ZSM-5 molecular sieve with self-supporting structure and synthesis method thereof

Abstract

The invention belongs to the technical field of synthesis of zeolite molecular sieves, and relates to a ZSM-5 molecular sieve with a self-supporting structure and a synthesis method thereof. According to the method, the characteristic that the intersection of the self-supporting structure is rich in aluminum is taken as a starting point, a system only contains a silicon source, an aluminum source, an alkali source and a proper amount of water, the raw materials are mixed and then aged at 40-100 DEG C for 4-48 hours, then the raw materials are transferred into a high-pressure reaction kettle to be crystallized at 140-200 DEG C for 1-7 days, and finally the ZSM-5 molecular sieve with the self-supporting structure and the playing card house shape is obtained. According to the method, additional organic template agents and molecular sieve crystal seeds do not need to be added, a rod-shaped ZSM-5 molecular sieve precursor and amorphous species are generated in the aluminum-rich gel part in the crystallization process, then a self-supporting structure and a playing card house shape are formed on the surface of the rod-shaped ZSM-5 molecular sieve precursor, the product yield exceeds 95%, green and efficient synthesis of the ZSM-5 molecular sieve with the self-supporting structure and the playing card house shape is achieved, and the method is suitable for industrial production. The method is beneficial to industrial large-scale production and has a relatively strong industrial popularization prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesis of zeolite molecular sieves, and in particular relates to a ZSM-5 molecular sieve with a self-supporting structure and a synthesis method thereof. Background Art

[0002] Oil is an important pillar resource for national production and life. With the continuous consumption of oil resources and the increasingly serious environmental pollution problems worldwide, how to improve the utilization efficiency of oil has become an important challenge facing people. Among them, heavy oil and low-quality oil in oil will cause the problem of reduced refining efficiency and increased economic and environmental costs. Therefore, how to efficiently utilize heavy oil and low-quality oil has become an important technical problem in the refining process.

[0003] Molecular sieves have excellent catalytic activity and shape selectivity due to their regular pore structure, abundant acidic sites and good hydrothermal stability. In addition, their low production cost makes them widely used as catalysts in the petrochemical industry. However, the catalytic efficiency of molecular sieves in heavy oil and inferior oil is seriously restricted due to the problem of diffusion obstruction of macromolecules in the micropores of molecular sieves. In order to solve this problem, scientists have proposed corresponding strategies: by preparing nanomolecular sieves and creating mesopores inside molecular sieves to shorten the diffusion path of molecules in the molecular sieve channels to improve the catalytic efficiency of molecular sieves. Among them, the synthesis of ZSM-5 molecular sieves with a house of cards morphology that has both of the above characteristics due to self-support perfectly solves this problem.

[0004] Tsapatsis et al. used tetrapropylammonium hydroxide and tetrabutylammonium hydroxide as templates, and used tetraethyl orthosilicate and aluminum sulfate as silicon and aluminum sources to synthesize a self-supporting ZSM-5 molecular sieve with a house of cards morphology (Science, 2012, 336, 1684). Inspired by this, Xiao et al. designed and synthesized a butyl-dimethylpyridine as a template, and successfully synthesized a self-supporting ZSM-5 molecular sieve with silica sol, aluminum sulfate and potassium hydroxide as silicon source, aluminum source and alkali source respectively (J.Am.Chem.Soc., 2022, 144, 6270). In addition, Che et al. used C6H5-C6H4-OC 10 H 20 -N + (CH3)2-C6H 13 (Br -) as a template, using the π-π interaction of the benzene ring for self-assembly, and using ethyl orthosilicate and sodium aluminate as silicon and aluminum sources, a self-supporting ZSM-5 molecular sieve was also successfully synthesized (Nat. Commun., 2014, 5, 4262). In a published patent (patent number CN 106809859 A), piperidine and piperazine were used as templates, and silica sol and sodium aluminate were used as silicon and aluminum sources to synthesize a self-supporting ZSM-5 molecular sieve with sheet-like staggered growth. In another published patent (patent number CN 112624144A), a homemade C 12 H 25 -N + Br-C6H 12 -N + Br-C6H 13 As a template, ZSM-5 molecular sieve is used as a crystal nucleus to form mutually supporting nanosheets on its surface. However, the above methods all require the use of organic amines as templates, which are expensive and not only greatly increase the preparation cost of molecular sieves, but also cause serious environmental pollution problems during the removal process such as calcination.

[0005] In order to avoid the use of templates, Rimer et al. reported that in the absence of organic templates, by introducing molecular sieves containing MEL or MFI structures as seeds, they successfully synthesized self-supporting ZSM-5 molecular sieves (Adv. Mater., 2021, 33, 2100897). However, since this method uses the MEL structure remaining in the seed crystal as the branching center to form a self-supporting structure, seeds must be used. Without adding seeds, not only can the ZSM-5 molecular sieve with a self-supporting structure and a house of cards morphology not be obtained (the product is mordenite), but it will also greatly prolong the crystallization time, which is 4 times the crystallization time of adding seeds. The addition of seeds increases the complexity and operating cost of the synthesis process to a certain extent.

[0006] So far, there has been no report on the synthesis of ZSM-5 molecular sieves with a self-supporting structure and house-of-cards morphology without adding seed crystals or using an organic template. Summary of the invention

[0007] The present invention uses a synthesis strategy of high-temperature aging of aluminum-rich gel, and by precisely controlling aging and crystallization conditions, realizes the synthesis of a self-supporting structure and a house-of-cards morphology of ZSM-5 molecular sieves without an organic template and without molecular sieve seed crystals. High-temperature aging refers to mixing the raw materials for preparing a self-supporting structure and a house-of-cards morphology of ZSM-5 molecular sieves and stirring them at a certain temperature for a certain period of time to promote the interaction between silicon and aluminum species. Crystallization refers to further crystallizing and growing the aged mixed solution at a certain temperature, and then obtaining a self-supporting structure and a house-of-cards morphology of ZSM-5 molecular sieves.

[0008] In order to achieve the above object, the present invention provides a method for synthesizing a ZSM-5 molecular sieve with a self-supporting structure, comprising the following steps:

[0009] Step 1, the material molar ratio of the raw materials required for synthesizing the self-supporting ZSM-5 molecular sieve is SiO2:xAl2O3:yM:zH2O, wherein: M is the alkali source, x=0.025-0.1, y=0.05-0.4, z=10-80; according to the required synthesis ratio, the amounts of silicon source, aluminum source, alkali source and water are calculated and weighed;

[0010] Step 2, stirring the alkali source and water to form a mixed solution;

[0011] Step 3, adding an aluminum source to the mixed solution and stirring evenly;

[0012] Step 4, adding a silicon source to the mixed solution, stirring evenly, and stirring and aging at 40-100° C. for 4-48 hours to obtain a synthetic mother solution;

[0013] Step 5, charging the synthetic mother liquor into a reactor, crystallizing at 140-200° C. for 1-7 days, performing solid-liquid separation on the mixture obtained after crystallization, washing and drying the obtained solid phase product, and obtaining a self-supporting structure and a house of cards morphology ZSM-5 molecular sieve.

[0014] The method of the present invention takes the aluminum-rich characteristics at the intersection of the self-supporting structure as the starting point. The preparation system only contains a silicon source, an aluminum source, an alkali source and an appropriate amount of water. The material molar ratio in step 1 refers to the molar ratio of the silicon source calculated as SiO2, the aluminum source calculated as Al2O3, the alkali source, and water is 1: 0.025-0.1: 0.05-0.4: 10-80.

[0015] Specifically, the material ratio of the silicon source calculated as SiO2 to the aluminum source calculated as Al2O3 can be 1:0.025, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, or a range between any two of the above ratio ranges.

[0016] The molar ratio of the silicon source to the alkali source calculated as SiO2 can be 1:0.05, 1:0.08, 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, or a range between any two of the above ratio ranges.

[0017] The ratio of the amount of silicon source calculated as SiO2 to the amount of water can be 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, or a range between any two of the above ratio ranges.

[0018] Compared with the existing self-supporting structure molecular sieve synthesis technology, the method of the present invention does not add any organic template and molecular sieve seed during the synthesis process. The formation of the self-supporting structure is mainly regulated by the silicon-aluminum ratio in the system. During the crystallization process, the aluminum-rich gel part generates a rod-shaped ZSM-5 molecular sieve precursor, and the amorphous species then forms a self-supporting structure and a house of cards morphology on its surface. The product yield exceeds 95%.

[0019] According to a specific embodiment of the present invention, in step 4, the aging temperature is 50-90°C, and the aging time is 8-16 hours. Specifically, the aging temperature can be listed as 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or a range between any two of the above values.

[0020] According to a specific embodiment of the present invention, in step 5, the crystallization temperature is 150-180°C and the crystallization time is 3-6 days. Specifically, the crystallization temperature can be 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C or a range between any two of the above values.

[0021] The present invention has no particular limitation on the types of the alkali source, aluminum source, and silicon source, and any conventional source may be selected.

[0022] Generally, the alkali source is at least one of lithium hydroxide, sodium hydroxide and potassium hydroxide.

[0023] The aluminum source is at least one of aluminum chloride, aluminum sulfate, aluminum foil, pseudo-boehmite, sodium aluminate and aluminum isopropoxide.

[0024] The silicon source is at least one of tetraethyl orthosilicate, silica sol, amorphous silicon dioxide and water glass.

[0025] The present invention also provides a ZSM-5 molecular sieve obtained by the above-mentioned synthesis method, wherein the ZSM-5 molecular sieve has a self-supporting structure and a house of cards morphology.

[0026] The beneficial effects of the present invention are:

[0027] (1) The present invention adopts a strategy combining high-temperature aging and crystallization to treat the aluminum-containing gel. By adjusting the amount of aluminum source added, aging temperature, crystallization temperature, and crystallization time, the grain morphology and crystal phase of the obtained sample can be adjusted. This method is simple and easy to operate, and is conducive to industrial scale-up production.

[0028] (2) The present invention realizes the synthesis of self-supporting ZSM-5 molecular sieves with house-of-cards morphology without organic templates and seeds, which reduces the cost and energy consumption in the synthesis process, has significant economic benefits and environmental friendliness, and the method without seed addition simplifies the synthesis operation, greatly reduces the operating cost, and is easier to achieve industrial scale-up production.

[0029] (3) The present invention adopts a strategy of combining high-temperature aging and crystallization to treat aluminum-containing gels without organic templates and seed crystals. By adjusting the amount of aluminum source added, aging temperature, crystallization temperature, and crystallization time, a product yield of more than 95% is achieved. This method significantly improves production efficiency and avoids waste of resources, which is of great significance for industrial scale-up production.

[0030] (4) The present invention uses aluminum-containing gel after high-temperature aging without organic templates and seed crystals as the basis for crystallization synthesis. It is found that during the crystallization process, the aluminum-rich gel part generates a rod-shaped ZSM-5 molecular sieve precursor, and then forms a self-supporting structure and a ZSM-5 molecular sieve with a house-of-cards morphology on its surface. This is different from the current self-supporting crystallization process centered on the MEL structure molecular sieve, and enriches the research on the synthesis mechanism of molecular sieves.

[0031] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings.

[0033] Figure 1 It is the XRD spectrum of the sample synthesized in Example 1.

[0034] Figure 2 This is a SEM photograph of the sample synthesized in Example 1.

[0035] Figure 3 This is a SEM photograph of the crystallization intermediate product during the crystallization process of Example 1.

[0036] Figure 4 This is the SEM photo of the sample synthesized in Comparative Example 1. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0039] The technical terms in the present invention shall be understood according to their definitions if they are defined, and shall be understood according to their general meanings in the art if they are not defined.

[0040] Herein, "at least one" means one or more than two.

[0041] Example 1

[0042] Synthesis method: 0.33g sodium hydroxide is dissolved in 35g water, then 0.56g sodium aluminate is added, stirred for 1h, and finally 11.7g tetraethyl orthosilicate is added. The mixed solution is aged at 90°C for 12 hours, then loaded into a polytetrafluoroethylene-lined hydrothermal reactor, crystallized at 175°C for 4.5 days, then cooled to room temperature, washed thoroughly with deionized water, and dried at 80°C to obtain the final product.

[0043] Figure 1 This is the XRD spectrum of the obtained product. It can be seen that the obtained sample has a typical ZSM-5 molecular sieve diffraction peak, a high degree of crystallinity and no impurity crystals. Figure 2 is a SEM photo of the obtained product. It can be seen that the overall size of the sample particles is about 25μm, and the surface is a 50-100nm nanosheet self-supporting structure with a house of cards morphology. Figure 3 This is the SEM picture of the crystallization intermediate product. It can be seen that in addition to amorphous species, the obtained sample also has rod-shaped particles with varying degrees of flaky protrusions on its surface, which are the core of forming a self-supporting structure and house-of-cards morphology.

[0044] Example 2

[0045] Synthesis method: Referring to the method of Example 1, the difference is that the molar ratio of the added silica to the alkali source is 1:0.1. The results show that the obtained product is mainly a ZSM-5 molecular sieve with a self-supporting structure and a house of cards morphology.

[0046] Example 3

[0047] Synthesis method: refer to the method of Example 1, except that the aging temperature is 60°C. The results show that the obtained product is mainly a ZSM-5 molecular sieve with a self-supporting structure and a house of cards morphology.

[0048] Example 4

[0049] Synthesis method: Referring to the method of Example 1, except that the crystallization temperature is 160°C, the results show that the obtained product is mainly a ZSM-5 molecular sieve with a self-supporting structure and a house of cards morphology.

[0050] Comparative Example 1

[0051] Synthesis method: refer to the method of Example 1, except that the molar ratio of silicon dioxide to aluminum added is 1:0.02. The results show that the obtained product is ZSM-5 molecular sieve. Figure 4 The SEM picture of the obtained sample shows that the sample has a conventional coffin-like morphology without a self-supporting structure or a house of cards morphology.

[0052] Comparative Example 2

[0053] Synthesis method: Refer to the method of Comparative Example 1, except that 10% by mass percentage of MEL or MFI molecular sieve seeds based on silica were added during the synthesis process. The results showed that the obtained product was still a conventional coffin-shaped ZSM-5 molecular sieve without a self-supporting structure and a house of cards morphology.

[0054] Comparative Example 3

[0055] Synthesis method: refer to the method of Example 1, except that there is no aging process. The results show that the obtained product is a mixed crystal of ZSM-5 molecular sieve and mordenite with a self-supporting structure.

[0056] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for synthesizing a self-supporting ZSM-5 molecular sieve, comprising the following steps: Step 1, the material molar ratio of the raw materials required for synthesizing the self-supporting ZSM-5 molecular sieve is SiO2:xAl2O3:yM:zH2O, wherein: M is the alkali source, x=0.025-0.1, y=0.05-0.4, z=10-80; according to the required synthesis ratio, the amounts of silicon source, aluminum source, alkali source and water are calculated and weighed; Step 2, stirring the alkali source and water to form a mixed solution; Step 3, adding an aluminum source to the mixed solution and stirring evenly; Step 4, adding a silicon source to the mixed solution, stirring evenly, and stirring and aging at 40-100° C. for 4-48 hours to obtain a synthetic mother solution; Step 5, charging the synthetic mother liquor into a reactor, crystallizing at 140-200° C. for 1-7 days, performing solid-liquid separation on the mixture obtained after crystallization, washing and drying the obtained solid phase product, and obtaining a self-supporting structure and a house of cards morphology ZSM-5 molecular sieve.

2. The method for synthesizing the self-supporting ZSM-5 molecular sieve according to claim 1, characterized in that: No organic template or molecular sieve seed is added during the synthesis process.

3. The method for synthesizing the self-supporting ZSM-5 molecular sieve according to claim 1, characterized in that: In step 4, the aging temperature is 50-90° C., and the aging time is 8-16 hours.

4. The method for synthesizing the self-supporting ZSM-5 molecular sieve according to claim 1, characterized in that: In step 5, the crystallization temperature is 150-180° C., and the crystallization time is 3-6 days.

5. The method for synthesizing the self-supporting ZSM-5 molecular sieve according to claim 1, characterized in that: The alkali source is at least one of lithium hydroxide, sodium hydroxide and potassium hydroxide.

6. The method for synthesizing the self-supporting ZSM-5 molecular sieve according to claim 1, characterized in that: The aluminum source is at least one of aluminum chloride, aluminum sulfate, aluminum foil, pseudo-boehmite, sodium aluminate and aluminum isopropoxide.

7. The method for synthesizing the self-supporting ZSM-5 molecular sieve according to claim 1, characterized in that: The silicon source is at least one of tetraethyl orthosilicate, silica sol, amorphous silicon dioxide and water glass.

8. A ZSM-5 molecular sieve obtained by the synthesis method according to any one of claims 1 to 7, wherein the ZSM-5 molecular sieve has a self-supporting structure and a house of cards morphology.

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