Fast synthesis of thin all-silica DDR zeolite membranes by co-template strategy

The separation performances of all-silica DDR membranes are inferior to other small pore zeolite membranes, which is the result of poor understanding of the corresponding zeolite powder and membrane syntheses. Issues like lengthy synthesis, tough detemplation, poor reproducibility, use of toxic solvent, make it difficult to prepare high performance DDR membranes. In this study, fast synthesis of thin all-silica DDR membranes (~1.6 μm) was achieved in only 3 h by conventional hydrothermal synthesis in a ethylenediamine-free gel. The addition of tetraethylammonium hydroxide (TEAOH), functioned as mineralizing agent and phase controller, is the key. The presence of TEAOH made high temperature synthesis possible by suppressing the formation of other phases, which led to significantly increased crystallization kinetics and shortened synthesis time. As a mineralizing agent, TEAOH may increase the solubility of silica source, favor nucleation and result into the formation of small crystals and thin membrane. The removal of ethylenediamine make the synthesis environment-friendly. Mild template removal under wet ozone environment oxidized template molecules effectively and minimized the formation of defects. Outstanding CO2–CH4 separation performance was obtained, with CO2 permeance of 4.1 × 10−7mol/(m2·s·Pa) and CO2–CH4 selectivity of 160 at 0.14 MPa pressure drop.