Understanding vacuum and boiling point relationship

If we take a look at the graph that I posted above, the key feature that’s the most important is the one on the right… It defines the vacuum depth relationship to the chart… The way this works is for a given midpoint, based on vacuum, you will be able to find the known boiling point under such vacuum compared to atmosphere (like a saw horse)… Or do the reverse and find out what the boiling point is at atmosphere from a known vacuum and temperature…

If you notice all the lines are more or less vertical except for the vacuum… This is due to the fact that as pressure decreases there is a diminishing return on vacuum depth relationship with boiling point… What I found from actual experience is the below 1×10^ -5 Torr, the boiling point of anything changes by no more than 2° maybe three at the most…

So that is more or less why they only go to a certain point on this graph… But we can see that vacuum depth has a logarithmic relationship with boiling point…

Using this graph, especially with a thin film session such as a wiper, knowing the exact temperature of distillation can guide you greatly.

If we take a look at these two graphs I have inputted a few numbers… If we consider the boiling point of THC between 420 and 435 Celsius… Then we would need at least 215°C to actually boil it… This does not mean that less temperatures would not create a steam.

When using temperatures slightly below 215 Celsius at the pressure of two torr… We made it still all the way up to the cannabinoid fraction off the wall of a wiper or within a boiling flask… The benefit of this comes from short path distillation… But can be translated to a wiper… The reason this has its benefits in short path as you were able to use your soge vac or (shitty vacuum depth with great CFM) pump…

On the wiper the benefit is that because the material is extremely hot it’s viscosity is extremely low this allows the material to express it’s lower boiling points a lot easier because the surface tension is also low… I consider the idea of distillation an expression because it Presses something out or Releases something.

The other benefit of low viscosity is that you can actually push more material down the column rather than relying on gravity… This is especially beneficial when working with a rolled film system… The process is not 100% foolproof and vacuum depths will need to be attenuated to work with the given temperature… As well as the fact that because some columns are extremely long we need to expect that there is a temperature gradient along them and we need to measure accordingly. As long as the material reaches 200°C by the time it reaches the bottom of the column the process should be complete if the vacuum depth is correct…

We use a condenser coil temperature of 20°C. This allows us to check the work because cannabinoids should be a solid at 20° C… So if we are seeing a lot of build up on the coil in a glass system then we know our vacuum depth is too low… There are many fractions besides the terp fraction…

The heads fraction seen in SPD is what really separates it from wiper oil… Many wipers get higher yields then SPD’s but I believe that some of this is due to the fact that heads fraction is left in the material… wiper oil typically has a flavor to it especially in not well processed material… This is not always the case of coarse.

Because we are no longer relying on gravity, the speed of distillation can be increased as long as the material on the column never reaches the temp at which cannabinoids will boil. We may get some loss due to cannabinoid steaming… but ive seen speeds as high as 10L/hr on an 8” glass rolled film system. Which is the equivalent to a 6” stainless system.

Of course there are fool proof sops out there to get basic wiper oil with good test scores… but as always, i like to see how far the rabbit hole goes.



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That chart you posted is just a visual representation of the Claussius-Clapeyron Equation (Clausius–Clapeyron relation - Wikipedia)

The reason why you’re experiencing “diminishing returns” on boiling point depression with vacuum is because you’re experiencing diminishing vacuum. Going from 1 x 10^-5 torr to 1 x 10^-6 torr is a 10000 times smaller step than going from 1 torr to 1 x 10^-5 torr.

The difficult part about playing with pressure and temperature ONLY to separate things out is everything in the mix is adjusted. So lowering vacuum to achieve a boiling point for THC also correspondingly lowering the BP of every other components in the mix. SPDs are great for their versatility and the ease with which you can capture different fractions. Wipers are large throughput production tools. You set them up to capture a large amount of a main body fraction and they run continuously. But changing parameters on the fly to capture different fractions is not their strong suit. This is why you will see wipers with multiple stages to capture different fractions as opposed to tweaking the settings on one stage.

IMO that is the main difference between the two pieces of equipment. They both do the same thing (in different ways)


100% agree.

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Good post. I find it hard to properly separate ALL of the heads fraction on a wiped film without sacrificing a little bit of distillate.

Why is the 6" stainless steel equivalent to an 8" glass? Is it just that steel conducts heat much better and can therefore warm up the material faster in the column?

It goes with the territory of azeotropes… and ya. Something about conductors vs insulators… i think… not entirely sure yet because ive really just seen the difference between a rolled film and a wiped film setup

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I have yet to even work with a rolled film…

That interactive nomograph is helpful but I ended up using higher temperatures than the ones it generated for MCT oils. I used it(and boiling points from wikipedia) to set the parameters in an experiment to separate MCTs from raw coconut oil in a stainless steel 2". Those parameters were about 30C too low which was surprising to me. Not sure if that is a testament to how long it takes to warm the material in the column or what.

Its not that theyre too low, they just dont take into consideratiob viscotity of liquods as well as consistuents of the vapor pressure around the materials, also where you measure vac from is essential. Expect a degree of difference in vac olacement and Immediate vicinity of the boiling surface


yup, I measure vac in my wiper body as well as post-trap. On “deep cut” I have seen anywhere from 40 to 250mtorr difference between the two points of measurement. (trap side holds a constant 1-2mtorr).


Ayee i remember our conversations on the importance of this :slight_smile: I’m not sure if i mentioned of a reoccurring incident that kept happening to me when i first started running the chemtech. Around 4-5 hours of continual running i would rapidly lose vacuum every time. Luckily i was on top of it to close off the gate valve right before the pump. . You bet i was catching a heart attack watching a turbo gain pressure lol. I solved this and concluded. The cold traps pathway collects terpenes/water/inpurtuties on the walls from using liquid nitrogen. I covered the entire trap with liquid nitrogen throughout the entire run Once this barrier is formed it will build up until a Small hole is created. The vacuum won’t read this on the backend Bc it’s a consistent vacuum suction. Eventually the barrier will break from getting enough heat traveling through that hole and the heat transfer of the overall wiper jacket…

I started filling up my trap where i kept the top part visible during the run. Also during my start up procedure i no longer froze down the trap for 5 minutes before cranking the pump on. Never had the issue again. If i had least another pressure gauge inside the jacket by the entrance of the vapor path heading to the cold trap i would have solved this quicker. The change of differential pressure wouldn’t stay consistent than the problem would of been between those points.


Great stuff! Thanks for the info

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The problem with such high vacuum is you need a ton more residence time to get the crude to terpene stripping temperatures.

Let’s compare

On the B and W Pope we run the feed at 80c.

When I terpene strip I strip at 158 on that glass machine.

You strip around 215 it sounds like.

This means you need to raise the temp of the crude by 73% more then me to even start your terpene strip.

This takes residence time and heating power

The reason most people dont get all the heads out is because they dont give the crude enough time at the proper temp to strip it all out. Think of it as pushing through heads on an spd because you dont wait long enough.

The benefit of stripping at lower temps is you need less residence time to get the crude to temp resulting in more time terpene stripping.

If you run your jacket at 215 and you calculate that your thc boils at 220, theres no way you’re getting anywhere close to 215 before the crude leaves the bottom of the wiper.

This makes controlling your crude temps impossible, especially when you’re running faster.

You need much more energy to evaporate terpenes at 2 torr vs 300 microns.

There will come a point when you’re heater will not be able to keep up because its using its heating power to raise the temperature of the crude to boiling.

This is simple thermo dynamics.

Stripping at 300 microns you wont be wasting as much heating energy.

Okay you’re running hotter so you have better heat transfer.

Let’s do some math.

At 215c you’re about 50 degrees warmer then me.

That’s about 30% higher temp then me

We will just say you get 30% better heat transfer because of this so you heat up 30% faster (even though you wouldnt because you’ll be fighting ambient air temps more then me so youd really probabaly get closer to 20% better heat transfer).

You’re still behind me by 43% in heat transfer / crude temp since you need to hit such high temps to even start the terpene strip.

Then you’re running double the speed (10L an hour compared to my 5) so you’re further cutting your heating efficiency in half.

There will come a point when my lower vacuum will allow me to terpene strip more then you because I’m not wasting as much heating power to raise the temps of my crude.

If you’re going for fast, high potency distillate it is better to raise the temp of the feed flask or lower the vacuum level then to raise the temp on the jacket.

You really dont know what the temp of your crude is when it exits the bottom, or even if it’s gotten to the correct temp or had enough time to terpene strip.

Running your jacket at the perfect temp for terpene stripping (like what I do, my jacket never gets within 25 degrees of the cannabinoids boiling point) will give you better control of the terpene strip.

If you just need to get your crude to temp then why cant I just terp strip in a roto? Residence time matters for the terpene strip. I can hit 200c and 2 torr in my roto, does that mean I’ve fully removed all heads and terpenes?


If this were true it would be best to set your feed and jacket temps at the same temp so you could instantly terpene strip as soon as the crude hit the evaporator.

Lower vacuum also causes less turbulence inside the wiper.

The lower the vacuum level the less vapor pressure is needed to evaporate your crude

This results in less turbulence inside your crude when it boils, giving you better separation.

Viscosity has never been an issue with terpene stripping crude in a wiper. My 99% test results prove that. If viscosity is an issue on a wiper it must be an even bigger issue on an spd and I’ve never seen you crank up the temp on an spd to get heads out lol how does an spd get all the terpenes/heads out if it cant run at 215c? The sogevac runs around 300 microns on my system which means I pull heads around 150-160 on my spd. Same temps as my wiper.

I’ve always gotten less disty on a wiper then a SPD as I can get much better seperation on a wiper which results in high purity which means less final product.

@Kingofthekush420 Look man, i made this post in order to not interact with you… because youre rude, disrespectful and lie about me. Youve threatened me and i dont care to read any of what you wrote due to my feelings towards you.

So saying all this, i hope you understand that none of what you say has any bearing on what i do… and the only reason you can see this post is there is no block function on this forum.

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Good for you

Im correcting your post

You’re know for spreading misinformation

This is a public forum, if you dont like it leave

Glad you’re not going to try and argue with facts

I rest my case…

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To the naysayers… i give you this… just got my wiper rolling agains… and well… here you go… 7.5L/hr first mains cut

300mtorr measured next to the column. (Dirty system or i would have used lower settings, not alot lower)
210C jacket,
150C condenser
7.5L/hr feed
300rpms roller wiper
160C feed temp (under vacuum)

If i had my vac as low as 90mtorr, i would run the jacket at 200C… thats about it…

My wiper ig is tarandfeatherfarms


Recent update,

I just ran 15L of unwinterized, non decarbd material through my wiper at 14L/hr with these settings.
90C hopper temp
140C primary feed tube
180C secondary feed tube
210C jacket temp
150C condenser temp.
800 micron measured at the column above the first cold trap (coil)

Material from residue and condenser were recombined and reran. This time at 2L/hr
150mtorr measure at the column. Diffusion below 0.75mtorr (gauge bottomed out)
Hopper temp 90C
Primary feed tube 140C
Secondary feed tube 190C
Jacket temp 190C
Coil temp 160C (measuring the outlet side of this coil im only seeing 115C… need a faster flow… or hotter temps but i do see mains try and leave the wiper body)

Seems like a beautiful mains split. I will rerun the tar fraction to see what comes out but i have a feeling not much will.