Boiling Point of THC


Well, in the spirit of sharing…

The enthalpy of vaporization of THC was experimentally determined to be EDIT 93kJ/mol (plus or minus 8%) in this paper: “Determination of cannabinoid vapor pressures to aid in vapor phase detection of intoxication” by Lovestead & Bruno (2017).

You can take the author’s values and plug them into the Clausius-Clapeyron equation and generate a nice graph. It seems to hold up. It is somewhat useless for short path distillation in most cases.

You want to know what’s really funny? The boiling point of THC at normal atmospheric pressure is predicted to be about 420 deg C. :laughing:


i know u guys r talking about cannabinoid distillation but ive been researching co2 and CXE and the same type of data is badly needed for those systems too. there is crazy stuff u can do with co2 lik extract or distill off ethanol without rotovap or vacuum oven or breaking the water-ethanol azeotrope or phase inversion. with selective crystallization u can decrease one compounds solubility while increasing the other’s solubility and kinetically drive crystallization by controlling the pressure and the only thing stopping us is that we dont have the necessary info. and the papers i read say that the standard equations of state dont predict quadrupole solvents like co2 well and that the closer they match the data with equations of state that have more variables the less predictive power they have.
Im good at chemistry and math but this equation of state shit is complicated, at least about co2 for me. love to hear any of your guys thoughts on applying equations of state for modeling co2 systems


There is an abundance of information on shifting azeotropes and altering solubility out there. Many ways to do it, small number of them have been adopted commercially. When it comes to cannabinoids, I think the necessary data is lacking, but will inevitably be generated in places where federal legalization permits mainstream engineering schools to study it. In any case, when you look at a multiphase multicomponent system with non ideal components and non condensible gases, the models (EOS and excess enthalpy models) get very very complex. Even straight forward EOS are fairly deep into chemical engineering thermodynamics. My two cents, if you want to understand EOS/excess enthalpy models, you should really read the text books. If you want some references that I found useful, I could link you to them. But in the end you will come to see that except for the most trivial systems, computer programs are necessary to do the computations. Furthermore, a databank of parameters are needed. In the end, decision makers rarely trust the models anyway, but they can be powerful in their ability to predict, improve and optimize. Selection of the right property model is a bit of a science in itself.


Wow, those values from McPartland & Russo are dead wrong for atmospheric pressure. Just goes to show that typos make it into peer reviewed papers sometimes.

Everything I have seen posted here seems to add up. @Beaker’s values are a little off from what I have observed, probably because the graph was made without the enthalpy of vaporization value. Very cool of him to share the info though! Thank you!




Oh that makes sense. Yes the numbers seem off for the higher temperatures. Definitely check out the paper that I cited. I think you will find it of value.


your right that the data just isnt there for cannabinoids. i have studied alot of texts about EOS’s used and even studies comparing different ones and ur def right about the complexity i am more comfortable with math then chemistry and it still blows me away how hardcore EOS predictions are. but there r so many things that could be done if we knew, from selective crystallization to purging ethanol or butane/propane without vacuum pumps


Can you explain more specifically what this selective crystallization is, and how you can purge without vacuum? I’m curious.


I cant find the study im specifically referring to in my collection but i found these. I’m still looking for the good description
Kinetically Driven Crystallization.pdf (2.5 MB)

“The tunability of GXLs has also been exploited to purify
compounds and to effect separation of mixed solutes in
solution. For example, GAS recrystallization with CO2 was
used to separate citric acid from oxalic acid246 and to isolate
and purify â-carotene from a mixture of carotene oxidation products”
"Sarrade et al.114 showed that the dramatic viscosity
reduction in oils upon expansion with CO2 could be applied
to the ultrafiltration "
Gas-Expanded LiquidsBettERjessop2007.pdf (504.8 KB)


for ethanol removal there r two options the extraction route where dense co2 is used or the high-pressure distillation route where the vapor contains some ethanol. if you look at the azeotrope breaking papers they talk about vapor-liquid-liquid equilibriums and how the vapor contains some ethanol even when its not as its boiling point at the pressure its under


Knowledge of the pure component boiling points is the starting point for all the more complicated designs with mixtures. That information is the first thing anybody would want to know. Any mixture boiling above or below the pure component boiling points is not behaving like an ideal mixture for example. Naturally, things get more complicated pretty fast though.


Thank you for reporting this. I have been using 82kJ/mol for the past couple of years, as that was the last reported value. Very interested in this and makes a lot of sense. I did some experimental calculations at 90 kJ/mol and they were lining up much better with my actual distillation temps. Of course given that this is a mixture I understand that it will never be accurate but it was more in the “ball park” at a higher enthalpy of vaporization.

Clausius Clapyron is how I developed a terpene stripping protocol on the Pope before I knew it was a thing people already did :smiley:


Thinking about how the addition of something like Wiped Film tech influences this point further.
(still learning)

WF reduces bp.

But, the balance of temperature/vacuum pressure/blade speed/feed rate/feed temp/etc… will all factor.

Under ideal conditions I wonder how much the WF influence could decrease the bp.


@gdmfsob You may find this article quoted below interesting; I was curious as to your statement because although one may calculate boiling point of a liquid based off its viscosity and gravity, I was not sure how the wiped-film hardware itself would influence boiling point.

This article states, "Because of low value of pressure drop during gas flow inside the evaporator the boiling temperature of liquid, which is evaporated, depends only on its composition and does not depend on liquid position in the evaporator, which is of great importance in case of evaporation at low pressure. "

So I would agree that as usual, temp and pressure will factor, I am not sure that I agree that wiper speed and feed rate do. If you have any mathematical equations that I would find interesting to support your claim, please let me know, I am truly interested. This is a subject I have often thought on and am only beginning to really understand at a deeper level. Thanks for your thoughts in advance.



Thanks for the reply and article. I def have a lot to grasp and understand.

I used shoddy language in my statements. Rather than boiling point, I should have said point of evaporation.

I dont have any supporting math because I was wrong in my statement.

I guess i’m trying to understand how I can think about the temperatures and bp and the thin film creation and what is happening there.

Thanks again for your article.


I’m definitely coming late to this conversation but I want to thank all involved. A great breakdown with supporting evidence, very nice indeed.

When I thought about trying to calculate bp and vapor pressure for a matrix as complicated as cannabis extracts I realized that this is not just science, it’s art. You may be able to build setpoints for a specific strain that is amazingly repeatable but I felt, and by no means do I think this is the gospel, but differing concentrations of all the participants will cause variability in bp. Minor? Maybe, depends on how different your components.

I may be totally off base here, I’ll be honest not a single calculation was performed, but I believe you could see how shift on the order of 3-5 degrees C on your fractions. With the spreads we see you his may not sound like much but if it’s programmed into a controller… I’m sure you get the idea.

Thanks for the amazing discussions held here.


This is a particularly fave topic of mine and I just vaped something potent so I took your post as a segway to present this idea. You are absolutely correct about this stuff being a complex makeup and it gets more complex as heated… you talked about thermal shifts according to compound composition.

The shift that tells the tale and then could be programmed into a computer because of the precision possible in measurement are the vacuum levels measured. Once you know the boiling point at blank off pressure for the vacuum pump for the target fraction it makes it then possible to determine when all lower fractions then have been removed so long as you can measure it accurately.

This of course assumes an ideal closed system. A sublimation apparatus like I employ is as close to an ideal system as is possible in this context. When the pressure drops micron by micron towards the blank off value of roughly ¾ of one micron at the set point temp for THC it begins collecting on the cold finger through evaporation at about 125C. At that moment without any doubt all lower boiling stuff is depleted from the boil once the vacuum hits ¾ of one micron. (In this example)

Pressure and temp are one and the same really as far as the pillar of modern physics is concerned (The Second Law of thermodynamics). It took mankind tens of thousands of years to finally codify the Second Law into our scientific foundation. Stated in purely technical terms the Second Law and pillar of modern physics states that when you put an ice cube into a hot cup of coffee that the coffee will warm up the ice but the ice will not warm up the coffee. Who knew, right? I bet burn injuries went down dramatically after they wrote that law? Of course some REALLY smart folks ran with the idea and now mankind benefits from nuclear fission… :flushed::flushed::flushed:… Some though are just born genius and somehow instinctively just know that ice does not warm up their coffee but we needed Universities in on the secret so they wrote a law. Knowledge is power!

Back on topic… pressure in a closed system is not a different thing than temp from this point of view and for us the instantaneous measurement of pressure in the closed system as a whole is actually much simpler than the same measurement but expressed as temperature.

Where it gets complex has to do with chaos theory insofar as there are so many possible permutations when you consider that organic compounds are breaking down into new compounds while distilling so it makes it very, very hard to predict the exact path a temperature pressure gradient will follow by the time it reaches a known “destination” of a final isolated product. I blame it on entropy. It just sounds cooler to say that, but you are right about art.

I would in this context define an art as a flexible application of scientific procedures and “knowns” as a guideline for action in a lab rather than a set of mandates, procedures and practices. An artist learns that in theory a practice may work, but in practice the theory might not and is flexible enough to alter the practice as a refinement.


I want whatever you dabbed before writing this :roll_eyes:

I had a teacher that explained entropy as every time we built a molecule a child would die somewhere. I feel very strongly that entropy should be blamed for all problems. You mirror a lot of what I have been reading. 1. Dabbing gets you high and 2. Pull vacuum till you can’t pull no more vacuum. Walking in the door I was sure I could control the vacuum so that I run above decarb level and convert to d9 in the flask. That illusion shattered quickly.

I looked on your Instagram and I like the sublimator setup, very nice and compact and the clarity of your D9 is amazing.


I’m sorry to throw a wrench in the works but is anyone also accounting for RPM of stir fluid velocity definitely effects what kinds of “work” can be forced and IMO most definitely would be an affect to boiling temperature . Revolves a lot around the vessocity especially under vacuum … the stir has an effect on basically everything at play during vac depths of almost absolute , surface tension coupled with temp can be night and day


Amazing tool, thanks a lot!!!