Specific conventional reactor types

The reaction progress is monitored ofF-Une by HPLC. Flow rates, residence times and initial concentrations of 4-chlorophenol are varied and kinetic parameters are calculated from the data obtained. It can be shown that the photocatalytic reaction is governed by Langmuir-Hinshelwood kinetics. The calculation of Damkohler numbers shows that no mass transfer limitation exists in the microreactor, hence the calculated kinetic data really represent the intrinsic kinetics of the reaction. Photonic efficiencies in the microreactor are still somewhat lower than in batch-type slurry reactors. This finding is indicative of the need to improve the catalytic activity of the deposited photocatalyst in comparison with commercially available catalysts such as Degussa P25 and Sachtleben Hombikat UV 100. The illuminated specific surface area in the microchannel reactor surpasses that of conventional photocatalytic reactors by a factor of 4-400 depending on the particular conventional reactor type. 

Additional experimental data not presented here are summarized in Refs. [66, 67]. As was pointed out also in Ref. [64], these results highlight the important point that in membrane reactors, besides differences in local concentration profiles, different residence time distributions occur that lead to specific reactor behavior. Others [71] have also suggested that the flexibility of this type of distributor membrane reactors allows a certain target component to be produced efficiently within a complex reaction network. In the present example, there exist certain operating conditions under which the membrane reactor outperforms the conventional reactor in terms of the production of CO or CO2 (if these are considered as target products instead of ethylene). 

Table 3.2 Specific interfacial areas of selected conventional and miniaturized reactor types. (Data from Ref. [40].)...

Type of conventional reactor Specific interface (m m ) Type of microreactor Specific interface (m m )... 

Reactor Activation of Short-lived Isotopes.— The use of nuclear reactions giving rise to very-short-lived isotopes supplements more conventional reactor activation analysis. It provides relatively specific methods of analysis for several elements, some of which cannot be measured by other activation methods, particularly the light elements. The main technical requirement for the utilization of very short-lived isotopes is a fast-transfer facility with an extremely short recall time, 1 s being the maximum for many applications. For example, Wiernik and Amiel describe a rabbit system for use in a thermal neutron flux region of 5 x 10 cm s" with a transit time of only 150 ms. It is necessary in systems of this type to arrange for the sample to be returned directly to the counting position. 

We shall adopt the convention in this and later chapters that the unqualified word reactor, occurring in any section or chapter specifically devoted to a certain type of reactor, will signify that particular type. Any other type referred to will be suitably qualified. 

In this chapter a specific type of membrane reactor, the so-called distributor was analyzed theoretically. In contrast to conventional tubular fixed-bed reactors (FBR), where all reactants are introduced together at the reactor inlet (cofeed mode), packed-bed membrane reactors (PBMR) allow dosing of one or several reactants via membranes over the reactor wall along the axial coordinate (distributed-feed mode). 

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