Membrane tool technology

For large mirrors with fast focal ratio, the membrane tool technology has been developed. Polishing is done with a strip-like membrane tool to correct the radial profile, and with a set of pressure-controlled tools the non-rotation-symmetric errors can be worked on. The membrane acts as a low-pass filter, avoids ripple structures, and is always in contact with the whole mirror surface. 

For large mirrors with fast focal ratio, the membrane tool technology has been developed. Polishing is done with a strip-like membrane tool to... 

Zakrzewska-Trznadel, G., Khayet, M., Membranes in nnclear science and technology Membrane modification as a tool for performance improvement, in Membrane Modification. Technology and Applications, N. Hilal, M. Khayet, C.J. Wright (eds.), CRC Press/Taylor Francis Group, Boca Raton FL, 2012, pp. 2-19. 

As documented in Chapter 5, zeolites are very powerful adsorbents used to separate many products from industrial process steams. In many cases, adsorption is the only separation tool when other conventional separation techniques such as distillation, extraction, membranes, crystallization and absorption are not applicable. For example, adsorption is the only process that can separate a mixture of C10-C14 olefins from a mixture of C10-C14 hydrocarbons. It has also been found that in certain processes, adsorption has many technological and economical advantages over conventional processes. This was seen, for example, when the separation of m-xylene from other Cg-aromatics by the HF-BF3 extraction process was replaced by adsorption using the UOP MX Sorbex process. Although zeolite separations have many advantages, there are some disadvantages such as complexity in the separation chemistry and the need to recover and recycle desorbents. 

Adsorptive separation is a powerful technology in industrial separations. In many cases, adsorption is the only technology available to separate products from industrial process streams when other conventional separation tools fail, such as distillation, absorption, membrane, crystallization and extraction. Itis also demonstrated that zeolites are unique as an adsorbent in adsorptive separation processes. This is because zeolites are crystalline soUds that are composed of many framework structures. Zeolites also have uniform pore openings, ion exchange abiUty and a variety of chemical compositions and crystal particle sizes. With the features mentioned, the degree of zeoUte adsorption is almost infinite. It is also noted that because of the unique characteristics of zeoHtes, such as various pore openings, chemical compositions and structures, many adsorption mechanisms are in existence and are practiced commercially. 

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 first membrane separation was performed with nitrocellulose in 1855. During the following 100 years, the technology played a limited role as a research tool in analytical chemistry. A major breakthrough occurred in 1958-1961 when the anisotropic or asymmetric membrane was developed. While membranes employed previously were uniform throughout, the upper portion of anisotropic membranes represents only 1% of the total film and is the actual filter, the other 99% acting as a support. The thinness of the membrane and the very fine pore structure promote excellent throughput for UF. 

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