Deborah Agboola   |   August 04, 2020

Chemical Solvents Used in Cannabis Extraction

What’s approved, what’s not, and why.
Deborah is an inquisitive writer with a forte in technical writing. Her desire to enlighten and inform gives her the extra edge of structuring her writes to an easily understandable form, while retaining its technicality. When she is not…

Cannabis extracts are a growing segment of the legal cannabis market. From industrial extractions to supply to the food and beverage sector of the cannabis industry to mass-produced vape cartridges to artisanal cannabis concentrates for the retail consumer, cannabis extracts provide the pure essence of the flower in a more concentrated format.

Solvent-based cannabis extraction is common-place in commercial and black market manufacturing.  However, precautions must be taken to ensure the products are safe for consumption. Let’s take a look at the various solvents, their benefits, their drawbacks, and their dangers.

Classification of Cannabis Extraction Solvents

Residual solvents can cause several health issues. Hence, to avoid this danger, many states have conformed to the guidelines created by the U.S. Pharmacopeial Convention and the Food and Drug Administration. These guidelines divide over 59 extraction solvents into three classes - listed in this order: those to be avoided entirely, those under strict regulations, and those with their use limited by only GMP and other quality-based standards.

Initially, the initial USP and FDA-guidelines did not include butane and propane, which were even then efficient in extraction. However, in 2019 the revised FDA-guidelines listed butane and propane as Generally Recognized as Safe (GRAS) under the Class 3 solvents.

Solvent-Based Cannabis Extraction

The solvent-based extraction is a favorite of the cannabis extraction industry, especially in producing extracts for food, pharmaceuticals, and personal care materials. There are currently four known types under this technique.

For each of the types listed below, certain solvents are preferred due to their efficacy, efficiency, and FDA-approval. Listed below are some of these solvents with the inclusion of formerly used compounds:

Hydrocarbon Extraction

Hydrocarbons are invaluable to the cannabis extraction industry, owing to their high potentials. In an earlier time, there were more hydrocarbons used for extraction, but due to their high toxicity and flammability, most were prohibited. A few of these hydrocarbons include hexane, methyl ethyl ketone, acetone, and ethyl ether. According to the FDA, the most suitable hydrocarbons for cannabis extraction are Butane and Propane.

Benefits of Butane and Propane

  • High volatility
  • Low toxicity risk
  • High efficacy and efficiency
  • High specificity

Alcohol Extraction

In extraction, hydroxyl-compounds are highly effective but less-specific in action, with a tendency to dissolve pigments and waxes, alongside the target extract. Nevertheless, there are two generally-preferred compounds: isopropyl alcohol and ethyl alcohol (ethanol) - the former is less preferred due to its acetone formation in the liver.

Other hydroxyl-compounds which were previously freely used but are now strictly regulated include:

(i)  Methanol and Toluene (class 2 solvents) - high risk of causing optical nerve diseases and seizures.

(ii) Acetone and Isopropyl alcohol (class 3) - high risk of neurological damage.

Grades of Ethanol

The following are the four grades of ethanol:

  • FCC-Grade Ethanol
  • USP- Grade Ethanol
  • HPLC-Grade Ethanol
  • GNS-Grade Ethanol

The USP-Grade is also known as the ACS –Grade; and the GNS-Grade as the GPC-grade.

Benefits of Ethanol

  • High efficiency
  • Laboratory and Health-safe
  • Easy storage
  • Relatively inexpensive

Super-Critical Fluid Extraction

It is the separation of target extracts from the plant’s matrix by the aid of supercritical fluids. At the supercritical point, the temperature and pressure rise above the critical point, conferring upon the fluid the properties of liquids (density) and gases (transferring and penetrating ability).

Several supercritical fluids have been either banned or are under strict regulations because of their hazardous effects on the health and environment, including Nitrous oxide, Ethylene dioxide, Ethane, and Benzene.

Of all types, the standard FDA-approved solvent for extraction is carbon dioxide, as a result of its eco-safety and high purity.

Benefits of CO2

  • Relatively inexpensive
  • Chemically inert
  • Low surface tension and safe critical point
  • Low viscosity and high diffusivity

 

 R134a Terpene Wash

The R134a “tetrafluoroethane” extraction is a novel technique similar to Carbon dioxide extraction, discovered by COMERG. The solvent, which was approved by the FDA as a GRAS solvent, produces full-spectrum, post-winterized extracts, isolates terpenes, live resins, and cannabinoids.

Dual –Solvent Wash

Though pioneered by R134a, this method is efficient with carbon dioxide extraction to eliminate the need for further procedures; R134a extracts terpenes and live resins in10-15 minutes, while ethanol separates cannabinoids in about 30-60 minutes.

Benefits of R134a

  • Simple to use
  • Safe and inexpensive
  • Easily scalable
  • Highly effective and efficient

Dealing with Residual Solvents

The primary goal of most solvent-based techniques is to produce a solvent-free output. However, this might not go as expected, owing to a persisting solvent(s) in the final product; these are called Residual Solvents.

Effects of Residual Solvent

Influenced by the type and quantity of solvent present, they generally pose a health risk. As a result, extraction industries run additional tests to check for these solvents, impurities, and other residues.

Testing for Residual Solvents

In extracts’ analysis for residual solvents, the most efficient method is the Headspace Gas Chromatography/Mass Spectroscopy (GC/MS) technique.

It is performed by dissolving the sample in a high-molecular-weight compound such as dimethylformamide before placing it in a headspace vial. The sealed vial containing the sample is heated, exciting the molecules to a gas phase. Then, technicians withdraw about 1mm of gas and inject it into a GC-detector - separating the compounds by size and polarity.

Finally, the compounds are moved into the Mass Spectrometer for the qualification and quantification of the solvents.

Advanced Market – Advanced Processes

The cannabis industry has matured, and with it, so has what we know about the various products. Today, cannabis products require advanced manufacturing and testing solutions to ensure consumer safety.

As federal legalization continues to inch forward, cannabis producers can expect more testing and regulation organizations to get involved in how products are made. Just as some solvents were nixed with state legalization, tighter restrictions from the federal government could change the playing field. By giving consumer safety the utmost importance, quality cannabis manufacturers will stand the test of time.

 

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