(518f) Unexpected Gas Separation Selectivity in SSZ-13 Zeolite Membranes

SSZ-13 (CHA structure) is among the most attractive small-pore zeolite membranes for small-molecule gas separations. In a recent permeation study of a few interested gas molecules with SSZ-13 zeolite membranes, unexpected high selectivity was found for a gas pair. Solution-diffusion model (Permeability = Solubility × Diffusivity) is generally applicable for analyzing gas permeation behaviors in zeolite membranes. So the adsorption isotherms and dynamic adsorption behaviors of the molecules were explored with SSZ-13 crystals. The solution diffusion model was used to help interpret where the selectivity comes from. However, selectivity based on adsorption data was about two orders of magnitude smaller than observed membrane selectivity. A hypothesis on the selectivity will be proposed and more experiments will be done to verify the consistency of the observation. This is an interesting phenomenon, and a better understanding could lead to new separation applications with polycrystalline zeolite membranes.