5 key points of supercritical co2 extraction of essential oil


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Video of supercritical fluid extraction of rose essential oils

What is supercritical CO2 extraction of essential oils?

The whole essential oil extraction process of supercritical co2 fluid is carried out in a closed reaction tank, and the time required is very short.

The supercritical CO2 extraction method of essential oils is referred to as SFE. In short, CO2 oil extraction is extracted by pressurized CO2 until it becomes a critical point in a liquid state. The liquid carbon dioxide then acts as a solvent to obtain natural plant matter and volatile oil content and dissolve the carbon dioxide in the liquid. Then, the CO2 is brought back to natural pressurization, the carbon dioxide evaporates back to its gaseous state and what remains is the resulting oily substance.

Material pretreatment

The main factors affecting the CO2 extraction process effect in the pretreatment process are the moisture content and particle size of the material.

Different extraction materials require different pretreatment methods. For example, when extracting fresh flavor substances such as ginger, garlic, onion, etc., it only needs to be peeled, cut into pieces, or extracted directly after juice extraction.
And the frankincense Pistacia Chinensis, cardamom, black pepper, etc., will be roasted, crushed, and other processing. The main factors affecting the CO2 extraction effect in the pretreatment process are the water content and particle size of the material.

Next, the plant material is processed to specified particle size and moisture content and placed in an extraction vessel. Carbon dioxide is subjected to high pressure and specific temperatures. The pressure and temperature variations put the CO2 into a supercritical state. It then flows through the biomass in the extraction chamber.

Supercritical CO2 pulls more compounds faster from the biomass.

co2 extraction machine
supercritical co2 extraction machine

CO2 density

The extraction conditions are generally between 8.0MPa~12.0MPa and 35℃~50℃. It is well known that under higher CO2 density (such as 40℃ and pressure higher than 20.0MPa), SC-CO2 exhibits strong solubility and lower selectivity. In fact, the increase in extraction rate under high-density CO2 is mainly due to the increase of surface wax and other undesired components. 
Under the condition of CO2 density lower than 0.6g/cm3, it is possible to extract as many essential oil components as possible, and other non-volatile components except surface wax will not be extracted. When the CO2 density is too high, such as higher than 0.85g/cm3, not only does the extraction rate decrease but also the technical difficulty is caused by the increase in the extraction amount of waxes and triglycerides.

The density and dielectric constant of supercritical fluid is large, and the solubility of substances is also large, and it changes rapidly with the change in temperature and pressure.

Therefore, it has strong solubility and selectivity for certain substances, and the solvent and extract are easily separated at room temperature.

The dissolving ability of supercritical fluid is proportional to its density. Near the critical point, if the pressure changes slightly, its density will have a relatively large change. Therefore, for many solid or liquid solutes, if the solute and the solvent are not infinitely miscible, the dissolving ability of the supercritical fluid is obviously related to the pressure. Under different pressures, the range of extracts is different. When extracting low-molecular-weight essential oils (aromatic components) under low pressure, the range of extractable substances expands with the increase of pressure, but the two are not linear. When the pressure increases to To a certain extent, the solubility increases slowly.

Extraction time

When determining the CO2 extraction time, the relationship between the equipment energy consumption and the extraction rate should be comprehensively considered. It is not necessary to select the limit time and a single CO2 extraction method but should choose the best time and method that can economically balance the energy consumption of the system way.

Under normal circumstances, when the flow rate is constant, at the beginning of the extraction, because the supercritical CO2 fluid and the solute have not reached a good contact, the extraction amount is small, with the extension of the extraction time, the mass transfer reaches a good state, and the extraction amount per unit time increases until Its maximum value, the corresponding time is the limit time of extraction. After that, the CO2 fluid extraction rate gradually decreased due to the decrease in the content of the components to be separated in the extraction object.

cosolvent pump of co2 extraction machine
cosolvent pump of co2 extraction machine

Co-solvent

Certain food-grade, GMP-compliant solvents’ affinities with important compounds in essential oil can also be used as a modifier to help the CO2 extraction process deliver a full spectrum of plant extract. The end result, after solvent recovery and evaporation of carbon dioxide, is a rich essential oil.

Co-solvent, also known as entrainer. The addition of a small amount of it can significantly change the phase behavior of the supercritical CO2 fluid system, especially it can increase the solubility of some substances that have little solubility in the supercritical CO2 fluid, and can also reduce the operating pressure, reduce the amount of supercritical CO2 fluid.

  • Adding 3% ethanol or methanol to egg yolk powder can more than double the solubility of egg yolk lipids at 36MPa and 40℃;
  • When extracting peanut oil and pepper oil, adding 10% ethanol at 34.5MPa and 60℃ can increase the yield by 230% compared with that without adding it, and adding 10% ethanol at 20.7MPa and 60℃ can increase the yield to 750%.

separate

The supercritical CO2 extraction and separation of fennel oil adopt two-stage separation. Under different separation conditions, the yields of the two products depend on the pressure of the first separator, but the pressure adjustment of the first separator has a certain range. If it is too high, fats, lipids, and pigments cannot be deposited in the first separator, which will lead to the inclusion of these three types of substances in the second separator, thus losing the advantages of fractionation.
Reasonable adjustment of the process parameters of the separator is the key to achieving the purpose of separating different substances.

After the extraction process, the density of the supercritical CO2 fluid must be reduced to selectively separate the extract in the separator.

To implement this separation, there are generally three adjustment methods, constant pressure-temperature increase or constant temperature pressure reduction, or pressure reduction and temperature increase. The specific optimal operating conditions must be obtained through specific experiments.

With different separation pressures, the chemical composition of the extracts will also be different. For extracts that do not perform well with single-stage separation, two-stage or even multi-stage separation should be considered.

Advantages and Disadvantages of CO2 extraction

Advantages


Compared with the solvent extraction method, the supercritical CO2 extraction method of essential oils does not have any solvent residue.

CO2 extracts usually smell thicker than distilled essential oils and often smell closer to natural grass. Carbon dioxide extract has been said to contain additional components than those extracted from the same plant using steam distillation. This seems to make sense because carbon dioxide extracts are usually thicker oils and often seem to have a more comprehensive aroma.

This method is a highly specialized extraction method. Due to the volatilization of the solvent, the essential oil contains no solvent impurities and the separation is relatively thorough. The extracted molecules can be larger than those extracted by distillation. There is a situation that needs to be explained. The distillation method uses steam to bring out aromatic molecules, but larger molecules cannot be extracted, such as the diterpene molecules in clary sage. This is already the limit, that is to say, It is rarely seen that terpenes with three carbon atoms are extracted by distillation.

co2 essential oil extraction equipment
co2 essential oil extraction equipment

Disadvantages

Of course, some people questioned that carbon dioxide is an acid gas, so this extraction method will more or less destroy the chemical structure of essential oils.

Although the plant essential oil extracted in this way will be very close to the original composition of the aromatic substances in the plant, it is a quite perfect extraction method. However, the equipment used in this extraction method is not only huge but also very expensive. Using it to extract essential oils often takes several years to balance the cost. To this day, the price of essential oils extracted with supercritical carbon dioxide is still very expensive.

Surprisingly, this approach to nature is not necessarily good. Take ginger as an example. The scent of ginger essential oil extracted with supercritical carbon dioxide is naturally better than that of distilled ginger essential oil, but it is also easy to irritate sensitive skin. In addition to the high price, the essential oil extracted by supercritical carbon dioxide has another drawback, that is, few manufacturers are willing to provide it, and it is not easy to buy.

What are the top 4 benefits of supercritical co2 extraction?

CO2 extraction delivers a pure essential oil

In the health, nutraceutical, and personal care markets, consumers value product purity. co2 oil extraction methods create essential oils that deliver on purity promises by eliminating harmful solvent residues and reducing unwanted compounds in the finished product.

CO2 is a highly “tunable” solvent, enabling extraction experts to target specific, desirable botanical compounds.

Unlike hydrocarbon solvents, supercritical co2 can be fine-tuned by adjusting temperature and pressure to achieve variable density, viscosity, and surface tension. this makes processing quicker and more efficient while also targeting only the desired compounds in the plant biomass.

Carbon dioxide is recoverable and nontoxic, making it environmentally friendlier than other solvents, and a safer, non-toxic choice.

You may be wondering: is co2 extraction safe? the carbon dioxide used for essential oil extraction is recovered, collected, and recycled, and it leaves behind no chemical solvent residue. this is not only an important consideration from an operational and environmental standpoint; it can also support specific “green” brand attributes that are often associated with hemp products.

The efficiency of co2 extraction can eliminate some post-processing steps.

Carbon dioxide-based methods not only extract more botanical compounds faster but also eliminate the need for some post-processing steps. this gets your essential oil into final products — and on its way to the shelf.

And when your toll processing partner can provide testing and analysis, formulation, and blending, as well as bottling, packaging, and logistics, your high-value essential oil products can quickly make their way to your consumers.

What is supercritical fluid extraction?

Using supercritical fluid as a solvent to selectively dissolve solutes in liquid or solid mixtures, supercritical fluid extraction as a new separation technology has developed rapidly in the past 20 years.

Supercritical fluid not only has high permeability and low viscosity comparable to gas but also has a density similar to liquid and excellent dissolving ability to substances.
Compared with traditional steam distillation and solvent extraction, supercritical fluid extraction is a new separation technology with many advantages.

Application

Supercritical fluid extraction technology was first industrially applied to decaffeinate natural coffee beans and to extract hop oil from hops. In the past 10 years, great progress has been made in the theoretical basis and application development of supercritical fluid extraction technology.

  • Supercritical fluid extraction technology has been applied to the extraction of special oils, seasonings, spices, and natural pigments;
  • Unsaturated fatty acids with high nutritional value and medicinal value can also be extracted from fish oil;
  • It is used to remove fat from fried food and cholesterol from milk fat and egg powder;
  • It is used for softening, decolorizing, and deodorizing alcoholic beverages.