Membrane flat filter

There are many filter configurations within the industry, such as sheet or modular depth filter types for prefiltration purposes, flat filter membranes mainly for microbial detection and, specifications, and, most commonly, filter cartridges containing either depth filter fleeces or membrane filters. Such membrane filters are available in a large variety of membrane polymers for different applications. These materials are discussed later in the chapter. 

In conventional membrane emulsification, droplets are formed at the membrane surface and detached from it by wall shear stress of the continuous phase (Figure 20.8, middle) [29,45,46]. In addition to tubular membranes made from ceramics such as aluminum oxide, special porous glasses such as SPG (Shiratsu Porous Class) membranes and polymers such as polypropylene (29, 47, 48], flat filter membranes made of PTFE [49, 50], nylon [51] and silicon (30, 51-55] have been used in emulsification. Silicon membranes are produced by microengineering techniques. This technology offers the possibility to influence precisely the structure of a membrane (arrangement of pores, pore shape, size and distance, porosity, surface characteristics, as shown in Figure 20.7). Very thin active layers reduce the pressure drop without losing mechanical stability. 

Crossflow units — Flat sheet membranes - Rotating filter elements... 

In Sittt Filter Membranes In situ membranes are being fitted into incinerator flue-gas stacks in an attempt to reduce hydrocarbon emissions. Two types of commercially available gas separation membranes are being stndied (I) flat cellnlose acetate sheets and (2) hoUow-tnbe fiber modules made of polyamides. 

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... 

Figure 1. Diagram of filtration mechanisms for A) flat-membrane filters and B) hollow-fiber filters, showing the concentration polarization on the flat filters.

An industrial application of dialysis is the recovery of caustic from hemi-cellulose solutions produced in making rayon by the viscose process. Flat-sheet membranes are placed parallel to each other in a filter-press arrangement (see Chap. 30, p. 1004) and water is passed countercurrent to the feed solution to produce a dialyzate with up to 6 percent NaOH. Recovery of salts or sugars from other natural products or other colloidal solutions could be achieved by dialysis, but ultrafiltration is more likely to be used because of the higher permeation rates that can be obtained. 

The spinning of asymmetric hollow fibers with the skin on the inside closely resembles the procedure used in casting flat-sheet membranes. Figure 3.1510 is a schematic diagram of a spinneret used to spin these fibers. The degassed and filtered polymer solution is forced under pressure into a coaxial tube spinneret. The liquid is extruded through an annular orifice and the hollow fiber (still liquid) is stabilized and precipitated by an internal coagulating fluid (usually water) which flows out the center tube. 

Tubular membranes Flat sheet membranes Rotating filter elements By gravity... 

As in flat-sheet filtration, the constant flow rate of the bottle filler dictates the nnmber of cartridges to nse. It has been calculated that three 30-inch cartridges (Alter surface of 1.8 m each, flow rate 720 Fh) are required to supply a bottling line operating at 3000 bottles/h or 2250 1/h. Filter membranes must be used for several weeks, or even months, before they become completely blocked in order to make this system cost-effective. 

For small-scale separation and purification Taylor flow Flat sheet membrane filters for small-scale... 

Concentration polarization is an another key parameter of polysaccharide filtration. When the MWCO of the membrane is adapted to the composition of the extract, hollow fibers seem to be more efficient than flat sheet membranes. Flat sheet membranes with turbulence promoters in the feed channel are used with low tangential velocity because turbulences are created by the screen. When filtering polysaccharides extracts, the viscosity of the solution is high, particularly in concentration mode, and the efficiency of the turbulence promoters is too low to avoid the creation of a gel layer. Hollow fibre membranes, which are used with high tangential velocity, thus give the higher permeate fluxes. 

Flat-sheet membranes are normally assembled in plate-and-frame devices together with porous support plates and spacers forming the feed flow channels. The feed solution is pressurized in the housing and forced across the membrane (Fig. 2.3a). The support plate provides a flow channel for the permeate that is collected from a tube on the side of the plate. Feed channel heights vary from 0.3 to 0.75 mm depending on the viscosity of the feed solution to be filtered. 

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