Probing the Kinetic Origin of Varying Oxidative Stability of Ethyl‐ vs. Propyl‐spaced Amines for Direct Air Capture

Abstract

Amine-based adsorbents are promising for direct air capture of CO 2 , yet oxidative degradation remains a key unmitigated risk hindering wide-scale deployment. Borrowing wisdom from the basic auto-oxidation scheme, insights are gained into the underlying degradation mechanisms of polyamines by quantum chemical, advanced sampling simulations, adsorbent synthesis, and accelerated degradation experiments. The reaction kinetics of polyamines are contrasted with that of typical aliphatic polymers and they elucidate for the first time the critical role of aminoalkyl hydroperoxide decomposition in the oxidative degradation of amino-oligomers. The experimentally observed variation in oxidative stability of polyamines with different backbone structures is explained by the relationship between the local chemical structure and the free energy barrier of aminoalkyl hydroperoxide decomposition, suggesting that its energetics can be used as a descriptor to screen and design new polyamines with improved stability. The developed computational capability sheds light on radical-induced degradation chemistry of other organic functional materials.

Microwave Regeneration and Thermal and Oxidative Stability of Imidazolium Cyanopyrrolide Ionic Liquid for Direct Air Capture of Carbon Dioxide

“…These results are in agreement with the report by Li et al. on the radical‐induced degradation of amino‐oligomer sorbents where varying oxidative stability (and kinetics) was observed based on the local environment of the amine [56] …”

“…The pairing of the imidazolium cation with a basic anion, such as [2‐CNpyr], is desired to increase the absorption capacity at low partial pressures of CO 2 . The amine functionality, similar to the case reported for amino‐oligomers in the context of their application in DAC can follow basic auto‐oxidation scheme [56] . Although the stabilities of the pyrrolides within ILs have not been examined before, the autoxidation of unsubstituted pyrrole and alkyl and aryl substituted pyrroles under air have been reported [57–59] .…”

“…These results are in agreement with the report by Li et al on the radical-induced degradation of amino-oligomer sorbents where varying oxidative stability (and kinetics) was observed based on the local environment of the amine. [56] To confirm the proposed degradation reactions, a series of analysis consisting of GC (for gaseous side products), NMR, and FTIR was performed. Off-gas operando GC analysis was conducted on Samples 1 and 4 throughout the period of the accelerated degradation experiments.…”

“…The amine functionality, similar to the case reported for amino-oligomers in the context of their application in DAC can follow basic auto-oxidation scheme. [56] Although the stabilities of the pyrrolides within ILs have not been examined before, the autoxidation of unsubstituted pyrrole and alkyl and aryl substituted pyrroles under air have been reported. [57][58][59] It is agreed that the degradation pathway of pyrrole, under the stimuli of oxidants (e. g., peroxides, singlet oxygen ( 1 O 2 ), meta-chloroperoxybenzoic acid, ferric chloride), pH, and temperature or by anodic oxidation, often leads to unconstrained de-aromatization, polymerization, and decomposition that form conducting (and/or nonconducting) polypyrrole (5 in Scheme 2).…”

Fundamental Insight into Humid CO2 Uptake in Direct Air Capture Nanocomposites Using Fluorescence and Portable NMR Relaxometry

“…The deployment of negative emissions technology is also projected to play an increasingly important role in limiting the effects of anthropogenic climate change. − Among the direct air capture (DAC) technologies currently being investigated for pilot and commercial scale deployment, solid adsorbents based on supported amines are garnering much enthusiasm . Indeed, a diverse array of recent work studying nonvolatile aminopolymers loaded onto mesoporous oxide composites is driving extraordinary advances in the field. − However, certain fundamental knowledge gaps remain that will influence how these and similar materials are employed over long cycle times, − in different environments, , and within different operational design constraints in real-world DAC systems …”