Supercritical fluid refers to a fluid between gas and liquid whose temperature and pressure are above its critical temperature (Tc) and critical pressure (pc). 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 their fixed critical points: critical temperature and critical pressure.
Supercritical fluid technology is a new separation technology in modern chemical separation. Supercritical extraction uses CO2 as a solvent, because CO2 fluid in a supercritical state has a greater density and dielectric constant, and has a greater solubility for substances. When the temperature and temperature change, its solubility will change suddenly. Therefore, not only is the solubility of certain substances selective, but the separation of solvents and extracts is also easy.
The supercritical CO2 extraction device can be used for extraction materials (solids and liquids) with high pressure and appropriate temperature under the condition of separator replacement, so that the soluble materials can decompose the target products during the extraction and separation process.
The influence of the chemical structure of plants on SCF extraction
When extracting natural plants with SCF, it is necessary to use the structure and chemical knowledge of plants. The main reasons are as follows.
① In order to improve the extraction efficiency, the knowledge of plant structure can be used to determine whether the raw materials need to be pretreated first, such as grinding, slicing, reducing particle size or destroying cell walls.
② To maximize the extraction rate, concentration and yield of the target component and minimize the extraction rate, concentration and yield of the impurities, relevant natural drug chemistry knowledge needs to be used; different extraction and separation conditions can produce different extracts.
Supercritical CO2 extraction process of curcumin
Curcumin is divided into dedimethoxycurcumin, demethoxycurcumin and curcumin. The main extraction methods can be divided into organic solvent extraction and water extraction. The existing extraction methods are prone to degrading curcumin during the extraction and recovery of solvents. Supercritical carbon dioxide extraction technology, as a new type of green extraction and separation technology, can effectively extract high-purity curcumin from turmeric.
After the turmeric raw material is crushed and sieved, it is placed in an extraction kettle for extraction. After the extraction is completed, the content of curcumin in the extracted turmeric residue is detected, and the extraction rate of curcumin is obtained by comparing it with the content of curcumin in the raw material.
Under the condition that other conditions remain unchanged, the effect of different raw material particle sizes on the extraction effect was studied: as the raw material particle size decreases, the efficiency of supercritical carbon dioxide extraction increases. When the particle size is reduced to 0.5mm, the extraction rate no longer increases, but the material will stick together due to the small particle size, thereby increasing the difficulty and cost of crushing. Therefore, the particle size of the raw material should be selected at 1mm.
Conclusion
The yield and composition of the extraction product are mainly determined by the following three processing conditions: raw material primary processing, extraction conditions and separation conditions. In industrial production, each product should optimize the parameters of the above conditions.
SFE is a typical operation at high solvent feed ratio, high air velocity and low fluid viscosity. It is generally believed that SFE-CO2 can selectively extract plant aromatic oils, esters, alcohols, aldehydes, terpenes and light fractions in waxes and resins, while leaving heavy fractions, fatty acids, triglycerides, chlorophyll, pigments and other high molecular weight substances in waxes and resins in the extraction phase.
Compared with traditional liquid-liquid extraction, SFE-CO2 has better selectivity, and supercritical fluid extraction technology has broad application prospects in the food, chemical and pharmaceutical industries.