A Critical Look at Solvent Extraction vs. Supercritical Fluid Extraction
Cannabis contains hundreds of compounds, cannabinoids, terpenes, and other fats and lipids. These compounds are extracted by using one form of either chemical separation or physical separation of the cannabinoids and terpenes from the rest of the plant biomass. These techniques can range from using heat and pressure to using solvents like ethanol and butanol to rip the cannabinoids and other chemicals off the plant and hold them in suspension in the solvent. There are predominantly two ways initial extraction of the cannabinoids and terpenes is done: either through supercritical fluid extraction or solvent extraction.
Supercritical fluid extraction, which either utilizes liquid CO2 or Nitrogen. In the supercritical state, the substance is both a gas and a liquid in the supercritical state. This state is achieved through high pressure and a low temperature that forces the substance to flow and have many of the same properties of a liquid but volumetrically fill space like a gas. This supercritical fluid then also takes on solvent-like qualities and has the ability to remove many of the compounds from the plant material much like a traditional solvent would.
Supercritical extraction has come a long way in the last few decades with many advances in both the efficiency of the extraction process and a large cost drop in system and operating costs. A large part of the cost reduction with supercritical fluid extraction is that CO2 is drastically less expensive than butanol or ethanol, and there are fewer steps involved than traditional solvent extraction methods. The two downsides to supercritical fluid extraction are that the initial cost of the equipment is usually 4x higher than that of a similarly sized solvent recovery system, and the operating pressures of a supercritical system are drastically higher than that of a traditional solvent recovery system. This extremely high pressure makes the systems potentially very dangerous, and the electricity cost to run such a system is usually higher than more traditional solvent systems.
The other main form of extraction is using a solvent to strip the cannabinoids off the plant and then distilling the solvent off using a simple distillation apparatus. This method can have varying results based on the quality of the equipment used and the experience of the technician using the equipment. Solvent extraction is the more common method for cannabinoid extraction and can produce an exceedingly good product if managed correctly. The problem with solvent extraction is that in some cases if the solvent has not been fully recovered from your crude product, the end product will contain trace amounts of solvent in it and could pose a serious health risk to a client if they were to ingest the problem extract. The FDA has a list of solvents that it has approved for use in pharmaceuticals. These are broken down into three classes. Class one solvents are not approved for use due to their unacceptable toxicity or their deleterious environmental effect. Class two solvents should be limited in pharmaceutical products because of their inherent toxicity. Class three solvents may be regarded as less toxic and of lower risk to human health. Class three includes solvents that do not pose human health hazard at levels normally accepted in pharmaceuticals. If using a class three solvent and using the correct solvent recovery equipment, the end product should not be any different in quality than its supercritical cousin and might even be cheaper to produce at scale.
The challenge of scalability is one of the largest reasons a solvent extraction setup is sometimes cheaper to run and produce. Supercritical extraction does have its upsides but it does still cost more at a large scale than traditional solvent extraction methods. Where CO2 extraction begins to make more sense is with smaller operations that are looking to streamline their production and cut the time needed to complete solvent recovery out of their production line. Ultimately each method should give the same end product if the right equipment is being used.