Catalytic hydrotreating of crude bio-oil from straw and its distillates obtained by molecular distillation: A comparative study

In this study, the crude bio-oil (CBO) obtained from hydrothermal liquefaction of peanut straw was separated into light oil (LO) and heavy oil (HO) by molecular distillation at 130 ℃ and different pressures (0.5, 1 and 3 kPa). With process variables fixed, the CBO and its distillates were subjected to catalytic hydrotreating to probe the behavior characteristics of CBO from straws during this process. The LO yield fluctuated between 29.8 and 34.8 wt% with the change of distillation pressure. LO presented lower C content and higher H and O content than the corresponding HO. The LO obtained at 1 kPa showed a significant content difference between ketones (34.50%) and phenolic compounds (5.84%), indicating the differential distribution of these chemical components in CBO and the possibility of component separation by molecular distillation. Hydrotreating of LO gained obviously higher yield of upgraded oil (82.1–89.7 wt%) and lower yield of solid (6.1–9.1 wt%) than the corresponding HO (61.2–69.4 wt% and 21.3–24.6 wt%, respectively). The addition of n-hexane in the hydrotreating of HO led to an increase in hydrocarbon content and a decrease in content of phenolic compounds in the upgraded oil, although it did not contribute to increasing the upgraded oil yield.