Highly oriented improved SAPO 34 membrane on low cost support for hydrogen gas separation

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Abstract
In this paper we investigated a path towards preparation of a highly oriented improved SAPO 34 zeolite membrane on a silica modified low cost clay-Al2O3 support by selective deposition of oriented seed crystals, followed by an epitaxial secondary growth hydrothermal technique. The membrane thickness was found to be ∼26 μm. The silica layer that have an abundance of reactive hydroxyl groups while its interior is connected by the siloxane group Si–O–Si. These Si–OH groups on the silica-coated substrate could provide a hydrogen bonding interaction with surface hydroxyl groups of SAPO 34 seed crystals. This outcome is a possible result of the formation of a uniform seed monolayer with the same orientation. The stronger intensity of the single peak in XRD pattern confirms the formation of an oriented membrane layer. For comparison, a seed layer was deposited on an unmodified support surface. A discrete and randomly oriented membrane layer was obtained on that support. Highly oriented SAPO 34 membranes on the silica modified support are better for hydrogen gas separation and attained higher selectivity values for the gas mixture. A selectivity of 16.66 and 20.91 was achieved for H2–CO2 and H2–N2, respectively, at room temperature. The obtained values were improved compared to the reported literature values. Herein, we report for the first time, that this work is an improvement towards a highly crystallographic orientation of the SAPO 34 membrane layer with reduced defects and higher gas separation efficiency. The synthesized membrane enhanced the reproducibility and long term durability for hydrogen gas separation with good results.

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