(571d) Tuning Ether Motifs in Polymers Membranes for Carbon Capture

CO₂ capture for utilization remains important since fossil fuels continue to be the number one energy source around the globe. Membrane technology is highly explored for CO₂ capture over the last decade due to its high energy efficiency and low carbon footprint. Polymer membranes suffer from design challenges due to the negative correlation between two principal features of separation performance (permeability and selectivity). We hypothesize increasing the ether oxygen content would increase the CO₂ permeance, CO₂/N₂ and CO₂/O₂ selectivity. 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). First, we used the group contribution (GC) method based on perturbed-chain statistical associating fluid theory equation of state to calculate the solubility. Our results show strong agreement in the absolute CO₂, N_2, and O₂ 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. The detailed investigation with molecular dynamics simulations showed POM has higher CO₂/N₂ and CO₂/O₂ diffusivity selectivity compared to the commonly used PEO. Additionally, we studied the effect of adding N₂ phobic functional groups (ex: azo, triazine, and triazole) to the ends of POM polymer membrane. We concluded adding functional groups to the chain ends of the polymer significantly slows down the gas diffusion thus makes these polymer membranes not optimal candidates for neither CO₂/N₂ nor CO₂/O₂ separation. We have also studied the effect of temperature on the gas diffusion in POM polymer membrane. We have showed that the gas diffusion increases with increasing temperature; however, the diffusion selectivity decreases for both CO₂/N₂ and CO₂/O₂ separation. Our future efforts will focus on studying gas diffusion in polymer mixtures to see enhancement of gas diffusion due to synergetic effects from the mixture.