By Rick Batten
Tetrahydrocannabinolic acid (THC-A), as well as other cannabinoids, can be extracted from cannabis reaching up to 99.97% purity depending on the methods used. The process of recrystallizing THC-A is highly dependent on many variables. In our research we have found that every strain reacts uniquely to this process, but for the most consistent results we recommend using fresh frozen plant material that has been extracted at sub-critical temperatures using a solvent with a low boiling point. This ensures maximum terpene retention, which aids nucleation. In order for THC-A to crystallize, we need to saturate the solution—meaning the solvent in the solution can no longer dissolve any additional solute (THC-A)—and then super-saturate the solution such that THC-A crystallizes out of solution. There are many methods for reaching super-saturation, but for simplicity let’s explore cooling and evaporation for secondary nucleation (seeding).
How it works
For the methods of cooling and evaporation, we want to focus on controlling the “state” of saturation by treating solubility as a function of temperature, which ultimately determines if crystals form. One strategy for increasing solubility is to increase the temperature of the solution, which allows the solvent to dissolve more solute and (at high enough temperatures) encourages evaporation of solvent. If you saturate the solution at elevated temperatures, by cooling the solution you will decrease solubility, thus dropping solute (THC-A) out of solution by either spontaneous nucleation or the introduction of a nucleation site (seeding), forming THC-A crystals until the systems reaches equilibrium. The remaining solution will likely consist of other cannabinoids and terpenes. You can also super-saturate a solution by slowly evaporating solvent from a saturated solution. It’s important to note that these methods may not result in 99.97% purity, as doing so often takes additional steps, such as using more aggressive solvents, centrifuges, and roto-evaporators, and it can be difficult to control all variables.
There are many methods and variables not covered in this brief Tech Tuesday article, so contact us to discuss which method(s) will work best for you or for help optimizing your process!
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Seodigeng, Tumisang, director. INTRODUCTION TO CRYSTALLIZATION FROM A SOLUTION. Youtube, Baas Technologies and Consulting, 5 Nov. 2015, www.youtube.com/watch?v=SHu_P-YRNuQ.