Bridge to zero-emission: Life cycle assessment of CO₂–methanol conversion process and energy optimization

CO₂-conversion technology provides both CO₂ emission reduction and new value chains and is now becoming a key player in moderating global temperature increase. In this study, CO₂-methanol synthesis processes are evaluated through life cycle assessment. Four conversion processes are selected to represent different technological readiness level (TRL) groups. Coal gasification and coking conversion process for high TRL while hydrogenation and photocatalytic conversion process represent mid and low TRL. Coal gasification conversion shows the highest global warming potential (GWP) with 17.7 kg CO_2eq, followed by hydrogenation conversion, and coal coking conversion. Photocatalytic conversion showed the lowest GWP with 2.28 kg CO_{2 eq}. The mid-to-low TRL conversion processes are analyzed by varying heat and electric sources. Through variation, feasibility of reducing CO₂ emission to low-TRL level is confirmed. Although emission reduction sensitives upon energy sources are varied, hydrogenation conversion process reduced the GWP from 10.7 to 1.65 kg CO_{2 eq.} Through the study, it is verified that hydrogenation conversion could be a bridge to green methanol until technological development of photocatalytic conversion, an acceleration to zero-emission.