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) x 10(-6) mol/(m(2) s Pa) [equals to 7500 +/-; 1200 GPU, 1 GPU = 3.34x10-10 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.

Automated summary

High-aspect-ratio SAPO-34 nanosheets were successfully fabricated by exfoliation of lamellar SAPO-34 zeolite using a solvent-mediated freeze-thaw method. The nanosheets exhibited excellent performance in CO2 permeation and CO2/CH4 selectivity when used as thin membranes.