文摘
A variety of gas-liquid microchannel reactors have been developed so far, using differentcontacting principles. Some devices utilize continuous-phase contacting (i.e., nondispersedseparate phases with large specific interfaces). Among these are microstructured falling film,overlapping channel, and mesh reactors. Dispersed-phase contacting is obtained when one ofthe phases is interdispersed into the other phase. Regular flow patterns are provided by thesegmented (Taylor) flow in a single microchannel or numbered-up versions such as themicrobubble column; other flow patterns such as annular flow may be achieved as well. Foammicroreactors utilize a moving rigid 3-D bubble network at high gas content. Miniaturized packed-bed microreactors follow the paths of classical engineering by enabling trickle-bed operation.Because of the often highly regular flow pattern, not obtained in conventional gas-liquidcontactors, an understanding of the underlying hydrodynamics and heat and mass transfer iscrucial for optimal performance of all types of gas-liquid microstructural reactors. Severalexamples are given, including film-thickness measurements, flow-pattern maps, determinationof mass-transfer coefficients, residence-time distributions, scale-out issues, etc. Numerousapplications demonstrate the improved performance of gas-liquid microreactors. Among theseare fluorinations, chlorinations, hydrogenations, sulfonations, photo-oxidations, etc. Recently,the scope of reactions has been widened, since there is now the possibility to carry out gas-liquid-solid processes in the same microreactors as used for noncatalytic reactions because ofthe development of catalyst washcoats and other materials deposited onto microchannels. Somerelevant examples are given for illustration.