One of our potential customers recently asked us how to remove dark color from their extracts. They were getting dark extracts and were wondering about their options to make them look better. The oil was coming from an ethanol extraction process.
As an illustration of how dark ethanol-extracted oil can be, refer to the photo above. The sample on the left is an oil produced by supercritical CO2 extraction and diluted in ethanol. The sample on the right is oil produced by ethanol extraction. This deep green coloration is caused by chlorophyll and xanthophyll that are extracted in solution from the biomass.
If you extract hemp or cannabis plant material with warm ethanol, pigments and waxes will be co-extracted. These pigments typically taste bad and give a poor-quality appearance to the oil. Rotary evaporators (rotovaps) or stills are typically used to remove the ethanol, but the pigments, waxes, and poor-quality elements remain in the extract.
To minimize the extraction of non-active compounds, some people use extremely cold ethanol chilled to below -20°C. The most common cold ethanol extraction is the quick wash ethanol (QWET) method. Chilling the ethanol has the effect of lessening the solvent’s hydrophilic properties, thus minimizing the waxes and pigments that are extracted.
However, just as with any other chemical process, as the process gets colder, friction factors increase exponentially. At the same time, diffusion coefficients of the actives in the ethanol plummet. While the level of extracted chlorophyll and plant waxes is reduced, the absolute amount of active compounds extracted (cannabinoids, terpenes, etc.) also decreases greatly. In short, you get to choose: low recovery or high pigments.
Another important thing to consider about ethanol is its high degree of flammability. You should familiarize yourself with the regulations around storage and use of ethanol before attempting to build a process based on large amounts of flammable liquid. Even if you are in a state where recreational cannabis is legal, you should consider the infrastructure requirements and permit barriers to using large volumes of ethanol.
If you’re planning a large-scale ethanol extraction operation, you should read our post about things to consider when scaling up ethanol production.
The National Fire Protection Association has published NFPA 30 guidelines for explosion proof fixtures and infrastructure required. You can also find OSHA regulations here.
Activated carbon (or activated charcoal) is one of the most popular options for removing chlorophyll and other unwanted non-active pigments in ethanol extracts. While activated carbon is quite effective at pigment removal, it is also very effective at removing active compounds. Due to the large pore diameter distribution and particle friability of activated carbon, it also results in a much smaller yield.
Another problem with activated carbon is its natural origin and the contamination that it carries. Activated carbon is typically derived from coconut shells or bitumen or wood. These products have significant ash content that contain heavy metals. When the carbon breaks up under use, these metals distribute throughout the oil as very small particles. They become very hard, if not impossible, to remove via filtration. Thus, they end up in your extracts.
The most overlooked aspect of using activated carbon however, is the solvation and dissolution of benzopyrenes into the extract. This class of compounds is produced as a consequence of the combustion of the coconut or bitumen. The Wikipedia entry for benzopyrene states the following:
Benzopyrenes are harmful because they form carcinogenic and mutagenic metabolites (such as (+)-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide from benzo[a]pyrene) which intercalate into DNA, interfering with transcription. They are considered pollutants and carcinogens.
So, care must be taken to use the right carbon. CarbonX has been shown to solve the problems above because it is not a natural product, but is engineered by vapor depositing carbon onto a porous substrate.
The substrate will not break up, so the introduction of micron-sized ash content that is not filterable is unlikely. Furthermore, the material is washed so that extractables are not leaching from the materials into the extract.
We typically use CarbonX in a couple different ways:
Here’s a video demonstrating how CarbonX removes unwanted pigments from an ethanol extract:
If you’re using activated carbon, then you should give the reusable alternative, CarbonX, a try!