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

Abstract

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 conditions range significantly constrains scale-up preparation. Herein, we proposed a facile interzeolite conversion approach using FAU zeolite to prepare SSZ-13 zeolite seeds, featuring a shorter induction and a longer crystallization period of the membrane synthesis. 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 synthesis time without compromising permeance (throughput). At 0.2MPa 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 (1530GPU), 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 6.1MPa 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.