A facile approach to synthesize SSZ-13 membranes with ultrahigh N₂ permeances for efficient N₂/CH₄ separations

Separation of inert nitrogen from natural gas by membranes is much more energy-saving than cryogenic distillation but very challenging because the size difference of both gas molecules is quite small. Herein, high-quality and N₂-selective SSZ-13 membranes on α-alumina tubes were prepared using a novel synthesis approach called seeded-gel synthesis. Seeded-gel synthesis was more convenient and credible than the conventional secondary growth because a seeding step on the substrate was omitted for the former method. The effect of calcination atmosphere on the quality of membranes was also discussed. SSZ-13 membranes had the fewest defects when ozone calcination was used. The predicted values of single-component N₂ and CH₄ permeances by the Maxwell-Stefan equations agreed well with the experimental ones. The SSZ-13 membrane exhibited ultrahigh N₂ permeance of 850 × 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹ (equals 2500 GPU) and a high N₂/CH₄ selectivity of 13.5 at 298 K and 0.303 MPa feed pressure (absolute). Membrane preparation by seeded-gel method had good reproducibility. The effects of temperature, pressure drop and feed flow rate on membrane performances were investigated for N₂/CH₄ mixture separations. The membrane also displayed good separation performance in N₂/CH₄ system either at 2.6 MPa feed pressure or under humid conditions. The continuous SSZ-13 thin membranes prepared by the simple seeded-gel synthesis showed great potentials for energy-efficient N₂ removal from unconventional gases.