Distribution and Transport of CO₂ in Hydrated Hyperbranched Poly(ethylenimine) Membranes: A Molecular Dynamics...

Hyperbranched poly(ethylenimine) (HB-PEI) has been distinguished as a promising candidate for carbon dioxide (CO₂) capture. In this study, we investigate the distribution and transport of CO₂ molecules in a HB-PEI membrane at various hydration levels using molecular dynamics (MD) simulations. For this, model structures consisting of amorphous HB-PEI membranes with CO₂ molecules are equilibrated at various hydration levels. Under dry conditions, the primary and secondary amines are highly associated with CO₂, indicating that they would participate in CO₂ capture via the carbamate formation mechanism. Under hydrated conditions, the pair correlations of CO₂ with the primary and secondary amines are reduced. This result suggests that the carbamate formation mechanism is less prevalent compared to dry conditions, which is also supported by CO₂ residence time analysis. However, in the presence of water molecules, it is found that the CO₂ molecules can be associated with both amine groups and water molecules, which would enable the tertiary amine as well as the primary and secondary amines to capture CO₂ molecules via the bicarbonate formation mechanism. Through our MD simulation results, the feasibilities of different CO₂ capture pathways in HB-PEI membranes are demonstrated at the molecular level.