Flat-sheet membranes module

In the supported liquid membrane process, the liquid membrane phase impregnates a microporous solid support placed between the two bulk phases (Figure 15.1c). The liquid membrane is stabilized by capillary forces making unnecessary the addition of stabilizers to the membrane phase. Two types of support configurations are used hollow fiber or flat sheet membrane modules. These two types of liquid membrane configuration will be discussed in the following sections. 

Ultrafiltration experiments were carried using the same setup, except the flat-sheet membrane module had a filtration area 38 mm long, 29 mm wide, and 1.6 mm high, with a surface area of 11 cm2. The permeate side had 11 grooved channels that supported the membrane, leaving an effective filtration area of 6.4 cm2. However, the total membrane area including the supports was used in calculating the fluxes. The feed consisted of cellulase enzyme solution (5.0 g/L of supplied cellulase, unless noted otherwise). 

FIGURE 8.31 Schematic diagram of vibrating flat sheet membrane module. 

To investigate the role of heat transfer in OMD and measure the asymptotic temperature difference, Celere and Gostoh [86] used the flat sheet membrane module shown in Figure 19.15. This contains a few flat sheet membranes placed 1 mm apart and supported by mesh-type spacers of 2 mm thickness, leaning against polypropylene walls. One stream (feed) flows between the membranes and other (extractant) flows cocurrently through the spacers. The mass transfer zone of each membrane is 80 mm in breadth and 200 mm in length. 

Vibratory mechanism was one more interesting technique for reducing fouling negative effect. Vibrations can be apphed to flat sheet membrane modules, but many researchers tested the technique on performance of hollow fibers for different separation processes [3, 136]. One example of construction is shown in Fig. 9.10 [136] to assess the effect of axial membrane vibrations on mass transfer in a hollow fiber oxygenator. 

For tubular and flat sheet membrane modules, one of the commonly used hydrodynamic techniques for the concentration polarization control is turbulence promoters, such as spacers used in spiral wound membrane modules, helical insert used in tubular membrane modules, and the corrugated membrane for the flat sheet membrane. Research has been conducted to assess the effect of the membrane flow channel spacers and inserts on the membrane filtration and to optimize their design. 

Figure 10.30. Flat sheet membrane module GS5 (GKSS). (Reproduced from [328] with permission.)...

A father development of the plate-and-frame module is the envelope module. In the GKSS module (Figure 5.5) flat sheet membranes are designed in the envelope type that enables membranes exchange easily. These modules are applicable in nanofiltration, vapor permeation and gas permeation processes and are suited for high operation pressure up 120 bars. The flat sheet membrane module can be used with sweep gas or vacuum operation on the permeate side. The feed gas flows around the membrane envelopes and the permeate is collected over a central collecting pipe, which lead to low pressure losses. The flexible distance between the membrane envelopes makes it possible to create relative constant retentate flows."... 

Spiral membranes are the usual way to form flat sheet into modules. They have the characteristic that the feed and the permeate move at right angles. Since the membrane is always cast on a porous support, point-permeate values are influenced by the substrate. 

Modules and Housings Modern gas membranes are packaged either as hollow-fiber bundles or as spiral-wound modules. The former uses extruded hollow fibers. Tube-side feed is preferable, but it is limited to about 1.5 MPa. Higher-pressure applications are usually fed on the shell side. A large industrial permeator contains fibers 400 pm by 200 pm i.d. in a 6-inch shell 10 feet long. Flat-sheet membrane is wound into spirals, with an 8- by 36-inch permeator containing 25 of membrane. Both types of module are similar to those illustrated in Background and Definitions. Spiral modules are useful when feed... 

Flat-Sheet Membranes and Spiral-Wound Modules... 

Flat-sheet membranes are made in continuous rolls 500-5000 m long. Sheets of membrane 1-2 m long are cut and folded and then packaged as spiral-wound module envelopes. A single module may contain as many as thirty membrane envelopes. Currently, the industry standard spiral-wound module is 8 inches (1 inch = 2.54 cm) in diameter and about 35-40 inches long it contains 20-40 m2 of membrane. 

Each membrane/module type has advantages and disadvantages [2,7]. Hollow fine fibers are generally the cheapest on a per-square-meter basis, but it is harder to make very thin selective membrane layers in hollow-fiber form than in flat-sheet form. This means the permeances of hollow fibers are usually lower than flat-sheet membranes made from the same material. Also, hollow fine fiber modules require more pretreatment of the feed to remove particulates, oil mist and other fouling components than is usually required by capillary or spiral-wound modules. These factors offset some of the cost advantage of the hollow fine fiber design. 

The investment in time and equipment to develop a new membrane material in a high-performance hollow fine fiber or capillary form is far larger than that required to develop flat-sheet membranes, and many materials cannot be formed into fiber modules at all. For this reason, flat-sheet membranes, formed into spiral-wound modules, are used in many niche applications which cannot support the development costs associated with fiber modules. Spiral-wound modules are also competitive in the natural-gas processing area, where their general robustness is an asset. 

The obtained results have shown that the configuration where the recirculation tank was irradiated and the catalyst was used in suspension appeared to be the most interesting for industrial applications [73]. Moreover, it was observed that the degradation rate was higher when an immersed lamp was used compared to a system with an external lamp [81]. Therefore, actually the studies in progress are realized in the system described elsewhere [39] consisting of a Pyrex annular photoreactor with a 125-W medium-pressure Hg lamp axially positioned inside the reactor. The separation module containing the flat-sheet membrane was connected to the photoreactor in a recirculation loop. 

The membrane module and design will obviously depend on the type of membrane used. The flat-sheet membranes are commonly constructed in a plate-and-frame configuration or as spiral-wound (SW) modules. F1F/CT/MTmembrane types are commonly manufactured into bundles that are installed in housing units or designed to be unconfined in the fluid, that is, immersed units. The membranes are... 

Polymeric flat sheet membranes are easy to prepare, handle, and mount. For gas separation, the flat sheet membranes are composites with a selective polymer coated on a support. A commercial configuration that has been quite successful for hydrocarbon vapor recovery is the Borsig envelope type module (see Figure 4.19) [107]. Packing densities for flat sheet membranes may be in the range of 100 00 m /m [1]. 

Cassette Cassette products are widely used in the biopharmaceutical industry and specifically dominate the protein concentration purification market due to their compactness, which provides excellent product recovery capabUity. Cassette modules contain presealed flat sheet membranes separated by feed and filtrate spacers. This is an improved design compared to earher plate and frame configurations, making installation and replacement much easier and more reliable for the end user (shown in Figure 14.5). 

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. 

Spiral Wound Spiral-wound membrane products are similar to cassettes since they combine flat sheet membranes and feed/permeate spacers, but the flat sheet membrane and the spacer pack are rolled or wound into a spiral form. Spiral-wound modules have much longer feed path lengths than cassettes. 

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