Investigation of anti-clogging mechanism of ultrasound-driven oscillating slugs/bubbles and its application on continuous crystallization process

A novel anti-clogging strategy by combining ultrasound and segmented flow was proposed and successfully applied to continuous crystallization process. The individual anti-clogging effect of ultrasound and segmented flow was first investigated, finding that both strategies only slow down the fouling process, but not capable of breaking the clogged solid sediment. As for the combining strategy, segmented slug/bubble was driven to oscillate intensely with ultrasound and dredge the fouled microchannel through three different mechanisms. Not only the long-term operation of microreactor system was guaranteed, but also the necessary energy input was reduced by 1–2 orders of magnitude compared to individual ultrasound. Finally, the ultrasound-driven oscillating slug/bubble was utilized for recrystallization of aspirin. Under Ev 0.54–2.60 J/mL, a product yield of 53 %-72 % (equilibrium yield 72 %) was obtained with aspirin average size in the range of 7.84–32.01 μm. The synergistic strategy can be well generalized to various crystallization process once properly designed.