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

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Science  31 Jul 2009:
Vol. 325, Issue 5940, pp. 590-593
DOI: 10.1126/science.1176095

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Optimizing Molecular Sieve Production

Microporous membranes composed of aluminosilicate minerals are known as zeolites and are often called molecular sieves because of their ability to filter or separate small molecules. The separation performance is partly governed by the selectivity for one species over another, and this can be compromised by defects, which allow for easy diffusion pathways. To create the porosity, structure-directing agents are used, which need to be removed during a long thermal treatment that can generate defects. Choi et al. (p. 590) show that for the silicalite-1 system, a rapid thermal treatment significantly reduces the defect density, with corresponding improvement in the filtration of very similar species, such as xylene isomers.


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.

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