Microwave reactor design

Overview of Microwave Reactor Design and Laboratory and Industrial Equipment... 

Signiflcant advantages of microwave reactors designed for operating with low-boiling solvents at elevated temperature and pressure are summarized below ... 

The Anton Paar Synthos 3000 is one of a number of parallel sealed-vessel multimode microwave reactors designed for scale-up. The first results using this unit... 

Moseley et al. (2008) reported a survey of some microwave reactors designed for scale-up by different manufacturers. The variety of instruments indicate that there is no satisfactory solution to the problem of microwave scale-up. Microwave chemistry is linearly scalable, from the level of a test tube to more than a liter. There is presently no commercial microwave scale-up solution. At present, commercially scale-up microwave reactor are not available, which is capable of meeting the needs of the pharmaceutical industry for the wide range of reactions, for example, for the proper process development and pilot scale. 

This chapter provides a detailed description of the various commercially available microwave reactors that are dedicated for microwave-assisted organic synthesis. A comprehensive coverage of microwave oven design, applicator theory, and a description of waveguides, magnetrons, and microwave cavities lies beyond the scope of this book. Excellent coverage of these topics can be found elsewhere [1—4]. An overview of experimental, non-commercial microwave reactors has recently been presented by Stuerga and Delmotte [4],... 

The Anton Paar Synthos 3000 (Fig. 3.16 and Table 3.5) is the most recent multi-mode instrument to come onto the market. It is a microwave reactor dedicated for scaled-up synthesis in quantities of up to approximately 250 g per run and designed for chemistry under high-pressure and high-temperature conditions. The instrument enables direct scaling-up of already elaborated and optimized reaction protocols from single-mode cavities without changing the reaction parameters. 

Operating with chemicals and pressurized containers always carries a certain risk, but the safety features and the precise reaction control of the commercially available microwave reactors protect the users from accidents, perhaps more so than with any classical heating source. The use of domestic microwave ovens in conjunction with flammable organic solvents is hazardous and must be strictly avoided as these instruments are not designed to withstand the resulting conditions when performing chemical transformations. 

For several years M. Delmotte et al. have designed a microwave reactor for high pressure chemistry [63]. The microwave applicator and reactor are identical in order to accommodate the mechanical constraints induced by high pressure within liquids. This is the main interest of this device. The metallic cylindrical pipe is simultaneously a waveguide and the reactor. The device is described by Fig. 1.15. 

D. Stuerga and P. Pribetich have designed an egg-shaped microwave reactor. Its name has been chosen in relation to its appearance (a black egg which reveals, after opening, a white core). The coconut reactor is described by Fig. 1.16. 

A 1969 paper presented a mathematical crystallization model for the continuous crystallization of zeolite A [174]. The successful implementation of continuous synthesis of zeoHtes must accommodate the relatively slow crystallization rates with the reactor design to allow sufficient residence time at the necessary digestion temperature. A recent patent publication describes continuous zeolite synthesis using microwave heating, which couples the often significant advantages of faster zeolite crystallization under microwave radiation with a continuous synthesis, dewatering and work-up process [175],... 

Figure 36. Design of continuous flow microwave reactor [64].

The continuous microwave reactor (CMR) was the first microwave system designed specifically for organic reactions (see Fig. 9.4)91. In that regard, as with the MBR, the... 

By coupling an ultrasonic probe with a microwave reactor and propagating the ultrasound waves into the reactor via decalin introduced into their double jacket design, Chemat et al. studied the esterification of acetic acid with propanol and the pyrolysis of urea to afford a mixture of cyanuric acid, ameline and amelide (Scheme 9.19)136. Improved results were claimed compared to those obtained under conventional and microwave heating. The MW-US technique was also used to study the esterification of stearic acid with butanol and for sample preparation in chemical analysis137,138. 

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