J.R. Hoffman, A.E. Baumann, C.M. Stafford
National Institute of Standards and Technology,
Keywords: CO2, capture, sorbents, polymers, amines
Summary:Poly(ethyleneimine) (PEI) is an attractive material for CO2-based carbon capture due to its high amine content (1 nitrogen for every 2 carbons). Hyperbranched PEI, specifically, is appealing due to its low glass transition temperature (Tg), which facilitates diffusion of CO2 through the polymer. However, due to viscous nature, hyperbranched PEI is typically imbibed into porous silicates to form a solid sorbent material. This coating process, while practical, leads to poorly defined PEI film thickness and local variations in PEI concentrations within the porous support. To understand fundamental aspects of CO2 uptake and release within PEI-based sorbents, we propose to study planar PEI thin films, which allows us to explore the effect of film thickness and temperature on CO2 sorption. In this presentation, I will discuss our measurements of adsorption/desorption at a function of temperature, humidity, and CO2 concentration for different PEI film thicknesses using tandem quartz crystal microbalance (QCM) and polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS). Uptake was shown to increase as temperature increased from 25 °C to 55 °C for samples > 25 nm, while a decrease was seen for films < 25 nm. CO2 sorption at lower temperatures appears to be regulated by reaction kinetics, while CO2 diffusion and mobility appear to be more important at higher temperatures. Coupling these two measurement techniques provides a unique testbed for quantification of mass uptake via QCM and spectral identification of reaction products via FTIR.