Sustainable microalgal biorefinery enabled by molecular dynamics-guided in-situ hydrothermal extraction using fatty-acid-based hydrophobic eutectic solvents: Integrated process performance and life-cycle assessment

Efficient lipid extraction from microalgae is essential for advancing sustainable biofuel production. In this work, fatty-acid-based hydrophobic eutectic solvents (FHES) were introduced for in-situ hydrothermal lipid extraction, offering a greener alternative to conventional post-hydrothermal hexane extraction that often causes lipid degradation. Molecular dynamics simulations were used to screen ten FHES with varying fatty-acid chain lengths, and the C8–C7 system was identified as the optimal candidate based on interfacial thickness, phase stability, hydrogen-bond lifetime, and cohesive density. Experimental validation confirmed the prediction, achieving an extraction efficiency of 87.2% under optimized conditions (HBA: HBD = 1:3, 200 °C, 1.3 mL, 20 min). Kinetic analysis demonstrated that the in-situ strategy suppresses lipid degradation during hydrothermal treatment and accelerates lipid release, outperforming post-hydrothermal extraction. Characterization of hydrothermal residues (TG, FTIR, EA, SEM) revealed enhanced nitrogen retention and the formation of aromatic carbonaceous solids with preserved nitrogen functionalities, suggesting potential for value-added utilization. A cradle-to-gate life-cycle assessment further showed that the FHES-based route reduces the net energy ratio (NER) by 45.8% and lowers greenhouse gas emissions from 287.2 to 256.9 g CO 2 -eq MJ −1 of biodiesel compared with the hexane pathway. Overall, this study establishes a molecular-dynamics-guided, efficient, and environmentally advantageous extraction strategy that simultaneously enables residue valorization within a sustainable microalgal biorefinery.