Hydrocarbon extraction is a widely used botanical extraction method that utilizes light hydrocarbon solvents like butane and propane to extract botanical compounds. Hydrocarbon extraction is preferred by many botanical extractors due to its high yields and low solvent recovery temperatures. These highly versatile extraction solvents lend themselves to producing a high purity botanical concentrate with little to no post-processing. Hydrocarbons are a classification of organic compounds made from carbon and hydrogen. Hydrocarbons are formed due to the compression of animal and plant remains over long periods and are pulled from porous rocks where they pool and concentrate. These alkane molecules have an even distribution of electrons, making them nonpolar and well suited for extracting nonpolar botanical compounds.
The most commonly used hydrocarbons for botanical extraction include butane and propane. These hydrocarbons can be utilized on their own to perform botanical extraction, or they can be combined into a blend of hydrocarbon solvents and utilized to extract a fuller spectrum of botanical compounds from biomass material. Typically a blend of n-butane, Isobutane, and propane is utilized to create an extraction solvent with greater affinity to extract a wider variety of compounds found within botanical biomass resulting in a more full-spectrum extract.
100LB 40/40/20 Butane/ISO Butane/Propane Blend By EcoGreen
Both butane and propane are class 1 group D flammable liquified gases that the Food and Drug Administration (FDA) have generally recognized as safe (GRAS). These light hydrocarbons are gaseous at room temperature and ambient pressure where they are denser than air and tend to pool near the floor. When pressurized or placed under reduced temperature they become liquified and can saturate biomass material and extract nonpolar botanical compounds.
20LB High Purity N-Butane By BVV
Butane and Propane are the preferred extraction solvent of many extractors looking to preserve highly volatile aromatic compounds due to their low boiling point -1C/30.2F for butane and -42C/-43.6F for propane. Since these solvents boil off at a lower temperature than most aromatic compounds, they can be recovered with minimal heat preserving more aromatic compounds in comparison to other high boiling point extraction solvents like ethanol. While butane and propane's low boiling points lend themselves to aromatic compound preservation, it also makes hydrocarbons highly volatile and more hazardous to work with.
Although butane is generally recognized as safe by the FDA and can be consumed by humans in trace amounts, utilizing these highly volatile and flammable hydrocarbons as organic solvents under extreme temperatures and pressures can be dangerous. While it is highly unlikely that hydrocarbon extraction will result in an explosion when performed properly, when utilizing these highly flammable gases, there is always an inherent potential ignition. For this reason, any and all potential sources of heat or flame should be kept far away from areas in which hydrocarbon gases are present. To further mitigate the potential for ignition, hydrocarbon extraction should be performed inside of aC1D1 extraction booth with all the proper safety and protective equipment.
C1D1 Extraction Booth By C1D1 Labs
Among the most important pieces of safety equipment for butane and propane extraction is a C1D1 extraction booth which greatly reduces the potential hazard when working with hydrocarbon solvents. A C1D1 hazardous location is where ignitable vapor concentrations exist under normal operating conditions and where a hazard is caused by frequent maintenance, repair work, or equipment failure. Both butane and propane extraction typically fall under a Class 1 Division 1 environment because ignitable concentrations of flammable gasses exist under normal operating conditions. Depending on a specific municipality, the fire inspector may also require said extraction booth to have a fireproof burn rating which is commonly required when dealing with larger volumes of solvent within the enclosed area.
C1D1 Hazardous locations require all electrical/electronics equipment to be designed, tested, and labeled acceptable for use in C1D1 areas. Beyond utilizing appropriately rated electrical/electronic components, most extraction areas will come equipped with an explosion-proof exhaust fan providing a high air exchange rate, along with a lower explosive limit gas detector to alert high levels of gas and trigger an increased rate of exhaust ventilation.
Lower Explosive Limit Gas Detector By Honeywell
While the use of appropriately rated electrical components within the extraction area drastically lowers the potential of a flammable substance being ignited, one of the more important functions of a C1D1 extraction area is to reduce the risk of an explosion by regulating the airflow of the enclosed space to keep the levels of gases below the lower explosive limit of the used gas.
A C1D1 extraction booth helps mitigate the risk of an explosion through the use of an explosion-proof exhaust fan, providing a high rate of air exchange. It comes with a lower explosive limit gas detector used to alert the user of high levels of gas and trigger an increased rate of exhaust ventilation. When extracting with butane or propane, it's best to keep the percentage of solvent vapors within the enclosure well below 25% of their lower explosive limit which is 1.86% for butane and 2.1% propane.
Portable Butane Leak Detector By BVV
When performing a butane extraction inside a C1D1 rated Explosion-proof enclosure, only appropriately rated explosion-proof electronics should be utilized, and great care should be taken to limit exposure to open flame or static electricity by bonding metal containers during flammable solvent transfer and grounding equipment. A C1D1 Environment is a must-have to safely and compliantly perform butane extraction and should be worked into the budget of every new butane extraction lab build. While an explosion-proof environment significantly reduces risk during hydrocarbon extraction, to ensure personal safety while performing hydrocarbon extraction, personal protective equipment in the form of safety goggles, nitrile gloves, and antistatic clothing should be worn at all times.
When operating within a C1D1 environment butane extraction is typically performed utilizing a closed-loop butane extractor. A closed-loop system allows for optimal safety as it contains all flammable solvents from the extraction process within a closed system and allows for the recapturing and reuse of solvent.
1LB MK-V Orthrus Bidirectional Flow Closed Loop Extractor By BVV
A typical closed-loop system can be broken down into three basic elements; The solvent tank/ recovery tank where the hydrocarbon blend is stored and recondensed, the material column where the plant matter is loaded and saturated, and the collection vessel where the botanical extract solution is collected and the solvent evaporation process is performed. While these three components are essential to the operation of a closed-loop system, several additional components can be utilized to improve the efficiency of a closed-loop system.
5LB EVO Closed Loop Extractor By BVV
Common optional additions to a closed-loop system include a dewax column used to precipitate and filter plant waxes from the solution, a color remediation column used to filter undesirable color pigments from the extract, and a molecular sieve column used to absorb any water from the solvent during the solvent recovery process. While the function of a dewaxing column can be substituted by chilling the extraction solvent prior to extraction and limiting its retention time, a molecular sieve and color remediation column are highly recommended to improve the overall efficiency of the extraction process. A color remediation column specifically is capable of drastically increasing the purity of the botanical extract and will be covered in great detail in the next chapter.
Hydrocarbon extraction is performed simply by saturating the biomass material with a liquid butane or propane solvent. As the liquid solvent saturates the biomass, it dissolves compounds from the plant material. While this process is rather straightforward, several variables to the initial saturation can be optimized to increase the overall yield and purity of the resulting extract. During the initial saturation, the most effective variables to optimize the efficiency of a butane extraction are solvent temperature, solvent to biomass ratio, and retention time.
Solvent temperature is commonly altered either to increase the purity or overall yield of the butane extraction. The extractor may choose to either chill the solvent to limit the pickup of impurities or extract using a room temperature or "warm" solvent to increase the overall yield of the extract. During extraction, the temperature of a solvent plays a big role in the solubility and saturation capacity of a solvent. Saturation capacity and solubility generally increase or decrease along with the temperature of the solvent.
When a solvent is chilled prior to extraction, its overall solubility is reduced, which helps limit the pickup of undesirable impurities like plant waxes and chlorophyll. While this altered selectivity does come at a price of reduced efficiency in extracting the target compounds, this can be combated by utilizing a higher solvent to biomass ratio.
Butane solvent is typically chilled within a -20C to -80C (-4F to -112F) range, increasing the selectivity of the extraction and limiting the co-extraction of impurities. Common methods of chilling butane solvent include an injection coil submerged in dry ice that the hydrocarbon solvent runs through prior to injection of the material column or a jacked solvent tank connected to a refrigerated circulator to chill the butane solvent prior to the initial saturation.
Conversely, a room temperature or "warm" butane solvent can be utilized to perform the initial saturation. When utilizing a room temperature or "warm" butane extraction, the solvent has greater solubility and saturation capacity allowing the solvent to more effectively dissolve target compounds from the plant matter. While this strategy allows for the target compounds to be more effectively dissolved from the plant matter, it also allows undesirable botanical compounds like color pigments and plant waxes to be more easily dissolved, resulting in a greater number of total impurities. Commonly, a warm extraction is paired with inline adsorbent filtration utilizing a color remediation column allowing for efficient extraction of the target compounds during the initial saturation and removing undesired impurities through filtering resulting in high yield and purity.
Regardless of the extraction temperature strategy, once the solvent has reached the desired extraction temperature, the solvent is then injected into the material column saturating the biomass material. There are two methodologies for saturating the biomass material. Closing the outlet to the material column allows the material column to fill with solvent and fully saturate the plant matter increasing retention time before draining the solvent into the collection vessel. Another way is to leave the outlet of the material column open, allowing the solvent to quickly pass through the material column into the collection vessel, limiting solvent retention time for what is referred to as a quick wash. Retention time is an important factor in allowing the solvent to dissolve the target compounds. Too little retention time can result in reduced yield of target compounds, while too long retention time can allow more undesirable compounds like chlorophyll and plant waxes to be dissolved.
Extended retention times are great for extracting everything from the plant matter. When this strategy is paired with inline adsorbent filtration, it can result in both high yield and purity. Conversely, a short retention time allows for greater purity by minimizing the time the solvent has to co-extract undesirables. When a quick wash/short retention time strategy is utilized in conjunction with chilled solvent, it can result in a concentrate with very low levels of impurities. Utilizing a short retention time and chilled solvent typically results in lower extract yield. This can be combated by utilizing a higher solvent to biomass ratio to ensure the majority of the target compounds are extracted while limiting the pickup of undesirable color pigments and plant waxes. Typically, a solvent to biomass ratio of 3-5:1 is commonly utilized to perform a butane extraction. Up to a 10:1 ratio can be utilized when extracting with cold solvent to ensure the majority of the desired compounds are extracted.
The solvent to biomass ratio is the final factor in the initial saturation that can be optimized. Most commonly, a ratio between 3-5 pounds of butane solvent will be utilized for every 1 lb of biomass loaded into the material column. The greater the total volume of solvent utilized during the initial saturation, the greater the extraction efficiency. More solvent used for the initial saturation typically allows for more of the target compounds to be dissolved from the plant matter. An increased solvent to biomass ratio is especially useful when utilizing a quick wash, short retention time saturation strategy. While this ratio can be further increased to ensure the target compounds are extracted from the plant matter it results in a greater total volume of solvent used, increasing production costs, extending the solvent recovery process, and increasing overall runtime.
After the initial saturation is complete and the entirety of the botanical extract-rich butane solution has been drained into the collection vessel, the bulk of the solvent recovery process is performed by heating the solution to evaporate the butane solvent from the botanical extract solution. The solvent recovery process is a distillation process initiated by applying heat to the extract solution to evaporate the extraction solvent from the botanical extract and the condensation of the ensuing solvent vapors inside a chilled recovery tank. Typically the solution is heated by either submerging the collection vessel in a hot water bath or recirculating hot water through the jacket of the collection base.
The solvent recovery process can be performed utilizing two separate methodologies: active solvent recovery or passive solvent recovery. Both passive and active solvent recovery utilize heat applied to the collection to evaporate the solvent from the extract and cool the recovery tank to condense the butane vapors inside a vessel separate from the extract. Active recovery assists the solvent recovery process by including a recovery pump that aids in the transfer and compression of the gaseous solvent, speeding up the solvent recovery process. While both methodologies have their benefits and drawbacks, both can be utilized to recover butane solvents effectively.
Regardless of the solvent recovery methodology, the collection vessel containing the extract solution is heated to initiate the solvent recovery process. The recovery tank is chilled and commonly pulled under vacuum only if the solvent tank is empty to create pressure and temperature differential between the heated collection base and the chilled recovery tank. This pressure and temperature differential between the two vessels results in the solvent vapors being attracted to the lower pressure and temperature recovery tank once the process connections between the two are opened.
Note that if the recovery tank contains solvent, do not attempt to pull the recovery tank under vacuum as solvent vapors can be pulled out of the vessel into the vacuum pump, potentially causing ignition of the solvent vapor. While reduced pressure within the recovery tank assists in the travel of vapor from the collection vessel to the recovery tank, if the recovery tank still has solvent within it, the solvent recovery process can still be performed relying solely on the temperature differential between the two vessels. However, the pressure from the collection vessel must be greater than the pressure within the recovery tank, which can be ensured by keeping the recovery tank as cold as possible during the recovery procedure.
During the solvent recovery process, the movement of the solvent vapor within the system operates under the principle that gas always seeks the lowest pressure region of a system. The pressure of a hydrocarbon gas directly correlates to its temperature by heating the hydrocarbon solvent within the collection tank, thus increasing its pressure. Moreover, by cooling the solvent recovery tank the ensuing vapors naturally are pulled towards the lower pressure chilled recovery tank where they are condensed and their pressure is reduced.
The efficiency of the solvent recovery process is a function of the thermal energy applied to the collection vessel and the amount of cooling applied to the solvent tank. Since butane and propane have relatively low boiling points, light heat is sufficient to perform the evaporative process. While increased heat will speed up the solvent recovery process, it is a double-edged sword as it may degrade or evaporate the more volatile compounds typically found in the botanical extract like terpenes. During this process, it is important to keep in mind the lowest boiling point of the compounds to be preserved, and stay under that temperature when determining the heat level to apply to the solvent recovery process.
The other side of this solvent distillation process is the condensation of solvent vapors inside the recovery tank. Condensation happens when vapor is cooled or condensed past its condensation point and is initiated by the molecular clustering of vapor within a gaseous volume or at the contact of vapor with a cool enough liquid or surface. This process can be assisted through the use of a condensing coil submerged in dry ice, which provides a high surface area low-temperature zone where vapors can be condensed before entering the recovery tank. Typically the colder the recovery tank or condensing coil, the more efficiently the solvent will be recovered and collected.
While it is typical for the bulk of the butane or propane to be recovered during this time, depending on the specific type of extract to be produced, more or less hydrocarbon solvent may be left to be recovered by the vacuum oven or used to perform evaporative crystallization.
After the desired amount of the hydrocarbon solvent has been recovered, The recovery tank and collection vessels are isolated, and the collection vessel is depressurized after the desired amount of the hydrocarbon solvent has been recovered. The extract is then harvested from the closed-loop system. The residual amount of butane or propane remaining within the extract is purged utilizing a vacuum oven. Once the extract has been purged of all residual solvent, it can be used as is or further refined through distillation or isolation.
After the closed-loop solvent recovery process has been performed and the extract has been harvested from the closed-loop system the butane extraction procedure is complete and the resulting extract can be purged of residual solvent and further refined. Now that we have covered the proper butane extraction safety protocols and extraction methodologies let's dive deeper into the extraction preparation and actual operation of a closed-loop system in Part 2.
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