Orientation-dependent CO2/H2 permselectivity of highly aligned DDR zeolite membrane

Abstract

Zeolite membrane is one of potential candidates to replace energy-intensive separation methods such as distillation or absorption, due to its uniform pore structure and superior thermal stabilities. Until now, it has been believed that 6 membered ring (MR) in zeolite is effective for selective capture of H2 over CO2, considering the kinetic diameters of adsorbates and the size of 6MR pore aperture. However, experimentally synthesized c-oriented zeolite membrane, where the 6MR was preferentially aligned along the diffusion path, exhibited unexpected CO2-permselectivity at room temperature. In this study, permeability of DDR membrane along particular orientation was investigated via non-equilibrium molecular dynamics simulation and density functional theory calculation. According to the simulation results, permeation rates of H2 and CO2 passing through 6MR was negligible, implying no intrinsic molecular sieving effect for H2. In contrast, 8MR showed CO2 and H2 permselective at 30 and 200°C, respectively, due to competitive effects of thermodynamic interaction and kinetic size. Through this study, new insights for H2/CO2 permselectivity with aligned zeolite membrane was suggested.