Hydrothermal liquefaction of Chlorella pyrenoidosa and effect of emulsification on upgrading the bio-oil

[Display omitted] •Bio-oil from liquefaction of microalgae was upgraded by emulsification.•A comparison on fuel properties between bio-oil and emulsion fuel was provided.•Storage stability of emulsion fuel was firstly explored by boiling point analysis.•A possible stability mechanism was proposed based on storage stability analysis. This work studied the hydrothermal liquefaction of Chlorella pyrenoidosa and effect of emulsification on upgrading the bio-oil. The fuel properties and storage stability characteristics of emulsion fuels were explored. The combustion characteristic analysis showed that the ignition temperatures of emulsion fuels (139.6–151.3 °C) were lower than that of bio-oil (176.9 °C). Besides, emulsion fuels had higher comprehensive combustion indexes (7.24–14.08 × 10−6 × min−2 × C−3) than bio-oil (1.51 × 10−6 × min−2 × C−3), indicating that emulsion fuels had better combustion performance. The kinetic analysis showed that emulsification could effectively reduce the activation energy, resulting in less energy input for combustion. Based on chemical composition evolution during the storage process, a possible stability mechanism was proposed. The storage stability analysis indicated that the diesel-solvable fractions in bio-oil had better stability. Overall, this work provides a feasible way for bio-oil upgrading through emulsification. In addition, a better understanding of the stability property of emulsion fuel was provided.