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.

Research highlights▶ CO2 permeance of SAPO-34 membranes doubled by removing template under vacuum. ▶ CO2 permeance was 8.2 ± 2 × 10−7 mol/(m2 s Pa) during CO2/CH4 separations at 4.6 MPa. ▶ Templates were removed at lower temperatures in the absence of oxygen. ▶ More stable compounds form in oxygen.