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Ein Interdigital-Mikromischer/Redispergierkapillare-Aufbau soll die in anderen Mikroreaktoren ubliche Tropfenkoaleszenz fur Flussig/Flussig-Stromungen verhindern oder minimieren. Die Redispergierkapillare beinhaltet 1 mm lange Einschnurungen mit 0,25 mm innerem Durchmesser, die jeweils in Abstanden von 0,5 m entlang der Kanallange positioniert werden. Die Leistungsfahigkeit dieses Systems wurde anhand der phasentransferkatalysierten Veresterung zu Benzylbenzoat getestet. Mithilfe der Einschnurungen konnte die Koaleszenz verhindert werden, was zu einer besseren Reproduzierbarkeit der Versuchsergebnisse fuhrte. Durch die Einstellung der Gesamtflussrate und des Verhaltnisses von wassriger zu organischer Phase wurden Oberflachen/Volumen-Verhaltnisse von bis zu 230 700 m2m–3 erreicht. Im Vergleich zur konventionellen phasentransferkatalysierten Veresterung konnten durch den Konti-Betrieb im Interdigital-Mikromischer/Redispergierkapillare-Aufbau das Losungsmittel, der Basenzusatz sowie ein energieintensiver Destillationsschritt eliminiert werden, wahrend die Prozesssicherheit erhoht wurde. An interdigital mixer – redispersion capillary assembly was applied to prevent the liquid-liquid bubbly flow coalescence in microreactors. The redispersion capillary consisted of 1 mm long and 0.25 mm inner-diameter constrictions placed every 0.50 m along the channel length. The system was tested on the phase transfer catalyzed esterification to produce benzyl benzoate. The application of constrictions to prevent coalescence resulted in a better reproducibility compared to a capillary without the constrictions. By controlling the total flow rate and the aqueous-to-organic ratio the bubbly flow surface-volume ratio could be increased up to 230 700 m2m–3. Compared to the conventional phase transfer catalyzed esterification, the continuous operation in the interdigital-redispersion capillary assembly eliminated the use of solvents and bases, removing an energy intensive step of distillation, while increasing process safety.

This paper gives an overview of the research done since 1999 at Eindhoven University of Technology in the Netherlands in the field of miniaturization of heterogeneous catalytic reactors. It is described that different incentives exist for the development of these microstructured reaction systems. These include the need for efficient research instruments in catalyst development and screening, the need for small-scale reactor devices for hydrogen production for low-power electricity generation with fuel cells, and the recent quest for intensified processing equipment and novel process architectures (as in the fine chemicals sector). It is demonstrated that also in microreaction engineering, catalytic engineering and reactor design go hand-in-hand. This is illustrated by the design of an integrated microreactor and heat-exchanger for optimum performance of a highly exothermic catalytic reaction, viz. ammonia oxidation. It is argued that future developments in catalytic microreaction technology will depend on the availability of very active catalysts (and catalyst coating techniques) for which microreactors may become the natural housing.