High resistant ultrafiltration membrane

In case of ultrafiltration membranes, resistance of membrane is owing to membrane material. Therefore, selection of membrane material is the most important. Figure 9 shows comparison of engineering plastics which have ever investigated for ultrafiltration membranes with solvent and high temperature resistance. It is the most difficult to find materials which satisfy both excellent resistivity and excellent processibility. Polyimide is an only material commercialized for a rather resistant ultrafiltration membrane. 

Tubular Modules. Tubular modules are generally limited to ultrafiltration appHcations, for which the benefit of resistance to membrane fouling because of good fluid hydrodynamics overcomes the problem of their high capital cost. Typically, the tubes consist of a porous paper or fiber glass support with the membrane formed on the inside of the tubes, as shown in Figure 24. 

Since none of the commercially available nano- or ultrafiltration membranes so far shows real long-term resistance against organic solvents under the reaction conditions needed for a commercially interesting hydroformylation process and since no prices are available for bulk quantities of membranes for larger scale applications, considerations about the feasibility of such processes are difficult and would be highly speculative. 

Zirconia membranes on carbon supports were originally developed by Union Carbide. Ultrafiltration membranes are commercially available now under trade names like Ucarsep and Carbosep. Their outstanding quality is their high chemical resistance which allows steam sterilization and cleaning procedures in the pH range 0-14 at temperatures up to 80°C. These systems consist of a sintered carbon tube with an ultrafiltration layer of a metallic oxide, usually zirconia. Typical tube dimensions are 10 mm (outer diameter) with a wall thickness of 2 mm (Gerster and Veyre 1985). 

Cake filtration could be used for some of these materials, but a cake of l-/rm particles would have a high resistance to flow, and the filtration rate would be very low. Ultrafiltration (UF) covers a wider size range, from 1-pm particles down to molecules about 10 /rm in size (Af= 300). The term hyperfiltration is sometimes used for separation of small molecules or ions, but reverse osmosis is a more descriptive term, because the osmotic pressure has a major effect on the flux. Furthermore, the separation in reverse osmosis occurs by a solution-diffusion mechanism in the dense polymer rather than by a screening action at the membrane surface (see Chap. 26). 

Improved membranes have been the key to recent advances in ultrafiltration. The finest niter papers have pore diameters of as small as 1000 nm (1 micron) whereas ultrafilter membranes can be made with pore diameters from 1000 nm to as small as 2-3 nm. For many years cellophane or freshly formed films from collodion (nitrocellulose) were used, but now a number of manufacturers supply strong, flexible, and durable membranes of remarkably uniform pore size yet with high porosity, permitting rapid flow of water. Porous glass membranes have also been developed as well as porous carbon. Po rous ceramic with a microporous coating provides an ultrafilter highly resistant to high temperature and chemical attack. 

The ultrafiltration membrane with high permselectivity and solvent resistance has been prepared from the butadiene-styrene copolymer. The copolymer on hydroboration with 9-BBN, followed by NaOH-HjO oxidation affords ultrafiltration membrane [8] with good permeation property and separation behavior for several solutes. 

Kim et al. (2007b) tested three different ultrafiltration membranes (Amicon Corp.) for power generation in two different types of two-chambered MFCs. They found that these membranes had high internal resistances, and thus produced less power than the CEM or AEM membranes (Table 5.1). The 0.5 K membrane had extremely high internal resistance values. As a result, power was only 5 mW/m in two-chamber bottle reactors whereas the other membranes did not appreciably impact power generation as they all produced 33-38 mW/m. In the cube reactors, where internal resistance was lower due to a closer electrode spacing and the use of an air cathode, the 1 K membrane produced only slightly less power than the CEM membrane. Thus, in theory it may be possible to replace the CEM membrane with a more conventional ultrafiltration membrane in an MFC, but membranes must be developed that result in lower internal resistances. 

As mentioned earlier, proteins can be removed by ultrafiltration through a very fine membrane filter. Ultracentrifugation at high speeds can also be used to separate proteins from smaller molecules based on size differences. The most commonly used protein removal techniques for HPLC involve protein denaturation. Heating denatures most proteins. If the compounds to be separated are temperature resistant, the crude mixture remaining can be boiled and then filtered or centrifuged. Particulates and denatured protein are removed together. 

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