The need to integrate mass- and energy-based metrics with life cycle impacts for sustainable chemicals manufacture

Abstract

Effective use of quantitative metrics is fundamental to guiding innovation toward more sustainable chemicals. At present, metrics employed in Green Chemistry, such as the E-factor, Process Mass Intensity, or Energy Intensity, focus on mass or energy efficiency at specific levels – reaction, process, or plant. However, a more holistic approach is needed, especially at early stages of research and development, utilising more complex impact-based indicators from Life Cycle Assessments (LCAs) to gain a deeper understanding of the environmental footprint of chemical systems. To date, the need to couple mass- and energy-based process metrics with life cycle impacts for more comprehensive assessments has been qualitatively discussed but not quantitatively demonstrated. Therefore, this study quantifies the level of correlation and linkages between five mass- and energy-based metrics and 16 LCA indicator scores by leveraging data for over 700 chemical manufacturing processes. The primary finding is the weak correlations between process metrics and life cycle impacts, as the former approach lacks appropriate weights for each input and output to account for their life cycle environmental implications. While improving process efficiency can lead to lower overall environmental impact, enhanced granularity for comparing alternative chemical routes provides insights into the relative impact levels throughout the supply chain, particularly concerning raw materials as they are major contributors to life cycle environmental impacts. This study also provides practical insights for expanding the application of LCA by making it more accessible to the research community through simplified approaches and working collaboratively with LCA practitioners.