Fast preparation of oriented silicalite-1 membranes by microwave heating for butane isomer separation

Highly (h0h)-oriented silicalite-1 membranes were fast prepared on the inner surface of α-alumina tubes by microwave heating within only 2 h. Membrane microstructure including orientation, thickness and defect densities are closely related to the synthesis conditions such as synthesis time, synthesis temperature and heating method. Membrane synthesis by microwave heating at optimized conditions displayed good reproducibility. The best silicalite-1 membrane displayed n-butane permeance of 1.3 × 10⁻⁷ mol (m² s Pa)⁻¹ and n-butane/i-butane separation factor of 45 for an equimolar n-butane/i-butane binary mixture at 333 K. The mixture n-butane/i-butane separation selectivity was higher than the ideal separation factor. Single gas permeations for six gases through the typical membrane were measured as functions of temperature and pressure. The effects of temperature, pressure and feed concentration on mixed-gas separation performance of the typical silicalite-1 membrane prepared by microwave heating were also studied in comparison with the membrane by conventional heating. Both membranes showed the similar trends with respect to temperature and pressure. Silicalite-1 membranes prepared by microwave heating were more n-butane-selective than these by conventional heating in the test ranges of temperature and pressure.