Microreactor large-scale

The development of microfabrication technologies for ceramic and metallic materials has significantly promoted, during the last decade, research in the field of microreactors, characterized by higher specific productivity, better control of operating conditions and a higher standard of intrinsic safety than large-scale reactors [33, 34]. 

A second field of application may be in the on-site and on-demand production [3,8,25]. A number of chemicals, especially those which are explosive or toxic, can not be efficiently produced at present on a medium or small scale, although large-scale processes exist. A parallelization of several microreactor units could synthesize flexible amounts of chemicals and may even allow a transport of the reaction units if desired. 

Based on these kinetic and microscopic observations, olefin polymerization by supported catalysts can be described by a shell by shell fragmentation, which progresses concentrically from the outside to the centre of the support particles, each of which can thus be considered as a discrete microreactor. A comprehensive mathematical model for this complex polymerization process, which includes rate constants for all relevant activation, propagation, transfer and termination steps, serves as the basis for an adequate control of large-scale industrial polymerizations with Si02-supported metallocene catalysts [A. Alex-iadis, C. Andes, D. Ferrari, F. Korber, K. Hauschild, M. Bochmann, G. Fink, Macromol. Mater. Eng. 2004, 289, 457]. 

Microreactors are chemical reactors that are much smaller than typical industrial scale reactors, on the order of 1000 times smaller than the smallest reactors that were used for large-scale chemical production in the 1990s. Generally, they have a volume of 10 cm or less and characteristic length scales on the order of 1 mm or less. Presently, microreactors are used mainly in research laboratories. However, projections suggest that the microreactors will soon be used in consumer products and in devices for medical laboratories. 

To date, microreactors have not yet appeared in consumer products or for other large-scale uses. Thus, while microreactors have significant potential, it is unclear when, or if, that potential will be realized. 

Researchers at Johnson and Johnson have reported the use of microreactors in the drug development process. They utilized a commercially available CYTOS benchtop system, shown in Fig. 15, to examine several reactions. One such reaction was the highly exothermic reaction to form A-methoxycarbonyl-L-rert-leucine by the addition of methylchloroformate to L-tert leucine. Such highly exothermic reactions present safety hazards in large-scale systems. Utilizing the CYTOS system, they were able to perform this reaction in the laboratory and achieved 91% yield. ... 

In this chapter, the microstructured devices are introduced underlying their potential benefits for the process industries. The reduced scale facilitates the temperature control giving an opportunity to maintain the temperature within any window required. Enhanced (heat/mass) transfer rates allow control of highly exothermic and hazardous reactions. It also increases production rates and thus reduces the total processing volume. In addition, microreactors can be simply numbered up for large-scale production, avoiding the problem of scale-up of conventional reactors. 

Due to their unique features, microsystems truly represent new process tools for the synthesis of polymer through free radical polymerization. Phenomena such as thermal runaway, Trommsdorff effect and segregation, which are commonly encountered in conventional polymer reactors, can be reduced or alleviated when microreactors and micromixers are employed. Moreover, successful implementation of microsystems, in an already-existing production line as well as the numbering approach have proved that despite their small internal volume microsystems can be considered for large scale polymer production. 

The clear advantage of this approach is that detailed kinetic information and accurate modeling of large-scale devices offer the possibility to design processes with high performance in standard industrial equipment. It should be noted that if microreactors can be used to provide some quantitative information, they can be used in laboratory studies to shorten time and improve knowledge for the scale-up of existing equipment. 

The alternative to traditional scale-up, proposed in the context of microreaction technology and coined scale-out or numbering-up , has attracted considerable academic interest. With this approach, the system of interest is studied only on a small scale in so-called microreactors and the final reactor design is simply a multiplication of interconnected small-scale devices. No attempt is made at large-scale optimization. Instead, the optimal functioning point is found for a small-scale device by empirical laboratory studies and then is simply reproduced by replication into the large interconnected structure. 

Upon reflection, one concludes that it is rather unlikely that individual laboratory microreactors will be coimected in this way in industrial designs. More likely is that large-scale macro-devices will be created with internal microstructuring and it is not evident that such devices will truly operate under identical conditions at all points in the intercoimected structure. Numbering-up is therefore not the complete answer to the scale-up problem, but it does provide a stimulating model for a totally new way to design and construct reactor devices. 

Microreactor Plant for the Large-scale Production of a Fine Chemical Intermediate a Technical Case Study... 

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