Monolith-type membrane

Figure 6.8 Schematic diagram of monolith-type membrane (CeraMem Corporation).

Because of the large surface area of the skin and its bypass of the liver as a first pass step in metabolism, many drug delivery systems have been developed that control the rate of drug delivery to the skin for subsequent absorption. Effective transdermal drug delivery systems of this type deliver uniform quantities of drug to the skin over a period of time. Technically, transdermal drug delivery systems may be classified into monolithic and membrane-controlled systems (9). 

The most characteristic features of structured catalysts are given in Table 1. The main difference between the three types of structured catalysts we have just distinguished consists in the rates of radial mixing in the reactor containing the structured catalyst from zero radial mass transfer in monolithic reactors to a very intense radial mass transfer in reactors with structural catalysts. For the sake of simplicity, reactors containing monolithic or membrane catalysis will be referred to as monolithic or membrane reactors, respectively. 

Most research on controlled release polymeric systems has, however, centered on compositions in which a drug is either encapsulated in the center of a polymeric membrane (reservoir type) or dispersed throughout the polymer (monolithic type). The drug diffuses through the polymeric material to the surface where it is released to the body fluids. Such systems have been used to give... 

Not only does the bulk chemical industry employ all of the membrane separation processes, but partly because of that, the sector gives home also to all of the various physical embodiments of membranes flat sheets, plate and frame, pleated cartridges, tubular, hollow fibre, capillary module, and spiral w ound. More particularly, this end Use sector has considerable demaitd for membranes able to resist high temperature or highly corrosive fluids, such that metallic membranes and ceramic materials, especially of the monolith type w ith parallel cylindrical chambers, are w idely used. 

TFF module types include plate-and-frame (or cassettes), hollow fibers, tubes, monoliths, spirals, and vortex flow. Figures 20-52 and 20-53 show several common module types and the flow paths within each. Hollow fiber or tubular modules are made by potting the cast membrane fibers or tubes into end caps and enclosing the assembly in a shell. Similar to fibers or tubes, monoliths have their retentive layer coated on the inside of tubular flow channels or lumens with a high-permeability porous structure on the shell side. 

There are other novel media with characteristics similar to functionalized membranes. Some of the commercially available media are listed in Table 2. These materials in many cases are at the cross-lines of definitions and are frequently compared in the MA literature. Organic separations in the reserve-phase (RP) and hydrophobic interaction chromatography (HIC) mode are not very common on filtration-based MA materials. However, the methacrylate copolymers can be used for this purpose. Also rodlike monolithic materials enable greater flexibility in these types of chemistry.13,14 The method of Tennikova and Svec15-17 has been used to commercialize a novel disk type separation media, called CIM (Convective interaction media, BIA, Ljubljana, Slovenia).18-21 Analytical-scale separations can be performed on... 

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. 

Many commercial ceramic membranes nowadays come in the form of a monolith consisting of multiple, straight channels parallel to the axis of the cylindrical structure (Figure 3.6). The surfaces of the open channels are deposited with permselective membranes and possibly one or more intermediate support layers. The porous suppon of these multi-channel structures are produced by extrusion of ceramic pastes described above with a channel diameter of a few millimeters. Their lengths are somewhat limited by the size of the furnaces used to dry, calcine and sinter them and also by such practical considerations as the total compact weights to be supported during heat ueatment and the risk of distortion in the middle section. It should be noted that this type of honeycomb... 

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... 

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. 

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. 

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... 

This also means that stress relief joints will be required on this type of floor to break the lines of stress from the slow growth of the brick or tile, and so prevent disbonding, followed by heaving, just as the stress relief joints in a monolithic floor provide for the cure shrinkage of the monolithic. It should also be remembered that, unlike brick on a membrane, if brick (or tile) are bonded to the substrate, and if the substrate cracks, so will the tile or brick structure. 

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