Stability and Separation Performance of Highly c-Oriented AFI-Type Aluminophosphate Membranes

Continuous, highly c-oriented aluminophosphate films (structure code AFI) were grown on porous α-Al₂O₃ supports in order to investigate their potential for molecular separation applications.  Variations in metal substitution (AlPO₄-5, CoAPO-5, CoSAPO-5), growth method (forced air convection oven, microwave), and calcination technique (conventional, rapid thermal processing) were chosen to examine the conditions by which membrane quality was optimized.  Following hydrothermal growth in a forced air convection oven, AlPO₄-5 and CoAPO-5 membranes underwent densification to an AlPO-tridymite phase following heat treatment, resulting in reduced membrane functionality which may be partially avoided through the use of rapid thermal processing. On the other hand, membranes prepared by an optimized method were found to be thermally stable with high membrane quality as inspected through pervaporation measurements consisting of a liquid hydrocarbon feed of n-heptane and 1,3,5-triisopropylbenzene.  We will discuss the new aspects that allowed fabrication of oriented, continuous, high-quality aluminophosphate membranes and we will provide useful insight into their potential for applications such as molecular separations, catalysis, or host-guest assemblies.