Integrated power to methanol processes with steam-assisted direct air capture

Carbon dioxide (CO₂) generated from the combustion of fossil fuels has resulted in global warming. Utilizing CO₂ from direct air capture (DAC) and green hydrogen to produce methanol is a potential method to reverse this process; however, its technical and economic feasibility remains controversial. In this study, three distinct power-to-methanol systems integrating adsorption-based DAC, alkaline water electrolysis, and thermochemical methanol synthesis were investigated. The modelling results showed that the energy consumption of the base case (PtM) was 49.58 GJ t_CH3OH⁻¹, which decreased to 45.89 GJ t_CH3OH⁻¹ using a steam-assisted DAC process (S-PtM). The heat-integrated S-PtM system (I-S-PtM) could further reduce the energy consumption to 37.84 GJ t_CH3OH⁻¹. In detail, high-grade waste heat (>100°C) was directly transferred to DAC and methanol distillation units via heat exchangers. Low-grade waste heat (>60°C) was upgraded and provided to DAC unit via heat pumps. In the I-S-PtM system, 93 % of the heat and 90 % of the cold demands could be satisfied, which achieved 23.7 % and 17.5 % reduction compared to that of the PtM and S-PtM systems. Consequently, the I-S-PtM system demonstrated a high total energy efficiency (53 %) and a low methanol production cost (801.79 $ t_CH3OH⁻¹) based on an electricity price of 60 $ MWh⁻¹. Moreover, when powered by renewable electricity with the electricity price less than 41.3 $ MWh⁻¹, the I-S-PtM is more cost-effective than the conventional fossil fuel-to-methanol process. In China, replacing gasoline with methanol from the I-S-PtM process using abandoned renewables could reduce gasoline consumption by 4.4 % and emissions by 8.47 Mt_CO2 per year.