Improved silicalite-1 membranes on 61-channel monolithic supports for n-butane/i-butane separation

High-quality large-area silicalite-1 membranes were reproducibly fabricated on 61-channel monolithic supports by single-step secondary growth via vacuum seeding. The packing density of module using this monolithic membrane is 5.7 times higher than that using our tubular membranes. Moreover, the mechanical strength of monolithic support is improved by one order of magnitude compared with that of tubular one. The high H₂/SF₆ and N₂/SF₆ ideal selectivities (3410 and 1970, respectively) of the typical monolithic membrane suggest that the monolithic membrane has few boundary defects. Four monolithic silicalite-1 membranes prepared under the optimized conditions showed n-butane/i-butane separation factors of 28 ± 1.8 and n-butane permeances of (8.1 ± 0.27) × 10^-8 mol (m² s Pa)^-1 in an equimolar n-butane/i-butane mixture at 393 K. It indicates that the synthesis of monolithic silicalite-1 membrane has a good reproducibility. Separation performance of the large-area monolithic membrane is comparable to these of tubular and disc ones with small areas. The effects of temperature, feed pressure and Reynold numbers of the feed on separation performance of the monolithic membranes were also discussed. The monolithic membranes displayed long-term stability for the actual butane mixture.