A Sealant-Free Preparation Technique for High-Temperature Use of a Composite Zeolite Membrane

A sealant-free technique for module assembly using a composite zeolite membrane was developed to enable high-temperature testing. MFI zeolite membranes prepared by in situ synthesis on porous tubular stainless steel supports were tightly mounted within a stainless steel membrane module utilizing a taper-fitting method. As a result, single-gas permeation for H 2, N 2, He, CO 2, n -butane, and i -butane and separation for mixtures of xylene isomers could be successfully examined at least up to 723 K. The sequence of the pure gas permeances was dependent on the combined temperature dependency of diffusion and adsorption during mass transfer through a zeolite membrane below 373 K, while the diffusion became dominant above 473 K as the effect of adsorption diminishes with increasing temperature. Ideal selectivities of p -xylene/ m -xylene greater than 1 were obtained below 473 K, but ideal selectivities became less than 1 above 473 K because of the higher temperature dependency of the permeance of m -xylene versus those of p -xylene. Small separation selectivities were obtained for the xylene mixtures below 473 K. At a sufficiently high temperature (above 523 K), m -xylene permeates faster than p -xylene, which is the same as the single-component permeation behavior.