Method for multi-field coupling reinforced synthesis of flaky molecular sieve

Abstract

The invention discloses a multi-field coupling reinforced synthesis method of a flaky molecular sieve, which is characterized by comprising the following steps: 1) pumping a silicon source and an aluminum source into a multi-field coupling reinforced reactor, and mixing and reacting for a period of time to form initial reaction gel; 2) transferring the obtained reaction initial gel into a crystallization kettle for reaction crystallization; after the reaction is finished, taking out a product, filtering, washing and drying to obtain the flaky molecular sieve. According to the method disclosed by the invention, the mass transfer efficiency is improved by utilizing a multi-field coupling strengthening technology, so that reaction crystallization is promoted, and the high-crystallinity flaky molecular sieve is synthesized under the condition of low / no template agent.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve synthesis, and in particular relates to a method for synthesizing a flaky molecular sieve by multi-field coupling enhancement. Background Art

[0002] Molecular sieves are composed of aluminum oxide tetrahedron (AlO 4 ) and silicon-oxygen tetrahedron (SiO 4 ) Inorganic crystalline materials formed by connecting shared vertex oxygen atoms are widely used in petrochemical, fine chemical and environmental chemical fields due to their high specific surface area, excellent hydrothermal stability, acidity, pores and adjustable surface properties. Molecular sieves are one of the most important molecular sieves in petrochemical catalytic cracking catalysts and the main source of active components. Therefore, the structure and diffusion path of molecular sieves have a crucial impact on the overall catalyst performance. Although the current process for synthesizing molecular sieves is relatively mature, the quality of the products is relatively stable, and they are widely used in industrial devices, there are still challenges in simplifying the synthesis steps, shortening the synthesis cycle, optimizing structural performance and improving synthesis efficiency. At present, traditional molecular sieves are mostly octahedral molecular sieves with a grain size of about 1μm or spherical molecular sieves with larger particles. They have long pores, and the active centers are mostly distributed in micropores. The action sites are not easy to access and cannot meet the existing reaction requirements. Therefore, how to optimize the crystal structure becomes particularly important for the catalytic application of molecular sieves. In the field of industrial catalysts, it is generally believed that the thinner the molecular sieve, the better (Nature, 2009, 461, 182-183). By reducing the molecular sieve of three-dimensional scale by one dimension, a sheet molecular sieve with short pores and large surface area can be obtained, thereby effectively reducing the diffusion restriction problem in the reaction process, so the sheet molecular sieve has a catalytic ability superior to conventional molecular sieves (Ind. Eng. Chem. Res. 1999, 38, 1350-1356). At present, most of the synthesis methods of sheet molecular sieves need to use a large amount of organic templates, which not only pollutes the environment, but also causes waste of resources. Therefore, it is of great significance to develop a high-efficiency sheet molecular sieve synthesis technology with low template dosage or no template.

[0003] In view of this, the hydrothermal method for synthesizing molecular sieves is the mainstream method for synthesizing molecular sieves because of its simple production process and low manufacturing cost. The hydrothermal synthesis method for preparing molecular sieves mainly includes: the process of contacting, dispersing and mixing the silicon source and the aluminum source to form the initial gel of the reaction and the crystallization process. At present, ordinary stirred tanks are mainly used in the industry to prepare molecular sieves. Since the low-viscosity silicon source and aluminum source are mixed to quickly form a high-viscosity system during the preparation stage of the initial gel of the reaction, the ordinary stirred tank preparation of molecular sieves has mass transfer limitation problems and amplification effects. In the process of industrial amplification production, there are problems such as low production efficiency and unstable product quality. Therefore, it is urgent to introduce other technologies to solve the mass transfer limitation problems and amplification effects of high-viscosity systems.

[0004] Multi-field coupling enhancement technology is an important means of enhancing mass transfer and improving reaction efficiency in the chemical industry. Through the multi-field coupling enhancement effect, the material is micro-mixed, and its mass transfer efficiency is higher than that of ordinary stirred tanks. Therefore, the introduction of multi-field coupling enhancement technology into the molecular sieve synthesis process can effectively improve the mass transfer efficiency of the reaction process and accelerate the reaction crystallization. For example, Chinese patent applications CN114870768A, CN114870663A and CN108217674A all disclose a supergravity reactor for synthesizing molecular sieves, which can overcome the problem of liquid phase discontinuity, tear the liquid into nano-microscale droplets or beads from the micro environment, and then enhance mass transfer, and generate nano-micro bubbles by supergravity reactor, reduce the nucleation barrier of crystals, accelerate the crystal reaction rate, promote uniform growth of grains, and make the crystal size more uniform and narrow.

[0005] Furthermore, Chinese patent applications CN111620349A, CN109574031A, CN109574034A, CN110436476A, etc. disclose the rapid synthesis of highly ordered pores and easily dispersible molecular sieves using ultrasound. The use of ultrasound technology can make the raw materials quickly dispersed and evenly reacted, and the process is simple, low cost, and good repeatability, and it is easy to apply to industrial production. Patents CN118183783A, CN116099575A, CN114804138A, CN114195169A, and CN112110454A use microwave technology to synthesize molecular sieves, which can greatly shorten the crystallization reaction time, reduce energy consumption costs, and improve production efficiency, which is helpful to promote the large-scale application of molecular sieves.

[0006] Furthermore, Chinese patent applications CN111268690A, CN106829993A and CN104876238A disclose that ultraviolet technology can be used to excite the system to produce hydroxyl radicals, triggering free radical reactions, thereby accelerating the synthesis process of molecular sieves. This not only shortens the synthesis cycle, but also reduces production costs and improves the quality of molecular sieves, and has certain industrial application prospects.

[0007] Furthermore, Chinese patent application CN101054186A discloses the use of a microchannel reactor to continuously and rapidly prepare molecular sieves, which has the advantages of simple production equipment and extremely short reaction residence time.

[0008] Furthermore, Chinese patent application CN113072078A discloses the use of ultrasound and microwave coupling to prepare a high-crystallinity 13X molecular sieve, which can effectively shorten the reaction time, increase the utilization rate of raw material resources, and improve production efficiency.

[0009] In summary, the introduction of multi-field coupling enhancement technology to synthesize molecular sieves can improve crystal quality, reduce crystal size, accelerate crystallization rate and improve synthesis efficiency. However, the above technical defects are: most of the reaction systems used are molecular sieves of other morphologies, and for the flake molecular sieve system, it is not disclosed how to synthesize high-crystallinity flake molecular sieves with low template dosage or without template. Summary of the invention

[0010] The technical problem to be solved by the present invention is to provide a method for synthesizing flaky molecular sieves by multi-field coupling enhancement; the method of the present invention utilizes multi-field coupling enhancement technology to improve mass transfer efficiency, thereby promoting reaction crystallization, and synthesizing high-crystallinity flaky molecular sieves under low / no template agent.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0012] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0013] 1) Pumping silicon source and aluminum source into a multi-field coupling enhanced reactor, and forming an initial reaction gel after mixing and reacting for a period of time;

[0014] 2) transferring the obtained initial reaction gel to a crystallization kettle for reaction crystallization; after the reaction is completed, taking out the product, filtering, washing, and drying to obtain a flaky molecular sieve.

[0015] Preferably, in step 1), the multi-field coupling enhancement includes one or more coupling of supergravity, ultrasound, microwave, ultraviolet, and microchannel.

[0016] Preferably, in step 1), the multi-field coupled enhanced reactor includes one of an external circulation supergravity reactor, an internal circulation supergravity reactor, a dynamic crystallization reactor, an ultrasonic coupled reactor, a microwave coupled reactor, an ultraviolet coupled reactor, and a microchannel reactor.

[0017] Preferably, the rotor speed in the multi-field coupling enhanced reactor is 300-2850 r / min; more preferably 1500-2850 r / min.

[0018] More preferably, the rotor type in the multi-field coupling enhanced reactor is one of a packing type, a column type and a stirring blade type.

[0019] Preferably, in step 1), the reaction temperature of the mixed reaction is 10-200° C., and the period of time is 0.1-30 h.

[0020] Preferably, in step 1), the silicon source is selected from one or more of water glass, silica sol, silica gel, tetraethyl silicate or white carbon black.

[0021] Preferably, in step 1), the aluminum source is selected from one or more of aluminum hydroxide, aluminum sulfate, sodium aluminate, sodium metaaluminate, aluminum nitrate, aluminum chloride, pseudo-boehmite, and aluminum sol.

[0022] Preferably, in step 2), the reaction crystallization temperature is 80-180° C., and the reaction crystallization time is 1-100 h.

[0023] Preferably, in step 2), the washing is performed by washing with deionized water for 3-6 times; the drying is performed by drying in a forced air drying oven at a temperature of 60-120° C. for 6-12 hours.

[0024] Preferably, in step 1), a guiding agent is added to the mixed reaction, and the guiding agent is obtained by simultaneously pumping the water glass solution and the high-alkali sodium aluminate solution into an external field enhanced reactor, mixing and reacting, and then standing for aging; the standing aging time is 0.1-72h; more preferably, the standing aging time is 6-24h. The high-alkali sodium aluminate solution refers to a sodium aluminate solution with a pH ≧10.

[0025] Any range described in the present invention includes the end value and any numerical value between the end values ​​and any sub-range formed by the end value or any numerical value between the end values.

[0026] Unless otherwise specified, all raw materials in the present invention can be purchased from the market, and the equipment used in the present invention can adopt conventional equipment in the relevant field or refer to the existing technology in the relevant field.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention utilizes multi-field coupling to enhance mass transfer and promotes reaction nucleation and crystallization, effectively shortens the crystallization time, improves the system element utilization rate, product crystallinity and synthesis efficiency, and has universal applicability to molecular sieve synthesis systems.

[0029] 2. The sheet-like molecular sieve synthesized by the present invention has a rich outer surface, which increases the proportion of active sites and the molecular diffusion capacity.

[0030] 3. The three-dimensional size of the flaky molecular sieve synthesized by the present invention has at least one dimension less than 200 nm.

[0031] 4. The multi-field coupling enhanced reactor used in the preparation method of the multi-field coupling enhanced synthetic flaky molecular sieve provided by the present invention has the characteristics of small equipment size, small footprint, no amplification effect, etc., and can be widely used in various fields such as catalytic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0033] Figure 1 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Example 1 of the present invention are shown;

[0034] Figure 2 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Example 2 of the present invention are shown;

[0035] Figure 3 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Example 3 of the present invention are shown;

[0036] Figure 4 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Example 4 of the present invention are shown;

[0037] Figure 5 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Comparative Example 1 of the present invention are shown;

[0038] Figure 6 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Comparative Example 2 of the present invention are shown.

[0039] Figure 7 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Comparative Example 3 of the present invention are shown.

[0040] Figure 8 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Comparative Example 4 of the present invention are shown.

[0041] Fig. 9 The XRD patterns (left) and SEM patterns (right) of the samples prepared in Example 8 of the present invention and Comparative Example 6 are shown. DETAILED DESCRIPTION

[0042] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0043] As one aspect of the present invention, a method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0044] 1) Pumping silicon source and aluminum source into a multi-field coupling enhanced reactor, and forming an initial reaction gel after mixing and reacting for a period of time;

[0045] 2) transferring the obtained initial reaction gel to a crystallization kettle for reaction crystallization; after the reaction is completed, taking out the product, filtering, washing, and drying to obtain a flaky molecular sieve.

[0046] According to some embodiments of the present invention, in step 1), the multi-field coupling enhancement includes coupling of one or more of supergravity, ultrasound, microwave, ultraviolet, and microchannel.

[0047] According to certain embodiments of the present invention, in step 1), the multi-field coupled enhanced reactor includes one of an external circulation supergravity reactor, an internal circulation supergravity reactor, a dynamic crystallization reactor, an ultrasonic coupled reactor, a microwave coupled reactor, an ultraviolet coupled reactor, and a microchannel reactor.

[0048] Preferably, the rotor speed in the multi-field coupling enhanced reactor is 300-2850 r / min; more preferably 1500-2850 r / min.

[0049] According to some embodiments of the present invention, the rotor type in the multi-field coupling enhanced reactor is one of a packing type, a column type and a stirring blade type.

[0050] According to certain embodiments of the present invention, in step 1), the reaction temperature of the mixed reaction is 10-200° C., and the period of time is 0.1-30 h.

[0051] According to some embodiments of the present invention, in step 1), the silicon source is selected from one or more of water glass, silica sol, silica gel, tetraethyl silicate or white carbon black.

[0052] According to some embodiments of the present invention, in step 1), the aluminum source is selected from one or more of aluminum hydroxide, aluminum sulfate, sodium aluminate, sodium metaaluminate, aluminum nitrate, aluminum chloride, pseudo-boehmite, and aluminum sol.

[0053] According to some embodiments of the present invention, in step 2), the reaction crystallization temperature is 80-180° C., and the reaction crystallization time is 1-100 h.

[0054] According to some embodiments of the present invention, in step 2), the washing is performed by washing with deionized water for 3-6 times; the drying is performed by drying in a forced air drying oven at a temperature of 60-120° C. for 6-12 hours.

[0055] According to some embodiments of the present invention, preferably, in step 1), a guiding agent is added to the mixed reaction, and the guiding agent is obtained by simultaneously pumping two streams of materials, a water glass solution and a high-alkali sodium aluminate solution, into an external field enhanced reactor, mixing the reaction, and then standing for aging; the standing aging time is 0.1-72h; more preferably, the standing aging time is 6-24h. The high-alkali sodium aluminate solution refers to a sodium aluminate solution with a pH ≧ 10.

[0056] If no specific experimental steps or conditions are specified in the embodiments and comparative examples of the present invention, the conventional experimental steps or conditions described in the literature in the art can be used. All raw materials in the present invention can be purchased on the market, and the equipment used in the present invention can be conventional equipment in the relevant field or can be carried out with reference to the existing technology in the relevant field.

[0057] Example 1

[0058] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0059] Weigh 190.5g of high-alkali sodium aluminate solution and 129.7g of water glass solution and pump them into a supergravity reactor for premixing and reaction for 1h, and keep the temperature at 32°C for static constant temperature aging for 12h to obtain a directing agent;

[0060] Weigh 320g of water glass solution, 60.61g of directing agent, 176g of deionized water, 135.15g of aluminum sulfate solution, and 70.91g of low-alkali sodium aluminate solution and pump them into the supergravity reactor in sequence. After premixing and stirring for 1h, an initial reaction gel is obtained. The initial reaction gel is transferred to a crystallization kettle for reaction and crystallization at 100°C for 18h. After the reaction is completed, the product is taken out for filtration and washing until the pH value of the solution is neutral. The product is dried at 100°C for 10h to obtain a flaky molecular sieve, whose particle size distribution is mostly concentrated at about 370nm, and the thickness of the flaky b-axis is about 100nm.

[0061] Figure 1 Shown are the XRD pattern (left) and SEM image (right) of the sample prepared in Example 1.

[0062] Example 2

[0063] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0064] Weigh 190.5g of high-alkali sodium aluminate solution and 129.7g of water glass solution and pump them into a supergravity reactor for premixing and reaction for 3h, and keep the temperature at 32°C for static constant temperature aging for 12h to obtain a directing agent;

[0065] 320 g of water glass solution, 60.61 g of directing agent, 176 g of deionized water, 135.15 g of aluminum sulfate solution and 70.91 g of low-alkali sodium aluminate solution were weighed and pumped into the supergravity reactor in sequence. After premixing and stirring for 2 hours, an initial reaction gel was obtained. The initial reaction gel was transferred to a crystallization kettle for reaction and crystallization at 100° C. for 18 hours. After the reaction, the product was taken out for filtration and washing until the pH value of the solution was neutral. The product was dried at 100° C. for 10 hours to obtain a flaky molecular sieve, whose particle size distribution was mostly concentrated at about 350 nm, and the thickness of the flaky b-axis was about 55 nm.

[0066] Figure 2 Shown are the XRD pattern (left) and SEM image (right) of the sample prepared in Example 2.

[0067] Example 3

[0068] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0069] Weigh 190.5g of high-alkali sodium aluminate solution and 129.7g of water glass solution and pump them into a microwave-coupled high-gravity reactor for premixing and reaction for 30 minutes, and keep the temperature at 32°C for static constant temperature aging for 12 hours to obtain a directing agent;

[0070] 211.2 g of water glass solution, 40 g of directing agent, 116.2 g of deionized water, 89.2 g of aluminum sulfate solution and 46.8 g of low-alkali sodium aluminate solution were weighed and pumped into a microwave-coupled ultragravity reactor in sequence. After premixing and stirring for 30 min, an initial reaction gel was obtained. The initial reaction gel was transferred to a crystallization kettle for reaction and crystallization at 100 ° C for 20 h. After the reaction was completed, the product was taken out for filtration and washing until the pH value of the solution was neutral. The product was dried at 100 ° C for 10 h to obtain a flaky molecular sieve, whose particle size distribution was mostly concentrated at about 480 nm, and the thickness of the flaky b-axis was about 100 nm.

[0071] Figure 3 The XRD pattern (left) and SEM image (right) of the sample prepared in Example 3 are shown.

[0072] Example 4

[0073] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0074] Weigh 50g of high-alkali sodium aluminate solution and 69.3g of water glass solution and pump them into an ultrasonic-coupled high-gravity reactor for premixing and reaction for 1h, and keep the temperature at 32°C for static constant temperature aging for 12h to obtain a directing agent;

[0075] 211.2 g of water glass solution, 40 g of directing agent, 116.2 g of deionized water, 89.2 g of aluminum sulfate solution and 46.8 g of low-alkali sodium aluminate solution were weighed and pumped into an ultrasonically coupled high-gravity reactor in sequence. After premixing and stirring for 2 h, an initial reaction gel was obtained. The initial reaction gel was transferred to a crystallization kettle for reaction and crystallization at 100 ° C for 18 h. After the reaction was completed, the product was taken out for filtration and washing until the pH of the solution was neutral. The product was dried at 100 ° C for 10 h to obtain a flaky molecular sieve, whose molecular sieve particle size distribution was mostly concentrated at about 350 nm, and the thickness of the flaky b-axis was about 70 nm.

[0076] Figure 4The XRD pattern (left) and SEM pattern (right) of the sample prepared in Example 4 of the present invention are shown.

[0077] Example 5

[0078] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0079] Weigh 50g of high-alkali sodium aluminate solution and 69.3g of water glass solution and pump them into a UV-coupled ultra-gravity reactor to stir and mix for 1h, and then continue to stand at a constant temperature of 32°C for 14h to obtain a directing agent;

[0080] 100 g of water glass solution, 18.94 g of directing agent, 55 g of deionized water, 42.23 g of aluminum sulfate solution and 22.16 g of low-alkali sodium aluminate solution were weighed and pumped into a UV-coupled ultragravity reactor in sequence for premixing and reaction for 50 minutes to obtain an initial reaction gel, and the initial reaction gel was transferred to a crystallization kettle for reaction and crystallization at 100° C. for 20 hours. After the reaction, the product was taken out for filtration and washing until the pH value of the solution was neutral, and the product was dried at 100° C. for 10 hours to obtain a flaky molecular sieve, whose particle size distribution was mostly concentrated at about 480 nm, and the thickness of the flaky b-axis was about 90 nm.

[0081] Example 6

[0082] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0083] Weigh 50g of high-alkali sodium aluminate solution and 69.3g of water glass solution and pump them into a microchannel coupled high gravity reactor for stirring and mixing for 50 minutes, and then continue to stand at a constant temperature of 32°C for aging for 12 hours to obtain a directing agent;

[0084] 100 g of water glass solution, 18.94 g of directing agent, 55 g of deionized water, 42.23 g of aluminum sulfate solution and 22.16 g of low-alkali sodium aluminate solution were weighed and pumped into a microchannel coupled supergravity reactor in sequence. After premixing and stirring for 50 min, an initial reaction gel was obtained. The initial reaction gel was transferred to a crystallization kettle for reaction and crystallization at 100 °C for 24 h. After the reaction, the product was taken out for filtration and washing until the pH of the solution was neutral. The product was dried at 100 °C for 10 h to obtain a flaky molecular sieve, whose particle size distribution was mostly concentrated at about 510 nm, and the thickness of the flaky b-axis was about 110 nm.

[0085] Example 7

[0086] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0087] Weigh 50g of high-alkali sodium aluminate solution and 69.3g of water glass solution and pump them into a UV-coupled ultra-gravity reactor to stir and mix for 1h, and then continue to stand at a constant temperature of 32°C for 14h to obtain a directing agent;

[0088] Weigh 320g of water glass solution, 60.61g of directing agent, 176g of deionized water, 135.15g of aluminum sulfate solution, and 70.91g of low-alkali sodium aluminate solution, and pump them into the ultra-gravity reactor in sequence. After premixing and stirring for 30 minutes, the initial reaction gel is obtained, and the initial reaction gel is transferred to a crystallization kettle for reaction and crystallization at 100°C for 24 hours. After the reaction is completed, the product is taken out for filtration and washing until the pH value of the solution is neutral. The product is dried at 80°C for 14 hours to obtain a flaky molecular sieve, and the particle size distribution of the molecular sieve is mostly concentrated at about 500nm, and the thickness of the flaky b-axis is about 100nm.

[0089] Example 8

[0090] A method for synthesizing a flaky molecular sieve by multi-field coupling enhancement comprises the following steps:

[0091] 66.2g of tetrapropylammonium hydroxide (25% aqueous solution) was dissolved in 100.0g of deionized water, and 70.1g of tetraethyl orthosilicate was added to the solution under stirring and stirred for 0.5h as a feed A. 0.62g of pseudo-boehmite and 13.07g of urea were dissolved in 129.0g of deionized water as a feed B, and the mixture was simultaneously pumped into an ultra-gravity reactor at room temperature for premixing and dispersion for 3h to obtain the initial reaction gel, which was transferred to an autoclave and crystallized at 180°C for 2d. After the reaction was completed, the product was taken out for filtration and washing until the pH of the solution was neutral, and the product was dried at 80°C to obtain a flaky molecular sieve, the particle size distribution of which was mostly concentrated around 2μm, and the thickness of the flaky b axis was about 90nm.

[0092] Comparative Example 1

[0093] The same as Example 1, except that the ultra-gravity reactor used in the initial gel preparation process of the reaction was replaced with a traditional stirring kettle. Due to the limited mass transfer of the traditional stirring kettle, the reaction was stirred for 2 hours after all the raw materials were added in the initial gel preparation stage of the reaction, and then transferred to the hydrothermal crystallization kettle for crystallization at 100° C. for 24 hours. After the same filtration, washing and drying, a flaky molecular sieve was obtained, and the particle size distribution of the molecular sieve was mostly concentrated around 480 nm, and the thickness of the flaky b axis was about 138 nm.

[0094] It can be seen that in Example 1, the directing agent and the initial reaction gel were premixed for 1 hour, and the conventional stirred tank extended the premixing time of the initial reaction gel stage with higher viscosity due to limited mass transfer. It was found that increasing the premixing time of the ordinary stirred tank during the raw material mixing process still could not reduce the particle size and thickness of the molecular sieve. Then, in Example 2, increasing the premixing time of the multi-field coupling enhancement technology can significantly reduce the particle size and thickness of the molecular sieve. Therefore, reducing the mass transfer mixing effect will affect the formation of the product structure morphology.

[0095] Figure 5 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Comparative Example 1 are shown.

[0096] Comparative Example 2

[0097] The same as Example 4, except that the ultrasonically coupled high gravity reactor used in the initial gel preparation process of the reaction was replaced with a conventional stirred tank. Due to the limited mass transfer of the conventional stirred tank, the stirring reaction was increased to 4 hours after all the raw materials were added in the initial gel preparation stage of the reaction, and then transferred to the hydrothermal crystallization kettle for crystallization at 100° C. for 24 hours. After the same filtration, washing and drying, a flaky molecular sieve was obtained, and the particle size distribution of the molecular sieve was mostly concentrated around 500 nm, and the thickness of the flaky b axis was about 135 nm.

[0098] It can be seen that in Example 4, the guiding agent was premixed for 1 hour in the ultrasonically coupled supergravity reactor, and the initial reaction gel was premixed for 2 hours, while the guiding agent and the initial reaction gel were premixed for 4 hours in the traditional stirred tank. It was found that extending the premixing time in the initial reaction gel stage did not reduce the particle size and thickness of the molecular sieve. This is because the materials cannot be completely mixed due to the limited mass transfer in the ordinary stirred tank during the premixing stage, which in turn limits the particle size and thickness of the molecular sieve. Therefore, reducing the mass transfer mixing effect will affect the formation of the product structure morphology.

[0099] Figure 6 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Comparative Example 2 are shown.

[0100] Comparative Example 3

[0101] The same as Example 2, except that the initial reaction gel was transferred to a hydrothermal crystallization reactor and crystallized at 140°C for 24 hours. The molecular sieve was obtained after the same filtration, washing and drying, and the obtained molecular sieve had a clustered morphology of about 10 μm.

[0102] It can be seen that although molecular sieves can be obtained when the temperature is increased, the morphology of the molecular sieve has changed. Therefore, the appropriate temperature is beneficial to the formation of flake molecular sieves.

[0103] Figure 7 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Comparative Example 3 are shown.

[0104] Comparative Example 4

[0105] Similar to Example 1, due to the high viscosity of the reaction system, in order to increase its fluidity, promote mixed mass transfer, and reduce retained materials, the amount of deionized water added in the initial gel preparation stage of the reaction was increased, and the initial gel of the reaction was prepared with a weight ratio of water glass, directing agent, aluminum sulfate, low-alkali sodium aluminate and deionized water of 1:0.19:0.42:0.22:1.1, and then transferred to a hydrothermal crystallization kettle and crystallized at 100°C for 24h. After the same filtration, washing and drying, a molecular sieve was obtained, but the molecular sieve obtained had a poor degree of crystallization and a large amount of amorphous products existed.

[0106] It can be seen that although increasing the amount of water can increase the fluidity of the system, the amount of water beyond a certain range will affect the synthesis of the molecular sieve in the reaction system. Therefore, the amount of deionized water added will affect the formation of the product structure morphology. The appropriate amount of water can promote the fluidity of the system materials while synthesizing flake molecular sieves with better crystal form.

[0107] Figure 8 The XRD pattern (left) and SEM pattern (right) of the sample prepared in Comparative Example 4 are shown.

[0108] Comparative Example 5

[0109] The same as Example 1, except that the aging time of the directing agent in the directing agent preparation stage is increased to 200 hours, and the other conditions remain unchanged. Under the same conditions, the initial reaction gel is transferred to a hydrothermal crystallization kettle for crystallization at 100°C for 24 hours. After the same filtration, washing and drying, a flaky molecular sieve is obtained, but the particle size distribution of the obtained molecular sieve is mostly concentrated around 800 nm, and the thickness of the flaky b axis is about 100 nm.

[0110] It can be seen that when the aging time of the directing agent is extended, the directing agent is basically aged completely, the system crystal nucleus particles grow larger, and a larger size of the flake molecular sieve is formed. Therefore, an appropriate aging time of the directing agent is beneficial to obtain a flake molecular sieve with an appropriate particle size.

[0111] Comparative Example 6

[0112] The same as Example 8, except that the ultra-gravity reactor in the initial gel premixing stage of the reaction was replaced with a common stirring kettle, and the premixing time was extended to 12 hours, and the other conditions remained unchanged. The initial gel of the reaction was transferred to an autoclave under the same conditions and crystallized at 180°C for 2 days. After the reaction was completed, the product was taken out and filtered and washed until the pH of the solution was neutral. The product was dried at 80°C to obtain a flaky molecular sieve, the particle size distribution of which was mostly concentrated at about 2 μm, and the thickness of the flaky b axis was about 110 nm.

[0113] It can be seen that in Example 8, the initial gel premixing in the supergravity reactor was 3 hours, while the initial gel premixing in the traditional stirred tank was 12 hours. It was found that the extension of the initial gel premixing time did not reduce the particle size and thickness of the molecular sieve. This is because the use of a supergravity reactor in the premixing stage can enhance mass transfer, improve the utilization of system elements, and thus promote crystallization and reduce the thickness of the molecular sieve. Therefore, increasing the mass transfer mixing effect can improve the quality of the product.

[0114] Fig. 9 The XRD pattern (right) and SEM pattern (left) of the sample prepared in Comparative Example 6 are shown.

[0115] In summary:

[0116] 1) By comparing Examples 1-8 and Comparative Examples 1-6, it can be seen that when the directing agent and / or the initial reaction gel are treated with different premixed reactions, the molecular sieve morphology and crystallinity are different. Compared with the comparative example, the multi-field coupling enhanced synthetic molecular sieve has a higher degree of crystallization, a smaller particle size distribution, and a reduced sheet thickness, and has similar effects on different molecular sieve systems, indicating that the multi-field coupling enhanced synthetic molecular sieve has universal applicability.

[0117] 2) Comparative Example 1 is a conventional synthesis scheme. Although it can ensure smooth crystallization, the molecular sieve structure is a mixture of lamellar and octahedral particles, and the lamellar is relatively thick.

[0118] 3) Although comparative example 2 has a flaky structure, its crystallization is poor, and compared with the multi-field coupling enhanced synthetic molecular sieve, the flaky layer is thicker.

[0119] In summary, the molecular sieve prepared by the preparation method of the flaky molecular sieve provided by the present invention has the characteristics of high crystallinity and thin flake layers, which also provides greater possibilities for the active site ratio and molecular diffusion capacity of the molecular sieve, and improves the synthesis efficiency of the molecular sieve through the multi-field coupling enhancement effect, and has a broader application prospect.

[0120] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all implementation methods here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for synthesizing flake molecular sieves by multi-field coupling enhancement, characterized in that: The steps include: 1) Pumping silicon source and aluminum source into a multi-field coupling enhanced reactor, and forming an initial reaction gel after mixing and reacting for a period of time; 2) transferring the obtained initial reaction gel to a crystallization kettle for reaction crystallization; after the reaction is completed, taking out the product, filtering, washing, and drying to obtain a flaky molecular sieve.

2. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 1, characterized in that: In step 1), the multi-field coupling enhancement includes one or more coupling of supergravity, ultrasound, microwave, ultraviolet, and microchannel.

3. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 1, characterized in that: In step 1), the multi-field coupled enhanced reactor includes one of an external circulation supergravity reactor, an internal circulation supergravity reactor, a dynamic crystallization reactor, an ultrasonic coupled reactor, a microwave coupled reactor, an ultraviolet coupled reactor, and a microchannel reactor.

4. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 3, characterized in that: The rotor speed in the multi-field coupling enhanced reactor is 300-2850 r / min; more preferably 1500-2850 r / min; More preferably, the rotor type in the multi-field coupling enhanced reactor is one of a packing type, a column type and a stirring blade type.

5. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 1, characterized in that: In step 1), the reaction temperature of the mixed reaction is 10-200° C., and the period of time is 0.1-30 hours.

6. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 1, characterized in that: In step 1), the silicon source is selected from one or more of water glass, silica sol, silica gel, tetraethyl silicate or white carbon black.

7. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 1, characterized in that: In step 1), the aluminum source is selected from one or more of aluminum hydroxide, aluminum sulfate, sodium aluminate, sodium metaaluminate, aluminum nitrate, aluminum chloride, pseudo-boehmite, and aluminum sol.

8. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 1, characterized in that: In step 2), the reaction crystallization temperature is 80-180° C., and the reaction crystallization time is 1-100 h.

9. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 1, characterized in that: In step 2), the washing is performed with deionized water for 3-6 times; the drying is performed in a forced air drying oven at a temperature of 60-120° C. for 6-12 hours.

10. The method for synthesizing flake molecular sieves by multi-field coupling enhancement according to claim 1, characterized in that: In step 1), a guiding agent is added to the mixed reaction, and the guiding agent is obtained by simultaneously pumping two streams of materials, a water glass solution and a high-alkali sodium aluminate solution, into a multi-field enhanced reactor, mixing the reaction, and then standing for aging; the standing aging time is 0.1-72h; more preferably, the standing aging time is 6-24h.

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