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

Hyperbranched poly(ethylenimine) (HB-PEI) has been distinguished as a promising candidate for carbon dioxide (CO) capture. In this study, we investigate the distribution and transport of CO 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 CO molecules are equilibrated at various hydration levels. Under dry conditions, the primary and secondary amines are highly associated with CO, indicating that they would participate in CO capture via the carbamate formation mechanism. Under hydrated conditions, the pair correlations of CO 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 CO residence time analysis. However, in the presence of water molecules, it is found that the CO 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 CO molecules via the bicarbonate formation mechanism. Through our MD simulation results, the feasibilities of different CO capture pathways in HB-PEI membranes are demonstrated at the molecular level.