Organic membrane filters

Large volumes of water often need to be processed to obtain sufficient quantities of aquatic humic substances filtration is the slowest step in this process. In a comparison of filter flow rates, Cranston and Buckley (1972) found filtering times for 47 mm (millimeter) diameter filters increased in this order glass-fiber filters < silver-membrane filters < organic-membrane filters (cellulose-acetate and cellulose-nitrate). They also report that substantial variation exists between different silver filters from the same manufacturer. This is caused by variation in permeability (number of pores per unit area), not pore size, and did not occur with the other filters studied. 

Filtration is used either to separate particulate matter in sea water fof analysis or to obtain a particle-free sample of water for the analysis of soluble material. Several types of filter have been recommended for marine work and continuous centrifugation at high speed can be surprisingly effective although it is generally inconvenient to manipulate. To replace paper filters, organic membrane filters and glass-fiber or silver-fiber filter papers are commonly employed. Vacuum may be controlled by one of the devices mentioned on p. 182. 

Figure 11. Photographs of the filtered organic phase for the product of benzyl alcohol oxidation reaction catalyzed by (a) RuC13, (b) Ru02, (c) Pyc powders, and (d) NPyc membrane catalyst with 15 ml CH2C12 + 6ml NaOCl (4.1 mol)/pH 11 PBS.

Porous materials and membranes used as filters have a number of small, often tortuous, pores. This type of filter includes sintered glass filters, organic... 

In some technological and medical applications protein adsorption and/or cell adhesion is advantageous, but in others it is detrimental. In bioreactors it is stimulated to obtain favourable production conditions. In contrast, biofilm formation may cause contamination problems in water purification systems, in food processing equipment and on kitchen tools. Similarly, bacterial adhesion on synthetic materials used for e.g. artificial organs and prostheses, catheters, blood bags, etc., may cause severe infections. Furthermore, biofilms on heat exchangers, filters, separation membranes, and also on ship hulls oppose heat and mass transfer and increase frictional resistance. These consequences clearly result in decreased production rates and increased costs. 

The term species refers to the actual form in which a molecule or ion is present in solution. For example, iodine in aqueous solution may conceivably exist as one or more of the species I2, I, la" HIO, IO , lOJ, or as an ion pair or complex, or in the form of organic iodo compounds. Figure 6.1 shows the various forms in which metals are thought to occur in natural waters. It is operationally difficult to distinguish between dissolved and colloidally dispersed substances. Colloidal metal-ion precipitates, such as Fe(OH)3(s) or FeOOH(s) may occasionally have particle sizes smaller than 100 A—sufficiently small to pass through a membrane filter. Organic substances can assist markedly in the formation of stable colloidal dispersions. Information on the types of species encountered under different chemical conditions (types of complexes, their stabilities, and rates of formation) is a prerequisite to a better understanding of the distribution and functions of trace elements in natural waters. 

Organic-membrane filters, such as cellulose-acetate and cellulose-nitrate filters, are often conditioned with organic surfactants to assist in wetting the filter. These surfactants will be leached from the filters, contaminate the... 

Filters can also sorb certain organic compounds possibly resulting in reduced recovery and fractionation of compounds of interest. Cranston and Buckley (1972) compared organic-membrane, glass-fiber, and silver-membrane filters for the sorption of humic acid. Organic-membrane filters sorbed 15%, glass-fiber filters 5%, and silver-membrane filters 3% of the humic acid in the solution passed through the filters. 

Dispersions of polyaniline in isopropanol-based organic solvents were investigated by photon correlation spectroscopy experiments and the results of these experiments are shown for neutral PAni in Figure 11,41 and for doped PAni in Figure 11,42, Therefore it is important to note that the dispersions used (0,1% concentration) are completely clear and have been filtered through 1 pm filters or pressure filtered through membrane filters [84],... 

Airborne particles commonly are collected from air on filter media such as organic membranes, paper (cellulose fiber), or glass fibers. Membrane filters are fragile and... 

Water samples are stored in flasks of polyvinyl chloride (PVC) or PTFE, cleaned with 50% nitric acid before use. The flask is subsequently prerinsed with the sample water. Contaminated samples are filtered through membrane filters directly into the sample flask and acidified, e.g., with high purity nitric acid to pH 1 - 2 the filter residue is analyzed separately. Water samples with little or no organic contamination are mixed with the chosen supporting electrolyte and immediately placed in the voltammetric/polarographic set-up. 

To get defect-free membranes, organic solvent-based polymer solutions should be filtered before casting. For large volumes, a glass filter or membrane filter can be used. For smaller volumes (<50 mL) the losses may be too high, and filtration through a syringe filter (0.45 pm)... 

In most cell culture and fermentation processes, air and liquid nutrient feed streams are clarified and sterile filtered to eliminate particulate and microbiological contamination of the fermenter. Serum and culture media feeds are sterile filtered with membrane cartridges to remove contaminating micro-organisms. Hydrophobic filters provide sterile filtration of inlet fermentation air. 

The earliest commercially available filters were manufactured in two pore sizes 0.45 and 0.8 pm. The 0.45 pm-rated membranes were considered to be stefilizing-grade filters and were successfully used in the sterile filtration of pharmaceuticals and parenterals. The membrane filters were qualified using Serratia marcescens a standard bacterium, having dimensions of 0.6 x 1 pm. However, in the late 1960s it became apparent that the matrix of the 0.45 pm-rated filters could be penetrated by some pseudomonad-like organisms (1). For sterile filtration apphcations in the 1990s, 0.2 pm-rated membranes are the industry standard in the manufacture of sterile parenterals and pharmaceuticals. 

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