Synthesis of zeolite L membranes with sub-micron to micron thicknesses

The growth of zeolite membranes with controlled thicknesses in the sub-micron to micron region is examined, using zeolite L as the example. It was demonstrated that by controlling the concentration of the zeolite solid load and suspension viscosity, dip-coating provided a method to prepare zeolite seed layers of controlled thicknesses. Disk-shaped zeolite L crystals, with size distribution of 0.5–2 μm in diameter, were used as seed crystals for the growth of 2–7 μm thick membranes. By choosing the composition of the secondary growth medium, as well as time and temperature, crystal growth primarily occurred along the xy-plane in these micron plus-thickness membranes, with eventual thickness similar to the originally deposited seed layer. For the synthesis of sub-micron-sized membranes, seed crystals from 20 to 60 nm were used and growth was observed along the z-axis. The optimum secondary growth conditions was found to occur at 60 h of growth time (40 h for sub-micron membranes) using a temperature of 110 °C with a solution composition of 10K₂O:1Al₂O₃:20SiO₂:2000H₂O. Membranes were characterized by electron microscopy and single gas permeation studies, providing confirmation of membrane densification.