Product Characteristics and Evidence-Supported Mechanistic Interpretation of Subcritical Hydrothermal Liquefaction of Lignocellulosic Biomass

Hydrothermal liquefaction (HTL) is a promising route for converting wet biomass into bio-oil, but isolated model-component results do not necessarily describe naturally integrated lignocellulosic matrices. Here, lignin, cellulose, and hemicellulose were examined under subcritical HTL conditions (240–320 °C, 5–60 min, and water-to-biomass ratios of 2:1–20:1), and peanut shell and bamboo were used as two representative real feedstocks. At 300 °C and 30 min, lignin gave the highest bio-oil yield (45.36 wt%) and an oil enriched in phenolic compounds (>80% relative GC-MS peak area), whereas cellulose and hemicellulose gave lower oil yields (23.00 and 13.06 wt%, respectively) and larger aqueous-phase fractions. Oil-phase carbon and energy recoveries followed the order lignin (48.2% and 50.5%) > cellulose (32.4% and 35.9%) > hemicellulose (17.7% and 19.2%). A weighted additive reference constructed from the independent model-component results underpredicted phenolics and overpredicted carbohydrate-derived oxygenates in the real-biomass oils. For peanut shell and bamboo, the measured phenolic fractions were 68.85% and 64.11%, compared with additive-reference values of 47.66% and 34.17%, while the measured furanic fractions were 1.27% and 9.76%, compared with 12.12% and 17.88%. These directionally consistent deviations indicate non-additive product redistribution in the tested real-biomass samples.