Principle introduction:
When ultrasonic propagates in liquid medium, a series of mechanical, thermal, optical, electrical and chemical effects are produced by mechanical, cavitation and thermal actions. In particular, high-power ultrasound will produce strong cavitation effect, thus forming instantaneous high temperature, high pressure, vacuum and micro jet locally.
As a kind of physical means and tools, ultrasonic technology can produce a series of conditions close to the extreme in the commonly used medium of chemical reactions. This energy can not only stimulate or promote many chemical reactions, speed up chemical reactions, but also change the direction of some chemical reactions and produce some unexpected effects and miracles. It is generally believed that the above phenomena are mainly due to the mechanical and cavitation effects of ultrasound, which are the result of changing reaction conditions and environment.
1. Sonochemistry is a new interdisciplinary subject, which mainly refers to the use of ultrasound to accelerate chemical reactions or trigger new reaction channels to improve the yield of chemical reactions or obtain new chemical reaction products. The main force of sonochemical reaction comes from acoustic cavitation and extreme physical conditions such as high temperature (more than 5 000 K), high pressure (more than 2.03 × 10 8 PA), shock wave or micro jet, etc
2. The application of sonochemistry is very wide, which can be classified into nine categories,
They are: biochemistry, analytical chemistry, catalytic chemistry, electrochemistry, photochemistry, environmental chemistry, mineral chemical treatment, extraction and separation, synthesis and degradation.
Mechanical action - ultrasonic wave is introduced into chemical reaction system. Ultrasonic wave can make material move violently and produce one-way force, which can accelerate the transmission and diffusion of material. It can replace mechanical stirring in appropriate range. Because ultrasonic stirring is produced from micro angle, the probability of contact and collision between reactants is greatly increased, so chemical reaction is greatly accelerated The corresponding rate.
Cavitation - in some cases, the generation of ultrasonic effect is related to cavitation mechanism. Acoustic cavitation refers to a series of dynamic processes: oscillation, expansion, contraction and even collapse of tiny bubbles (holes) in liquid under the action of sound waves. When cavitation occurs, the local state of the liquid changes greatly, resulting in extreme high temperature and high pressure. It provides a new and very special physical and chemical environment for chemical reactions which are difficult or impossible to be realized under general conditions
Catalytic chemical reaction——
① High temperature and high pressure are favorable for the decomposition of reactants into free radicals and divalent carbon to form more active reaction species;
② Shock wave and micro jet can desorb and clean the solid surface (such as catalyst), and remove the reaction products or intermediates on the surface and the passivation layer on the catalyst surface;
③ Shock wave may destroy the structure of reactants;
④ Dispersion reaction system;
⑤ Ultrasonic cavitation erosion of metal surface, shock wave leads to the deformation of metal lattice and the formation of internal strain zone, which improves the chemical reaction activity of metal;
⑥ It makes the solvent go deep into the solid to produce the so-called inclusion reaction;
⑦ The dispersion of catalyst was improved.