Decarboxylation during CO2 Extraction

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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:

https://www.researchgate.net/publication/315417305_Supercritical_carbon_dioxide_extraction_of_cannabinoids_from_Cannabis_sativa_L_plant_material

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
 
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I could almost guarantee the decarboxylation is happening from the high pressure, it is lowering the intial boiling point for co2 in the oil thats causing the decarboxylation. You have to imagine at standard atmospheric pressure the decarboxylation temp for THCA-->THC is about 200-225 over the course of about 20-30min

When i decarboxylate the Disillate before we even run it through the system i run anywhere from 200-500g in a heating mantle under vacuum and i only have to hit around 130F for about 30-45min to fully decarboxylate the oil.

Now vacuum is slightly different, but pressure is pressure!

120F under the amount of pressure you are at is way to high in my opinion, i would imagine its almost instantly decarboxylating. The best I could recommend is lower the initial temp to around 20-25C if you can and see if that makes a difference.

I will bet its the actual temp vs. The pressure!
 
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I could almost guarantee the decarboxylation is happening from the high pressure, it is lowering the intial boiling point for co2 in the oil thats causing the decarboxylation. You have to imagine at standard atmospheric pressure the decarboxylation temp for THCA-->THC is about 200-225 over the course of about 20-30min

When i decarboxylate the Disillate before we even run it through the system i run anywhere from 200-500g in a heating mantle under vacuum and i only have to hit around 130F for about 30-45min to fully decarboxylate the oil.

Now vacuum is slightly different, but pressure is pressure!

120F under the amount of pressure you are at is way to high in my opinion, i would imagine its almost instantly decarboxylating. The best I could recommend is lower the initial temp to around 20-25C if you can and see if that makes a difference.

I will bet its the actual temp vs. The pressure!
Thanks very much for your reply. In order to get to supercritical, the CO2 needs to be at least 1070 psi and 88F. I am going to try it at a bit higher than those parameters (1450psi/95F) to make sure it is supercritical and see what happens!
Almost everyone (e.g. except that research article I linked to) seems to say that decarbox shouldn't happen so it is a mystery to me...
Appreciate the advice though.
 
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Well i do know for a fact that if you increase pressure whether it be negative pressure (a vacuum) or positive pressure (pressure chamber) that you are lowing the boiling point/flash point of any molecule, i would guess since the supercritical is basically a pressure chamber for co2 you are lowing the atmospheric pressure below the boiling point of co2 for decarboxylation in the wax itself thus converting THCA--->THC!

But like I said the only way you would truly know if it worked would be to get it tested at that Temp

But may I ask why you are trying to keep the THCA from converting?

I mean if you are making just pure wax then I could understand, but if you are making cartridges you actually want your product to be fully converted.

Just curious, this was actually the main reason why my facility switched from CO2 extraction to Fractional Distillation.
 
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Well i do know for a fact that if you increase pressure whether it be negative pressure (a vacuum) or positive pressure (pressure chamber) that you are lowing the boiling point/flash point of any molecule, i would guess since the supercritical is basically a pressure chamber for co2 you are lowing the atmospheric pressure below the boiling point of co2 for decarboxylation in the wax itself thus converting THCA--->THC!

But like I said the only way you would truly know if it worked would be to get it tested at that Temp

But may I ask why you are trying to keep the THCA from converting?

I mean if you are making just pure wax then I could understand, but if you are making cartridges you actually want your product to be fully converted.

Just curious, this was actually the main reason why my facility switched from CO2 extraction to Fractional Distillation.
I agree with you - my hunch was that the pressure is changing the threshold of the reaction, I am hoping to get some more data to confirm that, I figure that if I am still decarboxylating when I am just on the brink of supercritical then there might be something else at play otherwise everyone would be seeing it. THCA is what is required in this case (otherwise it would be easy!) - it apparently has medicinal properties too.
 
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