48 February / March 2018 Table 2: Optimised Supercritical CO2
extraction conditions for targeting terpenes found in terpene rich Hemp. Stage 1
Extraction Temperature (°C) Extraction Pressure (bar) Flow Rate (g/min)
Extraction time (min) CS1
Pressure (bar) / Temperature (°C) CS2
Pressure (bar) / Temperature (°C) CS3
Pressure (bar) / Temperature (°C) SC4
Pressure (bar) / Temperature (°C) Extraction Time Terpenes 45 min
Extraction Time Cannabinoids 5.5 hours Extraction Efficiency
92% exchanger to bring the liquid CO2 to a
supercritical state before it entered into the extractor vessel. The supercritical stream dissolved the target components from the botanical material and directed them from the extraction vessel to the appropriate cyclone separators. The optimised conditions are summarised in Table 2.
Cannabinoids and terpenes have varying solubility in supercritical carbon dioxide. Furthermore, compounds within the classes of cannabinoids and terpenes have varying solubility in supercritical carbon dioxide. The extraction of terpene rich hemp is divided into three stages, with the density profile of supercritical carbon dioxide being increased at each stage in order to target different compounds.
To extract monoterpenes, the flow of supercritical carbon dioxide was first directed into CS4, bypassing cyclone separators one through three. Without the
addition of CS4, volatile monoterpenes evacuate with supercritical carbon dioxidefrom SC3 into the CO2
recycler.
With the addition of CS4, it is possible to create conditions that allow for the recovery of volatile monoterpenes. However, even with the addition of CS4, at ambient temperatures volatile monoterpenes will evacuate with the gaseous CO2
. To
remedy this, CS4 was cooled to -78°C with a solvent mixture of acetone and dry ice. Once chilled, the extraction vessel was pressurised to 70 bar and extraction occurred at 50°C. Monoterpenes have high solubility in supercritical carbon dioxide at these conditions, while sesquiterpenes have mild to low solubility. In Stage 2, both temperature and pressure were increased to target less volatile sesquiterpenes. During this stage, the flow of supercritical carbon dioxide was directed into CS1 and continued through CS3. After 45 minutes, sesquiterpenes were collected from CS3.
50 70
100 45
N/A N/A N/A Ambient / -78
Stage 2 55
150 150 45
103 / 50 65 / 45 51 / 35 N/A
Stage 3 55
300 200 45
103 / 50 65 / 45 51 / 35 N/A
Both terpene fractions were analysed using GC-FID, shown in Figure 3. In stage 3 of the extraction, the pressure parameter was increases to 300 bar for cannabinoid extraction. Total extraction time for monoterpenes was 45 minutes, extraction time for cannabinoids was 5.5 hours, and the total efficiency was 92% of the available target compounds were extracted.
Conclusion
In order to develop terpene extraction condition utilising supercritical carbon dioxide, it is essential to understand the relative solubility of terpenes in supercritical carbon dioxide. It was determined that monoterpenes have high solubility at 70 bar and 50°C while sesquiterpenes have low to mild solubility at these conditions. With the addition of a terpene specific collector (CS4), supercritical CO2
is an effective
solvent for the extraction of terpenes from Cannabis. The ability of supercritical carbon dioxide to return to a gaseous state once exposed to ambient conditions allows for simple terpene recovery and results in no detectable residual solvents. Monoterpene fractions were obtained from the terpene specific collector with high purity and no detectable cannabinoids. In order to recover highly volatile monoterpenes, CS4 needed to be chilled to -78°C. Plant waxes and cannabinoids co-elute with sesquiterpenes, which are collected from CS3. Due to the more robust nature of sesquiterpenes, these compounds can undergo post processing methods such as winterization with minimal to no degradation. The ability to separate monoterpenes from sesquiterpenes from cannabinoids allows for post processing of cannabinoids without the danger of terpene degradation.
Figure 6: Left chromatogram: Monoterpene fraction obtained at extraction conditions of 70 bar and 50ºC. Right chromatogram: Sesquiterpenes obtained at extraction conditions of 150 bar and 55ºC.
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