Enhancement of mass transfer performance of liquid–liquid system by droplet flow in microchannels

Two multiphase flow microfluidic devices based on the use of droplet flow to enhance the mass transfer performance have been specially developed. Mass transfer performance data has been obtained by monitoring the extraction of succinic acid from n-butanol to aqueous drops containing NaOH. Monodisperse aqueous droplets with average diameters of 130–550 μm were generated, and the mass transfer time was 0.4–4.0 s accordingly. The mass transfer rate was 10–1000 times higher comparing to the traditional liquid–liquid systems. Vortex flow patterns within the droplet were generated during droplet forming stage that enhanced mass transfer rate greatly. The mass transfer during droplet formation stage contributed at least 30% of the total mass transfer quantities from the theoretical analyzing. And the mass transfer coefficients were 10–100 times higher than that of droplet moving stage. These results were very different to the mass transfer in conventional extraction processes. The mass transfer mechanism during droplet forming stage in microscale should be investigated fundamentally in the further work. The mass transfer results from this study indicate that droplet flow within a microscale environment offers a viable alternative for two-phase reaction or separation systems.