Hollow fiber membrane modules

Hollow fiber refers to a membrane tube of very small diameter (e.g., 200 pm). Such small diameters enable a large membrane area per unit volume of device, as well as operation at somewhat elevated pressures. Hollow-fiber modules are widely used in medical devices such as blood oxygenators and hemodialyzers. The general geometry of the most commonly used hollow-fiber module is similar to that of the tubular membrane, but hollow fibers are used instead of tubular membranes. Both ends of the hollow fibers are supported by header plates and are connected to the header rooms, one of which serves as the feed entrance and the other as the retentate exit. Another type of hollow-fiber module uses a bundle of hollow fibers wound spirally around a core. 

Removal of carbon dioxide is the only membrane-based natural gas separation process currently practiced on a large scale—more than 200 plants have been installed, some very large. Most were installed by Grace (now Kvaerner-GMS), Separex (UOP) and Cynara and all use cellulose acetate membranes in hollow fiber or spiral-wound module form. More recently, hollow fiber polyaramide (Medal) membranes have been introduced because of their higher selectivity. 

Figure 11.13 The effect of replenishing a hollow fiber coupled transport module with fresh complexing agent. Membrane, polysulfone, hollow fiber/Kelex 100 feed, 0.2 % copper, pH 2.5 product, 2% copper, 100 g/L H2S04 [49]...

Figure 4.30 shows a hollow fine fiber membrane module. The fibers are folded in half and the open end of each fiber is "potted" in epoxy "tube sheet," while the folded end is potted in an epoxy, non-porous block. Feed to the module is outside in, which requires less strength on the part of the fiber than inside-out flow would. Also, the pressure drop on the outside of the fibers is much less than would be in the inside of the fiber (which is known as the lumen). 

Much effort has been expended in attempting to use membranes for separations. Reverse osmosis membranes are used worldwide for water purification. These membranes are based on size selectivity depending on the pores used. They do not have the ability to selectively separate target species other than by size. Incorporation of carrier molecules into liquid membrane systems of various types has resulted in achievement of highly selective separations on a laboratory scale. Reviews of the extensive literature on the use of liquid membrane systems for carrier-mediated ion separations have been published [15-20]. A variety of liquid membranes has been studied including bulk (BLM), emulsion (ELM), thin sheet supported (TSSLM), hollow fiber supported (HFSLM), and two module hollow fiber supported (TMHFSLM) types. Of these liquid membranes, only the ELM and TMHFSLM types are likely to be commercialized. Inadequacies of the remaining... 

Hollow Fiber. Hollow-hbers are open channel products however, due to their small fiber diameters, they do not require the high-energy consumption of tubular membrane products. Hollow fibers are self-supported they do not require additional support substrates like flat sheet membranes do. Figure 14.6 shows a schematic of a hoUow-fiber module. 

FIGURE 31.2 Pictorial depiction of a double module hollow fiber Uquid membrane set up. HFM—Hollow fiber module F— Feed O— Organic extractant S—Strip or receiver phase and P—Pump. (Reproduced from Mohapatra, P.K. and Manchanda, V.K., Indian J. Chem., 42A, 2925, 2003. With permission.)... 

According to configuration definition, three groups of hquid membranes are usually considered (see Fig. 1.1) bulk (BLM), supported or immobilized (SLM or ILM), and emulsion (ELM) liquid membrane transport. Some authors add to these definitions polymeric inclusion membranes, gel membranes, dual module hollow-fiber membranes, but, to my opinion, the first two types are the modifications of the SLM and the third is the modification of BLM. It will be discussed in detail in the respective chapters. 

Membrane separation devices are assembled in a number of forms. In a flat sheet form the membrane is laid over a flat porous support. A unit would include a large number of the flat sheets separated by spacers and stacked together. In another configuration the fiat sheet may be spiral-wound with spacers around a perforated tube. Other arrangements involve tubular membranes or hollow fiber membranes assembled in bundles. In the tubular module the membrane is wrapped around a tubular... 

A further generality of the MDPE is that knowledge of the actual shape and geometry of the membrane within the MCS is not necessary. The equation is not restricted, and can be applied to any chosen shape (plate module, hollow fiber, spiral wound, and so on). 

Mosaic Systems Mosaic Systems, the Netherlands Particle-loaded membranes, fuU/hollow-fiber modules PES 1EX,AF... 

Figure 18.7 Photos of (a) LSCF hollow fiber membranes (b) hollow fiber bundles and (c) hollow fiber membrane module. ...

Gas permeation systems typically use hollow-fiber or spiral-wound membranes, although hollow-fiber systems are more common tBaker. 2004k Cellulose acetate membranes are used for carbon dioxide recovery, polysulfone coated with silicone rubber is used for hydrogen purification, and conposite membranes are used for air separation. The feed gas is forced into the membrane module under pressure. Retentate, which does not go through the membrane, will become concentrated in the less permeable gas. Retentate exits at a pressure that will be close to the input pressure. The more permeable species will be concentrated in permeate. Permeate, which has passed through the membrane, exits at low pressure. The operating cost for a gas permeator is the cost of conpression of the feed gas and the irreversible pressure difference that occurs for the gas that permeates the membrane. A typical hollow-fiber unit will contain 5000 m membrane area per m at a cost of approximately 200/m. ... 

Rgure 8. Frequently Used Membrane Types. A, B, C, and D are bulk liquid membrane, emulsion liquid membrane, supported liquid membrane, and dual module hollow fiber membrane configurations respectively. (Reproduced with permission from ref. 47. Copyright 1990 CRC Press.)... 

Celgard polypropylene (PP) hollow fibers assembled in modules showed promise in removing more than 95% of the Am and 70% of the Pu from high nitrate (6.9 M) and low acid (0.1 M) feeds into 0.25 M oxalic acid strippants. Hollow-fiber membrane supports were chosen since they offer a greater membrane area/feed volume ratio than do flat of spiral-wound membranes. For hollow fibers imbibed with tributylphosphate (TBP), plutonium and americium were transported with maximum permeabilities of about 1 X 10 cm/sec (6). 

Ceramic membranes (a) hollow-fiber elements and modules and (b) ultrafUtration unit for fruit juice clarification. (Courtesy Mempro Ceramics Corporation.)... 

Plate-and-frame as well as spiral-wound modules house flat membranes. Capillary and hollow fibers are packed in larger bundles in a pressure vessel. Commercially relevant are flat membranes and hollow fibers. However, new developments in perovskite membranes for oxygen transport are based on tubular membranes as well. ... 

Key producers for the nitrogen separation membranes are Air Products, Air Liquide and Ube. They all use either polysulfone or polyimide polymer membranes in hollow fiber configuration. Other nitrogen membrane module producers (IGS Generon systems, Parker Henifiin, Aquillo, etc.) use poly(4-methyl-l-pentene), tetrabromobisphenol polycarbonate and polyphenelyne oxide membranes. 

Because membranes appHcable to diverse separation problems are often made by the same general techniques, classification by end use appHcation or preparation method is difficult. The first part of this section is, therefore, organized by membrane stmcture preparation methods are described for symmetrical membranes, asymmetric membranes, ceramic and metal membranes, and Hquid membranes. The production of hollow-fine fiber membranes and membrane modules is then covered. Symmetrical membranes have a uniform stmcture throughout such membranes can be either dense films or microporous. 

Fig. 23. Two types of hollow-fiber modules used for gas separation, reverse osmosis, and ultrafiltration applications, (a) Shell-side feed modules are generally used for high pressure appHcations up to - 7 MPa (1000 psig). Fouling on the feed side of the membrane can be a problem with this design, and pretreatment of the feed stream to remove particulates is required, (b) Bore-side feed modules are generally used for medium pressure feed streams up to - 1 MPa (150 psig), where good flow control to minimise fouling and concentration polarization on the feed side of the membrane is desired.

Hollow-fiber designs are being displaced by spiral-wound modules, which are inherently more fouling resistant, and require less feed pretreatment. Also, thin-film interfacial composite membranes, the best reverse osmosis membranes available, have not been fabricated in the form of hoUow-fine fibers. 

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