Continuous-flow microchannel reactor

Continuous-flow MicroChannel Reactors with Surface-immobilized Biocatalysts... 

Thomsen, M.S. and Nidetzky, B. (2009) Continuous-flow microchannel reactors with surface-immobilized biocatalysts, in Modem Biocatalysis (eds W.-D. Fessner and T. Anthonsen), Wiley-VCH Verlag GmbH, Weinheim, pp. S.43-S.54. 

Fabrication of catalyst immobilized microchannel reactors usually needs expensive, complex, and multistep methods. On the eontrary, reactors with simple structures (Figure 5) can also perform effieient hydrogenation reaetions. Yoswathananont et al. [21] reported an effieient hydrogenation reaction in a continuous flow system by the use of a gas-liquid-solid tube reactor. 

Novel microreactors with immobilized enzymes were fabricated using both silicon and polymer-based microfabrication techniques. The effectiveness of these reactors was examined along with their behavior over time. Urease enzyme was successfully incorporated into microchannels of a polymeric matrix of polydimethylsiloxane and through layer-bylayer self-assembly techniques onto silicon. The fabricated microchannels had cross-sectional dimensions ranging from tens to hundreds of micrometers in width and height. The experimental results for continuous-flow microreactors are reported for the conversion of urea to ammonia by urease enzyme. Urea conversions of >90% were observed. 

The specific MEMS reactors to be tested have been fabricated in an SCT-like mode and a bank of cylinders mode. Currently, the cylinders reactor has been tested and has shown operation nearly isothermal for the Prox reaction. Figure 7.11 shows a scanning electron micrograph (SEM) of the tested MEMS reactor where the flow is perpendicular to the cylinders as well as other substrates fabricated. This system differs from microchannel reactors and others in that there are no continuous channels where fully developed flow can exist.61... 

Owing to the complex and often dedicated equipment required to perform gas-liquid phase reactions within research laboratories, this area of synthetic chemistry is somewhat underutilized. Over the past decade, however, numerous research groups have developed an array of continuous flow reactors capable of conducting such reactions in a safe and efficient manner, including microchannel contactors, falling film micro reactors, and packed-bed reactors [68, 69]. 

MALDI-MS was also implemented as a detection system for monitoring the reaction products of chemical or biochemical reactions in microfluidic reactors. In one approach, a continuous flow glass or silicon microchip that comprised a microdigestion reactor was incorporated into the standard MALDI plate of the MS instrument (Figure 53.13). The vacuum of the MS chamber was used as a driving force for inducing flows in the reaction microchannels. The device was used for organic synthesis and biochemical reactions carried out entirely inside the MALDI-MS vacuum chamber. 

Two classes of gas-liquid microchannel reactors were developed in the past years -continuous-phase contacting falling film, overlapping charmel, mesh, and annular flow approaches, and dispersed-phase contacting by Taylor flow reactors, micromixers for bubble and foam formation, and miniaturized packed bed microreactors, which follow classical trickle-bed operation at smaller scale. Recently integration of operations inside a microdevice has been studied and led to the development of membrane microreactors. 

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