Study of the separation properties of FAU membranes constituted by hierarchically assembled nanozeolites

In this study, a modified procedure allowing for an easy synthesis of FAU membranes constituted by closely packed nanocrystals and the study of their permeation properties are reported. The FAU layers (Si/Al ratio of ca. 2.5) have a thickness of ca. 20 μm and are constituted by closely packed, well inter-grown nanocrystals, whose dimension was ca. 20-30 nm. The permeation properties of these membranes were measured by feeding H2 and CO2 pure gas. If compared to literature data, a relatively high H2 permeance of ca. 1.4 μmol m-2 s-1 Pa-1 (4177.4 GPU) was measured at 25°C in dry conditions, which can be attributed to the wide pores of the FAU zeolite and, most likely, to the presence of a secondary mesopore network. The ideal H2/CO2 selectivity was near the corresponding Knudsen coefficient over the entire temperature range investigated (25-75°C). Furthermore, the potential of these nanozeolite-based membranes for the removal of water vapours from gas mixtures was evaluated by feeding a H2O/N2 mixture, which was used as model system for mimicking a mixture of polar and non-polar components. The water permeation values at 200°C were ca. 39.9 (M1) and 31.9 (M2) μmol m-2 s-1 Pa-1 (119056.5 and 95185.5 GPU, respectively) at the steady state, with H2O/N2 separation factors of ca. 8 and 7, respectively.