(592b) Investigating Oxidative Degradation Products and Mechanisms of Aminopolymer Sorbents for Direct Air Capture (DAC)

Aminopolymer based sorbents have shown promising results in direct air capture (DAC) of CO₂ from ambient air owing to their high CO₂ adsorption capacity and selectivity. While those adsorptive properties are important, the stability of a sorbent is important in creating high-performing, cost-effective and long-lasting sorbents. The high concentration of molecular oxygen (O₂) in ambient air (~21 %) and temperature swings used during sorbent regeneration cause oxidative degradation of these sorbents with time. Either via process upsets that could cause rapid oxidation, or slow oxidation under milder, controlled operating conditions, oxidative degradation has the potential to increase operation costs.

This work investigates the oxidative degradation mechanism(s), pathways, and major products of aminopolymer sorbent reactions with O₂ using a model sorbent (45 wt% poly(ethylenimine) (PEI) on γ-Al₂O₃) under varied experimental conditions. We explore the effect of oxidative degradation on the CO₂ adsorption capacity using thermogravimetric analysis, ATR-IR spectroscopy, High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS), ¹³C NMR spectroscopy and elemental analysis (C/N ratio). The results show the formation of low molecular weight amine compounds, while the sorbent deactivation seems to follow a free radical initiated autoxidation, following autoxidation pathway that has been described for a class of polymers such as rubber during thermo-oxidation.