Methanol to polypropylene: life cycle assessment and a preliminary social impact analysis

Life Cycle Assessment (LCA) and Social Life Cycle Assessment (S-LCA) are currently essential tools for evaluating the sustainability of products and industrial systems. Although LCA is systematically applied today and is considered a stable methodology, supported by material-specific guidelines and rich databases, S-LCA remains immature in certain aspects. In the presented case study, LCA was applied to compare 11 methanol synthesis processes, all based on reverse Water-Gas Shift, but characterized by different sources of CO2 and H2 supply, to identify the most promising. Accordingly, the model was then integrated with that of propylene production (methanol to propylene-MtP), identified as a molecule of interest for the current and future market. Then, the authors propose an innovative approach to enhance the application of S-LCA in the industrial chemistry sector. The climate change impact of the different methanol production scenarios varies significantly: the most impactful is the methanol synthesis via coal gasification (2.76 kg CO2 eq), and the most promising are via CO2 generated by wood chips waste or dedicated biomass by employing hydrogen produce with wind electrolysis, which show the negative impacts of -0.40 kg CO2 eq thanks to cogeneration and the use of hydrogen from renewable sources. On the social level, the database shows a preference for productions occurring in Europe, across all the categories analyzed. The proposal of a sector-specific guideline represents a step forward that could facilitate the future application of the methodology. Moreover, the integration of LCA and S-LCA proves effective in delivering a richer and more comprehensive understanding of the issues addressed, offering valuable insights for stakeholders. The LCA should be applied to assess the environmental sustainability of alternative production routes in chemical processes, while the complexity of S-LCA can be mitigated by initiating preliminary assessments.