A ZSM-23 molecular sieve and its synthesis method

Abstract

The present invention relates to the field of molecular sieve technology, and more particularly to a ZSM-23 molecular sieve and a synthesis method thereof, comprising the following steps: step S1, mixing and grinding a silicon source, an aluminum source, and a seed crystal, and treating with water vapor to obtain a raw material powder mixture; step S2, mixing a crystallization aid, a template agent, and deionized water to obtain a mixed solution; step S3, adding the powder mixture to the mixed solution, stirring evenly, aging, and obtaining a synthetic gel; step S4, sealing the synthetic gel in a kettle, and hydrothermal crystallization; step S5, filtering, washing, drying, and roasting the crystallized product to obtain a ZSM-23 molecular sieve. The present invention is to pre-treat a mixture containing a silicon source, an aluminum source, and a seed crystal by water vapor, and then add a crystallization aid and a template agent for aging and crystallization to achieve the synthesis of a ZSM-23 molecular sieve with a large silicon-aluminum ratio of 20 to 120, and the mesoporous pore volume of the ZSM-23 molecular sieve is ≥0.45cm 3 / g.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieves, and in particular to a ZSM-23 molecular sieve and a synthesis method thereof. Background Art

[0002] ZSM-23 molecular sieve has MTT topological structure. It is a high-silicon zeolite molecular sieve first synthesized by Plank et al. of Mobil Corporation in the United States in 1978. Its skeleton structure includes five-membered rings, six-membered rings, and ten-membered rings, among which the ten-membered rings form a one-dimensional teardrop-shaped channel with a pore size of 0.45nm×0.52nm. Due to its unique channel structure and adjustable acid strength, it is widely used in the industrial field, showing excellent performance in reactions such as alkane isomerization, butene isomerization, and catalytic cracking, and has good industrial application prospects.

[0003] At present, there are the following problems in the synthesis of ZSM-23 molecular sieves: (1) ZSM-23 has a metastable phase structure, and impurities are prone to occur during synthesis. In addition, the silicon-aluminum ratio of the synthetic feed is narrow, and the silicon-aluminum ratio of the product is usually high; (2) ZSM-23 usually needs to be synthesized under weak alkaline conditions, and inorganic bases are basically required during synthesis, which makes the system alkalinity too high. Concentrated sulfuric acid is often required to adjust the pH, and the process is difficult to control. Existing ZSM-23 synthesis is mostly focused on finding new templates or optimizing its synthesis conditions and performance by adjusting the crystallization process; on the one hand, new templates are designed to change the pore structure and shape of the molecular sieve, thereby regulating its catalytic activity and selectivity. These templates often have complex molecular structures and can interact specifically with the aluminosilicate framework to guide the formation of molecular sieves with specific structures. However, the development cost of new templates is high, and their synthesis and recovery processes may have a certain impact on the environment.

[0004] On the other hand, the synthesis of ZSM-23 is optimized by adjusting the crystallization process, including changing parameters such as crystallization temperature, time, stirring speed, and adding various additives to regulate the growth rate and morphology of the crystals. These adjustments are intended to improve the crystallinity and purity of the molecular sieve and improve its pore structure and acid properties. However, these methods have limited room for improvement and often need to be carried out under strict experimental conditions, which increases the complexity and cost of the synthesis. Therefore, it is particularly important to develop a more efficient, environmentally friendly and low-cost synthesis method for ZSM-23 molecular sieves. Summary of the invention

[0005] The object of the present invention is to overcome the deficiencies in the prior art, and to provide a ZSM-23 molecular sieve and a synthesis method thereof. The present invention first pre-treats a mixture containing a silicon source, an aluminum source, and a seed by water vapor, and utilizes the structural guidance effect of the seed to first induce the silicon source and the aluminum source to interact, forming partial structural fragments, and then further through the effect of the template agent, complete crystallization. Selecting weakly alkaline alcohol amine as a crystallization aid can not only avoid the influence of the traditional scheme on the pH value of the synthesis system using inorganic alkali, but also does not need to use concentrated sulfuric acid to adjust the system pH, the synthesis process is controllable, the generation of heterophase can be avoided, and the silicon-aluminum ratio range of the synthesis feed can be expanded. In addition, the ZSM-23 molecular sieve synthesized using the present invention has a higher mesoporous pore volume and better diffusion performance than the traditional method.

[0006] The present invention is achieved through the following technical solutions: On the one hand, a method for synthesizing ZSM-23 molecular sieve is provided, comprising the following steps:

[0007] Step S1, mixing: mixing silicon source, aluminum source, and seed crystal according to a certain ratio, grinding, and steam treatment to obtain a raw material powder mixture; wherein the steam H 2 The mass ratio of O to the mixture of aluminum source, seed crystal, and silicon source is 10-50:1;

[0008] Step S2, mixed solution: mix the crystallization aid, template agent and deionized water, stir evenly to obtain a mixed solution;

[0009] Step S3, adding the powder mixture obtained in step S1 to the mixed solution obtained in step S2, stirring evenly, and aging to obtain a synthetic gel;

[0010] Step S4, the synthesized gel is placed in a kettle, sealed, and hydrothermally crystallized;

[0011] Step S5: The crystallized product is filtered, washed, dried and calcined to obtain ZSM-23 molecular sieve.

[0012] Through the above technical scheme, the present invention first pre-treats a mixture containing a silicon source, an aluminum source, and a seed by water vapor, and utilizes the structural guidance effect of the seed to first induce the silicon source and the aluminum source to interact, forming partial structural fragments, and then further through the effect of the template agent, complete crystallization. Selecting weakly alkaline alcohol amine as a crystallization aid can avoid the influence of the traditional scheme on the pH value of the synthesis system using inorganic bases, and it is not necessary to use concentrated sulfuric acid to adjust the system pH. The synthesis process is controllable, the generation of heterophases can be avoided, and the silicon-aluminum ratio range of the synthesis feed can also be expanded. In addition, the ZSM-23 molecular sieve synthesized using the present invention has a higher mesoporous pore volume and better diffusion performance than the traditional method.

[0013] Furthermore, the treatment temperature of the water vapor is 100-120° C., and the treatment time is 1-6 hours.

[0014] Through the above technical scheme, the solid powder mixture of the silicon source, the aluminum source and the seed crystal is treated with water vapor under the above treatment conditions, which can induce the seed crystal to play a structural guiding role, so that the silicon source and the aluminum source undergo partial solid phase structural rearrangement under the action of the seed crystal, forming the primary structural unit of the ZSM-23 molecular sieve, promoting the utilization of aluminum species in the crystallization process of step S4, thereby obtaining a product with a wider range of silicon-to-aluminum ratios.

[0015] Furthermore, in step S1, the aluminum source is selected from at least one of aluminum sulfate 18hydrate, aluminum nitrate, sodium aluminate, aluminum trichloride, pseudo-boehmite, and aluminum hydroxide.

[0016] Through the above technical solution, the aluminum source cannot use a liquid aluminum source such as aluminum sol, and the selected solid aluminum sources are all commonly used aluminum sources for molecular sieve synthesis.

[0017] Further, in step S1, the seed crystal is selected from Na-ZSM-23, H-ZSM-23, NH 4 - at least one of ZSM-23; the amount of the seed crystal added is 1-10% of the mass of the silicon source, and the silicon source is SiO 2 count.

[0018] Through the above technical solution, the seed crystal has two functions: (1) under the treatment conditions of step S1, it plays a preliminary structural guiding role, inducing the silicon source and the aluminum source to participate in the preliminary structural rearrangement to form molecular sieve structural fragments, thereby promoting crystallization; (2) in the crystallization process of step S4, together with the template agent, it plays a synergistic structural guiding role.

[0019] Furthermore, in step S1, the silicon source is a solid silicon source selected from at least one of silica gel powder and white carbon black.

[0020] Through the above technical solution, the silicon source cannot use a liquid silicon source such as silica sol. The selected silicon source is a solid silicon source, which is a commonly used silicon source for molecular sieve synthesis. The small amount of Na 2 O can provide cations to partially balance the positive charge of the framework during crystallization.

[0021] Further, in step S2, the crystallization aid is an alcoholamine compound, selected from at least one of ethanolamine, diethanolamine, triethanolamine, 3-aminopropanol, isopropanolamine, 2-amino-1-butanol, and 6-amino-1-hexanol.

[0022] Through the above technical scheme, an alcoholamine crystallization aid is selected, and different alcoholamines are only specific descriptions. The alcoholamine crystallization aid used in the above technical scheme has three technical advantages: (1) alcoholamine substances can provide weak alkaline conditions for molecular sieve crystallization; (2) the alcohol hydroxyl groups present therein can shorten the crystallization induction period, promote crystallization, and inhibit the formation of impurities; (3) it can play a partial mesoporous template role and increase the mesoporous pore volume of the product.

[0023] Furthermore, in step S2, the template agent is selected from one or both of isopropylamine and pyrrolidine; the molar ratio of pyrrolidine to isopropylamine is 0-0.7:1.

[0024] Through the above technical solution, the template is a commonly used template for synthesizing ZSM-23, which is cheap and easy to obtain. Its function is to guide the structure and induce the crystallization of silicon source and aluminum source to form ZSM-23 molecular sieve. Within the above template combination and molar ratio range, on the one hand, it can inhibit the generation of various impurities, and on the other hand, it can ensure the high crystallinity of the crystallized product.

[0025] Further, in step S3, the components in the synthetic gel, the silicon source is SiO 2 The aluminum source is Al 2 O 3 Calculated by mole, the SiO 2 :Al 2 O 3 :Template agent:Crystallization aid:H 2 The molar ratio of O is 1:0.008~0.05:0.10~0.80:0.05~0.4:10~80.

[0026] Through the above technical scheme, during the synthesis process, the template agent, as a structure-directing agent, can guide the silicon source and the aluminum source to arrange and combine in a specific way, thereby prompting them to crystallize and form a ZSM-23 molecular sieve with a specific structure. At the same time, water, as a solvent, not only provides the necessary fluidity for the entire reaction system, but also participates in the growth process of the molecular sieve crystals. The different ratios of crystallization aids have a profound impact on the crystallization process of the molecular sieve and the properties of the final product. By adjusting the molar ratio between the silicon source, aluminum source, template agent, crystallization aid and water, it can be ensured that the components in the reaction system interact with each other in the best way, thereby successfully synthesizing a ZSM-23 molecular sieve with a high degree of crystallinity and pure phase.

[0027] Further, in step S4, the hydrothermal crystallization is dynamic crystallization, the crystallization temperature is 140-190° C., the crystallization time is 12-96 h, and the dynamic crystallization stirring rate is 30-150 rpm.

[0028] Through the above technical scheme, crystallization conditions are crucial for the synthesis of highly crystalline pure phase ZSM-23 molecular sieves. Parameters such as crystallization temperature, crystallization time, and dynamic crystallization stirring rate need to be precisely controlled to ensure that the molecular sieve crystals can grow in the expected manner. Within the above-mentioned crystallization temperature range (140-190°C), crystallization time range (12-96h), and dynamic crystallization stirring rate range (30-150rpm), the molecular sieve crystals can obtain the best growth environment, thereby successfully synthesizing ZSM-23 molecular sieves with high crystallinity and pure phase. The selection of these condition ranges is based on a large amount of experimental data and theoretical calculations, so they can be considered to be the most appropriate.

[0029] Also provided is a ZSM-23 molecular sieve synthesized by the above method, wherein the silicon-aluminum ratio of the ZSM-23 molecular sieve is 20-120; the mesopore volume is ≥0.45cm 3 / g.

[0030] Beneficial Effects

[0031] The present invention first pre-treats a mixture containing a silicon source, an aluminum source, and a seed by water vapor, and utilizes the structural guiding effect of the seed to first induce the silicon source and the aluminum source to interact, forming partial structural fragments, and then further through the effect of the template agent, completes crystallization. Selecting weakly alkaline alcohol amine as a crystallization aid can avoid the influence of the traditional scheme on the pH value of the synthesis system using inorganic bases, and does not need to use concentrated sulfuric acid to adjust the system pH. The synthesis process is controllable, the generation of heterophases can be avoided, and the silicon-aluminum ratio range of the synthesis feed can also be expanded. In addition, the ZSM-23 molecular sieve synthesized using the present invention has a higher mesoporous pore volume and better diffusion performance than the traditional method. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The XRD diagrams of Examples 1-4 and Comparative Examples 1-4 of the present invention are shown. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The experimental methods without specific conditions in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0035] Unless otherwise specified, the reagents and raw materials used in the examples and comparative examples of the present invention can be obtained through commercial channels.

[0036] Example 1

[0037] 6.7g silica gel powder (90wt.%), 0.52g sodium aluminate (49wt.%Al 2 O 3 ), 0.3g H-ZSM-23 seed crystals, mixed and ground, loaded into a steam treatment device, added with 150g water, and steam treated at 120°C for 4h; 1.08g pyrrolidine, 1.12g ethanolamine, and 17.4g water were prepared into a mixed solution, and then the powder mixture after steam treatment was added thereto; the kettle was sealed and statically aged at 80°C for 4h; after the aging, dynamic crystallization was carried out at 180°C and 50rpm for 72h; the crystallized product was filtered, washed, dried, and calcined to obtain the product Z1.

[0038] Example 2

[0039] 3g white carbon black, 0.18g sodium aluminate (49wt.%Al 2 O 3 ), 0.2g Na-ZSM-23 seed crystals were mixed and ground, loaded into a steam treatment device, 100g water was added, and steam treatment was carried out at 100°C for 6h; 1.65g isopropylamine, 0.92g ethanolamine, and 31.5g water were prepared into a mixed solution, and then the powder mixture after steam treatment was added thereto; the kettle was sealed and statically aged at 90°C for 2h; after the aging, dynamic crystallization was carried out at 170°C and 80rpm for 72h; the crystallized product was filtered, washed, dried, and calcined to obtain product Z2.

[0040] Example 3

[0041] 6.32g silica gel powder (95wt.%), 0.67g aluminum sulfate 18hydrate, 0.18g NH 4 -ZSM-23 seed crystals were mixed and ground, loaded into a steam treatment device, 250g of water was added, and steam treatment was performed at 110°C for 2h; 1.19g of pyrrolidine, 1.42g of isopropylamine, 1.13g of 3-aminopropanol, and 80.0g of water were prepared into a mixed solution, and then the powder mixture after steam treatment was added thereto; the kettle was sealed and statically aged at 70°C for 8h; after aging, dynamic crystallization was performed at 180°C and 100rpm for 60h; the crystallized product was filtered, washed, dried, and calcined to obtain product Z3. The formula for calculating the molar ratio of pyrrolidine to isopropylamine is: n (pyrrolidine) / n (isopropylamine) = (m (pyrrolidine) / 71.11) / (m (isopropylamine) / 59.11). Among them, 71.11 is the molar mass of pyrrolidine, and 59.11 is the molar mass of isopropylamine.

[0042] Example 4

[0043] 15g silica gel powder (95wt.%), 0.99g sodium aluminate (49wt.%Al 2 O 3 ), 0.7gH-ZSM-23 seed crystals were mixed and ground, loaded into a steam treatment device, 750g water was added, and steam treatment was carried out at 120°C for 2h; 9.95g pyrrolidine, 3.57g 3-aminopropanol, and 76g water were prepared into a mixed solution, and then the powder mixture after steam treatment was added thereto; the kettle was sealed and statically aged at 60°C for 4h; after aging, dynamic crystallization was carried out at 160°C and 80rpm for 84h; the crystallized product was filtered, washed, dried, and calcined to obtain product Z4. The formula for calculating the molar ratio of pyrrolidine to 3-aminopropanol is: n (pyrrolidine) / n (3-aminopropanol) = (m (pyrrolidine) / 71.11) / (m (3-aminopropanol) / 75.11). Among them, 71.11 is the molar mass of pyrrolidine, and 75.11 is the molar mass of 3-aminopropanol.

[0044] Comparative Example 1

[0045] The same as Example 1, except that the steam treatment step is omitted, to obtain product D1.

[0046] Comparative Example 2

[0047] The same method as in Example 1 was used, but without adding a crystallization agent, to obtain product D2.

[0048] Comparative Example 3

[0049] Weigh 9.6 g of sodium hydroxide, 28.5 g of pyrrolidine, and 2.96 g of aluminum sulfate 18hydrate, add 205 g of water, stir thoroughly, add 80 g of 30% silica sol, stir evenly, put into a kettle, place at 170°C for static crystallization for 24 hours, cool to room temperature, take out, add 7.68 g of aluminum sulfate 18hydrate and 14.4 g of water, stir evenly, put into a kettle again, place at 175°C for crystallization for 48 hours; the crystallized product is filtered, washed, dried, and calcined to obtain product D3.

[0050] Comparative Example 4

[0051] 18 g of deionized water, 2.7 g of aluminum sulfate 18hydrate, 0.86 g of sodium hydroxide, 0.28 g of Na-ZSM-23 seed crystals, and 12 g of isopropylamine (70%) were mixed and stirred evenly, and then 46.8 g of silica sol (30%) was slowly added under stirring. The kettle was sealed and stirred at room temperature for 5 h, dynamically crystallized at 120 ° C for 3 h, and dynamically crystallized at 200 ° C for 36 h; the crystallized product was filtered, washed, dried, and calcined to obtain product D4.

[0052] Effect Example

[0053] The above Examples 1-4 and Comparative Examples 1-4 were subjected to nitrogen physical adsorption tests, and the specific mesopore volume data are shown in Table 1 below:

[0054] Table 1 Physical properties of examples and comparative examples

[0055]

[0056] In summary, according to Figure 1 As shown in Table 1, if the mixed powder of silicon source, aluminum source and seed crystal is not treated with water vapor or a crystallization aid is not used, the product will contain impurities. According to the results in Table 1, the ZSM-23 sample synthesized by the present invention has a higher mesoporous pore volume.

[0057] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing ZSM-23 molecular sieve, characterized in that: The following steps are involved: Step S1, mixing; grinding the silicon source, aluminum source and seed crystal according to a certain proportion, and treating with water vapor to obtain a raw material powder mixture; wherein the mass ratio of the water vapor H2O to the aluminum source, seed crystal and silicon source mixture is 10-50:1; the treatment temperature of the water vapor is 100-120°C, and the treatment time is 1-6h; Step S2, mixed solution: mix the crystallization aid, template agent and deionized water, stir evenly to obtain a mixed solution; Step S3, adding the powder mixture obtained in step S1 to the mixed solution obtained in step S2, stirring evenly, and aging to obtain a synthetic gel; Step S4, the synthesized gel is placed in a kettle, sealed, and hydrothermally crystallized; Step S5, filtering, washing, drying and calcining the crystallized product to obtain ZSM-23 molecular sieve; In step S2, the crystallization aid is an alcohol amine compound, selected from at least one of ethanolamine, diethanolamine, triethanolamine, 3-aminopropanol, isopropanolamine, 2-amino-1-butanol, and 6-amino-1-hexanol; in step S3, the components in the synthetic gel, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the molar ratio of SiO2:Al2O3:template:crystallization aid:H2O is 1:0.008~0.05:0.10~0.80:0.05~0.4:10~80.

2. The method for synthesizing ZSM-23 molecular sieve according to claim 1, characterized in that: In step S1, the aluminum source is selected from at least one of aluminum sulfate 18hydrate, aluminum nitrate, sodium aluminate, aluminum trichloride, pseudo-boehmite, and aluminum hydroxide.

3. The method for synthesizing ZSM-23 molecular sieve according to claim 1, characterized in that: In step S1, the seed crystals are selected from at least one of Na-ZSM-23, H-ZSM-23, and NH4-ZSM-23; the amount of the seed crystals added is 1-10% of the mass of the silicon source, and the silicon source is calculated as SiO2.

4. The method for synthesizing ZSM-23 molecular sieve according to claim 1, characterized in that: In step S1, the silicon source is a solid silicon source selected from at least one of silica gel powder and white carbon black.

5. The method for synthesizing ZSM-23 molecular sieve according to claim 1, characterized in that: In step S2, the template agent is selected from one or both of isopropylamine and pyrrolidine; the molar ratio of pyrrolidine to isopropylamine is 0-0.7:

1.

6. The method for synthesizing ZSM-23 molecular sieve according to claim 1, characterized in that: In step S4, the hydrothermal crystallization is dynamic crystallization, the crystallization temperature is 140-190° C., the crystallization time is 12-96 h, and the dynamic crystallization stirring rate is 30-150 rpm.

7. A ZSM-23 molecular sieve synthesized by the method according to any one of claims 1 to 6, characterized in that: The silicon-aluminum ratio of the ZSM-23 molecular sieve is 20-120; the mesopore volume is ≥0.45cm 3 / g.

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