Boiling Point of THC

Using this nomograph (borrowed from @canndchas on IG)

We can see how the boiling point of THC (or anything) is reduced as vacuum increases


great juxtaposition of relevant facts

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That chart is perfect. Good find. That chart (and the math that created it) was the basis for the computation for the pressure curve really I created. If you observe two known points of a boil at two different pressures then the math that created that curve chart you posted can be used to extrapolate all the rest of the points along the curve. The chart you posted uses mmHg for the pressure unit;
.01 mmHg listed as the top pressure value = ten microns. I use microns as a unit of reference. The math gives crude estimates.

If you take the two known points I used you can plot it on that chart. “Boiling” is somewhat a subjective term at these pressures. I used the bottom of the bottom of the cold finger glass of the sublimation apparatus to judge when accumulation became noticeable as the “boiling” point. The two data points used in the calculation for the D9 THC chart were 120C at ¾ of one micron, and 200C at 20 microns. You can plug these points into the chart above and see how high the boil would be at room pressure which is 760,000 microns (the middle of your chart is corrected to 760 Torr = 760,000 microns). A theoretical perfect vacuum is zero microns.

From that chart you posted it is also possible mathematically to compute the enthralpy of evaporation. This number means very little to the daily refinement but it does offer clues about what is going on inside the rig when it runs and it helped me to figure out my horizontal distillation set up. I run the distillation pass horizontally via kugelrohr bulbs but use a heating mantle and stir bar instead of a formal oven. The temps run much lower to pull across distillate this way and the high numbers suggested this would work better than a traditional vertical distillation. It does. It is because you are not sinking all that heat into the uptake path in a horizontal mode.

I get wordy when I am stoned and I am disabled/retired and use the med for daily treatment…so I get stoned a lot lolz. Thanks for posting that chart. Folks would do well to study it if they intend to refine medicine.


thanks for this great info!

Great chart. this is helpful.

I found the spreadsheet I used tucked away in a google drive directory. Here it is but with the numerical data points shown. Column A is the pressure in microns and column B is computed/observed boiling temps in C. Zero microns is a theoretical perfect vacuum and 760,000 microns is typical room pressure.

Understand this is a crude chart. It is based on observation and extrapolation and likely needs refinement. Look at the computed boiling point at room pressure lolz. It is just under a butane torch temp! Anyway it is a start and believe it’s accuracy improves the closer you get to one micron which is where I made direct observations.


Curve fitting is so powerful. Would love to see the spreadsheet myself :wink:

Check out sigma Aldrich’s tool

So why is the nomograph reading the normal boiling point as over 400C, when I always hear it reported as 157C?

also… 1896? Is that date correct?

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That lines up perfectly with what we saw during dial in of the BR Inst 9200. At .25-.08mmHg our THC fraction arrived between 172-165C.

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Well don’t all the lines on the nomograph have to go through the normal boiling point of the compound? If they’re all going through at the 425C, that would imply that the normal boiling point of THC is 425C. I thought the normal boiling was around 160C. Am I missing something?
Here’s a link to Russo’s paper and he says all the boiling point values are at 760 mm Hg unless stated otherwise. There’s a big table with a bunch of cannabinoids.

Then again, wikipedia says 155 C at .05 mmHg.

This probably explains what’s going on in the BR though. Wow. It’s a good thing my office is on the first floor.

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Damn! it is from 1896. cool.


The extended Antoine equation is the formal way of formulating vapor pressure data for pure components. Parameters are fitted to the equation with the relevant data very easily.

I remember discussing this with Photon_noir when it was fist released and wondering if it had been adjusted for enthalpy of evaporation. Has anyone verified this with real world data?

I believe the 157°C people see is for molecular distillation, so 0.01 Torr

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To call it anything less than a gong show would be dishonest.

Would be really helpful, and should be published in the journal of fluid phase equilibria. The Claudius Clapyron equation is theoretical, but arguably is valid at such low pressures where ideal gas law is approached. Chemical engineers use extended Antoine equation, based on actual physical property data (e.g. Dortmund databank), obtained in multiple experiments in controlled settings. That being said, this property of boiling point is only valid for a pure component, i.e. it’s pure component vapor pressure… When dealing with a mixture of cannabinoids and other shit, boiling point is supplanted by bubble point/dew point, and one needs to establish the vapor liquid equilibrium to answer the real question being asked, which I think is, ‘what temperature is my liquid phase when the condensing vapor phase is most enriched in THC, given a constant absolute pressure?’ .


Well said. Your boiling point in every distillation will be different unless your mixture is exactly the same. Therefore in things like an SOP, you would have a range of temps and another indicator of what the fraction is. A singular “boiling point” is pretty fucking useless honestly.

I think a binary approximation wouldn’t be too bad in this case (CBD+THC). Binary phase diagrams are still simple experimentally and easy to understand. Let’s say your crude is 50% cannabinoids. Then more than 95% of those cannabinoids are probably THC or CBD. The mol fractions in each phase of other cannabinoids/compounds is probably small enough to ignore at that point.


Agreed. What is needed for the industry is someone to determine the binary interaction parameters for the two prominent cannabinoids. Then activity coefficient models can do good job of predicting phase behavior in software like AspenPlus or the free ChemSep. I would bet a coffee someone somewhere actually has attempted the tests and published the data on the above, in a journal somewhere. Can anyone find it?