Membrane filter materials

Table 7. Inorganic Cross-flow Filters Membrane Materials and Module Geometries... 

As described above, a test fluid (usually water) is retained by the filter membrane material by surface tension and capillary forces). This adhesion is, amongst others, dependent on the pore size of the filter. In the bubble point test air pressure is applied to the moistened filter and it is observed at which pressure air bubbles are formed on the sterile side of the filter. The pressure at which the first bubbles are formed is called the bubble point. At this moment, the liquid is pushed out of the largest pores. 

In which y is the interfacial tension, 0 the contact angle, K a correction factor for the shape of the pores and d the pore diameter. Cos 0 is determined by the interfacial tensions between the three components filter membrane material, hquid and air. It is the same angle as in the wetting theory as discussed in (Sect. 18.3.2). The manufacturer supplies the value of the bubble point for hydrophilic filters for a filter moistened with purified water at a specified temperature. A different liquid or product or different temperature in the membrane results in a different interfacial tension and thus a different bubble point. 

Validation Considerations. Mechanisms other then size exclusion maybe operative ia the removal of vimses from biological fluids. Thus vims removal must be vaUdated within the parameters set forth for the production process and usiag membrane material representative of the product line of the filter. 

The vast increase in the application of membranes has expanded our knowledge of fabrication of various types of membrane, such as organic and inorganic membranes. The inorganic membrane is frequently called a ceramic membrane. To fulfil the need of the market, ceramic membranes represent a distinct class of inorganic membrane. There are a few important parameters involved in ceramic membrane materials, in terms of porous structure, chemical composition and shape of the filter in use. In this research, zirconia-coated y-alumina membranes have been developed using the sol-gel technique. 

Beside SILP experiments with silica as support material, reports have also been made on the use of membranes coated with ionic liquid catalyst solution for the hydrogenation reaction of propene and ethene. The membranes were obtained by supporting various ionic liquids, each containing 16 to 23 mmol Rh(I) complex Rh(nbd)(PPh3)2 (nbd=norbornadiene), in the pores of poly(vinylidene fluoride) filter membranes [118]. 

Filter a sample or blank (deionized or distilled water) with a PTFE filter membrane or other material to achieve clarity. 

The first major application of microfiltration membranes was for biological testing of water. This remains an important laboratory application in microbiology and biotechnology. For these applications the early cellulose acetate/cellulose nitrate phase separation membranes made by vapor-phase precipitation with water are still widely used. In the early 1960s and 1970s, a number of other membrane materials with improved mechanical properties and chemical stability were developed. These include polyacrylonitrile-poly(vinyl chloride) copolymers, poly(vinylidene fluoride), polysulfone, cellulose triacetate, and various nylons. Most cartridge filters use these membranes. More recently poly(tetrafluo-roethylene) membranes have come into use. 

The type of approach described here is obviously more important for systems where the solution chemistry of the nuclide (charge, oxidation state and degree of complexation) is more complicated. Without supporting laboratory data, it is possible that significant retention values may be incorrectly interpreted as being due to radionuclide association with material in a particular size fraction. The components of the environmental sample might contribute to the separation process and retain species which on a size basis should readily pass through the filter membrane. 

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. 

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