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

[Display omitted] •A quasi-solid gel matrix containing nanozeolite precursor species was formed at room temperature.•The gel matrix, coated on the support surface, was used as starting material for zeolite membrane synthesis.•The gel layer was easily converted in a FAU membrane by secondary growth.•The membranes are constituted by closely packed nanozeolites.•The separation properties of these FAU membranes have been studied. 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. 20μm and are constituted by closely packed, well inter-grown nanocrystals, whose dimension was ca. 20–30nm. 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. 1.4μmolm−2s−1Pa−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) μmolm−2s−1Pa−1 (119056.5 and 95185.5 GPU, respectively) at the steady state, with H2O/N2 separation factors of ca. 8 and 7, respectively.