A method for synthesizing NaY molecular sieves with a high silica-to-alumina ratio

Abstract

This invention discloses a one-step synthetic method for preparing high silica-to-alumina ratio NaY molecular sieves. The method promotes the synthesis of high silica-to-alumina molecular sieves by adding silica-to-alumina molecular sieve seeds to the synthetic gel system and introducing a dual-template agent into the synthetic gel system. This molecular sieve synthesis method provides high yield, high silica-to-alumina ratio, eliminates the need for directing agent preparation, has a short synthesis time, and directly synthesizes high silica-to-alumina ratio NaY molecular sieves in one step. The synthesis process is simple, reliable, and easy to implement.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, and in particular to a method for preparing high silica-to-alumina ratio NaY molecular sieves using a template agent. Background Technology

[0002] Y-type zeolite possesses a FAU topology, with its framework resembling SOD cages connected by double six-membered rings, including ellipsoidal supercages and a three-dimensional twelve-membered ring channel structure. Fluidized catalytic cracking (FCC), developed in the 1960s, is a core technology in modern oil refining, and Y-type zeolite is one of the main types used as catalysts and adsorption / separation agents. NaY is the most widely used molecular sieve catalyst material, with my country's annual consumption at approximately 50,000 tons and the world's annual consumption at approximately 500,000-700,000 tons. Due to its well-developed three-dimensional channels, tunable acidity, and good thermal and hydrothermal stability, it is widely used in petroleum refining processes such as catalytic cracking, hydrocracking, and isomerization.

[0003] Currently, zeolites with a silica-to-alumina ratio (S / A ratio) greater than 6.0 are classified as high-silica Y-type zeolites (as described in USP4714601S). The S / A ratio of the Y-type zeolite framework has a decisive influence on its catalytic performance. The higher the S / A ratio, the better the catalytic activity. In the preparation of Y-type zeolites, a lower S / A ratio makes preparation easier, while a higher S / A ratio requires more stringent preparation conditions and is more difficult to achieve. Currently, high-silica Y-type zeolites widely used in heavy oil cracking catalysts are generally obtained through post-processing methods such as dealumination or dealumination with silica replenishment. The advantage of this method is its ease of industrialization, but its disadvantages include complex processes, significant loss of zeolite crystallinity, low product yield, and environmental pollution. Direct hydrothermal synthesis of Y-type zeolites can effectively avoid the various disadvantages of post-processing and maintain crystal structure stability. Therefore, further exploration is needed.

[0004] The direct synthesis of high silica-to-alumina ratio Y zeolite is of great significance for catalytic cracking processes.

[0005] The American company Grace first proposed a method for synthesizing NaY molecular sieves using a crystallization directing agent in patent USP3639099. Due to the high alkalinity of the feedstock, the resulting NaY zeolite typically has a silica-to-alumina ratio of 4.0–4.5. Because of the low water content, the colloid has high viscosity, requiring vigorous stirring. Patent USP3671191 proposes an improved method, increasing the silica-to-alumina ratio and water content to obtain NaY products with a silica-to-alumina ratio greater than 5.0. Currently, most industrial methods for producing NaY molecular sieves employ methods similar to the directing agent method proposed by Grace in US3639099 and US3671191. This method can synthesize NaY molecular sieve products with a crystallinity of over 83% and a silica-to-alumina ratio of around 5.0 within 28 hours, but achieving a crystallinity of over 90% is difficult. A disadvantage of this method is the high water content, which leads to increased SiO2 emissions from the mother liquor, thus reducing silicon utilization. Furthermore, the Si / Al ratio (SiO2 / Al2O3 molar ratio) of the synthesized NaY molecular sieves is generally below 5.2. Without adding organic template agents, it is difficult to synthesize high Si / Al ratio Y molecular sieves with a Si / Al ratio greater than 6 by simply adjusting the gel ratio, crystallization time, adding seed crystals, or inorganic directing agents. Grace Company uses an inorganic template agent method, adding cesium ions and a conventionally prepared directing agent to the reactant gel to synthesize octahedral molecular sieves CSZ-1 and CSZ-3, etc., with Si / Al ratios between 5.0 and 7.0 (USP4333859, USP4309313). However, the cesium ions in the products obtained by this method are difficult to remove, requiring multiple exchange and calcination processes.

[0006] The use of organic structure-directing agents has made the synthesis of high silica-to-alumina ratio Y molecular sieves much easier. Patent USP4714601 uses alkyl or hydroxyalkyl quaternary ammonium salts as templates to synthesize a polymorph of FAU called ECR-4 with a silica-to-alumina ratio greater than 6; patent UPS4931267 uses tetrapropyl and / or tetrabutylammonium hydroxide as structure-directing agents to synthesize a polymorph of FAU called ECR-32 with a silica-to-alumina ratio greater than 6; other methods that add organic templates such as quaternary ammonium bases and quaternary ammonium salts of C1 to C4 to gels to synthesize high silica-to-alumina ratio octahedral zeolites with silica-to-alumina ratios of 6-30 include [USP5549881, USP5116590, USP4965059, EP0887310, CN1145278, CN1226875]. In 1990, Delprato et al. in France first used crown ether as a template agent to synthesize high silica-alumina ratio octahedral zeolite [Zeolites.1990,10(6):546-552]. However, crown ether is expensive and highly toxic, which limits its industrial application.

[0007] Yan Wenfu et al. used a dual-template method, employing high-silica Y molecular sieves as seed crystals, to synthesize Y molecular sieves with a SiO2 / Al2O3 ratio of 6.00–21.352 in one step [CN201911420547.6]. The first template agent was tetramethylammonium hydroxide, and the second template agent was any tetraalkylammonium hydroxide other than tetramethylammonium hydroxide; the SiO2 / Al2O3 ratio of the high-silica Y molecular sieve seed crystals was >50, and the hydrothermal crystallization treatment time was 8–15 days.

[0008] Developing a simple synthesis method for NaY zeolite with short crystallization time, high silicon-to-alumina ratio, and high crystallinity remains one of the urgent problems to be solved in this field. Summary of the Invention

[0009] The purpose of this invention is to provide a direct method for preparing NaY molecular sieves, wherein the method promotes the synthesis of high-silicon (silicon-aluminum oxide ratio of 22-44) Y molecular sieves by adding silica-alumina molecular sieve seeds to the synthetic gel system and introducing a dual template agent into the synthetic gel system.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] This invention provides a direct method for preparing high silica-to-alumina ratio NaY molecular sieves, comprising:

[0012] Step S110: Mix deionized water, silicon source, aluminum source, alkali source, and template agent R1 in a certain proportion, and stir for a period of time to obtain solution 1; add template agent R2, mix and stir evenly to obtain the initial gel; the molar ratio of each raw material is (10~150)SiO2:1Al2O3:(0.1~25)M2O:(0.5~5)R1:(0.2~6)R2:(40~5000)H2O; M is selected from alkali metal elements.

[0013] At least one of sodium, potassium, and cesium;

[0014] Step S120: Add the silicon-aluminum molecular sieve seed crystals with FAU or EMT structure to the initial gel obtained in step a), stir, and obtain the synthetic gel;

[0015] Step S130: The above-synthesized gel is dynamically crystallized at 70-120°C for 1-7 days to obtain the high-silica Y molecular sieve.

[0016] Template agent R1 is 1-benzyl-4-hydroxy-2-methyl-1H-benzimidazole-6-carboxylic acid;

[0017] Template agent R2 is 1-ethyl-3-methylimidazolium tetrafluoroborate;

[0018] The silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, silica sol, amorphous silica, solid silica gel, fumed silica, and sodium silicate.

[0019] The aluminum source is selected from at least one of sodium aluminate, aluminum oxide, aluminum hydroxide, aluminum isopropoxide, aluminum 2-butoxide, aluminum chloride, aluminum sulfate, and aluminum nitrate.

[0020] The alkali metal source is selected from at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide.

[0021] In step S120: the ratio of silicon aluminate to aluminum oxide in silicon aluminate molecular sieve seed crystals with FAU or EMT structures is ≥5;

[0022] In step S120, the silicon-aluminum molecular sieve seed crystals with FAU or EMT structures are selected from at least one of Na-type and H-type zeolite molecular sieves.

[0023] In step S120, the amount of silicon-aluminum molecular sieve seed crystals with FAU or EMT structure added is 5 to 30 wt.% of the mass of the silicon source in the initial gel, calculated as SiO2, preferably 5 to 20 wt.%.

[0024] In step S130, after crystallization is complete, the solid product is filtered and separated, washed with deionized water until neutral, and dried to obtain high-silica Y molecular sieve.

[0025] Compared with existing technologies, the one-step method for preparing high silica-to-alumina ratio Y molecular sieves provided by this invention uses deionized water, silicon source, aluminum source, alkali source, and dual template agent as raw materials to carry out a gelation reaction. Then, under the action of seed crystals, the gel undergoes a crystallization reaction. This process demonstrates that the preparation method for high silica-to-alumina ratio Y molecular sieves provided by this invention does not require the preparation of a directing agent, has a short synthesis time, and directly synthesizes high silica-to-alumina ratio Y molecular sieves in one step. The synthesis process is simple, reliable, and easy to implement. Specifically, this application uses 1-benzyl-4-hydroxy-2-methyl-1H-benzimidazole-6-carboxylic acid as the first template agent and 1-ethyl-3-methylimidazolium tetrafluoroborate as the second template agent. The seed crystals are silica-alumina molecular sieve seed crystals with FAU or EMT structures, and the silica-to-alumina oxide ratio ≥5 is sufficient. The crystallization time is short, and a higher silica-to-alumina ratio is obtained; that is, Y molecular sieves with a silica-to-alumina oxide ratio of 22-44 can be obtained in 1-7 days. Attached image description:

[0026] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1The image shows the XRD pattern of the product in Embodiment 1 of the present invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0028] Figure 2 This is an SEM image of the product in Embodiment 1 of the present invention;

[0029] Figure 3 The image shows the XRD pattern of the product in Comparative Example 1 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0030] Figure 4 This is a SEM image of the product in Comparative Example 1 of the present invention;

[0031] Figure 5 The image shows the XRD pattern of the product in Comparative Example 2 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0032] Figure 6 This is a SEM image of the product in Comparative Example 2 of the present invention;

[0033] Figure 7 The image shows the XRD pattern of the product in Comparative Example 3 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0034] Figure 8 This is a SEM image of the product in Comparative Example 3 of the present invention. Detailed Implementation

[0035] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0036] Example 1

[0037] This embodiment provides a one-step method for preparing high silica-to-alumina ratio NaY molecular sieves, including the following steps:

[0038] Step S110: Under 40℃ conditions, deionized water, sodium aluminate, sodium hydroxide, and 1-benzyl-4-hydroxy-2-methyl-1H-benzimidazole-6-carboxylic acid are mixed in a certain proportion and stirred for 2 hours. Then, 1-ethyl-3-methylimidazolium tetrafluoroborate is added and stirred evenly. Subsequently, silica sol is added dropwise and stirred for 30 minutes to obtain the initial gel. The raw material ratio is 20SiO2:1Al2O3:6M2O:2R1:3R2:600H2O.

[0039] Step S120: Add Y zeolite with a silicon-to-aluminum ratio of 6 as seed crystals to the initial gel. The amount (mass) of Y zeolite added accounts for 6% of the SiO2 content in the initial gel. Stir for 90 min.

[0040] Step S130: The synthesized gel was transferred to a hydrothermal reactor and dynamically crystallized at 110°C for 2 days. After cooling, the reaction slurry was filtered through a sintered glass funnel. The filter cake was washed three times with deionized water until the filtrate was neutral. The filter cake was then dried at 180°C for 2 hours. The high-silica Y molecular sieve was obtained after drying. This sample is designated as X1, with a silica-to-alumina ratio of 25 and a crystallinity of 98%.

[0041] Comparative Example 1

[0042] Template agent 1 was not used; only template agent 2 was used. The raw material ratio was adjusted to 20SiO2:1Al2O3:6M2O:5R2:600H2O, and the rest was the same as in Example 1. This was designated as sample 1.

[0043] X1 has a silicon-to-aluminum ratio of 5 and a crystallinity of 70%.

[0044] Comparative Example 2

[0045] Template agent 1 was used instead of template agent 2, and the raw material ratio was adjusted to 20SiO2:1Al2O3:6M2O:5R1:600H2O, with the rest being the same as in Example 1. This sample was designated as Sample X2, with a silicon-to-aluminum ratio of 7 and a crystallinity of 75%.

[0046] Comparative Example 3

[0047] No seed crystals were added; otherwise, the sample was the same as in Example 1. This sample was designated as Sample X3, with a silicon-to-aluminum ratio of 12 and a crystallinity of 83%.

[0048] Principles and steps not explicitly described in this invention are all obtainable by those skilled in the art through conventional technical means, and therefore will not be elaborated upon. Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for directly preparing high silica-to-alumina ratio NaY molecular sieves, characterized in that, Includes the following steps: Step S110: Mix deionized water, silicon source, aluminum source, alkali source, and template agent R1 in a certain proportion and stir for a period of time to obtain solution 1; add template agent R2 and mix and stir evenly to obtain the initial gel; Template agent R1 is 1-benzyl-4-hydroxy-2-methyl-1H-benzimidazole-6-carboxylic acid; Template agent R2 is 1-ethyl-3-methylimidazolium tetrafluoroborate; Step S120: Add the silicon-aluminum molecular sieve seed crystal with EMT structure to the initial gel obtained in step S110, stir, and obtain a synthetic gel, wherein the silicon-aluminum molecular sieve seed crystal with EMT structure has a silicon-aluminum oxide ratio ≥5. Step S130: The above-synthesized gel is dynamically crystallized at 70-120°C for 1-7 days to obtain the high silica-alumina ratio NaY molecular sieve.

2. The method for preparing high silica-to-alumina ratio NaY molecular sieves by direct method according to claim 1, characterized in that, In step S110, the molar ratio of each raw material is (10-150)SiO2:1Al2O3:(0.1-25)M2O:(0.5-5)R1:(0.2-6)R2:(40-5000)H2O; M is selected from at least one of the alkali metal elements sodium, potassium, and cesium.

3. The method for preparing high silica-to-alumina ratio NaY molecular sieves by direct method according to claim 1, characterized in that, The silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, silica sol, amorphous silica, solid silica gel, fumed silica, and sodium silicate.

4. The method for preparing high silica-to-alumina ratio NaY molecular sieves by direct method according to claim 1, characterized in that, The aluminum source is selected from at least one of sodium aluminate, aluminum oxide, aluminum hydroxide, aluminum isopropoxide, aluminum 2-butoxide, aluminum chloride, aluminum sulfate, and aluminum nitrate.

5. The method for preparing high silica-to-alumina ratio NaY molecular sieves by direct method according to claim 1, characterized in that, The alkali source is selected from at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide.

6. The method for preparing high silica-to-alumina ratio NaY molecular sieves by direct method according to claim 1, characterized in that, In step S120, the silicon-aluminum molecular sieve seed crystals with EMT structure are selected from at least one of Na-type and H-type zeolite molecular sieves.

7. The method for preparing high silica-to-alumina ratio NaY molecular sieves by direct method according to claim 1, characterized in that, In step S120, the amount of the silicon-aluminum molecular sieve seed crystals with EMT structure added is 5 to 30 wt.% of the mass of the silicon source in the initial gel, calculated as SiO2.

8. The method for preparing high silica-to-alumina ratio NaY molecular sieves by direct method according to claim 7, characterized in that, In step S120, the amount of the silicon-aluminum molecular sieve seed crystals with the EMT structure added is equal to the mass of the silicon source in the initial gel, calculated as SiO2. .

9. The method for preparing high silica-to-alumina ratio NaY molecular sieves by direct method according to claim 1, characterized in that, In step S130, after crystallization is complete, the solid product is filtered and separated, washed with deionized water until neutral, and dried to obtain high silica-alumina ratio NaY molecular sieve.

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