Polyethylene Glycol (PEG) Addition to Polyethylenimine (PEI)-Impregnated Silica Increases Amine Accessibility during CO₂ Sorption

Amine-impregnated sorbents can be applied in CO₂ sequestration, but they suffer from low amine utility due to slow diffusion of CO₂, leading to reduced accessibility of buried amines. We examined silica-supported polyethylenimine (PEI) sorbents and blended them with polyethylene glycol (PEG) as an additive to study the role of PEG in modifying sorption performance. We report an increase in amine efficiency, a decrease in the heat of sorption and regeneration temperature, and a change CO₂ amine speciation with the addition of PEG. The increase in viscosity due to CO₂ sorption leads to greater diffusion resistance; increases in viscosity were lower during CO₂ sorption in blends with higher PEG composition. ¹³C NMR results on CO₂-saturated PEI-PEG blends revealed the formation of carbamic acid and carbamate and showed a larger fraction of carbamic acid in PEG-rich samples. We propose PEG increases the amine efficiency by enabling the diffusion of CO₂ due to viscosity reduction and changes in the CO₂-amine speciation (carbamate versus carbamic acid), which modifies the theoretical CO₂/amine stoichiometry.