Comparative life cycle assessments of stand-alone and integrated green hydrogen and biofuel value chains: A case study on drop-in biocrude, biohydrogen and biomethanol production systems

Abstract

Biofuel production systems integration with green hydrogen (e.g., from proton exchange membrane electrolysers- PEM) can enable product yield improvements (e.g., gasification based biomethanol via hydrogenation of carbon-oxides) or co-production of synthetic methanol through hydrogenation of captured CO2. Environmental impact of these integrations compared to stand-alone systems is unknown. This study evaluates and compares the environmental performance of wood chip-based biofuel production systems, including advanced biocrude fuel (ABF), biomethanol (BMeOH), and biohydrogen (BH2), in stand-alone and integrated configurations with PEM-based hydrogen. The approach involved consequential life cycle analysis, focused on cradle-to-gate global warming potential (GWP), terrestrial acidification (TA), freshwater eutrophication (FE), and land use (LU) impacts. Gasification-based biomethanol yield enhancement with PEM hydrogen shows specific environmental benefits (e.g., in TA) while synthetic methanol co-production with ABF negatively impacts overall environmental performance. High electricity demand of PEM, influenced by the marginal electricity-mix, contributes to these trends. For biohydrogen, two-stage gasification route is preferable over pyrolysis-gasification due to higher biochar yield, which provide credit for replacing pulverized coal. Among the investigated systems, the stand-alone gasification-based biomethanol is the most environmentally efficient pathway for utilizing limited biomass. Meanwhile, the stand-alone two-stage gasification-based biohydrogen and stand-alone ABF show promise for decarbonizing hydrogen and diesel economies, respectively. All the biofuel systems outperform fossil fuels in GWP but lag in other categories (ABF- FE/LU, BMeOH- TA/FE/LU & BH2- TA/LU). The study emphasizes the importance of less resource-intensive green electricity supply and electrified logistics (e.g., biomass transport via freight trains) in enhancing the environmental performance of biofuel production systems.