The "magic" of supercritical extraction comes from the unique physical properties of carbon dioxide (CO ₂) in a supercritical state. When the temperature of CO ₂ exceeds 31.1 ℃ and the pressure exceeds 7.38MPa, it enters a supercritical state, where its density is close to that of a liquid and its viscosity is close to that of a gas, possessing both gas permeability and liquid solubility. This characteristic makes CO ₂ an efficient extraction solvent that can penetrate into the micropores of materials, dissolve and extract target components.
The key mechanism of CO ₂ transforming into a strong solvent:
Adjustable solubility: The solubility of supercritical CO ₂ changes significantly with changes in pressure and temperature. By adjusting the pressure, its ability to dissolve substances of different polarities can be controlled. For example, weak polar substances are preferentially extracted under low pressure, and as the pressure increases, components with higher polarity and molecular weight are gradually extracted. This selectivity enables precise extraction of target substances from CO ₂ while avoiding impurities from entering.
Advantages of low-temperature operation: Supercritical extraction can be carried out under conditions close to room temperature (35-40 ℃), effectively preventing the oxidation and dispersion of thermosensitive substances (such as volatile spices and active ingredients). For example, when extracting natural flavors, the low-temperature characteristics of CO ₂ can fully preserve the original flavor and activity of the flavors.
Environmental Protection and Safety: CO ₂ is non-toxic, odorless, non flammable, and does not undergo chemical reactions during the extraction process, avoiding the potential toxicity and environmental pollution caused by traditional organic solvents. In addition, CO ₂ is easy to purify and recycle, further reducing costs.
Application example: Supercritical CO ₂ extraction technology has been widely used in fields such as food, medicine, cosmetics, etc. For example, when extracting active ingredients such as flavonoids and alkaloids from plants, CO ₂ can efficiently dissolve these substances while avoiding high temperature damage to their structure, resulting in high-purity and high-quality extracts.