The energy density of the ultrasonic sound field compared to the energy density at which the cavitation bubble collapses, the energy density is enlarged by trillions of times, causing a huge concentration of energy; the sonochemical phenomenon and sonoluminescence caused by extreme high temperature and high pressure generated by cavitation bubbles , is the unique form of energy and material exchange in sonochemistry. Therefore, ultrasonic chemical extraction, biodiesel production, organic synthesis, treatment of microorganisms, degradation of toxic organic pollutants, chemical reaction rate and yield, catalytic efficiency of the catalyst, biodegradable treatment, ultrasonic anti-fouling, biological cell grinding, dispersion And cohesion, harmonic chemical reaction has an increasing role.
Ultrasound-enhanced chemical reactions.
Ultrasound enhances chemical reactions. The main force comes from the role of ultrasound cavitation. The collapse of the cavitation nucleus produces local high temperature, high pressure, and strong shock waves and micro-jets, providing a new and very special physical and chemical environment for chemical reactions that are difficult or impossible to achieve under normal conditions.
Ultrasonic Catalytic Reaction
As a new research field, ultrasonic catalytic reaction has attracted more and more intense interest from the industry workers. The role of ultrasound in catalytic reactions is mainly:
(1) High temperature and high pressure are favorable for the cracking of reactants into free radicals and divalent carbon, forming more active reactive species;
(2) Shock waves and micro-jets have desorption and cleaning effects on solid surfaces (such as catalysts) and can remove surface reaction products or intermediates and passivation layers on the catalyst surface;
(3) Shock waves may damage the reactant structure
(4) dispersion reaction system;
(5) Ultrasonic cavitation erosion of the metal surface, the shock wave leads to the deformation of the metal lattice and the formation of the internal strain region, increasing the chemical reactivity of the metal;
6) to promote the solvent into the solid interior, resulting in the so-called inclusion reaction;
(7) to improve the dispersion of the catalyst, in the preparation of the catalyst, commonly used ultrasonic, ultrasonic irradiation can increase the surface area of the catalyst to make the active component more uniform dispersion, enhanced catalytic activity.
High power ultrasonic application in biodiesel production
The key to biodiesel production is the catalytic transesterification reaction of fatty acid glycerides with lower alcohols such as methanol, while ultrasound has a significant role in enhancing the transesterification reaction, especially for the heterogeneous reaction system can significantly enhance the mixing (emulsification) The effect and promotion of the intermolecular contact reaction, so that the reaction that was originally required under high temperature (high pressure) conditions, can be completed at room temperature (or near room temperature) and shorten the reaction time. Ultrasound is used not only for the transesterification process but also for the separation of the reaction mixture. Researchers at the Mississippi State University in the United States used ultrasonic processing to produce biodiesel. The yield of biodiesel exceeded 99% within 5 minutes, while conventional batch reactor systems required more than 1 hour.