Supercritical fluids have the characteristics of liquids having relatively large solubility for solutes, and also have the characteristics of gases being easy to diffuse and move. Therefore, their mass transfer rate is higher than that of liquid phase processes, that is, supercritical fluids have the properties of both gases and liquids.
More importantly, near the critical point, slight changes in pressure and temperature can cause large changes in fluid density, which are manifested as changes in solubility accordingly. Therefore, changes in pressure and temperature can be used to achieve extraction and separation processes.
Six Major Differences Between Supercritical Fluid Extraction And Liquid-Liquid Extraction
| Differentiating items | Supercritical fluid extraction | Liquid-liquid extraction |
| Extraction principle | Substances with low volatility are selectively dissolved in the fluid and extracted, thus forming a supercritical fluid phase | The solvent is added to the mixture to be separated to form a liquid phase |
| Extraction capacity | The extraction capacity of supercritical fluid is mainly related to density, and it is controlled by selecting appropriate pressure and temperature | The extraction capacity of solvent depends on temperature and the composition of mixed solvent, and has little to do with pressure |
| Extraction pressure | Operation under high pressure (5~30Mpa), generally at room temperature, is beneficial for the treatment of heat-sensitive substances, so it is expected to be used in pharmaceuticals, food and biofunctional products | Operation at room temperature and pressure |
| Separation method | The separation between the extracted solute and the supercritical fluid can be done by isothermal decompression or isobaric heating | The liquid mixture after extraction is usually separated from the solvent and the solute by distillation, which is not conducive to the treatment of heat-sensitive substances |
| Mass transfer capacity | Due to the superiority of supercritical fluid, the mass transfer capacity of solute is improved | Mass transfer conditions are often different from supercritical fluid extraction |
| Solute concentration | In most cases, the concentration of solute in the supercritical fluid phase is very small, and the supercritical phase composition is close to that of pure supercritical fluid. | The extraction phase is liquid phase, and the solute concentration can be quite large. |
Conclusion
Due to these special properties of supercritical fluids, supercritical fluids are increasingly widely used in extraction and separation, environmental protection, materials science, biotechnology, cleaning industry, etc.
Supercritical CO2 extraction Process is a new separation technology in modern chemical separation. It has the characteristics of fast mass transfer rate, strong penetration ability, high extraction efficiency and low operating temperature. This technology has been widely used in medicine, food, chemical and other industries.