Membrane Ultrafiltration Techniques

5-10 nm nanofiltration D o Q sugars, divalent salts O dissociated acids 

1-1 nm reverse osmosis monovalent salts, o Undissociated acids 

For ultrafiltration as a unit operation for the separation of polymer-bound soluble catalysts in particular, the recovery process for a rhodium catalyst from the hydroformylation of dicyclopentadiene is an illustrative example (for another detailed example, see Section 7.5) [26, 27]. Toluene can be used as a solvent with the polyaramide membrane employed. TPPTS or also a sulfonated bidentate phosphine with large ammonium counterions, are used as ligands. For efficient recovery, molecular weights of the catalyst of more than 3000 g mofi were required on the membrane used. Separation is performed in two steps [28]. A pilot plant was run successfully over an extended period of time of three months. 

Other examples of ultrafiltration as a separation operation on a laboratory scale employing continuously operated membrane reactors (vide infra) have been reported [1, 29, 30]. These examples will be discussed throughout Section 7.4. Continuous ultrafiltration of polymer-stabihzed metal colloids, in addition to polymer-bound metal complexes, has also been studied [31]. 

Vg = volume of solvent pumped through cell Cj.(0) = initial solute concentration 

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Blatt, W. F., Dravid, A., Michaels, A. S. and Nelson, L. In Membrane Science and Technology, Flinn, J. E. (ed.) (Plenum, New York, 1970). Solute polarisation and cake formation in membrane ultrafiltration Causes, consequences and control techniques. 

Methodological artefacts may arise for a number of reasons, most notably as a result of specific interactions of species with the filter membrane. Therefore the choice of the ultrafiltration system, the properties and influence of the membrane and the operating conditions must be carefully considered before the ultrafiltration technique is applied for the separation of different radionuclide species in environmental samples. 

Membrane separation techniques, which are used mainly in industrial processes, include dialysis, electrodialysis, reverse osmosis, ultrafiltration,... 

Killing groups of animals at given time points obviously requires large numbers of animals to be used in these studies. One promising development to reduce the number of animals necessary is the use of microdialysis and ultrafiltration as membrane sampling techniques, discussed by Garrison... 

Plastic microdevices for high-throughput screening with MS detection were also prepared for detection of aflatoxins and barbiturates. These devices incorporated concentration techniques interfaced with electrospray ionization MS (ESI-MS) through capillaries [2], The microfluidic device for aflatoxin detection employed an affinity dialysis technique, in which a poly (vinylidene fluoride) (PVDF) membrane was incorporated in the microchip between two channels. Small molecules were dialyzed from the aflatoxin/antibody complexes, which were then analyzed by MS. A similar device was used for concentrating barbiturate/antibody complexes using an affinity ultrafiltration technique. A barbiturate solution was mixed with antibodies and then flowed into the device, where uncomplexed barbiturates were removed by filtration. The antibody complex was then dissociated and electrokinetically mobilized for MS analysis. In each case, the affinity preconcentration improved the sensitivity by at least one to two orders of magnitude over previously reported detection limits. 

Membrane-production techniques listed below are applicable primarily or only to MF membranes. In addition, the Loeb-Sourirjain process, used extensively for reverse osmosis and ultrafiltration membranes, is used for some MF membranes. 

Blatt, W.F. et al.. Solute polarizahon and cake formation in membrane ultrafiltration. Causes, consequences, and control techniques, in Membrane Science and Technology, J.E. Flinn (Ed.), pp. 47-97. Plenum Press, New York, 1970. 

Nanofiltration is a rapidly advancing membrane separation technique for concentration/separation of important fine chemicals as well as treatment of effluents in pharmaceutical industry due to its unique charge-based repulsion property [5]. Nanofiltration, also termed as loose reverse osmosis, is capable of solving a wide variety of separation problems associated with bulk drug industry. It is a pressure-driven membrane process and indicates a specific domain of membrane technology that hes between ultrafiltration and reverse osmosis [6]. The process uses a membrane that selectively restricts flow of solutes while permitting flow of the solvent. It is closely related to reverse osmosis and is called loose RO as the pores in NF are more open than those in RO and compounds with molecular weight 150-300 Da are rejected. NF is a kinetic process and not equilibrium driven [7]. 

Most problems with this procedure have involved tracer impurities and the separation of bound and free labeled fractions. Several separation techniques have been used, including equilibrium dialysis, membrane ultrafiltration, and steady-state gel filtration. Their deficiencies include a requirement for a large sample volume, the need for complicated correction of sample volume changes that occur during the separation, and difficulties of collecting and measuring radioactivity in numerous fractions of each sample. Equilibrium dialysis has been used most often in the past, but serious errors often arise from the sample dilution required by this method. Symmetrical dialysis of undiluted samples is reported to be less susceptible to tracer contamination and dilution effects. Ultrafiltration also appears to overcome these problems and to obviate errors caused by dilution. 

Brun, J.-P. "Ultrafiltration et Microfiltration In Precedes de separation par membranes Transport, Techniques membranaires. Applications Masson Paris, France, 1989 pp 137-158. 

Blatt, W.F. et al. "Solute Polarization and Cake Formation in Membran Ultrafiltration Causes Consequences and Control Techniques," Ultrafiltration Membranes and Applications, Polymer Science and Technology, Volume 13. 

Cross-flow filtration (CFF) also known as tangential flow filtration is not of recent origin. It began with the development of reverse osmosis (RO) more than three decades ago. Industrial RO processes include desalting of sea water and brackish water, and recovery and purification of some fermentation products. The cross-flow membrane filtration technique was next applied to the concentration and fractionation of macromolecules commonly recognized as ultrafiltration (UF) in the late 1960 s. Major UF applications include electrocoat paint recovery, enzyme and protein recovery and pyrogen removal. 

The potential of membrane separation techniques (such as cross-flow microfiltration(MF), ultrafiltration (UF), Reverse Osmosis (RO)and electrodialysis (ED) ) and membrane reactors in the treatment of fermentation broths are huge. The synergistic effects obtainable by designing the overall biotechnological process combining various membrane technique are particularly significant. 

Using ultrafiltration techniques, several investigators have reported protein-bound and nonprotein-bound fractions of plasma aluminium. Lundin et al. (1978) studied the partition of aluminium in the plasma of 10 normal individuals using ultrafiltration with membranes having a cutoff of 6,000-8,000 daltons. The results obtained showed that the protein binding averaged 59% of total serum aluminium. 

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