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  • 1
    Electronic Resource
    Electronic Resource
    Stepped water activity control for efficient enzymatic interesterification (1998)
    Springer
    Applied microbiology and biotechnology 50 (1998), S. 318-322 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The benefits of controlling water activity, a w, during enzymatically catalysed synthesis reactions, such as reverse-hydrolytic reactions promoted by lipases, are now well recognized. Numerous techniques for controlling a w in the laboratory and their implementation in continuous reactors have been discussed in the published literature. However, in enzymatic interesterification reactions, such as acidolysis and transesterification, it is not appropriate merely to maintain the a w of the reaction system at one value since the two stages of the reaction, namely the cleavage of the original acyl bond and the formation of a new one, are best carried out at different levels of water activity – the former at a high a w and the latter at a lower one. The use of a continuous packed-bed hollow-fibre reactor has been described in this article for carrying out solvent-free acidolysis of ethyl laurate with octanoic acid with in situ a w control, using air that has been pre-equilibrated with saturated salt solutions to the desired a w. At a single optimum (a w = 0.54), the highest steady-state conversion to ethyl octanoate was 32%. However, it is possible to obtain a steady-state conversion of 46% by operating the reactor with a step change in the water activity, from an initial value of unity to 0.23.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530051298
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Twin-core packed-bed reactors for organic-phase enzymatic esterification with water activity control (1995)
    Springer
    Applied microbiology and biotechnology 44 (1995), S. 283-286 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  A method for the removal of water and the control of water activity, a w, during enzymatic esterification is the use of salt hydrate pairs. When this technique is used on a laboratory scale, the recovery and reuse of the salt are not critical. Potential problems, such as the reactivity of some salts, can also be overcome simply by substituting another salt. However, if this technique is to be used on a larger scale, economic constraints would require salt recovery and restrict the range of salts that could be used. In this article a twin-core packed-bed reactor – used for the esterification of an equimolar mixture of decanoic acid and dodecanol catalysed by lipase from Candida rugosa – which facilitates salt recovery and permits a w control without direct contact between immobilized enzyme and salt, has been described. a w control was maintained by using suitable salt hydrate mixtures in the inner core of the reactor. The substrate mixture was esterified by pumping it through the outer core of the reactor, which contained enzyme immobilized on a macroporous polypropylene support. Complete conversion, albeit at different rates, was obtained with a w buffering at 0.48 and 0.8 by using hydrates of Na4P2O7 and Na2HPO4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530050555
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Twin-core packed-bed reactors for organic-phase enzymatic esterification with water activity control (1995)
    Springer
    Applied microbiology and biotechnology 44 (1995), S. 283-286 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A method for the removal of water and the control of water activity, a w, during enzymatic esterification is the use of salt hydrate pairs. When this technique is used on a laboratory scale, the recovery and reuse of the salt are not critical. Potential problems, such as the reactivity of some salts, can also be overcome simply by substituting another salt. However, if this technique is to be used on a larger scale, economic constraints would require salt recovery and restric the range of salts that could be used. In this article a twin-core packed-bed reactor — used for the esterification of an equimolar mixture of decanoic acid and dodecanol catalysed by lipase from Candida rugosa — which facilitates salt recovery and permits a w control without direct contact between immobilized enzyme and salt, has been described. a w control was maintained by using suitable salt hydrate mixtures in the inner core of the reactor. The substrate mixture was esterified by pumping it through the outer core of the reactor, which contained enzyme immobilized on a macroporous polypropylene support. Complete conversion, albeit at different rates, was obtained with a w buffering at 0.48 and 0.8 by using hydrates of Na4P2O7 and Na2HPO4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169917
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Novel reactor for aqueous-organic two-phase biocatalysis: A packed bed hollow fiber membrane bioreactor (1993)
    Springer
    Biotechnology techniques 7 (1993), S. 441-446 
    Details
    ISSN: 1573-6784
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Hollow fiber membranes were potted in a tubular shell with a particulate, microporous, enzyme bearing support packed in the shell space. A bicontinuous system was thus formed with the reactants, supplied through the shell and the fiber lumen, forming an interface at the surface of the particles. Acid production rates, without any reactor optimization, up to four times greater than with membrane reactors were obtained during the lipase catalyzed hydrolysis of ethyl laurate and olive oil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151881
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Surfactant-induced breakthrough effects during the operation of two-phase biocatalytic membrane reactors (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 765-771 
    Details
    ISSN: 0006-3592
    Keywords: membrane bioreactors ; two-phase ; surfactant adsorption ; membrane wettability ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Surface-active components, both reactants and products, are frequently encountered in two-phase, aqueous-organic, biocatalytic reactions, When such reaction are carried out in a membrane reactor, employing a membrane selectively wetted by one of the two reactants, changes in the content of these surfactants- as a consequence of the progress of the reaction-can lead to wetting transitions at the two membrane-liquid interfaces as a result of adsorption of the tenside. This can lead to a decrease in the pressure required to cause the, initially, nonwetting phase to break through the membrane. Such effects render difficult the operation of two-phase membrane bioreactors. Hence, it is necessary to make a careful selection of the membrane material and type by considering factors such as UF versus MF and low MWCO versus high MWCO to enable the reactor to be operated without breakthrough, but without significantly compromising the reaction rates that can be maintained.The phenomena leading to breakthrough effects are discussed in this paper, and experimental results for the hydrolysis of ethyl laurate by lipase from Candida rugosa in a batch flat sheet membrane reactor are presented with the reactor operated with a variety of membranes. An experimental result showing the decrease in the pressure required to cause breakthrough of the organic phase (for the system ethyl laurate-lauric acid-water) as the content of the highly surface-active lauric acid in the organic phase is increased is also presented for an asymmetric, hydrophilic meta-aramid ultrafiltration membrane. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260440613
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Continuous in situ water activity control for organic phase biocatalysis in a packed bed hollow fiber reactor (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 49 (1996), S. 284-289 
    Details
    ISSN: 0006-3592
    Keywords: organic phase biocatalysis ; esterification ; water activity ; lipase ; biocatalysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Packed bed hollow fiber membrane reactors were used to carry out organic phase biocatalysis at constant water activity. The performance of the device was tested by carrying out the esterification of dodecanol and decanoic acid in hexane. Lipase from Candida rugosa, immobilized on microporous polypropylene and packed in the shell space of the reactor, was used to catalyze the reaction. In situ water activity control was accomplished by pumping appropriate saturated salt solutions through the microporous hollow fiber polypropylene membranes. Water generated by reaction in the organic phase, pumped continuously through the shell of the reactor, was transferred into the bulk of the aqueous phase under the water activity gradient. The reactor performance was found to be strongly dependent on the controlling water activity. By carefully selecting this control activity it was found possible to obtain complete esterification. The water activity of the organic phase could be maintained very close to that of the saturated salt solution used. The reactor could be operated in the continuous mode for 100 h without any degradation in its performance. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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