Two-Stage Hydrothermal Liquefaction of Sweet Sorghum Biomass-Part II: Production of Upgraded Biocrude Oil

The hydrothermal liquefaction (HTL), followed by hydrodeoxygenation (HDO) of lignin-rich biomass has a potential to improve the yield and the quality of upgraded biocrude oil. In this study, the lignin-rich biomass obtained from the low-temperature HTL (stage 1) of sweet sorghum bagasse was investigated to evaluate the biocrude oil yield and its compositions using catalytic high-temperature HTL-HDO (stage 2) and was compared with the conventional, whole-stage HTL-HDO process. Biocrude oil yield was achieved up to 38% during a high-temperature HTL, while 42% was obtained after catalytic (5% Ru/C) HDO process. Up to 96% hydrocarbon content of biocrude oil was achieved, which is twice as high as that of the conventional whole-stage HTL-HDO process. Aromatic hydrocarbons and long-chain alkanes were also dominant in the upgraded biocrude oil, which collectively accounted for 28% of the total hydrocarbons. From raw sweet sorghum bagasse, the hydrocarbons yield from second-stage HTL-HDO process (11%) was substantially increased by 78%, compared to that of the whole-stage HTL-HDO process (7%). The upgraded biocrude oil could be directly processed or co-processed in the existing refinery to produce drop-in fuels.