The extraction stage of cannabis processing is of great importance in producing the best yield and the proper compounds for the desired application. For instance, extracts intended for medicinal CBD preparations must have enriched levels of the cannabinoid in an oil-based product, free from excipients such as excess lipids, waxes, solvents, and other components. On the other hand, preparations that require increased purity such as products used for vaporization and inhalation, may necessitate the complete absence of trace levels of extraction solvents or contaminating compounds.
The type of product dictates not only the plant strain and enrichment for specific components, but the extraction method to isolate those compounds. Extraction methods of the past have been limited to organic extraction coupled with temperature treatment, distillation, and fractionation. 2017 has seen increasing adoption of advanced extraction methodologies, including several techniques adapted from the petroleum and other industries – emerging approaches that may prove useful for the evolving cannabis landscape.
A basic organic extraction method may involve ethanol treatment and agitation prior to filtration and isolation of the organic phase. This solution is then subjected to solvent removal through vacuum distillation or the use of a rotary evaporation device or rotovap. Heat treatment prior to extraction serves to drive decarboxylation of cannabinoids, thereby enriching for the bioactive forms of the compounds. Cooling the extraction solvents and extract solution helps increase yield and prevent thermal decomposition or loss of product.
This approach has a history for isolation of relatively crude cannabis extracts for various uses. Individual compounds - cannabinoids such as THC and CBD – terpenes and flavonoids – can be further fractionated downstream through the use of HPLC, TLC, and other analytical methods. A drawback for use of these extraction methods for medicinal or other sensitive applications is the fact that residual solvents are typically present in the final product. These may range from moderately volatile to highly flammable, depending on the chemical nature of the solvent. Complete removal may equal significant loss of product or overly laborious and expensive methods. In addition, testing for residual solvent is often necessary with this approach to provide safety data for consumer uses.
An alternative to the above involves the use of liquefied hydrocarbon extraction conditions. Here, systems pressurize hydrocarbons such as butane, propane or other low molecular weight compounds to a liquefied state. Extraction through the use of these liquid hydrocarbons enriches for organic cannabis compounds in solution. A subsequent reduction in pressure results in conversion of hydrocarbons to gas thereby removing all traces and creating a solvent free preparation.
Extreme caution must be used in this technique due to the flammability of the hydrocarbons and the pressure used. The method also relies on temperature control devices which must handle ultralow levels (-80°F) in addition to heating required for effective phase transitioning during extraction. The impact on the environment is also an issue – particularly as processes and the industry as a whole see further growth.
Another technique based on the same basic premise involves use of super critical carbon dioxide as the extraction solvent. CO2 is pressurized to it’s supercritical state, and the resulting liquid is passed through a vessel containing cannabis material. After filtration, the CO2 is removed by dropping the pressure thereby returning it to the gas phase and rendering the extract solvent-free. Advanced equipment can even include downstream fractionation components in order to further isolate specific compounds.
Notable benefits to this method include: significantly fewer safety concerns compared with volatile and flammable solvents, and the absence of residual organic solvents and potential effects on health. A huge advantage of the supercritical carbon dioxide method includes the fact that the solvent can be reused and recirculated trough the device. That and the fact the CO2 has a much subtler effect on the environment, make it a superior approach from a sustainability standpoint.
Efficiency will be key as the industry gains momentum and cannabis operations scale up in production. Efficiency of extraction – in terms of yield, material costs, production time, safety, and sustainability – all play a major role in the cannabis pipeline. Expect to see advances in extraction efficiency and multiplexing of downstream fractionation steps as further steps in processing evolution.