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| Dissertation / PhD Thesis/Book | PreJuSER-24023 |
2002
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/119
Report No.: Juel-4055
Abstract: Homogeneous catalysis is an indispensable tool for synthetic organic chemistry. So far it has proved to be the only means for achieving high selectivity and asymmetric induction, deriving enantiomeric highly enriched compounds by catalytic means. Among the most successful systems for homogeneous catalysis, hydrogenation catalysts capable of activating molecular hydrogen, take outstanding roles in research laboratories and in industry. Nevertheless, the generation of catalysts is highly specialized, laborious, and cost-intensive. Their rational usage implies optimization by reaction engineering. These efforts aim for the accelaration of reaction rate (turnover frequency: tof), and increase capacity of the number of catalyzed reactions per catalyst (total turnover number: ttn). For the latter, this is achieved easily if means are available for the selective separation of catalyst from the other reaction partners. One possibility is exploited by immobilization methods; but restricting the catalyst to one phase creates problems associated with phase barriers. Another approach has been demonstrated by utilizing membrane filtration, selectively retaining high molecular weight homogeneous soluble catalysts. This has been especially successful for catalysts, for which the macromolecular property is intrinsic to their catalytic activity: enzymes, the catalysts of bie,logical systems. Examples for transferring this principle to manmade chemical catalysts using soluble polymers as support-se called chemzymes- are capable of taking advantage of non-aqueous solvents. This principle of continuous recycling is realized in the enzyme or in the chemzyme membrane reactor (EMR or cmR, respectively) A major goal of this work was to open up the vast field of catalytic hydrogenation with molecular hydrogen for the scope of possible reactions in the membrane reactor. This has been demonstrated by two catalytic systems: 1. Chemical: Asymmetric hydrogenation with the Pyrphos catalyst 21 -Rh, and the polymer bound catalyst 33, deriving enantiomerically enriched amine, acids. 2. Enzymatic: Hydrogenation with the hydrogenase from Pyrococcus furiosus (PfH), deriving NADPH (38), an important redox equivalent for biological systems. A new technique for hydrogen supply via dense membranes was developed, thus allowing the decoupling gas and liquid phase pressures. By this means the development of a continuously operated membrane reactor for the employment of both enzyme and chemzyme was possible. Besides their usage in other reactor systems, both catalysts were employed in this newly developed membrane reactor. This was especially beneficial for the enzyme, with unmatched du of more than 60,000 and a space-time-yield of more than 130 gL-ld-1. Both systems were investigated kinetically. The chemical catalyst proved to be strongly dependent on the hydrogen concentration; whereas the enzyme showed a time-dependent activation of catalytic activity whereby the initial activity was more than doubled. Furthermore it could be shown that adhesive properties of the enzyme preparation, discovered during electrochemical investigations, could be applied for immobilization and consequent utilization in a continuous fluidized bed reactor.
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