Molecular simulations of porous coordination network-based mixed matrix membranes for CO2/N2 separations
In this study, the challenge of selecting porous coordination networks (PCNs) as filler particles in mixed matrix membranes (MMMs) was examined using molecular simulations. PCNs are promising nanoporous materials in gas separations because of their tunable pore sizes, high porosities, good thermal and mechanical stabilities. Gas permeability and selectivity of 200 new MMMs composed of 20 different PCNs and 10 different polymers were calculated for CO2/N2 separation. We showed that selecting the appropriate PCN as filler particles in polymers results in MMMs that have high CO2/N2 selectivities and high CO2 permeabilities compared with pure polymer membranes. Several PCN/polymer MMMs were identified to exceed the upper bound established for CO2/N2 separation. Effect of framework flexibility of PCNs on the performance of MMMs was also examined. Results showed that considering the flexibility of PCNs is important for predicting gas permeability of pure PCNs but has less significance for predicting gas permeability of PCN-filled MMMs whenever the PCN volume fraction is low. For rapid screening of PCN/polymer MMMs, flexibility of the fillers can be neglected as a reasonable approximation if the filler volume fraction is < 0.3. The methods introduced in this study will create many opportunities for selecting PCN/polymer combinations for MMMs with useful properties in CO2 separation applications.