Microwave industrial-scale

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). 

Consequently, we consider that the industrial scale technological management of microwave assisted chemical reaction is no compatible with batch reactors coupled with multimode applicators. Some typical processes with a systematic decrease of the dielectric losses of the concerned reactant, such as filtration and drying of mineral or pharmaceutical powders are compatible with multimode applicators. To our knowledge, the only industrial batch microwave device is the microwave variant of the Turbosphere ( all in one solution mixer/granulator/dryer designed by Moritz... 

It is well known that microwave drying of many solid materials is a very efficient and widely used process even on an industrial scale [3] it is also an attractive means of drying of heterogeneous catalysts. Microwave drying of catalysts and supported sorbents has several advantages ... 

Microwave heating and catalysis have been successfully used in the solvent-free synthesis of cosmetic fatty esters (Villa et al., 2003). Two kinds of reaction were performed acid-catalysed esterification (Figure 3.11) and phase-transfer catalysed alkylations, both reactions affording near quantitative yields when microwave heating was used. It should be noted that diethyl ether and water were used in the purification of the product, and alternative purification/separation procedures would be required if this process was performed on an industrial scale, due to the flammability risk of diethyl ether. 

An alternative approach to the reaction conditions described above employs microwave irradiation for the quaternization reaction of 1-methylimidazole with various haloalkanes and l,reaction times (minutes instead of hours) and scaling up this technology to an industrial scale can easily be achieved. 

Also, in solid materials, microwaves are used on an industrial scale for heating purposes. The ability of the solid material to absorb microwave heating depends on two properties the dielectric constant and the loss tangent. Some materials absorb the microwave energy very easily, while others are transparent or impermeable to it. 

Despite the often large increase in the reaction rate the use of microwave-assisted reactions has still not been implemented on an industrial scale. One of the main barriers for industrial applications is reliable scale-up of microwave reactors [116], but there are also other engineering problems that have to be solved. The use of microwaves to speed-up distillation processes has also been indicated [123]. 

Many microreactors are at the research level but a few are already commercially available. Microwave-assisted flow processing in microreactors (MAFP) [93] or radiofrequency-heated flow reactors [94,95] are promising alternatives for conventionally heated, multistep production of fine chemicals in batch reactors. Realization of MAFP at an industrial scale requires a proper design of multitubular reactors integrated with microwave heating [96]. 

Patil, N.G., Benaskar, F., Rebrov, E.V., Meuldijk, J., Hulshof, LA., Hessel, V., and Schouten, J.C. (2012) Continuous multitubular milli-reactor wilh a Cu thin film for microwave assisted fine-chemical synthesis at industrial scale. Ind. Eng. Chem. Res., 51,14344-14354. 

The advent of commercial laboratory microwave reactors and the corresponding industrial-scale equipment [10] has given rise to worldwide activity concerning the... 

Overall, the authors expect that it is now clear to the reader that microwave technology not only can reduce reaction times from hours to seconds and improve yields and selectivities of known transformations but also can facilitate the discovery of new and unforeseen stereoselective reactions because of convenience in reactions parameters control provided by modem dedicated equipment. Also, the early scalability issues of microwave-assisted processes have been solved, and dedicated industrial-scale systems are available. Although the actual reasons for the beneficial effect of microwave irradiation are not completely well understood and are still debated, the bottom line is that when a thermal activation is needed to perform an organic transformation, microwave irradiation should be the first choice and not the last resort. 

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