Effect of Extended Aging and Oxidation on Linear Poly(propylenimine)-Mesoporous Silica Composites for CO₂ Capture from Simulated Air and Flue Gas Streams

Physical aging or degradation of amine-containing polymers and supported amine adsorbents is a critical issue that could limit the practical application of such materials for CO2 capture. However, to date, there is a scarcity of studies that evaluate the long-term stability of amine-based sorbents without the exclusive use of accelerated aging tests. Here, we demonstrate that extended aging (∼2 years) of linear poly(propylenimine) (LPPI) confined in mesoporous silica (SBA-15) supports does not drastically impact the CO2 adsorption performance under simulated flue gas (10% CO2) and direct air capture (DAC, 400 ppm CO2) conditions, although the behavior of the aged sorbents and polymers in the two CO2 concentration regimes differs. The sorbents made with aged LPPI have modestly decreased CO2 uptake performance (≲20% lower) compared to the fresh polymers, with overall good CO2 cycling performance. The data indicate that only slow degradation occurs under the deployed ambient storage conditions. Even after extended aging, the LPPI-based sorbents preserved their ability to display stable temperature-swing cycling performance. In parallel, the impact of blending LPPI polymers of different number-average molecular weights, Mn, is evaluated, seeking to understand its impact on adsorbent performance. The results demonstrate that the blends of two Mn aged LPPI give similar CO2 adsorption performance to adsorbents made from a single-Mn LPPI, suggesting that molecular weight will not negatively impact adsorbent performance in the studied Mn range. After an accelerated oxidation experiment, the aged LPPI sorbents retained a larger portion of the samples’ original performance when cycling under simulated flue gas conditions than under DAC conditions. However, in each case, the oxidized sorbents could be cycled repeatedly with consistent uptake performance. Overall, these first of their kind extended aging tests suggest that LPPI-based amine adsorbents offer promise for long-term, stable use in carbon capture applications.