Preparation of defect-free DDR zeolite membranes by eliminating template with ozone at low temperature

A dilute synthesis precursor was developed to prepare high-quality DDR zeolite membranes on α-Al₂O₃ four-channel hollow fibers by secondary growth method. However, the as-membranes were susceptible to crack during high temperature activation (>873 K) for the template removal. A molecular simulation demonstrated that a large contraction of ~ 5% occurred for the DDR zeolite framework after template removal. Ozone environment was employed for membranes activation at low temperature (473 K) to prevent the formation of cracks. The occluded template in zeolite cages was successfully removed by this way and high quality DDR zeolite membranes were achieved reproducibly without any cracks. The membranes were further evaluated for single gas permeation and separation of CO₂/CH₄ mixture. The ideal selectivities for CO₂/CH₄, CO₂/N₂, CO₂/C₃H₈, CO₂/H₂, N₂/CH₄ and O₂/N₂ were 305, 32, 1500, 5, 10 and 1.7, respectively. For the separation of equimolar CO₂/CH₄ mixture, a high selectivity of 500 and CO₂ permeance of 3.5×10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ could be achieved. The membranes also exhibited high stability in wet environment. A stable permeance of 3.5×10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ and selectivity of 140 could be achieved during 40 h test for the separation of CO₂/CH₄ mixture containing 1.5% vapor at 353 K.