This is a personal project of mine, one of many i hope to share over time with the community.
I encourage others to play around with this and other solvents, so we can get a better idea of
how we can isolate crystalline cannabinoids from raw oleoresins.
Crystallization of THC-A with acetone
This tek is to explore other possible routes of isolation of carboxylic THC, using acetone,
instead of a traditional non-polar solvent like butane, hexane, pentane, etc. Acetone tends
to be fairly volatile at room temp, and can be removed via vacuum and heat, over time, in a
vacuum oven. The strength of this is that we can remove the solvent without reaching temps
that will cause decrboxylation to occur, therefore, preserving the fragile compound we are after.
As long as there is no acids or bases with heat, there will be no side reacitons or isomerizations.
I have tested and confirmed this on my GC-MS, by running a sample before acetone dissolution, and after. The only changes were the removal of fats, narrowing the amount of compounds present, and increasing cannabinoid concentration per ml of oil.
First off, there are a few methods to end up with the same result.
- Freeze cannabis and acetone as cold as you can get it. the colder the better. fresh dry cured
material is the best as it will have high THC-A content. (I havnt tried fresh frozen yet, im
worried that water pickup would cause issues later in the process.)
- Quickly pass the solvent through the cannabis to extract the cannabinoids.
- Refreeze the solution for 24 hours to drop out any fats and waxes (Winterization). Acetone does not really like fats, thus they should be minimal.
- Take BHO and dissolve in acetone. A large amount of fats will drop out immediately, filter these at room temp.
- Freeze solution and filter, like a standard winterization. 24 hours at -25C does well for me.
- Rotovap the solution around 35C under vacuum. this is important as you dont want to decarboxylate the material.
- When it becomes thick like syrup but still contains about 5-10% solvent shut er down.
- Pour the remaining solution into a mason jar or a crystallization dish. The key here is to have a “skin” form on the top of the oil/acetone solution so it slowly releases the solvent over time.
- The solution will decrease in volume over the next day or 2, depending on the room temp.
- Take a sterilized needle or glass rod and scratch the bottom of the dish to create nucleation sites.
- Do not agitate or move the dish from this point on. Less movement = More defined crystal formations.
- Let it sit in a dark place around 18C for a week or 2. Crystals will form on the glass underneath the oil. They will eventually stop growing and stall out allowing you to pour off the terp/cannabinoid sauce on top.
- Remove the best looking cluster, and redissolve the crystals that remain by adding a small amount of fresh acetone over a couple hours with no mixing or agitation.
- Re-nucleate the solution by evaporating the solvent off in the crystallization dish at room temp until gets a skin again, or re-seed with your collected crystals from before.
This step can be challenging because if you add them too early it will dissolve them too.
- Let it do its thing. Its best to kinda leave it for a while and forget about it. This tek is not for impatient people.
Alternative methods i have played with:
- Pour butane rich oil from closed loop into a mason jar.
- Let evap for a bit until it is thick.
- Put on lid and wait 14 days.
- Small crystals will crash out and stay on bottom of the jar.
- Open jar and pour off sauce layer.
- Dissolve crystals and start at method 2 above.
This concentrates THCa right off the bat, allows for faster work.