A closed-loop system is a term used to describe the equipment that allows processors to extract the active compounds from the cannabis plant using a variety of solvents in a safe, efficient environment. It is referred to as closed-loop because the solvent being used to extract the compounds from the plant matter does not come into contact with the external environment at any point during the extraction process. Also, the solvent makes a full loop on its phase change from liquid to gas and back to liquid again — the solvent starting and finishing in the same space.
How does a closed-loop system work?
Closed-loop systems vary mechanically, depending on the solvent that will be used. However, the general method remains the same. There are three main containment areas: a vessel that contains the primary solvent, one for the cannabis plant material, and one that is used to collect the resulting extract.
Depending on the type of solvent being used, e.g. butane or carbon dioxide (CO2), the solvent may need to pass through the cannabis plant matter multiple times in order to strip off all the precious compounds, such as the cannabinoids and terpenes. For instance, butane is one of the most effective solvents and is capable of extracting almost all of the essential properties in one loop through the system. On the other hand, CO2 is a much more selective solvent and will take several more runs, and several more hours, to fully capture all the intoxicating and therapeutic properties of the cannabis plant.
The process begins with a tank of liquid solvent or a gas that is mechanically converted into a liquid solvent. The next step is to allow the liquid solvent to flow into the tank with the cannabis buds or trim. At this point, the solvent will dissolve the active compounds in the plant and create a solution. The final tank is where the resulting extract goes and where the initial solvent used is evaporated from the solution through the use of heat. When the solvent evaporates into a gas, it rises and is condensed back into the first tank. The solvent can then be reused, either on the same cannabis or for a fresh batch.
What are the risks?
Each solvent has its own hazards and precautions are taken according to the solvent being used. Some solvents are flammable, while some are asphyxiants. Some operate at low pressure, others operate at high pressures. Each solvent is different and requires different engineering controls to ensure that all hazards are mitigated during the extraction process.
Though it gained a bad reputation in the media for explosions that happened during “open blasting” — where the solvent is exposed to air during the extraction process — butane has a “Generally Regarded As Safe” GRAS rating by the FDA, meaning it is Its flammability, however, makes using a closed-loop system the only available method of butane extraction, as open blasting has proven to be a dangerous alternative.
CO2, while not flammable, is an asphyxiant that requires an extremely high amount of pressure to convert it from a gas into a supercritical fluid form that is capable of extracting the compounds from cannabis. The engineering controls used in these systems monitor the relative CO2 concentration in the air in order to ensure that workers are safe throughout the entire process. Safety measures are taken no matter the solvent, with sensors in place to detect even trace amounts of gas.