Essential Oil Extraction Processes: Solvent Extraction
Some plant material cannot tolerate the heated forms of extraction such as steam distillation. High heat damages these plants and once damaged, their essential oils too are damaged and are no longer able to be extracted. For these plants, as well as others, solvents such as ether, ethanol, methanol, hexane, alcohol and petroleum are used instead. The problem with using solvents to extract essential oils is that most of the time, residual solvents or impurities remain in the end product. Because they’re impure, those true to aromatherapy refuse to use them.
As mentioned above, there are times when solvent extraction makes sense. This process involves a lot of chemistry and is somewhat confusing to understand but in general it is as follows.
Plant material is first washed in a bath of hydrocarbon solvents. This process dissolves the necessary plant materials including the aromatic molecules, waxy matter and pigment and the dissolved matter mixes in with the solvent. The solvent mixture is then filtered and distilled using low pressure. After distillation and further processing, either a resin or a concentrated concrete remain. Additional processing using alcohol helps extract the essential oils.
This is a very fast and cost-effective method of essential oil extraction, but there is a downside. With solvent extraction, residual solvents remain and their presence can cause problems if used by individuals with allergies or sensitive skin. That’s another reason why essential oils extracted using solvents are used in the manufacturing of perfumes and fragrances, not in aromatherapy or skin care products.
Super Critical Carbon Dioxide (CO2) Extraction
The end result of super critical carbon dioxide (CO2) extraction – one of the newest extraction technologies – is a super-concentrated, high-quality version of essential oil. This rapid extraction method uses lower temperatures and higher pressure to transform carbon dioxide, a gas, into a liquid. It’s an inert solvent meaning that it’s non-reactive and therefore cannot form another chemical compound. When the extraction process is complete, the carbon dioxide is returned back to a gaseous state therefore, no residual remains. All that is left is pure essential oil.
Although this technology produces one of the purest forms of essential oil, it is not yet widely used. The equipment needed for this extraction process is very expensive, which keeps production costs high. And because production costs are high, so too are the costs of the essential oils that are produced via carbon dioxide extraction.
With this essential oil extraction method, hot oil is used as a way to rip apart cell membranes. The plant material is first saturated with hot oil and allowed to soak until the cell membranes rupture. As they break apart, essential oils are released into the oil in which the plant material is soaking. When the release period is complete, the plant material is removed from the oil. The oil that remains then gets decanted.