Competitive Sorption in Polymers of Intrinsic Microporosity favoring selectivity for CO2

The increasing importance of membrane-based gas separation processes necessitates the development of novel materials with enhanced permeability and selectivity. Polymers of Intrinsic Microporosity (PIMs) are promising candidates due to their rigid and highly contorted polymer backbone [1], which causes a high free volume. The latter confers to PIMs a very high permeability, while the backbone rigidity causes a high size selectivity. Since the introduction of archetypal PIM-1, many different PIMs were synthetized, with different backbones [2] and/or functional groups [3], to improve their properties. Here, we present a study on modified PIM-1 with amine functional groups, which enhance the CO2 affinity. The original study [4] demonstrated that the amine-introduction leads to an unexpected reduction of the CO2 permeability. In the present paper, we show via mixed gas analysis that the enhanced CO2-philicity increases the CO2/N2 and CO2/CH4 selectivity due to competitive sorption. CO2 preferentially interacts with the amine groups, hindering the transport of the other species in the membrane. Molecular dynamics simulations, a powerful tool to investigate molecular structure and transport properties of the polymeric membranes [5], give a molecular insight of the experimental results and demonstrates how diffusivity and solubility in mixtures can be coherently obtained.