(579c) Tuning Ether Motifs in Polymers Membranes for CO2/N2 Separation | AIChE

(579c) Tuning Ether Motifs in Polymers Membranes for CO2/N2 Separation


Basdogan, Y. - Presenter, University of Pittsburgh
Wang, Z. G., California Institute of Technology
Polymer membranes suffer from design challenges due to the negative correlation between two principal features of separation performance (permeability and selectivity). We aim to develop polymer membranes that will achieve both high CO2 permeance as well as high CO2/N2 and CO2/O2 selectivity. (PEO)-based polymers have been leading membrane materials for CO2/N2 separation. The ether oxygen moiety is a unique functional group that exhibits affinity towards CO2 but not N2, which leads to high CO2 solubility and CO2/N2 solubility selectivity. We hypothesize increasing the ether oxygen content would increase the CO2 solubility and CO2/N2 solubility selectivity. First, we used the group contribution (GC) method based on perturbed-chain statistical associating fluid theory equation of state. By invoking simple combination rules for the chemical functional groups, the GC method allows the properties of any molten polymers to be easily calculated from their chemical structure without the use of any adjustable parameters. We have investigated five different polymer materials that range in O:C ratio, including polyethylene (PE, O:C=0), polytetramethylene oxide (PTMO, O:C=0.25), polyethylene oxide (PEO, O:C=0.5), poly(1,3-dioxolane) acrylate (PDXLA, O:C=0.67), and polyoxymethylene (POM, O:C=1). Our results show strong agreement in the absolute CO2 and N2 solubility and the solubility selectivity with the experimental data for PE, PEO, and PTMO. In addition, we predict higher solubility selectivity for the two new candidate polymers, PDXLA and POM. Next, the promising candidates are further studied with computationally intensive atomistic molecular dynamics (MD) simulations to predict their gas diffusivity. The detailed investigation with MD simulations showed POM has higher CO2/N2 diffusivity selectivity compared to commonly used PEO. By combining CO2/N2 solubility and diffusivity selectivity, we reveal high CO2/N2 separation performance for POM, supporting our hypothesis that increasing O:C ratio leads to better performing polymers. Furthermore, we investigated the solvation environments of the gas molecules and showed that the chain termination with CO2-philic and N2-phobic functional groups enhances polymers’ separation performance. The framework outlined in this work helps us down select polymers with high CO2/N2 solubility selectivity to conduct complete and targeted computational investigations on the new and improved polymer membranes.