The widely used separation process of liquid-liquid extraction is performed in a variety of contactors. The interfacial area in these conventional contactors is often poorly defined, because of the complex hydrodynamics involved, and the intensity of mass transfer is limited by the constraints imposed by the underlying buoyancy or gravitational effects being exploited. Similar shortcomings are apparent in most of the laboratory equipment presently used for investigating extraction and biphasic reactions. In the present work, a new contactor concept, liquid-liquid slug flow in a capillary, is presented as an alternative to conventional equipment. Experiments were performed to investigate the effect of operating conditions on mass-transfer coefficients for different nonreacting systems. In addition, a flow splitter was developed for downstream separation of two liquid phases. The combination of this flow splitter with the capillary provides miniature mixer-settler modules, which can be networked in a wide variety of configurations. Finally, the results obtained were compared with the literature data, and it was determined that such a microextractor-reactor offers superior performance and greater efficiency, in comparison to conventional equipment for liquid-liquid extraction. The results also show that such equipment can be exploited to enhance mass-transfer-and heat-transfer-limited liquidphase reactions.

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A so-called “slug-flow” capillary microreactor has been proposed for the investigation of mass-transfer-limited liquid−liquid reactions. Internal circulation within the slug leads to an intensified and tunable mass transfer. Understanding the development of the circulatory flows and the influence of operating parameters upon them is thus crucial. In this study, experiments were carried out to visualize the internal circulations using particle image velocimetry (PIV) technique. State-of-the-art computational fluid dynamics (CFD) simulations were used to predict the internal circulation within the liquid slugs and a CFD particle tracing algorithm employed to visualize them. Each slug was modeled as a distinct single-phase flow domain. The effect of the flow velocity and slug length on the velocity profile and stagnant zones of the internal circulations for a slug with and without a wall film is discussed. The internal circulations could be qualitatively and quantitatively characterized with the help of the PIV measurements and particle tracing algorithm.

The performance of microstructured reactors (or microchannels) for mass-transfer-controlled liquid–liquid reactions depends on flow regimes that define the specific interfacial area for the mass transfer. In the present work, experiments were carried out to investigate the two phase-flow regimes and the mass transfer at relatively high throughput for a single microchannel (of 1–18 mL/min) in five generic microchannel designs (with and without structured internal surfaces), using a nonreacting water–acetone–toluene system. When the flow results were analyzed collectively in all microchannels, six different flow regimes such as slug, slug-drop, deformed interface, parallel/annular, slug-dispersed, and dispersed flow were observed. The mass-transfer comparison shows that the microchannel with structured internal surfaces shows better performance, because it creates a very fine dispersion, providing high interfacial area, compared to other microchannels. Finally, the mass-transfer data were correlated, which can be used for a priori predictions of mass-transfer rates in microchannels.