Rational Design of the Polymeric Amines in Solid Adsorbents for Postcombustion Carbon Dioxide Capture

Substantial efforts have been made to increase the CO₂ working capacity of amine adsorbents for an efficient CO₂ capture. However, the more important metric for assessing adsorbents is the regeneration heat required for capturing a fixed amount of CO₂. In this work, we synthesized polyethyleneimine (PEI)/SiO₂ adsorbents functionalized with various epoxides. This provided adsorbents with six different amine structures showing various CO₂/H₂O adsorption properties. Our studies revealed that the CO₂ working capacity was not a decisive factor in determining the regeneration heat required for CO₂ capture. This is because the benefit of large CO₂ working capacity was canceled out by the difficulty of CO₂ desorption. Instead, the suppression of H₂O co-adsorption was critical for reducing the regeneration heat because substantial latent heat is required for H₂O desorption. Consequently, the PEI/SiO₂ functionalized with 1,2-epoxybutane required a much lower regeneration heat (2.66 GJ tCO₂^-1) than the conventional PEI/SiO₂ (4.03 GJ tCO₂^-1) because of suppressed H₂O co-adsorption as well as moderately high CO₂ working capacity.