Ordered mesoporous membranes: Effects of support and surfactant removal conditions on membrane quality

Ordered mesoporous MCM-48 membranes with cubic pore structure were prepared by solution growth method and characterized by XRD, SEM/EDS and unsteady-state gas permeation. The membranes were fabricated on symmetric α-alumina supports of different pore sizes under hydrothermal conditions using cetyltrimethylamonium bromide (CTAB) as a surfactant. The surfactant was removed by calcination and Soxhlet extraction at 100 °C using ethanol/HCl mixture. The X-ray diffraction showed that these membranes possessed a cubic MCM-48 pore structure. The N2 adsorption studies at 77 K indicated high pore volumes and pore size distribution in the mesoporous regime with an average pore diameter of ∼2.6 nm. The membranes prepared on the A15 α-alumina support (0.3 μm average pore size) exhibited the presence of pinhole defects. The single gas N2 and CO2 permeation experiments showed that the best quality membranes were synthesized on the α-A16 alumina supports (average pore size ∼0.2 μm) when the surfactant was removed by Soxhlet extraction. For these membranes the N2 and CO2 permeation was found to be governed by Knudsen diffusion. The permeance was independent of the feed pressure, indicating the absence of viscous flow contribution to gas transport.