New Process Regimes

Micro reactors can open up new process regimes [5, 18, 70, 147, 180, 184—186]. Actually, the term new is used in this respect in the micro-reactor literature with ambiguous meanings. There are at least three types of new processes  

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Some authors even speak of inaccessible regimes when processes are operated with maximum selectivity [110]. As pointed out above, there is no clear definition of what a new process regime is and what just a change of process parameters is. Hence the definitions given here may be taken as a guideline until there are better ones. 

The investigations refer to the general capability of micro reactors to perform short-time processing with highy intensified mass and heat transfer. A special focus of most investigations on the oxidation of ammonia was the heat management. The use of new concepts for heat supply and removal opens the door to operation in new process regimes with very different product spectra. 

The activities are at present related to two major topics, namely chemical production and mass screening [3, 8, 25]. While miniaturization in the first field focuses on new process regimes due to enhanced heat and mass transfer, the second field of application results in an increase of reaction and detection units per reactor volume. Thus, miniaturization - the reduction of characteristic dimensions - directly influences the process performance in the first case, while in the last case this is only indirect by an increase in flexibility and multiplicity. 

The exploration of new process regimes is tightly correlated to the task of chemical production [3, 8, 25]. Microreactors will then not only serve to investigate processes of macroreactors under ideal or otherwise not feasible conditions, but are expected to partially replace macroreactors for different applications. An example for a reaction which can hardly be achieved even on a laboratory scale is the direct fluorination of aromatics. 

Gezdhmte Chemie im Mikroreaktor, VDI Nachrichten, June 2000 Micro-reactor enterprises shape and material variety of micro reactors selectivity gains and new project regimes direct fluorination faster process development BASF investigations safety increase speed-up of catalyst development production for fine chemistry and pharmacy numbering-up first industrial examples for micro-reactor production [215]. 

Baldauf, H., Scoen.Herr, J., and Schubert, H., Alkane Dicarboxilic Acids and Amino Naphthol-Sulphonic Acids - a New Reagent Regime for Cassiterite Flotation, International Journal of Mineral Processing, Vol. 15, pp. 117-133, 1985. 

When design rules invade the sub-micron regime, new process problems will occur. These problems are partly caused by the increased aspect ratios which are inherent to sub-micron design rules. For example, low temperature oxides such as SiH4/02-LT0 or plasma enhanced Si3N4... 

The scale-down approach can be applied both in the case of an existing process and for a new process. In the latter case a process design is made for the new process from available process data, experimental evidence, and rules of thumb. Regime analysis is applied to this process design. Based on the results a further sm l-scale research strategy is developed, and eventually changes are made in the process design. 

Due to their small characteristic dimensions, microreactors have fundamental advantages in comparison with conventional macro-scale systems. As a consequence, microreactors are suitable for performing and/or studying reactions under relatively safe conditions, which is important in the case of potentially dangerous processes, such as highly exothermic reactions, reactions in which flammable, explosive or toxic chemicals are involved or reactions that require harsh conditions in terms of temperature or pressure. In fact, microreactors open the way to new operating regimes and applications [1,2],... 

A new area in dynamics, characterized by collision times shorter than hitherto studied, is discussed with special reference to four-center reactions. Under the unusual combination of conditions made possible within an impact heated cluster, the nominally four-center reactions can be made to proceed (on the computer) via the four-center mechanism as suggested by Bodenstein. It is even possible to achieve multi-center (> 4) reactions. The unique features of the new dynamical regime are discussed and illustrated by a variety of high-barrier processes, including the four center H2 +12 2HI and N2 + O2 2NO reactions and a multi-center "burning of air" process. 

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