Separations 494 - immobilized

The methods developed by EBC and others in the late 1990s using hydrocyclones and phase-inversion techniques may be sufficient for separation of the treated oil from the aqueous phase and biocatalyst. However, a cost analysis of such methods may be necessary to determine the economic feasibility. Recent work using hydrophobic membranes, magnetically separable immobilized biocatalysts and other techniques may provide alternate methods for separation of oil and recycling biocatalyst. A comparison of these techniques with each other and the previously investigated hydrocyclone techniques is needed to demonstrate improvements in the separation efficiency. 

Fig. 7. Cofermentation of model solutions of glucose and xylose with P. st ip it is and S. cerevisiae separately immobilized (system G) and coimmobilized (system H) in Ca-alginate beads. The gel fraction in system G was made of 0.20 g/g of beads containing P. stipitis and 0.05 g/g of beads containing S. cerevisiae. The initial concentrations of P. stipitis and S. cerevisiae cells were 5.64 x 1012 and 1.89 x 10u cells/L, respectively. The gel fraction in system H was made of 0.25 g/g of beads containing P. stipitis and S. cerevisiae coimmobilized with a loading ratio of P. stipitis/S. cerevisiae of 4 g/g of dry cells. The total cells concentration was 6.01 x 1012 cells/L.

Despite the prospect of some productivity gains, the idea was never tried. We also never had a chance to determine whether a single phenylene ring separating immobilized substrate molecules would have other consequences in terms of neighboring molecule interactions, especially if applied to peptide synthesis where tangling of elongated chains may be problematic. 

Yao et al. reported a flow injection analytical system for the simultaneous determination of acetylcholine and choline that made use of immobilized enzyme reactors and enzyme electrodes [25]. Acetylcholineesterase-choline oxidase and choline oxidase were separately immobilized by reaction with glutaraldehyde onto alkylamino-bonded silica, and incorporated in parallel as the enzyme reactors in a flow injection system. The sample containing acetylcholine and choline in 0.1 M phosphate buffer (pH 8.3) carrier solution was injected into the system. The flow was split to pass through the two reactors, recombined, and mixed with 0.3 mM K4Fe(CN)6 reagent solution before reaching a peroxidase immobilized electrode. Because each channel had a different residence time, two peaks were obtained for choline and total acetylcholine and choline. Response was linear for 5 pM-0.5 mM choline, and for 5 pM 1 mM acetylcholine plus choline. The detection limits were 0.4 pM for choline and 2 pM for acetylcholine. 

Magnetic carriers (MC) can be used in biochemistry and biotechnology for cell separation, immobilization of enzymes and other biologically active compounds [1,2]. The use of MC is particularly important for extracorporeal blood purification [3 - 5],... 

Control of stereoselectivity is easier with homogeneous than with heterogeneous catalysts. On the other hand, these soluble catalysts are more difficult to separate and to handle than the technically well-established heterogeneous catalysts. A promising strategy to combine the best properties of the two catalyst types is the heterogenization or immobilization of active metal complexes on insoluble supports or carriers [1, 2, 3]. Besides easy separation, immobilization opens opportunities like, e.g., the use of continuous flow reactors [4,5,6], site isolation [7], or the tuning of the catalyst environment [8,9,10] which in some cases can lead to improved catalytic performance. On the other hand, immobilization increases the complexity and the costs of the catalytic system. 

In order that sequential acids and bases can be used in a one-pot reaction, attractive, separately-immobilized acid and base catalysts have been developed. These catalysts anchor, or dope acid and base sites onto different polymers, or sol-gel matrices (63) and use interlayer acid sites and surface base sites in two different clays (36). In these catalysts, acid and base sites are isolated from each other and can productively function in multistep reactions without their mutual destruction. 

Dried cross-linked (-l-)-Y-lactamase mixed with controlled pore [163] glass in a 1 1 ratio stability of immobilized enzyme for 8h at 80 °C kinetic constants determined in the microreactor Glucose oxidase or choline oxidase were separately immobilized [162] on the surface of PEI coated monolith. Method is simple based on preparation of monolith with controlled porosity low pressure drop, mass transfer limitations avoided enzymes immobilized on PEI-activated surface of monolity through electropositive (PEI and electronegative (enzyme) nature... 

Two EHs, one from S. tuberosum and the other from A. niger LCP 521, were separately immobilized onto DEAE-cellulose by adsorption and used sequentially for the transformation of racemic pflra-chlorost5rene oxide into the corresponding (R)-diol with an enantiopurity of 89%. In total, five cycles were performed, each immobilized biocatalyst being recovered after each cycle and reused in the following biotransformation reaction [61]. 

The problem of separate immobilization arises for firee cofactors, such as NAD, NADP, ADP, and ATP, which pass from one apoenzyme to another during a reduction followed by a reoxidation. Biosensors that use dehydrogenase are of little use unless the cofactor is also immobilized. Moreover, the cofactor must remain sufficiently mobile after immobilization to pass from the active site of one apoenzyme to the active site of anoAer for regeneration. 

Other SFA studies complicate the picture. Chan and Horn [107] and Horn and Israelachvili [108] could explain anomalous viscosities in thin layers if the first layer or two of molecules were immobile and the remaining intervening liquid were of normal viscosity. Other inteipretations are possible and the hydrodynamics not clear, since as Granick points out [109] the measurements average over a wide range of surface separations, thus confusing the definition of a layer thickness. McKenna and co-workers [110] point out that compliance effects can introduce serious corrections in constrained geometry systems. 

Immunoaffinity chromatography utilizes the high specificity of antigen—antibody interactions to achieve a separation. The procedure typically involves the binding, to a soHd phase, of a mouse monoclonal antibody which reacts either directly with the protein to be purified or with a closely associated protein which itself binds the product protein. The former approach has been appHed in the preparation of Factor VIII (43) and Factor IX (61) concentrates. The latter method has been used in the preparation of Factor VIII (42) by immobilization of a monoclonal antibody to von WiHebrand factor [109319-16-6] (62), a protein to which Factor VIII binds noncovalenfly. Further purification is necessary downstream of the immunoaffinity step to remove... 

In open fibers the fiber wall may be a permselective membrane, and uses include dialysis, ultrafiltration, reverse osmosis, Dorman exchange (dialysis), osmotic pumping, pervaporation, gaseous separation, and stream filtration. Alternatively, the fiber wall may act as a catalytic reactor and immobilization of catalyst and enzyme in the wall entity may occur. Loaded fibers are used as sorbents, and in ion exchange and controlled release. Special uses of hoUow fibers include tissue-culture growth, heat exchangers, and others. 

Enzymatic hydrolysis is also used for the preparation of L-amino acids. Racemic D- and L-amino acids and their acyl-derivatives obtained chemically can be resolved enzymatically to yield their natural L-forms. Aminoacylases such as that from Pispergillus OTj e specifically hydrolyze L-enantiomers of acyl-DL-amino acids. The resulting L-amino acid can be separated readily from the unchanged acyl-D form which is racemized and subjected to further hydrolysis. Several L-amino acids, eg, methionine [63-68-3], phenylalanine [63-91-2], tryptophan [73-22-3], and valine [72-18-4] have been manufactured by this process in Japan and production costs have been reduced by 40% through the appHcation of immobilized cell technology (75). Cyclohexane chloride, which is a by-product in nylon manufacture, is chemically converted to DL-amino-S-caprolactam [105-60-2] (23) which is resolved and/or racemized to (24)... 

Heterogeneous hydrogenation catalysts can be used in either a supported or an unsupported form. The most common supports are based on alurnina, carbon, and siUca. Supports are usually used with the more expensive metals and serve several purposes. Most importandy, they increase the efficiency of the catalyst based on the weight of metal used and they aid in the recovery of the catalyst, both of which help to keep costs low. When supported catalysts are employed, they can be used as a fixed bed or as a slurry (Uquid phase) or a fluidized bed (vapor phase). In a fixed-bed process, the amine or amine solution flows over the immobile catalyst. This eliminates the need for an elaborate catalyst recovery system and minimizes catalyst loss. When a slurry or fluidized bed is used, the catalyst must be separated from the amine by gravity (settling), filtration, or other means. 

Manufacture. HFS containing 42% fmctose is produced commercially by column isomerization of clarified and refined dextrose hydrolyzate using an immobilized glucose isomerase. Enriched symp containing 90% fmctose is prepared by chromatographic separation and blended with 42% HES... 

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