Ionic-Functionalized Polymers of Intrinsic Microporosity for Gas Separation Applications

Ionic-functionalized microporous materials are attractive for energy-efficient gas adsorption and separation processes and have shown promising results in gas mixtures at pressure ranges and compositions that are relevant for industrial applications. In this work, we studied the influence of different counterions (Li⁺, Na⁺, K⁺, Rb⁺, and Mg²⁺) on the porosity, carbon dioxide (CO₂) gas adsorption, and selectivity in ionic-functionalized PIM-1 (IonomIMs), a polymer belonging to the class of linear and amorphous microporous polymers known as polymers of intrinsic microporosity (PIMs). It was found that an increase in the concentration of ionic groups led to a decrease in the free volume, resulting in a less porous polymer framework, and Mg²⁺-functionalized IonomIMs exhibited a relatively larger porosity compared to other IonomIMs. The CO₂ adsorption capacity was affected by the different counterions for IonomIM-1, and a higher loading capacity for pure CO₂ was observed for Mg²⁺. Furthermore, the IonomIMs showed an enhanced CO₂ selectivity in CO₂/CH₄ and CO₂/N₂ gas mixtures at conditions used in pressure swing adsorption and vacuum swing adsorption applications. It was also observed that the concentration of ionic groups plays a vital role in changing the CO₂ gas adsorption and selectivity.