Tailoring Chemical Absorption-Precipitation to Lower the Regeneration Energy of a CO₂ Capture Solvent

Solvent-based CO₂ capture consumes significant amounts of energy for solvent regeneration. To improve energy efficiency, this study investigates CO₂ fixation in a solid form through solvation, followed by ionic self-assembly-aided precipitation. Based on the hypothesis that CO₃²⁻ ions may bind with monovalent metal ions, we introduced Na⁺ into an aqueous hexane-1,6-diamine solution where CO₂ forms carbamate and bicarbonate. Then, Na⁺ ions in the solvent act as a seed for ionic self-assembly with diamine carbamate to form an intermediate ionic complex. The recurring chemical reactions lead to the formation of an ionic solid from a mixture of organic carbamate/carbonate and inorganic sodium bicarbonate (NaHCO₃), which can be easily removed from the aqueous solvent through sedimentation or centrifugation and heated to release the captured CO₂. Mild-temperature heating of the solids at 80–150 °C causes decomposition of the solid CO₂-diamine-Na molecular aggregates and discharge of CO₂. This sorbent regeneration process requires 6.5–8.6 GJ/t CO₂. It was also found that the organic carbamate/carbonate solid, without NaHCO₃, contains a significant amount of CO₂, up to 6.2 mmol CO₂/g-sorbent, requiring as low as 2.9–5.8 GJ/t CO₂. Molecular dynamic simulations support the hypothesis of using Na⁺ to form relatively less stable, yet sufficiently solid, complexes for the least energy-intensive recovery of diamine solvents compared to bivalent carbonate–forming ions.