Synthesis method and application of high-crystallinity mesoporous ZSM-5 molecular sieve

Abstract

The invention discloses a green and environment-friendly synthesis method for preparing a high-crystallinity mesoporous ZSM-5 molecular sieve and application thereof, and belongs to the technical field of catalysts and synthesis thereof. On the basis of a template-free synthesis scheme, a mother liquor waste liquid with a template is added as a seed crystal liquid to prepare a high-crystallinity ZSM-5 molecular sieve, and then the high-crystallinity mesoporous ZSM-5 molecular sieve is prepared through alkali treatment. The ZSM-5 molecular sieve prepared by the invention does not need to be roasted in the whole preparation process, is a green and environment-friendly synthesis route, and can effectively save the production cost and reduce the energy consumption. The molecular sieve has a rich pore structure and a larger specific surface area at the same time, oil and gas components can enter pores of the molecular sieve easily, the diffusion path is short, the mass transfer rate in the reaction process is higher, the generated product can be rapidly diffused out, and the conversion rate of the molecular sieve in the cyclohexene hydration reaction can be effectively improved.

Description

Technical Field

[0001] This invention relates to a green and environmentally friendly method for preparing highly crystalline mesoporous ZSM-5 molecular sieves and its application, belonging to the field of catalysts and their synthesis technology. Background Technology

[0002] Cyclohexanol is an important chemical intermediate in the preparation of nylon monomers such as caprolactam and adipic acid. Its production methods mainly include phenol hydrogenation, cyclohexane oxidation, and cyclohexene hydration. Compared to the first two methods, the cyclohexene hydration method for producing cyclohexanol has advantages such as high selectivity, low hydrogen consumption, and mild reaction conditions, making it the mainstream process for cyclohexanol production. The cyclohexene hydration to cyclohexanol reaction is an acid-catalyzed reaction. ZSM-5 molecular sieve catalysts are widely used in the cyclohexene hydration process due to their advantages such as water insolubility, easy separation and regeneration, good catalytic shape selectivity, high mechanical strength, and high thermal stability. However, existing ZSM-5 molecular sieves still have disadvantages in the cyclohexene hydration to cyclohexanol reaction, including slow reaction rate, low cyclohexene conversion, and low selectivity.

[0003] To improve the activity of existing catalysts for the preparation of cyclohexene hydration-based ZSM-5 molecular sieves from cyclohexene, CN201510044292.3 discloses a hydrothermal synthesis system for ZSM-5 zeolite molecular sieves and its application. This system uses a template agent to prepare small-crystal ZSM-5 molecular sieves. While this method achieves fast mass transfer and good diffusion performance, it requires a large amount of template agent, resulting in high synthesis costs and environmental unfriendliness. CN202111217893.1 discloses a ZSM-5 molecular sieve, its preparation method, and its application. By adding urea, glucose, hexadecyltrimethylammonium bromide, or polydiallyldimethylammonium chloride as auxiliaries, short b-axis ZSM-5 molecular sieves are synthesized. However, the actual molecular sieve crystals are relatively large, resulting in low mass transfer rates. Furthermore, the acid gas produced by urea decomposition corrodes equipment and is also environmentally unfriendly.

[0004] The template agent method for preparing ZSM-5 molecular sieves is a lengthy and costly process. A large amount of mother liquor is typically generated after the filtration step, containing unconsumed silicon sources, organic bases, and other substances. Directly discarding this mother liquor would cause environmental pollution, while wastewater treatment would increase costs. Furthermore, discarding unused components in the mother liquor would also increase the production cost of the molecules. Therefore, effectively utilizing the mother liquor generated during molecular sieve preparation is of great significance for the industrial production of molecules. Summary of the Invention

[0005] This invention provides a green and environmentally friendly method for preparing highly crystalline mesoporous ZSM-5 molecular sieves and its application. The method yields ZSM-5 molecular sieves with high crystallinity and mesoporous characteristics, avoiding the use of large amounts of organic template agents and ZSM-5 seed crystals. Furthermore, the obtained molecular sieve can improve the conversion rate of cyclohexene in the cyclohexene hydration reaction and has high catalytic performance.

[0006] This invention is achieved through the following technical solution: This invention provides a method for synthesizing highly crystalline mesoporous ZSM-5 molecular sieves, comprising: (1) Prepare a synthetic slurry containing silicon source, aluminum source, alkali source, water and seed solution, and perform hydrothermal crystallization to obtain crystallized slurry; The seed solution is the mother liquor waste liquid after crystallization in the preparation of ZSM-5 molecular sieve by the template agent method, wherein the template agent is a propylammonium template agent; (2) Add alkali solution to the crystallized slurry for alkali treatment; (3) After filtration, washing and drying, acid exchange is carried out.

[0007] Further, the amount of the seed crystal solution added accounts for 0.9wt% to 2.5wt% of the synthetic slurry; the template agent is selected from at least one of tetrapropylammonium bromide, tetrapropylammonium hydroxide, tri-n-propylamine, ethyltripropylammonium chloride and ethyltripropylammonium hydroxide, and the content of the template agent accounts for 1% to 3% of the mass of the seed crystal solution.

[0008] Furthermore, the alkaline solution is consistent with the alkaline source used in the synthesis process, the concentration of the alkaline solution is 20wt~40wt%, the amount of the alkaline solution added accounts for 1.5%~3.5% of the mass of the synthesized slurry, and the alkaline treatment conditions are 50~80℃ for 2~6h.

[0009] Furthermore, the concentration of the alkali solution is 30 wt%.

[0010] Furthermore, the hydrothermal crystallization is a segmented crystallization, with the first stage crystallization conditions being crystallization at 30~120℃ for 5~25h, and the second stage crystallization conditions being crystallization at 170~190℃ for 24~72h.

[0011] Further, the silicon source is selected from at least one of silica sol, type C silica gel, and water glass; the aluminum source is selected from at least one of aluminum sulfate, sodium aluminate, and aluminum sol; and the alkali source is selected from at least one of sodium hydroxide and potassium hydroxide. In the synthetic slurry, the molar ratio of each substance is SiO2: Al2O3: M2O: H2O = 20.0~40.0: 1: 1.5~4.0: 530~1100, where M is sodium or potassium.

[0012] Furthermore, the drying temperature is 80~120℃, and the drying time is 6~12h.

[0013] Furthermore, the acid exchange conditions include treatment with 2wt%~6wt% H2SO4 or hydrochloric acid solution, a solid-liquid mass ratio of 1:(3~6), and exchange at 20~60℃ for 2~4h.

[0014] Furthermore, the solid-liquid mass ratio in the acid exchange is 1:4.

[0015] The present invention also provides a highly crystalline mesoporous ZSM-5 molecular sieve prepared by the above synthesis method, wherein the highly crystalline mesoporous ZSM-5 molecular sieve has a crystallinity of 105%~110% and a specific surface area of ​​390~420 m². 2 / g, pore volume 0.30~0.35cm³ 3 / g, with a pore size of 3.0~3.5nm.

[0016] The present invention also provides an application of the highly crystalline mesoporous ZSM-5 molecular sieve prepared by the above synthesis method in cyclohexene hydration reaction and olefin catalytic cracking reaction.

[0017] Furthermore, the cyclohexene conversion rate is 12.0%~12.5%, and the cyclohexanol selectivity is 99.0%~99.5%.

[0018] The beneficial effects of this invention are as follows: (1) The green and environmentally friendly method for preparing highly crystalline mesoporous ZSM-5 molecular sieve provided by the present invention, based on the template-free synthesis scheme, uses the synthesis mother liquor waste liquid containing tripropyl or tetrapropyl template agent as seed liquid, which avoids the large-scale use of organic template agents in the traditional method and reduces environmental pollution.

[0019] (2) The present invention adopts a segmented crystallization and post-crystallization alkali treatment process, which significantly improves the crystallinity of ZSM-5 molecular sieve and forms a mesoporous structure, making the prepared molecular sieve have higher catalytic activity and selectivity. Compared with the traditional template-free method for preparing ZSM-5 molecular sieve, the crystallinity is increased by 5%~10%.

[0020] (3) The ZSM-5 molecular sieve preparation process of this invention does not require calcination, which is a green and environmentally friendly synthesis route that can effectively save production costs and reduce energy consumption. Compared with traditional methods, the method of this invention is not only environmentally friendly and economical, but also produces products with rich pore structures and larger specific surface areas, which is conducive to the entry of oil and gas components into its pores. The diffusion path is short, the mass transfer rate is faster during the reaction, and the generated products can diffuse out quickly, which can effectively improve its conversion rate in the cyclohexene hydration reaction. Attached Figure Description

[0021] Figure 1The X-ray diffraction (XRD) pattern of the highly crystalline mesoporous ZSM-5 molecular sieve prepared in Example 1.

[0022] Figure 2 Electron micrograph (SEM) of the highly crystalline mesoporous ZSM-5 molecular sieve prepared in Example 1.

[0023] Figure 3 The pore size distribution diagrams are shown for the highly crystalline mesoporous ZSM-5 molecular sieve prepared in Example 1 and the ZSM-5 molecular sieve synthesized by the template-free method in Comparative Example 1.

[0024] Figure 4 Electron micrograph (SEM) of the ZSM-5 molecular sieve prepared for Comparative Example 1. Detailed Implementation

[0025] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0026] In this embodiment of the invention, the seed solution is a synthesis mother liquor obtained by mixing silica sol, sodium aluminate, sodium hydroxide, template agent, and deionized water evenly, dynamically crystallizing at 170°C for 24 hours, and then filtering. The molar ratio of each substance is SiO2:Al2O3:Na2O:ROH:H2O = 120:1:6.5:4.0:2200, where R is the template agent, which is tetrapropylammonium hydroxide or tetrapropylammonium bromide.

[0027] The silica sol uses silica sol with a SiO2 content of 30%, and the C-type silica gel uses C-type silica gel with a SiO2 content of 99%. Example 1

[0028] A green and environmentally friendly method for preparing highly crystalline mesoporous ZSM-5 molecular sieves is as follows: (1) Mix 29.84g silica sol, 0.77g sodium aluminate, 0.54g sodium hydroxide, 48.65g deionized water and 1.50g seed solution containing tetrapropylammonium hydroxide, crystallize at 80℃ for 20h, and then crystallize at 180℃ for 48h.

[0029] (2) After crystallization, add 2g of 30% sodium hydroxide solution when the temperature drops to 60℃ and treat for 3h.

[0030] (3) After alkali treatment, the slurry is washed to neutral and dried at 120°C for 12 hours to obtain a highly crystalline mesoporous Na-ZSM-5 molecular sieve.

[0031] (4) Then, using 3% H2SO4 solution, with a solid-liquid ratio of 1:4, and exchanging at 40℃ for 3h, we obtained 1# high crystallinity mesoporous H-ZSM-5 molecular sieve.

[0032] Depend on Figure 1 As can be seen, sample #1 exhibits the characteristic "five-finger peak" of ZSM-5 molecular sieve, which perfectly matches the standard sample, proving the successful synthesis of pure-phase ZSM-5 molecular sieve with a crystallinity of 110%. Its electron microscopy morphology is as follows: Figure 2 Specific surface area is 400 m² 2 / g, pore volume 0.32 cm³ 3 / g, with a pore size of 3.1nm. Example 2

[0033] A green and environmentally friendly method for preparing highly crystalline mesoporous ZSM-5 molecular sieves is as follows: (1) Mix 9.47g of C-type silica gel, 0.77g of sodium aluminate, 0.63g of sodium hydroxide, 68.93g of deionized water and 1.50g of seed solution containing tetrapropylammonium hydroxide, crystallize at 80°C for 20h, and then crystallize at 180°C for 48h.

[0034] (2) After crystallization, add 2g of 30% sodium hydroxide solution when the temperature drops to 60℃ and treat for 3h.

[0035] (3) After alkali treatment, the slurry is washed to neutral and dried at 120°C for 12 hours to obtain a highly crystalline mesoporous Na-ZSM-5 molecular sieve.

[0036] (4) Then, using 3% H2SO4 solution, with a solid-liquid ratio of 1:4, and exchanging at 40℃ for 3 hours, high-crystallinity mesoporous H-ZSM-5 molecular sieve #2 was obtained. Its XRD and SEM results were consistent with those of sample #1, with a crystallinity of 106% and a specific surface area of ​​395 m². 2 / g, pore volume is 0.31cm 3 / g, with a pore size of 3.3nm. Example 3

[0037] The raw materials and synthesis steps are the same as in Example 1. The difference is that the seed solution containing tetrapropylammonium hydroxide in the synthesis step (1) of Example 1 is replaced with a seed solution containing tetrapropylammonium bromide. The high crystallinity mesoporous H-ZSM-5 molecular sieve product is designated as 3#. Its XRD and SEM are consistent with those of sample 1#, with a crystallinity of 107% and a specific surface area of ​​402 m². 2 / g, pore volume is 0.31 cm³ 3 / g, with a pore size of 3.1nm. Example 4

[0038] The raw materials and synthesis steps were the same as in Example 1, except that the 30% sodium hydroxide solution in the alkali treatment step (2) of Example 1 was replaced with 1.2g. The high-crystallinity mesoporous H-ZSM-5 molecular sieve product was obtained and designated as 4#. Its XRD and SEM results were consistent with those of sample 1#, with a crystallinity of 110% and a specific surface area of ​​410 m². 2 / g, pore volume 0.32 cm³ 3 / g, with a pore size of 3.5nm. Example 5

[0039] The raw materials and synthesis steps are the same as in Example 1. The difference is that the crystallization conditions in the synthesis step (1) of Example 1 are changed to crystallization at 100℃ for 24h and then at 170℃ for 72h to obtain a high crystallinity mesoporous H-ZSM-5 molecular sieve product, designated as 5#. Its XRD and SEM are consistent with those of sample 1#, with a crystallinity of 110% and a specific surface area of ​​405 m². 2 / g, pore volume 0.33 cm³ 3 / g, with a pore size of 3.4nm. Comparative Example 1

[0040] The raw materials were the same as in Example 1, but the synthesis steps differed in that no seed solution was added in Comparative Example 1. The resulting mesoporous H-ZSM-5 molecular sieve product was designated as #6, and its XRD pattern was consistent with that of sample #1. SEM analysis showed... Figure 4 As shown, the crystallinity is 100% and the specific surface area is 350 m². 2 / g, pore volume 0.24 cm³ 3 / g, with a pore size of 2.6nm. Comparative Example 2

[0041] The raw materials were the same as in Example 1. The difference in the synthesis steps was that there was no alkali treatment step in Comparative Example 2. After crystallization, the product was directly washed and dried, followed by acid exchange to obtain a highly crystalline H-ZSM-5 molecular sieve product, designated as #7. Its XRD and SEM results were consistent with those of sample #1, with a crystallinity of 104% and a specific surface area of ​​385 m². 2 / g, pore volume 0.29 cm³ 3 / g, with a pore size of 2.9nm. Comparative Example 3

[0042] The raw materials were the same as in Example 1. The difference in the synthesis steps was that no seed crystal solution was added and no alkali treatment step was performed in Comparative Example 3. After crystallization, the product was directly washed and dried, followed by acid exchange to obtain H-ZSM-5 molecular sieve product, designated as 8#. Its XRD and SEM results were consistent with those of sample 5#, with a crystallinity of 96% and a specific surface area of ​​332 m². 2 / g, pore volume 0.20 cm³ 3 / g, with a pore size of 2.4nm. Comparative Example 4

[0043] The raw materials were the same as in Example 1, but the synthesis steps differed. This comparative example used a one-step crystallization method to synthesize ZSM-5 molecular sieves, with crystallization conditions of 180℃ for 72 hours. After subsequent experimental processing, the mesoporous H-ZSM-5 molecular sieve product, designated as #9, was obtained. Its XRD pattern was consistent with sample #6, with a crystallinity of 90% and a specific surface area of ​​330 m². 2 / g, pore volume 0.22 cm³ 3 / g, with a pore size of 2.3nm. Application examples

[0044] The ZSM-5 molecular sieves prepared in the above examples and comparative examples were used to evaluate the preparation of cyclohexanol from cyclohexene hydration. The evaluation procedure was as follows: 50g of the dry-balanced molecular sieve was weighed and added to the evaluation vessel, followed by 110g of deionized water for slurry preparation. Then, 72g of cyclohexene was added to the sealed high-pressure reactor. The reactor was pressurized with nitrogen to maintain a pressure of 0.4MPa, heated to 125℃, and reacted for 0.5h with a stirring speed of 800r / min. After the reaction, the temperature was lowered to below 10℃ in situ, the pressure was released, and samples were taken for gas chromatography analysis.

[0045] Table 1 shows the evaluation results of each sample. As can be seen from the data in the table, the cyclohexene conversion rate and cyclohexanol selectivity of the samples prepared in each embodiment are higher than those of the samples prepared in the comparative example, indicating that the catalyst prepared by this patent has better catalytic performance.

[0046] Table 1

[0047] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for synthesizing highly crystalline mesoporous ZSM-5 molecular sieve, characterized in that, include: (1) Prepare a synthetic slurry containing silicon source, aluminum source, alkali source, water and seed solution, and perform hydrothermal crystallization to obtain crystallized slurry; The seed solution is the mother liquor waste liquid after crystallization in the preparation of ZSM-5 molecular sieve by the template agent method, wherein the template agent is a propylammonium template agent; (2) Add alkali solution to the crystallized slurry for alkali treatment; (3) After filtration, washing and drying, acid exchange is carried out.

2. The synthesis method according to claim 1, characterized in that, The amount of seed solution added accounts for 0.9wt% to 2.5wt% of the synthetic slurry; the template agent is selected from at least one of tetrapropylammonium bromide, tetrapropylammonium hydroxide, tri-n-propylamine, ethyltripropylammonium chloride and ethyltripropylammonium hydroxide, and the content of the template agent accounts for 1% to 3% of the mass of the seed solution.

3. The synthesis method according to claim 1 or 2, characterized in that, The alkaline solution is the same as the alkaline source used in the synthesis process, and the concentration of the alkaline solution is 20wt~40wt%, preferably 30wt%. The amount of the alkaline solution added accounts for 1.5%~3.5% of the mass of the synthesized slurry, and the alkaline treatment conditions are 50~80℃ for 2~6h.

4. The synthesis method according to any one of claims 1 to 3, characterized in that, The hydrothermal crystallization is a segmented crystallization process. The first stage crystallization is carried out at 30~120℃ for 5~25 hours, and the second stage crystallization is carried out at 170~190℃ for 24~72 hours.

5. The synthesis method according to any one of claims 1 to 4, characterized in that, The silicon source is selected from at least one of silica sol, type C silica gel, and water glass; the aluminum source is selected from at least one of aluminum sulfate, sodium aluminate, and aluminum sol; and the alkali source is selected from at least one of sodium hydroxide and potassium hydroxide. In the synthetic slurry, the molar ratio of each substance is SiO2:Al2O3:M2O:H2O = 20.0~40.0:1:1.5~4.0:530~1100, where M is sodium or potassium.

6. The synthesis method according to any one of claims 1 to 5, characterized in that, The drying temperature is 80~120℃, and the drying time is 6~12h.

7. The synthesis method according to any one of claims 1 to 6, characterized in that, The acid exchange conditions include treatment with 2wt%~6wt% H2SO4 or hydrochloric acid solution, a solid-liquid mass ratio of 1:(3~6), preferably 1:4, and exchange at 20~60℃ for 2~4h.

8. A highly crystalline mesoporous ZSM-5 molecular sieve prepared by the synthesis method according to any one of claims 1 to 7, characterized in that, The highly crystalline mesoporous ZSM-5 molecular sieve has a crystallinity of 105%~110% and a specific surface area of ​​390~420 m². 2 / g, pore volume 0.30~0.35 cm³ 3 / g, with a pore size of 3.0~3.5nm.

9. The application of a highly crystalline mesoporous ZSM-5 molecular sieve prepared by the synthesis method according to any one of claims 1 to 7 in cyclohexene hydration reaction and olefin catalytic cracking reaction.

10. The application according to claim 9, characterized in that, The cyclohexene conversion rate is 12.0%~12.5%, and the cyclohexanol selectivity is 99.0%~99.5%.

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