Impact Assessment and Interpretation

The ReCiPe 2016 method was used to perform the life cycle impact assessment, which can be used to calculate midpoint and end point indicators.⁴² Midpoint indicators represent environmental impacts at a specific point in the cause-effect chain, such as climate change or land use, while end point indicators represent environmental impacts at a higher level of aggregation, i.e., human health, biodiversity, and resource scarcity. ReCiPe includes three different perspectives representing groupings of assumptions and value choices. The individualist perspective is based on short-term interests and a best-case scenario for human technological adaptation, the hierarchist is a consensus-based middle point, and the egalitarian includes all known impact pathways and focuses on the long-term.⁴² All three perspectives were considered here as well as both midpoint and end point impacts. To match the needs of premise, notably for the future deployment of carbon capture technologies, some modifications were made to the characterization factors of ReCiPe for climate change impacts as listed in Table S5 in the SI.⁴³

For visualizations, the upscaling of the chemical synthesis was broken down into steps following the framework of van der Hulst et al.²⁵ The effect of size scaling and process changes were isolated from those of process synergies by modeling TRL 9 without synergies. Distillation is the only process synergy that we considered. We also modeled an alternative way to recover the solvent, namely, direct solvent reuse. Reuse of the water solvent was validated experimentally for one reuse cycle. Reuse up to four times is assumed to be practically achievable before the quality of the synthesis is affected, based on expert judgment for this reaction. The impacts of water use and waste stream were allocated equally between each synthesis that was part of a reuse cycle. An additional use of acetic acid was included for each cycle, which is used to correct the pH of the solvent before each reuse (approximately 0.3 g/kg of solvent).