Membranes ultrafiltration with

Ultrafiltration utilizes membrane filters with small pore sizes ranging from O.OlS t to in order to collect small particles, to separate small particle sizes, or to obtain particle-free solutions for a variety of applications. Membrane filters are characterized by a smallness and uniformity of pore size difficult to achieve with cellulosic filters. They are further characterized by thinness, strength, flexibility, low absorption and adsorption, and a flat surface texture. These properties are useful for a variety of analytical procedures. In the analytical laboratory, ultrafiltration is especially useful for gravimetric analysis, optical microscopy, and X-ray fluorescence studies. 

Generally, the effectiveness of the separation is determined not by the membrane itself, but rather by the formation of a secondary or dynamic membrane caused by interactions of the solutes and particles with the membrane. The buildup of a gel layer on the surface of an ultrafiltration membrane owing to rejection of macromolecules can provide the primary separation characteristics of the membrane. Similarly, with colloidal suspensions, pore blocking and bridging of... 

Figure 4.18 Enzyme membrane reactor synthesis of L-tert-leucine from trimethylpyruvic acid in an continuously operated enzyme membrane reactor with ultrafiltration followed by a crystallization step...

Porter, M. C. Ind. Eng. Chem. Prod. Res. Develop, 11 (1972) 234. Concentration polarisation with membrane ultrafiltration. 

For the production of chemicals, food additives and pharmaceutical products, homogeneous catalysis offers some attractive features such as a high selectivity and activity, e.g. in asymmetric synthesis. However, since most homogeneous catalysts are relatively expensive, their current industrial application is limited [3]. On the other hand, heterogeneous catalysts can easily be separated from the products and can be recycled efficiently. Membrane separations with emphasis on nanofil-tration and ultrafiltration will allow for a similar recyclability of homogeneous catalysts, which is important both from an environmental as well as a commercial... 

Filtration can remove fine suspended solids and microorganisms, and microfiltration membranes of cellulose acetate or polyamides are available that have pores 0.1-20 /xm in diameter. Clogging of such fine filters is an ever-present problem, and it is usual to pass the water through a coarser conventional filter first. Ultrafiltration with membranes having pores smaller than 0.1 fim requires application of pressures of a few bars to keep the membrane surface free of deposits, water flows parallel to the membrane surfaces, with only a small fraction passing through the membrane. The membranes typically consist of bundles of hollow cellulose acetate or polyamide fibers set in a plastic matrix. Ultrafiltration bears some resemblance to reverse osmosis technology, described in Section 14.4, with the major difference that reverse osmosis can remove dissolved matter, whereas ultrafiltration cannot. 

Figure Five (5) illustrates reverse osmosis which typically separates materials less than. 0001 microns (10 angstroms in size). Reverse osmosis offers the added advantage of rejecting ionic materials which are normally small enough to pass through the pores of the membrane. As with ultrafiltration, reverse osmosis is used to remove dissolved materials.

The single-chain RIPs are generally more stable to a wider range of experimental conditions than ricin A chain However, loss of material can occur in the course of procedures based on selective passage through membranes. Ultrafiltration may be performed using a membrane with a lower Mr cut-off. 

In addition to equipment used in the actual fractionation processes, a variety of other items are needed. In particular it should be possible to change buffers quickly and to concentrate protein solutions with ease. These operations require such things as dialysis membranes, ultrafiltration cells, and gel-exclusion columns of various sizes. 

The concentration procedure in Step (5) was developed by trial and error. Other methods tried were solvent precipitation with acetone and/ or alcohol, Amicon ultrafiltration with a PM-10 membrane, lyophilization alone, and ammonium sulfate precipitation alone. 

The pH of the feed solution is another factor that affects permeation through ultrafiltration membranes, particularly with polyelectrolytes. For example,... 

Relatively few biochemicals can be measured directly in natural waters because concentrations of individual compounds are low (nanomolar) and salts and other components often interfere with these analyses. DOM can be concentrated and isolated from natural waters for more thorough chemical characterization, and two approaches for DOM isolation, adsorption onto solid phases and ultrafiltration are now widely used. The adsorption of DOM onto XAD resins is used to isolate a fraction of DOM that is operationally defined as humic substances (Thurman, 1985). More recently, tangential-flow ultrafiltration with 1000 Da cutoff membranes has been used to isolate the high-molecular-weight or colloidal fraction of DOM (Benner et al., 1992, 1997). 

Theory of Ultrafiltration. Ultrafiltration is a membrane process with the ability to separate molecules in solution on the basis of size (Ghosh, 2003). Particles are separated with the use of pressure and specially designed semipermeable membranes (Figure 13.5). An ultrafiltration membrane acts as a selective barrier. It... 

Sometimes the surfactants used for cleaning in manufacturing processes create undesirable O/W emulsions. This can be difficult to deal with since emulsification is usually an important aspect of a cleaning process. If the process or the detergent formulation cannot be adjusted to prevent the undesirable emulsion formation then a separate demulsification/separation step may be needed. In some cases these emulsions can be broken by separating out and concentrating the dispersed phase, such as by membrane ultrafiltration [454],... 

Ultrafiltration was applied to examine the size fractionation of Al, Ca, Cu, Fe, K, Na, and Pb in white and red wines [91]. Metal determinations were performed on the unfiltered wine, the 0.45 p,m membrane-filtered wine and each ultrafiltrate fraction. Aluminum was determined by ET-AAS, while FAAS was employed for Cu and Fe. An electroanalytical technique, stripping potentiometry, was selected for Pb measurement, whereas flame photometry was chosen for K and Na quantification. Fractionation patterns were evaluated and discussed. Castineira et al. [92] combined on-line tangential-flow multistage ultrafiltration with a home-built carbon analyzer and ICP-MS for size fractionation of nonvolatile dissolved organic compounds and metal species in three German white wines. The study showed that the major part of the elements investigated (up to 25) were dissolved in the size fraction of < 1 kDa, with the exception of Ba, Pb, and Sr, which also appeared in other fractions. 

Al-binding proteins Ultrafiltration membranes Washing with 1 mol L 1 sodium citrate + water + 0.1 mol/L NaOH + water and 500 mg L 1 DFO [88]... 

Al determination in serum Ultrafiltration membranes Washing with 5 mL portions of 5% HN03 and water until negative test for Al [93]... 

Collins, J. W., Boggs, L. A., Webb, A. A., and Wiley, A. A. (1973). Spent sulfite liquor reducing sugar purification by ultrafiltration with dynamic membranes. Tappi 56(6), 121 -124. 

Continuous mns were carried out in a stirred cell ultrafiltration module using the fluoropolymer membrane FS61PP with a nominal molecular weight cut-off of 20kDa. The reactor, loaded with an appropriate amount of resting cells, was fed with a buffered substrate solution by a peristaltic pump with the flow rate set at... 

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