Commercial Microwave Reactors - Market Overview

There is, nevertheless, experimental evidence that some reactions occur faster than conventionally heated reactions at the same temperature. Although this suggests that nonthermal effects are involved, these rate enhancements could also be attributable to localized superheating or hot spots. In fact, most reports of substantial rate enhancements under the action of microwaves seem to be in heterogeneous reactions, for example under dry media conditions or when solid catalysts are used [75, 76]. In these circumstances localized heating of a microwaveabsorbing solid support or catalyst could lead to an increased reaction rate [136, 137]. 

The question of reproducibility and scale-up will always imply the question about reaction conditions. In addition, the reaction medium (phase) plays a much more important role for this kind of power input compared with classical reactions. Besides the molecular mass, reaction mixture polarity is essential for absorption of microwave power. Because dielectric constants are known for a few compounds only and, moreover, at near room temperature, more problems are predictable and require dose contact with neighboring disciplines, for example with electrical engineering. The primary literature reflects the incomplete nature of results from microwave-assisted reactions and processes, as it does for conventional syntheses. The dependence of reaction engineering on technical considerations is, however, greater for microwave-assisted reactions, so improved description of reaction conditions is crucial. 

Here we would like to remark that correct and/or complete description of the setup used, the method of temperature measurement, the reaction size, and the energy input are especially important in a microwave procedure [20, 76). 

The market for installations used in microwave chemistry can be estimated to about 90 million dollars (2003), cf. Fig. 2.4 and Ref. [28]. 

By contacting the homepages of these enterprises [41, 58, 77, 78], one can follow recent developments and the availability of microwave equipment. A recent state-ofthe-art-overview of this subject has been written by Kappe and Stadler [6b]. 

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