Caterpillar micromixer-reactor

Hessel, V., Lowe, H., Hofmann, C., ScHONFELD, F., WeHLE, D., WeRNER, B., Process development of a fast reaction of industrial importance using a caterpillar micromixer/tubular reactor set-up, in Proceedings of the 6th International Conference on Microreaction Technology, IMRET 6, pp. 39-54 (11-14 March 2002), AIChE Pub. 

The corresponding semibatch process is a rather slow reaction at 90 °C with simultaneous exothermic decomposition of DAST. Thus, the processed volume is restricted to laboratory scale (< 11) [ 50]. The transfer to production in a stirred tank is prohibited because of these safety reasons. A micromixer-tube reactor approach was chosen using the convective-flow-driven bas-relief caterpillar micromixer and tubes with diameters of 1-5 mm and lengths up to 20 m, respectively, and tube reactor volumes up to 500 ml (see Figure 5.16). 

A triangular interdigital or a caterpillar micromixer followed by a tube were used (Fig. 6.30) [45]. The micromixer-tube reactor was submersed into a thermostat bath for temperature setting. The temperature was set to -10 °C to room temperature. Piston and HPLC pumps fed the bromine and aromatic flows, respectively. The use of bromine demands special materials that are stable under such harsh conditions. Fluorinated reactor materials like PVDF or glass turned out to be suitable. 

Typical industrial process for the synthesis of phenyl boronic acid from phenylmag-nesium bromide and boronic acid trimethoxy ester requires strict temperature control (—25 to —55 °C) to minimize the formation of side products. Recently, Hessel and coworkers reported that a micromixer (width 40 pm and depth 300 pm)/ tubular reactor system gave the phenyl boronic acid at high yield (>80%) even at higher temperatures (22 or 50 °C) with minimum amounts of the side products (Scheme 4.48) [66]. They also achieved a pilot-scale production by employing a caterpillar minimixer (width range 600-1700 pm and depth range 1200-2400 pm). 

Micromixer-tube reactor plants have been employed both at laboratory and pilot-scale [30]. For initial process development, a triangular ( focusing ) interdigital micromixer was used (Fig. 6.18), while for the pilot scale-out a caterpillar mixer was connected to four tubes of different hydraulic diameter by a five-port valve. 

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