# Effect of Storage Conditions on Efficacy of Poly(ethylenimine)-Alumina CO2 Sorbents

## TL;DR

This paper investigates how storage conditions affect the long-term stability of a CO2 capture material, finding that storage under CO2 minimizes degradation.

## Contribution

The study reveals that storing a PEI/γ-Al2O3 CO2 sorbent under CO2 gas significantly improves its long-term stability compared to other gases.

## Key findings

- Storage under CO2 at 40 °C prevents sorbent degradation, unlike N2, O2, or ambient air.
- At 23 and −4 °C, ambient air or inert gas (Ar) storage maintains reasonable stability with <13% degradation over months.
- Nonoxidative thermal reactions under N2 at 40 °C cause significant sorbent deactivation over time.

## Abstract

Solid amine sorbents
are one of the primary components
of DAC technologies
that allow for the removal of ultradilute CO2 from the
atmosphere. A main drawback in the implementation of solid amine sorbents
in industrial-scale DAC applications is their instability under certain
operational or storage conditions over an extended period. In this
work, the effect of storage temperature and gas composition in the
storage headspace on the long-term stability of a poly­(ethylenimine)-alumina
(PEI/γ-Al2O3) sorbent is explored. PEI/γ-Al2O3 sorbents with 70 and 100% pore filling are aged
under varying gases (N2, O2, Ar, 0.04% CO2–N2, CO2, and ambient air) in
an oven (40 °C), at common ambient indoor temperature conditions
(23 °C), or in a freezer (−4 °C). The CO2 sorption capacity, as measured by thermogravimetric analysis (TGA),
along with FTIR spectra of the fresh and aged sorbents, reveal that
at 23 and −4 °C, storage under ambient air or inert gas
(Ar) provides reasonable long-term stability, with <13% degradation
over 12 and 5 months of storage. Interestingly, with storage at 40
°C, similar levels of deactivation were observed under pure O2 and N2 after 4 months of storage, which suggests
that nonoxidative thermal reactions can occur under prolonged storage
conditions under N2. In contrast, with storage under CO2, sorbent degradation is substantially suppressed compared
to storage under N2, ambient air, O2, or Ar,
yielding sorbents with no observable loss in capacity after 2 months,
compared to a 66, 63, and 62% loss under N2, ambient air,
and N2 in the same period at 40 °C, respectively.
Overall, these findings provide guidance for practical amine sorbent
storage in academic or industrial settings where amine sorbents are
used for carbon capture.