Lignin first-lignin modification outperforms lignin-first strategies: Environmental and economic insights in second-generation ethanol biorefineries

Abstract

The trade-off between lignin incineration for energy and its valorization for biofuels and biochemicals is a central challenge in lignocellulosic biorefineries. This study introduces the lignin first-lignin modification (LF-LM) method - an enhanced version of the lignin-first (LF) method that improves lignin recovery and quality - offering a promising alternative to incineration and conventional LF strategies. To identify the most sustainable lignin utilization route, we performed a combined life cycle assessment (LCA) and techno-economic analysis (TEA) of four scenarios using sugarcane bagasse: (1) dilute acid (DA) pretreatment with lignin incineration (SC-base); (2) DA pretreatment with lignin pyrolysis (SC-1); (3) glycerol organosolv (GO) pretreatment with lignin pyrolysis (SC-2); and (4) PEG-assisted GO pretreatment with lignin pyrolysis (SC-3). The environmental impacts were evaluated using ReCiPe 2016 (H) in SimaPro, and the economic performance was assessed by calculating the ethanol minimum selling price (EMSP) via discounted cash flow analysis, supported by simulations in SuperPro Designer v9.0. Results show that SC-3 reduced total environmental damage by 36.66% and EMSP by 30.62% compared to SC-base, driven primarily by reductions in CO2 emissions and improvements in energy integration. Human health impacts accounted for over 90% of total environmental damage across all scenarios. Although SC-3 incurred higher capital costs, its environmental and economic advantages make it the most sustainable option. This study highlights the critical role of lignin valorization and process integration in improving the viability of second-generation ethanol production and underscores LF-LM as a superior strategy for sugarcane-based biorefineries. © 2025 Elsevier Ltd.