Sooooooo, why not passive SCFE CO2 extraction! The sabriousness of CO2 certainly makes it attractive, and C02 becomes supercritical at only about 31C/87.8F at 1073 psi/7.38MPa.
Just too too bad that the equipment is so expensive, compared to some of the other extraction methods, that it is pretty much priced out of ma and pa’s medical cannabis budget, but how about DIY Passive SCFE CO2 extraction?
Here is the story of my quest for easily affordable CO2 extraction and how you might assemble one yourself.
My first design was this simple minded system that relied on dry ice to provide the CO2 as well as the pressure required for SCFE.
You load the material, along with “enough” dry ice to raise the assembly to the desired pressure once it warms and vaporizes. The rule of thumb I worked from was that 500 grams of dry ice produced about 250 liters at atmospheric pressure.
From that, if we assume fixed volume, we can use Boyles and Charles gas laws to determine pressure at temperature.
P1V1 = P2V2 and V1/T1 = V2/T2
A back pressure regulator would vent anything above set pressure, so over pressurization wouldn’t be a concern or issue:
Simple Minded DIY sub critical and SCFE CO2 extraction conceptual
The system is flooded by simply turning it upside down so that the material is soaking and right side up again to drain. Repeating that step not only soaks the material, but keeps the boundary layers minimized. After the final soak, the liquid is bled off into an expansion chamber, that bleeds to atmosphere, which leaves behind the harvested oil.
Before building it, I had already moved on to the following passive system using liquid CO2 instead. It uses vapor head pressure in the Dewar to transfer liquid, instead of a pump:
Simple Minded CO2 SCFE schematic
My original idea was to use an existing hydraulic cylinder offered to me for the purpose, but alas it was carbon steel, which embrittles and becomes a fragmentation grenade at cryogenic temperatures.
This system uses 304SS Schedule 180 pipe for the pressure vessel. It has a burst of around 17,700 psi. http://www.gfistainless.com/assets/resources/StainlessSteelPipe.pdf
I chose 4” X 24” so it would fit in my existing lathe and planned to machine plugs for each end, which sealed with O-rings and were prevented from blowing out with a simple yoke.
I planned to use 4” pipe band heaters to supply the required heat:
The expensive component was an off the shelf back pressure regulator and before I found one that fit my budget, enter Jyndustriez, whom loaned us their passive system test sled to play with, which consisted of an off the shelf CO2 tank, which we simply packed with material and flooded with liquid CO2 from a second off the shelf tank, and then heated it using silicone heat mats to achieve super critical state.
The designer went on to market a more refined version of the system, and followed up with a design using a CAT pump, before accepting a position with one his clients and moving on. Sadly I since lost track, so not sure where his final studies led him.
Here is the package as we received it laid out on a sheet, which covered everything we needed except a tank of liquid CO2, which we rented from Industrial Source:
The scuba tank used for the extraction vessel is the black bottle in the upper left, and the shiny stainless tank in the upper right is an Eagle ASME pressure tank, which we transferred the laden liquid CO2 into and vented to atmosphere via a 150 psi PRV.
The shinny blanket in the lower left is a fiberglass welders blanket used for insulation and the red mat on the right is a 12" square silicone heat mat. On the far right is a PID wire tied to a plank which has the SSR for the heat blanket attached. This was the designers test sled, so doesn't meet IEC electrical standards with regard to shock protection, though adequate for our experiments.
Here is a picture from one of their advertisements, showing what their final design ended up looking like. Sorry for the lack of clarity, but it is an enlarged thumbnail, rather than one of my own pictures.
As you can see, they are purdier than the test sled........:
The slick part was that it worked and we did an extraction at about 3500 psi, and after washing it out of the Eagle decompression tank with ethanol, here is a picture of the solution after the plant waxes had precipitated.
Winterized SCFE Extract in ethanol, ready for filtration.
Wowza, what a purdy extraction, virtually devoid of undesirable elements with color, and made a purdy concentrate, which alas smelled and tasted like Alfalfa, so process refinement required.
One suggestion was to do an initial subcritical extraction of the terpenes at 850 psi, followed by one at 4500 psi to harvest the cannabinoids.
I also sampled SCFE CO2 concentrates, supplied by Paddy when he was at Eden Labs, using one of their machines to do an active SCFE CO2 extraction, and fractioning off the terpenes on decompression, so I'm keenly aware of the potential.
While still not gem stone bragging rights purdy, I believe a strong contender in most blind smell and taste contests, restoring my faith in the process, especially for medibles, pharma, or e-pen carts.
While we've confirmed that it works, I am tongue in cheek about a couple of limitations with passive SCFE that I've noted.
1.0 The first is that because we are using heat to apply pressure and the pressure rise is relatively slow, we subject the extraction to the full temperature pressure curve, rather than arriving at a targeted temperature and pressure rapidly.
2.0 CO2 is a relatively small molecule, so limited in carrying capacity. A passive system is limited in solvent volume and flow, so isn't optimum efficient extraction.
On the other hand, it is more inline with most of our household budgets, so for those of ya'll hankering to try it for yourself, here is what JYNdustries shared before moving on:
How-to CO2 Extracts, by JYNdustries
Yes, you read correctly. I am sure there are still missing details, but I wanted to get this up for you guys and gals. Here goes a small piece of my brain trust.
Disclaimer: This process is inherently dangerous. There is zero guarantee of safety as there are many ways that this can go wrong. You can die or get severely injured when handling pressurized metal vessels.
Please allow me to add at this point, that building and operating any DIY equipment featured here is at your own risk. They are passed on here for information only!
I will post pictures soon for your enjoyment, though a lot of them are available on my blog.
Ok, so you want to get super-critical fluid extracted oils and you are not sure of the most practical way to do so. Good news, this thread is for just that! I will outline some simple methods that I have VERIFIED personally to work consistently, these are not concepts. This is not cheap to do when compared with hydrocarbons. This is just the nature of high pressure extractions. You need quality parts that will be under pressure and survive. So that way you too, can survive. There are a million and one custom designed extraction chamber and extraction system possibilities. This is how to accomplish extractions without needed extensive machining capability. I would love to see some complicated ones too.
There are many ways to accomplish carbon dioxide extraction and I welcome those who have knowledge to share some tidbits and opinions. This is not complete by any means (I am just really tired right now); I will edit the thread as time goes on and add things when others have some cool stuff to input. I would like to make this a thread on working concepts and not untested ones.
Please do not insult anyone’s ideas to make these extractions better, safer, cheaper, etc. All ideas are welcome here and I would appreciate polite group construction of protocols and ideas for safety and efficiency's sake.
Please respect that even getting to this level of success has been a long and not easy journey of more trial and error cycles than I care to think about. Much blood, sweat, tears have been spilt on this journey and I am giving away my experience for FREE. I do not want thanks, only respect for those facts. I AM NOT GIVING THIS AWAY SO THAT YOU CAN TAKE THE IDEAS AND SELL THEM. THIS IS FOR DIY’s THAT LIKE MYSELF CANNOT AFFORD TO BUY EVERYTHING THAT THEY WANT OR NEED AT RETAIL. I hope that everyone enjoys clean fresh extracts as much as I do.
STANDARD ALUMINUM/STEEL CO2 TANK LOW PRESSURE EXTRACTION
• 10# or greater CO2(extraction) tank and valve (with a siphon is best)
• 10# or greater CO2(storage/collection) tank and valve (without siphon)
• PTFE O-Rings (They last much longer than the rubber versions)
Thread Designation Valve Designation O-ring Size
.625 - 18 UNF CGA 323 206
.750 - 16 UNF CGA 320 210
1.125 - 12 UNF CGA 320 216
• Small swatch of SS 400 MESH or finer
• Crow’s foot
• Torque Wrench
• 2 x CGA 320 Nut (Typically have a max rating of 3000PSI)
• 2 x CGA 320 Inlet Nipple (Typically have a max rating of 3000PSI) - Nylon washers often come with these and are great because when they wear out, suitable replacements can be found at home improvement stores. Nylon does absorb moisture however, and any washer you use here will need replacement regularly.
• 2 x High-Pressure Stainless Steel Tee ¼ FNPT (3000PSI or >)
• 1 x High-Pressure SS Coupling ¼ FNPT (3000PSI or >)
• 2 x High-Pressure Oxygen Service Ready Gauges ¼ MNPT (0-4000 or 5000PSI Commonly Available)
• 2 x High-Pressure Stainless Steel Needle Valves ¼ MNPT (or 1 x Needle + 1 x Ball Valve) - It will be up to you to adapt the valves to the hose, often this changes due to stock availability, fittings are easy to find in ¼ NPT so I order whichever combination is suitable and cheapest. PTFE or Delrin seats are suitable; Delrin requires more pressure to seal.
• 1 x High-Pressure Transfer Hose with ¼ MNPT (Use Smooth-Bore PTFE Lined SS Braided Hose) - Be aware of the operating pressure ratings. I like to use hose with brass ends against the SS to lessen galling from constantly modifying set-ups.
• 1 x Roll of High-Pressure (10000PSI Oatey is suitable) or High-Pressure Thread Sealant
• 1 x Digital Temperature Controller and Thermocouple - This is vague because the requirements will change depending on the wattage and voltage of your circuit. If you go with 115v, 720w heating pad you will need a controller that can handle (720w/115v) = ~6.26 amps (call it 6.5 amps to be safe). A great option is find a controller that has a solid-state relay attachment point, or hack one that has a 12v circuit to be able to use an SSR. Most controllers come equipped with electro-mechanical relays that have low amperage capability and short lives. Using an SSR gives the user more freedom to choose the wattage of their heating pad. The temperature range should be appropriate for the pads, no aquarium controllers, etc.
• 1 x Solid-State Relay (optional)
• 1 x Appropriately Rated In-Line 115V Fuse – By appropriately rated I mean the same amperage as the home fuse of the circuit it will be plugged in to or LESS.
• 1 x Flexible Silicone Heater (500W or >) Watts/Volts=Amps
• 1 x Heat Resistant and Flame Retardant Blanket (Welder’s Blanket)
Without a photo this is the easiest way to explain the transfer assembly:
CGA 320 Nut and Nipple - Needle Valve - SS Tee With Gauge on Top - Hose - Ball or Needle Valve - SS Tee With Gauge on Top – CGA 320 Nut and Nipple
The reasoning is to have the exit valve, a needle valve, as close to the collection container as possible when collecting your oils and purging the CO2. Later, I will outline how to make a container with ideal conditions for collection, but it will require drilling and tapping threads into metal, or drilling and welding so it is a little more advanced but not terribly. Remember the concept of expression valve placement being as close as possible to the end product container is VERY important. RAMBLE>Also IMO having the immediate area surrounding the opening of the valve should be many times larger in diameter than the opening of the needle valve itself. Using a prebuilt valve and container such as SCUBA or CO2 tank as a collection container cannot utilize this. That would require using the tank valves, with rubber seats, as the expansion valve. Do not do this, for many reasons. If you cannot make a collection vessel or obtain one made custom, resign to the fact that you will be releasing the oils beginning at the brass CGA fittings on the transfer assembly first and they slide and spit down into your container this way. Not the most ideal of situations but it works OK and you can collect your oils stuck in the assembly with a small amount of alcohol, which you will need anyways to get the oils from your large collection vessel.<END RAMBLE.
Use the PTFE/Teflon tape around the threaded fittings and tighten securely. You should conduct a dry pressurization of the transfer assembly with clean CO2 first and tighten as needed where any leaks are found using dish soap and water.
Have your storage tank filled with a beverage grade or higher carbon dioxide source.
Take thoroughly dried plant material and grind it to a fluff. Use a small funnel and load the cylinder. Replace the valve and siphon with filter (small SS Mesh secured to bottom via SS Clamp) into the neck always checking the o-ring for signs of stress.
The final tightening should be done with some indication of torque. Aluminum is VERY prone to galling on the threads, a form of frictional wear. This is one of the reasons why brass valves are used almost uniformly across the cylinder industry. Brass is resistant to galling and using two different metals for thread on thread contact is usually a better situation for preventing this. IME 35ft-lbs is a safe number that will adequately seal the PTFE ring and valve threads to the aluminum tanks. Steel tanks usually require slightly higher torque on the valve, but they can handle more as well. Since they are non-stainless they are OK as far as galling is concerned.
When using a crow’s foot to torque the valve on remember that the torque on the wrench will read lower than the torque on the valve due to the increased distance from the rotational axis. Torque=Force*(Perpendicular Distance From Force Applied to Rotational Axis). Using this I have also torqued my cylinders with a combination wrench and hanging a dumbbell at the right distance from the valve on the wrench.
Once the setup is packed and the valve is properly torqued attach the transfer assembly firmly to both tanks. Use a wrench if you need to, to ensure the nylon washer seats well against the valve inlet. Open the valves across the assembly. The carbon dioxide will flow and stop. Attach the heating pad to the bulk storage tank and begin to warm it. Be careful that the entire system never rises above the operating pressures of the tank. In fact with increased heating (above 100F is when the rated pressure is considered lowered for most metals) tanks are less able to withstand pressure and so should be run below the normal operating pressure or else you are taking SEVERE risk. When you achieve a pressure you are comfortable with across the system let it stand and continue transferring CO2 as long as the hose furthest away from the tank with the heating pad is still warm. This means warm molecules from sending tank are still making their way across the line into the receiving tank. THE MORE CO2 YOU HAVE IN YOUR EXTRACTION TANK, THE LOWER THE INTERNAL TEMPERATURE MUST BE TO ACHIEVE DESIRED EXTRACTION PRESSURE. This is important because when you get into pressurizing the extraction tank for extended periods the metal is not as hot and so does not lose its strength properties as much. Place the extraction tank into a very cold bath to help transfer even more.
When the transfer is complete shut the valve on the storage tank and the valves on the transfer line. Disconnect the storage tank and place the heating assembly on the extraction tank. Always place the thermocouple in between the heating pad and the extractor. You want the temperature reading to be as related to the actual container as possible. This is an acceptable way to monitor if the temperature of the container is constant, but not an accurate way to determine the actual internal temperature of the carbon dioxide. The temperature inside will be much lower than the reading at this point. In fact the temperature at this point will not tell you much besides the fact that you are putting a consistent amount of heat energy into this system. If you want to know pretty close to what the internal temperature of the carbon dioxide is without a probe, you will need to know the weight(but really the mass) of the CO2 inside the tank, and the pressure reading.
Pressurize the extraction tank by raising the temperature setting on the controller. Until you are familiar with the heating ability of your heating set-up raise the temperature slowly. Say 5C increments every ten minutes. When you get close to your comfortable pressure, slow this down until you determine what temperature will give you the pressure you desire continuously. Remember this will change to some extent based on the amount of carbon dioxide inside the container. The pressure in the system is MOSTLY dictated by temperature but very small or very large amounts of carbon dioxide will change little, or GREATLY with temperature increase respectively.
I AM SPECIFICALLY OMITTING AN EXACT TEMPERATURE OR PRESSURE YOU SHOULD OPERATE AT, THIS IS 100% ON YOU, THE READER.
Each low pressure extraction should cook IMO at least six hours. If you agitate the container in some fashion throughout the extraction to increase flow you can lower your times for extracting.
In these low pressure tanks you will most likely want to send the carbon dioxide back and forth to reuse the solvent, mostly clean, for many extractions on the same plant material. At low pressures without some kind of an automated cycle this is very laborious. You accomplish this first via sending heated and pressured CO2 with oils dissolved through the siphon into the storage vessel. In this situation you will ideally have two containers of the same size so that the receiving collection container is almost empty from filling the extractor. Initiate the transfer with all valves open besides the final needle valve before the collection tank. Even the collection tank valve should be completely open. Slightly open the needle valve and allow the carbon dioxide to begin transferring restricted in a way that the pressure drops very slowly on the high pressure side. When that transfer is complete shut off the valves and cool the collecting container so that you can be certain via the pressure that the carbon dioxide is no longer supercritical. Go well below 1000PSI. Remove the collector from chilling bath. Leave the transfer line attached.
You will now need to place the extraction tank in some cold liquid bath. Attach the warmer to the storage tank. Allow as much carbon dioxide to transfer to the cold tank as possible before turning the warmer on. Set to a low temperature and never allow the transfer to exceed 1000PSI. If the pressure goes above 1000PSI and most of the gas has transferred from the storage tank you can bet that the temperature inside must be above 87F and so there is some transfer of oils back out of the collection tank happening. Avoid this or you are wasting your time transferring in this manner. The idea is that the liquid CO2 and massive oil molecules sit at the bottom of the subcritical mix inside the collection container, as long as the CO2 does not go supercritical only the less dense gas and some aromatics will transfer back into the extraction tank. This means you have clean CO2 with fresh ability to solubilize the essential oils. This is very important in low pressure extractions like these because the solubility of carbon dioxide and essential oils together are low. If you not transfer dirty CO2 back into the extraction tank not only did you waste the time from the previous extraction but because of the small amounts of carbon dioxide we are dealing with you likely are not picking up as many oils from this run either because the solution is closer to saturation. Conduct and repeat these cycles at least four times unless you want to be utterly disappointed by the yield.
On the final transfer of hopefully saturated carbon dioxide to the collection vessel be very careful to maintain the pressure as high as you are comfortable with considering safety recommendations and the amount of heat involved. This will ensure that the CO2 has the highest solubility for the period that it is transferring, meaning more oil will move in the transfer of saturated CO2 of the same amount of mass of carbon dioxide with all things being equal besides the pressure being higher. So always strive to have this condition.
I always shut the transfer off to allow the extraction tank to regain pressure when I notice it dropping low. Again, I caution as the CO2 leaves the hotter chamber it will take higher temperature to maintain the same pressure. This makes the situation more dangerous.
During these times that I intermittently shut the transfer off I vent carbon dioxide from the collection tank so that the transfer of CO2 out of the extractor will be complete. This is only done on the final run.
When the transfer is complete, depressurize both tanks ENTIRELY. You will want to store them empty, no need in leaving them under pressure and increasing the strain they endure from your abuse. It is easily imaginable how to reclaim the carbon dioxide with either a third tank, or by cleaning the depressurized extraction tank and using it as a storage cylinder. I no longer do this due to labor/gain ratio IMO.
Collect your oils by removing the valve from the COMPLETELY DEPRESSURIZED collection tank and pouring some warm ethanol inside. Slosh around and pour out. Repeat this until you are confident you have everything. You will wish to filter this solution if using aluminum tanks, I find they often leave shavings, especially if they are not thoroughly cleaned. Shavings are often from valving the cylinder and can be prevented by using the appropriate size wrench, and also die threading a piece of pipe to be a spout for pouring the alcohol. Then evaporate the alcohol with a small fan and time, or light heat.
MODIFICATIONS TO GET THE MOST OIL (MY PREFERRED AND RECOMMENDED METHODS)
Stronger Tank and No More Yo-Yoing
Reasoning that lead me here was the increased solubility at increased pressure and temperature of most varieties of plant oils. More oil can be dissolved in the same amount of carbon dioxide. The same idea here is behind transferring the saturated solution when possible as supercritical fluid. I no longer cycle the CO2 back and forth between tanks. Now I conduct individual high pressure extraction runs and vent the CO2 off as gas through a relief valve while collecting the oils in a convenient container that is much smaller than CO2 or other large pressure vessels. No more PITA manipulating of a large tank to drip out the last of my oil and alcohol inside.
Replace the normal extraction tank with a STEEL SCUBA TANK that has a pressure rating of 3442 PSI or greater. I easily fill five pounds into 3.3L tanks and seven into 4L tanks. Do not judge the capacity by the cubic foot of air the tanks will hold if filled to a certain pressure. Find the internal volume of the tank. You will need to safely adapt the scuba valve to CGA 320 fittings so that it may be connected to the carbon dioxide transfer line easily. Most US Scuba valves have a removable threaded insert that allows them to adapt to European DIN specifications. This threading is 5/8 BSPP (British Standard Pipe Parallel). Adapters with this exact threading can and should be sourced to reduce the diameter and change the thread standard to NPT. You will also no longer have the siphon and filter option in that manner. There is a dip tube threaded in to most SCUBA valves and is a great potential source for a filter. For my purposes I find it easier to use in line high pressure instrumentation filters between the the BSPP adapter and the necessary MNPT to CGA adapter for transfer connection to the SCUBA.
To increase yield I upturn the SCUBA tank while collecting oils. This allows for continued collection of the dissolved compounds in the CO2 when it goes back subcritical and separates into two distinct phases. The heavier liquid and oils will be wherever gravity puts them.
Never leave carbon dioxide or wet plant material for extended periods or these tanks will rust. You must store them dry and run plant material as dry as possible to prevent this. I have conducted many runs in the same steel tanks and have no rust upon visual inspection with a search mirror, eventually some will show up as it does commonly in SCUBA tanks normal use. The goal is to lessen this, and prevent it as much as possible.
There are many other options for high pressure vessels that are used in all corners of industry. Be ever searching for the most accurate and detailed specifications by the manufacturers and safe pressures based on temperature ratings so that YOU can make an informed decision on risk.
Notice that even the SCUBA tank has a pressure rating greater than the operating pressures of the fittings on the transfer line. Therefore pressures should be kept below the LOWEST maximum pressure of any component under pressure, know your weakest link. Fittings, hoses, and gauges are easily found that have operating pressures of 7000PSI and above. The limit is available parts, the limit is cost.
Build Your Own Collection Vessel
The benefit is tremendous in terms of ease of collecting the oils. Not only can you use a much smaller container, or a large diameter opening container, you can also place the expansion valve right at the collection vessel itself making for a better environment for expansion. Honestly I do not know enough to speak on this particular point explicitly but I do know that turbulence at the expansion valve and releasing the oils into small diameter pipe is not a good thing from my experience alone. So far I have collected more oil with all things the same except for the better release point. Take it for what it is worth.
The collection vessel does not need to be able to withstand the pressure that the extraction tank does. But it does NEED a relief valve of some sort set at a safe pressure based on the ability of the container. I find that there is less sputtering during the release if the pressure is high enough that carbon dioxide can exist as a liquid. 150PSI is a decent number to prevent immediate sublimation.
Using my modifications described above I consistently yield 20% weight from good quality flowertops in THREE EXTRACTIONS with five and a half pounds of carbon dioxide and four to five hours each run. This has been tested to be true up to four ounces of flowertops at one time. That is less than twenty dollars in CO2 if you take care. More plant may require more extractions, but carbon dioxide does appear to remove similar weight to hydrocarbons given proper care. Also I take care to keep the transfer above 2400PSI to be above the inversion point where solubility does not increase with increased temperature, since we are using heat this is important if it is possible to achieve safely. Which it is NOT in CO2 storage tanks of any kind that I have found
Always dissolve the final oils in a small amount of alcohol and then evaporate it. This is NOT winterizing although some wax will separate but you do not have to remove it, just stir it back in after the alcohol evaporates. Regardless of how they are collected you will want to remove the carbonation from the oils. If they are not freed of carbon dioxide they lower in quality and taste, quickly. If they are applied to heat while carbonated they will pop and jump.
Some viewing material by yours truly. Some methods are so dangerous I no longer practice them, ever. Such as strapping a rocket ship upside down on my back porch while collecting oil. I now rest the tanks secured upside down with the valve against the ground. If the tank is strapped above the ground like this is could fall and the valve may break which would send your tank into your neighbors house, or YOU, or SOMEONE ELSE. Always be sure the tanks are supported by an immovable base when upturned.
Hee, hee, hee, I noticed this desk top SCFE CO2 unit with pumping system at a gathering!
OCO Labs Tabletop SCFE CO2 Extractor