Integrating the Reverse Boudouard Reaction for a More Efficient Green Methanol Synthesis from CO2 and Renewable Energy.

Green methanol is an important renewable platform chemical that could be used to produce a wide range of sustainable products and fuels. However, it is currently economically unappealing. This high cost is mainly driven by the CO2 hydrogenation process, which requires 50% more H2 consumption than the classic fossil-based CO-rich syngas to methanol. To overcome this limitation, here we evaluate the economic and environmental implications of producing green methanol from electrolytic H2 and captured CO2 integrated with the reverse Boudouard (RB) reaction. We designed an integrated process based on a standard green methanol plant, adding an RB reactor to reduce CO2 to CO using biochar prior to the methanol synthesis loop. Combining process simulation with life cycle assessment, we find that integrating both technologies leads to an economic and environmental win-win scenario compared with the base green methanol case. More specifically, production costs are decreased by 5% in an expanded system that assumes the simultaneous production of methanol, biogenic hydrogen, and industrial high-temperature heating under both scenarios. Furthermore, this alternative synthesis shows a reduced carbon footprint of 5% and a 4 to 10% improvement in human health, ecosystems quality, and resource scarcity, revealing no significant probability of associated burden shifting when expanding the system. Finally, when compared with fossil-based methanol, the RB integration makes green methanol competitive when H2 is available at 3.5-2.0 $/kg, compared to the 2.3-1.3 $/kg required for the standard green methanol configuration. Our results highlight a potentially better alternative to direct CO2 hydrogenation for green methanol synthesis and, in a broader context, demonstrate the benefits of integrating processes to exploit their synergies.