Sustainable biofuel production through anaerobic digestion, SOEC and carbon-capture-and-utilization (CCU): techno‑economic, exergy and Life‑cycle analysis

The global transition towards sustainable energy emphasizes biofuels, particularly biomethanol and biomethane, as critical pathways for decarbonizing the chemical industry and maritime transport. This study proposes an integrated hybrid biofuel production system combining anaerobic digestion, biogas upgrading via amine scrubbing, solid oxide electrolysis cells (SOEC), methanol synthesis, and an oxy-fuel gas turbine. Thermodynamic, exergy, techno-economic, life cycle assessment (LCA), and transient analyses using real-scale industrial data were performed to evaluate system performance comprehensively. Results indicated an overall energy efficiency of 58.09 %, producing 188.68 kg/h of biomethane and 269.54 kg/h of biomethanol. Exergy analysis revealed high efficiency in methanol synthesis (86.95 %) and biogas upgrading (95.23 %), though anaerobic digestion showed significant irreversibilities. Economic assessment demonstrated favorable profitability, with a minimum payback period of 5.72 years and biomethanol production cost as low as 233 €/ton under optimal conditions. LCA analysis confirmed significant environmental benefits, showing the system as a net carbon sink (−1.31 × 10⁻² kg CO₂-eq/kg biomass) under renewable-dominated electricity scenarios. Transient simulations validated the system's robustness against seasonal variations in renewable energy availability. The proposed system, demonstrating low-carbon emissions (0.017 kg CO₂ per kg biofuel), presents a viable solution supporting the EU's net-zero goals by providing efficient, sustainable, and economically attractive biofuel production.