Influence of sodium ion on high-silica SSZ-13 membranes for efficient CO2/CH4 and N2/CH4 separations

Here, high-silica SSZ-13 membranes were prepared on macroporous supports by regulating sodium sources (NaOH, NaCl, Na2SO4 and sodium-free) under fluoride and aluminum free gel. A pure phase and high gas permeation SSZ-13 membrane with oval-shaped crystals on the membrane surface was obtained by NaCl. It suggests that alkali metal sodium ion promoted crystal crystallization. The influence of Na2O (2NaCl)/SiO2 ratio (from 0.025 to 0.2) on the crystallization process of zeolite membranes was investigated in detail by XRD, SEM and gas permeation tests. The content of NaCl hardly affected the structure of SSZ-13 but could affect the morphology and size of the crystals. The best membrane (NaCl/SiO2 = 0.2) had a mixed CO2 and N-2 gas permeance of 5.4 x 10(-7) mol/(m(2) s Pa) and 5.2 x 10(-8) mol/(m(2) s Pa), along with the CO2/CH4 and N-2/CH4 selectivity of 155 and 12.3, respectively. The effects of pressure drop, temperature and feed concentration on membrane separation performance were explored. In addition, the obtained SSZ-13 membrane exhibited the hydrothermal stability in the humid N-2/CH4 mixture under 298K, indicating the application prospects in natural gas separation.