A method for the synthesis of a zsm-22 molecular sieve

Abstract

A synthesis method of ZSM-22 molecular sieve, comprising the following steps: S1, dissolving an aluminum source, an alkali source, a template agent, seeds, and an auxiliary solvent in deionized water respectively, then mixing, and then heating to 40-90 DEG C, to prepare a pre-prepared solution; S2, adding the pre-prepared solution to a solid silicon source at multiple addition points, the addition amount of the pre-prepared solution per minute is 3-10 wt% of the total amount of the pre-prepared solution, the feeding process is carried out at 40-70 DEG C and under stirring conditions, to obtain a gel; the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3), the silicon source, the alkali source, the template agent, the auxiliary solvent, the seeds, and water in the gel is 1:0.005-0.02:0.10-0.18:0.2-0.3:0.01-0.05:0.1-0.5:5-15; S3, crystallizing the obtained gel, then filtering and washing, and drying, to obtain a ZSM-22 molecular sieve.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve synthesis, specifically relating to a method for synthesizing ZSM-22 molecular sieve. Background Technology

[0002] ZSM-22 is a high-silica molecular sieve with a TON-type topology, first synthesized by ExxonMobil in the 1980s. Its pore structure consists of one-dimensional ten-membered ring straight channels with dimensions of [missing information]. Due to its unique structural characteristics, ZSM-22 exhibits good catalytic performance in petrochemicals and has achieved industrial application in the hydroisomerization and dewaxing of base oils. Therefore, reducing the synthesis cost of ZSM-22 is of practical significance. Currently, the hydrothermal method is mainly used to produce ZSM-22 industrially. However, to avoid the problems of viscosity and dispersion difficulties when the raw material system has a high solid content, the water content of the system remains high, resulting in a single-batch yield of only about 7%, which restricts production efficiency and cost. Current research reports on the preparation of molecular sieves under high solid content raw material conditions are as follows:

[0003] Patent CN113135577A discloses a method for rapidly synthesizing high-silicon ZSM-22 molecular sieves. By adding different types (specifically, different silicon-to-aluminum ratios) and masses of seed crystals, ZSM-22 can be rapidly synthesized within a relatively wide water-to-silicon ratio range. The specific steps are as follows: 1. Mix the silicon source, alkali source, template agent, and deionized water evenly, then add different types and masses of ZSM-22 seed crystals and stir until a mixed gel is formed; 2. Transfer the obtained mixed gel to a reaction vessel for crystallization; 3. Filter, wash, dry, and calcine to obtain rod-shaped ZSM-22 molecular sieve powder. This method can only synthesize molecular sieves with a silicon-to-aluminum ratio above 600, and cannot synthesize molecular sieves with lower silicon-to-aluminum ratios. The product quality is greatly affected by the purity of the seed crystals, and the product crystal size is relatively large, which is detrimental to catalytic performance.

[0004] Patent CN111434611B discloses a method for synthesizing NaY molecular sieves to improve single-reactor yield. According to the required proportions for NaY molecular sieves, a certain amount of directing agent is selectively added to a solid silicon source and an aluminum source. After stirring until homogeneous, the mixture becomes a solid reaction mixture, which is then loaded into a reactor for crystallization. The temperature is controlled at 90℃-140℃, and the crystallization time is 24-120 hours. Finally, after filtration, washing, and drying, NaY molecular sieves with a relative crystallinity greater than 60% are obtained. This method differs from traditional hydrothermal crystallization methods for producing NaY molecular sieves, and features high utilization of silicon and aluminum sources and high product yield. However, because the reactants are solid, this method adversely affects mass and heat transfer during the synthesis process, making it difficult to improve the crystallinity of the molecular sieve and hindering industrial-scale production.

[0005] Patent CN108264054B discloses a method for synthesizing silicon-rich or all-silicon ZSM-22 molecular sieves using a seed crystal method. The method involves mixing an alkali source, silicon source, seed crystals, organic additives, and an R source in a mortar, grinding for two minutes, and then transferring the mixture to a reaction vessel for crystallization at 100–200°C for 12 hours–9 days. The reaction product is then filtered and dried to obtain the molecular sieve powder. Because no solvent or organic template agent is used, the yield is increased and the raw material cost is reduced. However, this method is carried out in a mortar, resulting in a small-scale synthesis with limited industrial significance. Although an organic template machine is not used, the addition of methanol and organic additives increases the difficulty of post-synthesis processing.

[0006] The literature "Rapid Synthesis of P-type Molecular Sieves with High Calcium and Magnesium Ion Exchange Performance via Solid-Phase Method" achieved the crystallization of P-type molecular sieves in a high-solids-content system by first preparing a silica-alumina dry gel. The method involved dissolving Na₂SiO₃·9H₂O and Al₂(SO₄)₃·18H₂O in an appropriate amount of water, heating to 60°C and stirring thoroughly. After mixing, the mixture was cooled to room temperature and filtered. The solution was then washed multiple times until no SO₄²⁻ was present in the washings. 2- The product was then dried in a constant temperature drying oven at 100℃ for 3 hours to obtain a silica-alumina dry gel. The silica-alumina dry gel was placed in a stainless steel crystallization vessel lined with polytetrafluoroethylene (PTFE), and sodium hydroxide and water were added in a certain proportion. After thorough mixing, the mixture was statically crystallized at a certain temperature for a period of time. After crystallization, the product was removed and filtered. The solid phase product was washed with deionized water and dried to obtain the P-type molecular sieve product. Compared with conventional methods, the solid-phase method achieved by first preparing the silica-alumina dry gel is more complex. As a first-generation molecular sieve, the P-type molecular sieve does not require a template agent during synthesis, resulting in a wide synthesis phase region. Therefore, its theory and methods are not applicable to ZSM-22.

[0007] The literature "Synthesis of SAPO-34 and its eutectic molecular sieves in an ultra-concentrated system" utilizes a solid-phase transformation mechanism and method, introducing fluoride salts to enhance mineralization and facilitate the crystallization of SAPO-34 and its eutectic molecular sieves in an ultra-concentrated system. However, this method results in a narrow synthesis phase region that is difficult to control; the introduction of fluorides into the raw material system is detrimental to safety and environmental protection.

[0008] In summary, although various molecular sieves have been successfully synthesized in high solids content systems, ZSM-22, as a one-dimensional porous molecular sieve, has a metastable crystal structure. Under conditions of high raw material viscosity, it is prone to crystallization and the formation of impurities due to mass transfer. Therefore, it is difficult to synthesize highly crystalline pure-phase molecular sieves. Summary of the Invention

[0009] The purpose of this invention is to provide a method for synthesizing ZSM-22 molecular sieves. This method can overcome the problems of mass transfer and impurity crystals in the gelation process under high solid content raw materials, enabling the rapid and stable synthesis of highly crystalline pure-phase ZSM-22 molecular sieves.

[0010] To achieve the above objectives, the present invention provides a method for synthesizing ZSM-22 molecular sieve, comprising the following steps:

[0011] S1, dissolve the aluminum source, alkali source, template agent, seed crystal and auxiliary solvent in deionized water and mix them, then heat to 40-90℃ to prepare a pre-prepared solution;

[0012] S2, the pre-prepared solution is added to the solid silicon source at multiple addition points. The amount of pre-prepared solution added per minute is 3-10 wt% of the total amount of pre-prepared solution. The addition process is carried out at 40-70°C under stirring conditions to obtain a gel. In the gel, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the molar ratio of silicon source: aluminum source: alkali source: template agent: auxiliary solvent: seed crystal: water is 1:0.005-0.02:0.10-0.18:0.2-0.3:0.01-0.05:0.1-0.5:5-15.

[0013] S3. The obtained gel is crystallized, then filtered, washed and dried to obtain ZSM-22 molecular sieve.

[0014] The method for synthesizing ZSM-22 molecular sieve according to the present invention uses an organic template agent, preferably 1,6-hexanediamine.

[0015] The synthesis method of ZSM-22 molecular sieve of the present invention uses one or more of diethylamine, anhydrous ethanol and ethylenediamine as the auxiliary solvent.

[0016] The method for synthesizing ZSM-22 molecular sieve according to the present invention involves 2-6 addition points.

[0017] In the synthesis method of ZSM-22 molecular sieve of the present invention, the temperature at which the pre-prepared solution is added in step S1 is 50-60℃.

[0018] The method for synthesizing ZSM-22 molecular sieve according to the present invention uses silica gel and / or silica as the solid silicon source.

[0019] In the synthesis method of ZSM-22 molecular sieve of the present invention, the crystallization time in step S3 is 10 to 20 hours.

[0020] The aluminum source, alkali source, and seed crystals described in this invention are commonly used substances in the field. This invention does not impose specific limitations, and those skilled in the art can select them according to the actual situation.

[0021] Beneficial effects of this invention:

[0022] 1. This invention promotes the dissolution of solid silicon source by heating the pre-prepared solution and the gel, significantly reducing the viscosity of the system; the multi-point pulse feeding method when adding the pre-prepared solution is beneficial to the uniform dispersion of each raw material component in the gelation process; the addition of auxiliary solvent is beneficial to the dissolution of template agent and helps to disperse in a low-water raw material system, thereby achieving gelation and crystallization in the case of high solid content raw materials (water-silicon ratio 5-10).

[0023] 2. Due to the reduction in water content in the raw material system, less template agent can be added to achieve the corresponding template agent concentration, which can reduce the amount of template agent used by more than 20% (from 0.35 to below 0.3 based on the template agent / SiO2 molar ratio). At the same time, due to the reduction in water content, the yield per batch can be increased to more than 32%.

[0024] 3. Due to the high solid content of the raw materials, on the one hand, the concentration of the template agent in the system is objectively increased, which makes it easier to nucleate in the early stage of crystallization, forming more crystal nuclei and single crystals. On the other hand, the high concentration makes it easy for single crystals to accumulate, forming secondary stacked mesoporous channels, increasing the mesoporous structure of the molecular sieve, and giving it a high degree of crystallinity. Attached Figure Description

[0025] Figure 1 The XRD pattern of ZSM-22 in Comparative Example 1;

[0026] Figure 2 Here is a SEM image of ZSM-22 in Comparative Example 1;

[0027] Figure 3 The XRD pattern of ZSM-22 in Comparative Example 2;

[0028] Figure 4 The image shows the XRD pattern of ZSM-22 in Example 1.

[0029] Figure 5 Here is a SEM image of ZSM-22 in Example 1;

[0030] Figure 6a The N2 adsorption-desorption isotherm of ZSM-22 in Comparative Example 1;

[0031] Figure 6b The N2 adsorption-desorption isotherm of ZSM-22 in Example 1. Detailed Implementation

[0032] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0033] Source of raw materials or equipment: including raw material name, specifications, manufacturer, etc.

[0034]

[0035] Analytical characterization methods:

[0036] Crystal form determination was performed using XRD on a Bruker D2 diffractometer. A Cu target K was used. α The light source was λ = 0.15432 nm, the tube voltage was 40 kV, and the tube current was 40 mA. The scanning speed was 4° / min in the 5–40° range. Qualitative analysis was performed using JCPDS (Junior High-Performance Diagram Data Sheet).

[0037] Morphological analysis was performed using a FEI NanoSEM 450 emission scanning electron microscope with an operating voltage of 5–20 kV and a magnification of 1,000–50,000 times.

[0038] Pore ​​structure and specific surface area analysis were performed using the N2 isothermal adsorption-desorption method on a Micrometrics ASAP 2460 physical adsorption instrument.

[0039] Comparative Example 1 (conventional synthesis, high water-to-silicon ratio)

[0040] Molecular sieves were synthesized using the method disclosed in US Patent US4902406: Aluminum sulfate, silica sol, potassium hydroxide, and 1,6-hexanediamine were dissolved in deionized water to obtain a gel ratio (molar ratio) as follows: silica sol:potassium hydroxide:aluminum sulfate:1,6-hexanediamine:water = 1:0.20:0.011:0.30:40. The gel was then crystallized at 160°C and 400 rpm for 50 hours. After removal from the reactor, the gel was filtered, dried, and calcined (at 110°C) to obtain the product. XRD analysis confirmed it to be a pure-phase ZSM-22 molecular sieve. Figure 1 Scanning electron microscopy (SEM) analysis revealed that the product has a rod-like morphology, with a length of approximately 1 μm. Figure 2 The comparative product was used as a seed crystal.

[0041] Comparative Example 2 (High solids content, no auxiliary solvent added)

[0042] (1) Gel preparation: Dissolve aluminum sulfate, potassium hydroxide, 1,6-hexanediamine and seed crystals in deionized water and mix them. Then heat to 70°C. Add the mixture slowly to the coarse-pore silica gel at a rate of 3% per minute through 4 feeding points. During this process, stir and keep warm (60°C) until the mixture is completely added. The final gel ratio (molar ratio) is: silicon source (SiO2): aluminum source (Al2O3): alkali source: template agent: seed crystal: water = 1:0.01:0.10:0.21:0.04:5.

[0043] (2) Crystallization and evacuation: The obtained mixed gel was added to a synthesis reactor for crystallization for 20 hours. After crystallization, it was filtered, washed, and dried to obtain the product. XRD analysis showed it to be ZSM-22 molecular sieve, containing obvious white silica and ZSM-5 impurities, such as... Figure 3 .

[0044] Comparative Example 3 (High solids content, no heating during gelation process)

[0045] (1) Gel preparation: Aluminum sulfate, potassium hydroxide, 1,6-hexanediamine, seed crystals, and diethylamine were dissolved in deionized water and mixed. The mixture was added slowly to the coarse-pore silica gel at a rate of 3% per minute through 4 feeding points, while maintaining stirring until it was completely added. The final gel ratio (molar ratio) was: silicon source (SiO2): aluminum source (Al2O3): alkali source: template agent: auxiliary solvent: seed crystals: water = 1:0.01:0.15:0.21:0.08:8.

[0046] (2) Crystallization and discharging: The obtained mixed gel was added to a synthesis reactor for crystallization for 20 hours. After crystallization, it was filtered, washed, and dried to obtain the product. XRD analysis showed that it was a ZSM-22 molecular sieve, containing obvious white silica and ZSM-5 impurities, with the following characteristics: Figure 3 .

[0047] Comparative Example 4 (high solids content, no control over the rate and method of adding the pre-prepared solution)

[0048] (1) Gel preparation: The aluminum source, alkali source, 1,6-hexanediamine, seed crystal, and diethylamine were dissolved in deionized water and then mixed and added to the coarse-pore silica gel at one time. During the process, stirring was required until the gel was completely added. The final gel ratio (molar ratio) was: silicon source (SiO2): aluminum source (Al2O3): alkali source: template agent: seed crystal: auxiliary solvent: water = 1:0.01:0.10:0.21:0.04:0.5:6.

[0049] (2) Crystallization and discharging: The obtained mixed gel was added to a synthesis reactor for crystallization for 20 hours. After crystallization, it was filtered, washed, and dried to obtain the product. XRD analysis showed that it was a ZSM-22 molecular sieve, containing obvious white silica and ZSM-5 impurities, with the following characteristics: Figure 3 .

[0050] Example

[0051] Example 1

[0052] (1) Gel preparation: Sodium aluminate, potassium hydroxide, 1,6-hexanediamine, seed crystals, and diethylamine were dissolved in deionized water and mixed, and then heated to 70°C. The mixture was slowly added to the coarse-pore silica gel at a rate of 10% per minute through 6 feeding points, while maintaining stirring and keeping the temperature (60°C) until it was completely added. The final gel ratio (molar ratio) was: silicon source (SiO2): aluminum source (Al2O3): alkali source: template agent: seed crystals: auxiliary solvent: water = 1:0.01:0.10:0.21:0.04:0.5:6.5.

[0053] (2) Crystallization and discharging: The obtained mixed gel was added to a synthesis reactor for crystallization for 20 hours. After crystallization, the product was obtained by filtration, washing, and drying. XRD analysis showed it to be a pure-phase ZSM-22 molecular sieve. Figure 4 Scanning electron microscopy (SEM) analysis revealed that the product morphology consisted of rod-like and crack-like structures, with a length of approximately 1-2 μm. Figure 5 .

[0054] Example 2

[0055] (1) Gel preparation: Sodium aluminate, potassium hydroxide, 1,6-hexanediamine, seed crystals, and anhydrous ethanol were dissolved in deionized water and mixed, and then heated to 90°C. The mixture was slowly added to the fumed silica at a rate of 6% per minute through four feeding points, while maintaining stirring and temperature (60°C) until it was completely added. The final gel ratio (molar ratio) was: silicon source (SiO2): aluminum source (Al2O3): alkali source: template agent: seed crystals: auxiliary solvent: water = 1:0.015:0.10:0.21:0.05:0.4:6.5.

[0056] (2) Crystallization and evacuation: The obtained mixed gel was added to a synthesis reactor for crystallization for 20 hours. After crystallization, the product was obtained by filtration, washing, and drying. XRD analysis showed it to be a pure-phase ZSM-22 molecular sieve. XRD and scanning electron microscopy (SEM) results showed... Figure 4 , Figure 5 Its characteristics.

[0057] Example 3

[0058] (1) Gel preparation: Aluminum sulfate, potassium hydroxide, 1,6-hexanediamine, seed crystals, and diethylamine were dissolved in deionized water and mixed, and then heated to 60°C. The mixture was slowly added to the fumed silica at a rate of 6% per minute through four feeding points, while maintaining stirring and keeping warm (50°C) until it was completely added. The final gel ratio (molar ratio) was: silicon source (SiO2): aluminum source (Al2O3): alkali source: template agent: seed crystals: auxiliary solvent: water = 1:0.015:0.15:0.22:0.03:0.3:9.

[0059] (2) Crystallization and evacuation: The obtained mixed gel was added to a synthesis reactor and crystallized for 16 hours. After crystallization, the product was obtained by filtration, washing, and drying. XRD analysis showed it to be a pure-phase ZSM-22 molecular sieve. XRD and scanning electron microscopy (SEM) results showed... Figure 4 , Figure 5 Its characteristics.

[0060] Example 4

[0061] (1) Gel preparation: Sodium aluminate, potassium hydroxide, 1,6-hexanediamine, seed crystals, and ethylenediamine were dissolved in deionized water and mixed, and then heated to 60°C. The mixture was slowly added to the silica gel at a rate of 3% per minute through two feeding points, while maintaining stirring and keeping warm (50°C) until it was completely added. The final gel ratio (molar ratio) was: silicon source (SiO2): aluminum source (Al2O3): alkali source: template agent: seed crystals: auxiliary solvent: water = 1:0.020:0.18:0.2:0.02:0.2:14.

[0062] (2) Crystallization and evacuation: The obtained mixed gel was added to a synthesis reactor and crystallized for 16 hours. After crystallization, the product was obtained by filtration, washing, and drying. XRD analysis showed it to be a pure-phase ZSM-22 molecular sieve. XRD and scanning electron microscopy (SEM) results showed... Figure 4 , Figure 5 Its characteristics.

[0063] Example 5:

[0064] (1) Gel preparation: Aluminum sulfate, potassium hydroxide, 1,6-hexanediamine, seed crystals, and anhydrous ethanol were dissolved in deionized water and mixed. The mixture was then heated to 50°C. The mixture was slowly added to the silica gel at a rate of 3% per minute through two feeding points. During this process, stirring and heat preservation (40°C) were maintained until the mixture was completely added. The final gel ratio (molar ratio) was: silicon source (SiO2): aluminum source (Al2O3): alkali source: template agent: seed crystals: auxiliary solvent: water = 1:0.012:0.16:0.3:0.01:0.1:14.

[0065] (2) Crystallization and evacuation: The obtained mixed gel was added to a synthesis vessel for crystallization for 10 hours. After crystallization, the product was obtained by filtration, washing, and drying. XRD analysis showed it to be a pure-phase ZSM-22 molecular sieve. XRD and scanning electron microscopy (SEM) results showed... Figure 4 , Figure 5 Its characteristics.

[0066] Example 6:

[0067] The pore structure of the products in Comparative Example 1 and Example 1 was characterized using BET. Figure 6a The N2 adsorption-desorption isotherm of ZSM-22 in Comparative Example 1 is shown below. Figure 6b The N2 adsorption-desorption isotherm of ZSM-22 in Example 1 is shown. Comparison revealed that the product of Example 1 exhibits a large hysteresis loop at p / p0 > 0.5, indicating the presence of a mesoporous structure. Analysis of the hysteresis loop type suggests it may be a slit-like channel, which is consistent with the SEM results of Example 1, confirming that the product of Example 1 possesses a mesoporous structure.

[0068] 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 ZSM-22 molecular sieve, characterized in that, Includes the following steps: S1, dissolve the aluminum source, alkali source, template agent, seed crystal and auxiliary solvent in deionized water and mix them, then heat to 40-90℃ to prepare a pre-prepared solution; S2, the pre-prepared solution is added to the solid silicon source at multiple addition points. The amount of pre-prepared solution added per minute is 3-10 wt% of the total amount of pre-prepared solution. The addition process is carried out at 40-70℃ under stirring conditions to obtain a gel. In the gel, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the molar ratio of silicon source: aluminum source: alkali source: template agent: auxiliary solvent: seed crystal: water is 1:0.005-0.02:0.10-0.18:0.2-0.3:0.01-0.05:0.1-0.5:5-15. S3, the obtained gel is crystallized, then filtered, washed and dried to obtain ZSM-22 molecular sieve; The auxiliary solvent is one or more of diethylamine, anhydrous ethanol, and ethylenediamine.

2. The method for synthesizing ZSM-22 molecular sieve according to claim 1, characterized in that, The template agent is an organic template agent.

3. The method for synthesizing ZSM-22 molecular sieve according to claim 1, characterized in that, The template agent is 1,6-hexanediamine.

4. The method for synthesizing ZSM-22 molecular sieve according to claim 1, characterized in that, The number of insertion points is 2-6.

5. The method for synthesizing ZSM-22 molecular sieve according to claim 1, characterized in that, The temperature at which the pre-prepared solution is added in step S1 is 50-60℃.

6. The method for synthesizing ZSM-22 molecular sieve according to claim 1, characterized in that, The solid silicon source is silica gel and / or silica.

7. The method for synthesizing ZSM-22 molecular sieve according to claim 1, characterized in that, The crystallization time in step S3 is 10-20 hours.

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