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The synergistic effects of gas agitation and ultrasound on mass transfer between immiscible liquids were investigated in an in-house made ultrasonic microreactor. With the introduction of inert gas (N 2 ), a three-phase slug flow with slug bubbles either dispersed in continuous aqueous phase or encapsulated in oil plugs was observed. Under ultrasound irradiation, slug bubbles underwent surface wave oscillation and induced agitation in microchannel. In addition, microbubbles were generated by acoustic cavitation, oscillating intensely and resulting in the formation of O/W emulsion. Bubble oscillation (i.e., slug bubbles and microbubbles) as well as emulsification promoted liquid-liquid mass transfer significantly. Extraction of vanillin from aqueous solution to toluene was employed to demonstrate the mass transfer enhancement. Compared with silent operation, both mass transfer coefficient and extraction efficiency were largely improved by the combined use of gas agitation and ultrasound. With gas flow velocity being 0.005–0.083 m/s at fixed ultrasound power of 30 W, the overall mass transfer coefficients ranged from 0.047 s −1 to 0.429 s −1 , which was 2.33–17.20 times larger than the corresponding liquid-liquid two-phase process without ultrasound irradiation. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the influence of surface properties on the flow characteristics and mass transfer performance of two immiscible liquids are investigated in the opposed and cross-flow configuration microchannels, as the volumetric flux ratio is far <1. For visually identifying flow patterns in transparent PMMA microchannels, dyed de-ionized water and kerosene are selected as test fluids. To investigate the mass transfer characteristics in stainless steel microchannels, water–succinic acid–n-butanol is chosen as a typical system. Reynolds number varied between 11 and 275. Only at low ReM numbers, the dispersed phase flow pattern can occur in the opposed T-shaped PMMA microchannel before surface modification. At higher ReM numbers, only the continuous phase flow pattern (parallel flow) is observed before and after surface modification. Moreover, the fluctuation amplitude after surface modification is larger than before surface modification at the opposed T-junction. To eliminate the effects of the sampling intervals and separation process of oil–water two phases on mass transfer performance, one new testing method is established by manufacturing the novel oil–water separator based on the principle of siphon. For the conditions applied during the study, the overall volumetric mean mass transfer coefficients range from 0.19 to 11.96s−1, which are one or three orders of magnitude higher than those in typical conventional large scaled contactors. [Copyright &y& Elsevier]