Supercritical CO₂ extraction of hemp flowers: A systematic study to produce terpene-rich and terpene-depleted cannabidiol fractions

Despite their high-added value, terpenes currently have limited exploitation in the hemp industry, often ending up in the sidestream of cannabidiol extraction and/or purification. In this work, the influence of different combinations of pressures (80–300 bar) and temperatures (40–50 °C) on the recovery of three representative terpenes (caryophyllene, humulene, caryophyllene oxide) and, secondarily, cannabidiol, from hemp flowers by supercritical fluid extraction with carbon dioxide (SC-CO₂) was investigated systematically. In the preliminary experiments, the influence of the particle size and storage time on the SC-CO₂ process was evaluated, being noticed that a good recovery of the target compounds was obtained with freshly grounded hemp flowers. By comparing the extraction curves obtained for the studied pressure and temperature conditions, it was observed that pressures from 90 to 110 bar and temperatures from 40° to 50°C could allow a fast and efficient extraction of the three hemp terpenes. In contrast, higher pressures (200–300 bar) are needed for a superior recovery of cannabidiol. Based on the isocratic experiments, the gradient temperature (from 40° to 50°C) and pressure (from 100 to 300 bar) conditions were selected for the online fractionation of hemp flowers; thus, the proof-of-concept step-gradient SC-CO₂ experiment generated terpene-rich and terpene-depleted cannabidiol fractions. In conclusion, our study brings essential knowledge on selecting the SC-CO₂ process parameters for efficiently extracting hemp terpenes or performing the simultaneous removal of terpenes and extraction of cannabidiol from hemp flowers using step-gradient SC-CO₂.