Principle of RESS method
A certain degree of solubility of the solute in SCF is a necessary condition for the RESS process to proceed.
First, the solute is dissolved in the SCF, and then the supercritical solution is expanded in a very short time (10-8 ~ 10-5s) through a fine nozzle.
During the expansion process, the sudden change of pressure and temperature causes the solute supersaturation to rise suddenly, and a large number of micronuclei are precipitated, and they grow rapidly in a very short period of time to form uniform micron or nano-sized particles.
Principle of SAS method
The SAS method uses SCF as an anti-solvent, dissolving the material to be prepared into a certain organic solvent to make a solution, and mixing this solution with a supercritical fluid.
Although the supercritical fluid is basically insoluble to the solute in the solution, the solvent in the solution can be miscible with the supercritical fluid.
When the solution and the supercritical fluid dissolve each other, the volume of the solution will expand, which will greatly reduce the dissolving ability of the original solvent and cause the solute to separate out.
Principle of PGSS method
The PGSS method dissolves supercritical CO2 into a liquid solute or a suspension of solute. After reaching saturation, this high-pressure gas-liquid or gas-liquid mixture is rapidly expanded and depressurized through a nozzle to form an aerosol.
The CO2 in the aerosol H2O volatilizes at high temperature in the expansion chamber, solute precipitates, and fine particles are produced.
Difference of supercritical micronization equipment
RESS method has a simple device and can be achieved by using only one nozzle when producing a small amount of material. But the biggest limitation of the RESS method micronization equipment is that the solubility of SCF for most substances is too small.
SAS method micronization equipment is more widely used, especially for the production of high-quality drugs, food additives, cosmetics, etc. The nature and composition of these substances are controlled by controlling the operating conditions, but these methods have disadvantages such as relatively complicated processes and high investment costs.
PGSS method micronization equipment is simple in principle, low in equipment cost, and has a wide range of applications, but the prepared particle size is uncontrollable and the particle size is relatively large.