Suitability of hydrothermal liquefaction as a conversion route to produce biofuels from macroalgae

The brown algae Fucus vesiculosus, Laminaria saccharina and Alaria esculenta were subjected to hydrothermal liquefaction (HTL) for 15 min at 350 °C in batch microautoclaves. Further optimization was carried out in view of optimizing the biocrude oil yield, varying the temperature from 330 to 370 °C. The maximum conversion to biocrude was 29.4 ± 1.1 wt.% at 360 °C for A. esculenta. The reaction pathways for macroalgae HTL and its capability for recycling nutrients were also investigated. The aqueous phase showed potential for a partial recovery of the nitrogen (21.2-28.6 wt.%) and sulfur (25.8-34.6 wt.%) from the initial biomass, and an almost total recovery of potassium and sodium. Results indicate that HTL as a sole conversion method to produce biofuel as single product is not recommended for macroalgae due to the low conversion to biocrude oil. At such conditions, its use as post-treatment for the remaining biomass after extracting valuable compounds (especially from the carbohydrate fraction) might be more interesting, and is suggested as the future direction for research.