Hydrothermal Upgrading of Industrial Hemp Waste: Effect of Cultivars and Fibre Sheath Presence on Bio-Oil Yield

Industrial hemp is an abundant agricultural residue with potential for sustainable fuel production. In this work, stalks of two hemp cultivars (Futura-75 and Fedora-17), considered either before or after fibre extraction (with and without fibre sheath), were processed by hydrothermal upgrading (HTU) to obtain bio-oil. A total of twelve autoclave reactions were conducted using 10 g of biomass and 2–4 g of potassium carbonate as a catalyst. The resulting bio-oils exhibited significantly reduced oxygen content (26–36%) compared to the raw feedstock (47%) and achieved higher heating values of 25.9–32.1 MJ/kg versus 17.7–17.9 MJ/kg for the untreated biomass. Fractionation analysis revealed that the main products were high-boiling (>360 °C) and diesel-range fractions, while overall yields ranged from 21.3% to 32.8%. The highest yield was obtained from Fedora-17 with the fibre sheath and 2 g of catalyst. Overall, the study highlights the potential of hemp waste as a renewable feedstock for liquid fuel production and demonstrates how fibre content and cultivar type influence both yield and product quality.