Questions about Headspace volume in CBD isolation vessels. And pictures of beautiful crystals

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Hi.

I have some experiences that I’d be willing to share in the hopes that someone with greater knowledge than myself can help fill in the gaps regarding Headspace volume in a CBD isolation vessel.

When I first started doing medium scale CBD isolations, I was using hexane (terrible idea) with a headspace of 20% of total vessel volume. I switched to heptane, and i noticed different structuring but I kind of saw the same trend using both solvents that I will describe now.

Under employer pressure, I began to cram as much solution as I could into the vessels, lowering my headspace first to 15%, and then to 10%. What I noticed at 10% was I could see a pretty clear variation in crystal structure from the bottom of the tank to the top of the tank. For example, the crystals at the bottom of the vessel would be like those in the pictures. Generally very well formed, beryl type (hexagonal) crystals with glassy sides. However at the top of the vessel, I’d get crystals that much more resemble snowflakes. Relatively irregular, pointy, needle shaped, and crystals projecting out of other crystals. Clarity and color didn’t seem to vary much. Anyway, I backed off a bit, back to 15% and the entire vessel seemed more consistent.

here are my questions.

As far as structure goes, is there an ideal headpsace %? Why?
Does the pressure change as compound is leaving solution and forming crystals?
How does pressure affect structure?
If I switch to a more or less volatile solvent, does that affect the ideal headspace %?
If yes, how should I adjust % volume of the headspace?

I’m likely going to switch to pentane, and beside not wanting to over pressurize the vessels, I want to have solid understanding about crystal growth under different pressures.

If anyone could help increase my understand here, it’d be very much appreciated.
Enjoy my beautiful crystals <3 Sadly I don’t seem to possess pictures of the snow flake type crystals produced at %10 headspace. I forget exactly, i mighta really pushed it and done 8% Hopefully the pics upload alright

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Don t know much about pressure and crystelization
But I do know that choice of solvent influence s crystal form
Alas i do not know wich crystal form go s with wich solvent for cbd
But crystelizing compounds in singel solvent or solvent mixtures defenatly make diffrent crystal forms
The most beautiful crystals are formed when the crystal is suspended in liquid
Like an alkane and a solvent mixture of water./ethyl acetate even thou that compound was a salt so not sure it can be achieved with cannabinoids
Maybe an alkane with brinewater :thinking:

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Those look like hexane crystals to me.

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the only hexane ones are the ones im holding. others are hept

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:heart_eyes:

I accidentally made some crystals like that a week ago. Now I can’t get em out of my beaker.

Edit spelling

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hexane always seems to produce clearer and much denser (and therefore more difficult to break) crystals. IME. I have done pentane but only at a really small scale. they never looked quite as good as either my hex or hept but they came back at 99.5% using esentially same process i used here

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I’ve heard that any water in the non polar will cause variations in clarity. like on my bottom photo you can see the tips of the crystals are clear while the rest isnt. Cosolvents. But i dunno the person who told me that has told me many very good things, and some things i take with a grain of salt.

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Would the crystal growth not push containment to the end of the lattice?

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not from my understanding of crystal growth. impurities tend to get trapped in missing steps of the crystal lattice and often become new nucleation sites, and therefore smaller overall structures

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Ph also alters the form of the crystal
But sometimes results in co crystelization so carefull with that unless it is wanted

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Forgive my stupidity. Not well versed in isolate or thc.

If your crystals are large - like they are - would it then be possible?

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i don’t really plan on messing w ph. again my primary curiosity is concerning the % volume of the sealed vessel that doesn’t have liquid in it.

Rationally i feel like the less headspace, means more pressure as every solvent has a vapor pressure at a certain temperature and if theres less space for the the vapor to occupy, it means the system has a higher pressure.

Like I said I also wonder if the pressure can change as the CBD drops out of solution to form the crystal. Like maybe pressure slightly increases over time as more and more crystals form, and thats why i was seeing 2 very clearly differnt structures in my tank

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no worries man im a total newb i never went to school for this stuff. would what be possible exactly?

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Yes maybe you get into the realms of abiatic pressure
I imagine it intervenes but I don t realy know

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So your crystal growth is making large crystals. Which would be the opposite of impurities. Theoretically, with the right ratio of containment’s Could they be pushed to the end?

if crystal lattice is not obstructed

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I think i understand what you mean. You are saying that as the crystal lattice of cbd is growing it dislodges the impurities molecule by molecule pushing them to the end. This “seems” unlikely to me but I don’t really know. I’ve always assumed that the impurities cocrystallize and stay where they are. Now that im thinking about it, i have heard, and this is complete myth as far as i know, that some substances like LSD for example have impurity gradients in the crystals. if they are evaporating the solvent on a watch glass for example there will be clearly different concentric gradients or bands if you will, of different crystal structure and purity. like maybe the top band is the purest and the band closest center is impurest. again, i really am not an expert but i have heard thats the case.

maybe my old pal @Photon_noir could shed light on some of the topics discussed in this thread.

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another theory i have is as the cbd is crystallizing the ratio of remaining cbd molecules to impurities decreases, make it more likely that the impurities will form in the outer edge of the crystals. However that “appears” to disagree my crystals as the base is cloudy and the tips are clear. But it seems pretty presumptuous that clarity=purity. Total newb here folks

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Clarity =purity doesn t sound presumptuous at all
I imagine only a perfect lárice to be crystal clear

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Kinda true…it’s more of a misunderstanding.
We simply would recystslize and take loss to get pure crystals.

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I’ve been traveling and working a lot, so please forgive my absence, @MyThirdEye_1! I will paste your original questions here to answer them:

As far as structure goes, is there an ideal headpsace %?
Yes and No. Yes, there is most likely an ideal for a given temperature and solution concentration… but it can NOT be practically maintained continuously throughout a precipitation, for what should be obvious reason: continuous change of concentration.

Why?
Vapor pressure is what it is… there is not more pressure in a small headspace than a larger one. That said, the interface of a smaller headspace is more active than that of a larger headspace… At a given temperature, the individual molecules that leave the surface of the liquid have less room to float around in a smaller headspace, so they statistically re-enter the liquid body (while others leave) more rapidly than that which occurs in a larger headspace.
THAT is the reason for the difference in structures as the headspace becomes smaller. Tiny crystallites are actually able to form at the interface (liquid surface) in the concentrated pool of gas molecules, especially when cold, as if the layer of gas closest to the liquid is actually liquid, itself!
For a similar example (but a solid/gas interface), on my Instagram page, a few years ago, I have a magnified picture of crystals (most likely of plant waxes) growing on the surfaces of some spent biomass in a pool of hexane vapor after a hexane extraction, as the biomass sat in a bucket in a cold, still airspace.

Does the pressure change as compound is leaving solution and forming crystals?
YES. The vapor pressure of a solution of solid solute is lower than that of the pure solvent… so as precipitation proceeds, the vp genrally increases to meet that of the pure solvent for the given temperature. That said, the vapor pressure of super cold heptane is quite low, already.

How does pressure affect structure?
That depends on the nature of the crystalline solid versus that of the solvent. Generally speaking, pressure does not affect anthing underneath the surface of the liquid, since liquids are “incompressible”… which is why headspace is really important to have inside a vessel; hydraulic pressure is an incredibly powerful force! However, pressure does affect the surface, which is an interface where a lot of nucleation happens, as aforementioned. Therefore, pressure above a liquid changes what happens depending on what that pressure is made of… if it is solvent gas, then the pressure can induce more nucleation (the same thing that happens with the cold vapor in a small headspace), but if the pressure is air or N2 or other non-solvent (which does not dissolve in the liquid), then it can minimize surface nucleation, allowing larger crystals to grow underneath the liquid surface.
Note that neither of these are actually directly related to pressure so much as what they do to the vapor of the solvent.
Also know that pressure can induce faster reactive chemistry… so BEWARE: heat and pressure can cause isomerization!

If I switch to a more or less volatile solvent, does that affect the ideal headspace %?
Yes and no, again… see my answer to your first question.

If yes, how should I adjust % volume of the headspace?
Just always make sure you have at least 20% headspace. That should be sufficient to keep surface activity to a minimum and avoid over-nucleation.

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