Disclaimer – this post does not address all the safety issues for the crystallization of CBD, Pentane, and other volatiles. They can be very dangerous due to their low flash points. Don’t try this without consulting your safety officer and evaluating all of the possible safety concerns. As always, wear safety glasses and other personal protective gear when working in a lab.
Quality CBD crystals begin with Quality CBD distillate
The starting material should be extracted from CBD oil that has been winterized and distilled. The CBD distillate should be clear. Any cloudiness means there are contaminants like water, waxes, and fats. If the oil is cloudy, try winterizing again until the oil becomes clear.
If you crystallize oil with contamination, it will lead to poor yields.
Use a jacketed vessel with stirring to dissolve and crystallize the CBD. A heating/cooling bath is connected to the vessel jacket. Use this to control the temperature of the vessel.
The ACS-grade pentane will be the solvent. This can be dangerous stuff, so make sure to consult your safety officer!
Dissolving CBD Oil
Next, dissolve the clear CBD oil in pentane. Make sure the jacketed vessel’s vent/condenser is connected to an appropriate blower motor or fume hood for pentane vapors. The boiling point of pentane is 36 °C. Even at lower temperatures, pentane will release many vapors.
BE CAREFUL AND TAKE ALL PROPER PRECAUTIONS! Make sure the vessel condenser is cooled to -20 °C. Add 1 part pentane to 2 parts CBD oil (some oils require slightly more or less pentane) in the jacketed vessel. Turn on stirring and turn on the heating bath and set to 45 °C. Wait until the solution reaches 45 °C and all the oil has dissolved.
Set the bath to 5 °C, and slow the stirring. As the solution cools it will become more viscous. Then, adjust the stirrer to keep the RPM above 120.
CBD crystals will spontaneously form or “crash out” of the pentane solution. Keep reducing the temperature to at least -10 C. What temperatures you use and how they change over time can change the growth of the crystals.
Collect CBD Crystals
Once precipitation stops, flush or physically remove The CBD crystals from the reactor. Vacuum filter the crystal/liquid slurry to remove the mother liquor from the CBD crystals. Rinse the crystals with ice-cold pentane to rinse impurities from the crystal surfaces. More rinses with pentane can improve poor color, but losses in total yield will occur. Keeping the CBD and materials cold during this step will help give you a better yield.
Reprocess Mother Liquor
The mother liquor still will contain dissolved CBD. However, you can reprocess this solution! One caveat is that the mother liquor will accumulate THC over time. This sets a practical limitation to the number of crystallization.
CBD distillate with 70 – 75% CBD content can be crystallized to produce CBD isolate (crystals) with a 90+% purity or higher.
Conversely, CBD distillate with less than 70% CBD can be crystallized to produce CBD isolate with 85+% purity or higher.
You can re-dissolve CDB crystals and then recrystallize them to improve their potency even further.