Microwave and ultrasonic processing: Now a realistic option for industry

Environmentally friendlier preparations of chemical compounds and organic or inorganic materials are generally accompanied by the concept of saving resources by optimizing reaction conditions and/or introducing new process technologies. The use of ionic liquids and a solvent-free approach are among these technologies, but in terms of the minimisation of energy and optimization of reaction control both microwave and ultrasound irradiation have now proved to be real options. This review starts from the basic considerations on the separate interaction of microwaves and ultrasound with matter and goes on to explore some laboratory and industrial applications of each type of activation. It is also possible to enhance the effects of high frequency electromagnetic fields, typical of microwaves, or the cavitational energy associated with sonochemistry by combining them with other extreme conditions such as plasmas, high pressure and UV. Finally the simultaneous use of microwaves and ultrasound in a single reactor is described. This novel mixing of technologies has been implemented in order to combine the effects of enhanced energy with improved matter transportation.