Hollow-fiber membrane shapes

As the name suggests, flat-sheet membranes are flat, like a sheet of paper, and can be made as thin as less than 1 pm. However, they need special holders to hold them in place. Hollow-fiber membranes are shaped like tubes (200 to 500 pm ID), allowing fluids to flow inside as well as on the outside. Hollow fibers are self-supported and offer the advantage of larger surface area per unit volume and high packing density. A large number of parallel fibers can be packed into a small volume. 

Shape Bead, flat sheet or hollow fiber membrane, amorphous aggregate Crystal Ease of filtration, Control of diffusion path length and flow properties Simple preparation... 

The term encapsulation has been used to distinguish entrapment preparations in which the biocatalyst environment is comparable to that of the bulk phase and where there is no covalent attachment of the protein to the containment medium (Fig. 6-1 D)[21J. Enzymes or whole cells may be encapsulated within the interior of a microscopic semi-permeable membranes (microencapsulation) or within the interior of macroscopic hollow-fiber membranes. Liposome encapsulation, a common microscopic encapsulation technique, involves the containment of an enzyme within the interior of a spherical surfactant bilayer, usually based on a phospholipid such as lecithin. The dimensions and shape of the liposome are variable and may consist of multiple amphiphile layers. Processes in which microscopic compart-mentalization (cf. living cells) such as multienzyme systems, charge transfer systems, or processes that require a gradient in concentration have employed liposome encapsulation. This method of immobilization is also commonly used for the delivery of therapeutic proteins. 

U) Various shapes of trunk polymers can be supplied in response to the demanded functionality adsorbents based on porous hollow-fiber membranes and nonwoven fabrics enaWe high-speed recovery of target molecules and ions by utilizing convective flows through the pores of the membranes and among the fibers, respectively. 

The formation of a porous structure results from phase separation (or phase inversion) mechanisms that are not limited to electrospraying. It is the process that controls membrane formation, as the solvent exchanges with a nonsolvent, polymer solution solidifies and polymeric device forms. The phase separation is fully investigated in fabrication of flat or hollow fiber membranes or in situ forming drug delivery systems. - Usually, quick evaporation of the solvent produces particles with porous or golf ball-shaped surfaces (Figure 22.26). 

Disadvantages of the known porous polymeric membrane preparation processes are that they involve additional process steps after the formation of the fiber to come to a final product. It is therefore desirable to have a more efficient preparation process. A new method to prepare structures of any geometry (Figure 6.13c through f) and large variety of functionality was recently proposed [61]. The authors proposed to incorporate the functionality by dispersion of particles in a polymeric porous structure formed by phase inversion. A slurry of dissolved polymer and particulate material can be cast as a flat film or spun into a fiber and then solidified by a phase inversion process. This concept is nowadays commercialized by Mosaic Systems. The adsorber membranes prepared via this route contain particles tightly held together within a polymeric matrix of different shapes, which can be operated either in stack of microporous flat membranes or as a bundle of solid or hollow-fiber membranes. 

Wei, Y, Liao, Q., Li, Z. and Wang, H. (2013) Enhancement of oxygen permeation through U-shaped K2NiF4-type oxide hollow fiber membranes by surface modifications. Separation and Purification Technology, 110,74-80. 

Hollow-fiber membranes. The membranes are in the shape of very small diameter hollow fibers. The inside diameter of the fibers is in the range of 100 to 5(X) p.m and the outside 200 to I0(K) pm with the length up to 3 to 5 m. The module resembles a shell-and-tube heat exchanger. Thousands of fine tubes are bound together at each end... 

An interesting work on perovskite membrane reactors has been reported by Liao et al, who prepared a U-shaped BCFT based membrane and tested it for methane conversion. The membrane has been prepared by phase inversion after spinning a hollow fiber membrane [73]. The picture of the setup used in their work is shown in Figure 33.21. 

Figure 33.21 Configuration of the U-shaped BCFT hollow fiber membrane reactor for POM [73],...

Liao, Q., Chen, Y., Wei, Y., Zhou, L., and Wang, H. (2014) Performance of U-shaped BaCoo.7Feo.2Tao.i03 8 hollow-fiber membranes reactor with high oxygen permeation for methane conversion. 

The shape of the membranes employed in laboratory studies is usually tubular (i.e. tubes with an external diameter of around 1 cm), and this is clearly the preferred option when a catalyst bed is located inside a membrane. However, flat membranes are also used when the material is made in the laboratory and in some pilot plant applications. In some of the most recent works, hollow fiber membranes have been developed. This shape has the advantage of providing a large surface-to-volume ratio and requires a smaller amount of material per unit of surface area, both factors contributing to a lower cost. 

Membrane Module Membrane modules have a feature of cylindrical structure and are constmcted of a header and a skirt to bundle the hollow-fiber membranes both having cylindrical shapes (Fig. 5.22). It has the following dimensions diameter ca. 0.2 m, length ca. 2 m, and membrane outer surface area 25 w . 

The principle of a three-phase membrane extraction is illustrated in Figure 1.28. An organic solvent is immobilized in the pores of a porous polymeric support consisting of a flat filter disc or a hollow fiber-shaped material. This supported liquid membrane (SLM) is formed by treating the support material with an organic solvent that diffuses into its pores. The SLM separates an aqueous... 

Two configurations of liquid membranes are mainly used in analytical applications flat sheet liquid membranes that give acceptable extraction efficiencies and enriched sample volumes down to 10-15 pL, and hollow fiber liquid membranes that allow smaller enriched sample volumes. Flat sheet liquid membrane devices consist of two identical blocks, rectangular or circular in shape, made of chemically inert and mechanically rigid material (PTFE, PVDF, titanium) in which channels are machined so that when... 

The method of impregnating liquid membranes has become more and more popular. By impregnating fine-pore polymer films with a suitable membrane liquid, relatively stable heterogeneous solid-liquid membranes are obtained. These membranes are shaped as thin, flat barriers or hollow fibers. Usually they are manufactured from oleophilic polymers, wettable by membrane liquid. The two interfaces, F/M and M/R, have equal or close areas which can be made very large by employing modules of spirally wounded flat membrane or bundles of hollow fibers. 

Polymers themselves, cast into membranes, spinned into hollow fibers, pressed into sheets, or extruded into selected shapes and configurations, have been widely used as compartments for the generation and stabilization of... 

Figure 2.1 Polymeric membrane shapes and cross-sectional structures. Tubular membranes are similar to flat sheet membranes because they are cast on a macroporous tube as support. Capillary membranes are hollow fibers with larger diameter, that is, >0.5 mm.

Schlosser, S. and Sabolova, E. (2002) Three phase contactor with distributed U-shaped bundles of hollow fibers for pertraction. Journal of Membrane Science, 210,331. 

Different membrane shapes are used, such as plates, foils, spirals, hollow fibers, tubes, and even monilithic multichannel elements have been mentioned in the context of membrane reactors. In the following section, a general survey will be given indicating the main characteristics of the different types of inorganic membranes used in CMRs. More details can be found elsewhere [13-15]. 

Polymeric membrane elements and modules which consist of elements come in different sh4>es. The shape strongly determines the packing density of the element or module which is indicative of the available membrane filtration area per unit volume of the element or module the packing density, in turn, can affect the capital and operating costs of the membranes. The packing density is often balanced by other factors such as ease and cost of maintenance and replacement, energy requirements, etc. Most of the polymeric membranes are fabricated into the following forms tube, tubes-in-shell, plate-and-frame, hollow-fiber, and spiral-wound. 

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... 

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