A comparative study on permeation and mechanical properties of random and oriented MFI-type zeolite membranes

Changes to microstructure of a zeolite membrane can affect defect formation, degree of intergrowth, stability, and performance of the membrane. In this work, random, c- and h,0,h-oriented membranes are synthesized under similar conditions (i.e. same structure directing agent, seed layer solution, calcination procedure) and characterized with performance based methods. Moderate ideal selectivities for H₂/SF₆ around 20 were observed for those membranes most effected by defects induced during the template removal step including both the random and h,0,h-oriented membranes. In contrast, the c-oriented membrane was less susceptible to crack formation and showed H₂/SF₆ selectivity around 46. Single component pervaporation studies yielded no ideal selectivity for p-xylene over o-xylene for random membranes while a selectivity of 2-3 was observed for the oriented membranes. Furthermore, membrane degradation was observed in all microstructures of MFI membranes that were subjected to pervaporation experiments and subsequent heat treatment to remove the adsorbed xylenes. It is believed that this effect is due structural deformations induced by high loadings of adsorbed xylene which upon burn out cause permanent damage to the membrane.