Improved Synthesis of Hollow Fiber SSZ-13 Zeolite Membranes for High-Pressure CO₂/CH₄ Separation

High-silica CHA zeolite membranes are highly desired for natural gas upgrading because of their separation performance in combination with superior mechanical and chemical stability. However, the narrow synthesis condition range significantly constrains scale-up preparation. Herein, we propose a facile interzeolite conversion approach using the FAU zeolite to prepare SSZ-13 zeolite seeds, featuring a shorter induction and a longer crystallization period of the membrane synthesis on hollow fiber substrates. The membrane thickness was constant at ~3 μm over a wide span of synthesis time (24-96 h), while the selectivity (separation efficiency) was easily improved by extending the synthesis time without compromising permeance (throughput). At 0.2 MPa feed pressure and 303 K, the membranes showed an average CO₂ permeance of (5.2±0.5)×10^-7 mol m^-2 s^-1 Pa^-1 (1530 GPU), with an average CO₂/CH₄ mixture selectivity of 143±7. Minimal defects ensure a high selectivity of 126 with a CO₂ permeation flux of 0.4 mol m^-2 s^-1 at 6.1 MPa feed pressure, far surpassing requirements for industrial applications. The feasibility for successful scale-up of our approach was further demonstrated by the batch synthesis of 40 cm-long hollow fiber SSZ-13 zeolite membranes exhibiting CO₂/CH₄ mixture selectivity up to 400 (0.2 MPa feed pressure and 303 K) without using sweep gas.