Bubbling a flue gas mixture through an aqueous solution of a simple bis-iminoguanidine (GBIG) leads to CO2 capture as a crystalline bicarbonate salt. The X-ray crystal structure revealed ‘anti-electrostatic’ bicarbonate dimers stabilized by hydrogen bonding from guanidinium cations and water. Mild heating of the crystals releases the CO2 and regenerates the GBIG sorbent quantitatively so it can be recycled.
Scientific Achievement
Energy-efficient CO2 capture from flue gas is demonstrated via crystallization of structurally unique bicarbonate-water clusters with an aqueous guanidine sorbent.
Significance and Impact
Limiting global temperature rises relies on the development of energy-efficient carbon-capture methods. This novel CO2-separation cycle requires 24% less energy than industrial benchmarks based on aqueous amines.
Research Details
X-ray structural analysis revealed the formation of (HCO3–)2 dimers in the crystals, linked by water molecules into ladder-shaped clusters.
Experimental and computational investigations support a CO2-release mechanism consisting of proton transfer from guanidinium groups to bicarbonate anions with the formation of carbonic acid dimers, followed by low-energy CO2 and H2O release in the rate-limiting step.
The minimum energy required for sorbent regeneration is 151.5 kJ/mol CO2, which is 24% lower than the regeneration energy of monoethanolamine, a benchmark industrial sorbent.