Microreactor microchannel

Photocatalytic reduction using a Ti02-coated microchannel device was reported by Ichimura et al. [44], By using a quartz microreactor (microchannel, 500 pm wide, 100 pm deep and 40 mm long) and a 365-nm UV-LED light source, benzaldehyde was reduced to benzyl alcohol (yield of 11%) and p-nitrotoluene to p-toluidine (yield of 46%) after 1 min in the presence of ethanol (Scheme 4.30). 

Figure 9.5 Flow pattern of a falling film in falling film microreactor (microchannel cross-section 1000pm X 300pm liquid 110ppm SLS solution), (a) Corner rivulet flow (Ql = 2 ml/min) (b) falling film flow with dry...

The advantages of microreactors, for example, well-defined control of the gas-liquid distributions, also hold for photocatalytic conversions. Furthermore, the distance between the light source and the catalyst is small, with the catalyst immobilized on the walls of the microchannels. It was demonstrated for the photodegradation of 4-chlorophenol in a microreactor that the reaction was truly kinetically controlled, and performed with high efficiency [32]. The latter was explained by the illuminated area, which exceeds conventional reactor types by a factor of 4-400, depending on the reactor type. Even further reduction of the distance between the light source and the catalytically active site might be possible by the use of electroluminescent materials [19]. The benefits of this concept have still to be proven. 

Micro heat exchangers based on microchannel architecture. Top left and bottom Reprinted with permission from W. Ehrfeld et al., Microreactors New Technology for Modern Chemistry. Wiley-VCH Weinheim, Germany, 2000. Top right Courtesy of the Institut fuer Mikrotechnik Mainz, GmbH. 

Method //was designed for a bonded microreactor. After the channel was sealed with a Pyrex top plate using the anodic bonding technique, the liquid precursor was infiltrated into the microreactor through the outlet of the reactor under slight pressure and withdrawn. A thin film of solution remained on the walls of the microchannel. 

Figure 18. (a) Scanning electron microscope pictures of the microchannels cut onto a porous stainless steel, (b) Schematic diagram of the multi-channel microreactor set-up [36]. 

Because of the very small fluid layer thickness of the microchannels, the specific interfacial areas (i.e., the interfacial areas per unit volume of the microreactor systems) are much larger than those of conventional systems. 

Paul, B. K., Hasan, H., Dewey, T., Ahman, D., Wilson, R. D., Development of aluminide microchannel arrays for high-temperature microreactors and micro-scale heat exchangers, in Proceedings of the 6th International Conference on Microreaction Technology, IMRET 6 (11-14 March 2002), AIChE Pub. 

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 combination of PDMS and urease enzyme to form a microreactor from the resulting "bioplastic" material (PDMS-E) has been reported previously (7). When enzyme concentrations were maintained at 2.5% (w/w) or less, the resulting microreactor cured with good structural integrity and high definition (e.g., well-formed microchannels and >90% retention of triangular transverse packing features in the microchannels). 

The PDMS-E described in the batch studies was used to mold reactors. These microreactors were fed the same 0.1 M urea solution as used in batch experiments. Reactors were operated for approx 1 hbefore acquiring operational data to reduce the effects of any loosely bound enzymes that may wash out from the surfaces of the microchannel walls. 

Novel applications have been developed from the combination of microreactor technology and nonequilibrium microplasma chemistry. Here we discuss a selection from the recent literature on this topic to illustrate several main trends. We will focus on microplasmas in confined microchannels for the purpose of chemical synthesis and environmental applications. 

An important advantage of the use of EOF to pump liquids in a micro-channel network is that the velocity over the microchannel cross section is constant, in contrast to pressure-driven (Poisseuille) flow, which exhibits a parabolic velocity profile. EOF-based microreactors therefore are nearly ideal plug-flow reactors, with corresponding narrow residence time distribution, which improves reaction selectivity. 

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