Wenbin Xie,Libo Zhang,Jianyu Yang,Lihua Zhang,Shaohua Ju,Yaoyao Luo
Separation of Zn 2+ from sulphate solution containing Ni 2+ and Co 2+ using di-(2-ethylhexyl)phosphoric acid (D2EHPA) has been carried out in capillary microreactors. Well-defined slug flows are formed at total flow rates of 0.1–4 mL/min, and the slugs size and specific interfacial area are determined. The effects of saponification degree of D2EHPA, extractant concentration, and residence time on extraction and separation of these three metal ions are investigated. Meanwhile, conventional batch experiments at 94 s and equilibrium experiments at 8 h are also done in parallel at different extractant concentrations. Compared with conventional batch experiments, better extraction and separation performance, e.g. 2.7–38.9 times higher of β Zn/Ni and 3.9–34.9 times higher of β Zn/Co , is obtained in the slug flow microreactor. In addition, the overall volumetric mass transfer coefficient k L a and overall mass transfer coefficient k L are measured. Compared with other microreactors and the batch mixer-settler, the used slug flow microreactor shows higher k L a values of Zn.
Continuous slug flow in microreactors are featured by alternative presence of regulate segments of immiscible phases in microchannel or capillaries with lateral dimensions below 1 mm. Due to the high interfacial area and short diffusive distance therein, such microreactors have been widely applied in chemical engineering processes that are sensitive to mass transfer. Therefore, mass transfer rates in microreactors have long been broadly investigated via either typical offline or online methods. Compared to these conventional methods, the colorimetric technique based on the oxidation of resazurin with oxygen enables direct determination of physical mass transfer rates. However, this technique was currently applied only to the gas-liquid system in microreactors, and mostly in rectangular channels due to the simplicity in image processing. Based on this, the current paper showed a demo where the colorimetric technique using resazurin was adapted to a liquid-liquid system for the mass transfer study of flowing droplets within a slug flow capillary. Experimental tips and tricks were summarized, and a sliced color-concentration calibration strategy was proposed to balance analyzing efficiency and accuracy.
Cryogel beads are novel adsorbents with potential applications in biotechnology, environmental and tissue engineering. However, the controllable preparation of cryogel beads with expected small and uniform diameters is a challenging work. The micro-flow-focusing method combining with the cryo-polymerization has been suggested as a new approach for the fabrication of cryogel beads. In order to form the uniform droplet, the slug flow is generated in the microchannel, so the slug flow hydrodynamics are crucial and fundamental for this process. In the present work, the dextran-methacrylate (Dex-MA-PEGDA) solution and ethyl acetate containing surfactant of Span 80 were used as the aqueous phase and the water-immiscible, respectively. The fabrication of dextran-based cryogel beads and the slug flow hydrodynamics in a rectangular microchannel were investigated experimentally. The flow regime map was proposed and the typical regime boundaries were measured and correlated, and the formation mechanisms of slugs were also discussed. The regime boundaries were correlated by Weber number and Capillary number, i.e., We o = 58.16 Ca w 0.92 for the boundary between the annular and the slug flow, and We o = 4.12 Ca w 0.09 for the slug and the bubbly flow, respectively. Several crucial parameters of the droplets generated by the slug flow, i.e., the aqueous slug length, the aqueous slug velocity and the aqueous droplet size, were measured and correlated. The Dex-MA-PEGDA cryogel beads were prepared successfully under different conditions and their diameters were correlated to the sizes of the droplets. Eventually, the uniform size distributions and supermacroporous microstructures of dextran-based cryogel beads were demonstrated.
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