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

Abstract

AbstractSolvent‐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.