Highly Permeable and Well-Oriented SAPO-34 Membranes for CO₂ Removal

In this work, a multistep procedure was developed to synthesize thin and well-oriented SAPO-34 zeolite membranes that exhibit high permeability in the CO₂/CH₄ separation process. In this method, various combinations of zeolite membrane synthesis techniques, including support masking, cationic linkage, chemical functionalization, dip coating, hydrothermal synthesis, and dry-gel conversion (DGC) were investigated. To determine the orientation of the crystals in the zeolite layer and its effect on membrane structural characteristics and separation performance, the crystallographic preferred orientation (CPO) index was applied in a quantitative comparison evaluation. The results showed that a higher crystal orientation leads to thinner membranes, lower diffusion resistance, shorter diffusion paths of molecules, and more uniform membranes through reduced cracks and defects. Furthermore, masking the support before the synthesis reduces the effective thickness of the membrane. Cationic bonding and functional groups also increase the CPO index, which favors better permeability along with higher selectivities. The CPO value of 0.97 was obtained for a thin membrane (thickness less than 2 μm), which showed a permeability of 27 mol m^-2 S^-1 Pa^-1 and selectivity of 146 for CO₂/CH₄ mixture.