Factors affecting supercritical CO2 fluid extraction
The extraction process of supercritical CO2 fluid is affected by many factors, including the nature of the extracted substance and the state of the supercritical CO2 fluid. In the actual extraction process, the extracted substances are diverse and their properties are very different. Different substances have different performances in the extraction process, and the state of CO2 in the extraction system also has a great influence on the extraction process. These effects (such as CO2 temperature, pressure, flow rate, entrainer, sample physical form, particle size, viscosity, etc.) are intertwined, making the extraction process more complicated
The relative molecular mass and molecular polarity of organic compounds are the most important factors affecting the solubility of supercritical CO2 fluid, and it is the key to determine whether the substance can be extracted by supercritical CO2 fluid. However, compared with a large number of process studies, the solubility data of different solutes in supercritical CO2 fluids is very lacking.
Dandge measured the solubility data of a series of organic compounds in supercritical CO2 fluid (experimental conditions: 25℃,=0.895g/mL and 32℃,=0.86g/mL, the solubility is expressed as the mass percentage of the supercritical CO2 fluid solute. ), combined with previous work, the empirical law of solute molecular structure and its solubility in supercritical CO2 fluid is as follows
The n-alkanes with carbon atoms below 12 can all be mutually soluble in supercritical CO2 fluids. If more than 12 carbon atoms, the solubility will decrease sharply. Compared with normal alkanes, isoalkanes have greater solubility
Normal alcohols with less than 6 carbons can dissolve each other in supercritical COz fluid. If the carbon number is further increased, the solubility will decrease significantly. Adding side chains to n-alcohols can appropriately increase solubility just like alkanes.
The solubility of phenol is 3%, and the solubility can be increased when methyl is substituted for phenol. Etherified phenolic hydroxyl will significantly increase solubility4. Carboxylic acidAliphatic carboxylic acids with less than 9 carbons are mutually soluble in supercritical CO2 fluids, while dodecanoic acid (laurel has only 1% solubility. The presence of halogens, hydroxyl groups and aromatic groups will reduce the solubility of aliphatic carboxylic acids
Esterification will significantly increase the solubility of the compound in supercritical CO2 fluid
Simple aliphatic aldehydes such as acetaldehyde, valeraldehyde and heptaldehyde, etc., can dissolve aliphatic aldehydes in supercritical CO2 fluids. The unsaturated structure of aliphatic aldehydes has no obvious effect on its solubility. However, phenyl substitution will reduce unsaturated aldehydes. The solubility of supercritical CO2 fluids.
It occupies an important position in plant mucosal oil and is a key component of various natural fragrances. In the process of supercritical CO2 fluid extraction of natural products such as spices and food, the solubility of terpenoids in supercritical CO2 fluid has a very strong influence. Important practical value.
The relative molecular mass of terpenoids has a certain effect on the solubility. From monoterpene pinene to sesquiterpene phyllene and diterpene pintetraene, the solubility of terpene compounds in supercritical CO2 fluid gradually decreases, and terpene molecules For every 5 more carbon atoms, the solubility drops about 5 times. The reason for this difference may be that as the relative molecular mass increases, the volatility of the compound decreases.
Compared with the influence of relative molecular mass, the polarity of the compound has a greater influence on its solubility in supercritical CO2 fluids. Monoterpene compounds such as camphor, citral, citronellol and 1,8 terpene diol have different Substituents and polarity, although the relative molecular masses are not much different, the solubility is very different. This fully shows that the molecular structure of the solute is a key factor affecting its solubility in supercritical CO2 fluid. The data shows that as the oxygen-containing substituents in terpenoids increase, the polarity of viscous compounds increases, and their solubility in supercritical CO2 fluids decreases sharply.