Microstructured microchannels

Microstructures on Macroscale MicroChannel Reactors for Medium- and Large-Size Processes... 

The Nernst-Einstein relationship plotted in Fig. 36.1 motivated the development of DiagnoSwiss technology, namely reducing the analysis time and reaction volumes by replacing the commonly used microtitre plate wells with typical dimensions of 100 pL volume and 1 cm2 surface area by a microchannel with a volume of 60 nL and a surface area of 0.03 cm2. The microchannel is an isotropically etched microstructure (see Section 36.2) with a minimal cross-section dimension of 40 pm,... 

Numerical simulations have been conveniently used to describe complex fluid dynamic behavior in microstructures [21, 86]. Van der Linde et al. [87] solved the coupled diffusion equation for reacting species and compared the results with data from the oxidation of CO on alumina-supported Cr using the step-response method. Transient periodical concentration changes in microchannels have been numerically calculated by various authors [19, 58, 88]. 

FIGURE 9.14 Optical image of the xPEG-DA hydrogel microstructures photopolymer-ized within the microchannels for sealing off microchambers (B, C), which also contained weirs to retain the beads. Scale bar, 100 pm [960]. Reprinted with permission from the American Chemical Society. 

Figure 1.5 Rhodium honeycomb catalyst microstructure device. The microchannels have been manufactured by wire erosion.

The device consisted of a 75 -pm thick polyimide foil containing microstructured slits (250 pm wide and 45 mm long) sandwiched between the working and counter electrodes (Scheme 4.34). The reaction took place inside the microchannels that were in contact with both electrodes. To maintain a constant reaction temperature, a heat exchanger block was also mounted above the working electrode. This microreactor-based electrolysis afforded 98% product selectivity, which was higher than that for common industrial processes (about 85%). 

Microfabrication uses photolithography and etching [277,278]. A time-multiplexed inductively coupled plasma etch process was used for making the microchannels. The microstructured plate is covered with a Pyrex wafer by anodic bonding. 

The fluorination of quinoline was performed in a microstructured reactor operated in the annular-flow regime, which contained one microchannel with two consecutive feeds for gas and liquid [311,312]. The role of the solvent was large. The reaction was totally unselective in acetonitrile and gave only tarlike products. With formic acid, a mixture of mono- and polyfluorinated products besides tar was formed. No tar formation was observed with concentrated sulfuric acid as solvent at 0-5 °C. In this way, a high selectivity of about 91% at medium conversion was achieved. Substitution was effective only in the electron-rich benzenoid core and not in the electron-poor pyridine-type core. The reactivity at the various positions in the quinoline molecule is 5 > 8 > 6 and thus driven by the vicinity to the heteroatom nitrogen that corresponds to the electrophilic reactivity known from proton/deuterium exchange studies in strong acid media. 

The process was performed for many months yielding 700 g of monofluorinated product with a nine-channel microstructured reactor [60]. A continuous 150 h operation was performed without decline of yield or conversion. Even in the scale-out to a 30-channel reador (see Figure 5.27), no loss in performance was noticed. A single feed system distributed the reactants and reagents to the various microchannels. 

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