Affordable method for batch supercritical extraction using solid carbon dioxide–Extraction of cannabis threshing residues

Abstract

The change in the existing regulations in different countries regarding cannabis crops management and trading has enabled the commercial exploitation of the plant parts and of their extracts, metabolites and derivatives. Industrially, key metabolites such as cannabinoids and terpenoids are commonly extracted from the flowers by using supercritical CO2. However, supercritical units require an extremely high capital investment even at low production capacities becoming a main drawback for exploratory and de-risking research stages. In this direction, this works aims to assess a low-cost CO2 supercritical extraction technique for exploratory experiments employing solid CO2 (known as dry ice) within a high-pressure vessel. By heating the solid CO2 within the vessel, supercritical conditions can be achieved enabling extraction and recovery of the extract by subsequent depressurization. P-V-T curves were experimentally obtained to determine the required dry ice loadings to achieve specific supercritical conditions. Evaluated ranges corresponded to temperatures in-between 291 and 365 K, specific molar volumes of 47–90 mL/mol and the corresponding pressures ranging between 54 and 300 bar. Subsequently, the developed technique was validated in the lab-scale for the supercritical extraction of cannabis sativa threshing residues at CO2 loadings of 0.63–0.73 g/mL, temperatures between 313 and 343 K and the corresponding pressures of 91–176 bar. The proposed technique enabled extraction yields of 3.9–6 % wt. with respect to dry biomass, with cannabinoids contents in extracts of 191.86 mg/g for CBD and 28.48 mg/g for THC. Results were comparable with those obtained in commercial supercritical equipment.