Proton NMR Relaxometry as a Rapid and Non-Destructive Technique for Probing Degradation of Supported Poly(ethylenimine) for CO2 Direct Air Capture

06 June 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Aminopolymer-based adsorbents are commonly investigated for CO2 direct air capture (DAC). In the presence of high temperature and O2, which could happen during process upset, oxidative degradation can significantly contribute to limiting the adsorbent lifetime. Here, we demonstrate the use of a portable, benchtop NMR sensor to collect proton relaxometry profiles to track the degradation of a PEI/Al2O3 sample exposed to controlled accelerated oxidation conditions and correlate the extent of oxidation as measured by loss in amine efficiency with T2 (spin-spin) relaxation times. We hypothesize that T2 relaxation accurately tracks oxidative degradation in aminopolymers because of reduced polymer mobility resulting from radical-induced crosslinking that can occur during the oxidation process. The advantage of using NMR relaxometry as a non-destructive technique to probe degradation is demonstrated on a 1-inch square-channel monolith adsorbent exposed to actual DAC service conditions, highlighting the potential for using this technique as a rapid and non-destructive method of probing adsorbent health.


direct air capture
NMR relaxometry
oxidative degradation

Supplementary materials

Supporting Information
Additional information regarding the materials and methodology, fitting functions for relaxometry data, and supplementary figures and tables related to material characterization and relaxometry on samples exposed to atmospheric CO2 and water.


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