Heating devices microwave

Other microwave-assisted parallel processes, for example those involving solid-phase organic synthesis, are discussed in Section 7.1. In the majority of the cases described so far, domestic multimode microwave ovens were used as heating devices, without utilizing specialized reactor equipment. Since reactions in household multimode ovens are notoriously difficult to reproduce due to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distribution, and the unpredictable formation of hotspots (Section 3.2), in most contemporary published methods dedicated commercially available multimode reactor systems for parallel processing are used. These multivessel rotor systems are described in detail in Section 3.4. 

A wide variety of heating devices have been introduced for use in HIER. Among these, the microwave oven (MWO), commercial pressure cooker (PC), and autoclave (AC) have proven to be the most employable. 

Fig. 2. Heat-input methods Tor freeze-drying processes la) conduction, tb) radiation, (cl microwave. CC = cold condenser RHS = radiam-heat device...

A halogen lamp (100 W) suffices to dry samples with low moisture contents however, a more powerful heating device is required for wet samples. Direct contact with a heating element provides good results, but introduces the risk of external contamination. Alternatives such as microwave heating can be effective for this purpose. 

Heating Devices A wide variety of heating devices have been adapted for use in HIER, including microwave ovens (MWO), pressure cookers, vegetable steamers, autoclaves, and water-baths. The most reproducible results may be achieved with MWOs that incorporate time and temperature control even above the atmospheric boiling point (combined with a plastic pressure cooker). The archetypes are the professional laboratory microwave instruments, which... 

Perhaps the most common types of electrical equipment found in a laboratory are the devices used to supply the heat needed to effect a reaction or a separation. These include ovens, hot plates, heating mantles and tapes, oil baths, salt baths, sand baths, air baths, hot-tube furnaces, hot-air guns, and microwave ovens. The use of steam-heated devices rather than electrically heated devices is generally preferred whenever temperatures of 100 °C or less are required. Because they do not present shock or spark risks, they can be left unattended with assurance that their temperature will never exceed 100 °C. 

Karuehanon et al. (2012) reported the microwave-assisted S Ar reaction of 2,4,6-trichloro-l,3,5-triazine with various unprotected amino acids for the synthesis of Cj-symmetrical polycarboxylate ligand. These products can be used as structural directing units in metal-organic frameworks. A domestic microwave oven was used as the heating device and the reactions were performed in water. Comparison between the reactions performed under conventional heating and microwave irradiation was made. It was observed that the microwave method takes 20 minutes less time to afford the desired ligands than the conventional method. 

The microwave power could be adjusted in order to allow constant pressure within the vessel. A incorporated pressure release valve permits to use this experimental device routinely and safely. Furthermore, an inert gas as argon could be introduced within the reactor to avoid sparking risk with flammable solvents. This experimental device is able to raise temperature from ambient to 200 °C in less than 20 s (pressure is close to 1.2 Mpa and heating rate is close to 7° s 1). The RAMO system has been designed for nanoparticles growing and elaboration [59-62]. The RAMO system is a batch system. It could be easily transpose to continuous process with industrial scale (several hundred kilograms by seconds). 

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