Life Cycle Carbon Footprint Assessment of Different Methanol Production Processes

Renewable methanol has gained global attention for its carbon-neutral potential, yet a unified definition and standardized evaluation framework are still lacking internationally. This study employs life cycle assessment (LCA) to quantify CO 2 emissions across five representative methanol synthesis pathways, including coal-to-methanol (CTM), natural gas-to-methanol (NGTM), biomass-to-methanol (BTM), biomass and green hydrogen-to-methanol (BHTM), and CO 2 and green hydrogen-to-methanol (CHTM), under both cradle-to-gate and cradle-to-grave boundaries. The results show that fossil-based pathways exhibit higher life-cycle CO 2 -eq emissions than renewable pathways. Within the cradle-to-grave boundary, CTM and NGTM show 4.75 and 2.83 kg CO 2 -eq/kg CH 3 OH, respectively, whereas BTM and BHTM decrease emissions to 0.81 and 0.67 kg CO 2 -eq/kg CH 3 OH. For CHTM, the cradle-to-grave emissions range from 0.58 to 1.29 kg CO 2 -eq/kg CH 3 OH depending on the CO 2 source scenario. A normalized Z factor was introduced as a unified metric for comparing methanol synthesis pathways. It links life-cycle CO 2 -eq emissions to the amount of CO 2 temporarily stored in methanol. Overall, this study provides a consistent basis for comparing the carbon performance of different methanol production routes.