Oxidatively-Stable Linear Poly(propylenimine)-Containing Adsorbents for CO2 Capture from Ultradilute Streams

Aminopolymer-based solid sorbents have been widely investigated for the capture of CO2 from dilute streams such as flue gas or ambient air. However, the oxidative stability of the widely studied aminopolymer, poly(ethylenimine) (PEI), is limited, causing it to lose its CO2 capture capacity after exposure to oxygen at elevated temperatures. Here, we demonstrate the use of linear poly(propylenimine) (PPI), synthesized through a simple cationic ring-opening polymerization, as a more oxidatively stable alternative to PEI with high CO2 capacity and amine efficiency. The performance of linear PPI/SBA-15 composites was investigated over a range of CO2 capture conditions (CO2 partial pressure, adsorption temperature) to examine the tradeoff between adsorption capacity and sorption-site accessibility, which was expected to be more limited in linear polymers relative to the prototypical hyperbranched PEI. Linear PPI/SBA-15 composites were more efficient at CO2 capture and retained 65-83% of their CO2 capacity after exposure to a harsh oxidative treatment, compared to 20-40% retention for linear PEI. Additionally, we demonstrated long-term stability of linear PPI sorbents over 50 adsorption/desorption cycles with no loss in performance. Combined with other strategies for improving the oxidative stability and adsorption kinetics, linear PPI may play a role as a component of stable solid adsorbents in commercial applications for CO2 capture.