In the past 20 years, ultrasonic accelerated chemical reactions have been proven by a large number of experiments, and are widely used in chemical, petroleum, metallurgy, coal, electronics, medicine, building materials, light industry, and other laboratory fields. Compared with traditional methods, the ultrasonic method has simple operation, mild chemical reaction conditions, shortened reaction time, and improved reaction yield. It provides a new chemical reaction that is difficult or impossible to achieve under ordinary conditions. A very special physical and chemical environment opens up new ways of chemical reactions. In the laboratory, a small ultrasonic cleaner is commonly used as an ultrasonic reaction instrument.
Basic principles of ultrasonic accelerated chemical reactions
So far, the reasons for the ultrasonic accelerated chemical reaction are still inconclusive, but generally accepted are the following:
1. Cavitation effect. It may be the key to accelerating chemical reactions, that is, the formation and rupture of microbubbles and the accompanying energy release in liquid media. The instant implosion produced by cavitation has a strong vibration wave, which produces a short-term high-energy environment (it is calculated that it can reach 2000-3000 ° C and hundreds of atmospheres in nanosecond intervals). Utilize ultrasonic high-frequency vibration and cavitation pressure and high-temperature effects to accelerate the progress of chemical reactions, promote the mutual penetration of molecules between two liquids, two solids, or liquid-solid, liquid-air interfaces, and open chemical bonds. Formation of new material properties. At the same time, chemical reactions can be further accelerated by secondary effects such as emulsification and macroscopic heating effects caused by the absorption of sound, the resonance properties of the medium and the container.
2. When the cavitation bubble bursts, the active substances, such as ions and free radicals, generated from the solvent or reaction reagents, if ions and free radicals compete, different products may be produced.
3. The destruction of the structure of the chemical solvent by ultrasonic waves. As a result of the single or combined effect of the ultrasonic effect, the chemical reaction speed of the reaction system is greatly enhanced.
4. During the periodical cavitation or cracking of cavitation bubbles, transient local high temperature, high pressure, heating and cooling rate greater than 1010Ks will be generated, and a strong electric field will be generated, which will cause many mechanical, thermal, chemical, biological effects Accelerate chemical reaction.