THC/CBD separation using short path



There’s an issue I’d like to have cleared up and I’d appreciate your feedback.

I was wondering if it’s feasible to separate THC/CBD fractions using a short path system. If so, can it be done reliably? What are the test results like and how easy is it to over-shoot the BP of THC?

Because state regulations here don’t allow concentrations of THC to exceed 70%, the plan is to add CBD oil to batches that need it in order to dilute the THC. I’ll have a very strong vacuum, high quality equipment and high quality starting material (~20% of grow space dedicated to CBD).

Here’s the thing: I feel like a wiped film system used to purify a whole-cannabinoid extract from CBD dominant strains for the purposes of diluting the high-THC batches makes more sense. Does WF not make more sense here? Anyone have experience with THC/CBD separation using short path?


I’ve ran 1:1 thc/cbd nug run bho crude through a short path and tried to see if the vapor temps were noticeable enough to separate them and did not find a drastically noticeable difference in vapor temp so I’d assume it would not be easy. The distillate tested higher in thc and looked fantastic


Fraqtioning of your 1 pass oil by distillation
Can be done but a short path is not the right glass wear
A hempel column with vigreax is what You need
Problem is for a good seperation You Need to set iT up with a high reflux rate so low temp( amount of heat administration)
Making your oil in the boiling flask have a long residence time Wich Gives You high CBN % in the end


Assuming azeotropic behavior you likely cannot typically seperate those two cannabinoids via fractional vacuum distillation. Simple distillation is called for under vacuum. Frankly fractional distillation under deep vacuum conditions is contraindicated even though attempted frequently from what I can see. Fractionating devices in this situation create a slew of problems and it is unusual to shoot for deep vacuum but then go on to install fractionating devices if you have had experience trying this before.

If you can pull a very deep vacuum then your temperature is your fractionating device although once again using a distillaton column of any kind hobbles seperation attempts owing to the enormous relative amount of energy you must pump into the compound simply to transfer the heat up into the column and attempt refluxing the thing to achieve fractionating. In fact if you can pull down to mean free path flow (MFP) conditions of say under ten or twenty microns then the nature of MFP flow nearly precludes the use of fractioning devices without some means to actually bypass the device and usually at the expense of adding heat into the process.

In MFP conditions molecules can no longer be herded up and around fractioning devices or corners - straight lines only as a rule. Vacuum distillation at all is generally not the kind of task a seperation expert is going to attempt to employ fractionating devices with and outside of this industry I see no references to widespread use of fractioning columns in vacuum distillations. Witness the super high bypass mode distillation rigs now being seen where the design calls for complete bypass of the column itself of lighter fractions being pulled up simultaneously with the heavy fractions and quasi-seperation is accomplished by blowing the terps past the collection vessel. Messy and perhaps needed for production but an inelegant solution to say the least. The cost associated with doing this is enormous comparatively.

The fractionating possible via an evaporative process will rely on strict temp control. I measure the boil routinely at 127°C nominal and at 3/4 of one micron indicated as measured on the glass between the boiling flask and heat mantle (for temp). This is an order of magnitude lower than can be accomplished in a verticle distillation rig owing to the need for the thermal carrier to be the oil itself which then introduces unknowable periods of reflux. The best system imo for such a delicate seperation therefor is one in which reflux is avoided altogether. I have posted many videos of how I go about refining THC into very high purity. This can only be accomplished by keeping fractional equipment out of the way and thus enable very deep vacuum levels that represent MFP flow condtitions. Remember, in MFP flow conditions a fractionating device is a barrier and cannot provide the kind of delicate fractioning you seek without significant mods. We often see in literature the term “molecular distillation”. From what I can tell the term “molecular fractional distillation” is not normally envisioned outside of this young and learning industry. Residence times get brutal and it is not the right tool for the job at all.

A horizontal or other single theoretical plate distillation with tight temperature control is the best shot at separating such closely related high boiling point oils. I personally have switched most of my operations to just a cryogenic sublimation apparatus operations modified for short path MFP molecular distillation. The collection point is one inch above the puddle and the unit is easily converted to a true single plate distillation rig. However a deviation of just 20-30°C above the target temp very easily causes fractions to overlap. In a vertical rig you simply have to carry this much extra heat from bottom of boiling flask compared to just the top of it really just to pump the needed heat into the top of the column. This is the achilles heal of vertical distillation columns.

The solution is to skip the notion that simple vacuum distillation be carried out as a fractional vacuum distillation and instead target a more controlled temperature solution like a simple horizontal configuration. The upside is the unit is super simple to set up and run as a horizontal rig and then the fractioning done is controlled by heat and stir bar energy alone and not relying on carrying excess heat up into a column which also carries along with it contamination of your twrget compound. :nerd_face:


Thanks for your input.


Is that what’s being attempted here?


could be. although I don’t see anything in the boiling flask, so guessing what the object of the game is is non-trivial from the isolated 1k word substitute (picture :wink: )

it might be what was being attempted here…but the boiling flask looks really full for that.


Looks like it. I’d love more details.


That an ashtray in the pic ? :rofl:


Hard to say what the idea is there except that for sure lower heating mantle temps could be used to pull off the volitiles this way. The condenser situated like that seems odd but I have run an adapter that way shown which is just a simple branching adapter but plumbed like that. It just does not have a condenser built in is all and my sruff is all small stuff (14/20). If the goal is only to remove terps using that rig it should work well if the hope is to keep temperatures low. Fractioning power is reduced to a single plate theoretical but this is plenty to fraction terps from cannabinoids like that.


Based on the data I have seen I would guess it is not possible to separate CBD and THC using fractional distillation. The boiling points are very similar. You can separate them with chromatography.


This is a some type of non-rotating Kugelrohr-type distillation unit (which is another type of short-path distillation thats not really used much any more). The picture in Cylopaths post is a home made Kugelrohr apparatus.


This is a homemade Kugelrohr apparatus (which is used for short path distillation). They aren’t really used much by any industry anymore.
Sigma-Aldrich used to make one, I believe they still do, however the newer models have a rocking motion instead of the old spinning type. I’ve built a lot of these for clients in the past out of old rotovap motors.
My first type of cannabis distillation was using an old Sigma-Aldrich spinning-type Kugelrohr. Very small versions are still used for drug purification in drug-development R&D.


Shulgin as in the shulgin writer of Some marvolous books ?


Yes Sir. @ Roguelab I’ve edited my previous post so as not to derail this thread


Shit, you should make a post about your interaction/relationship with Sasha!


Hi Beaker;

This is real interesting and actually is not too different from wiped film which also does indeed operate under MFP. But I think you did not quite answer the money question here. Have you been able to use molecular distillation to take a sample partially THC and partially CBD and separate them into distinct fractions?


Not my work. I do like the spirit of it.

I was merely noting that the boiling flask on the toaster oven rotovap love child looked precariously full for any distillation attempt.

In contrast to the non-rotating unit which was probably not in use when photographed.

I wasn’t aware that there was such a thing as a non-rotating kugelrohr, but I’m willing to bet the @circus_animal responsible for the lab art posted above could say the same thing.


In my 5 years experience it is not possible to separate ∆9-THC from CBD.
I was operating dual 2" POPE WFMS at single digit pressures (3-5mTORR). The boiling points and molecular weights are just way too similar. Chromatography seems to be the way to go ATM. Now, if there were some nice mid-sized (5-20L/day) machines out there similar to the Buchi x2.


If it doesn’t spin or rock I don’t think you could call it a Kugelrohr. But you can indeed fill a rotating Kugelrohr reaction flask that full during a cannabinoid distillation (meaning that a volatiles removal distillation, or terp-stripping distillation was performed on the material first) and not get any spill over.