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CO2 Essential Oil Extraction: 10 Most Frequently Asked Questions

What are Essential Oils?

Essential oils are simply highly concentrated organic compounds extracted from the seeds, leaves, flowers, bark, roots, or fruits of plants and trees. They are natural oil that is obtained through distillation. It has the characteristic fragrance of the herb, flower, or plant from which it has been extracted. They are also known as ethereal oils, aetherolea, and volatile oils. It is called “essential” since it has the “essence of” the plant or herb’s fragrance and it can be over 75 times more potent than their source material (for example, it takes roughly 16 pounds of peppermint leaves to make a single ounce of peppermint essential oil!)

How to extract essential oils?

Extraction separates oils and waxes from botanical plant materials. This can be accomplished mechanically or through solvent-based methods with CO2, steam, ethanol, or butane/propane:

Mechanical extraction methods don’t require special equipment but can require more labor, time, and manual processes to extract the oil.
Solvent-based extraction processes require specialized equipment that utilizes a solvent to extract the oil. Common solvents are CO2, ethanol, butane, or propane.

What Essential Oil Extraction Equipment do You Need?

CO2 Essential Oil Extraction: 10 Most Frequently Asked Questions

The extraction methods of essential oils from different types of plants are different. There is no absolutely correct extraction method, only appropriate extraction techniques.
The following is an introduction to the four extraction methods:

Steam distillation

The desired plants are placed in a large Still and then steam is infused. The steam seeps through the plants and then vapor rises to be captured in a condensation chamber. This vapor will then return to its liquid form and the oil can be separated from the water as oil rises. The technology can be quite basic or be scaled up to industrial sizes depending on the need.

Solvent extraction

This solvent (ethanol, or butane/propane) essentially is injected into a chamber housing the plants and then the chemical reaction produces something oddly named concrete.

CO2 extraction

CO2 Extracts are produced by using a method known as supercritical carbon dioxide extraction.
Using specialized CO2 supercritical extraction equipment, however, carbon dioxide can be pressurized until it achieves a fascinating state where it’s simultaneously a liquid and a gas. This is known as its supercritical state. The carbon dioxide that has reached the supercritical state is able to act as a superior solvent that can dissolve the natural components present in the botanical material that is exposed to the supercritical CO2 inside the specialized equipment used for this purpose.
Afterward, the CO2 is brought back to natural pressurization, and the CO2 returns to its normal gaseous state. What remains is the resulting natural CO2 Extract.

Maceration

The Essential Oils can also be extracted through a process called maceration. The plants are crushed or ground into a fine powder and then placed in a closed vessel. A solvent called menstruum is then added and then the mixture is left to sit for a week, being shaken occasionally until the right infusion has been achieved. It is then filtered for use. This again is quite a simple process and can be tried at home. You only need the most basic of technology which you can either devise yourself if you are creative or source from the internet.

The truth is that essential oil extraction can be accomplished with a wide range of processes and equipment. Only a partner with deep expertise can help you select the equipment that can enable you to get high-quality products to market efficiently and profitably.

What are the pros and cons of each essential extraction process?

Ethanol extraction offers higher throughput compared to CO2 and hydrocarbon systems; it’s perfect for making distillates and isolates at scale. The method removes terpenes, which add flavor and aroma to the extract.

CO2 extraction has a lower throughput than ethanol but utilizes an inert gas for processing, as opposed to a liquid solvent or explosive gas. The carbon dioxide allows the processor to capture terpenes prior to extraction for later use. CO2 raw extract requires a fair amount of post-processing to remove lipids, fats, and waxes, but this can be repurposed into topical ointments. The gas does operate off at high pressures and varying temperatures but without volatile compounds. As such, it does not require a control zone.

The difference between traditional distillation and supercritical CO2 extraction is that instead of heated water or steam, CO2 is used as a solvent in the latter method. The supercritical extraction process operates at temperatures between 95 to 100 degrees F whereas steam distillation operates at temperatures between 140 to 212 degrees F.

Butane/propane extraction also has a lower throughput than ethanol but enables the processor to capture all essential oil and major terpenes in one operation.

Steam distillation vs CO2 extraction

In steam distillation, the molecular composition of both the plant matter and the essential oil are changed due to the temperature applied. On the other hand, a CO2 extract is closer in chemical composition to the original plant from which it is derived, as it contains a wider range of the plant’s constituents.

The steam distillation process can generally extract all the terpenes in a single round with a single distillation chamber. It can be scaled into a larger industrial operation with ease. Since the process does not use any solvents, it preserves the natural terpenes in the product while reducing the chances of contamination.
Steam distillation may not work for all plants – Since the specimens will be exposed to high temperatures, not all plants may be able to handle such a range, especially delicate ones.
Due to the high temperature, there can be degradation of certain fragile molecules and terpenes. Some of the terpenes can also be lost in the water fraction. The process requires high energy usage, contributing to the overall operational cost.

What is the Difference Between CO2 Select Extracts and CO2 Total Extracts?

When you shop for CO2 Supercritical Extracts, you should come across extracts that are described as being either a CO2 Select Extract or a CO2 Total Extract. The difference between Select and Total CO2 Supercritical Extracts can be important.

CO2 Select Extracts

To create a CO2 Select Extract, low pressure is used during the extraction process. CO2 Select Extracts generally contain the volatile (aromatic) components of the botanical that are soluble in liquefied CO2. Aromatic molecules each have their own molecular weight. Some aromatic molecules are too heavy to be present in a steam-distilled essential oil. However, some of the heavier aromatic molecules are present in CO2 Select Extracts. Therefore, CO2 Select Extracts often smell closer to the aroma of the natural herb than do some steam distilled essential oils.

CO2 Total Extracts

To create a CO2 Total Extract, much greater pressure is used. CO2 Total Extracts contain all (or most all) of the molecules that are soluble in supercritical CO2. CO2 Total Extracts tend to be much thicker than CO2 Select Extracts as they typically contain both the volatile aromatic CO2 soluble constituents, and they also contain the natural lipids, waxes, and other CO2 soluble molecules present in the botanical. For information on working with thick essential oils and CO2 Extracts, see Using and Blending Thick Aromatic Oils.

How to grind the biomass for (essential oil) extraction?

When grinding biomass for an extractor/CO2 essential oil extraction equipment, size matters a lot. Grinding the plant material too small can create low-quality oil, and even reduces the extraction efficiency in the CO2 extraction process; grinding too large can leave valuable target extract in the waste material.
Whether extracting with supercritical CO2, hydrocarbons, or ethanol, finding the right particle size for solvent and extractor will increase returns and may even speed up the production.

For information on grinding biomass with essential oils extraction, see How to grind the biomass for (essential oil) extraction.

How do CO2 Supercritical Extracts Compare With Absolutes?

Absolutes are typically solvents extracted using hexane as the solvent. Trace amounts of the hexane may remain in the final absolute. However, with CO2 supercritical extraction, CO2 is used as the solvent, and all of the CO2 returns to its normal gaseous state after the extraction is completed. CO2 supercritical extraction eliminates the risk of trace amounts of chemical solvents remaining in the finished extract.

How Do CO2 Supercritical Extracts Compare With Essential Oils?

The production of essential oils requires heat in order to distill the plant material. Even for cold-pressed citrus oils, some heat can be involved due to the friction involved. CO2 Extracts possess an advantage over essential oils because the botanical material and CO2 supercritical extraction process require much less heat.

What are CO2 Subcritical Extracts?

The process used to create CO2 subcritical extracts is similar to that of the supercritical extraction process except that the pressure and temperature used do not allow the carbon dioxide to reach the supercritical phase. CO2 subcritical extraction typically extracts the most lightweight aromatic molecules that have carbon structures ranging between C5 to C22. Essential Oils typically consist of aromatic molecules ranging in size from C5 to C20. Of all the classifications of CO2 Extracts, CO2 Subcritical Extracts most closely resemble the consistency and aroma of essential oils. However, CO2 Subcritical Extracts tend to smell more closely to that of the fresh botanical material than do their essential oil counterparts.

How Does the Cost of CO2 Extracts Compare With Essential Oils?

CO2 Extracts tend to cost more than their essential oil counterparts. This is primarily because the cost of the equipment to produce CO2 Extracts is significantly more expensive than the cost of the stills needed to produce essential oils. However, the cost of some CO2 Extracts are comparable or near comparable to their essential oil counterparts. I’ve come across CO2 Extracts that have been slightly less expensive. It really depends on the market and the quality of the essential oils that you are comparing them to. I hesitate to give specific examples because essential oils and CO2 extracts fluctuate in price.

Works Cited

  • “Cannabis Extraction: 10 Most Frequently Asked Questions (and Our Answers)”, Analytical Cannabis, Visited 17 Aug, https://www.analyticalcannabis.com/articles/cannabis-extraction-10-most-frequently-asked-questions-and-our-answers-313173
  • “What Technology Do I Need To Extract Essential Oils?”, TechSiting, Visited 17 Aug, https://www.techsiting.com/what-technology-do-i-need-to-extract-essential-oils/
  • “CO2 Supercritical Extract Guide”, AromaWeb, Visited 17 Aug, https://www.aromaweb.com/articles/whatco2s.asp
  • “Terpene Extraction Methods: Weighing Up the Pros and Cons”, Medical Terpenes, Visited 17 Aug, https://www.medicalterpenes.com/terpene-extraction-methods/

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