Ultrafiltration definition

Polyelectrolyte complexes are very promising materials for preparing semi-permeable membranes of definite permeability and selectivity The methods of preparation and the properties of membranes made of polyelectrolyte complexes based on strong polyelectrolytes, e.g. poly(sodium sterene sulfonate) and poly(vinylbenzyl-trimethyl ammonium chloride) were described These membranes may be applied for reverse osmosis in the desalting of sea-water, for dialysis and ultrafiltration in purifications and concentration of water solutions containing coUoids or micro-and macroparticles ... 

In this review dealing with recent advances in membrane science, the term membrane" will be used to indicate any medium which acts as a barrier to transport into or out of a region, provides selective transfer of one species over another or regelates the transport of a material to its environment at a controlled rate. In addition to the common usage of the word membrane" to indicate a dense polymer film, the above definition includes a variety of interesting cases such as highly porous ultrafiltration membranes and hydrophobic liquid membranes with selectivity properties which can be tailored by incorporation of materials which selectively complex with one of the species to be processed. The important topics of controlled release of chemicals from polymeric devices and removal of volatile monomers from addition polymers such as poly (vinyl chloride and poly (acrylonitrile are also treated here. 

In this chapter, we will introduce fundamental concepts of the membrane and membrane-separation processes, such as membrane definition, membrane classification, membrane formation, module configuration, transport mechanism, system design, and cost evaluation. Four widely used membrane separation processes in water and wastewater treatment, namely, microfiltration (MF), ultrafiltration (UF), nanofiltrafion (NF), and reverse osmosis (RO), will be discussed in detail. The issue of membrane foufing together with its solutions will be addressed. Several examples will be given to illustrate the processes. 

Even with control sera in which some of the constituents have been removed by dialysis or ultrafiltration and then returned as weighed amounts of pure material, it is essential to check the composition of the final product by the appropriate methods of chemical analysis, unless the use to which the control serum is to be put is distinctly circumscribed (e.g.. Section 3.1.1.2). Laboratories that prepare their owi) control sera establish the true analytical values, using the methods they employ, by performing a suflScient number (usually about 20) of replicate determinations under conditions that meet the definition of repeatability. 

Rejection characteristics of ultrafiltration membrane were analysed and method to determine the transport coefficients is developed. Also the rejection characteristics of membrane with gel layer were analysed and it is found that the transport coefficients of gel layer have a definite relation with the gel layer resistance, and perhaps with gel layer thickness. 

This brief overview describes some experiences using tangential-flow and dead-end ultrafiltration techniques for concentration of eukaryotic cells, proteins and virus. The data and conclusions presented here have been drawn from process development work employing available apparatus and should be considered preliminary, rather than definitive or exhaustive. Previous ultrafiltration systems have been described (1-14) for both bench and pilot scale separations of proteins and virus. This paper primarily summarizes work on cartridge and sheet filter systems and their application to processes requiring sterilizable and contained systems. 

By definition, enzyme immobilization is the conversion of an enzyme to a form with artificially restricted mobility and retention of catalytic function W. This restricted mobility allows for containment and recovery of the enzyme and is often achieved by either conversion to an insoluble form (for example by linking to insoluble particles) or by containment within a semi-permeable barrier (for example entrapment within an ultrafiltration membrane). In the course of this immobilization, enzymes can acquire four advantageous properties ... 

It can be argued that any turbulent flow correlation should not be applied for Re <10,000. However, in current thin-channel ultrafiltration devices, the entrance geometry is such that fully developed turbulent flow occurs at much lower Reynold s numbers. Measurements of fluid velocity versus pressure drop show a definite transition from laminar to fully developed turbulent flow at Re = 2000. 

A decrease in hydrostatic pressure along the fiber due to resistance to substrate solution flow occurs so that at a definite distance from the inlet, say Lc, transmembrane pressure is nil. Fiber-to-shell solution flux from that point on is negative and becomes a shell-to-fiber flux. Neglecting the shell pressure drop, the overall fiber-to-shell ultrafiltration net flow rate can then be obtained upon integration of the flux equation over the length of the fiber from the inlet to Lc, that is ... 

Membrane Process for Recovery of Alkanesulfonates. Many attempts have been made over the years to reduce the wastewater load—which represents a loss of product—by a number of different methods. These include evaporation, extraction, reverse osmosis, and ultrafiltration. All of these processes have the disadvantage of high equipment cost and high energy requirements, and the space-time yield is low. The first breakthrough came with the development of new types of membrane with a definite separating efficiency and a large surface area, so-called spiral-wound modules. 

This implies that microfiltration membranes are porous media containing macropores and ultrafiltration membranes are also porous with mesopores in the top layer. Hence, the definition porous covers both the macropores and mesopores. With membranes of these type it is not the membrane (material) which is characterised but the pores in the membrane. Here the pore size (and pore size distribution) mainly determines which particles or molecules are retained and which will pass through the membrane. Hence, the material is of little importance in determining the separation performance. On the other hand, with dense pervaporation/gas separation membranes, no fixed pores are present and now the material itself mainly determines the performance. 

U should be noted that this definition does not characterise the membrane nor the pores ot the membrane, but rather the size of the particles or molecules retained by it. "nw separation characteristics are determined by the large pores in the membrane.. Another factor of interest is the surface porosity. This is also a very important variable in determining the flux through the membrane, in combination with the thickness of the top layer or the length of the pore. Different miciofiltration membranes exhibit a wide range of surface porosity as discussed in chapter III. from about S to 70%. In contrast, the ultrafiltration membranes normally show very low surface porosities, ranging from 0.1-1. ... 

In batch ultrafiltration, the volume concentration ratio (VCR) (definition (6.4.98)) is (10/1) = 10. The retentate concentration of each protein can be determined using Cm = Cio(VCR) . Here we assume ... 

The retained components, the ones to which the medium is impermeable, may be particles of solid, droplets of liquid, colloidal material, or molecular or ionic species in solution, while the permeate (or filtrate) will normally be the suspending fluid or solvent, possibly together with some of the other components. (Note this definition includes the diffusion processes of reverse osmosis and nanofiltration, which are not strictly filtration processes, because of their similarity to membrane ultrafiltration and microfiltration, which are.)... 

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