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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:

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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