Exfoliation of lamellar SAPO-34 zeolite to nanosheets and synthesis of thin SAPO-34 membranes by a nanosheet-seeded secondary growth approach

High-aspect-ratio SAPO-34 nanosheets were fabricated by exfoliation of lamellar SAPO-34 zeolite using a solvent-mediated freeze-thaw method for the first time. A novel biomass-based organic structural directing agent (OSDA) together with triethylamine was used to induce the formation of lamellar SAPO-34 zeolite. These nanosheets had a thickness of several nanometers and aspect ratio as high as 230–560. A thin nanosheet layer with thickness less than 100 nm was deposited on the surface of tubular alumina support. High-quality SAPO-34 thin membranes were reproducibly synthesized after nanosheet-seeded secondary growth. Four SAPO-34 membranes prepared under the optimized synthesis conditions displayed average CO₂ permeance of (2.5 ± 0.40) × 10^-6 mol/(m² s Pa) [equals to 7500 ± 1200 GPU, 1 GPU = 3.34×10^-10 mol/(m² s Pa)] with average CO₂/CH₄ selectivity of 102 ± 12.6 in an equimolar CO₂/CH₄ mixture at room temperature and 0.2 MPa feed pressure.