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. C-13 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.