Enhanced antisolvent processes in an ultrasonic capillary microreactor: Cavitation, mixing and application in mini-emulsion preparation.

• The mixing of antisolvent process was intensified by combining power ultrasound and microreactor. • Transient cavitation become easier to initiate in antisolvent process compared to pure liquids. • Two distinct cavitation patterns of bubbles group were observed, bubble array and bubble cluster. • Mixing under the cluster pattern was significantly better than that under the array pattern. • The prepared mini-emulsion exhibited good performance in droplet size, size distribution and stability. An approach combining power ultrasound and microchannel was proposed to promote the mixing of miscible fluid in antisolvent processes. Cavitation microbubbles evolved and oscillated during ultrasound actuation, with antisolvent processes facilitating easier initiation of transient cavitation compared to pure liquids. Interaction among microbubbles led to two distinct group patterns, bubble array and bubble cluster, which greatly impacted mixing. Both patterns could increase mixing efficiency by at least one order of magnitude compared to microfluidic devices and previously-studied ultrasonic microreactors in the literature. Mixing time under the array pattern ranged from 100 to 250 ms, while that under the cluster pattern ranged from 50 to 200 ms. The approach produced high-quality mini-emulsion with unimodal size in the range of 180–290 nm for a model system (acetone-soybean oil–water). [ABSTRACT FROM AUTHOR]