Green methanol production under carbon constraints: pathways, system integration, and deployment conditions

Green methanol links low-carbon carbon sources with renewable electricity while retaining liquid-fuel handling advantages. We reviewed 155 publications covering genuinely green routes based on renewable hydrogen and sustainable carbon (CO 2 hydrogenation with renewable H 2 and biomass- or waste-derived methanol), transitional low-carbon retrofits of fossil-based plants, and less mature electrochemical, photocatalytic, or methane-conversion routes. Retrofits are treated as transitional, not genuinely green, because their carbon remains fossil-derived unless the feedstock is replaced. Authors adopt different system boundaries and functional units, and assumptions about electricity, CO 2 supply, plant scale, and cost are rarely identical. Our comparison places each pathway in its operating conditions and avoids ranking isolated performance values. It considers technical maturity, energy demand, life-cycle emissions, levelized methanol cost, feedstock supply, infrastructure, and operating flexibility, and examines when power-hydrogen-carbon integration is justified. The review provides four outputs: a protocol for checking the comparability of techno-economic assessment and life-cycle assessment (TEA/LCA) evidence, conditional rules for evaluating integration, a qualitative regional pathway-selection matrix, and a dynamic-validation gap analysis linking demonstrated performance to availability, load-following, capacity factor, and degradation. No route is universally preferred; a defensible choice depends on consistent accounting and on regional electricity, carbon resources, industrial assets, and end use. The integration comparison distinguishes H 2 -to-CO 2 power-to-methanol (PtM), H 2 -enhanced biomass/waste conversion, retrofit/carbon capture, utilization, and storage (CCUS) in fossil methanol hubs, and multi-source industrial symbiosis, and shows that no archetype is universally superior.