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Is the supercritical CO2 extraction technology marvelous, gorgeous, splendid and posh?

It is estimated that manyaromatherapy enthusiasts have heard of supercritical CO2 extraction technology.It feels very high when they hear it. There is a feeling of high-tech bursting.Is there wood? But are you sure you really understand what supercritical fluidextraction technology is?

Supercritical Fluid Extraction (SFE),the full name of Super Critical Fluid Extraction, refers to fluids abovecritical temperature and critical pressure.

When the fluid is in a supercriticalstate, it has unique physicochemical properties, combining the advantages ofgas and liquid: low viscosity (approximating gas), high density (close toliquid), and diffusion coefficient is several tens or even hundreds of timesthat of liquid. It has amazing solubility, can dissolve insoluble or slightlysoluble compounds in general solvents, and has strong selective solubility fororganic compounds. Especially in the supercritical region, the solubility oforganic compounds in SCF is highly correlated with the density of the fluid.Small changes in temperature and pressure can cause changes in fluid density,causing changes in the solubility of the compound in SCF. People control thedensity of the fluid by adjusting parameters such as temperature and pressure,so as to achieve the purpose of selecting the crude compound by SCF.

Everyone knows that matter has threestates, solid, liquid, and gaseous. For example, water, ice-solid,water-liquid, water vapor-gaseous.


CO2 also has three states. Theconversion between the three states is mainly related to temperature andpressure, the temperature drops low enough, and CO2 can become liquid or evensolid. It is also possible to compress CO2 into a liquid with a strong pressure,such as a dry ice fire extinguisher, which compresses CO2 into a liquid stateand stores it in a steel cylinder by a strong pressure.


When you talk about it, everyoneshould be able to understand it. Here, what is the meaning of a criticaltemperature concept? The critical temperature is the highest temperature atwhich the gas changes to a liquid state. That is to say, beyond this problem,no matter how strong the pressure you use, the gaseous substance cannot beconverted into a liquid state, even if you use the power of the wild, even ifyou are a superman, a hulk, iron Man……


The critical temperature of CO2 is31.1 °C, and the critical pressure is 7.37 MPa, because whenthe temperature exceeds 31.1 ° C and the pressure is higher than 7.37 MPa, CO2is in a supercritical state. In this state, CO2 is both liquid and gaseous, andthe fluid has the dual characteristics of gas-liquid two phases. It has highdiffusion coefficient and low viscosity comparable to gas, and has similardensity to liquid and good solubility to materials. You can think ofsupercritical CO2 as a very heavy gas floating in the air... The density ofthis supercritical carbon dioxide is hundreds of times that of carbon dioxidegas! !


Moreover, CO2 as a solvent has thefollowing advantages:

(1) CO2 is non-toxic, odorless,non-flammable, and inexpensive and readily available.

(2) The critical temperature of CO2is 31.1 ° C, which is close to normal temperature. Under suchlower temperature conditions, the loss of volatile components in heat-sensitiveflavor plants is small, and the oxidation reaction can be controlled to aminimum.

(3) The separation of the solute andthe solvent does not require the use of a conventional distillation operation,and can be easily carried out under reduced pressure, thereby avoiding thedecomposition change of the heat sensitive substance due to heating andconcentration.

(4) The finished product is not easyto deteriorate during storage, and the gas released from the evaporator can berecycled and recycled, and is environmentally friendly.


I believe many people see this, butthey also seem to understand. It’s good to watch it twice, because it’s easierto understand.

Supercritical CO2 looks socomplicated, how good is it? Here, the shopkeeper must first say that thesupercritical CO2 extraction technology is not as advanced as it is. Thistechnology has been in existence for more than 40 years and should be regardedas an old technology. The construction cost of supercritical extraction is onlyhigh, and the investment cost is very high. Generally, the production of smallbatches does not have much value and significance.


Benefits of supercritical CO2extraction

The special properties ofsupercritical CO2 make supercritical CO2 fluids ideal for the extraction offat-soluble volatile oils, pastes, resins and heat sensitive products innatural plants. Its near-normal temperature operating temperature can retainalmost all natural aroma components, so the product has a good natural aroma,pure aroma and high yield, which is much better than the traditional extractionmethod.

Specific to the extraction of roseessential oil, supercritical CO2 extraction of rose essential oil, due to thelower temperature, avoiding the decomposition of heat-sensitive components causedby high temperature during steam distillation, and possible hydrolysis andwater dissolution The loss of ancestral points. That is to say, there are someingredients in the rose essential oil that will decompose or dissolve into thewater, resulting in the loss of some ingredients. This is not the case with theCO2 extraction method, so that the extracted essential oil is closer to thetaste of the natural flavor itself.


Figure 2  Laboratory supercritical extraction device

1, high pressure valve; 2, pressure gauge; 3, sapphireobservation port; 4, cooling tube; 5, pressurized cylinder; 6, siphon glassextractor; 7, glass storage tank; 8, constant temperature water bath

Disadvantages of supercritical CO2extraction technology

However, supercritical CO2 extractiontechnology is also disadvantageous. The extraction rate of Damascus roseessential oil extracted by distillation is about 0.03%, and the extraction rateof supercritical CO2 extraction can reach 0.1% or even 0.2%. (The dispenserscan see that the extraction rate of the literature can reach 0.7%. I don’t knowHow much wax is extracted from the rose), it can be said that the supercriticalCO2 extraction rate is 3 to 5 times that of the distillation method. So, haveyou ever wondered why the extraction rate of supercritical CO2 can be so high?

This is because the rose essentialoil extracted with supercritical CO2 contains a part of the wax with highboiling point and strong non-polarity. Their presence increases the weight ofthe rose essential oil, increases the freezing point of the rose essential oil,and lowers the rose essential oil. Volatility. The aroma of the essential oilis weakened and an unpleasant odor is added, which degrades the quality of theessential oil.

Figure 3  Flow chart of laboratory supercritical CO2extraction

1. Carbon dioxide gas cylinder; 2. Pressure gauge; 3.Carbon dioxide compressor; 4. Cooling unit; 5. Intake valve; 6. Constanttemperature extractor; 7. Exhaust valve; 8. Temperature controller; ; 10, microvalve; 11, collection bottle; 12, flow meter; 13, gas flow meter


Therefore, one of the disadvantagesof SFE technology is that it is impossible to obtain a product with highpurity. This requires that the SFE extraction technique must be combined withother separation and purification techniques to repurify the supercriticalextraction product to obtain a highly pure product.

Specific to the supercritical CO2extraction technology of rose essential oil, in order to obtain high-purity,high-quality rose essential oil, it is necessary to refine the waxy rose oil.The traditional dewaxing treatment method is to extract the crude essential oilby using an organic solvent such as ethanol, petroleum ether or diethyl ether,and then to freeze it for a certain period of time in a low temperatureenvironment, and finally concentrate under reduced pressure to recover anorganic solvent to obtain a purer rose. Essential oils. Using this method toobtain rose essential oil can remove waxy well, but when concentrated and concentratedby distillation, it is easy to cause rearrangement, oxidation, hydrolysis,polymerization and other reactions of molecules due to high temperature,resulting in changes and destruction of plant essential oil components; Thecolor of the essential oil is heavy and the aroma is rough, and at the sametime, the solvent may remain, which has a great influence on the quality of theessential oil.

In addition, there are still someproblems in the application of supercritical carbon dioxide extraction technologyin the industrial scale application of rose essential oil extraction. Firstly,the carbon dioxide is close to liquid pentane, which is suitable for theextraction of lipophilic compounds. In addition to a large number of oilycompounds, rose essential oils have many A polar alcohol is present, and thecomponents of the supercritical extract are still different from the rose.


In addition, the industrializationinput cost of supercritical CO2 extraction is very high, and an industrialsupercritical extraction production line has to be invested by tens ofmillions. The output of rose essential oil itself is very low, so under normalcircumstances will not make ends meet.

Industrialized supercritical CO2 extractiontechnology is currently mainly used in products with relatively largeproduction volume. Supercritical fluid extraction technology is used for earlylarge-scale industrial application of decaffeination of natural coffee beans;the other is supercritical CO2 extraction technology. Extract hops. At present,some Chinese herbal medicine active ingredient extraction has also begun to usethis technology.