What is Closed-Loop Extraction?
A "closed-loop" refers to a system in which the entire process is done within a "closed" vessel. The solvent used to extract does not ever come in contact with the outside atmosphere. The "loop" portion refers to the recovery and reuses aspect of the system. The solvent will start inside one vessel, and then move through another containing botanical material, after which it will return back into the original vessel hence creating a "loop". Closed-loop extraction is a fast, efficient way to remove essentials oils from botanical material and, when operated properly, is extremely safe.
What is Solvent?
A solvent is a substance which is able to dissolve and absorb other substances when it comes in contact with them. There are many different types of solvents, some of those are; butane, propane, iso-butane, pentane, hexane, ethanol, isopropyl alcohol, acetone, benzene, chloroform, methanol, and even water. These are just a few of the many solvents found throughout the chemical world. Many solvents are carcinogenic or extremely flammable, which means proper safety procedures should be observed at all times.
When performing a closed-loop extraction, the most common types of solvents used are hydrocarbons. These compounds consist entirely of hydrogen and carbon molecules. Many of these hydrocarbons occur naturally on Earth in crude oil. The production of these hydrocarbons is done in large petroleum factories around the world where the hydrocarbons are separated and used as a combustible fuel source, aerosol sprays, and solvents.
The most common hydrocarbons used in our industry for botanical extraction are butane and propane. Butane and propane are both gases at standard atmospheric pressure. This means that if butane or propane were exposed directly to air, they would boil off into the atmosphere. To turn butane or propane into a liquid, we need to adjust the temperature and/or pressure accordingly. Please refer to the vapor pressure chart below for more information:
The Major Components of a Closed-Loop System
There are three major components of a closed-loop system. These are the solvent tank, material column, and collection base. Every system uses a combination of these three components interspersed with valves and different connections. Some more advanced systems may have multiple material columns, multiple solvent tanks, or a combination of all three. Some systems may even have a fourth component known as a "dewaxer", these will be discussed in a future post. For now, just remember the three major components. When looking at a system for the first time, try to identify the three major components first before trying to figure out the valve layouts. Once you can easily identify all three parts, it will become much easier to understand where and how solvent will move through the system. Refer to the picture below for identification of the three major components:
The Chemical Process
So how does a closed-loop actually work? Your solvent tank will contain your desired solvent. In this example, we will use butane as our solvent. Your material column will contain your desired material. For this example, we will say it is 1lb of freshly trimmed indoor-grown Girl Scout Cookies (one of my personal favorite strains).
The first step to remove the oil from our material is to input our butane solvent. We will open our solvent tank and allow butane to begin flooding our material column. As the butane makes contact with our material, the essential oils will begin to dissolve into the butane. As our solvent works its way through the material, the essential oils continue to be dissolved, leaving us with a butane/oil mixture.
Once the butane/oil mixture falls into the collection base, we must now separate the two. To do this, we must evaporate the butane. Since this is a "closed-loop" we will also need to recollect the evaporated butane back into our solvent tank. This is done by placing the collection base in warm water and placing the solvent tank in dry ice or ice water. This will create a temperature differential. The butane will begin to evaporate and escape the collection base, which will be pulled into the solvent tank by this temperature differential.
Butane vapor is attracted to the cold solvent tank so, the colder you can make the solvent tank, the faster and more efficiently the butane will be recovered. Inside the solvent tank, the vapor butane will re-condense into low-pressure liquid. Once all butane has been evaporated from the collection base, all that will be leftover is the oil we extracted from the Girl Scout Cookies. Our solvent tank will be filled with butane which we can reuse and the "loop" will be completed.