Fast synthesis of thin all-silica DDR zeolite membranes with inorganic base as mineralizing agent for CO2-CH4 separation

Compared with other small pore zeolite membranes, all-silica DDR membrane has unique advantages like smaller pore size and outstanding stability, which makes it perfect for the separation of light gases, like CO2-CH4 and O2-N2 separations. However, the development of DDR membrane has fallen behind due to the following issues like long synthesis time, poor control on membrane thickness, use of toxic solvent etc. In this study, fast synthesis of high-performance all-silica DDR membrane was realized by conventional hydrothermal synthesis in a mother liquor with inorganic base as mineralizing agent and reduced template concentration. Thin DDR membranes with thickness ~1 μm can be prepared in 3–6 h with high reproducibility. High CO2 permeance of 8.6 × 10-7mol/(m2·s·Pa) and CO2-CH4 selectivity of 150 were obtained on 1.3 μm thick DDR membrane (0.14 MPa pressure drop and room temperature, permeability = 3339 Barrers). The elimination of organic solvent (ethylene diamine), reduced consumption of organic template and use of cheap inorganic bases make membrane synthesis cheaper and more environment-friendly. Compared with other all-silica DDR membranes, the current method is superior on membrane performance (permeance and membrane thickness), material cost, synthesis time and waste disposal.