Synthesis of Na+-gated nanochannel membranes for the ammonia (NH3) separation

Na+-gated nanochannel membranes were synthesized on α-Al2O3 supports by secondary growth for ammonia (NH3) separation from a mixture gas containing NH3, hydrogen (H2) and nitrogen (N2) at high temperature and pressure. The effects of synthesis parameters (number of seeding steps, aging time, synthesis time, and Si/Al ratio) on membrane properties were investigated by characterization and gas permeation testing. Under the optimized condition (two-time seeding, 8 h aging time, 5 h synthesis time, and gel composition of 1.05 Al2O3: 5 SiO2: 50 Na2O: 100 H2O), the best membranes achieved NH3/H2 and NH3/N2 selectivities of 328 ± 60 and 1106 ± 207, respectively at 200 °C and 21 bar. Separation performance of the membrane was shown to be highly dependent on the permeances of N2 and H2, which were greatly influenced by the membrane quality.