Abstract
This study demonstrates the possibility of “contactless” mass transfer between two aqueous slugs (droplets) separated by an oil slug in Taylor flow inside milli-channels. Separation of the alternating aqueous slugs at the outlet was performed by switching a couple of solenoid valves at branched outlets according to signals obtained by an optical sensor at the branch. Transfer of bromothymol blue (BTB) from acidic to basic aqueous slugs was performed for demonstration. In some cases, aqueous slugs separated by oil, merged catching on each other due to the velocity difference. Interfacial tension which was affected by the solute concentration was responsible for the velocity difference. Position-specific mass transfer activity at the rear end of the aqueous slugs was found on the course of the experiment. A meandering channel decreased the velocity difference and enhanced mass transfer. Almost complete (93%) transfer of BTB was achieved within a short residence time of several minutes under optimized conditions. The presented system opens a way for advanced separation using minimum amounts of the oil phase and allows concentrating the solute by altering relative lengths of the sender and receiver slugs.
Highlights
This study demonstrates the possibility of “contactless” mass transfer between two aqueous slugs separated by an oil slug in Taylor flow inside milli-channels
The setup contains 4 syringe pumps, 6 solenoid valves, and an optical sensor, all controlled by a computer with a bespoke LabVIEW software
We studied two different pump models and three operation modes where the flows of syringe pumps are controlled by the solenoid valves, the syringe pumps, or both
Summary
This study demonstrates the possibility of “contactless” mass transfer between two aqueous slugs (droplets) separated by an oil slug in Taylor flow inside milli-channels. Mass transport rate in the slug flow can be orders of magnitude faster than conventional batch mixing processes[7] Such rapid transport enhances liquid-liquid extraction[8], gas absorption[9], and heterogeneous reactions[10]. With the sequential mass transport from one aqueous slug to the continuous oil phase, and to another aqueous slug, we can dramatically increase the potential and possibility of slug flow for applications in extraction and reaction. Demonstration of the application of the intra-slug mass transfer requires a method for separating and sorting individual slugs from a stream. We show the concept of intra-slug material transfer and a simple system for the detection and sorting of slugs at the milli-reactor outlet
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