The Role of Humidity in Enhancing CO2 Capture Efficiency in Polyethyleneimine Thin Films

Published

February 6, 2025

Author(s)

Christopher Stafford, Avery Baumann, John Hoffman

Abstract

Amine impregnated sorbents have been extensively studied for use in direct air capture (DAC) of CO2. In a dry environment, CO2 capture follows a carbamate formation mechanism, where capture capacity and amine efficiency are controlled by thickness of the adsorbent layer. In order to improve capture capacity, the amine efficiency needs to be improved by allowing more amine sites to participate in the reaction process. Water vapor in the air has been shown break up internal hydrogen bonding within the amine-based polymer, which increases both the polymer mobility and accessibility of amine sites. In this work, we evaluate the effect that humidity has on the CO2 capture of 2-dimensional polyethyleneimine (PEI) thin films using tandem quartz crystal microbalance (QCM) and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). We show that tandem QCM/PM-IRRAS enables more accurate CO2 uptake measurements in a humid environment, as the combined techniques can separate mass changes due to CO2 and H2O sorption. CO2 adsorption capacity and amine efficiency were evaluated for a 10 nm and 100 nm film at varied temperature, humidity, and CO2 concentrations. We find that water sorption greatly enhances CO2 uptake when the capture is limited by diffusional resistance (at higher CO2 concentration and in 100 nm films) but has less influence in conditions where CO2 availability is limiting uptake (at lower CO2 concentration in 10 nm films). Thus, we argue that humidity does improve capture, but not at all conditions, with clear limitations seen for the 10 nm films under DAC conditions. Our approach enhances the understanding of H2O-assisted sorption of CO2 in PEI across a range of conditions while also presenting a measurement strategy to apply to, and hopefully optimize, component uptake in a broad array of materials of interest to the CO2 capture community.

Citation

Chemical Engineering Journal

Volume

507

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.cej.2025.160347

Local Download

Keywords

CO2 adsorption, amine efficiency, QCM, PM-IRRAS, humidity, diffusion

Citation

Stafford, C. , Baumann, A. and Hoffman, J. (2025), The Role of Humidity in Enhancing CO2 Capture Efficiency in Polyethyleneimine Thin Films, Chemical Engineering Journal, [online], https://doi.org/10.1016/j.cej.2025.160347, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958626 (Accessed April 12, 2025)