In membrane technology

In order to maintain a definite contact area, soHd supports for the solvent membrane can be introduced (85). Those typically consist of hydrophobic polymeric films having pore sizes between 0.02 and 1 p.m. Figure 9c illustrates a hoUow fiber membrane where the feed solution flows around the fiber, the solvent—extractant phase is supported on the fiber wall, and the strip solution flows within the fiber. Supported membranes can also be used in conventional extraction where the supported phase is continuously fed and removed. This technique is known as dispersion-free solvent extraction (86,87). The level of research interest in membrane extraction is reflected by the fact that the 1990 International Solvent Extraction Conference (20) featured over 50 papers on this area, mainly as appHed to metals extraction. Pilot-scale studies of treatment of metal waste streams by Hquid membrane extraction have been reported (88). The developments in membrane technology have been reviewed (89). Despite the research interest and potential, membranes have yet to be appHed at an industrial production scale (90). 

Electrodialysis. Electro dialytic membrane process technology is used extensively in Japan to produce granulated—evaporated salt. Filtered seawater is concentrated by membrane electro dialysis and evaporated in multiple-effect evaporators. Seawater can be concentrated to a product brine concentration of 200 g/L at a power consumption of 150 kWh/1 of NaCl (8). Improvements in membrane technology have reduced the power consumption and energy costs so that a high value-added product such as table salt can be produced economically by electro dialysis. However, industrial-grade salt produced in this manner caimot compete economically with the large quantities of low cost solar salt imported into Japan from Austraha and Mexico. 

Emerging Membrane Control Technologies The recent improvements in membrane technology have spawned several potentially commercial membrane filtration uses. 

Typical areas where titanium has found widespread industrial use in membrane technology are cells, anodes, anolyte headers, anolyte containers, filters, heat exchangers, chlorate removal systems and various parts of the brine system. 

Many chlorine producers are having to tolerate impurities originating from standard plastic materials used in membrane technology. Flot chlorine and hot anolyte emerging from the anodic compartment of the cell place tremendous stresses on these plastic construction materials. 

The emergence of commercial fuel cell cars will depend on developments in membrane technology, which are about one third of the fuel cell cost. Improvements are desired in fuel crossover from one side of a membrane to the other, the chemical and mechanical stability of the membrane, undesirable side reactions, contamination from fuel impurities and overall costs. 

One breakthrough occurred in membrane technology when PolyFuel, in Mountain View, CA, produced a hydrocarbon polymer membrane with improved performance and lower costs than the current perfluorinated membranes. This cellophane like film has performed better than more common perfluorinated membranes, such as DuPoint s Nation material. 

T.A. Davis, V. Grebenyuk, O. Grebenyuk in Electromembrane Processes in Membrane Technology in the Chemical Industry (Eds. S.P. Nunes, K.-V. Peinemann), Wiley-VCH, Weinheim, 2001. 

Improvements in membrane technology, validation of membrane integrity, and methods to extend filter usage should further improve the performance of membrane filters in removal of viral particles. Methods to improve or extend filter life and increase flow rates by creating more complex flow patterns could possibly be the focus of the next generation of membrane filters designed to remove viral particles. 

The approximate operating costs for brackish and seawater reverse osmosis plants are given in Table 5.3. These numbers are old, but improvements in membrane technology have kept pace with inflation so the costs remain reasonably current. 

The current ethanol dehydration technology - two-stage distillation followed by a molecular-sieve dryer, as shown in Figure 8.18(a) - uses approximately 16 000-20 000 Btu of energy/gal of ethanol produced. This is about 20% of the energy value of the ethanol produced. There is a considerable interest in membrane technology that would be lower in cost and less energy intensive. 

The wall-thickness of 2 mm provides the CC tubes with sufficient mechanical strength to withstand gas and liquid pressures that are common in membrane technology. The measured pore diameters of 120 and 184 nm are well in the range used for mesoporous membrane preparation and it is expected that y-alumina layers can be applied on the supports by conven-... 

Other noteworthy developments in membrane technology include the following ... 

Finally, participants mentioned the potential for spin-off technologies and applications. For example, advances in membrane technologies for fuel cells may have medical applications. Other spin-offs could occur, and while it is not possible to quantify these benefits now, the potential opportunities from spin-offs could be great. 

In all fermentation processes, it is necessary to have contamination-free fermentation media and seed cultures. Liquid sterilization of the fermentation medium is conducted by two means.1011 Contaminating microorganisms can be removed from fluids by filtration. With improvements in membrane technology, sterile filtration is finding wider use, but can only be used with completely soluble media. 

Entirely new approaches are based upon recent advances in membrane technology. It is now possible to produce membranes which have small holes or pores in them. A cross-section of such a membrane is shown in Figure 10-9. Remarkably, the pore size (Table 10-4) may be controlled to... 

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