Dispersed-phase Microstructured Reactors

In segmented flow gas-Uquid-solid reactors, the liquid usually flows over the solid surface while the gas flows through the liquid in the form of bubbles or annular flow, depending on the MSR geometry and the catalyst arrangement. 

The hydrodynamic characteristics of three-phase reactors, such as pressure drop and residence time distribution, can be determined from those for fluid-solid and fluid-fluid reactors. The difference between the gas-liquid and gas-liquid-solid systems is that due to the reaction at the surface of the catalyst, there is always a concentration gradient in the liquid phase in the latter case. Unlike in gas-liquid reactions, it is always important to saturate the liquid film with the gaseous 

The global transformation rate of a gas-liquid reaction catalyst by a solid catalyst is influenced by the mass transfer between the gas-liquid and the liquid-solid mass transfer. Mass transfer and surface reaction are in series and, for fast chemical reactions, mass transfer will influence the reactant concentration on the catalytic surface and, as a consequence, influence the reactor performance and the product selectivity. Forthe gaseous reactantthree mass transfer steps can be identified [96] (1) the transfer from the bubble through the liquid film to the catalyst (fecs Gs). (2) the transfer from the caps of the gas bubbles to the liquid slug (fecs Gs) and (3) the transfer of dissolved gas to the catalytic surface (fersaLs). Steps 2 and 3 are in series and in parallel with respect to step 1, respectively. The following expression describes the overall mass transfer (feov )  

Different attempts were made to determine the mass transfer coefficient separately in non-reactive systems. However, the concentration profiles in the liquid surface film and in the slugs are strongly affected by fast chemical reactions and the results must be interpreted with caution. 

Mini heat exchanger medium supply and withdrawal 

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Figure 8.8 Mass transfer in dispersed phase microstructured reactors where gas solute diffuses through liquid toward solid surface, (a) Schematic representation, (b) Resistance model.

Volume 1 covers fluid dynamics, modelling, mixing of one-phase and dispersed two-phase systems, heat and mass transfer. One chapter is concerned about purification and separation focusing on extraction, membrane technology, and capillary electrochromatography. This is rounded off by a description on microstructured reactors and their engineering/design for various applications. 

Basically, there are two possibilities for bringing two phases into contact The first (Type A) is to keep both fluid phases continuous in order to create a defined interface. Consequently, the reactor should embody microstructures that generate two stable continuous phases with a preferably high exchange area. The second pos sibility (Type B) is to disperse one phase into the other by using a suitable inlet or a micromixer upstream of the reactor section. The goal to create an exchange area is also a dominant aspect for this type. 

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