Microreactors microstructured reactors

Recently, microstructured reactors have stepped into chemical production [4] and thus microreactor process and plant design, including economic incentives, is the issue at this time. For this purpose, large-capacity microstructured apparatus is needed ( micro inside, fist- to shoebox size outside ) and plant concepts have to be proposed which include all process steps. 

Jahnisch K, Baerns M, Hessel V, Ehrfeld W, Haverkamp V, Lowe H, Wille C, Guber A (2000) Direct Fluorination of Toluene Using Elemental Fluorine in Gas/Liquid Microreactors. J Fluor Chem 105 117-128 Jahnisch K, Hessel V, Lowe H, Baerns M (2004) Chemistry in Microstructured Reactors. Angew Chem Int Ed 43 406 -46 Jensen KF (2001) Microreaction Engineering - is Small Better Chem Eng Sci 56 293-303... 

The issues to be solved for direct fluorinations are heat release and mass transfer via the gas-liquid interface. Multiphase microstructured reactors enable process intensification [230,248-250,304—306]. Often geometrically well-defined interfaces are formed with large specific values, for example, up to 20 000 m2/m3 and even more. These areas can be easily accessible, as flow conditions are often highly periodic and transparent microreactors are available. For the nondispersing... 

Lin C, Tsai C, Fu L (2005) A rapid three-dimensional vortex micromixer utilizing selfrotation effects under low Reynolds number conditions. J Micromech Microeng 15 935 Ehrfeld W, Hessel V, Haverkamp V (2000) Microreactors. In Ullmann s encyclopedia of industrial chemistry. Wiley-VCH, Weinheim. doi 10.1002/14356007.bl6 b37 Jahnisch K, Hessel V, Lowe H, Baems M (2004) Chemistry in microstructured reactors. Angew Chem Int Ed 43(4) 406 146... 

Integration of various components is an important issue for the DCF systems. The simple scale-up of microreactors is not enough as the DCF system. A DCF system should consist of not only reactors but also other factory parts like a mixer, separator, and temperature controller. Many integrated microreaction systems have been reported and some of these are commercially available. For example, K. F. Jensen s group has reported an integrated microreactor system for gas-phase catalytic reactions using microstructured reactors and other devices on a computer board [13]. They have achieved computer control over the reaction system through this device as shown in Fig. 6. 

Therefore, one of the major drivers for running Friedel-Crafts alkylations in microstructured reactors is to improve the selectivity of monoalkylation products under reasonable stoichiometric conditions, in particular by achieving significantly accelerated and intensified mixing and mass transport than achievable in macroscopic processes. Moreover, it is also expected that the exothermic alkylation reactions additionally benefit from the improved heat transfer characteristics of microreactors. 

Sulfonations are a further important type of electrophilic substitution reaction. However, only very few examples can be found in the literature describing the use of microstructured reactors for the strongly exothermic liquid-phase sulfonation of aromatics (sulfonation of toluene wdth gaseous SO3 was described by Jaehnisch et al. [34]). Burns and Ramshaw [25, 35] claimed that their concept of performing liquid/liquid nitration reactions in a slug-flow capillary-microreactor can be also... 

Of course, not all multiphase microstructured reactors are presented in Table 9.1. Either because they have attracted (too ) little interest, because they may have been qualified as microreactors in spite of their overall size but caimot be considered as microstmctured , or because they combine several contacting principles. Examples are a reactor developed by Jensen s group featuring a chaimel equipped with posts or pillars, thus resembling more a packed bed but with a wall-coated layer of catalyst [20], and a string catalytic reactor proposed by Kiwi-Minsker and Renken [21], that may applied to multiphase reactions. 

A clear hurdle for the application of a microstructured reactor in a multi-product or multi-purpose environment is that a relatively large part of the fine chemical processes contain solids. Some newer reactor concepts seem to be able to handle solids better than the early microreactors but this still needs to be developed further. 

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