Microfiltration, applications

The discussion so far implies that membrane materials are organic polymers, and in fact most membranes used commercially are polymer-based. However, in recent years, interest in membranes made of less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafiltration and microfiltration applications for which solvent resistance and thermal stability are required. Dense, metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported liquid films are being developed for carrier-facilitated transport processes. 

In contrast to dense inorganic membranes, the rate of advances toward industrial-scale applications of porous inorganic membranes has been rapid in recent years. In the early periods of this century, microporous porcelain and sintered metals have been tested for microfiltration applications and, in the 1940s, microporous Vycor-type glass membranes became available. Then in the mid-1960s porous silver membranes were commercialized. These membranes, however, have not seen large scale applications in... 

For microfiltration applications, pore diameters of ceramic membranes in the range of 0.1 to 10 im arc typical These membranes can be prepared by dip or spin coating of... 

Matis KA, Peleka EN, Zamboulis D, Erwe T, and Mavrov V. Air spargbng during the solid/liquid separation by microfiltration application of flotation. Sep. Purif. Technol. 2004 40 1-7. 

Goel V, Accomazzo MA, et al., Deadend microfiltration Application, design and cost. In Ho WSW, Sirkar KK, Eds., Membrane Handbook. Chapman HaU, New York, NY, 1992 506-570. 

In the past ten to fifteen years or so, the applications sphere of cross-flow filtration has been extended to include microfiltration (MF) which primarily deals with the filtration of colloidal or particulate suspensions with size ranging from 0.02 to about 10 microns. Microfiltration applications are rapidly developing and range from sterile water production to clarification of beverages and fermentation products and concentration of cell mass, yeast, E-coli and other media in biotechnology related applications. 

Polymeric membranes are prepared from a variety of materials using several different production techniques. Table 5 summarizes a partial list of the various polymer materials used in the manufacture of cross-flow filters for both MF and UF applications. For microfiltration applications, typically symmetric membranes are used. Examples include polyethylene, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) membrane. These can be produced by stretching, molding and sintering finegrained and partially crystalline polymers. Polyester and polycarbonate membranes are made using irradiation and etching processes and polymers such as polypropylene, polyamide, cellulose acetate and polysulfone membranes are produced by the phase inversion process.f Jf f ... 

Nandi BK, Uppaluri R, and Purkait MK. Preparation and characterization of low cost ceramic membranes for microfiltration applications. A/ / /. Clay Sci. 2008 32 102-110. 

Ceramic Membranes. A number of companies have developed ceramic membranes for ultrafiltration and microfiltration applications. Ceramic membranes have the advantages of being extremely chemically inert and stable at high temperatures, conditions under which polymer films fail. Most ceramic membranes are made by the slip-coating-sintering or sol-gel techniques outlined in Figure 16 (56-58). 

The commercial versions of those instruments are developed by GEPS Company, already well introduced in porous media characterisation and separation studies. The last activity will be significantly supported by the extension of numerical code to ultra and microfiltration applications, at present in progress. 

The same type of developments is in current for ultra and microfiltration applications membrane characterisation device coupled with data-base and numerical code. 

Early systems based on visible light used high-zoom video cameras positioned to view the membrane from the side. The ability to continuously record, in real time, activity at the membrane surface made this type of system ideal for in situ imaging of cake deposition, provided the particles were sufficiently large. A 15 x zoom video camera was used to record in situ particle motion of large polyethylene particles (125-180 pm) dose to a stainless steel mesh filter 3]. The particles in this study were much larger than those typically found in microfiltration applications. Another study [4] used a similar system to record the deposition of more realistic caldte (2.6 pm, 25 pm) and anatase (0.5 pm) particles. Individual particles could not be resolved and only a cake thickness was quoted. In both studies the cakes thicknesses were in the millimeter range. 

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