Filtration resistances, membrane

PPS fiber has excellent chemical resistance. Only strong oxidising agents cause degradation. As expected from inherent resia properties, PPS fiber is flame-resistant and has an autoignition temperature of 590°C as determined ia tests at the Textile Research Institute. PPS fiber is an excellent electrical iasulator it finds application ia hostile environments such as filter bags for filtration of flue gas from coal-fired furnaces, filter media for gas and liquid filtration, electrolysis membranes, protective clothing, and composites. 

The rates of filtration of microbes (particles) at a constant pressure difference decrease with time due to an accumulation of filtered microbes on the surface and inside the pores of the membrane. Hence, in order to maintain a constant filtration rate, the pressure difference across the membrane should be increased with time due to the increasing filtration resistance. Such data as are required for practical operation can be obtained with fluids containing microbes with the use of real filter units. 

Kimura, K., Y. Watanabe, and N. Ohkuma (1998). Filtration resistance induced by ammonia oxidizers accumulating on the rotating membrane disk. Water Science Techno. Wastewater Industrial WastewaterTreatment., Proc. 199819th Biennial Conf. Int Assoc, on Water Quality. Part 4, June 21-26, Vancouver, Canada, 38,4—5,443 52. Elsevier Science Ltd., Exeter, England. 

The culture media used in fermentation processes contains a variety of unwanted cells and spores which need to be inactivated or removed before fermentation. The most commonly used inactivation method is heat sterilization. Most cells and some spores can be destroyed at60°C-80°C, while some heat-resistant spores such as bacterial spores require more than 120°C. Heat-based methods, however, cannot be used when the product molecules, such as vitamins and antibiotics, are heat sensitive, because the application of high temperatures changes their properties. In these cases, sterile filtration with membrane filters or depth filters is used. 

It has been shown recently [11] that the experimental hydraulic resistance of such a composite structure can be much larger than the theoretical resistance obtained by simply summing the resistances of the different layers. As an interpretation, the existence of highly resistant transition boimdary layers due to infiltration between adjacent media of drastically different particle sizes has been suggested (Fig. 12.3). In order to check this theory, infiltrated and nonin-filtrated Ti02 membranes deposited on a-alumina support have been prepared. Scanning electron micrograph of their interfaces is shown in Fig. 12.4. From them, complementary resistances have been measured. 

Membrane filters (Whatman 40, Whatman 41) have exceedingly low contents of impurities and ash. They can be easily mineralized and they exert a low filtration resistance. Their disadvantages are their high hygroscopicity and lower efficiency for the capture of particles of sizes below 1 /im. 

Membrane fouling may result in a significant increase in filtration resistance, leading to unstable filtration behavior. The pressure-driven membrane processes can be operated either with constant feed pressure or in constant flux mode. For constant pressure operation where the transmembrane pressure (TMP) is maintained at a constant value during the filtration, the flux will decline with time due to the... 

In addition to high rates of filtration, asymmetric membranes are more resistant to fouling. Membranes act as conventional symmetrical filters and traps particles deep within its internal structure. These particles trapped blocked the pores of the membrane, and thus, the trausmembraue flow decreases during the process. Asyuunetric manbranes behave as filters for surface and retain all rejected particles on the surface, where they can be removed by shearing forces applied by the feed solution during its passage parallel to the membrane surface, the tangeutial filtration mode [2],... 

At the veiy start of the filtration the membrane resistance alone opposes permeate flow and Equation (10.10) can be written as ... 

Filter papers are imsuitable for filtration. The membrane filters so far commercially available, could not be used on account of their poor resistance to organic solvents. The successful use of methanol-insoluble membrane filters in the extraction of TLC spots, has however been recently reported [799]. Glass or porcelain filters are generally used. The filtrate from a G4 sintered glass filter can be sucked directly into a small standard flask in an evacuated vessel [213, 215]. An extractor functioning under increased pressure has also been employed [695]. 

Basu, S. Maes, M. Cano-Odena, A. Alaerts, L. De Vos, D. E. Vankelecom, 1. F. J. solvent resistant nano filtration (SRNF) membranes based on metal-organic frameworks. J. Membrane Science, 2009, 344, 190-198. 

A fouling layer formed and compressed during a membrane filtration process causes a decline in permeate flux due to the increase in filtration resistance from the compressed fouling layer. The Kozeny equation can be used for estimating pressure drop through a fouling layer under a specified filtration rate, that is ... 

These drawbacks resulted in serious limitations in the use of membrane filtration in the pulp and paper industry. However, today, with the development of more pH and temperature resistant membranes, membrane filtration is getting more and more acceptance as a separation process in the pulp and paper industry. One of the major problems of membrane application to pulp and paper stream treatment is the flux decline due to fouling. 

The ceramic membrane has a great potential and market. It represents a distinct class of inorganic membrane. In particular, metallic coated membranes have many industrial applications. The potential of ceramic membranes in separation, filtration and catalytic reactions has favoured research on synthesis, characterisation and property improvement of inorganic membranes because of their unique features compared with other types of membrane. Much attention has focused on inorganic membranes, which are superior to organic ones in thermal, chemical and mechanical stability and resistance to microbial degradation. 

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