Grain Boundary Defect Elimination in a Zeolite Membrane by Rapid Thermal Processing

Abstract

Microporous molecular sieve catalysts and adsorbents discriminate molecules on the basis of size and shape. Interest in molecular sieve films stems from their potential for energy-efficient membrane separations. However, grain boundary defects, formed in response to stresses induced by heat treatment, compromise their selectivity by creating nonselective transport pathways for permeating molecules. We show that rapid thermal processing can improve the separation performance of thick columnar films of a certain zeolite (silicalite-1) by eliminating grain boundary defects, possibly by strengthening grain bonding at the grain boundaries. This methodology enables the preparation of silicalite-1 membranes with high separation performance for aromatic and linear versus branched hydrocarbon isomers and holds promise for realizing high-throughput and scalable production of these zeolite membranes with improved energy efficiency.

Molecular engineering design of the SAPO-34 and ZIF-8 membranes for CO2 separation from CH4 and N2.

“…93 Various porous materials have been used as supports for depositing zeolite membranes, and among them, porous alumina 93 or stainless steel supports 94 are most common. The flow resistance is an important factor in choosing a support, especially for thin zeolite layers.…”

Neue nanoporöse Molekularsiebmembranen: Zeolithe contra MOFs – Gewinner und Verlierer

“…Dieses Aufheizen erfolgte nach bisherigen Vorstellungen mög-lichst langsam, um die Differenzen der thermischen Ausdehnung (i) zwischen der Zeolithschicht und dem porösen keramischen oder metallischen Träger und (ii) innerhalb der polykristallinen Zeolithschicht durch anisotrope Ausdehnung unterschiedlich orientierter Kristalle, nicht plötzlich auftreten zu lassen. Kürzlich berichtete Tsapatsis, dass extrem schnelles Aufheizen, sogenanntes "rapid thermal processing, (RTP)", vorteilhaft ist [11]. …”

Effective manipulation of the microstructure of zeolite film by hydrothermal pretreatment

“…Taking Mordenite Framework Inverted (MFI) zeolite [1] (symmetry: orthorhombic; space group: P nma ; unit cell constants: a = 20.1 Ǻ , b = 19.9 Ǻ , and c = 13.4 Ǻ ) as an example, the pore system consists of straight channels (pore size: 0.53 9 0.56 nm) interconnected by zigzag channels (0.51 9 0.55 nm) [2]. In addition to their traditional uses as catalysts, adsorbents and ionic exchangers [3], zeolites can also be fabricated into thin films and used as separation membranes [4][5][6][7][8], selective sensors [9,10], low-k materials [11,12], corrosion-resistant coatings [13], and optical materials [14,15]. In the synthesis of high-quality zeolite films, the accurate manipulation and optimization of their microstructures, such as crystallographic preferred orientation (CPO), thickness, intergrowth and grain boundary structures, is critical.…”