Application of Algae as Cosubstrate To Enhance the Processability of Willow Wood for Continuous Hydrothermal Liquefaction

This work proposes a novel strategy to improve the continuous processing of wood slurries in hydrothermal liquefaction systems by coprocessing with algae. Of all algae tested, brown seaweeds and microalgae perform best in preventing slurries dewatering, the main reason for pumpability issues with wood slurries. Rheological tests (viscosity–shear rate profile) indicate that the addition of these two algae to the wood slurry causes the highest increase in viscosity, which coincides with improved wood slurries stability and pumpability. Hydrothermal liquefaction of wood-algae slurries at 400 °C and 15 min in 10 mL tubular batch reactors shows that macroalgae slightly decrease the biocrude yield from 28.5 to 21.6–25.5 wt %, while microalgae increase the biocrude yield by more than 40% relative to pure wood liquefaction due to the lower biocrude yields from macroalgae carbohydrates and higher fractions of lipids and proteins in microalgae. Another benefit of microalgae addition is that the total biomass loading and the organic mass fraction of the slurry can be increased by 100% and 90%, respectively. Therefore, when coprocessed with wood, microalgae can improve the wood feedstock pumpability, biomass loading, organic matter, and biocrude yield.