Solute solubility in supercritical CO2
It is of theoretical and practical significance to study the solubility of solutes in supercritical CO. The CO2 solubility rules summarized by the research results of francisah, Dandge, Hyat and other scholars are helpful for people to initially understand the solubility and selectivity of various solutes in supercritical CO2. The solubility rules are as follows:
① The solubility values of solutes in subcritical CO2 and supercritical CO2 generally differ by about an order of magnitude, but no phenomenon has been found that any substance does not dissolve in subcritical CO2 but dissolves in supercritical state. Consistency of solubility behavior in critical CO2 and supercritical CO2
② CO2 has a strong homogenization effect. Studies have shown that at least 14 compounds can form a homogeneous miscible state with CO2 at moderate pressure and room temperature, that is, liquid CO2 and supercritical CO2 can interact with many non-polar, weak Polar solutes are miscible, such as normal alkanes with less than 12 carbon atoms, normal olefins with less than 10 carbon atoms, lower alcohols with less than 6 carbon atoms in the main chain, and lower carbons with less than 10 carbon atoms in the main chain Esters produced from fatty acid acids with less than or equal to 12 carbon atoms in the main chain and alcohols with less than or equal to 4 carbon atoms in the main chain, low carbon aldehydes with less than 7 carbon atoms, low carbon ketones with less than 8 carbon atoms, carbon Low-carbon ethers with less than 4 atoms, etc.
③ Liquid CO2 and supercritical CO2 under moderate pressure show excellent solubility for the above-mentioned aliphatic hydrocarbons and low-polar lipophilic compounds, but as the number of carbon atoms increases, that is, as the chain length and As molecular weight increases, its solubility in liquid CO2 and supercritical CO2 will change from miscible state to partial dissolution, and the solubility will gradually decrease.
④ The introduction of strong polar functional groups (such as OH, COOH) will reduce the solubility of the compound, so polyols, polyacids, and multiple hydroxyl and carboxyl aromatic substances are difficult to dissolve in compressed CO2. Such as ethylene glycol, glycerol and polyphenols have very low solubility in liquid CO2 and supercritical CO2
⑤ Liquid CO2 and supercritical CO2 are for most mineral inorganic salts and highly polar substances (such as sugar, amino acid, starch, protein, etc.) are almost insoluble, so they will not be extracted during sub-supercritical and supercritical CO2 extraction
⑥ Liquid CO2 and supercritical CO2 are almost insoluble to compounds with a molecular weight exceeding 500.
The above rules provide a preliminary qualitative judgment on whether a substance can use supercritical CO2 as an extraction solvent, and also provide a basis for the range of substances that can be selected as a co-reagent when a CO-solvent is required in the CO2 extraction process.