The impact of water vapor on CO2 separation performance of mixed matrix membranes

A series of mixed matrix membranes (MMMs) using nanoparticles involving carbons, porous organic polymers and metal organic frameworks (MOFs) were prepared to investigate the impact of water vapor on CO2 separation performance. The water uptake of MMMs using hydrophilic MOFs increased relative to more hydrophobic particles such as the porous organic polymers and carbons and this trend was reflected in the water vapor permeability, which varied by a factor of three between the hydrophobic and hydrophilic MMMs. These changes in water vapor permeability were strongly correlated with the water solubility, indicating that it is this solubility that is the controlling parameter. The calculated water diffusivity was consistent with previously published results. The gas permeability of MMMs in the presence of water vapor was also strongly affected by the nanoparticle hydrophobicity, with membranes composed of hydrophobic fillers out-performing hydrophilic fillers of comparable porosity. However in general, the differences in performance between MMMs and the pure polymer narrowed in the presence of water vapor.