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[Title] Ultrasonic Technology and Application [Author] Science and Technology Lecture [Title] Daily Chemical Industry Volume 35 Issue 6 December 2005 Sonochemistry is the cross-penetration of acoustics and physical chemistry, and is also a branch of physical chemistry. Ultrasound can accelerate conventional chemical reactions, accelerate the decomposition and synthesis reactions of substances in organic solvents, etc., and can also strengthen chemical units (cleaning, extraction, crystallization, emulsification, flocculation, adsorption, membrane separation, etc.). These applied technologies are called sonochemistry or sonochemistry. Sonochemical technology is an emerging, multi-disciplinary edge science developed in the 20th century. 1. Application in cleaning At present, ultrasonic wave is the most widely used in industrial cleaning and is also the most successful. The physical mechanism of ultrasonic cleaning is attributed to the effects of acoustic cavitation, shock waves, microacoustic flow and the ultrasonic vibration of the cleaning fluid itself. It is mainly manifested in: (1) Microbubbles (cavitation nuclei) existing in the liquid vibrate under the action of the sound field. When the sound pressure reaches a certain value, the bubbles will rapidly grow in size and then suddenly close. The impact water wave generated when the bubbles close can instantly generate thousands of atmospheric pressures around them, thereby destroying insoluble dirt and dispersing them in the cleaning fluid. (2) The direct and repeated impact of vapor cavitation on the dirt layer destroys the adsorption between dirt and the surface of the cleaning parts on the one hand. ； On the other hand, it will also cause fatigue damage of the dirt layer and detachment from the surface of the cleaning part. (3) The vibration of gas bubbles scrubs the solid surface. Once there are cracks in the dirt, the bubbles can "drill" into the cracks and vibrate, causing the dirt layer to fall off. (4) For solid particles wrapped in oil, due to the effect of ultrasonic cavitation, the two liquids quickly disperse and emulsify at the interface, and the solid particles fall off. For dead corners such as cavities, slits, micropores and holes on precision workpieces, ordinary cleaning is difficult to achieve, and ultrasonic cleaning can achieve ideal results. Ultrasonic has the following advantages compared with other cleaning methods: ① The cleaning effect is better than other methods. If the ultrasonic cleaning effect is set as 100%, then brushing, steam cleaning, solvent pressure cleaning and soaking are 90%, 35%, 30% and 15% respectively. ； ②High cleaning quality, uniform cleaning effect and good consistency ； ③Shorten cleaning time and save energy, reducing production costs ； ④Reduce workers’ production intensity and improve working conditions ； ⑤Green and environmentally friendly, the detergent used in ultrasonic cleaning is low-pollution and easy to degrade. Table 1 is a comparison of the washing effects of ultrasonic washing machines and ordinary washing machines. Cui Yunhua studied the effect of ultrasonic hair washing under different conditions and compared it with traditional emulsified hair washing. Research results show that the use of ultrasonic washing can reduce the washing temperature, shorten the washing time, and reduce the dosage of lotion and auxiliaries. The washed wool obtained by using ultrasonic waves has good fluffiness, no entanglement between wools, high whiteness and almost no small impurities in the washed wool. In addition, ultrasonic waves have an etching effect on the wool scales while washing the wool. After ultrasonic washing, the washed wool fiber scales become dull and shiny, and the friction effect is reduced. Moreover, the fineness distribution of washed wool fibers obtained by ultrasonic washing becomes more concentrated. Long-term ultrasonic washing will make the wool fiber diameter smaller and the breaking elongation increased, but there will be no obvious damage to the fiber breaking strength. At present, domestic manufacturers have launched ultrasonic washing machines. Different from traditional washing methods, ultrasonic washing machines mainly use the "cavitation" effect of ultrasonic waves to generate huge energy, "shock" the dirt from the clothes and dissolve them into the water, and then beat the clothes through the rotation of the inner cylinder and penetrate the water to clean the clothes. ； Ordinary washing machines generally use detergent to chemically react with the dirt on the clothes, and then use clean water to discharge the dirt out of the machine to achieve the purpose of washing the clothes. However, this cleaning effect is relatively limited and can only clean the surface of the clothes. The remaining washing powder or detergent on the surface of the clothes may irritate human skin. The biggest advantage of using ultrasonic laundry is environmental protection. Among ordinary phosphorus-containing laundry detergents, sodium tripolyphosphate is used to soften water. The washing wastewater from this laundry detergent is discharged into the sewer and then flows into rivers and lakes, which is one of the phosphorus sources that causes eutrophication of water quality. ； The 4A zeolite used in phosphorus-free laundry detergent as a phosphorus-substituting additive may block sewers, generate a large amount of waste, and increase the amount of three wastes treated. Ultrasonic washing machines are not only pollution-free, but also save 1/3 of water than ordinary washing machines. In addition, someone has applied for a patent for an ultrasonic dishwasher. Table 1 Comparison of the washing effects of ultrasonic washing machines and ordinary washing machines. Ordinary ultrasonic low-foaming washing powder cleaning rate/% 51.70 91.87 High-foaming washing powder cleaning rate/% 31.85 41.30 2. Application in the synthesis of daily chemical raw materials. Currently, the use of ultrasound in chemical synthesis has aroused widespread interest among chemistry and chemical engineering scholars around the world. The cavitation effect of ultrasound is used to provide more reaction active centers and reduce the activation energy of the reaction. Accelerate chemical reactions and open new reaction channels. Chitin is a natural amino polysaccharide, non-toxic, tasteless and has good biocompatibility. Chitin and water-soluble derivatives of chitosan have good film-forming properties and can be attached to keratin and lipids. They have moisturizing and antibacterial effects without causing any allergic irritation. They are increasingly used in cosmetics. Since chitin is insoluble in water, acid, alkali and general organic solvents, chitosan is only soluble in acid or acidic solution. Application scope * * Being restricted, improving their solubility and biological activity is an important topic in the application development of chitin and chitosan. Lin Youwen et al. used ultrasonic waves to modify chitin to prepare carboxychitin (CM-Chitin). The modified CM-Chitin is less hygroscopic than hyaluronic acid (HA), but has better moisturizing properties than HA, and its hygroscopic and moisturizing properties are better than glycerin. Cao Ya et al. used ultrasound to synthesize a series of polymer surfactants called carboxymethyl cellulose (CMC), and studied the degradation reaction of CMC under the action of ultrasound and the ultrasonic copolymerization of CMC and active macromonomers with different hydrophilic-lipophilic ratios. Experimental results show that the ultrasonic reaction time has a great influence on the composition of the copolymer, and the copolymer has good viscosity-increasing ability and high surface activity. The CMC series of polymer surfactants synthesized by ultrasonic waves expands the concept of preparing surfactant structures with excellent performance. Zhu Jianliang and others studied the intermediate 3,5-diisopropyl salicylic acid, the active ingredient of anti-ultraviolet salicylate in ultrasonic synthesis of cosmetics. Through optimization experiments, they found that when the ultrasonic power is 220 W, 65 ℃ and the amount of concentrated sulfuric acid is 130 mL, the product yield can reach 17.42% under normal pressure reaction for 120 minutes. Compared with organic synthesis without ultrasound, the yield is significantly improved. This is mainly caused by the "turbulence effect", "perturbation effect", "interface effect" that causes macroscopic fluid turbulence and particle collisions such as ultrasonic cavitation and microfluidic impact, as well as the "energy concentration effect" that accumulates energy. 3. Application in emulsification Ultrasonic emulsification has many advantages compared with general emulsification processes and equipment (such as propellers, colloid mills and homogenizers): ① The average droplet size of the emulsion formed is small, which can be 012μm ~ 2μm ； The droplet size distribution range is narrow, which can be 011μm ~ 10μm or narrower ； High concentration, the mass fraction of pure emulsion can exceed 30%, and the mass fraction of added emulsifier can be as high as 70% ； ②The formed emulsion is more stable. An important feature of ultrasonic emulsification is that it can produce extremely stable emulsions without or with less emulsifiers. ； ③The type of emulsion can be controlled. Using ultrasonic emulsification, under certain sound field conditions, both O/W (oil-in-water) and W/O (water-in-oil) emulsions can be prepared. ； ④The power required to produce emulsion is small. For example, to prepare 4155 m3/h emulsion with a droplet size of 1 μm, if a reed whistle is used, when the working pressure is 9186 × 105 Pa ~ 1138 × 105 Pa, only 3167 kW ~ 5114 kW of driving power is needed, while when a high-pressure homogenizer is used, the working pressure is 6190 × 105 Pa ~ 3145 × 107 Pa. A driving power of 2914 kW to 3617 kW is required. In addition, the reed ultrasonic generator has the advantages of simple structure, firmness, stable operation, low cost, easy maintenance and easy implementation of industrial-scale production. The obvious advantages of phacoemulsification have led to its increasing application in many industrial processes such as food, paper, paint, chemicals, medicine, textiles, petroleum and metallurgy. At present, there are two main explanations for the mechanism of phacoemulsification. One is the cavitation mechanism. It is believed that emulsification is caused by the burst bubbles near the container wall causing the liquid to be injected incompletely into another liquid and further dispersed into fine droplets. ； The other is the interface instability mechanism. It is believed that when ultrasound hits the interface between two liquids, the interface is subject to high periodic acceleration. When the acceleration direction is from the lighter liquid to the heavier liquid, instability begins. The instability can increase the disturbance of the interface, and finally cause one liquid to be injected into another liquid incompletely, resulting in emulsification. Tan Bien et al. prepared a series of styrene (St)/butyl acrylate (BA) miniemulsions using stirring and ultrasonic emulsification methods respectively. The results show that the monomer droplets without ultrasonic treatment are obviously much thicker than those that have been treated with ultrasonic waves, and the conductivity value is also larger. When the emulsion is processed under constant ultrasonic intensity, the ultrasonic time is within a certain range. As the value increases, the stability of the emulsion also increases. However, beyond this range, increasing the ultrasonic time will have a negative effect on the stability of the emulsion. 4. Application of spice aging. Due to the limited sources of natural spices, synthetic spices are currently commonly used. Synthetic spices are prepared by mixing aromatic compounds with a small amount of natural spices. However, their aging speed after mixing is very slow, and it generally takes several months to achieve better results. The reason may be that some special aromas are produced by the generation of certain substances (such as esters, aldehydes, homologs, ethers, etc.), and the generation of these substances is very slow under normal conditions, but their generation speed can be significantly accelerated under the action of ultrasonic waves. Ultrasound is now commonly used in Western European countries and Japan to process this spice. 5. Outlook As an emerging interdisciplinary subject, sonochemistry has received widespread attention and great development in recent years. Currently, ultrasonic waves are mainly used in cleaning, welding, detection, etc. What is gratifying is that domestic manufacturers have applied ultrasound to the industrial extraction of traditional Chinese medicine, and the results have been remarkable. Foreign scholars have discovered the phenomenon of sono-induced nuclear fusion, which will undoubtedly continue to set off an upsurge in sonochemistry research. However, research on the theory of sonochemistry is still very imperfect. Many aspects of research need to be further developed and discussed in depth. Some basic research data are still lacking. The research and verification of the mechanism of ultrasonic action requires the development of more advanced and sensitive detection instruments, which requires the joint efforts of physicists, chemists, and photovoltaicists. In addition to its application in the above-mentioned daily chemical industry, sonochemical technology will also show broad application prospects in the production of microcapsules, the preparation of ultrafine particles and nanomaterials, and the synthesis of various functional surfactants. This post was last edited by zhangyong6404 on 2009-3-9 23:07 ]