Targeted valorization of high-solid microalgal biocrude via molecular distillation: Preparing precursors for sustainable aviation fuels

Decarbonizing the aviation sector necessitates scalable Sustainable Aviation Fuels (SAF), yet the complex composition of microalgal biocrude oil (BCO) impedes direct upgrading. This study establishes a fractionation protocol using short-path molecular distillation to valorize BCO derived from the hydrothermal liquefaction of high-solid-content (60 wt%) Chlorella vulgaris. The process effectively separated the complex BCO into three functionalized streams, avoiding the energy-intensive total hydrotreating of raw oil. The light bio-oil (LBO) was characterized by high concentrations of monocyclic aromatics and heteroatomic compounds. The medium bio-oil (MBO) fraction was identified as a superior aviation fuel precursor, exhibiting a favorable C8-C16 carbon distribution (59.40%), a high HHV (38.83 MJ/kg), and a molecular weight (276 g/mol) aligning with jet fuel specifications. Conversely, the heavy bio-oil (HBO, 56.20 wt%) sequestered refractory polycyclic aromatics and long-chain heteroatoms, rendering it suitable as a low-carbon asphalt modifier. By physically removing unstable components (concentrated in LBO) and coke precursors (in HBO) prior to hydrotreatment, this targeted valorization strategy significantly lowers theoretical hydrogen consumption and process severity. These findings demonstrate a techno-economically viable pathway for converting high-density algal biomass into drop-in SAFs and value-added co-products, directly advancing United Nations Sustainable Development Goals 7 and 13.