Comparative life cycle assessment of first‐ and second‐generation bio‐isobutene as a drop‐in substitute for fossil isobutene

Abstract

AbstractIsobutene (IBN, C4H8) is widely used in industry. Currently, IBN production relies on petrochemical processes. The current work assesses the comparative environmental sustainability of bio‐based IBN production routes based on first‐ and second‐generation sugar compared with fossil IBN by applying the ISO 14044‐based Life Cycle Assessment methodology. In total nine scenarios are examined. Scenarios 1–6 used first‐generation sugar for IBN fermentation and scenarios 7–9 use cereal straw‐based second‐generation sugar. The scenarios also differ in their process energy source. The savings in Global Warming Potential for first‐generation IBN are up to 68% (scenario 1); for second‐generation IBN, the savings reach 105% if an avoided burden approach for utilizing lignin as an energy source is applied (scenario 8). It is found that applying renewable process energy is a prerequisite to maximizing greenhouse gas savings. Special attention has to be drawn to the eutrophication potential, were none of the scenarios show savings. This is driven by sugar crop cultivation owing to fertilizer usage, thermal energy from solid biomass or natural gas due to NOx emissions and nutrient use for fermentation (e.g. ammonia). Scenarios 4, 7 and 8 show savings in the acidification potential compared with fossil IBN. A driver of acidification is biomass‐based process energy generation, mainly due to SO2 and NOx emissions from biomass combustion. In contrast, all scenarios show a better environmental performance concerning the freshwater aquatic ecotoxicity potential, the abiotic depletion and the photochemical ozone creation potential. Process development should focus on conversion efficiencies and a fully renewable process energy supply. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.