How to Crystallize CBD – Make CBD Isolate

Disclaimer – this post does not address all the safety issues for crystallization of CBD, Pentane and other volatiles 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 CBD oil that has been winterized and distilled.  CBD distillate should be clear.  Cloudiness means there are contaminants like water, waxes and fats.   If the oil is cloudy try winterizing again until the oil becomes clear.

Crystallizing oil with contamination will lead to poor yields.

Note: High purity CBD distillate will start to slowly crystallize at room temps and below.

CBD Distillate Self-Crystallizing

CBD Crystalization Equipment

A glass or stainless jacketed vessel with stirring will be used to dissolve and crystallize the CBD.  A heating/cooling bath is connected to the vessel jacket and will be used to control the temperature of the vessel.

ACS grade pentane will be the solvent. This can be dangerous stuff.  Consult your safety officer!

Crystallize CBD

 

 

 

 

 

 

 

 

 

Dissolving CBD Oil

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 3 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.

Precipitation

Set the bath to 5 °C.  Slow the stirring. As the solution cools it will become more viscous.  Adjust the stirrer to keep the RPM above 120.  CBD crystals will spontaneously form or “crash out” of the pentane solution.

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.

CBD Isolate Drying
CBD Isolate ready for drying in a vacuum oven.

Reprocess Mother Liquor

The mother liquor still contains dissolved CBD. This solution can be reprocessed! One caveat is that the mother liquor will accumulate THC over time. This sets a practical limitation to the number of crystallization.

CBD Purity

CBD distillate with 70 – 75% CBD content can be crystallized to produce CBD isolate (crystals) with a 90+% purity or higher.

CBD distillate with less than 70% CBD can be crystallized to produce CBD isolate with 85+% purity or higher.

 

CDB crystals can be redissolved and then recrystallized to improve the potency even further.

18 Comments


  1. I have been making my isolate with 70 + percent distillate. Could you make isolate with a lower percentage? Say like 50%?

    Reply

    1. Hi,

      Yes it is possible to crystallize CBD from low purity crude or poorly refined oil. However, low starting purity will reduce both yield and purity of the crystallized CBD. The lower purity CBD “isolate” will have more color, smell, and THC content than if you used distillate. This will cause you to need a recrystallization step which is not the end of the world but has a real cost.

      Luke

      Reply

  2. I am interested in doing this process not on a lab, but more industrial process, do you know of someone who sells this equipment? Regards

    Reply

    1. At this time, there is not an industrial scale solution on the market. Anything like that would be custom designed and manufactured.

      Reply

  3. My CBD isolate smells like pentane when it comes out of the tank we use for crystalization. However when it is distillate I have that same smell is it the the terpenes causing it? The ratio used is 2:1 pentane being 2 and left for 20 hours in the tank at -10 Degrees C.

    Reply

    1. Hi,

      The isolate will contain solvent molecules trapped within and on the surface of the crystals.

      To remove residual solvent (pentane):

      1) Wash the raw crystals with cold (probably around -40 C) pentane on a vacuum filter
      2) Crush/Grind the crystals finely
      3) Use a vacuum oven to gently purge more solvent
      4) Flip the crystals in the vacuum oven to expose any trapped surfaces and continue the purge until tests indicate no pentane.

      -Luke

      Reply

  4. What (inexpensive but effective) testing equipment would you suggest we buy to test the pentane levels and CBD content of our isolate?

    Reply

    1. Hi,

      You are probably best having two different pieces of equipment for pentane and CBD. The reason being the types of detectors that can be used to quantify those compounds are different. For example CBD gives a UV spectrum where pentane does not. Also, due to the underlying principles of the two methods, their separations will occur differently.

      For detecting residual pentane levels, Gas Chromatography system with a basic detector should be relatively inexpensive. The most workable cheap option would be an FID (flame ionization detector). Slightly more expensive would be a quadrupole mass spectrometer. The quadrupole mass spec is a great detector for GC because compounds are fully separated and identified. Liquid Chromatography is better for quantifying CBD. This can be paired with a DAD (diode array detector, a form of UV-Vis spec.) or a mass spec too.

      Luke

      Reply

  5. Two questions. Firstly, why is pentane used instead of hexane ? Secondly, is it possible to grow a seed crystal for larger structures using the process described above ? Thanks for the well written instructions!

    Reply

    1. Hello,

      A big reason is due to the lower boiling point of pentane. The increased volatility makes handling and safety a little trickier, but with the benefit of easier removal from the final product. Since hexane and heptane require basically the same level of equipment precautions it isn’t a big deal to work with pentane.

      Other reasons may come down to availability, price, and what solvents are permitted in a state or particular lab. Also, I have heard anecdotally that hexane has a lower residual ppm limit than pentane in some areas. However I am not familiar with all laws so take that with a grain of salt.

      If you want to grow large single crystals you will need a modified process. Some steps would include much slower temperature changes, fewer seeds crystals/nucleation points, and a less saturated solution.

      -Luke

      Reply

  6. When you use pentane to crystallize your distillate is it somehow attracted to the CBD molecule specifically?
    Or is the process simply reducing all cannabinoids in the same ratios and pulling out the remaining liquids?

    Reply

    1. Pentane is chosen because at warm temperatures it can dissolve the full spectrum of cannabinoids. When cooled however, CBD becomes very insoluble and crashes out. THC and the tons of the other cannabinoids stay in the pentane creating a pretty pure crystal of CBD. Impurities in/on the crystals would be small amounts of things like cannabinoids, terpenes, and solvent.

      Reply

  7. Luke,

    We are trying to determine how many vacuum ovens we will need to process our CBD isolate. When our lab is operational, or when your distillation equipment arrives ; ) , we will be able to produce approximately 600 kilos of Isolate per month. Based on that figure how many vacuum ovens would you recommend? Lets use the Across International 1.9 CF oven as a starting point.
    I really appreciate all your input!
    Ross

    Reply

    1. Hi Ross,

      I am not sure of how exactly cubic feet converts to actual capacity for CBD. Especially considering different shelving/tray styles. You are probably looking at at least 24 hours total purging in the oven. 12 hours, flip, and then 12 more hours. So independent of what the vacuum can hold, you are looking at each oven be locked up for a day.

      AS A GUESS you are looking at 15-20 ovens. 600 kg/month -> 20 kg isolate a day -> Probably 1-2 kg per oven?

      Luke

      Reply

  8. We have a customer asking for a completely free isolate of any residual pentane. Is this possible? Right now we are at 200 ppm on a scale of allowable 750 ppm. What are your thoughts?

    Reply

    1. Hey,

      In short, yes getting an ND (None Detected) is possible. But, a better answer would take into account this the precision of the test you are using. How hard is the lab going to look? ppm, ppb, ppt? Lower thresh holds will obviously require more effort.

      750 ppm is pretty high even if legal. That’s realistically almost 1 part per thousand. In my opinion you should strive for the lowest possible amount anyways. People, even children will be consuming it daily so the more thorough the better!

      Using a vacuum oven at low heat for 24-48 hours may be required to fully purge. If this still proves to not reduce levels enough, try grinding to a finer size and intermittently flip the crystals in the oven.

      Reply

  9. Hello
    I was wondering if you had any suggestions on why sometimes my isolate will turn back into oil after it is crashed even at -30 c?

    Reply

    1. Hi,

      When is this happening? Over time in storage or when filtering and collecting the crystals? If this is happening over time then maybe it is being stored too warm. If this is happening during or after collection you may have too much solvent that is rapidly warming to room temp.

      Let me know some more details and maybe I can give a better answer.

      Reply

Leave a Reply

Your email address will not be published. Required fields are marked *