A section of Molecules (ISSN 1420-3049).
The intensification of chemical processes by means of ultrasound has been extensively investigated. The main phenomenon that can explain chemical effects under sonication is the acoustic cavitation generated by piezoelectric or magnetostrictive ultrasonic units. A similar behaviour is observed applying hydrodynamic cavitation generated by venturi tubes, throttling valves, orifice plates, cavitation jet mixers, high-pressure liquid whistles, high-pressure jet fluidisers and high-speed rotor–stator homogenisers. Cavitation phenomena generate unique high-energy microenvironments that may be compared to sub-microreactors where very high pressure and temperature can be focalised almost at the molecular level. In addition to chemical effects, intense mechanical forces are generated that offer great opportunities for physical treatments such as emulsification, dissolution, extraction and crystallization. Considering that water is the ideal solvent in sonochemistry, this technique plays a relevant role in green chemistry. Ultrasound chemistry is environmentally friendly, because milder conditions may improve yields and selectivities, with shorter reaction times. Acoustic and hydrodynamic cavitation can easily generate reactive species and catalysts and can replace hazardous reagents. Ultrasound could also enhance processing in many areas, such as food, pharma or fine chemistry, via intensification of unit processing such as extraction, transformation or preservation.
- hydrodynamic cavitation
- sono processing
- sono extraction
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