Selective extraction of HTL biocrude: A decision-oriented framework for s-CO2 fractionation and mild separations

Hydrothermal liquefaction (HTL) converts wet biomass into energy-dense biocrude; however, its storage and refinery co-processing remain limited by rapid aging, high TAN/TBN, and heteroatom-rich fractions that increase viscosity, hydrogen demand, and catalyst deactivation. We present a decision-oriented, bin-aware framework that conditions biocrude through selective, low-severity extraction using supercritical CO 2 (s-CO 2 ) as the baseline fractionation platform complemented by mild downstream methods (pH-swing liquid-liquid extraction, adsorption/ion exchange, organic-solvent nanofiltration, short-path distillation). To simplify compositional complexity, HTL biocrude is organized into five extraction-relevant “bins”: A (non-polar hydrocarbons), B (phenolics), C (carboxylic acids/free fatty acids), D (basic N-heterocycles), and E (heavy polar residue). Routine analytical metrics are linked to operating levers, including s-CO 2 density, entrainer loading, pH, and resin. We synthesize operating envelopes, integration strategies, and method-selection rules, while highlighting research gaps in selectivity data, co-solvent recovery, interfacial operability, and techno-economic validation. The framework is intended to guide early removal or segregation of reactive oxygenated, nitrogen-containing, and heavy polar fractions before storage and upgrading. By concentrating heteroatom, metal, and high-molecular-weight burdens into targeted streams, this approach is expected to improve feed stability and may reduce the downstream upgrading severity, hydrogen demand, fouling tendency, and catalyst exposure. These anticipated benefits require validation through integrated fractionation–hydrotreating studies. Overall, the framework provides a composition-guided roadmap for developing and evaluating refinery-compatible HTL-biocrude conditioning strategies.