Silicalite Membrane Preparation, Characterization, and Separation Performance

Abstract

Silicalite membranes were prepared by a single hydrothermal synthesis on seeded porous tubular supports. The support tubes were simply seeded by a water slurry of silicalite particles or by repeated dip coating in a suspension of colloidal silicalite particles. It was found that a crystal growth behavior was strongly dependent on seeds. Silicalite crystals slowly grew onto the unseeded and nanoscale-silicalite-seeded supports under the present synthesis conditions, leading to the formation of an incompact crystal layer, especially on the unseeded support. On the other hand, silicalite crystals preferentially grew onto the support tubes seeded with silicalite powders (particle size up to 4 μm) under the same synthesis condition. The silicalite seed particles mainly provided nucleation sites and enhanced silicalite crystal growth in all directions onto the support, resulting in the formation of a thin and dense crystal layer. The higher crystallization temperature, faster crystal growth rate is the favorable condition for preparation of the silicalite membranes with high pervaporation performance. For example, the high ethanol/water separation factor of 89 with a high flux of 1.8 kg/m2·h for a feed concentration of 5 wt % ethanol at 60 °C was obtained through the silicalite membranes prepared on silicalite-seeded α-Al2O3 tubes at 185 °C for 5.5 h of hydrothermal treatment. The silicalite membranes prepared by the same method also showed good separation for n-butane and isobutane (an ideal separation factor larger than 10 at 200 °C).

Pervaporation of Ethanol/Water Mixtures Through a High-Silica MFI Membrane: Comparison of Different Semi-Empirical Mass Transfer Models

“…Otherwise, the reported apparent activation energies for the flux of water [16,56,57] are similar to those in this study. However, the previously reported apparent activation energies for ethanol with MFI membranes, 32-36 kJ mol -1 [16,56,57] are smaller than those for water, 41-42 kJ mol -1 [16,56,57]. In contrast to the present study, Lin et al [16] and Matsuda et al [57] reported a decreasing trend of ethanol/water separation factor with increased temperature.…”

“…For organic removal from water-containing streams, MFI membranes have been studied the most, especially silicalite-1 membranes. The advantage of silicalite-1 membranes in the separation of ethanol from aqueous solutions is attributed to the hydrophobic properties and well-defined pore size of silicalite crystals [16]. Ethanol-water separation factors of up to 106 [17] have been reported in pervaporation through MFI membranes, with the typical value being around 40 [2].…”

“…The typical value for total flux is around 1 kg m -2 h -1 . However, a flux of as much as 4.02 kg m -2 h -1 (at 60 °C) on a tubular support has been reported [16].…”

“…Zeolite membranes are typically synthesized on porous inorganic supports, which are needed to supply the mechanical strength to the thin membranes. The MFI membranes prepared are typically tens of micrometers [16,17,[19][20][21] or several hundreds of micrometers thick [22][23][24]. However, as thin as ca.…”

Preparation of high selectivity silicalite-1 membranes by two-step in situ hydrothermal synthesis

“…Zeolite membranes with excellent separation performance in a wide range of industrial processes, including gas separation, catalysis, pervaporation, and membrane reactors, have been produced [4][5][6]. Zeolite membranes can be used to separate different mixtures, and have low energy consumption and are environmentally friendly.…”