Decarboxylation during CO2 Extraction

Hi Experts,

We have a strange problem. We are performing CO2 extraction on cannabis and we are seeing considerable decarboxylation.

We have high quality temperature sensors at the heat exchangers, the extractor vessels, and the separator. We have not observed any temperature spikes that would explain it.

Various parameters have been tried, i.e.

40 - 50C (104-122F) / 115 - 280 bar (1770 - 4050 psi)

We can’t find any correlation between the temperatures / pressures and the level of decarboxylation.

The system has been run for 24 hours at 120bar/50C and we are getting approximately equal amounts of THC and THCA out.

The starting materials has been tested to being only slightly decarboxylated. Disturbingly, the spent material is also being decarboxylated.

The same equipment is used to test both the starting and spent material. The results on the starting material have been verified by a 3rd party lab. It seems unlikely to be a testing problem.

We have multiple extractors and we are seeing the same behaviour so it is unlikely to be a sensor issue. The temperature controllers also have their own thermostat that agrees with the extractor sensor. The extractors are all temperature controlled and all temperatures are logged every 30 seconds.

There is a research paper by Rovetto et al. that also observes significant decarboxylation but not to the extent that we are observing it:

Is it possible that the normal decarboxylation threshold (e.g. 115C) is lowered when at high pressure?

I understand that THC extracts far more readily than THCA, however looking at the mass balance it seems that selective extraction can not explain it.

If anyone has any insights to share, I would very much appreciate it.

Thanks

I’ve not heard of this decarb threshold of which you speak (links?), and would absolutely expect at least partial decarb at 50C for 24hrs. staying under 35C (or even 30C) has been my go-to to reduce decarb when aiming at THCA.

eg here they show noticeable decarb in 1hr at 80C

…and we all know leaving it in the barn for a year will get the job done too.

I don’t however use CO2 to extract, so cant address the specifics of temp profiles to reduce the unwanted decarb, or offer any insight to strange things that may be happening because of the solvent of choice, and the pressure at which extraction is occurring.

@ExTek90?

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When I did godforsaken CO2 extraction in Oregon I typically would see half of the total THC decarboxylated when Testing crude oil

If I recall correctly the extraction vessel temperature was around 60 or 65C and we were running at 400 bar

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Thanks so much, that’s a great article and I hadn’t come across it before. Going to try to extract at 35C and see what happens.

@shamanr00t
Thanks for the info - I wonder why it isn’t talked about much?! Glad to see that it happens for other people too!

Might get a bunch of crumble like product in your separator. Major pain to get it out, especially if you try to drain out of the needle valve on the separator

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I reckon you are right. However, I’m willing to put up with the inconvenience if it tells me something about what is going on!

More pressure, less time. 150 bar @ 50C is supercritical terp stripping range. The decarb is normal at that temperature and time. Think of it this way, the cannabinoids are normally protected by waxes, you’re separating those components and exposing them all to 50C for 24 hours, it’s gonna decarb.

How big are your extraction vessels and what is your flow? (e.g. grams of CO2 per minute)

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Thanks for your help - the extraction vessels are 20L and the flow can be up to ~40kg/hr (700g/min)
So what level of decarboxylation would you expect with 150bar and 50C, even for say 5 hours at 40kg/hr? Will flow rate change the decarboxylation rate?
If you wouldn’t mind suggesting a pressure/temperature/time/flow set of parameters to minimise decarboxylation, I would be forever grateful!

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Flow has a dynamic influence on extraction based on the operational parameters, in general, more flow equals faster extractions. Be sure to investigate what the safe operating pressures are for your system before attempting to adjust your parameters from their suggestions.

At 300-350 bar you will be able to extract significantly faster, you can then drop your temp to 40C as a means to reduce decarb. You will however extract significantly more waxes, this should be a non-issue if you are properly post processing your crude. You may need some intermediary steps to avoid clogging lines, as in, different pressures along the way to that 300-350 range. (i.e. 200, 250, etc.)

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That’s great info. We are winterizing so the waxes aren’t too much of a problem and we have been going up to 280bar (but can go higher) and we will need to deal with the clogging issues. It’s a shame because the low pressures produce a beautiful extract that flows easily!

The problem is that we are still observing decarboxylation at 40C. Runs of 4-5hrs at 240+ bar still cause considerable decarb.

Do you think that the high pressure reduces the threshold for decarboxylation? The literature seems to indicate that 80C is the start of decarboxylation under normal conditions, but perhaps at 200+ bar, the decarboxylation is evident at lower temperatures and shorter times?

Ideally we would have no decarboxylation, but it sounds from what you said that we are going to have to live with it! So in summary, we want to keep extractor/separator temperatures 40C or lower, extraction times as short as possible (so high pressures), and as much flow as possible? Is 35C feasible or is that too low?

Thanks again, the help on this forum is invaluable.