One of the first questions a cannabis or hemp manufacturing company asks itself is which extraction method should they use and why. In this article, we outline some of the advantages and disadvantages of various extraction methods including liquefied petroleum gasses (LPGs), cold ethanol, and CO2. Delta-9 Technologies is a strong proponent of LPGs for botanical extractions because of the many optimal physical properties they offer. Two important properties to consider when choosing an extraction solvent are solubility and selectivity for the target compounds. Both of these parameters will determine the quality of the product and efficiency of the process. The amount of solvent required to extract a given quantity of biomass is a key indicator of solubility. Butane and propane are naturally selective for cannabinoids and terpenes leaving unwanted byproducts behind. The cannabinoids and terpenes are highly soluble in propane and butane LPGs making them ideal to obtain high quality product right off of the initial extraction. Moreover, the capital expenses and operating costs attributed to operating LPG systems are relatively low.
LPG solvents by definition boil at low temperatures under atmospheric pressure. That translates into reduced energy input to convert these solvents from the gas to liquid phase and vice versa. In any extraction process you will need to evaporate the solvent to obtain desired extract. The evaporation of LPGs does not require significant heat and leaves your product in a preserved natural state with the aromatic and chemical complexities of the original plant. Butane, isobutane, and propane have boiling points of -1, -12, -42 C, respectively at atmospheric pressure (1 atm). These gasses can be converted to liquids by either increasing the pressure or reducing the temperature. If we consider the pressures required to convert these same gasses to liquids at room temperature (21 C) we find that butane, isobutane, and propane will undergo the gas to liquid phase change at 24 (10 C), 30, 124 psi, respectively. Not only does this allow for the operator to produce native strain specific extracts, but it also allows for a more rapid and energy efficient recovery of the LPG extraction solvent. Purging the extract of trapped residual LPG solvent is relatively easy to do when the boiling point is so low. This gives the operator the ability to produce a wider variety of high quality extracts with LPG extractions. Low quality trim and waste biomass input material can easily be converted into +65% cannabinoid content extract. Lower temperature methods with high quality input material can yield +85 - 98% diamonds and high quality crumble. LPG extraction offer the most wide array of products that include crumble, shatter, diamonds, sauce, crude, winterized, decarboxylated, distillate, vapes, and formulated products. There is no product that LPGs can't make and is a great option for operators that have a divers product portfolio.
One other property of LPGs worth mentioning is their thermodynamic cooling properties when released from a tank. The lower the boiling point the higher the cooling effect. Releasing propane from the tank will cool the extraction tubes significantly to the point of freezing or condensing moisture from the atmosphere on the outside wall of the extraction tubes. The chemical selectivity of butane and propane are nearly identical; however, propane has a larger cooling effect and results in a colder extraction. Typically, first-pass crumble from propane extract is extremely high quality because of these thermodynamic refrigerant properties. In fact, propane was used as a refrigerant in refrigerators before non-flammable fluorinated hydrocarbons were discovered. We touch on their use as extraction solvents below.
In order for CO2 to be in a supercritical state the pressures must be above 1071 psi with temperatures above 31 C. Subcritical liquid CO2 extractions take prohibitively long to conduct and inefficiently remove the cannabinoids from the biomass. There have been advances made in the CO2 extraction space where tuning the temperatures and pressures have yielded high quality product. However, you are limited to above 31 C temperature extractions and a high level of understanding is required to make quality concentrates. On the other hand, butane and propane LPGs are naturally tuned to the desired selectivity at low temperatures and pressures. Subcritical LPGs offer a wider operating temperature range and give the operator flexibility to make a wide range of concentrates. Another advantage is that pressures above 250 psi are generally never observed with traditional LPGs, and in this regard, is safer than CO2 extractions. A fitting or part popping off at 5,000 - 10,000 psi could easily injure or lead to the death of an operator.
One common misconception is that CO2 is inherently safer than LPGs. Scenes of open blasting explosions from amateurs extracting in their garages has been propagated in the media and scared the public. Closed-loop extractors do not release flammable gas into the surroundings increasing the safety tremendously. Cooking on your grill with an open flame hooked up to a propane tank seems more dangerous than running a computer controlled Delta-9 Technologies extractions system with integrated gas sniffers, alarms, and computer controlled exhaust venting. The Class I Division I rooms that the systems operate in are highly ventilated with no chance for a spark if levels had reached the ~2% lower explosion limit (LEL).
There is also the perception that CO2 is healthier than LPGs because CO2 is naturally occurring in our atmosphere and a natural byproduct of respiration. The poison is in the dose. The truth is that CO2 can lead to performance impairment at a 3% concentration and can lead to death by asphyxiation at concentrations above 10%. Symptoms can onset within minutes.
LPGs can also act as asphyxiants, but the toxicity profile for butane and propane is surprisingly low. Interaction with LPGs would be brief since general procedures would limit exposure times in well ventilated areas. From the table below you can see that concentrations above the lower explosion limit are required to cause drowsiness and would not be obtained when complying with regulations. Lethal levels at 10 min exposure times exceed 77,000 ppm and only caused 1% mortality in mice. The flammability at these concentrations is a larger concern compared to exposure. As mentioned previously, the low boiling point make it easy to remove residual solvents from the product following typical vacuum purging protocols.
- Low solubility requires large amounts of ethanol to extract the biomass. Incredibly Inefficient – ethanol extractions are usually done at very low temperatures and recover just 60%-70% of cannabinoids per extraction.
- Ethanol soaked waste biomass at the end of run presents a safety hazard.
- Low selectivity. At higher temperatures ethanol can extract chlorophyll rich, dark extracts – the exact opposite of what consumers are looking for.
- Expensive high capacity chillers required to chill ethanol. Expensive energy input.
- Expensive high capacity solvent evaporators required to recover ethanol. Expensive energy input. Typical rotary evaporatoras are not sufficient to distill large volumes of ethanol.
- Limited range of products. Cannot make crumbles, diamonds, sauce, and shatter.
- Ethanol extracts tend to extract impurities that can damage expensive short-path distillation equipment in post refinement steps.
- Federal excise tax on ethanol is expensive. It is not uncommon for larger processors to spend $50,000 + PER MONTH on Ethanol. Lose +20% ethanol in soaked biomass per run. LPGs leave a dry biomass because it is a gas not a liquid at room temperature and pressure.
Previously, we touched on the naturally selectivity and high solubility of cannabinoids and terpenes in LPG solvents. Until now, we have only considered the three solvents butane, isobutane, and propane. Although the solubility and selectivity profile is excellent, there is the potential that there are other LPG solvents that offer even better profiles. Some areas currently being explored include fluorinated hydrocarbons like R134A. This LPG solvent boils at -26 C and a non-toxic FDA approved material. This tetra-fluorinated ethane is non-flammable and could provide a safer alternative to traditional LPGs. Alternatively, there has been interest in dimethyl ether as an LPG. Ultimately, we want to reduce the amount of solvent required to extract a given amount of biomass while selectively extracting the target cannabinoids and terpenes. The diverse array of possible LPG solvents offers a much more tunable solubility and selectivity profile when compared to limiting the operator to only CO2. It is likely that even better LPGs than the traditional butane and propane solvents will be identified in the not to distant future.
It our belief that when choosing LPGs as an extraction method is the wisest decision an operator can make. LPG systems can produce the most diverse array of products of all the extraction methods available. Automating the systems for repeatability and scalability are the main goal of Delta-9 Technologies. We build solutions to automate every aspect of the process that include grinding, loading and unloading of biomass, extraction, winterization, distillation, crystallization, analytical testing, SOPs, lab design, formulations, regulatory compliance, training of staff, and any support that your company may need.