Gas−Liquid−Liquid Slug Flow for Improving Liquid−Liquid Extraction in Miniaturized Channels

To increase the maximum flow rate that enables slug flow formation in miniaturized channels, gas-phase slugs are added in a liquid−liquid slug flow to form a gas−liquid−liquid slug flow. Effects of channel size, void fraction (ratio of volumetric flow rate of gas phase to that of total flow rate), and volume ratio of aqueous phase to organic phase on flow regime are examined. Results indicate that the total liquid-phase flow rate that forms a stable gas−liquid−liquid slug flow increases up to 200 mL/min with air addition (void fraction > 0.1) in a poly(tetrafluoroethylene) (PTFE) tube (inner diameter (i.d.), 3 mm). The mass-transfer rate in the gas−liquid−liquid slug flow was also high because internal circulation flow is enhanced by increased flow rate. The mass-transfer coefficient was then correlated with the channel i.d. and the flow velocity.