Storage stability of biocrude oil fractional distillates derived from the hydrothermal liquefaction of food waste

Biocrude oil produced via hydrothermal liquefaction (HTL) is a promising precursor for transportation fuels and biochemicals. Present studies have highlighted the inherent instability of the biocrude oil, which poses significant challenges for its subsequent storage, upgrading and transportation. On the other hand, biocrude oil distillates showed the potential to serve as a transportation fuel blendstock. To this end, this study aimed to investigate the influence of the distillation temperature (199–238 °C and 238–274 °C), storage atmosphere (air and nitrogen), temperature (25 °C and 55 °C), and time (0–16 weeks) on the physical, chemical, and boiling point distribution properties of the distillates. Results demonstrated that changes in the stored distillates due to different distillation temperature were drastically higher than that between different storage atmospheres and temperatures. Comparing with the raw distillate, the distribution of compounds with a molecular weight < 300 Da in low-temperature (199–238 °C) distillates (LD) and medium-temperature (238–274 °C) distillates (MD) was improved with the increasing storage time. In addition, storage led to a decrease in O:C ratio (21.6 % and 86.5 %), and an increase in the HHV (3.6 % and 12.3 %) in the LD and MD, respectively. Furthermore, only slight deviations were observed in the density (5.2 % and 7.4 %) and viscosity (5.2 % and 0.8 %) for LD and MD, respectively. In particular, the MD group exhibited comparable characteristics to transportation fuels with decreased acidity (1.8–2.8 mg KOH/g) and increased HHV (46.2–46.8 MJ/kg) after long-term storage. At last, the mechanism of superior distillates stability was discussed. This study indicated that distillation not only presents a potential approach for producing transportation fuel blendstock but also improves the stability of HTL biocrude oil.