Extraction & van der Waals Force

Thanks for my incessant drivel this time goes to @Dred_pirate for tagging me in a thread started by @Merakian_Hash! Here: Propane vs n-Butane

Propane vs. n-Butane vs. Alcohol vs. [Insert Solvent]
WHY you should read this!
Propane and n-butane are very similar, but they definitely extract cannabis differently. Ethanol and other alcohols work, but they also extract more or less undesirables, depending on the alcohol. They key differences between these molecules lie in the differences between their van der Waals interactions, so it is important to understand precisely just what those are!

By the way, you don’t have to read my interpretations of these concepts, but definitely surf around, starting here: Wikipedia: van der Waals force

As you might guess from the plural (interactionS or forceS) there are several different types of atomic and molecular interactions that make up the broad category called “van der Waals”, named after the Dutch scientist, Johannes Diderik van der Waals, which is why it is unusually capitalized. It is somewhat misleading (but not wrong) to call these interactions “forceS”, because they are actually just different applications, permutations and combinations of aspects of the fundamental Electromagnetic Force in relatively “weak” intermolecular ways that are highly dependent on distance. All of any van der Waals force is observed only at very short distances between atoms and molecules, and has attractive & repulsive components:
《…》 Closer than 0.4 nanometers, the total force is repulsive.
->… .<- Between 0.4 and 0.6nm is where the attractive behaviors dominate.
||…_…|| Any further apart than 0.6nm, all van der Waals force is too weak to observe.

There are 4 major components of intermolecular interactions:

  1. Exclusion - Pauli (repulsive fermion behavior)

  2. Orientation - Keesom (attractive/repulsive, electrostatic permanent/permanent polarity)

  3. Induction - Debye (attractive, permanent/induced polarization)

  4. Dispersion - London (attractive, instantaneous random multipoles)

  5. The Pauli exclusion principle just says that 2 fermions (particles with half-integer spin states) with equal characteristics in the same quantum system (such as 2 electrons in the same atom) cannot exist in the same quantum state (same energy, shell, orbital, and spin) at the same time. Basically, this is what keeps atoms and molecules “hard” (discrete and relatively incompressible). This principle gives rise to an overall repulsive force that keeps atoms and molecules from intermingling inside one other, despite all the vacuum space involved… much the same way a concrete block repels a human skull, and that no, you are not actually dissolving into the couch.

  6. The electrostatic Keesom force is the one we all know and love, between 2 permanently polar moietes. The electronegative regions of polar molecules get snuggly with the electropositive regions of other polar molecules. That said, MANY molecules have some degree of permanent polarity, including cannabinoids (which are alcohols and often acids), fats (fatty acid), and entire groups of molecules like aldehydes, ketones, etc., along with the usual suspects like water, ions, salts, acids, bases, et al.

  7. The inductive Debye force is where things get a little unusual, because permanently polar molecules can cause (induce) instantaneous polarity in non-polar molecules. This is the main reason that polar solvents like water (aka: The Universal Solvent) can keep a little bit of totally non-polar material, such as carbon dioxide or butane, completely and truly dissolved. This is also the main key to unlock the mysteries posited in this thread!

  8. The dispersive London force is probably to what most people are referring when they say “van der Waals force”. It is usually predominant of the three attractive van der Waals forces (orientation, induction, dispersion) between atoms and molecules that are not small and highly polar (like water). This is the “sticky” force that keeps non-polar and barely polar molecules together with each other and amongst themselves. It is due to the natural fluctuations of electron fields around atoms and molecules, which create momentary or instantaneous polarity in just about everything in the universe. Naturally, this is also very important for extractions, in general.
    To show you how important this effect really is, I will paste a Wikipedia table here:

Ahem! Now that that’s over with, let’s see what it means for extractions!

Propane (and CO2) vs. Butane(s)
As you might surmise, propane has slightly less dispersive force, because it is smaller. It has only 3 carbons in CH3-CH2-CH3 configuration. Although they are single bonds and can therefore spin, there is not a lot of variation between V and A except possibly an extremely brief — .
Carbon dioxide is H2C=O=CH2, which is a perfectly straight, stiff, short molecule. Double bonds cannot spin or flex (vibrate out of plane),
so CO2 is just stuck as >—<
…with the >< representing the hydrogens that cannot budge.
These factors actually make propane and CO2 more non-polar than butane, because the momentary polar regions are literally smaller (and therefore disappear/change more rapidly) than those momentary dipoles possible in n-butane, which is a big wiggly
CH3-CH2-CH2-CH3, giving rise to:
N, U, and their inverses,
with several very brief L variations between.
Simply put, propane and CO2 are also, for these same reasons, harder and much harder, respectively, to induce into polarity.
Consequently, propane and CO2 can only dispersively “adhere” to small parts of large molecules like cannabinoids for very brief times. For example, it takes up to 4 molecules of propane just to surround the top and bottom of the C5 “tail” on THC and CBD, and that’s not including the front and back in the 3rd dimension!
Also, although propane (and CO2 even more rarely) can be very briefly induced, they are mostly repelled by slightly electronegative regions like the alcohol -OH group(s), and the O= in the carboxylic O=C-OH, and by electropositive regions like the acidic H in the O=C-OH region.
Therefore, propane and, to an even greater degree, CO2 are not as well-suited to dissolve cannabinoids as longer alkanes like n-butane. Luckily there are lots of terpenes and terpenols that have already dissolved the cannabinoids with their larger dipole moments, giving propane and CO2 at least a shot at moving the bulky cannabinoids.

As an aside, the small-but-wiggly nature of n-butane is one proposed reason why it has a slightly higher affinity for water than other alkanes. The area between the two middle HCH groups is a sort of easily induced region in the electron cloud that may mimic the natural +_+ shape of water molecules! A similar hypothesis goes for isobutane, as I will describe.

Just to mention isobutane, its shape is that of a triangular star composed of
…where all three of the CH3 groups radiate symmetrically outward from the central CH group, but bent slightly toward the side opposite the lone H on the central C. This gives the whole molecule a mild tetrahedron 3D shape. This shape, strained by “steric hindrance,” to have most of the hydrogen (9 of them!) all crammed together on 1 side, gives rise to a semi-permanent and more easily induced dipole! In other words, isobutane is actually more willing to dissolve slightly polar materials from the herb than n-butane or any of the super-non-polars like CO2 and propane.
Some folks truly believe in isobutane’s ability to give them better extractions than n-butane alone, and this explanation may lend some credit as to why, considering the mild polarity in cannabinoids. However, it also could explain why isobutane extracts performed above -40° (and even above -60°C) have a higher tendency to autobudder!
Personally, I think n-butane by itself is the perfect mix of [non-polar, flexible, easily (temperature) controlled rates of dipole induction] to effectively extract almost all of the cannabinoids and other desired compounds from cannabis.

I’m sure most of you are like “Oh shit, alcohol! Here he goes again! :roll_eyes:,” but I’m actually getting tired, so I’ll keep this as brief as I can. These are more about hydrogen bonding than van der Waals interactions, anyway, so no worries! Promise! :call_me_hand:
You guys know that alcohols are amphiphilic (amphipathic), right? That just means they are both polar (hydrophilic, lipophobic) and non-polar (lipophylic, hydrophobic) at the same time. The OH groups are capable of hydrogen bonding, which is the strongest of the weak bonds, and which is orders of magnitude stronger than any van der Waals force!
Well, that’s the blessing and the curse. It is one of the reasons why alcohols are so awesome with very short contact times and low temperatures, but also why they grab a lot of grunk when contact time and temps are too high. They require cold to become selective, but they are very selective… much more so than CO2 and the alkanes.
The non-polar-ness (lipophylic character) of alcohols varies according to their size; larger alcohols (e.g. isopropanol, THCannabinOL) are more non-polar in character than smaller alcohols (e.g. methanol and ethanol), which have more polar character.
Amphiphylic character of alcohols also varies with the number of alcohol groups (-OH, denoted by the OL, usually at the end of name) on the molecule, relative to its size. CannabiDIOL, for example, has 2 OH groups, so even though it is the exact same size and composition as THC, CBD is more polar than THC! Considering the relative power of hydrogen bonding, it is plain to see why a selective alcohol is the best solvent for extracting CBD… especially with the lower abundance of CBD in plants than THC.

Done! See? :yum:

Edit: Apparently backslash doesn’t show up here, @sidco @Future ? Is that a bug, or is it a prompt for some script?
Edit: Wow! The autocorrupt built into the publishing is strong with this one! No more ASCII chemistry explanations…:disappointed_relieved:


I very much appreciate you putting this together for us! Very informative and corrects a few innacurate assumptions I was running on. Do you think butane is sufficiently nonpolar to grab all the terpenes present in live resin extracts? Do you have any insights as to the trends towards a 70/30 solvent blend?


I’m not all scientific and edumacated like Photon but i think the blends like 70/30 lean towards more of a balance. This being between grabbing the most canibinoids and terps in one pass. Just my personal thoughts. :man_shrugging:


@Photon_noir thanks for that post. Been a long time…
Been many years since I’ve done any hydrocarbon extractions but very likely returning to it and I’m curious about Dimethyl ether. Haven’t seen too many people using or posting about it here…
If I go back to using any hydrocarbon my only intention was for ln2 flash frozen, fresh off the tree biomass and straight into low temp DMe for diamonds terps sauce etc. the idea behind dme is its relationship with water…and aim of getting terps flavor and smell…

It’s value constant is greater than C02 burn much less than butane and Ethanol. Is the idea here that the higher value a constant leads to a better solvent or in terms of residence time = higher value = less time (longer interactions result in greater funk contamination)?



This is a good read…definitely worth spending a minute to visit.
I’ll have to do a second read but from what I Can gather there’s a difference mainly with oxygenated monoterpenes and different terps for greater yields.


What happens to the water after?
Or are you using the DME for the aromatics then another solvent after?

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I’m not sure. I’m guessing worst case it would form layers. The DME isn’t really miscible if any water passes through could grab it in filter portion??
Has anyone ran into water issues with fresh biomass with high water content?
I think this requires real trial and error I definitely don’t know — stopped doing bho back in 2015

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Seems like dimethyl ether needs to be kept real cool. Diethyl ether might be better? And it seems like you can make it from ethanol. But only just read the wiki sites. I guess you’d use the DME the same way as butane though in liquid form and pump in loop.

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Ya it Runs The same. Definitely would keep it as cold As possible though or maybe run more weight liquid than butane etc

For crystals…might evaporate too quickly but maybe that’s a good thing.
Gonna be at least 2-3 weeks I would guess before I get around to doing any testing.

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Yes, @Krative, butane is plenty non-polar or apolar, as they say in the paper in post 5. It’s important to remember that when it is said that a non-polar solvent is…

  1. “more polar” or
  2. “has a longer dipole moment” or
  3. “is easy to induce polarity within”…
    that the solvent is still non-polar.

In the order written, those statements mean…

  1. “has a little bit of hydrophilic or mildly polar character, but still has no permanent polarity” or
  2. “tends to stick to things (better than PTFE does, for example) but is still apolar” or
  3. “may be slightly soluble in polar solvent and may dissolve some strongly polar things, but still ain’t no permanently polar thang, dammit!”
    Ya dig it, Man?

@BG305 I know it’s probably confusing if it’s not something you live and breathe consciously everyday for most of your life, and I value the opinions of those with practical experience, so no worries at all! I’m sure 70/30 works great as long as you keep reupping the butane after every run! It may even seem fine when you don’t, but you can be certain that every run after the first will be richer and richer in pure propane until you put more blend in your solvent tank, which will then do the same thing, but from a higher propane starting point, until eventually you are probably extracting with maybe 10% butane and you noticed after 27 runs that it’s not working like it used to for some reason!

Just be aware, folks, you have to top off with pure butane every blend run, and it’s best to just add enough propane to get the pressure you want. That’s really what propane is all about, anyway; higher vapor pressure, lower viscosity, and generally just improving the performance of the extraction in tightly packed columns. Think HPLC methods when using tight packing… or just don’t use tight packing with cannabis, since it’s actually best not to do that when you don’t need what’s inside the plant cells!

By the way, @Dred_pirate, I think I think I just answered one of your questions from the other thread. No, butane and propane do not form an azeotrope, so one does end up with FAR more butane in the soup after recovery than propane when using a mix!

Which leads to your questions, @anon86230761, I think… I am not sure what you mean by “value constant”. That’s kinda like saying “number concept” instead of saying “12 meters,” you know? DME has been sold in cans, supposedly for use in open blasting for some ungodly reason (probably because it can be used in methaphetamine production and they cannot legally sell diethyl ether because it is a drug unto itself, @tweedledew), but unfortunately that doesn’t mean one should use it!
First, if it dissolves a lot of water or vice versa, it’s going to pick up a LOT of water if you extract wet! I’m with @tweedledew on that one! Sure, it may extract well (probably not wet cannabis, though), and it may evaporate super fast, but what are you going to do with that watery mess afterward?
Second, unless it forms some really strong azeotrope with water (it might, but I haven’t looked it up) and you keep it super cold, you have just extracted lots of water and cellular material that you probably didn’t want. It’s a lot like the idea of extracting wet flower with ethanol without freezing the living shit out of everything.
Finally, no, rapid evaporation is not a good thing for trying to crystallize THCa from its parent resin… and excess water will definitely screw you there, too!

Good questions! Best of luck, all! :blush:


Oh. I was typing and thinking at same time — was referring to van der Waals constants a/b values referring to the a


HFor some reason I have a feeling that DME won’t pull water through. It will just Be able to extract better than said others with material that has more water content.
I will find out either way.
Based on the purpose of that study one would assume when it suggests using butane on very dry material (is the better solvent) and using DME for wet…the purpose was for attaining terpenes etc

They had old women smell the extracts it’s pretty funny @Photon_noir I guess u didn’t waste time on that one


Righto… I wasn’t sure if you meant aromatics as in things with benzene rings or as in odoriferous. If all you want to do is pull smelly stuff, then it should work okay on some macerated wet plant materials like flower petals and lavender leaves. If you’re going for cannabis resin, it should also be okay, but it needs to be really cold to keep cells resistant to solvent permeation. To answer your other question, small ethers tend to behave a little like larger monoalcohols… a little dissolves into the water, and the rest forms a layer after the aqueous layer is saturated. Ethers have more hydrophobic character than their alcohol counterparts.
I will also add, especially since it hasn’t been mentioned even once, that ethers are HIGHLY INFLAMMABLE!!!
In fact, diethyl ether (aka ether), for example, likes to autoignite on the very static electricity formed by itself moving across the surface of its own container! Ethers are SO inflammable that they are practically considered explosive!!!


I’m definitely NOT an expert on this…but “I DID STAY AT a Holiday Inn last night”
…and I found these two pamphlets…could be wrong like my health care going up 5x since 2014…


This, amongst other reasons is why I switched to etoh cryo many years ago…and ln2.
Not a fan of hydrocarbons but they do some pretty cool stuff and I’ve all but given up on terpene collection


@anon86230761 jus curious why don’t you like hydrocarbons. I think it’s a wonderful group of solvents. N-butane and propane are not carcinogens. You can also technically say hydrocarbons are a natural solvent that are produced by organic matter decomposing. I was starting to lean towards ethanol for large scale production especially for cbd. I’m having second thoughts after what came to be in the crc water clear shatter. I believe it’s entirely possible to perform hydrocarbon extractions and end up with a final product that’s just terpenes and cannabinoids and the water clear tek is paving the way to make this happen


Lower Explosion Limit for butane is lower meaning it can explode at lower concentrations than dem. However higher concentrations of dem are required before the air ratio is too rich to burn. Dem may be slightly more powerful of a boom. Idk “ether” way I think you’re not in a good place if you hit fucked town.

Seems like you’re playing with similar odds here.

@Homegrown34 well I agree with you. And what you mentioned is mostly why. Several years ago…I think 2014, a close friend got cancer and we began making rso pills with coconut oil carriers and bho extracts.
When the push came in cali (lab testing, ppm/ppb/ppt…dewaxing And other things) cryo ethanol was absolutely amazing. Cryo temps, LN2 cold boils and good biomass…runs consistently hit 83-88% cannabioids, great yields and great taste. The raw oil was by far hands down better than co2 and hydrocarbon.
Also, in terms of production size, it’s still unmatched imo, unless you know of 4000lbs per day limits with hydro carbon setups. That’s about to scale for a 100 acre farm.
ACO alcohol clear oil or crude is also likely the most “certified organic” food grade oil you can make.
Medicinal value seemed(s) to be the best also.
I am definitely biased I will admit that.
I also don’t like things exploding or poisoning me or damaging my health or employees. I’ve been a master mechanic, professional fisherman, special Ed teacher, nutraceuticals lab and extraction labs and I will say that mistakes happen…and they will. I really like cognac, and I won’t cry over spilled etoh. But like @Photon_noir makes a point, :fuelpump::fire: boom, now your face is grafted ass skin.

Also why this forum is a godspeed, we can soundboard and say dumb things and think and plan and have some peer feedback…also get schooled by those with greater knowledge.
Loving the progress of the CRC tec
It’s impressive.
throw membrane tech to etoh though and again it outpaces everything else by miles…maybe. How about the hash people though?! Bringing it back to the Caveman era! My friends in Spain lovin’ it. Went past blonde hash now we got white


That being said wouldn’t decarbing your material prior to a bucket tek alcohol wash be more effective in reducing soak time because you’d be removing the COOH. Causing less residence time for soak.

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That’s the plan for hemp moving forward.

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Ethers go boom! Bottles of old ether in labs get the bomb squad called. Peroxides can be contact explosives. How to Work Safely with : OSH Answers

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