Ultrafine particulate materials
Due to their special physical and chemical properties, ultrafine particulate materials have important application Due to their special physical and chemical properties, microcrystals materials have important application value in the fields of light industry, metallurgy, electronics, medical materials, chemical industry, biology, etc., and have been widely used, such as energetic materials, polymers, biological Macromolecules, drugs, superconductors, pigments, catalysts, etc.
Supercritical fluid micronization technology
Supercritical fluids have received more and more attention in the preparation of microcrystals (supercritical fluid micronization technology) due to their special properties. SCF has a strong dissolving ability, a large diffusion coefficient, and a low viscosity, which makes it reflect good mass transfer and permeability performance, and SCF is very sensitive to changes in pressure and temperature and is easy to adjust.
Supercritical fluid micronization technology is a new type of microparticle preparation technology that uses the above properties of SCF to prepare ultrafine particles.
Supercritical fluid micronization
In 1984 Krukonisl2 first proposed the concept of supercritical fluid micronization technology.
Compared with traditional methods such as grinding, liquid phase deposition, solution crystallization, vapor deposition, chemical reaction, etc., the preparation of particles by supercritical micronization technology has some significant advantages, such as:
- The prepared nanoparticles are small in size and the particles The size distribution is concentrated, the fluidity is good, the crystal purity is high, and the surface is rounded. By controlling different operating conditions, the crystal form purity of the particles can reach a very high level;
- The ultrafine particles of the composite material have a high degree of uniformity and are rapidly nucleated During the process, all components are precipitated at the same time under extreme supersaturation, so the uniformity of the generated composite particles is very high;
- It is suitable for the ultrafine particles of special substances such as heat sensitivity and biological activity, and can also improve the drug Chemical purity and effective utilization, reduce the residual amount of solvent;
- The manufacturing process is simple and the operation has good controllability: By adjusting the parameters such as temperature and pressure, it is convenient to control and adjust the supersaturation of the solution, which in turn affects the size of the particles And morphology to control the particle size within a certain range.
At present, using supercritical fluid micronization technology has successfully prepared nano-scale particles, although it has not been applied to actual Industrial production process, but has shown great potential.
Three main types
According to the solvation behavior of supercritical fluids, there are three main types of SCF particulate technology:
Rapid expansion of supercritical fluid (RESS);
Supercritical fluid anti-solvent (SAS) or Gas anti-solvent (GAS);
Chemical reaction method in SCF, such as hydrothermal synthesis method in supercritical water, reverse micelle method of supercritical CO2 in water, etc.
RESS treatment is mainly a binary system with good solubility characteristics of solute in supercritical CO2, generally does not involve the use of conventional solvents. However, because polar substances and large molecules are difficult to dissolve in supercritical carbon dioxide, this greatly limits the application of the RESS method.
When the solubility of solutes in supercritical CO2 is not good, the SAS method becomes an option. The SAS method first dissolves the material that needs to be prepared in a conventional solvent (depending on the nature of the solute, it can be an inorganic or organic solvent), and then the supercritical fluid (usually SC-CO2) comes into contact with the solution.
Conventional solvents are rapidly dissolved in supercritical fluids and the density decreases rapidly, resulting in a rapid decrease in the dissolving power, and the solutes crystallize out.
The morphology and size of the crystallized solute are mainly related to the nature of the solute itself, the expansion rate of the solution, and the supercritical fluid addition rate.
Using different supercritical fluid micronization methods can process many kinds of materials, so as to obtain solid particles in a suitable form.
Chemical reaction method in SCF
The preparation of particles by the chemical reaction method in SCF has also made progress in recent years. After the heating and reaction, the reacted solution leaves the reactor and rapidly cools to obtain particles.
The reverse micellar method of supercritical carbon dioxide-in-water is adopted, with AgNO3 and KBH4 as the reactants, isooctane as the continuous phase, and sodium succinate (AOT) and tetraethylene glycol lauryl ether (C12E4) as the surface. The active agent and co-surfactant successfully synthesized nano-Ag particles.The research results show that the inter-diffusion between micellar core and supercritical carbon dioxide is the rate control step in the formation of nanoparticles.
Supercritical fluid micronization technology
Ultrafine particulate materials have important application value in light industry, metallurgy, electronics, medicine, materials, chemicals, biology and other fields, such as energetic materials, polymers, biological macromolecules, drugs, superconductors, pigments, catalysts, etc. (; According to the morphology and structural properties of the material, nano-sized particles, microspheres, microcapsules, liposomes, nanowires, nanotubes, etc. can be prepared.
However, the use of supercritical fluid micronization technology for large-scale production still faces great challenges.
At present, the supercritical antisolvent technology has been tested on a larger scale and is gradually moving towards large-scale production.