What is Ultrasonic Sonochemical Treatment? What Kind of Function does it have?
The essence of ultrasonic sonochemical effect is cavitation, which includes three steps: the appearance of gas nuclei, the growth of microbubbles, and the bursting of microbubbles. Under the action of ultrasound, the fluid undergoes rapid motion. Due to changes in sound pressure, the solvent is compressed and sparsely affected. In the sparse phase region of ultrasound, the gas cavity expands and grows, filling the surrounding liquid vapor or gas. In the compressed phase region, the air pockets quickly collapse and rupture, producing a large number of microbubbles that can then serve as new gas nuclei.
The main reason for the influence of ultrasound on chemical reactions is that these microbubbles can generate strong shock waves when they grow and suddenly rupture. It is estimated that when microbubbles burst, a pressure of up to megabars can be generated in the local space, with a central temperature of 104-106K. The explanation for the effect of the ultrasound field has not yet entered the molecular level, but remains at the level of the mechanical mechanism of the molecular population.
For example, the cavitation and cleaning effect on solid surfaces; The emulsifying effect of immiscible liquids; The impact of high temperature and pressure caused by shock waves in the micro space on mass and energy transfer during microbubble burst.
Ultrasonic chemical reactions can be divided into two categories based on the medium: ① sonochemistry in the aqueous phase. Under the action of ultrasound, water decomposes into hydroxyl radicals and hydrogen atoms, which can trigger a series of chemical reactions.
Organic halides, such as CH2Cl2, CHCl3, and CCl4, undergo ultrasonic action in aqueous media, causing hydrogen hydrogen bonds to break and generating free radicals. Studies on sonochemistry of biomolecules such as proteins and enzymes have shown that sonoredox reactions are the main mechanism leading to many simple products, such as sonochemistry in non-aqueous liquid phases. The research work in this field is still in its early stages.
The role of ultrasound sonochemistry:
When ultrasound propagates in liquid media, it generates a series of effects such as mechanics, thermodynamics, optics, electronics, and chemistry through mechanical, cavitation, and thermal effects. Especially high-power ultrasound can generate strong cavitation, resulting in instantaneous high temperature, high pressure, vacuum, and micro jet formation locally.
Ultrasonic technology, as a physical means and tool, can generate a series of nearly extreme conditions in commonly used chemical reaction media. This energy can not only stimulate or promote many chemical reactions, accelerate the speed of chemical reactions, but also change the direction of certain chemical reactions, producing unexpected effects and miracles. It is generally believed that the occurrence of the above phenomena is mainly due to the mechanical and cavitation effects of ultrasound, which change the reaction conditions and environment as a result.
Mechanical action - introducing ultrasound into a chemical reaction system, ultrasound can cause substances to undergo intense forced motion, generate unidirectional force to accelerate the transfer and diffusion of substances, replace mechanical stirring, can cause substances to peel off from the surface, and thus update the interface.
Cavitation effect - In some cases, the generation of ultrasonic effect is related to the cavitation mechanism. Ultrasonic cavitation refers to a series of dynamic processes that occur under the action of ultrasonic waves, including oscillation, expansion, contraction, and even collapse of small bubbles (holes) existing in the liquid. At the point of cavitation, the local state of the liquid undergoes significant changes, resulting in extreme high temperature and high pressure. Provided a new and very special physical and chemical environment for chemical reactions that are difficult or impossible to achieve under general conditions
Catalytic chemical reaction--
① High temperature and high pressure conditions are conducive to the cracking of reactants into free radicals and divalent carbon, forming more active reaction species;
② Shock waves and micro jets have desorption and cleaning effects on solid surfaces (such as catalysts), which can remove surface reaction products or intermediates, as well as passivation layers on catalyst surfaces;
③ Shock waves may damage the structure of reactants;
④ Disperse reactant system;
⑤ Ultrasonic cavitation erodes the metal surface, causing deformation of the metal lattice and the formation of internal strain zones, thereby enhancing the chemical reactivity of the metal;
⑥ Promoting the penetration of solvents into the interior of solids, resulting in so-called inclusion reactions;
⑦ Improve catalyst dispersion;
The application of ultrasound sonochemistry:
Ultrasonic sonochemistry can be applied to almost all chemical reactions, such as extraction and separation, synthesis and degradation, biodiesel production, microbial treatment, degradation of toxic organic pollutants, biodegradation treatment, biological cell crushing, dispersion and aggregation, etc.
◆ Traditional Chinese Medicine Extraction: It refers to the ultrasonic crushing (fragmentation) of traditional Chinese medicine cells to achieve efficient extraction of useful substances. Compared with traditional extraction techniques, ultrasound assisted extraction has advantages such as fast speed, low cost, high efficiency, safety, low cost, and wide applicability.
◆ Biodiesel production: biomass oil is prepared through ultrasonic emulsification – diesel lotion actually disperses bio oil droplets into another immiscible diesel fluid. Compared with other technologies, the prepared droplets can be finely dispersed, with narrow distribution, high efficiency, good dispersion effect, and can increase the stability of lotion.
◆ Ultrasonic anti marine organisms: Based on the cavitation effect of ultrasound, when the microbubble core in the liquid is activated by ultrasound, it exhibits a series of dynamic processes, such as bubble oscillation, growth, contraction, and collapse. The bubbles in the liquid generate hundreds of atmospheres and thousands of degrees Celsius of high temperature at the moment of rupture, causing the adhesion of marine organisms to quickly peel off and crush their epidermal cells, thereby achieving the goal of preventing marine organisms.
◆ Ultrasonic catalysis: Ultrasound is applied to catalytic reaction processes, which can simulate high-temperature and high-pressure reactions in reactors at the microscopic scale, providing a very special physical and chemical environment for catalytic reactions that are difficult or impossible to achieve under general conditions. Catalytic reactions can be carried out in milder environments. It can further improve the reaction rate, shorten the reaction time, and increase the yield of the target product. The main applications include metal surface catalysis, phase transfer catalysis, enzyme catalysis, etc.
Ultrasonic dispersion: refers to the process in which liquid is used as a medium, and the action of ultrasonic waves in the liquid disperses and disassembles particles through cavitation. Ultrasonic dispersion can be divided into lotion dispersion (liquid-liquid dispersion) and suspension dispersion (solid-liquid dispersion), which have been applied in many fields. The application of ultrasonic dispersion in suspension is also dispersed in water or solvents in the paint industry, dyes in molten paraffin, drug particles in the pharmaceutical industry, and food industry, among others.
