Unveiling environmental impacts of methanol production via electrocatalysis against conventional and thermochemical routes by life cycle assessment

A comparative life cycle assessment is performed to understand the environmental sustainability of methanol production via electrochemical CO2 reduction (EC), thermochemical CO2 hydrogenation (TC), and conventional processes. At the midpoint and endpoint levels, three processes present significant results in global warming (GW), terrestrial ecotoxicity (TE), human non-carcinogenic toxicity (HNC), and fossil resource scarcity (FS). TC and EC pathways have higher scores in these selected impact potentials, and the EC pathway is the least sustainable with a highest impact contribution of around 76%. This research also highlights the significance of integrating the recycling streams in the process flows to effectively reduce the environmental burden. Out of the several, it is meaningful to observe a total reduction of 87.53 kg CO2 eq and 718.28 kg CO2 eq for the GW potential of TC and EC pathways, respectively. In view of the uncertainty analysis, the NHC indicator demonstrates the highest uncertainty for all three processes, which can be traced back to its higher environmental relevance to the impact indicators. In the primary midpoint and midpoint analysis, TC and EC pathways indicate inferior positions in terms of sustainability, but once changing the electricity mix to 100% renewable sources based (hydropower, solar power, and wind power), a large reduction of 41%-88% in impact potentials is realized. Among all, electricity mix optimization based on a 100% hydropower source gives the best result. In this way, the TC pathway has a lowest environmental impact potential, standing out among the three processes. As a whole, this study highlights the importance of developing emerging technology for sustainable fuel production and enlightens the future direction of developing emerging thermochemical and electrochemical methanol production from CO2.