The storage stability of biocrude obtained by the hydrothermal liquefaction of microalgae

Hydrothermal liquefaction (HTL) is a promising technology that can produce biocrude oil from wet biomass. The biocrudes, while generally acknowledged to be more stable than pyrolysis oils, are still thought to degrade relatively quickly, which limits their applicability. In this investigation, the storage stability of biocrude produced from hydrothermal liquefaction of microalgae was systematically studied over 60 days, and the effect of the storage material, feedstock species, liquefaction temperature and storage temperature were assessed. Biocrudes obtained at 300 degrees C and 350 degrees C from the microalgae Spirulina and Chlorella vulgaris were stored at three temperatures: cold (4 degrees C), ambient (20 degrees C) and elevated temperatures (35 degrees C), over the two-month period. The dynamic viscosity, higher heating value, thermogravimetric analysis and elemental and chemical composition were assessed. The viscosity of the biocrudes only increased considerably at 35 degrees C. The reaction temperature and biomass type were also strong determining factors of the impact on biocrude stability. Biocrudes produced from C. vulgaris were more stable than the Spirulina, and the crudes formed at 350 degrees C were considerably less reactive than those produced at 300 degrees C. This demonstrates that biocrudes can be stored without substantial degradation, allowing a more flexible approach to upgrading to value products. (c) 2019 Elsevier Ltd. All rights reserved.