On stability and performance of highly c-oriented columnar AlPO4-5 and CoAPO-5 membranes

Continuous films comprised of highly c-oriented aluminophosphate AlPO4-5 or cobalt-substituted AlPO4-5 (CoAPO-5) were grown on porous supports and subjected to heat treatment in order to investigate the potential for membrane applications. A study in the early stages of in-plane crystalline intergrowth revealed a potential mechanism for flake-like crystal formation between the original oriented columnar crystals. Variations in metal substitution (AlPO4-5, CoAPO-5), support (glass, silicon, porous alumina), and calcination method (conventional, rapid thermal processing) were chosen to examine the conditions by which structural integrity was compromised following secondary (or tertiary) growth, resulting in reduced membrane functionality. Through the use of rapid thermal processing, the structure debilitation could be partially avoided. The membrane quality was inspected through pervaporation measurements consisting of a liquid hydrocarbon feed of n-heptane and 1,3,5-triisopropylbenzene. By investigating the effect of template removal on the oriented, columnar crystalline structure, useful insight is provided into the potential for the membranes to participate in applications such as molecular separations, catalysis, or host–guest assemblies.

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► Continuous, c-oriented AlPO4-5 and CoAPO-5 membranes for separation applications.
► Flake-like crystals grow parallel to the support upon tertiary hydrothermal growth.
► Conventional calcination induces a phase transformation to densified AlPO4-tridymite.
► Rapid thermal processing partially avoids structure change.