A method for synthesizing high-crystallinity sodium-free ZSM-5 molecular sieve by a pre-crystallization liquid adding method
The synthesis of highly crystalline sodium-free ZSM-5 molecular sieves via the pre-crystallization solution addition method solves the ammonia nitrogen pollution problem caused by ion exchange, achieving efficient and low-cost molecular sieve synthesis, suitable for adsorption separation, petrochemical and environmental protection fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHONGKE CATALYSIS NEW TECH (DALIAN) CO LTD
- Filing Date
- 2023-12-26
- Publication Date
- 2026-04-24
AI Technical Summary
In the existing ZSM-5 molecular sieve synthesis process, the problems of ammonia nitrogen pollution and acid pollution caused by ion exchange are difficult to solve effectively, and the synthesis process is complex and costly.
Highly crystalline sodium-free ZSM-5 molecular sieves were synthesized using a precrystallization solution addition method. By adding the precrystallization solution, the use of sodium-containing raw materials was avoided. The molecular sieve framework structure was induced by the crystal nuclei in the precrystallization solution, the particle size distribution was controlled, and the synthesis process was simplified.
The preparation of sodium-free ZSM-5 molecular sieves with high crystallinity has been achieved, which reduces ammonia nitrogen wastewater discharge, lowers production costs, simplifies the operation process, and is suitable for large-scale production.
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Figure CN117923511B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for synthesizing a sodium-free ZSM-5 molecular sieve with high crystallinity, belonging to the field of catalyst preparation technology. Background Technology
[0002] ZSM-5 molecular sieve, first synthesized by Mobil in 1972, is a zeolite molecular sieve with a unique three-dimensional pore structure. Its pore structure consists of two intersecting pore types: elliptical ten-membered ring straight channels, approximately 5.4 × 5.6 nm in size, and near-circular ten-membered ring Z-shaped channels, approximately 5.2 × 5.8 nm in size. ZSM-5 molecular sieve possesses a unique and uniform intersecting pore structure, strong selective adsorption performance, good thermal and hydrothermal stability, and moderate acidity, making it widely used in adsorption separation, petrochemicals, fine chemicals, and environmental protection. Therefore, ZSM-5 zeolite has attracted considerable attention. The synthesis of ZSM-5 zeolite is crucial, and the synthesis of sodium-free ZSM-5 zeolite is one of the research challenges.
[0003] The current production of ZSM-5 molecular sieves is generally carried out in a synthesis system involving sodium ions. The synthesized molecular sieve is a sodium-type molecular sieve, which requires sodium exchange to transform it into an ammonium-type ZSM-5. This is then calcined to obtain the hydrogen-type ZSM-5, which exhibits acid-catalyzing activity. The ion exchange step typically uses excess ammonium salts or acidic solutions, generating large amounts of high-concentration ammonia nitrogen wastewater or acidic wastewater, which, when directly discharged, impacts the environment. Summary of the Invention
[0004] This invention provides a method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a precrystallization solution. By adding a precrystallization solution, not only can ZSM-5 molecular sieves with high relative crystallinity be prepared without adding any sodium-containing raw materials, but also the problem of ammonia nitrogen pollution or acid pollution caused by ion exchange can be solved.
[0005] This invention is achieved through the following technical methods:
[0006] The technical solution of the present invention is as follows:
[0007] This invention provides a method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves using a pre-crystallization solution addition method. First, a silicon source, an organic template agent, and deionized water are mixed and crystallized to obtain a pre-crystallization solution. Then, an aluminum source, a silicon source, an organic template agent, deionized water, and the pre-crystallization solution obtained in step S1 are mixed and sealed in a reaction vessel for dynamic crystallization. Finally, the mixture is filtered, washed, dried, and calcined to obtain the ZSM-5 molecular sieve.
[0008] The molar ratio of silicon source, organic template agent, and water in the precrystallization solution is (5-8):1:(90-120), wherein the silicon source is calculated as oxide SiO2.
[0009] The molar ratio of silicon source, aluminum source, organic template agent, and water is (100-120):1:(5-10):(1000-1500), wherein the silicon source and aluminum source are calculated as oxides SiO2:Al2O3; the amount of precrystallization liquid added is 15%-25% of the mass of silicon source in the raw materials.
[0010] As a preferred option:
[0011] The silicon source is at least one of silica sol and fumed silica.
[0012] The aluminum source is at least one of aluminum hydroxide and aluminum oxide.
[0013] The organic template agent is at least one of tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, and tetrapropylammonium hydroxide aqueous solution.
[0014] The rotational speed for dynamic crystallization is 15–45 rpm.
[0015] The pre-crystallization liquid has a dynamic crystallization temperature of 80-100℃ and a crystallization time of 8-12h; the crystallization temperature of the ZSM-5 molecular sieve synthesis stage is 170-200℃ and the crystallization time is 24-48h.
[0016] The drying temperature is 65-110℃, and the drying time is 8-24h.
[0017] The roasting temperature is 500-550℃, and the roasting time is 2-6 hours.
[0018] The washing process uses deionized water.
[0019] This technical solution is based on the presence of crystal nuclei formed during the initial crystallization stage in the pre-crystallization solution. This induces the formation of a ZSM-5 molecular sieve framework structure while ensuring the uniformity of particle distribution in the synthesis system. Consequently, the synthesized product exhibits smaller crystallites, better uniformity, and higher dispersion. Therefore, adding a pre-crystallization solution to the synthesis system not only induces nucleation and controls the particle size distribution of the product but also ensures that the synthesized sample has a high relative crystallinity. Furthermore, the pre-crystallization solution can be stored for a long time, meeting the standards for industrial applications.
[0020] The beneficial effects of this invention are as follows: the addition of pre-crystallization solution in the synthesis method provided by this invention can improve the crystallinity of the product, shorten the reaction time, and the reaction process does not contain sodium-containing raw materials, so the prepared ZSM-5 type zeolite molecular sieve does not contain Na. +This method eliminates the need for ammonium exchange, reducing production costs and ammonia nitrogen wastewater discharge. Furthermore, the preparation method described in this invention is not only low-cost and simple to operate, but also requires no special production equipment or processes, making it suitable for large-scale production. Attached Figure Description
[0021] Figure 1 The image shows the XRD pattern of sample Z1 synthesized in Example 1.
[0022] Figure 2 The image shows the XRD pattern of sample Z2 synthesized in Example 2.
[0023] Figure 3 The image shows the XRD pattern of sample Z3 synthesized in Example 3. Detailed Implementation
[0024] The present invention is described in detail below through embodiments, but the present invention is not limited to these embodiments.
[0025] Examples 1–3
[0026] Example 1
[0027] Preparation of precrystallization solution: 12.49 g of deionized water and 18.13 g of 40% tetrapropylammonium hydroxide solution were stirred in a 100 mL polytetrafluoroethylene-lined reactor for 10 min until fully mixed. Under stirring, 43.55 g of 25% silica sol was added dropwise to the above solution. After shaking fully at room temperature for 1 h, the mixture was sealed in a polytetrafluoroethylene-lined reactor and dynamically aged at 100 degrees Celsius for 10 h to obtain the precrystallization solution.
[0028] Synthesis of ZSM-5: 0.29 g aluminum hydroxide, 7.27 g 40% tetrapropylammonium hydroxide aqueous solution, and 6.59 g deionized water were added to 100 mL of a polytetrafluoroethylene (PTFE)-lined reactor and stirred until homogeneous. 47.52 g 25% silica sol was added dropwise to the PTFE-lined reactor under thorough stirring and vigorous shaking at room temperature for 1 h. 2.59 g of the pre-crystallized solution was added to the PTFE-lined reactor and stirred for another 1 h. The reactor was then sealed and crystallized at 190°C and 35 rpm for 46 h. After cooling, the mixture was centrifuged and washed until neutral, dried at 100°C for 20 h, and calcined at 550°C for 3 h to synthesize a highly crystalline sodium-free ZSM-5 molecular sieve, namely Z1. The relative crystallinity of Z1 was determined to be as high as 114%. The XRD pattern of the sample is shown below. Figure 1 As shown.
[0029] Example 2
[0030] Preparation of precrystallization solution: 43.03 g of deionized water and 17.28 g of 40% tetrapropylammonium hydroxide solution were stirred in a 100 mL polytetrafluoroethylene-lined reactor for 10 min until fully mixed and homogeneous; 10.4 g of fumed silica was added to the above solution while stirring, and the mixture was shaken thoroughly at room temperature for 1 h. The mixture was then sealed in a polytetrafluoroethylene-lined reactor and dynamically aged at 100 degrees Celsius for 10 h to obtain the precrystallization solution.
[0031] Synthesis of ZSM-5: 0.32 g aluminum hydroxide, 9.07 g 40% tetrapropylammonium hydroxide aqueous solution, and 39.6 g deionized water were added to 100 mL of a polytetrafluoroethylene (PTFE)-lined reactor and stirred until homogeneous. 13.23 g fumed silica was added to the PTFE-lined reactor under thorough stirring and vigorous shaking at room temperature for 1 h. 2.73 g of the pre-crystallized solution was added to the PTFE-lined reactor and stirred for another 1 h. The reactor was then sealed and crystallized at 190°C and 30 rpm for 24 h. After cooling, the mixture was centrifuged and washed until neutral, dried at 100°C for 20 h, and calcined at 550°C for 3 h to synthesize a highly crystalline sodium-free ZSM-5 molecular sieve, namely Z2. The relative crystallinity of Z2 was determined to be as high as 112%. The XRD pattern of the sample is shown below. Figure 2 As shown.
[0032] Example 3
[0033] The precrystallization solution was prepared according to the method in Example 2.
[0034] Synthesis of ZSM-5: 0.32 g aluminum hydroxide, 9.07 g 40% tetrapropylammonium hydroxide aqueous solution, and 36.00 g deionized water were stirred in a 100 mL polytetrafluoroethylene (PTFE)-lined reactor until thoroughly mixed. 12.02 g fumed silica was added to the PTFE-lined reactor under thorough stirring and vigorous shaking at room temperature for 1 h. 2.73 g of the pre-crystallized solution was added to the PTFE-lined reactor and stirred for another 1 h. The reactor was then sealed and crystallized at 190°C and 30 rpm for 46 h. After cooling, the mixture was centrifuged and washed until neutral, dried at 100°C for 20 h, and calcined at 550°C for 3 h to synthesize a highly crystalline sodium-free ZSM-5 molecular sieve, namely Z3. The relative crystallinity of Z3 was determined to be as high as 96%. The XRD pattern of the sample is shown below. Figure 3 As shown.
[0035] Table 1. Summary of XRF content of ZSM-5 molecular sieves synthesized in Examples 1-3
[0036]
[0037]
[0038] As shown in Table 1, a sodium-free ZSM-5 molecular sieve sample with a high silica-to-alumina ratio can be synthesized according to the experimental method, proving the feasibility of the experimental scheme.
[0039] This invention has been described through embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this invention.
Claims
1. A method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves using a pre-crystallization solution addition method, characterized in that, Includes the following steps: S1. Mix silicon source, organic template agent and deionized water, and crystallize to obtain pre-crystallized solution, wherein the molar ratio of silicon source, organic template agent and water in pre-crystallized solution is (5-8):1:(90-120), and the silicon source is calculated as oxide SiO2; S2. Mix the aluminum source, silicon source, organic template agent, deionized water and the precrystallization solution obtained in S1, seal it in a reactor and perform dynamic crystallization. S3. After filtering, washing, drying and calcining the crystallized product in S2, a sodium-free ZSM-5 molecular sieve with high crystallinity is obtained.
2. The method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a pre-crystallization solution according to claim 1, characterized in that: The molar ratio of silicon source, aluminum source, organic template agent, and water in S2 is (100-120):1:(5-10):(1000-1500), wherein the silicon source and aluminum source are calculated based on oxides SiO2:Al2O3, and the amount of precrystallization liquid added is 15%-25% of the mass of silicon dioxide in the silicon source of S2.
3. The method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a pre-crystallization solution according to claim 1, characterized in that: The silicon source is at least one of silica sol and fumed silica.
4. The method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a pre-crystallization solution according to claim 1, characterized in that: The aluminum source is at least one of aluminum hydroxide and aluminum oxide.
5. The method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a pre-crystallization solution according to claim 1, characterized in that: The organic template agent is at least one of tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, or tetrapropylammonium hydroxide aqueous solution.
6. The method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a pre-crystallization solution according to claim 1, characterized in that: The rotational speed for dynamic crystallization is 15–45 rpm.
7. The method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a pre-crystallization solution according to claim 1, characterized in that: The pre-crystallization solution has a dynamic crystallization temperature of 80-100 ℃ and a crystallization time of 8-12 h; the ZSM-5 molecular sieve synthesis stage has a crystallization temperature of 170-200 ℃ and a crystallization time of 24-48 h.
8. The method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a pre-crystallization solution according to claim 1, characterized in that: The drying temperature is 65-110 ℃, and the drying time is 8-24 h.
9. The method for synthesizing highly crystalline sodium-free ZSM-5 molecular sieves by adding a pre-crystallization solution according to claim 1, characterized in that: The roasting temperature is 500-550 ℃, and the roasting time is 2-6 h.