Monolith membrane elements

A membrane module may contain many membrane elements as shown in Figure 3.16, where 19 monolithic membrane elements each with 19 channels... 

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

Figure 3.6 Cross-sectional view of a muiti-channcl monolithic membrane element [Courtesy of U.S. Filter]...

Two types of connection (and therefore sealing) are involved in assembling membrane modules. The first type connects tubular or monolithic membrane elements in bundles using header plates at the ends and, in some cases, in the middle of the module length. The second type provides sealing between the plates and the module housing. 

Only a limited number of studies has begun to emerge in this area. The available studies encompass various levels of details. Some use CFD to focus the simulation on the How of liquid and particles through membrane pores while others model fluid flow through a single membrane tube. CFD simulation of fluid flow through a multi-channel monolithic membrane element has also been done. 

Fig. 2.8. Schematic picture of a porous multichcumel monolithic membrane element.

FIGURE 9.4 Image of a monolith membrane element, 150 mm in diameter and 1.5 m long, produced by CeraMem. 

Prior to spin coating, both ends of a pre-fabricated porous support, either in the form of a tube or a monolithic honeycomb element, are filled with the slip and temporarily sealed with gaskets. Slips of Ni, A1 and AI2O3 have been spin coated at a rotational speed of up to about 1300 rpm to form membrane layers [Sumitomo Electric Ind., 1981 NGK Insulators, 1986]. The development of a coating layer is expected to be faster with the in coating process than the dip coating process due to the centrifugal force. 

The overall membrane element shape comes in different types sheet, single tube, hollow fiber, and multi-channel monolith. Photographs of some commercial membrane elements are shown in Figure 5.1. The use of disks (or sheets) has been confined to medical, pharmaceutical and laboratory applications, while tubes and monoliths are employed in larger-scale applications ranging from removal of bacteria from wine and beer fermentation to oil-water separation to waste water ueatmenL... 

Figure 5.1 Photograph of alumina membrane elements in tubular and monolithic honeycomb shapes [Courtesy of U.S. Filters]...

The porosity at both ends of a tubular or monolithic honeycomb membrane element can be a potential source of leakage. These extremities need to be made impervious to both permeates and retentates so that the two streams do not remix. Typically the end surfaces and the outer surfaces near the ends of a commercial membrane element are coated with some impervious enamel or ceramic materials. 

Membranes that arc catalytically active or impregnated with catalyst do not suffer from any potential catalyst loss or attrition as much as other membrane reactor configurations. This and the above advantage have the implication that the former requires a lower catalyst concentration per unit volume than the latter. It should be mentioned that the catalyst concentration per unit volume can be further increased by selecting a high "packing density" (surface area per unit volume) membrane element such as a honeycomb monolith or hollow fiber shape. 

Current commercial inorganic membranes come in a limited number of shapes disk, tube and monolithic honeycomb. Compared to other shapes such as spiral-wound and hollow-fiber that are available to commercial organic membranes, these types of membrane elements have lower packing densities and, therefore, lower throughput per unit volume of membrane element or system. 

FIGURE 6.5 Details of the structure of a monolithic ceramic membrane element with filtrate conduits, from CeraMem. 

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]. 

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... 

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. 

A monolithic monofunctional enzymatically coupled FET sensitive to urea was first fabricated by Kuriyama and Kimura s group (44). Their integrated FET chip has two hydrogen ion-sensitive FET elements. One FET element has a urease-immobilized membrane, working as an enzyme FET, and the other has a ultraviolet (UV) light-inactivated, urease-immobilized membrane (see Section 3), working as a reference FET. 

The advanced type of enzymatically coupled FET utilizes an integrated FET transducer chip with several FET elements closely spaced to each other (see Section 2.3 and Fig. 7). The monolithic enzymatically coupled FET requires that small and well-defined enzyme-immobilized membranes be patterned on the specific areas of such a FET chip. In addition, the method for depositing the enzyme on the membrtme should be compatible with mass-production processes. Therefore, a more sophisticated procedure is needed to deposit enzyme on the membranes used in the monolithic enzymatically coupled FET. 

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. 

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