High-silicon ZSM-5 molecular sieve adsorbent for adsorbing methylbenzene and preparation method of high-silicon ZSM-5 molecular sieve adsorbent

Abstract

The invention provides a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene and a preparation method thereof, and belongs to the technical field of adsorbents, the preparation method comprises the following steps: S1, preparing a uniform sol from a silicon source I, a reaction aid I and water according to a molar ratio of 1: 0.27: 37, placing in a hydrothermal kettle, crystallizing at 120 DEG C for 48 hours, filtering, washing, and drying to obtain Silicate-1 seed crystal; s2, preparing a molecular sieve mother solution from a silicon source II, an aluminum source, a reaction aid II and water according to a molar ratio of 100: 0.083: 20: 4000, adding Silicate-1 seed crystal accounting for 3wt% of the molecular sieve mother solution, uniformly mixing, putting into a hydrothermal kettle, reacting at 100-160 DEG C for 6-24 hours, filtering, washing, drying, and roasting at 550 DEG C for 6 hours to obtain a high-silicon ZSM-5 molecular sieve; and S3, screening the high-silicon ZSM-5 molecular sieve, and drying in a muffle furnace at 400 DEG C for 4 hours to obtain the high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene. The methylbenzene adsorption capacity of the prepared adsorbent can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of adsorbents, and particularly relates to a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene and a preparation method thereof. Background Art

[0002] Toluene, a common volatile organic compound (VOC), poses a serious threat to the environment and human health. Therefore, the search for efficient toluene adsorption materials is of great significance. High-silica ZSM-5 molecular sieve, due to its unique structure and properties, has become a potential ideal adsorbent. ZSM-5 molecular sieve, a zeolite molecular sieve with an MFI structure, was first developed by Mobil Corporation in the United States. It features three-dimensional, cross-channel, mesoporous, and microporous pores with pore sizes close to the molecular dynamic diameters of common industrial pollutants. It also boasts a wide range of silicon-to-aluminum ratios, high hydrophobicity and hydrothermal stability, excellent ion exchange properties, and a rich and tunable surface property profile. Due to its unique properties, high-silica ZSM-5 molecular sieve has been widely used in numerous fields. It demonstrates excellent performance in adsorbing toluene. Its pore size matches the size of toluene molecules, providing a suitable adsorption space for toluene molecules.

[0003] The silicon-aluminum ratio is a key factor affecting the adsorption performance of molecular sieves. A high silicon-aluminum ratio molecular sieve means fewer aluminum-oxygen tetrahedral units, which reduces the polarity of the molecular sieve and has better adsorption of non-polar substances such as toluene. It also has better hydrophobicity. However, the direct synthesis of high silicon-aluminum ratio ZSM-5 molecular sieve is relatively difficult, and generally requires the addition of a template to the synthesis system to improve silicon utilization.

[0004] CN114772609A reports that tetrapropylammonium bromide is first used as a template agent, and a silicon source is added to form a pure silicon ZSM-5 crystal cluster. The crystal cluster is then mixed with a pore-expanding agent and water, and a silicon source and an aluminum source are added. After a certain period of high-temperature crystallization, a high-silicon ZSM-5 molecular sieve is obtained. The preparation process is cumbersome and the cost is relatively high.

[0005] CN113491998A reports a method for seed-assisted synthesis of ZSM-5 molecular sieves. The method involves mixing an aluminum source, a silicon source, water, and sodium hydroxide for a predetermined period of time, then adding seed crystals (one of silicate-1, Y-type zeolite, or ZSM-11) and continuing to stir. The ZSM-5 molecular sieve is obtained by high-temperature crystallization for a predetermined period of time. However, the ZSM-5 molecular sieve synthesized by this method has a silicon-to-aluminum ratio of 40-100, making it difficult to synthesize molecular sieves with higher silicon-to-aluminum ratios.

[0006] CN117263203A reports a method for preparing amine-free, high-silicon ZSM-5 molecular sieves by varying the basicity. The method involves mixing a silicon source, an aluminum source, an alkali source, water, and seed crystals to obtain a first mixture, subjecting it to a first hydrothermal reaction to obtain a product. The product of the first hydrothermal reaction is then mixed with additional water to obtain a second mixture, subjecting it to a hydrothermal reaction to produce a ZSM-5 molecular sieve having a silicon-to-aluminum ratio of 60. This method utilizes a template-free ZSM-5 molecular sieve, but the synthesized silicon-to-aluminum ratio is low, and two hydrothermal reactions are required, resulting in a long preparation time and unsuitable for industrial production.

[0007] CN115818663A reports that a first silicon source, an aluminum source, a first alkali source, water, and a first seed crystal are mixed, and the resulting first mixture is subjected to a first hydrothermal reaction to obtain a first hydrothermal reaction product. The first hydrothermal reaction product is then mixed with a second silicon source, a second alkali source, water, and a second species, and the resulting second mixture is subjected to a second hydrothermal reaction to produce a molecular sieve with a silicon-to-aluminum ratio of 40-60. This method produces a ZSM-5 molecular sieve with a low silicon-to-aluminum ratio, requires more materials, and requires two crystallization steps, making the process cumbersome.

[0008] In summary, while the use of organic amine templates reduces raw material costs, it is difficult to synthesize high-silicon-to-aluminum ZSM-5 molecular sieves. Furthermore, the process for synthesizing high-silicon ZSM-5 molecular sieves is complex, increasing process costs and hindering industrial production. Therefore, developing an efficient and low-cost method for producing high-silicon ZSM-5 molecular sieves is crucial. Summary of the Invention

[0009] In order to solve the problems existing in the background technology, the present invention provides a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene and a preparation method thereof, which can significantly improve the adsorption capacity of the prepared adsorbent for toluene.

[0010] In order to achieve the above objectives, in a first aspect, the present invention provides a method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene, comprising the following steps:

[0011] Synthesis of S1, Silicate-1 seed crystals;

[0012] Silicon source I, reaction aid I and water were prepared into a uniform sol at a molar ratio of 1:0.27:37, placed in a hydrothermal autoclave at 120°C for crystallization for 48 hours, and filtered, washed and dried to obtain Silicate-1 seed crystals;

[0013] S2, synthesis of high-silicon ZSM-5 molecular sieve;

[0014] Silicon source II, aluminum source, reaction aid II and water are prepared into molecular sieve mother liquor in a molar ratio of 100:0.083:20:4000, Silicate-1 seed crystals obtained from S1 are added, and the Silicate-1 seed crystals are 3wt% of the molecular sieve mother liquor. After mixing, the mixture is placed in a hydrothermal autoclave at 100-160°C for 6-24h, filtered, washed, dried, and finally calcined at 550°C for 6h to obtain a high-silicon ZSM-5 molecular sieve;

[0015] S3, preparation of high silicon ZSM-5 molecular sieve adsorbent;

[0016] The high-silicon ZSM-5 molecular sieve obtained in S2 was sieved and then dried in a muffle furnace at 400°C for 4 hours to remove impurities, thereby obtaining a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene.

[0017] Furthermore, in S1, the silicon source I is ethyl orthosilicate.

[0018] Furthermore, in S1, the reaction auxiliary agent I is tetrapropylammonium hydroxide.

[0019] Furthermore, in S2, the silicon source II is water glass.

[0020] Furthermore, in S2, the aluminum source is aluminum sulfate.

[0021] Furthermore, in S2, the reaction auxiliary agent II is n-butylamine.

[0022] Furthermore, in S2, the pH of the molecular sieve mother liquor is adjusted to 11-12 using a pH buffer.

[0023] Furthermore, the pH buffer is sulfuric acid.

[0024] Furthermore, in S3, the particle size of the high-silicon ZSM-5 molecular sieve obtained by screening is 0.4 to 0.6 μm.

[0025] In a second aspect, the present invention provides a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene, which is prepared by the above-mentioned preparation method.

[0026] This application has the following beneficial effects:

[0027] 1. This invention utilizes a seed-assisted hydrothermal synthesis method to prepare high-silicon ZSM-5 molecular sieves, which not only improves the molecular sieve's crystallinity but also enhances production efficiency. The silicon-to-aluminum ratio of the product can be adjusted by adjusting the feed ratio. The synthesized molecular sieve has a small particle size, a large specific surface area, good hydrophobicity, and excellent VOCs adsorption performance.

[0028] 2. The ZSM-5 molecular sieve prepared by the method of the present invention is mainly used for toluene adsorption. It has low synthesis cost and can be directly used in the adsorption removal process without ammonia exchange. It has good adsorption and regeneration performance and is easy to realize industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 , schematic diagram of X-ray diffraction (XRD) spectra of the high-silicon ZSM-5 molecular sieve adsorbent prepared in Examples 1 to 7 of the present invention and commercial standard ZSM-5;

[0030] Figure 2 , schematic diagrams of scanning electron microscope (SEM) images of high-silicon ZSM-5 molecular sieve adsorbents prepared in Examples 1 to 7 of the present invention;

[0031] Figure 3 , a comparative trend chart of adsorption performance test data of the adsorbents prepared in Examples 1 to 7 of the present invention and Comparative Examples 1 to 2. DETAILED DESCRIPTION

[0032] The present application is further described in detail below with reference to the embodiments.

[0033] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0034] Example 1: A method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene, comprising the following steps:

[0035] Synthesis of S1, Silicate-1 seed crystals;

[0036] Silicon source I ethyl orthosilicate, reaction aid I tetrapropylammonium hydroxide and water were prepared into a uniform sol in a molar ratio of 1:0.27:37, placed in a hydrothermal autoclave for crystallization at 120°C for 48 hours, and filtered, washed and dried to obtain Silicate-1 seed crystals.

[0037] S2, synthesis of high-silicon ZSM-5 molecular sieve;

[0038] According to the molar ratio of substances of 100:0.083:20:4000, the raw materials of the molecular sieve mother liquor, silicon source II water glass, aluminum source aluminum sulfate, reaction auxiliary agent II n-butylamine and water are taken respectively, and then the Silicate-1 seed crystals obtained in S1 are taken. The Silicate-1 seed crystals are 3wt% of the molecular sieve mother liquor.

[0039] After sampling, water glass and Silicate-1 seed crystals were added to water and thoroughly stirred. Aluminum sulfate was dissolved in 5 mol / L sulfuric acid, and n-butylamine was slowly added dropwise to obtain a mixed solution. The mixed solution was then added to the solution containing water glass and Silicate-1 seed crystals, with a pH of 11. The mixture was then placed in a reactor for crystallization at 140°C for 24 hours. The resulting suspension was filtered and washed, and the resulting powder was dried in a 110°C oven for 12 hours, followed by calcination at 550°C for 6 hours to obtain ZSM-5 molecular sieve.

[0040] S3, preparation of high silicon ZSM-5 molecular sieve adsorbent;

[0041] The ZSM-5 molecular sieve obtained from S2 was sieved to obtain a particle size of 0.4 to 0.6 μm, and then dried in a muffle furnace at 400°C for 4 hours to remove impurities, thereby obtaining a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene, which was recorded as ZSM-5-140.

[0042] Example 2: The difference between this example and Example 1 is that in S2, the crystallization reaction temperature is 100°C; the obtained product is recorded as ZSM-5-100.

[0043] Example 3: The difference between this example and Example 1 is that in S2, the crystallization reaction temperature is 110°C; the obtained product is recorded as ZSM-5-110.

[0044] Example 4: The difference between this example and Example 1 is that in S2, the crystallization reaction temperature is 120°C; the obtained product is recorded as ZSM-5-120.

[0045] Example 5: The difference between this example and Example 1 is that in S2, the crystallization reaction temperature is 130°C; the obtained product is recorded as ZSM-5-130.

[0046] Example 6: The difference between this example and Example 1 is that in S2, the crystallization reaction temperature is 150°C; the obtained product is recorded as ZSM-5-150.

[0047] Example 7: The difference between this example and Example 1 is that in S2, the crystallization reaction temperature is 160°C; the obtained product is recorded as ZSM-5-160.

[0048] Comparative Example 1: This comparative example differs from Example 1 in that Silicate-1 seed crystals were not introduced.

[0049] Specifically, water glass is added to water and stirred thoroughly to a water-silicon ratio of 40. Aluminum sulfate is dissolved in 5 mol / L sulfuric acid, and n-butylamine is slowly added dropwise to obtain a mixed solution, which is then added to the water glass solution. The mixture is then placed in a reactor for crystallization at 110°C for 36 hours. The resulting suspension is filtered and washed, and the resulting powder is dried in a 110°C oven for 12 hours, followed by calcination at 550°C for 6 hours to obtain the ZSM-5 molecular sieve.

[0050] Comparative Example 2: The difference between this comparative example and comparative example 1 is that the crystallization temperature is 120°C.

[0051] Test Example 1: Test subjects: products obtained in Examples 1 to 7 and commercial standard ZSM-5.

[0052] Test content: Test the X-ray diffraction (XRD) spectrum of each test object product.

[0053] Test results: see Figure 1 .

[0054] Test example 2: Test objects: products obtained in Examples 1 to 7.

[0055] Test content: Test the scanning electron microscope (SEM) images of each test object product.

[0056] Test results: see Figure 2 .

[0057] Test Example 3: Test objects: products obtained from Examples 1 to 7 and Comparative Examples 1 to 2.

[0058] Test Details: The toluene adsorption capacity of the present invention's samples was measured using a dynamic adsorption method. The entire adsorption system consists of a generator, adsorption bed, and detector. Nitrogen was used as the carrier gas, and a flowmeter controlled the gas flow rate to simulate a gas containing a certain toluene concentration and relative humidity. The toluene concentration in the exhaust gas was then measured using a gas chromatograph.

[0059] 1g of each test product was loaded into the adsorption bed, and the adsorption tube was placed in a fixed reaction bed at 35°C to evaluate the adsorption performance.

[0060] Test results: The adsorption performance test results are shown in Table 1.

[0061] Table 1. Test data of Experiment 3

[0062]

[0063]

[0064] Result analysis: Analyze Example 1-Example 7 and Comparative Example 1-Comparative Example 2 and combine the data in Table 1 and Figure 1-Figure 3 The molecular sieve prepared with the aid of Silicat-1 seed crystals in the present invention contains a structure dominated by micropores and a small amount of mesopores, which increases the silicon-to-aluminum ratio of the molecular sieve, eliminates the need for subsequent dealumination, and improves the hydrophobicity of the molecular sieve. Furthermore, this method also reduces the crystal size, which means that the diffusion path of toluene within the molecular sieve is shortened, while the specific surface area of ​​the molecular sieve is increased, thereby improving the molecular sieve's adsorption capacity for toluene. The adsorption capacity for toluene (volatile organic compounds VOCs) is excellent under high humidity conditions.

[0065] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0066] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene, characterized in that: The following steps are involved: Synthesis of S1, Silicate-1 seed crystals; Silicon source I, reaction aid I and water were prepared into a uniform sol in a molar ratio of 1:0.27:37, placed in a hydrothermal autoclave at 120°C for crystallization for 48 hours, filtered, washed and dried to obtain Silicate-1 seed crystals; S2, synthesis of high silicon ZSM-5 molecular sieve; Silicon source II, aluminum source, reaction aid II and water are configured to form molecular sieve mother liquor according to the molar ratio of 100:0.083:20:4000, Silicate-1 seed crystals obtained from S1 are added, and the Silicate-1 seed crystals are 3wt% of the molecular sieve mother liquor. After mixing, place in a hydrothermal autoclave at 100-160°C for reaction for 6-24h, filter, wash, dry, and finally roast at 550°C for 6h to obtain a high-silicon ZSM-5 molecular sieve; S3, preparation of high silicon ZSM-5 molecular sieve adsorbent; The high-silicon ZSM-5 molecular sieve obtained from S2 was sieved and then dried in a muffle furnace at 400° C. for 4 hours to obtain a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene.

2. The method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene according to claim 1, characterized in that: In S1, the silicon source I is ethyl orthosilicate.

3. The method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene according to claim 1, characterized in that: In S1, the reaction aid I is tetrapropylammonium hydroxide.

4. The method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene according to claim 1, characterized in that: In S2, the silicon source II is water glass.

5. The method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene according to claim 1, characterized in that: In S2, the aluminum source is aluminum sulfate.

6. The method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene according to claim 1, characterized in that: In S2, the reaction aid II is n-butylamine.

7. The method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene according to claim 1, characterized in that: In S2, the pH of the molecular sieve mother solution is adjusted to 11-12 using a pH buffer.

8. The method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene according to claim 7, characterized in that: The pH buffer is sulfuric acid.

9. The method for preparing a high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene according to claim 1, characterized in that: In S3, the particle size of the high-silicon ZSM-5 molecular sieve obtained by screening is 0.4 to 0.6 μm.

10. A high-silicon ZSM-5 molecular sieve adsorbent for adsorbing toluene, characterized in that: The method is prepared according to any one of claims 1 to 9.

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