Polypropylene filter membranes

Membrane polymeric materials for separation applications are made of polyamide, polypropylene, polyvinylidene fluoride, polysulfone, polyethersulfone, cellulose acetate, cellulose diacetate, polystyrene resins cross-linked with divinylbenzene, and others (see Section 2.9) [59-61], The use of polyamide membrane filters is suggested for particle-removing filtration of water, aqueous solutions and solvents, as well as for the sterile filtration of liquids. The polysulfone and polyethersulfone membranes are widely applied in the biotechnological and pharmaceutical industries for the purification of enzymes and peptides. Cellulose acetate membrane filters are hydrophilic, and consequently, are suitable as a filtering membrane for aqueous and alcoholic media. 

The implementation of new materials for filter membrane and plastics (e.g. polypropylene with FIFE) for the ultrafiltration units has diminished the disad-... 

Polypropylene membranes of this type can be used where the chemical resistance of polypropylene and tight control of pore size are needed. These polypropylene membranes, known as ACCUREL, are more chemically resistant than the remaining polypropylene filter cartridge components due to a proprietary process used during membrane manufacture and have replaced poly(tetrafluoroethylene) membranes In many applications. 

Meiny different supports have been used to prepare ILMs Including cellulose acetate reverse osmosis membranes (1 6, 25, 29, ), micro-porous polypropylene ultrafiltration membranes (31-3 T7 polyvinyl chloride filters (35), and hollow fiber cellulose acetate reverse osmosis membranes T36). Way et al. ( ) discuss the chemical and physical properties that must be considered when an ILM support Is selected. 

Microfilters, Fig. 1 Left. (a) schematic and (b) picture of a microfiuidic blood filtration device [32]. The top and bottom pieces are made up of PDMS, and the membrane is a commercially available hydrophilic polypropylene filter. Right, schematic of another device fabricated similarly but with multiple layers of nanoporous membranes [33]... 

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. 

Other factors to consider in the selection of cartridge filters are the type of filter medium and its characteristics. As an example, polypropylene cartridges are a better selection than cotton for water service, since cotton swells. The compatibihty of filter membranes and binders with chemical additives or impurities in the water should be checked. The designer should contact specific manufacturers for detailed information. 

Sterilizing filtration is usually performed using commercially available membrane filter units of standard design. These arc normally installed in special cartridges that often are made from polypropylene. Figure 10.5 [5] shows the sectional views of a membrane filter of folding fan-like structure, which uses a pleated membrane to increase the membrane area. 

In the integrated membrane system fed with seawater (Figure 12.4A) the pretreatment consists of two rotating microscreens of 150 pm used to remove the larger suspended particles from the water. Successively 8MF units (polypropylene (PP) hollow membranes placed in a vertical position and operated according to the deadend principle) are used to remove the suspended solids completely, algae and to disinfect the water. The MF section is designed to filter 700-750 m3/h [15]. 

In micro- and ultrafiltrations, the mode of separation is by sieving through line pores, where microfiltration membranes filter colloidal particles and bacteria from 0.1 to 10 mm, and ultrafiltration membranes filter dissolved macromolecules. Usually, a polymer membrane, for example, cellulose nitrate, polyacrilonytrile, polysulfone, polycarbonate, polyethylene, polypropylene, poly-tretrafhioroethylene, polyamide, and polyvinylchloride, permits the passage of specific constituents of a feed stream as a permeate flow through its pores, while other, usually larger components of the feed stream are rejected by the membrane from the permeate flow and incorporated in the retentate flow [10,148,149],... 

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