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Preparation of Low-silica EMT/FAU Zeolite

IP.com Disclosure Number: IPCOM000019365D
Publication Date: 2003-Sep-12
Document File: 2 page(s) / 30K

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Abstract

Faujasite-type zeolites (FAU) have been synthesized hydrothermally with a wide range of composition from Y zeolites with Si/Al ratios as high as 5 to a low-silica X zeolite (LSX) with a Si/Al ratio of 1.0. A closely related structure to FAU is the hexagonal polymorph denoted with EMT. EMT zeolites with Si/Al ratios from 3.0 to 5.0 have been synthesized hydrothermally by Delprato et al. using 18-crown-6 ether as a structural directing agent [ref. 1]. Davis reported the synthesis of VPI-6, an intergrowth of EMT/FAU with Si/Al ratio of about 1.2 [ref. 2]. However, the synthesis of VPI-6 is rather complicated and the materials obtained had low micropore volumes. Low-silica EMT zeolite with Si/Al ratio of 1.0 has not been reported. Low-silica zeolites have potential uses for laundry detergents and air separation adsorbents, both of which require the highest possible ion-exchange capacity of zeolites. This paper discloses the preparation of low-silica EMT/FAU intergrowth zeolites with Si/Al ratio as low as 1.0.

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Preparation of Low-silica EMT/FAU Zeolite

         Faujasite-type zeolites (FAU) have been synthesized hydrothermally with a wide range of composition from Y zeolites with Si/Al ratios as high as 5 to a low-silica X zeolite (LSX) with a Si/Al ratio of 1.0. A closely related structure to FAU is the hexagonal polymorph denoted with EMT. EMT zeolites with Si/Al ratios from 3.0 to 5.0 have been synthesized hydrothermally by Delprato et al. using 18-crown-6 ether as a structural directing agent [ref. 1]. Davis reported the synthesis of VPI-6, an intergrowth of EMT/FAU with Si/Al ratio of about 1.2 [ref. 2]. However, the synthesis of VPI-6 is rather complicated and the materials obtained had low micropore volumes. Low-silica EMT zeolite with Si/Al ratio of 1.0 has not been reported. Low-silica zeolites have potential uses for laundry detergents and air separation adsorbents, both of which require the highest possible ion-exchange capacity of zeolites. This paper discloses the preparation of low-silica EMT/FAU intergrowth zeolites with Si/Al ratio as low as 1.0.

Detailed description of preparation

         The approach to prepare low silica EMT/FAU zeolite was by reacting a silica-rich EMT zeolite with a caustic solution containing aluminum. Two examples are given below.

Example 1.

EMT with Si/Al ratio of 3.3 was synthesized according to the method developed by Delprato et al. [ref. 1] with some modification. A gel was prepared with the following molar composition: 0.3 18-crown-6 : 2.4 Na2O : Al2O3 : 10 SiO2 : 140 H2O. The mixture was stirred at room temperature for 2 days and crystallization was carried out in a Teflon-lined autoclave at 110ºC for 10 days. The solid was recovered by vacuum filtration and washed with deionized water until the pH of filtrate was neutral. X-ray diffraction (XRD) pattern indicated the solid is highly crystalline EMT. The EMT zeolite powder (Si/Al=3.3) was then mixed in a strong basic solution containing NaOH, KOH and Al(OH)3 (Na-K-Al solution) with the following molar composition: 7.25 Na2O : 3.27 K2O : Al2O3 : 160 H2O. The mixture was sealed in a Teflon bottle and heated in a water bath at 40°C for a period of time from a few hours to a few days. The solid was recovered in the same manner as for the synthesis of EMT, and identified as EMT/FAU intergrowth by XRD. Depending on the time of reaction, products obtained had Si/Al ratios ranging from 1.0 (>24 hours) to 2.7 (4 hours).

Example 2.

Low-silica EMT/FAU intergrowth zeolite was also prepared by mixing a Na-K-Al solution with EMT and its crystallization mother liquor. EMT (Si/Al=3.3) was prepared in the same way as in Example 1. At the end of crystallization, filtration of EMT crystals was not performed. EMT solid together with its crystallization mother liquor were blended into a Na-K-Al solution prepared similar to the one in Example 1. The mixture was sealed in a Teflon bottle and heated at 50°C for two days. Table 1 lists the XRD reflections of the solid recovered by vacuum fil...