Process Modeling and Techno-Environmental Assessment of Lignin Hydrothermal Liquefaction to Aromatics and Sustainable Aviation Fuel

Abstract Hydrothermal liquefaction (HTL) is a promising approach that converts lignin into oxygenated aromatics, which serve as precursors of phenolic resins and sustainable aviation fuel (SAF) blendstock. However, its rigorous modeling and evaluation remain underexplored due to complexities in reaction mechanisms. Here, we introduce a model-compound-based process modeling framework and evaluate two HTL-based lignin conversion processes using techno-economic analysis (TEA) and life cycle assessment (LCA). Scenario 1 considers oxygenated aromatics as a precursor for phenolic resins, while Scenario 2 upgrades them to SAF blendstock via hydrotreating. Our LCA reveals that Scenario 1 achieves a net negative global warming potential (GWP) across various lignin sources, driven by carbon storage credits from solid co-products. Among the lignin species, using pulp waste offers the lowest GWP at −2.30 kg CO2 eq. In Scenario 2, the SAF blendstock is produced at a GWP of 5.9 g CO2 eq/MJ, with additional contributions from green hydrogen via alkaline electrolysis (AEL), while values across practical lignin sources range from −28.3 to 41.9 g CO2 eq/MJ. Solid co-product credits enable the blendstock to significantly outperform the 83.8 g CO2 eq/MJ baseline for conventional jet fuel. Furthermore, implementing this technology in highly decarbonized grids is essential for maximizing climate benefits. Concurrently, TEA shows that the minimum selling price (MSP) is $3.32/kg and $8.03/kg for producing resin precursor (Scenario 1) and SAF blendstock (Scenario 2), respectively. Applying US IRA tax credits ($1.53/gal) further reduces the latter to $7.52/kg.