(18e) 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 focuses on identifying major oxidation products of aminopolymer sorbent (45 wt.% poly(ethylenimine) (PEI) on γ-Al₂O₃) to develop a deeper insight into the oxidative degradation mechanisms and pathways of aminopolymer sorbents under varied experimental conditions. We explore the effect of oxidative degradation on the CO₂ adsorption capacity using thermogravimetric analysis, in situ HATR-IR spectroscopy, High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS), ¹³C NMR spectroscopy and elemental analysis (C/N ratio). Preliminary results show the formation of low molecular weight amine compounds formation as gas-phase products and the degradation mechanism seems to follow free radical initiated autoxidation.