Microwave Batch Reactor

CherrieBaby · chouchou

Also see:
A Microwave of good use--methyl_ethyl
https://www.synthetikal.com/synthforum/viewtopic.php?t=138

Modification of a commercial microwave oven ()
https://www.synthetikal.com/synthforum/viewtopic.php?t=104
(M.A.B. Pougnet. Rev. Sci. Instrum. 1993, 64, 529-31.)

The following is from: Microwave Catalysis in Organic Synthesis, Ed. A. Loupy, Wiley-VCH 2002 (ISBN: 3527305149). Chp 10. pp. 369-370

...
10.3.4

Microwave Catalytic Reactors

10.3.4.1 Batch Reactors

The instrumentation which has been used for microwave catalytic reactions varied from domestic multi-mode ovens to continuous-flow single-mode reactors. In domestic microwave ovens the microwave output is changed by varying the patterns of on-off cycles. Thus, for example, a half microwave output does not mean real half output power but only that the full power is switched on and off for a certain period (e.g. half power corresponds to 10 s full power and 10 s of no power). In this case the catalyst and/or reaction mixture suffer thermal shocks, which is not desirable. Moreover, in domestic microwave ovens the microwaves are randomly distributed in oven space, thereby yielding ill-defined regions of the high and low intensities inside the oven. The second disadvantage of domestic ovens is the problem of temperature measurement, because in the absence of correct temperature profile in the reaction mixture, the reaction is not comparable with conventional heating and may not be reproducible when performed in two different microwave systems.

The problem of switch on-off system of the most domestic ovens has been overcome by an inverter circuit that allows power levels to be adjusted in increments (e.g. 10% of output) [109]. The desired power is continuous at different levels, as compared to the long pulsed operations of the magnetrons in most domestic ovens. The advantage of this system for laboratory applications, where small loads are normally used, is that lower power levels can be applied, which minimizes the amount of the reflected power reaching the magnetrons. Therefore, a simple unmodified microwave domestic oven operating on multi-mode system cannot be recommended for catalytic reactions (and generally for organic synthesis) induced by microwaves. Disadvantages are quite evident:

no possibility of temperature measurement and no temperature control.
reaction mixtures subjected to thermal shocks by switch on-off cycles.
nonhomogenity of microwave field.

However, an inexpensive and safe modification of domestic ovens can be made, which almost eliminates these disadvantages and allows independent temperature measurement as well as reasonable temperature control. For temperature measurement IR thermometer or better fiber optic thermometer [58-60] have been recommended. Such a batch microwave reactor made by modification of microwave domestic oven is represented in Fig. 10.1 and was described in some papers [40, 58-60, 109-112] and references cited therein.

[img=http://img201.exs.cx/img201/378/fig1014sv.th.gif]
Fig. 10.1 Microwave batch reactor: 1. microwave cavity, 2. magnetron, 3. stirring bar, 4. aluminum plate, 5. magnetic stirrer, 6. IR pyrometer, 7. switch on/off, 8. water cooler.

Details of another reactor:

{I have included this more complicated setup (below) but have not given references.}

A complementary, more advanced, laboratory-scale microwave batch reactor for synthesis and kinetics studies was developed by Strauss et al. [113] (Fig. 10.2).

The reactor is equipped with magnetic stirrer, microwave power and temperature control by computer and can operate under pressure. Even though it was developed for homogeneous organic synthetic reactions, it can be used also for heterogeneous catalytic reactions in the liquid phase.

[img=http://img201.exs.cx/img201/7048/fig1027yl.th.gif]
Fig. 10.2 Schematic diagram of the microwave batch reactor: 1. reaction vessel, 2. retaining cylinder, 3. top flange, 4. cold finger, 5. pressure meter, 6. magnetron, 7. power meters, 8. power supply, 9. stirrer, 10. fiber optic thermometer, 11. computer, 12. load-matching device, 13. waveguide, 14. microwave cavity. Reproduced from Ref. [114] by permission of CSIRO Publishing.

The first continuous-flow reactor was developed by Strauss [113, 115, 116] and has recently been commercialized.

The reactor (Fig. 10.3) consists of microwave cavity fitted with a tubular coil (3 × 3 mm) of microwave-transparent, inert material. The coin is attached to a meter- ... (continued in book)

References.
40. Breccia, Esposito, Fratadocchi. J. Microwave Power Electromagn. Energy 1999, 34, 3-8.
58. Hájek, Radiou. J. Mol. Catal. A: Chemical. 2000, 160, 383-92.
59. Hájek, Radiou. Ceram. Trans. 2001, 111, 257-64.
60. J. Kurfürstova, M. Háyek. 8th Int. Conf. Microwave and High Frequency Heating. Bayreuth, Germany, 3-7 Sept. 2001. Book of Abstracts pp. 269-270.
109. M.A.B. Pougnet. Rev. Sci. Instrum. 1993, 64, 529-31.
110. Pagnolta, Nolan, Kim. J. Chem. Ed. 1992, 69, 599-600.
111. D.M.P. Mingos. Chem. Ind. 1994, 596-9.
112. Raner, Strauss, Trainor, Thorn. J. Org. Chem. 1995, 60, 2456-60
113. Strauss, Trainor. Aust. J. Chem. 1995, 48, 1665-92.

Other References (Microwave batch reactor construction).
Klán, Hájek, Církva. J. Photochem. Photobiol. A: Chemistry 2001, 140, 185-9
Klán, Literák, Hájek. ibid. 1999, 128, 145-9
Literák, Klán. ibid. 2000, 160, 383-92

IndoleAmine · Dreamreader Deluxe

I remember seeing a very detailed image at the hive, showing this - think it was drawn by hest, and it looked kinda funny (windows paint style Laughing

)...
(still explained the thing well)

Just makes sure you use a copper tubing longer than the waves of your microwave for the condenser exit hole, and it also has to be smaller than a certain diameter (?), then no microwaves are able to escape the apparatus...
(else you'll become fried! Shocked

)

i_a