Rapid synthesis of oriented silicalite-1 membranes by microwave-assisted hydrothermal treatment

The objective of this work was to evaluate the potential of microwave (MW) heating for the rapid synthesis of thin silicalite-1 membranes by secondary growth from microwave-derived silicalite-1 seeds. The MW seed suspension was deposited by slip-casting on commercial α-Al2O3 supports and zeolite membranes were obtained after a synthesis time as short as 30–150 min, by MW-assisted secondary growth at 393–453 K. The membrane thickness varied typically from 200 nm to a few μm, with glassy-like or columnar morphologies, respectively, depending on the synthesis conditions. The morphology, thickness, homogeneity, crystal preferential orientation (CPO) and single gas permeation properties of the silicalite-1 membranes have been studied in relation to the synthesis parameters. The highest single gas permeances and medium n/i-butane selectivity were obtained with the membrane prepared at the lowest temperature (120 min at 403 K), although a higher synthesis temperature (433 K) was needed to get a higher n/i-butane selectivity (40–50). An oblique crystallographic preferred orientation (101-CPO) was found for this attractive membrane whose N2 permeance reached 1.5 × 10−6 mol m−2 s−1 Pa−1 at 294 K. A very low ideal selectivity was obtained for the membrane prepared at 453 K for 120 min, which is more clearly c-oriented (c-axis CPO), and in which defects were detected.