(89d) Enhanced Mass Transfer by Liquid-Liquid Slug Flow in Microchannels for Efficient Extraction

Laminar flow in microreactors enables us a precise control of liquid-liquid slug flow. Since slugs in the channel move like a periodic plug flow, narrow residence time distribution can be achieved precisely. Internal circulation flow in droplet derived from the friction between the channel wall and fluid in the slug is expected to enhance the performance of mixing, which is mainly driven by molecular diffusion in laminar flow. The circulation flow also enhances mass transfer between the slugs of the two phases, since the concentration near the interface is renewed by the flow [1]. The liquid film formed between the reactor wall and droplet phase increase the area of active interface between the two phases, leading to improved mass transfer. Thus, liquid-liquid slug flow can be used for fast extraction. In addition, the two phases can be easily separated after the extraction using liquid-liquid slug flow, since the droplet size is over several ten times larger than the emulsion size required to a fast extraction. Therefore, extraction in liquid-liquid slug flow is effective for extraction. To establish a design method of liquid-liquid slug flow for efficient extraction, we investigated the relation between operation conditions such as flow rate, temperature, and channel size and mass transfer rate through the interface of the liquid-liquid slug flow. We also discussed the mass transfer enhancement by the liquid-liquid slug flow as compared with the stationary contact.

[1] Harries, N., J.R. Burns, D.A. Barrow, C. Ramshaw; "A numerical model for segmented flow in micro-reactor," Int. J. Heat Mass Transfer, 46, 3313-3322 (2003).