Hydrothermal liquefaction (HTL) is an emerging thermochemical technology for converting biomass into biofuels and valuable chemicals while contributing to greenhouse gas reduction. Operating under subcritical water conditions (200–374 °C, 10–25 MPa), HTL transforms biomass into four main fractions: a bio-oil rich in energy, an aqueous phase containing dissolved organic compounds, a solid residue (bio-char), and a gaseous phase mainly composed of CO₂. Its ability to process wet biomass without prior drying, combined with high conversion efficiency and feedstock flexibility, makes HTL a promising pathway for sustainable energy production.
This study aims to develop a kinetic model for biomass HTL that integrates operational parameters (temperature and residence time) and biomass biochemical composition. Three types of biomass with different compositions—walnut (lipid-rich), walnut cake (protein-rich), and sunflower cake (fiber-rich)—were investigated. Experiments were conducted at 300 °C and 350 °C with reaction times ranging from 5 to 15 minutes. Product distribution and composition were analyzed using gas chromatography–mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC), and ion chromatography (IC).
The results demonstrate a strong influence of biochemical composition on bio-oil yield and optimal reaction conditions. The highest bio-oil yield (92%) was obtained from lipid-rich biomass at 300 °C for 5 minutes. Protein-rich walnut cake produced a maximum yield of 54% at 300 °C after 15 minutes, while fiber-rich sunflower cake required a higher temperature (340–350 °C) to reach its best yield (53%). These findings confirm that lipids favor bio-oil production under milder conditions, whereas fiber-rich biomass requires more severe processing.
Identified compounds were grouped into chemical families to construct a general reaction scheme. Overall, this work provides insight into biomass-dependent HTL behavior and supports the development of predictive kinetic models for process optimization.
