass the amount of permeate removed is relatively small. The operating pressure determines the tangential velocity. 

To increase the mechanical robustness and the surface area-to-volume ratio, which gives more filtration area per unit volume of membrane element, alumina multichannel monolithic elements have been developed, as shown in Fig. 2.8. These monolithic elements can again be combined into modules. Surface area-to-volume ratios of 30-250 m /m for tubes, 130-400 re /re for multichannel monolithics and up to 800 m /m for honeycomb multichannel monolithics are reported by Hsieh [9]. 

The structural elements of commercial inorganic membranes exist in three major geometries disk, tube or tube bundle, and multichannel or honeycomb monolith. The disks are primarily used in laboratories where small-scale separation or purification needs arise and the membrane filtration is often performed in the flow-through mode. The majority of industrial applications require large filtration areas (20 to over 200m ) and, therefore, the tube/tube bundle and the multichannel monolithic forms, particularly the latter, predominate. They are almost exclusively operated in the cross-flow mode. 

Figure 3.15. Schematic of permeate flow path through a porous multichannel monolithic membrane element (Hsieh 1988, Hsieh, Bhave and Fleming 1988).

Multichannel (ceramic) monolithic element with 6-18 channels,... 

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... 

Cross-sectional schematic of a monolithic multichannel element. (After Hsieh. -)... 

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