Separation methods ultrafiltration

The use of two types of liquid membranes is described in [302] liquid emulsion membranes (LEMs), and supported liquid membranes (SLMs), where isoparaffin or kerosene and their mixtures were used as organic phases. A surfactant of the type of Span 80 served as emulsifier. LEMs are used, for example, for selective separation of L-phenylalanine from a racemic mixture of L-leucine biosynthesis as well as conversion of penicillins to 6-APA (6-aminopenicillanic acid). SLMs have a higher stability. A number of their commercial applications have been studied, e.g. in separation of penicillin from fermentation broth, as well as in the recovery of citric acid, lactic acid and some aminoacids. Compared with other separation methods (ultrafiltration, ultracentrifugation and ion exchange), LEMs and SLMs are advantageous in the separation of stereospecific isomers in racemic mixtures. 

Finally, micellar systems are useful in separation methods. Micelles may bind heavy-metal ions, or, through solubilization, organic impurities. Ultrafiltration, chromatography, or solvent extraction may then be used to separate out such contaminants [220-222]. 

Elimination of Cellulases from Xylanases. Classical methods of protein fractionation can be used for to separate cellulases and xylanases on a large scale only when they differ considerably in molecular weight or isoelectric point. The Tricho-derma harzianum enzymes were separated by ultrafiltration because the xylanase was smaller and passed through the membrane into the ultrafiltrate 18). Fractional precipitation with organic solvents is another possibility (7). 

Several variants of separation methods based on dialysis, ultrafiltration, and size exclusion chromatography have been developed that work under equilibrium conditions. Size exclusion chromatography especially has become the method of choice for binding measurements. The Hummel-Dreyer method, the vacancy peak method, and frontal analysis are variants that also apply to capillary electrophoresis. In comparison to chromatographic methods, capillary electrophoresis is faster, needs only minimal amounts of substances, and contains no stationary phase that may absorb parts of the equilibrium mixture or must be pre-equilibrated. 

Figure 13.2 Schematic drawing of laboratory dialyzer developed by Craig [4] to separate low-molecular-weight impurities from biological solutions. This was the best method of performing this separation until ultrafiltration membranes became available in the late 1960s. The feed solution was circulated through the inside of the membrane tube solvent solution was circulated on the outside. Boundary layer formation was overcome by rotating the outer shell with a small motor...

The follow-up section will deal with separation methods based upon (a) molecular size and related to it hydrodynamic volume (size-exclusion chromatography and ultrafiltration), (b) molecular size and related to it molecular diffusivity (field-flow fractionation), and (c) charge/size ratio and related to it molecular polarity (electrophoresis and mass spectrometry). Also reviewed will be hyphenated techniques or those that combine separation by chromatography or electrophoresis with spectral detection. 

Techniques can be classified into two main categories those that detect total metal concentrations and those that detect some operationally defined fraction of the total. Methods which detect total concentrations such as inductively coupled plasma spectrometry, neutron activation analysis, atomic absorption spectrometry and atomic emission spectrometry have no inherent speciation capabilities and must be combined with some other separation technique(s) to allow different species to be detected (approach A in Fig. 8.2). Such separation methods normally fractionate a sample on the basis of size, e.g. filtration/ultrafiltration, gel filtration, or a combination of size and charge, e.g. dialysis, ion exchange and solvent extraction (De Vitre et al., 1987 Badey, 1989b Berggren, 1989 1990 Buffle et al., 1992). In all instances the complexes studied must be relatively inert so that their concentrations are not appreciably modified during the fractionation procedure. 

From the great variety of methods for the determination of protein binding three separation methods, equilibrium dialysis (ED), ultrafiltration (UF), and ultracentrifugation (UC) and a non-conventional method with the binding to immobilized proteins has been chosen. The first methods are undoubtedly the most widely used because of their simplicity and general applicability to many different systems. Other methods e.g. size exclusion chromatography, capillary electrophoresis, or spectroscopic methods have been not described. Oravcova et al. (1996) gives a comprehensive review and comparison for these applications. 

The use of membrane-based separation methods for gas separation is being routinely done in the industry. Reverse osmosis (RO) and ultrafiltration (UF) technologies are also very popular in treatment of industrial wastewater. Nevertheless, ultrafil-... 

Hollow-fiber ultrafiltration can be a very usefiil tool in obtaining size-fractionated samples for chemical and physical analyses of humic and fulvic acids in surface and groundwaters. The technique is very reproducible because it is strictly a physical separation, it minimizes the potential artifacts associated with the more classical chemical separation techniques. The separation method assumes a spherical structure for the cutoffs and therefore is an empirical approach. Nevertheless, hollow fibers can be used much as 0.45 im filters are used to separate particulate versus dissolved material with a great deal of success. 

When ultrafiltration as a separation method is combined with soluble polymers as reagents, the result is a technique that allows to separate solutes, which do bind or not to the polymer, in the homogenous phase. This process was termed Liquid-phase Polymer-based Retention (LPR). ... 

The most recent membrane-separation methods competitive with dialysis are essentially ultrafiltration for separation and concentration of solutes, reverse osmosis for solvent purification and electrodialysis for the separation of charged species from solvents and other solutes or from each other according to charge and mobility. Standardization of membranes and equipment for these newer methods also has more or less been accomplished during the past several decades. In all these methods it is an external driving force or source of energy which is essentially responsible for effecting the desired separation. 

Hamilton, P. B. Biochemical Analysis, in Anal. Chem. 38, Ann. Rev. (1966) pp. I9R and 20R have references to various separation methods dialysis, countercurrent distribution, liquid-liquid extractions, and ultrafiltration p. 21R column chromatography, electrophoretic methods, and paper and thin-layer chromatography p. 22R ion-exchange and gas chromatography. 

Susanto, H. and Ulbricht, M. 2009. Characteristics, performance and stability of polyethersulfone ultrafiltration membranes prepared by phase separation method using different macromolecnlar additives. Journal of Membrane Science 327 125-135. 

Ultrafiltration (UF) is another membrane separation method used to purify liquids. UF is commonly used for recovery of proteins and in food and pharmaceutical applications. It is useful for separating permanent emulsions since the oil droplets will not pass through the membrane. UF is used for the removal of fine colloidal particles, and for recovery of dyes from wastewater. In many applications such as whey processing UF and RO are used in series. The valuable proteins are recovered by UF, and permeate from the UF system is sent to the RO system. The remaining sugars and salts are concentrated in the RO system by removing water. The concentrated permeate can then be fermented to produce ethanol, lactic acid or other products. 

X 10" to 1 X 10 in physiological solutions. On the other hand, the molecular weights of proteins are generally about 1 X 10" to 5 x 10 . Therefore, it is extremely difficult to separate LPS from protein solely by size-separation methods, such as size-exclusion chromatography (SEC) and ultrafiltration. Various procedures of LPS removal, such as ion-exchange membrane, ultrafiltration, and extraction, have been developed for pharmaproteins. These procedures, however, are unsatisfactory with respect to selectivity, adsorption capacity, and protein recovery. 

Suspended materials and macromolecules can be separated from a waste stream using a membrane and pressure differential, called Ultrafiltration. This method uses a lower pressure differential than reverse osmosis and doesn t rely on overcoming... 

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