Advancing e-methanol systems via direct air carbon capture, CO2 hydrogenation, and hydrothermal co-electrolysis

Abstract

Climate change mitigation is increasingly driven by the urgent need for carbon-neutral fuels and chemicals, particularly in sectors where direct electrification is impractical. Among emerging solutions, e-methanol, synthesized from captured CO₂ and green hydrogen, has been recognized as a scalable liquid energy carrier compatible with existing infrastructure. However, current system designs often evaluate carbon capture, hydrogen production, and methanol (MeOH) synthesis in isolation, with limited emphasis on integration or region-specific deployment. In this study, a novel process design, simulation model, and life cycle CO₂ performance analysis have been developed for two integrated e-MeOH production pathways based on Direct Air Capture (DAC): one using direct CO₂ hydrogenation (DS) and the other relying on hydrothermal co-electrolysis synthesis (HS). In both configurations, internal integrations are leveraged, such as the use of raw MeOH as an internal fuel, electrolytic oxygen reuse, and thermal integration between subsystems. The hydrothermal co-electrolysis pathway was found to outperform the direct synthesis route in both environmental and energy metrics. For a conceptual 0.3 Mt/y MeOH plant located in Japan, cradle-to-gate emissions were reduced to −0.367 kg-CO₂eq/kg-MeOH for HS, compared to 0.519 for DS and 1.370 for the conventional route. Greater heat recovery further lowered energy demand. A regional sensitivity analysis indicated that in regions with low-carbon electricity (for example, in Canada), DAC-based e-methanol could achieve near-zero emissions. These findings underscore the importance of process integration and geographic energy context in determining e-methanol viability. A quantitative basis is provided to inform the scalable and regionally adaptive implementation of synthetic fuel technologies.