Highly selective and permeable SSZ-13 zeolite membranes synthesized by a facile in-situ approach for CO₂/CH₄ separation

High-quality tubular SSZ-13 zeolite membranes were fabricated by a facile in-situ approach for the first time. The in-situ approach requires only a single hydrothermal step for membrane growth, which is much simpler than the normal multi-step secondary-growth approach with seed preparation and seeding steps. The proper aging time and relatively high synthesis temperature provide sufficient nuclei for SSZ-13 growth, which further facilitates the in-situ formation of continuous membranes on the substrates. Three SSZ-13 zeolite membranes fabricated by the simple in-situ approach displayed ultrahigh average selectivity of (233 ± 46) and high average carbon dioxide permeance of (1220 ± 100) × 10⁻⁹ mol (m² s Pa)⁻¹ [∼3660 ± 300 Gas Permeation Unit (GPU), 1 GPU = 3.348 × 10⁻¹⁰ mol/(m² s Pa)] at 298 K in the CO₂/CH₄ (50/50 in mol) mixture. The overall separation performance of the current membranes exceeded that of most reported zeolite membranes in the CO₂/CH₄ mixture. It indicated that the current in-situ synthesis approach had good reproducibility. The typical membrane also showed excellent separation performance in the CO₂/N₂ mixture toward the carbon capture from flue gas. The long-term stability of this membrane was investigated in the humidified CO₂/CH₄ mixture with a relative humidity close to 100%. This simple in-situ approach is suitable to prepare other zeolite membranes for gas separation after improving the gel nucleation.