Biobased bitumen analogue formation during hydrothermal treatment of microalgae residues, part 2: influence of residence time on reaction products

Abstract The hydrothermal conversion of industrial Spirulina sp. residues at 260 °C under autogenous pressure is investigated. This second part of the study, focuses on the influence of the residence time on the final reaction products. The hydrophobic phase obtained after 60 min. at 260 °C has a rheological behaviour similar to that of an elastomeric bio-binder. Removal of solid residues from the hydrophobic fraction by filtration leads to a pure conventional bitumen-like material pointing out their strong influence on rheology. The investigation of lower and larger residence times suggests that bio-bitumen formation first involves the formation of bio-char by hydrothermal carbonization during heating of the reactor to 260 °C followed by hydrothermal liquefaction during the isothermal plateau.