Improving SAPO-34 membrane synthesis

Previously, SAPO-34 membranes prepared using aluminum isopropoxide (Al(O–i–Pr)3) and two templates (tetraethylammoniumhydroxide (TEAOH); dipropylamine (DPA)) were shown to separate CO2/CH4 mixtures with high fluxes at high pressures and room temperature. In this study, the synthesis was simplified, made safer, and modified to create less toxic waste by using only one template (TEAOH), but at twice the concentration, and Al(OH)3 instead of Al(O–i–Pr)3. However, some membranes prepared with the new procedure had low fluxes because they had impermeable regions. The impermeable regions were determined to be due to synthesis gel that remained in the support following a 15-min, post-synthesis rinse with water. Rinsing the membranes for at least 24 h in deionized water before calcination removed most of the residual gel and formed spatially-uniform membranes with high permeances (maximum of 1.2×10−6 mol/(m2 s Pa)) and high CO2/CH4 separation selectivities (70) for 46-bar feed pressure. Additional benefits of these changes in membrane preparation include a 200-K increase in the temperature at which template could be removed, increased stability of calcined membranes contacted with liquid water, and better long-term stability during storage.