Highly reproducible high-flux silicalite-1 membranes: optimization of silicalite-1 membrane preparation

Silicalite-1 membranes were prepared on a TiO2 coated porous stainless steel support. Different thicknesses of the membranes were achieved by changing the synthesis temperature. Increasing the crystallization temperature resulted in the formation of a monolith-type layer, which is close to a perfect microporous phase (without pores between crystals forming the layer). The silicalite-1 membranes were characterized by permeation measurements using single gases and a mixture of n-butane and i-butane in a Wicke-Kallenbach set-up. A direct relationship between the membrane thickness and the selectivity of n-butane to iso-butane: was observed; the selectivity improved with an increase in the membrane thickness. The improvement in the selectivity was correlated with decreasing the intercrystalline spaces between the crystals forming the membrane. The best performing membranes were synthesized in the temperature range of 453-463 K. The competitive adsorption of the butanes at 303 K was governing the separation properties of the membranes. The selectivity for n-butane in a 50:50 n-butane/iso-butane mixture was as high as 55, and the flux equal to 2.75 mmol/m(2) per s (WK method at 101 kPa, 303 K). The ideal selectivities, calculated from the single component measurements towards n-butane, were between 33-48 and n-butane fluxes between 7-12 mmol/m(2) per s (WK method at 101 kPa, 303 K). Small variations in the selectivity performance of the membranes synthesized under the same conditions show that the optimized preparation method was highly reproducible. (C) 2001 Elsevier Science B.V, All rights reserved.