Rational Design of Polymer Ionic Liquid Membranes through Uncovering Fundamental Gas Transport Mechanisms

Achieving widespread decarbonization in the United States requires the development of energy-efficient technologies for separating carbon dioxide (CO2) from natural gas and flue gas produced by fossil fuel combustion. Membrane-based CO2 separations can potentially lower the energy demands and cost of carbon capture compared to other technologies like absorption.

However, this necessitates the development of membrane materials that maximize throughput and separation efficiency while remaining robust under variable operating conditions. "Facilitated Transport Membranes" (FTMs), using polymers tailored for specific molecular interactions with CO2, show promise in meeting these goals. Yet, the fundamental transport mechanisms of CO2 in many of these materials are not fully understood, particularly in the presence of water vapor, which is common in many carbon capture applications.

This project aims to develop a new modular synthetic strategy for controlling CO2-membrane interactions in FTMs using the versatility of "click chemistry." These polymer membranes will be used to investigate the underlying mechanisms of CO2 selective transport at both microscopic (≤ 1 μm) and macroscopic (~100 μm) scales in the presence and absence of water vapor, utilizing advanced nuclear magnetic resonance (NMR) spectroscopy and other unique experimental tools. The fundamental knowledge gained from this project will enable the strategic design of FTMs for highly efficient CO2 capture from a wide range of gas streams, advancing long-term goals for energy sector decarbonization and promoting sustainability.

The research will also be integrated into graduate and undergraduate training and course curricula at the University of Florida. Additionally, new outreach activities aimed at high school teachers across Florida will educate the broader community about how STEM researchers are developing solutions for environmental challenges and global sustainability.

This research project aims to design a versatile strategy for functionalizing polymer ionic liquid (PIL) membranes to enable systematic structure-property studies of CO2 transport over different length scales. PIL networks will be formed by copolymerizing polyethylene glycol (PEG)-based monomers with co-monomers containing active ester groups, which can be readily post-functionalized in solution with a wide range of protic PIL ligands (Lewis bases) via a simple click reaction.

Gas sorption and permeation measurements will reveal macroscopic gas transport properties across the length scale of the membrane thickness, while advanced NMR spectroscopy tools will quantify gas self-diffusion and dynamics at micrometer and sub-micron length scales. Investigating transport over length scales spanning different orders of magnitude will reveal how CO2-ligand interactions and percolated domains of PIL ligands control diffusion barriers for CO2 transport.

In particular, creating interconnected domains of ligands with modest CO2 interactions should increase both CO2 sorption and diffusion, whereas disconnected domains or interactions that are too strong may inhibit CO2 transport. Both macroscopic transport and microscale NMR experiments will then be extended to mixed gas-water vapor mixtures to reveal how sorbed water alters CO2 diffusion rates compared with those of other gases like nitrogen and methane.

These findings will reveal how to strategically leverage FTM functionality and architecture to optimize CO2-selective separations of dry and humid gas streams. Achieving the goals of this project will ultimately guide the future development and upscaling of advanced carbon capture membranes, leading to reduced carbon emissions and increased awareness of sustainability challenges in the United States.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.