Alkali-Free ZSM-5 Membranes: Preparation Conditions and Separation Performance

Abstract

Alkali-free, H−ZSM-5 membranes were synthesized by in-situ crystallization on porous α-alumina, γ-alumina, and stainless steel tubular supports. Membranes prepared from different Si sources were characterized by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. Membranes prepared under different conditions were also characterized by single-gas permeances of H2, N2, n-C4H10, i-C4H10, and SF6 and by separation selectivities of n-C4H10/i-C4H10 mixtures from 300 to 473 K. The effects of preparation procedure, crystallization time and temperature, number of synthesis layers, gel dilution, Si source, and type of support were studied. The permeation and separation properties of the membranes depend strongly on the preparation procedure. Permeating synthesis solution into the pores of the support before hydrothermal treatment allows zeolites crystal growth within those pores. Increasing the crystallization time and temperature increases the n-C4H10/i-C4H10 separation selectivities...