Due to the non-polar nature of pure CO2, its application range is greatly limited.
The solubility of grease in supercritical CO2 fluid is generally low. In order to improve the solubility, you can consider adding a co-solvent.
Adding a co-solvent can increase the extraction rate or improve the selectivity, and effectively reduce the extraction pressure. According to literature reports, when the mass fraction of the co-solvent reaches 10%, the oil extraction rate can be increased to about 97%.
When supercritical CO2 was used to extract γ-linolenic acid from Mortierella, 10% methanol was used as a co-solvent to increase the extraction rate by 4 times, and the operating pressure was reduced from 38.3 MPa to 13.4 MPa.
Amount of co-solvent
However, the amount of co-solvent must be relative to the CO2 flow rate, which often has an optimal value, too large or too small is not good.
It needs to be pointed out that a good solvent is also a good entrainer compared to the solute.
Recommended supercritical CO2 extraction co-solvent for vegetable oils
In order to avoid residual organic solvents in oil extraction, ethanol is often used as a co-solvent.
Ethanol is a polar substance with strong nucleophilic addition properties. It can easily provide a pair of electrons to combine with the positively charged carbonyl carbon, increasing the polarity of the solvent CO2, and at the same time increasing the polarity of the oil to be extracted. The separation factor of the entire system is increased, thereby increasing the extraction rate.
CO2 flow flow affects the CO2 extraction of vegetable oils
The change of CO2 flow rate has two effects on supercritical CO2 fluid extraction.
On the one hand, the increase in CO2 flow rate can increase the mass transfer driving force of the extraction process, and correspondingly increase the mass transfer coefficient, so that the mass transfer rate is accelerated, and the equilibrium solubility is reached faster, thereby increasing the extraction capacity and shortening the extraction time;
On the other hand, if the CO2 flow rate is too large, it will increase the CO2 flow rate in the extractor and shorten the CO2 residence time, thereby reducing the time for CO2 to contact the extract, which is not conducive to the improvement of the extraction rate and increases the production cost.
Therefore, the CO2 flow rate has an optimal value in extraction. Generally, when the oil content of the raw material is high, the large CO2 flow rate is beneficial to the extraction. But in fact, CO2 flow is not easy to control during operation.