Supercritical CO2 fluid extraction technology 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 industry and other industries.
Supercritical fluid refers to a fluid between gas and liquid whose temperature and pressure are above its critical temperature (Tc) and critical pressure (pc). All stable pure substances can have a supercritical state (stable means that their chemical properties are stable and they will not decompose into pure substances when they reach the critical temperature), and they all have fixed critical points: critical temperature and critical pressure.
The critical temperature Tc is the temperature at which no large pressure can cause the pure substance to transform from gas phase to liquid phase when the temperature is higher than a certain value; and the critical pressure pc is the lowest pressure at which the gas can be liquefied at the critical temperature.
When the temperature of a substance is higher than the critical temperature and the pressure is greater than the critical pressure, the substance is in a supercritical state. If the fluid is heated or compressed to a state above its critical temperature (Tc) and critical pressure (pc), and the gas in this state is pressurized, the gas will not liquefy, but the density will increase, and it will have liquid-like properties while retaining the properties of gas.
Common substances that can be used as supercritical fluids include CO2, alkanes, low-carbon alcohols, water, etc. Since CO2 has the advantages of being non-toxic, non-combustible, non-corrosive, non-polluting, chemically inert, cheap and easy to obtain, and having a low critical point, it is a more commonly used supercritical fluid.
Three major categories of supercritical CO2 extraction equipment
According to different process flows, the development of different supercritical CO2 fluid extraction equipment is a key part of the entire technology.
When designing a supercritical CO2 fluid extraction device, the bearing capacity of the extraction device should be considered. Since the separation process requires the use of high-pressure equipment and the supercritical fluid has certain special properties, there are more special requirements for process equipment.
At present, supercritical CO2 extraction equipment is mainly divided into three categories based on its use function.
- Laboratory extraction equipment The volume of the extraction kettle is generally below 500mL, with a simple structure, no CO? circulation equipment, high pressure resistance (up to 70Mpa), and is suitable for laboratory exploratory work.
- Pilot equipment The volume of the extraction kettle is generally between 1 and 20L, which is suitable for process research and small batch sample production. The pilot equipment currently used mainly has the characteristics of good supporting equipment performance and CO2 recycling.
- Industrial production equipment The volume of the extraction kettle ranges from 50L to several cubic meters.
Conclusion
Supercritical CO2 fluid can be used to separate and extract specific substances from solid media, and can also be used to separate and purify specific components in liquid media. The practical application of supercritical CO2 fluid extraction in production is achieved through safe and reliable extraction equipment.