Control of CO2 Adsorption and Desorption Using Polyethylene Glycol in a Tetraethylenepentamine Thin Film: An In Situ ATR and Theoretical Study

The reversible adsorption of CO 2 on tetraethylenepentamine (TEPA) and the polyethylene glycol (PEG)-modified amine sites were investigated using attenuated total reflection infrared (ATR-IR) spectroscopy, mass spectrometry (MS), and density functional theory (DFT). The presence of PEG at the amine site increased the rate of formation of adsorbed CO 2, enhanced the formation of weakly adsorbed CO 2 which can be removed from flowing inert gas at room temperature, and decreased CO 2 desorption peak (i.e., sorbent regeneration) temperature. The calculated CO 2 binding energy (BE) and optimized structures suggest CO 2 adsorbed on TEPA primarily in the form of ammonium carbamate. The presence of PEG promoted the formation of a species which exhibited an experimental IR spectrum resembling the simulated spectrum of a low BE zwitterion species. The observation suggests PEG controlled the formation of the adsorbed intermediate species. Modeling of the transient CO 2 adsorption profiles further showed PEG accelerated the rate of diffusion of adsorbed CO 2 species in TEPA film by decreasing viscosity. The IR spectra of TEPA-PEG revealed PEG could assist in breaking up hydrogen bonding between amine sites, further supporting the promotion of diffusion of adsorbed CO 2 through decreasing TEPA viscosity. This study unravelled the mechanism of the effects of PEG on CO 2 capture kinetics and capacity on amine sites.