Unveiling the Desorption Performance and Thermal Stability of Unmodified Polyamine-Containing CO2 Adsorbents

Polyamines confined within mesoporous supports have shown great potential as materials for postcombustion CO2 capture. However, previous research has focused on improving adsorption performance, with little attention given to identifying practical desorption temperatures that can enable fast desorption and preserve the thermal stability of the sorbent. To address this, we impregnated pentaethylenehexamine (PEHA) and branched polyethylenimines (PEIs) onto silica gel and studied the effects of polymer structural and physical properties, polymer loading, and temperature on adsorption/desorption efficiency and cyclic thermal stability. At 40 °C, the adsorption efficiency and capacity followed this order: PEHA-40 < PEI12-40 < PEI8-40, which was consistent with their structural openness and primary/secondary (P/S) amine ratio. At 60 °C, the efficiency followed the same order, whereas the highest capacity was reached by PEHA-40, the sorbent with the polymer having the smallest molecule and highest amine density. The desorption kinetics was influenced by the S/P amine ratio, polymer loading, and temperature. PEHA-40, the sorbent with the lowest isosteric heats, likely due to its high S/P amine ratio, exhibited the fastest desorption of CO2 at 60 °C followed by PEI12-40 and PEI8-40. Nevertheless, when performing the desorption at 100 °C, all three sorbents exhibited similar desorption rates. The sorbent with the lowest polymer loading (PEI8-30) enabled the fastest CO2 desorption because of high CO2 diffusion. The results from the thermal stability analysis indicated that the use of high-molecular-weight polymers (PEI MW 1200) and high polymer loadings (filled pores) can effectively suppress polymer leaching, the latter being attributed to a denser hydrogen bond network and reduced polymer concentration gradient. Through this systematic study, the identification of a sorbent with excellent thermal stability and rapid regeneration at 100 °C (PEI12-40) was made possible. This sorbent has significant promise for use in CO2 capture systems utilizing vacuum-assisted desorption, and using unmodified polymer structures can lead to substantial cost savings in sorbent preparation.