The early application of ultrasound in biochemistry should be to smash the cell wall with ultrasound to release its contents. Subsequent studies have shown that low-intensity ultrasound can promote the biochemical reaction process. For example, ultrasonic irradiation of liquid nutrient base can increase the growth rate of algal cells, thus increasing the amount of protein produced by these cells by three times.

Compared with the energy density of cavitation bubble collapse, the energy density of ultrasonic sound field has been enlarged by trillions of times, resulting in a huge concentration of energy; Sonochemical phenomena and sonoluminescence caused by high temperature and pressure produced by cavitation bubbles are unique forms of energy and material exchange in sonochemistry. Therefore, ultrasound plays an increasingly important role in chemical extraction, biodiesel production, organic synthesis, microbial treatment, degradation of toxic organic pollutants, chemical reaction speed and yield, catalytic efficiency of catalyst, biodegradation treatment, ultrasonic scale prevention and removal, biological cell crushing, dispersion and agglomeration, and sonochemical reaction.

1. ultrasonic enhanced chemical reaction.

Ultrasound enhanced chemical reaction. The main driving force is ultrasonic cavitation. The collapse of cavitating bubble core produces local high temperature, high pressure and strong impact and micro jet, which provides a new and very special physical and chemical environment for chemical reactions that are difficult or impossible to achieve under normal conditions.

2. Ultrasonic catalytic reaction.

As a new research field, ultrasonic catalytic reaction has attracted more and more interest. The main effects of ultrasound on catalytic reaction are:

(1) High temperature and high pressure are conducive to the cracking of reactants into free radicals and divalent carbon, forming more active reaction species;

(2) Shock wave and micro jet have desorption and cleaning effects on solid surface (such as catalyst), which can remove surface reaction products or intermediates and catalyst surface passivation layer;

(3) Shock wave may destroy reactant structure

(4) Dispersed reactant system;

(5) Ultrasonic cavitation erodes the metal surface, and the shock wave leads to the deformation of the metal lattice and the formation of the internal strain zone, which improves the chemical reaction activity of the metal;

6) Promote the solvent to penetrate into the solid to produce the so-called inclusion reaction;

(7) To improve the dispersion of catalyst, ultrasonic is often used in the preparation of catalyst. Ultrasonic irradiation can increase the surface area of catalyst, make the active components disperse more evenly and enhance the catalytic activity.

3. Ultrasonic polymer chemistry

The application of ultrasonic positive polymer chemistry has attracted extensive attention. Ultrasonic treatment can degrade macromolecules, especially high molecular weight polymers. Cellulose, gelatin, rubber and protein can be degraded by ultrasonic treatment. At present, it is generally believed that the ultrasonic degradation mechanism is due to the effect of force and the high pressure when the cavitation bubble bursts, and the other part of the degradation may be due to the effect of heat. Under certain conditions, power ultrasound can also initiate polymerization. Strong ultrasound irradiation can initiate the copolymerization of polyvinyl alcohol and acrylonitrile to prepare block copolymers, and the copolymerization of polyvinyl acetate and polyethylene oxide to form graft copolymers.

4. New chemical reaction technology enhanced by ultrasonic field

The combination of new chemical reaction technology and ultrasonic field enhancement is another potential development direction in the field of ultrasonic chemistry. For example, the supercritical fluid is used as the medium, and the ultrasonic field is used to strengthen the catalytic reaction. For example, supercritical fluid has the density similar to liquid and the viscosity and diffusion coefficient similar to gas, which makes its dissolution equivalent to liquid and its mass transfer capacity equivalent to gas. The deactivation of heterogeneous catalyst can be improved by using the good solubility and diffusion properties of supercritical fluid, but it is undoubtedly the icing on the cake if ultrasonic field can be used to strengthen it. The shock wave and micro jet generated by ultrasonic cavitation can not only greatly enhance the supercritical fluid to dissolve some substances that lead to catalyst deactivation, play the role of desorption and cleaning, and keep the catalyst active for a long time, but also play the role of stirring, which can disperse the reaction system, and make the mass transfer rate of supercritical fluid chemical reaction to a higher level. In addition, the high temperature and high pressure at the local point formed by ultrasonic cavitation will be conducive to the cracking of reactants into free radicals and greatly accelerate the reaction rate. At present, there are many studies on the chemical reaction of supercritical fluid, but few studies on the enhancement of such reaction by ultrasonic field.

5. application of high-power ultrasonic in biodiesel production

The key to the preparation of biodiesel is the catalytic transesterification of fatty acid glyceride with methanol and other low-carbon alcohols. Ultrasound can obviously strengthen the transesterification reaction, especially for heterogeneous reaction systems, it can significantly enhance the mixing (emulsification) effect and promote the indirect molecular contact reaction, so that the reaction originally required to be carried out under high temperature (high pressure) conditions can be completed at room temperature (or close to room temperature), And shorten the reaction time. Ultrasonic wave is not only used in the transesterification process, but also in the separation of reaction mixture. Researchers from Mississippi State University in the United States used ultrasonic processing in the production of biodiesel. The yield of biodiesel exceeded 99% within 5 minutes, while the conventional batch reactor system took more than 1 hour.