Synthesis of granular sorbent based on zeolite LSX for obtaining oxygen from air

The paper considers the synthesis of a granular sorbent based on LSX zeolite. Zeolite LSX refers to low-silicafaujasite-type zeolites with Si:Al ratio = 1-1.2. The crystal structure of zeolites is formed from SiO4 and AlO4 tetrahedra connected to each other. The aluminum content in the zeolite framework determines the amount of extraframework cations compensating for the excess negative aluminum charge. The nature of the extraframework cation determines the sorption properties of LSX zeolite. Thus, Ca2+, Li+, Ag+ substituted zeolites are used to separate air components and produce oxygen. A separate task is the formation of zeolite in the form of granules and balls using a binder without losing the adsorption capacity of the zeolite. Available natural materials (kaolin, bentonite, metakaolin) most often act as a binder. In this research, sorbent granules were obtained by molding crystalline LSX with metakaolin in a ratio of 1:1 and subsequent hydrothermal treatment in an alkaline solution at 50 °С for 14 days. Using the low-temperature nitrogen adsorption method, it was found that with an increase in the time of hydrothermal treatment, the specific surface area of zeolite granules increases and practically reaches the value of the specific surface area of the initial LSX powder zeolite. X-ray phase analysis showed that the degree of crystallinity in the granule increases during hydrothermal treatment, which indicates the dissolution of metakaolin and the formation of a new LSX crystal structure on primary zeolite crystals. Thus, it has been shown that this synthesis method makes it possible to increase the specific surface area and the content of crystalline LSX relative to the initial granules due to the dissolution of metakaolin and its crystallization into the LSX structure. The resulting granules will be used as the basis for an adsorbent to obtain oxygen from the air. The authors declare no conflicts of interests.

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