Microreactors mixing mechanisms

EOF has been applied as a pumping or mixing mechanism in microreactors (Fletcher et al., 2002). Mixing concepts include the introduction of two (or more, see Kohlheyer et al., 2005) parallel streams from a T- of Y-junction, where mixing at the low Reynolds numbers achieved occurs principally by interdiffusion of the two streams. This is a relatively slow process which may take tens of seconds to complete. Faster mixing can be achieved by injection of a sample of a specific composition via, for example, a double T-injector into a stream of liquid with a different composition. 

Microreactors are defined by their size rather than construction. Microreactors are miniaturized with channels between the (sub-)millimeter scale and nanometer scale. Microreactors mix the gas and liquid phases pneumatically or mechanically. The size of the complete bioreactor construction is less important. A microreactor example is shown in Figure 10.6. Microreactors are generally compounded into microreactor elements, which are placed into nuxing units. These units are placed into microreactor devices, which have inputs and outputs for all the microreactor units placed within it. Microreactor devices are placed in parallel or in series in order to achieve the necessary conversion. Finally, the output is treated... 

When the catalyst is available in a small amount, a microreactor assembly is often used (Miller, 1987). This is a simple T-type reactor heated by a fluidized sand bath. The mixing is provided by mechanical agitation that shakes the reactor up and down within the fluidized bed. Because of the small amount of slurry, and an effective heat transfer in the fluidized sand bath, the heat-up period in such a reactor is small. The nature of mechanical agitation is, however, energy-efficient. The reactor provides only a small sample for the product analysis, which makes the usefulness of the reactor for detailed kinetic measurements somewhat limited. The reactor has been extensively used for laboratory catalyst screening tests in coal liquefaction. 

Notably, a key problem with the use of microreactors is that, historically, many reactions have been developed to be driven to complehon by relying on the formation of either small molecules or precipitates if small molecules are one of the reachon products, they would be boiled off to drive the reaction. Both mechanisms can be a problem in microreactors. Consequenhy, work is underway to couple membranes and other separahon concepts to enable the small molecules to be extracted from the reaction mix and drive the reachon. With solids formation, the requirement is that the solids exit the system without plugging. While this has been demonstrated it is not clear whether solids formahon will be a major problem when dealing with these types of reachons. 

The kinetics of styrene hydrogenation to ethylbenzene have been investigated with a platinum/polyamide-66 catalyst and using a differential flow microreactor and a reactor with mixing [111]. The reaction mechanism changes at temperatures above 160°C. The activation energy of the reaction is 54 kJ/mol, at T< 160°C and 33 kJ/ mol at r = 160-225°C. In the first case the reaction kinetics are described by the equation v = k k P, whereas in the second case they are delineated by the equa-... 

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