Thermodynamic and exergoeconomic evaluation of an integrated sugarcane bagasse biorefinery for polylactic acid and multi-product valorization

The economic viability and resource efficiency of lignocellulosic polylactic acid biorefineries remain constrained by high energy demand, complex downstream processing, and the underutilisation of biomass-derived co-products. Although agricultural residues such as sugarcane bagasse offer significant potential as sustainable feedstocks, the thermodynamic and economic implications of integrating multiple value-added co-products within such systems remain insufficiently understood. This study develops an integrated thermodynamic–exergoeconomic framework to evaluate multi-product sugarcane-bagasse biorefineries co-producing polylactic acid, electricity, and value-added co-products, including succinic acid, xylitol, and lignin-based adhesive. Four process configurations were modelled in SuperPro Designer (v13) and analysed using exergy, exergoeconomic, and unit-operation-level diagnostics. Overall exergy efficiencies ranged from 47.2 % to 65.5 %, while functional exergy efficiencies varied between 27.17 % and 48.18 %, indicating strong sensitivity to co-product integration and energy-recovery strategies. Core process units, including pretreatment, fermentation, polymerisation, and lactic-acid purification, exhibited high thermodynamic performance, whereas electricity generation and co-products recovery were identified as the dominant sources of exergy destruction. Exergoeconomic analysis revealed that cost formation is primarily governed by downstream separation processes, with purification units exhibiting the strongest coupling between thermodynamic irreversibility and economic penalty. Purification units were predominantly destruction-cost-dominated, whereas adhesive-production stages were capital-dominated, highlighting distinct economic drivers across process blocks. Although lignin-to-adhesive valorisation improved exergy utilisation, it significantly increased capital intensity, revealing a trade-off between thermodynamic performance and investment requirements. Overall, this study provides a unified exergy–exergoeconomic framework and delivers new insights into the interactions among efficiency, cost formation, and co-product strategy, thereby supporting the design of scalable and resource-efficient lignocellulosic biorefineries.