plc controlled experimental supercritical fluid_extraction equipment

Supercritical co2 extraction using an entrainer

What is supercritical co2 extraction systems

  • Extension of supercritical carbon dioxide extraction technology


    In order to further improve the extraction ability and selectivity of target solutes by CO2, researchers have studied various ways to expand the supercritical CO2 extraction technology, so that the application range of the supercritical extraction technology has been expanded.

  • Supercritical co2 extraction process using entrainer


    However, the disadvantage is that the entrainer complicates the separation of the solute from the solvent and requires the addition of a special recovery system, such as the use of operation units such as evaporation and rectification.It is far less simple than using a single SCF process. The advantages and disadvantages of the method are determined.

  • Supercritical co2 extraction using an entrainer

  • Supercritical extraction of CO2 as a single medium


    In SFE technology, supercritical CO2 extraction using CO2 as the extraction medium is the most widely used.

    Supercritical fluid extraction with CO2 as a single medium is mainly used for lipophilic, non-polar materials with small molecular weight, which is mentioned in the solubility rules and Compounds that are miscible or highly soluble with supercritical CO2. If the components contained in the raw materials belong to the mentioned compounds, it is difficult to extract and remain in the raffinate.

  • 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:

  • The latest version of 2020 supercritical fluid 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.

  • Supercritical fluid extraction separation technology


    Supercritical fluid extraction is a new type of extraction and separation technology.

    It uses a supercritical fluid, that is, a fluid in a thermodynamic state at a temperature higher than the critical temperature and a pressure higher than the critical pressure, as an extractant. Extract specific components from liquid or solid to achieve the purpose of separation.

    The characteristics of supercritical fluid extraction are: the extractant is a gas at normal pressure and room temperature, and it is easy to separate from the raffinate phase and the extraction group after extraction; it operates at a lower profitability, and is particularly suitable for the separation of natural substances; it can adjust the pressure , Temperature and attractive entraining agent can adjust the dissolving ability of the transboundary fluid, and can gradually extract the components into the desired product through the gradually density and temperature and pressure.

Supercritical carbon dioxide extraction using an entrainer

Soy lecithin deoiled in supercritical CO2 fluid using ethanol as entrainer

Soy lecithin deoiled in supercritical CO2 fluid using ethanol as entrainer

Non-polar CO2 can only effectively extract non-polar lipophilic substances of starch derivatives, and selectivity. In order to improve the extraction ability and selectivity of target solutes by CO2, add an appropriate amount of non-polar or polar solvents to utilize co-solvents. Is an effective way to extend the application range of wide supercritical CO2 extraction technology. Co-solvents are also called entrainers (entrainers) or modifiers (modifiers).

The role of entrainers

The role of the entrainer has two main points:

First, it can significantly increase the solubility of the separated components in supercritical fluids;

Secondly, the selectivity (or separation factor) of the solute can be significantly improved when an appropriate entrainer that plays a specific role with the solute is added.

Entrainers can be divided into two categories:

One type is miscible supercritical solvents, where the smaller content is considered as an entrainer.For example, the separation of heavy oils often uses two or more C3 ~ C3 light hydrocarbon mixtures.The synergy between the solvents makes the mixing Solvents are better than single solvents.

The other type is to add subcritical organic solvents to pure supercritical fluids. Depending on the amount of addition, they may form a single-phase miscible supercritical mixed fluid, or they may be entrained by the supercritical fluid. A mixed solvent of two phases, but the latter case is generally undesirable.

Entrainers can affect the solubility and selectivity of solutes in supercritical gases in two ways:

One is the density of the solvent;

The second is the interaction between solute and entrainer molecules.

In general, the addition of a small amount of entrainer has little effect on the density of the solvent gas, and the determining factor affecting solubility and selectivity is the Van der Waals force between the entrainer and the solute molecules or the specific intermolecular between the entrainer and solute Role, such as the formation of hydrogen bonds and other various chemical forces. In addition, after adding an entrainer, the critical point of the mixed solvent will change accordingly.

Some commonly used solvents are often used as entrainers of CO2 for research. They can form a homogeneous miscible state with CO2 under moderate pressure and room temperature conditions.

For example, when polar solvents with high solubility parameters, such as methanol, ethanol, and acetone, are used as entrainers and added to CO2, not only the continuous tunability of the fluid solubility parameter δ can be maintained, but also the δ value of the mixed fluid is improved; Because a special molecular force (such as Lewis acid-base force, hydrogen bonding force, association force, etc.) may be formed between the polar solute and the polar co-solvent, the solubility and selectivity of the solute are enhanced.

 Use and selection criteria of entrainer

There are two ways to add an entrainer:

The first is to directly add the entrainer to the raw material, and then pass the supercritical fluid (such as CO2) and maintain a certain contact time under constant temperature and pressure conditions, which is called the static method

The other is that the supercritical fluid and the entrainer are mixed by a high-pressure metering pump at a certain ratio and flow into the extraction device at a suitable flow rate to contact the raw materials.

Studies have shown that when the binding effect of the raw material matrix on the solute is the first influencing factor, the static method is effective. The infiltration of the raw material by the entrainer is beneficial to the release of the component to be extracted; and when the solubility of the component to be extracted in the supercritical fluid is The main influencing factor is that the continuous method of dynamic method will produce better extraction effect than the static method. The combination of the two is also common in the literature.

The choice of entrainer should consider three aspects:

First, in the extraction section, the interaction between the entrainer and the solute is required to improve the solubility and selectivity of the solute;

Second, in the solvent separation section, the entrainer and the supercritical solvent should be able to be separated easily, and the entrainer and the target product should also be easily separated;

The third is to consider that the residue of the entrainer will not cause product pollution. The specific selection can refer to the selection method of the extractant during the solution extraction, or consider from the aspects of solubility parameters, Lewis acid-base dissociation constant, and changes in the absorption spectrum after the action of the entrainer with the solute

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