Integrated CO2 capture and conversion to methanol

Inspired by the CO₂ hydrogenation to methanol in the presence of dimethylamine, integrated CO₂ capture and utilisation for methanol production were proposed by Kar et al. (https://doi.org/10.1021/jacs.5b12354). As shown in the following figure, CO₂ capture happens at room temperature, forming carbamate and bicarbonate salts, which are hydrogenated to methanol in the presence of a catalyst. Up to 79% yield of methanol was reported when PEHA was used as the solvent for carbon capture, and Ru-Macho-BH was used as the hydrogenation catalyst (https://doi.org/10.1021/jacs.5b12354).

https://doi.org/10.1021/jacs.5b12354

The process was reviewed by the same research group, who also discussed the use of aqueous amine and hydroxide solutions for carbon capture and various homogeneous metal complexes for in-situ CO₂ utilisation producing methanol (https://doi.org/10.1021/acs.accounts.9b00324). The use of heterogeneous catalysts and renewable energy have also been covered in this Accounts paper.

Almost at the same time (2015), Milstein’s group (https://doi.org/10.1021/acscatal.5b00194) also reported the integrated CO₂ capture and hydrogenation for methanol production. Up to 92% yield of methanol was reported using aminoethanols (e.g. 2-methylamino ethanol and valinol) as solvents and PNN pincer Ru catalysts as catalysts. However, Cs₂CO₃ catalysts were required for CO₂ capture.

This concept was applied to direct air capture in 2020 (https://doi.org/10.1021/jacs.9b12711). An alkali hydroxide-based system was used for capturing CO₂ from the air in the presence of ethylene glycol. The produced bicarbonate and formate salts were hydrogenated to methanol using Ru-PNP catalysts and produced methanol. The concept is shown in the following figure.

https://doi.org/10.1021/jacs.9b12711