Multifluidic gas-liquid, liquid-liquid, gas-liquid-liquid and gas-liquid-solid flow are used for many applications for the synthesis of fine chemicals or materials preparation. For demanding reactions such as exothermic fast hydrogenations or oxidations, small scale structured reactors are used to attempt decreasing limitations du to physical limitations. Several principles may be used to ensure gas-liquid contacting. Small channel size can give raise to segmented flow in which gas bubbles are constrained by the channel walls. Small geometrical features may also be used to design gas-liquid bi-continuous contactors. Mesh type structures based on capillary forces to stabilize meniscus can be built to separate channels or chambers still allowing a large gas-liquid interface for mass transfer. Bi-continuous gas-liquid contacting can also be achieved using free gas-liquid interface such as in falling film reactors. When chemical reactions with solid catalysts are required, the walls play a further role as catalyst support to make new type of fixed-catalysts reactors. In the case where fast deactivation occurs, new solutions aiming at catalyst circulation through the structured reactor are proposed with powdered -slurry- gas-liquid-solid contactors. In this paper, several laboratory gas-liquid and gas-liquid-solid micro-contactors, based on different multiphase contacting principles, will be presented and evaluated with respect to demanding gas-liquid and gas-liquid-solid reactions (see figure).
Dispersed phases reactors (Taylor flow) represent a convenient way to contact gases and liquids under high pressure and temperature conditions. To help understanding of microflows and the design of gas-liquid contactors, computational fluid dynamics was used to simulate the hydrodynamics in each of these contactors, and to investigate bubbles formations and phenomena involved in gas-liquid mass transfer at the micro-scale. The impact of the injector geometric dimensions will be presented and discussed. Pillared films with dimensions down to 5 ?m, all based on the bi-continuous interface free principle, have been used to stabilize air-water interfaces for flow rates up to 100 ?L/min. Silicon or nickel mesh contactors, with openings smaller than 5 ?m have also been fabricated. Finally, the mass transfer characteristics of an interface free falling film microreactor will be discussed.
1- Gas-liquid Taylor flow in square micro-channels: New inlet geometries and interfacial area tuning.
A. Leclerc, R. Philippe, V. Houzelot, D. Schweich, C. de Bellefon Chem. Eng. J., 2010, 165, 290-300.
2- Gas-liquid selective oxidations with oxygen under explosive conditions in a micro-structured reactor.
A. Leclerc, M. Alame, D. Schweich, P. Pouteau, C. Delattre, C. de Bellefon Lab on Chip 2008, 8, 814 – 817.
3- Deposition of Pt-catalyst in a micro-channel of a silicon reactor: Application to gas micro-TAS working at high temperature. M. Roumanie, C. Pijolat, V. Meille, C. De Bellefon, P. Pouteau, C. Delattre Sensors and Actuators B 2006, B 118, 297-304