Why co-solvents are used in CO2 extraction processes
Does CO2 extraction use solvents?
Advantages of using co-solvents in the CO2 extraction process
Taking the extraction of effective components from Andrographis paniculata as an example to illustrate the advantages of the supercritical CO2 extraction process using a co-solvent. Studies have shown that andrographolide and dehydroandrographolide are the effective components of andrographolide, both of which are diterpene lactones. However, andrographolide and dehydrated andrographolide are unstable under heat and are easily damaged during the traditional alcohol extraction pharmaceutical process.
pure CO2 extraction process VS ultrasonic ethanol extraction and cold extraction with ethanol
Supercritical pure CO2 extraction has the lowest yield, only 1/10 of other extraction methods; when using 95% ethanol as a co-solvent, operate according to optimized process conditions (extraction pressure 25MPa, extraction temperature 40 ° C, extraction time At 4h, the amount of co-solvent is 1/2 of the raw material), the rate of extracting andrographolide (8.3%), the content of andrographolide (19.79%), and the content of dehydrated andrographolide (12.27%) are much higher than the traditional extraction method, and the product quality is stable and the drug effect is high, and all the indicators are better than the original solvent method.
Although the ultrasonic ethanol extraction method and cold extraction with ethanol have better extraction results, the amount of solvent treatment is large and the solvent loss is large.
The following table compares the effects of different extraction methods on Andrographis paniculata.
|Extraction method||Extraction rate /%||Andrographolide content /%||Dehydrated andrographolide content /%|
|Ultrasonic ethanol extraction||5.05||10.17||3.43|
Effect of different extraction methods on Andrographis paniculata
Advantages and Disadvantages of using co-solvents in the CO2 extraction process
The supercritical CO2 extraction process using co-solvents can broaden the application range of supercritical extraction, especially when the extracted components have little solubility in supercritical solvents or require highly selective extraction.
The SFE process using a co-solvent not only improves the solvent’s ability to extract solutes and reduces the amount of solvent required, but also greatly reduces the required pressure.
However, the disadvantage is that the co-solvent complicates the separation of the solute from the solvent and requires the addition of a special recovery system, such as the use of operational 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.
why and how are co-solvents sometimes used in CO2 extraction processes?
A small amount of a co-solvent increases the ability of supercritical carbon dioxide to dissolve polar compounds. Neat supercritical CO2 has to dissolve properties similar to hexane. This means that, by itself, carbon dioxide is very good for dissolving relatively non-polar materials. The addition of just a small quantity of co-solvent enhances the solubilizing power of the supercritical carbon dioxide, making it possible to extract much more polar molecules. Typical co-solvents include methanol, ethanol, and water.
A liquid co-solvent can be added to CO2 to increase its solvent power on polar molecules.
By adding a polar or medium polar co-solvent (ethanol or light alcohols, esters, or ketones) in the right percentage and for a correct and pre-determinated time during the extraction, it is possible to fine-tune total polarity of the supercritical solvent.
Entraining agents have different properties than supercritical CO2. The critical point (CP) of CO2 is 73.8 bar and 31.5° C; ethanol’s CP is 63 bar and 241° C. A mathematical description requires computational chemistry to show how the entraining agents interact with the CO2. Suffice it to say, CO2 will be in the supercritical phase and the entraining agents will be in the liquid phase. This changes the solvent characteristics of the CO2 and improves extraction yields.