The Influence of Hydrogel Aging Conditions on the Crystal Size and Morphology of LSX Zeolite in the NaK-Form
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e Influence of Hydrogel Aging Conditions on the Crystal Size and Morphology of LSX Zeolite in the NaK-Form I. N. Pavlovaa, O. S. Travkinaa, *, and G. F. Garievab aInstitute
of Petroleum Chemistry and Catalysis, Ufa Federal Research Center, Russian Academy of Sciences, Ufa, 450075 Bashkortostan, Russia b Ishimbay Specialized Chemical Catalyst Plant, Ishimbay, 453203 Bashkortostan, Russia *e-mail: [email protected] Received February 20, 2020; revised March 16, 2020; accepted April 10, 2020
Abstract—The influence of the temperature and duration of aging of a hydrogel on the particle size and morphology of crystals of LSX zeolite in the NaK-form has been studied. It has been found that hydrogel aging should be carried out at a temperature not exceeding 30°C for a time of 48–72 h to prepare crystals with a narrow particle size distribution and an average size of up to 2 μm. Keywords: LSX zeolite, hydrogel aging, dispersity of crystals, morphology of crystals DOI: 10.1134/S0965544120080101
The industrial processes of adsorption separation of gas mixtures including air separation are based on the use of microporous adsorbents. Currently, the production of nitrogen and oxygen is to a significant extent executed by the separation of air with the use of adsorption technologies [1–6]. Various ion-exchange forms of an LSX zeolite are the most promising adsorbents in these processes. The advantage of an LSX zeolite over zeolites A and X consists in the fact that it combines a porous structure characteristic of zeolite X and the maximum number of exchange cations inherent in zeolite A. The efficiency of using any zeolite in adsorption depends on its phase purity, crystallinity, and crystal particle size. There are papers [7–11] describing in close detail various versions of the synthesis of a powdered NaKLSX zeolite with high phase purity and crystallinity, which are based on the hydrothermal crystallization of alkaline silica–alumina hydrogels prepared by mixing sodium and potassium hydroxides and sodium aluminate and silicate in a range of temperatures of 60 to 100°C for 40–48 h. Note that the crystallization of the gels is preceded by the step of their aging at temperatures below 50°C. It is known [12, 13] that the conditions of the preliminary holding of silica–alumina hydrogels have a great effect on the crystal size of zeolites. Gel aging at a relatively low temperature leads to an increase in the number of crystal nuclei and, as a consequence, makes it possible to decrease the crystal size. In addition, an increase in the crystal size is promoted by an increase in the gel aging time. In recent years, a number of works have appeared that are devoted to the investiga-
tion of the effect of gel aging conditions on the crystal size of zeolites A and Y [14–17]. However, the information on the influence of the gel aging conditions on the particle size of a NaKLSX zeolite, which determines the efficiency of zeolite use in adsorption, is very scarce. It is to clarifying this question that the present work is devoted. EXPERIMENT
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