Propylene/propane separation on a ferroaluminosilicate levyne zeolite

The propylene/propane separation properties of levyne zeolites with different framework Si/Al and Fe/Al ratios have been examined and compared with those of the four well-studied zeolite adsorbents (i.e., Na-A, Ca-A, Na-X and ITQ-12) for this separation. Both zeolite framework structure and composition were found to be critical for the propylene uptake, kinetic separation and adsorbent durability. Among the zeolites studied here, the mixed CaNH4 form of a ferroaluminosilcate levyne (Si/Al = 15.5 and Fe/Al = 0.27) showed the highest propylene/propane selectivity (11). Under vacuum-swing adsorption mode at 298 K and reservoir pressure of 1.2 bar, this partially iron-substituted zeolite was characterized by a higher propylene uptake (ca. 1.0 vs 0.7 mmol g−1) than its aluminosilicate version, which can be attributed to a combination of the molecular sieve effect of its framework topology and relatively weaker acidity. The results of this study demonstrate that, in contrast to widely held belief, zeolite adsorbents selective for propylene/propane separation do not need to be a pure-silica composition.