The following are some notes from the 212 page report by Hélène Perrotin-Brunel in the Netherlands, ISBN 978-90-8570-730-1, Copyright © 2011,
Their copyright forbids copying, but I can share some of their critical results and suggest that you read the whole thing at:
According to the report, between 315-345 K and pressures up to 26 MPa, the solubility of D9-THC increases as the CO2 pressure rises. Solubility decreases with decreases in temperature up to about 15MPa.
Feasible extraction conditions, with solubility above 1×10-4, requires pressures above about 20 MPa and temperatures above 325 K.
D9-THC decomposes into Cannabinol (CBN) and between 314 and 334K, and pressures from 13.0 to 20.2 MPa, showed a molar solubility ranging from 1.26 x 10-4 to 4.16 x 10-4 and demonstrated different behavior as compared to D9-THC, with regard to molar solubility.
The Peng-Robinson equation of state in combination with quadratic mixing rules were used to correlate the data. Deviations between calculated results and the experimental data ranged from 4.14 to 4.46 % AARD (Absolute Average Relative Deviation).
9-tetrahydrocannabinol (D9-THC) is recognized for medical application as an neuroprotective and an analgesic, showing about an equal affinity for the CB1 and CB2 receptors.
It isn’t the only biologically active compound present in cannabis however, as there are more than 400 volatile compounds, including 66 cannabinoids all producing biological activity.
Cannabinol (CBN) is one of these cannabinoids and is mildly psychoactive, with sedative or stupefying properties. It’s the primary degradation product of 9-THC, with low presence in fresh plants, but after harvest increases as 9-THC degrades through exposure to light and oxygen in the air.
This dehydrogenation chemical reaction changes the 9-THC cyclohexene ring to an aromatic benzoic ring.
In the Sustainable Production of Cannabinoids with Supercritical Carbon Dioxide Technologies (SPOCWSCDT) study, the solubility of the cannabinoid CBN in supercritical CO2 was measured between 314 and 334 K, at pressures between 13.0 to 20.2 MPa.
The highest solubility was achieved using highest pressures and an intermediate temperature of 326 K.
CBD’s solubility behavior differs that of 9-THC, in CO2, which demonstrates greater higher solubility at higher temperature.
Due to those differences, the SPOCWSCDT study concluded that supercritical CO2 could be a good solvent for isolating CBN and 9-THC by extraction.
The solubility of cannabigerol (CBG) and cannabidiol (CBD) in SCFE CO2, were established at 315, 326 and 334 K, between 11.3 to 20.6 MPa pressure.
Within those parameters, the molar solubility of CBG ranged from 1.17 to 1.91 x 10-4 and the molar solubility of CBD ranged from 0.88 to 2.69 x 10-4.
Arranging the different cannabinoids by solubility in supercritical CO2, at 326 K, they fall in the order D9-THC < CBG < CBD <CBN.
Actual results deviated from calculated results and the experimental data from 0.81 to 6.35% AARD, with the exception of CBD at 334 K, with an AARD of 18.4%.