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Hydrocarbon Extractions

With the plethora of methods and extractions out there for cannabinoids, producers and distributors might be wondering which extraction is the right one for their products. A once popular extraction technique used in the illicit cannabis market, along with legalization and increasing consumer demand, newer state regulations have kept hydrocarbon extractions at the forefront of the legal cannabis market. This article aims to explain how hydrocarbon extractions work in the cannabis industry as well as the pros and cons of said extraction method.

What is a Hydrocarbon?

A hydrocarbon (Figure 1) is a molecule, consisting of only hydrogen and carbon atoms, hence the name “Hydro-Carbon”(1). There are various hydrocarbon structures, but the main hydrocarbons used in cannabis extractions are propane (C3H8) and butane (C4H10) (2,3). These solvents are preferred during extractions for their non-polar properties that allow them to extract the cannabinoids with ease since cannabinoids are also non-polar and can be dissolved by these solvents (4).

Figure 1. Examples of various hydrocarbons using both Lewis-Structures and Bond-Line Formulas

How a Hydrocarbon Extraction Works

Similar to supercritical carbon dioxide (CO2) extraction (5), the hydrocarbon extraction process (as shown in Figure 2 below) has the solvent (i.e. propane, butane, or a mix of the two) cooled down to a liquid which is then washed over the plant material in a closed system extraction (6). The solvent, with the cannabinoids now extracted from the plant material, is run through a collection tank that vaporizes the solvent off while the extract is collected. The vaporized solvent is then condensed back into a liquid to be reused for another extraction. A closed loop system should be optimized to minimize solvent loss. Improper systems may harm the operator, equipment, or the facility should there be a malfunction or solvent is exposed to an ignition source. Normal operation of a hydrocarbon extraction system occurs under a class 1 division 1 rated hazardous environment since there are high concentrations of ignitable, explosive gasses present in the work environment (7). Since hydrocarbon extractions carry a greater risk than other extractions, many processors and manufacturers prefer safer techniques such as supercritical CO2.

Figure 2. The hydrocarbon extraction process (Retrieved from: precisionextraction.com)

How Effective is a Hydrocarbon Extraction?

Under the right conditions, a hydrocarbon extraction can be very effective at extracting the cannabinoids on a large scale, without losing the terpenes from the plant material. Butane and propane are not as effective as supercritical CO2 or ethanol in terms of extraction efficiency, but the nonpolar properties of the solvents make for a more rich terpene content than the other extractions methods, despite having to wash the material multiple times with butane/propane to achieve the same extraction efficiency as CO2 or ethanol (8).

Even between the two solvents, there are differences in the efficacy of the extraction from butane versus propane. Butane has a boiling point of -1℃ compared to propane’s boiling point of -42℃, meaning both solvents can be condensed after the extraction without the use of extreme temperatures (9) that can degrade the extract or terpene content (10). The lower temperatures of the propane extraction, allow more terpenes to be extracted along with the cannabinoids making for a more flavorful product at the cost of running at a higher pressure load. These temperature differences affect the extract in terms of consistency, while butane produces a more brittle/glass-like extract, propane produces a softer/more oil-like extract due to more terpenes being in the propane extract (11).

Most professional extractors prefer to use a blend of both butane and propane to get a mixture of the soft/oily and brittle/glass-like extract while also getting more terpenes in the extract as well. When mixing butane and propane, they create an azeotropic mixture, where the boiling point equalizes between the two solvents (12). Depending on the concentration of both solvents, the pressure increases as the concentration of propane increases with the ideal ratio of 70% butane and 30% propane to keep the pressure under 100PSI for optimal terpene preservation during the extraction (9). This 70/30 ratio has a boiling point of -21℃ (13), which can preserve the terpene content as some terpenes begin to evaporate off at 21℃ (14).

Testing Hydrocarbon Extracts

Propane and butane are easily accessible and are generally regarded as safe by the Food and Drug Administration (FDA) when used as a propellant or additive in food (15,16). However, in terms of an industrial processing solvent, propane and butane can pose numerous risks to operators during the extraction process due the explosive nature of these solvents. Also important to note is the quality of solvent being used for processing in food applications; when using high purity propane/butane, the residual levels of solvent left residing in the product after proper processing might pose little risk to a consumer’s health (due the GRAS designation of high purity propane/butane as a residual food additive), but it is unclear the long term exposure risks when industrial grade propane and butane are used during the commercial extraction process.

While the FDA does not regulate cannabis products or extracts on a federal level, professionals can still adhere to their Current Good Manufacturing Practices (cGMPs) (17) when preparing these extracts. cGMPs take into consideration the various solvents, equipment, and methods used to ensure the integrity of the products as well as ensuring there are no harmful amounts of by-products made or residual solvents left over from the extraction process.

There are regulations in place on a state level for those states that have legalized either medical and/or recreational such as California that allows cannabis products to be sold or distributed as long as the residual solvent levels for either butane or propane does not exceed 5000µg/g (18). Butane and propane can still cause harmful effects if the residual solvents levels are too high, more specifically these solvents can damage the central nervous system when inhaled or ingested (2,3).

In addition to residual solvent testing, manufacturers would also want to test for the potency of their extract, whether to make sure it is within compliance with state regulations or to make sure that the manufacturer is getting the cannabinoid they want out of the extraction process. Here at Ionization Labs, our Cannabinoid Testing Services are able to test the potency of hydrocarbon extracts you develop or buy from a manufacturer. You can get verified and accurate results in as little as 24 hours! Any comments or questions about testing can be directed to [email protected] or call us at 737-231-0772. In addition to our Cannabinoid Testing Services, we also offer CannID, an in-house testing solution for quality assurance/quality checks during the product development cycle for our customers that manufacture their own products.

References Used:

  1. 16.2: Hydrocarbons - Chemistry LibreTexts
  2. Propane | CH3CH2CH3 - PubChem
  3. Butane | C4H10 - PubChem
  4. 3.2: Solubility - Chemistry LibreTexts
  5. Supercritical Fluid Extraction - Ionization Labs
  6. 5.4: Open Versus Closed Systems - Chemistry LibreTexts
  7. HAZARDOUS LOCATION CLASSIFICATION.
  8. Complete Comparison of Extraction Solvents | Ethanol vs. Butane vs. CO2
  9. Butane vs. Propane In Plant Extraction | BVV
  10. A Guide to Extracting Terpene Oil
  11. What Is Propane Hash Oil? PHO Definition | Weedmaps
  12. What Is an Azeotrope? Definition and Examples
  13. 70% n-Butane & 30% Propane Mix (Extraction Grade™) by High Pre
  14. Terpene Boiling Points and Temperature.
  15. CFR - Code of Federal Regulations Title 21 (Propane)
  16. CFR - Code of Federal Regulations Title 21 (Butane)
  17. Facts About the Current Good Manufacturing Practices (CGMPs) | FDA
  18. Residual Solvents and Processing Chemicals Testing, Cal. Code Regs. tit. 4 § 15718 | Casetext Search + Citator