Template removal from SAPO-34 crystals and membranes

SAPO-34 membranes had 95–100% higher CO2 permeances and 9–17% lower CO2/CH4 separation selectivities when their structure-directing templates were removed at 673 K in flowing N2 or under vacuum instead of in flowing air. The average CO2 permeance was 8.2 ± 2 × 10−7 mol/(m2 s Pa) during CO2/CH4 separations at 4.6 MPa feed pressure for five membranes whose templates were removed under vacuum. The average CO2/CH4 separation selectivity was 55 ± 6. Membranes heated in N2 or under vacuum were white in color, whereas those heated in air were darker. Membrane preparation was reproducible. Temperature-programmed desorption (TPD) and oxidation (TPO) of SAPO-34 crystals showed that more of the templates decomposed and were removed at lower temperature in inert gas than in air or oxygen. Over 90% of the templates were removed by 773 K during TPD in helium, and ethylene was the main decomposition product. In contrast, only 70% of the templates were removed by 773 K during TPO in air or oxygen, and CO2 and water were the major products When the SAPO-34 crystals were heated in air or oxygen, some of the template, before it decomposed to form ethylene, was oxidized to more stable compounds that were only removed at higher temperatures.