The latest version of 2020 supercritical fluid extraction entrainer
supercritical co2 extraction entrainer
In the supercritical state, CO2 has a selective dissolution. SFE-CO2 shows excellent solubility for low-molecular, low-polarity, lipophilic, low-boiling components such as volatile oils, hydrocarbons, esters, lactones, ethers, epoxy compounds, etc., like aroma components of natural plants and fruits.
Learn more:What is supercritical co2 extraction systems
For compounds with polar groups (-OH, -COOH, etc.), the more polar groups, the more difficult it is to extract, so the polyol, polyacid and polyhydroxy aromatic substances are difficult to dissolve in supercritical carbon dioxide. For compounds with high molecular weight, the higher the molecular weight, the more difficult it is to extract, and the polymer compounds with molecular weight exceeding 500 are also almost insoluble.
For the supercritical fluid extraction of traditional Chinese medicine propolis for the active ingredients of Chinese herbal medicines with larger molecular weight and more polar groups, a third component needs to be added to the binary system composed of active ingredients and supercritical carbon dioxide to change the original effective The solubility of the components. In the research of supercritical liquid extraction, the third component with changing the solubility of the solute is usually referred to as the entrainer (there are also many literatures that refer to the entrainer as a subcritical component).
Generally speaking, solvents with good dissolving properties are often good entraining agents, such as methanol, ethanol, acetone, and ethyl acetate.
Function and principle:
Because CO2 is a non-polar substance, simple SC-CO2 can only extract lipophilic substances with lower polarity and low-molecular-weight aliphatic hydrocarbons, such as alcohols, ethers, aldehydes, and vinegar.
For the more polar hydrophilic molecules, the extraction effect of metal ions and substances with relatively large molecular weight is not ideal.
In 1989, Yu Enping introduced the use of entrainer in supercritical CO2 extraction. That is, an appropriate entrainer is added during extraction. Such as ethanol, methanol, acetone and so on. Not only improves and maintains the extraction selectivity, but also improves the solubility of hardly volatile and polar solutes.
The use of entrainer enhances the solubility and selectivity of SC-CO2. The entrainer can affect the solubility and selectivity of the solute in SC-CO2 in two ways, that is, the density of CO2 and the interaction between the solute and the entrainer molecule.
Generally speaking, the amount of entrainer in use is small, and it has little effect on the density of carbon dioxide. It even reduces the density of SC-CO2. The determinants that affect solubility and selectivity are the van der Waals force between the entrainer and the solute molecules or the specific intermolecular interaction between the entrainer and the solute, such as hydrogen bonding and other various forces.
For example, supercritical CO2 extracts heavy metals. The heavy metal ions have a positive charge and have a strong polarity, which makes the van der Waals force between the heavy metal ions and SC-CO2 very weak and difficult to directly extract. The generally adopted method is to select a negatively charged entrainer (also referred to herein as a metal complexing agent) to neutralize the positive charge of the metal ions. Due to the coordination derivative effect, the polarity of the neutral complex has been greatly reduced. Combined with another polar entrainer. Enhance its solubility in SC-CO2 for extraction. In addition, near the critical point of the solvent, the solute solubility is most sensitive to changes in temperature and pressure.
After the entrainer is added, the research of supercritical fluid extraction technology can make the critical point of the mixed solvent change correspondingly, which is closer to the extraction temperature. Enhance the sensitivity of the solute solubility to temperature and pressure, so that the separated components can be greatly reduced in solubility under the condition of constant operating pressure, and separated from the circulating gas to avoid the high energy consumption of gas compression.
Entrainers also play a very important role in supercritical CO2 microemulsion extraction technology.
Supercritical CO2 microemulsions are formed by dissolving a suitable surfactant (SAA) in SC-CO2. Because the solubility of SC-CO2 to most SAAs is limited, the formation of supercritical CO2 microemulsions is difficult. Adding an entrainer (mostly an alcohol containing 3 to 6 carbon atoms) can not only increase the solubility of SAA in SC-CO2, but also can be used as a co-surfactant to facilitate the formation of supercritical CO2 microemulsions. Supercritical CO2 microemulsion extraction technology has made great achievements in the extraction of bioactive substances and metal ions, and has a very broad development prospect.
select:The selection of entrainer is a more complicated process, which can be summarized as follows:Fully understand the nature of the extract and the environment in which it is extracted. The properties of the extract include molecular structure, molecular polarity, molecular weight, molecular volume, and chemical activity. It is also necessary to know the environment of the extract, which can guide the choice of entrainer. For example: DHA is distributed in low-polarity glycerolipids, medium-polar galactose esters, and very polar phospholipids, and is mainly present in polar lipids, so to extract DHA, various polarities must be extracted. The lipid composition can in turn determine the appropriate entrainer.
Pre-selection of the entrainer based on the nature of the entrainer (molecular polarity, molecular structure, molecular weight, molecular volume), the nature of the extract and the environment in which it is extracted. For acids, alcohols, phenols, esters and other extracts, an entrainer containing the -OH, C = 0 gene can be selected; for extracts with a greater polarity, a more polar entrainer can be selected.
⑶ experimental verification. The determining factors are the entraining effect of entrainer (taken by pure CO2 extraction) and the selectivity of the entrainer, which are collectively called the entrainment effect of the entrainer. Zang Zhiqing et al. Introduced this in detail in a screening study of supercritical CO2 extraction of red pepper entrainers. For the selection of entrainer, it is necessary to master the phase change and phase equilibrium of the extraction conditions. Supercritical fluid extraction machine. However, the experimental determination in this way is more difficult, and there are not many relevant publications and introductions. In addition, while the entrainer improves the solubility of SC-CO2, it will also weaken the capture effect of the extraction system, leading to the increase of co-extracted substances, and may also interfere with the analytical determination. % mol.
(4) Supercritical CO2 extraction technology has been widely used in the fields of biology, medicine, food, etc. Therefore, entrainers in these areas must also meet the requirements of low cost, safety, and medical food hygiene.
Existing problems and development direction:
The introduction of the entrainer has given the wider application of supercritical CO2 extraction technology, and also brought two negative effects.
This is because the use of an entrainer increases the difficulty of separating and recovering the entrainer from the extract. And because of the use of entrainer, some extracts have residual entrainer. This loses the advantage of no solvent residues in supercritical CO2 extraction.
Industry has also increased difficulties in designing, developing and operating processes. It is necessary to study these further. Because of the different extracts, different extraction systems, the type, amount and effect of the entrainer will be different, so the development of new, easy to separate and harmless entrainer, and study its mechanism of action is the direction of future research one.