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.

NFPA Pentane
NFPA Rating
Credit https://cameochemicals.noaa.gov/chemical/1288

Quality CBD crystals begin with Quality CBD distillate 

Crystallize CBDThe 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.

 

CBD Crystalization Equipment

A glass 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!

 

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. 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 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

      1. Hi Luke, great info, thank you so much!
        I was curious about how you remove the pentane used to wash the crystals. In a comment above you recommend leaving the crystals in the reactor until tests show no pentane. GC-MS testing takes time. Are you recommending leaving your batch in place until testing is done?

        Reply

        1. Hi Tom,

          Once the majority of the pentane has been removed by vacuum filtering, it should be perfectly safe to transfer. You will need to transfer the crystals to a vacuum oven to remove residual levels that will show up on GC-MS. The isolate would probably not get purged correctly if left to dry in place.

          We need to use a vacuum oven because in a regular oven the CBD would somewhat obviously melt! The vacuum helps reduce the boiling point of everything and anything. This way, less heat and time are needed to fully purge.

          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

  8. Hey folks,
    I’m looking to explore how much mass loss is typically experienced when processing distillate in to Iso.

    Considering the 70-75% distillate becoming +90% isolate example used, with a 75% distillate starter ending with a 90% isolate is the mass loss at all related to the change in CBD % (a 15% loss in mass from start to finish)?
    What observation in mass change have you experienced from start to finish?
    Any co-relations you base expected yield outcomes on?

    Thanks!

    Reply

    1. Hi,

      For distillate to isolate yields, the range is normally between 60-80% dependent on many factors. So if you have 1000 g of 80% CBD Distillate, you can expect between 480 and 640 grams of isolate. I have not heard of yields getting much better than 80%. It is very easy to get worse yields though!

      1) 1000 mg * 0.8 = 800 mg of potential CBD.
      2) 800 mg * 0.6 = 480 mg
      3) 800 mg * 0.8 = 640 mg

      After the initial crystallization, you must generally “wash” your crystals with cold solvent. This takes away a lot of impurities, but does take some CBD away as well. After this point the losses are mostly based on transfer from container to container.

      Reply

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