Automating Solvent Removal From Winterized Cannabis Oil Extract

Featured Article

Winterization is a key process in the refinement of cannabis extract to produce tetrahydrocannabinol (THC) oil for the medical and legal recreational marijuana markets. The process removes higher-melting-point components by cooling in the presence of alcohol. Raw extract is heated with ethanol before freezing. The solidified elements, i.e., plant waxes, fats and chlorophyll, are then filtered out, leaving the purified oil in solution. Subsequently, the ethanol must be removed, most commonly by rotary evaporation.

Figure 1 – Rocket 4D Synergy evaporator.

California Gold Extractions (San Diego, Calif.), which specializes in the extraction and refinement of THC oil for the medical marijuana market, evaluated the Rocket 4D Synergy from Genevac (Ipswich, U.K.) (Figure 1) as an alternative evaporation method. Rocket Synergy centrifugal evaporators evaporate up to six 400-mL flasks in parallel. Fitted with a removable 5-L bowl rotor, they offer fast, unattended evaporation of batch product. Higher volumes (tens of liters) can be processed with the option of a feed system. The current study compared the Rocket 4D Synergy and a rotary evaporator to evaluate the former as a potential tool for production scaleup.

Method

Raw cannabis extract was obtained by supercritical fluid CO₂ (SFC) extraction of cannabis plant material. In addition to THC and other cannabinoids, the raw extract contained a variety of fats and waxes. These inert materials were removed by winterization; the raw extract was dissolved in multiple volumes of ethanol before filtration.

Two liters of dissolved extract were loaded into a 5-L round-bottom flask fitted to a rotary evaporator. Water bath temperature was set to 50 °C and vacuum was manually adjusted to optimize evaporation rate. In order to maintain an appropriate evaporation rate, the rotary evaporator required frequent attention during the run. The rotational rate and depth of the flask in the bath required adjustment, and the cold trap needed to be monitored and filled. It was necessary to pause the system once to drain the solvent collection flask and to stop it manually at the end of the run.

Table 1 – Residual ethanol by headspace-gas chromatography, process time and final extract volume

For comparison, 2 L of dissolved extract were loaded into a 5-L stainless-steel bowl rotor in the Rocket 4D Synergy. The “Medium BP” method was selected with a run temperature of 50 °C and operation was initiated. Rocket automatically controlled vacuum and supplied heat energy using a patented, low-temperature steam method to drive evaporation. The system monitored evaporation rate throughout the run, collecting and draining solvent from the integral condenser, and stopping automatically when the ethanol was removed. No user intervention was required.

Dried samples were analyzed for residual ethanol by headspace-gas chromatography; results using both evaporators are shown in Table 1.

Figure 2 – Refined THC oil extract. Left: from rotary evaporator; right: from Rocket 4D Synergy evaporator.

The Rocket stopped automatically after 60 minutes, while the rotary evaporator was stopped manually after 80 minutes. In both cases, the volume of solvent recovered was around 1.4 L and refined extract approximately 200 mL (see Figure 2). Residual ethanol data for both samples was within operational limits.

Conclusion

Overall, the Rocket Synergy provided a better drying solution than the rotary evaporator.

Evaporation time was reduced, while acceptable residual ethanol content was maintained. No user input was required following startup, allowing for unattended evaporation. More consistent operation and product quality are achievable due to the system’s ability to automatically control and monitor system parameters during a run.

Alison Wake is product and marketing manager, Genevac Ltd., part of SP Scientific, Unit 6, Farthing Rd., Ipswich IP1 5AP, U.K.; tel.: +44 (0) 1473 240000; e-mail: [email protected]; www.spscientific.com/genevac. Jim Bilotta is owner, California Gold Extractions, San Diego, Calif., U.S.A. The authors thank Danton Brown, SP Scientific (Gardiner, N.Y.), for his valuable assistance.