Decarboxylation under Vacuum?

That’s what I’m wondering… Will decarb still happen at 250 degrees if it’s under pressure in a pressure cooker? Would this pressure keep terps from boiling off? I’ve heard mention of nitrogen or use of other blanket gas to help preserve terps

1 Like

uh huh…

is this more obvious?

4 Likes

That’ll do

1 Like

turn your rotovap into an ice bath and apply vacuum. watch for bubbles?

The reaction emits carbon dioxide gas, so keep that in mind when you’re decarbing at 250 degrees in a pressure cooker. ka-boom?

There’s a few other things to consider.
Decarbing under vacuum also implies a low oxygen environment so it’s hard to separate the two factors. i’ll read the other paper which is referenced by the first and report back. There are some misconceptions floating around in here for sure.

1 Like

de-carboxylation is based upon heating not vacuum. Vacuum will not make any difference on the de-carboxylation rate

9 Likes

CO2 will not combust in a pressure cooker if thats what youre implying? If you mean it will build up pressure and blow, most pressure cookers have a relief on them that open at “X” pressure.

3 Likes

When it vents you’re losing terpenes and it’s not at the same pressure, the point being that the pressure is not going to be controlled. I think also you’ll find that the pressures you would need to reach to not lose terpenes when the temperature is 250 are not practical. That’s just a hunch though. It could be calculated using the max pressure of the system before the relief valve vents. That would tell you what your maximum temperature would be.

There’s also the possibility of dissolved gasses becoming insoluble during venting and your oil shooting out the valve in a process akin to muffining in a vacuum oven, only with liiquids at high temperatures. This would be more likely the more full it was. If it was very full, it would be guaranteed to happen.

I would be very very careful unless you want to have oil at 250 degrees shooting all over the room. Unless i’m very wrong, that is not a “hey let’s try it and see what happens” experiment.

1 Like

@Macleod122

perhaps you could expand on that a little…

or give a reference that indicates that retaining or removing the CO2 actually effects the reaction rate in this case.

1 Like

started doing some back of the envelop calculations on this.

say 1kg in a 4"x12" spool (~155cu.in. 2l = 122cu.in so ~1x headspace)
with a MW of 358g/mol for THCA, one might expect 3mols of CO2.

getting three times 22.4l/mol into a ~1liter headspace is going to be problematic. on the order of 1000PSI at 275K if I did the math right. and 275k wont get you decarb. you’ll need 375K for that.

with 10x head space rather than 1x, it becomes manageble…maybe.

yet I didn’t see pressures over 150PSI when I tried it…with ~1x headspace (not sure I would have tried it if I’d done the math first!!)

1 Like

Side question would it be efficient to decarb prior to extraction? Like if I were to describe my material previous to an alcohol or butane extraction (of course letting the decarbed material cool down first before pitting I in any solvent) would it make it any better or would I be losing everything because from what I got from the comment was concentrates decarb in the vacuum oven or rotovap.

Vacuum doesn’t change the thermodynamics of breaking a bond. It lowers boiling points, which is why it is used in distillation but that is just a manipulation of vapor pressure, not breaking bonds. There is no reason vacuum would speed up decarb, thermodynamically speaking. If anything I would think it would complicate decarb by pulling off volatiles like terpenes to an excessive degree in the process.

I decarb at 110c for 30 minutes to burn off water and residual solvent then 90c for another hour and a half. That should get you full decarb without losing all of your terps.

14 Likes

It’s not unusual for labs to do this when extracting with CO2 because it helps increase yield somewhat. I don’t know that it helps any with ethanol or butane though. If you’re a volume producer it would actually probably create work for you. Decarbing hundreds of pounds of biomass vs. the crude oil would make your oven requirements sizeable to say the least.

That’s hot. Decarboxylation is a continuous process. Heat speeds it up but it’s happening by itself just sitting there. 135c is where I go when I’m decarbing crude, but only because I want to burn off terps for crude. For an oil that will be used as an oil 110c for 30 minutes then 90c for an hour and a half gets you full decarb reliably and preserves a lot of the terps.

4 Likes

Correct. Vacuum does not change the thermodynamics of breaking a bond.

5 Likes

All reactions are an equilibrium. It just depends how far and on which side. Removing a product as it forms will drive a reaction. See Le Chatlier’s
principle.

Everyone is saying that vacuum doesn’t seem to speed it up, so the rate isn’t largely effect I guess. I’d bet you decarbing is sped up even if just a little bit though.

I think the biggest advantage however as some people have pointed out is that you remove oxygen. Heat + oxygen + time = cbn or other isomer. If you can decarb under vacuum or inert gas, that would be ideal as far as preventing degradation goes.

I’ve seen some graphs that illustrate why you shouldn’t decarb hot with oxygen. I’ll post them tomorrow if I can find them.

10 Likes

I think the biggest advantage however as some people have pointed out is that you remove oxygen. Heat + oxygen + time = cbn or other isomer. If you can decarb under vacuum or inert gas, that would be ideal as far as preventing degradation goes.

I never thought of this - it seems like a great reason to decarb under vacuum… especially if you’re doing so to oil/distillate rather than biomass.

3 Likes

Decarbing is a majorly temp dependant reaction. vacuum help remove the water it creates, and reduce the foaming effect of static decarb. but it shouldnt really speed up the decarboxylation reaction

1 Like

Agreed about the crude bit, I would never try to decarb something that had terpenes in it unless I was vaping it, haha.

If you’re trying to decarb large volumes of oil the time/temp ratios you listed simply wouldn’t do the job.

you asking me or whoever Macleod is? Either way, I know the reaction is, for all intensive purposes, not isentropic (i.e. irreversible) because you don’t observe an equilibrium between THCA and THC during decarb, it all pushes to THC eventually. That is to say, no THC reacts with CO2 (at least during typical decarb conditions, you need other reagents to achieve this) to produce THCA. Otherwise, after 10 hours of vigorous decarb you would still be seeing some amount of remaining THCA because that would be the equilibrium condition. My point is, Le Chatelier’s principle only applies to reversible reactions with dynamic equilibria, which decarb of THCA is not. So removing CO2 from the system will have no effect on the direction that the reaction proceeds. You could always attempt the corollary by decarbing at 2500 psig of CO2 and see if it goes any slower :stuck_out_tongue:

1 Like

I think regardless of vacuum or not, decarboxylation is going to require the same energy to break the bond keeping the carboxylate group attached to rest of molecule. It’s a chemical process. Decarbing under vacuum can prevent subsequent oxidation though.

3 Likes