A review of the evolution of the ethanol extraction method within the cannabis industry, where it stands today, and the other alcohols that are being introduced to the cannabis extraction space.
Ethanol has maintained its position as one of the most scalable extraction methods because of its simple methodology and solvent properties. Over time, the technology used in ethanol extraction has increased the selectivity of the method and resulted in shortened post-processing times and increased purity. In this article, we will walk through the evolution of the extraction method within the cannabis industry, where it stands today, and the other alcohols that are being introduced to the cannabis extraction space.
Ethanol has been used for centuries as an extraction method and an ingredient to produce perfumes, food colorings and flavorings, medicinal bases, and essential oils. The US Food and Drug Administration (FDA) has found production of consumer goods using food-grade ethanol to be safe for human use and consumption, which cannot be said of other alcohols. It is the second most popular solvent behind water. It is also the least toxic of all alcohols, making it one of the most widely used solvents in consumer goods. Because of all the aforementioned characteristics, it is no surprise that ethanol has also maintained its position in the cannabis industry as one of the most widely used solvents for extraction of cannabinoids.
Ethanol is a polar solvent, but can have both polar and nonpolar properties. It attracts polar and ionic molecules, through its hydroxyl group, and can attract nonpolar molecules because of the nonpolar nature of the ethyl group. Hydrogen bonding of ethanol and water with the hydroxyl group can be seen in Figure 1.
Tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA) are both polar compounds due to their acidic hydroxyl group. Therefore, they are both easily extracted with ethanol at room temperature. Chlorophyll is an undesired polar compound that easily coextracts with the cannabinoids during most methods of ethanol extraction. This is why crude ethanol extracts, such as modern products listed as Rick Simpson oil (RSO), have a dark green color and concentrations in the 40–60% range. Advancements have been made in methodology to optimize for the extraction of cannabinoids and exclude chlorophyll and waxes.
This method has been used for centuries and is considered a “traditional” medicinal preparation method for phytochemicals (2).
This method has been used for decades and is considered a “traditional” medicinal preparation method for botanicals.
Cold Ethanol Extraction
This method has developed over the past decade to improve the selectivity of ethanol and optimize extraction of cannabinoids.
Liquid-Solid Mix and Separation Centrifuge Extraction with Cold Ethanol
This is the most common method used in cannabis and hemp ethanol
Other alcohols, like isopropyl or methanol, have been utilized in botanical extraction for many years. Isopropyl alcohol and methanol are significantly lower in cost than ethanol, but have their own pros and cons including being toxic to inhale or ingest at far lower concentrations than ethanol (6). Methanol has a lower boiling point, which also indicates a lower polarity. Being less polar than ethanol, methanol is less efficient at extracting THCA and CBDA. Isopropyl alcohol has a higher boiling point and higher polarity, this results in higher yields of cannabinoids in a shorter amount of time, but also extracts higher quantities of chlorophyll. The evaluation of solvents is heavily focused around the cost of a solvent, a company’s ability to remove all of the residual solvent to minimize consumer risk, and post-processing time and methods. These alternative alcohols are strong candidates for any business that further refines the extract using distillation. Wiped or thin-film distillation can produce a pure cannabinoid distillate, reducing the need for purity in the crude form.
As hemp and cannabis processors continue to scale up, technology must keep up with rapid improvements and development to address the bottlenecks in processing massive amounts of biomass. These bottlenecks are in the grinding process, loading and unloading inputs, and solvent evaporation. Leading manufacturers, such as Eden Labs, are introducing continuous-feed centrifuge technology to the cannabis industry. This methodology involves a continuous stream of ground plant material and ethanol flowing through a centrifuge which creates a solid-liquid slurry where the extraction occurs. The slurry is then continuously pumped into a separation centrifuge where the solid and liquid materials are separated. The liquid ethanol-extract solution is then continuously pumped into a solvent evaporation step. While falling film evaporators have become the chosen evaporation method, the continuous feed technology has forced an even better method to be utilized called membrane filtration. Using scalable membrane technology, the extract and solvent are easily separated and can accommodate continuous feed. Ethanol extraction is primed for continuous feed and complete automation, reducing costs and bottlenecks in scalability.
Through advancements in technology, such as the coldfinger or cold-ethanol extraction of cannabis and hemp, efficiency and selectivity of the solvent has dramatically increased and improved the extraction of desired compounds. After the solvent evaporation process, the cannabinoid concentrate is ready to be formulated for end products. With the right temperature, extraction time, and equipment, ethanol extracted cannabis and hemp can produce relatively high purity (60–70%), golden cannabinoid extract, with extraction efficiencies of +90%. Ethanol continues to be the solvent of choice for high-throughput cannabis processors aiming to extract hundreds to thousands of pounds of cannabis and hemp biomass daily. Ethanol extraction is a prime candidate for automation, which will translate to improved efficiency, lower costs, higher throughput, and much more. It will be interesting to watch as automation is integrated into ethanol extraction and refinement processes in the coming years.