Improving life cycle assessment consistency for biomass-derived processes: A case study on triacetic acid lactone production with CO2 recycling

Abstract

This study addresses methodological inconsistencies in Life Cycle Assessment (LCA) for biomass-derived processes, focusing on system boundary selection, biogenic carbon accounting, and allocation methods. Using both a hypothetical example and a case study on triacetic acid lactone (TAL) production with carbon capture and utilization (CCU), this work evaluates the impact of methodological choices on greenhouse gas (GHG) results. This work identifies three major inconsistencies between LCA goals (e.g., attributional LCA and consequential LCA) and methodologies: (1) system boundary choices (cradle-to-gate vs. cradle-to-grave) for biogenic carbon flows, (2) multi-output allocation methods (system expansion, substitution method, economic allocation, mass allocation, and carbon content-based allocation), and (3) carbon footprint of CO₂ feedstocks, focusing on the impacts of CO₂ recycling, particularly for co-products. Results show that GHG emissions for TAL vary from 0.3 to 13.1 kg CO₂-eq/kg depending on the allocation method and system boundary applied. Substitution and system expansion methods reveal net-negative emissions when CO₂-derived formic acid displaces fossil-based alternatives, while economic and mass-based allocations shift the burden significantly between TAL and co-products (GHG emissions for TAL vary from 2.4 to 13.1 kg CO₂-eq/kg). The study emphasizes that consistent alignment between LCA type, system boundaries, and allocation choices is essential to avoid overestimating climate benefits. Aligning system boundaries, carbon assumptions, and allocation methods with study goals is crucial for consistent and robust LCA results. This work provides practical recommendations to improve transparency and comparability in evaluating biomass-derived processes and carbon recycling systems.