Preparation of High Performance ZSM-5 Zeolite Membranes for CO2/H2 Separation

Abstract

High-quality ZSM-5 zeolite membranes were successfully synthesized on the outer surface of tubular α-alumina substrates by manipulating the microstructure of the zeolite layer using a new different-sized seeding (DSSM) in combination with variabletemperature/time (VTT) methodd. In this method the microcracks/defects in the primary seed layer are filled by smaller seeds and effectively eliminated using a proper temperature/time profile, resulting in a significant increase in selectivity without scarifying permeance. The effects of number and combination of seed layers, seed size, and synthesis conditions on the microstructure, N2/SF6 gas permeation, and H2/CO2 separation performance of membranes are evaluated in detail. The synthesized ZSM-5 membranes show the microstructure of thin, fully inter-grown, and densified zeolite layer that is responsible for high selectivity without any negative effect on the permeance. The best synthesized defect-free membranes exhibited a very low H2/CO2 selectivity of 0.1 with CO2 permeance of 3×10-5 mol m-2 s-1 Pa-1.

Zeolite-based catalytic membrane reactors for thermo-catalytic conversion of CO2

“…A large seed size follows the secondary growth route, resulting in poor crystal intergrowth and rough zeolite surface. Also, the low steric hindrance leads to a random growth of the seeds ( Mirfendereski and Mazaheri, 2021 ). However, a large crystal strengthens the support-zeolite interaction and enhances the diffusivity ( Mirfendereski, 2019 ).…”

“…During the synthesis, the small seeds on the top accelerated the nucleation kinetics and narrow the intercrystalline space. Besides, the gaps of the bottom layer consisting of large seeds were filled by the smaller seeds growing toward the support ( Mirfendereski and Mazaheri, 2021 ).…”

“…For example, the diffusion coefficient was much higher in the all-silica MFI zeolite with b-orientation and [010] channels than those perpendicular channels to [010] ones ( Caro et al., 1993 ). In another scenario where large amounts of small seeds were present on the top of the ZSM-5 (MFI) membrane, crystallization in c-orientation was exhibited, which favored the out-of-plane growth rather than in-plane direction, realizing a highly selective CO 2 permeation ( Mirfendereski and Mohammadi, 2011 ; Banihashemi et al., 2018 ; Mirfendereski and Mazaheri, 2021 ). Similarly, CO 2 diffusion was promoted in the CHA zeolite membrane with an out-of-plane orientation due to the short transport pathway ( Lee et al., 2019 ).…”