CO₂ Capture Characteristics of Hyperbranched Poly(alkylene imine): A Molecular Dynamics Simulation Approach

Area of Science:

• Materials Science
• Chemical Engineering
• Computational Chemistry

Background:

• Developing efficient solid amine sorbents is crucial for direct air capture (DAC) of carbon dioxide (CO2).
• Hyperbranched polymers offer tunable properties for CO2 adsorption applications.

Purpose of the Study:

• To investigate and compare the CO2 capture characteristics of hyperbranched poly(ethylenimine) (HB-PEI) and poly(propyleneimine) (HB-PPI).
• To elucidate the structure-function relationships governing CO2 and water interactions within these polymers.

Main Methods:

• Molecular dynamics simulations utilizing density functional theory-calibrated force fields.
• Systematic investigation of polymer density, free volume, glass transition temperature, CO2/H2O distribution, and molecular diffusion.
• Analysis of pair correlation and coordination to understand CO2-amine interactions.

Main Results:

• HB-PEI exhibits higher density and lower free volume than HB-PPI but demonstrates superior CO2 capture capacity due to higher amine concentration.
• HB-PEI shows enhanced CO2 diffusivity, attributed to higher thermal mobility and favorable interactions with primary and secondary amines.
• Despite a more compact structure, HB-PEI displayed superior CO2 and H2O transport properties, evidenced by higher diffusion coefficients under various hydration levels.

Conclusions:

• A critical balance between polymer architecture, amine accessibility, and hydration is essential for designing effective solid amine sorbents.
• HB-PEI presents a promising candidate for next-generation sorbents in direct air capture technologies.
• Understanding molecular-level interactions is key to optimizing sorbent performance for CO2 capture.