Selectivity gains and energy savings for the industrial phenyl boronic acid process using micromixer/tubular reactors

An industrial production-scale process currently conducted at Clariant site/Frankfurt, termed Phenyl Boronic Acid Process from here on, was investigated at laboratory-scale using two micromixer/tubular reactor configurations, being equipped with either a glass interdigital (for details see (1) Ehrfeld, W.; Golbig, K., Hessel, V.: Lowe, H.; Richter, T. Characterization of mixing in micromixers by a test reaction: single mixing units and mixer arrays. Ind. Eng. Chem. Res. 1999, 38, (3), 1075-1082; (2) Hessel, V., Hardt, S.; Lowe, H.; Schonfeld, F. Laminar mixing in different interdigital micromixers - Part 1: Experimental characterization. AIChE J. 2003, 49, 566-577; (3) Hardt, S.; Schonfeld, F. Laminar Mixing in Different Interdigital Micro-mixers - Part 2: Numerical Simulations. AIChE J. 2003, 49, 578-584; (4) Herweck T.; Hardt, S.; Hessel, V.; Lowe, H.; Hofmann, C.; Weise, F., Dietrich, T.; Freitag, A. Visualization of Flow Patterns and Chemical Synthesis in Transparent Micromixers. In Topical Conference Proceedings; IMRET 5, 5th International Conference on Microreaction Technology, AIChE Spring National Meeting; Matlosz, M., Ehrfeld, W., Baselt, J. P., Eds., Springer-Verlag: Berlin, 2001; pp 215-229) or a steel split-recombine mixer (for details see Schonfeld, F.; Hessel, V.; Hofmann, C. An Optimised Split-and-Recombine Micro Mixer with Uniform 'Chaotic' Mixing. Lab Chip 2004,4,65-69). The best yield of the microreactor investigations was 89%, exceeding the performance of the industrially employed stirred-tank process by nearly 25%. Moreover, the total amount of side and consecutive products was decreased from 10-15% to 5-10%. In addition to these yield improvements, the energy expenditure of the microreactor processing was also notably reduced, first of all because of carrying out the reaction at favorable ambient temperature. In contrast, the former batch process had to be carried out at cryogenic temperatures of -35 degreesC. Even at temperatures as high as 50 degreesC, a high selectivity was maintained when using the microreactor. As a further cause for energy savings, the higher purity of the product eliminated the need for distillation; in total therefore, only one heating-cooling cycle with reduced temperature difference was required for the microreactor process in contrast to the three cycles with large temperature differences used in conventional processing. Facing production and process liability issues, a specially made pilot-scale configuration was constructed entirely out of stainless steel components, among them a split-recombine caterpillar mixer having larger internal fluid channels than the interdigital glass mixer. The new configuration allowed one to perform scale-up studies at throughputs as high as 10 L/h.