Preparation method of mesoporous molecular sieve and mesoporous molecular sieve prepared thereby

Abstract

The application discloses a mesoporous molecular sieve preparation method and a prepared mesoporous molecular sieve. The mesoporous molecular sieve preparation method comprises the following steps: (1) preparing solution a, which is a silicon source and water; and preparing solution b, which comprises an aluminum source, a template B and water; (2) feeding the two solutions into an ultra-gravity aging and crystallization integrated device to mix the two solutions to obtain an initial gel, then performing pressurized premixing to form an initial gel circulation system, directly performing crystallization, and after the device, performing washing, drying and calcination to prepare the molecular sieve. The method not only realizes the integration of the aging and crystallization processes, but also shortens the aging and crystallization time. The two solutions are pumped into an ultra-gravity rotating bed at a certain feeding rate, and are circulated for multiple times to obtain the mesoporous molecular sieve.

Description

Technical Field

[0001] This invention belongs to the field of zeolite molecular sieve synthesis technology, specifically a method for synthesizing mesoporous zeolite molecular sieves. Background Technology

[0002] Hierarchical porous molecular sieves have attracted widespread attention due to their combination of the excellent mass transfer and diffusion properties of mesoporous materials and the tunable acidity of microporous molecular sieves, making them an effective way to solve the aforementioned problems. The artificial manufacture of molecular sieves mainly relies on simulating the conditions under which natural molecular sieves are produced through hydrothermal synthesis. The hydrothermal method is commonly used to synthesize molecular sieves, producing products with high purity, good dispersibility, and easily controllable particle size.

[0003] CN201310020530.8 describes a method for synthesizing ZSM-5 zeolite. This method uses a polar molecule, hexadecyltrimethylammonium bromide, to intercalate layered silicate Na-kenyaite, obtaining a Na-kenyaite-CTAB intercalation complex. Then, using tetraalkylammonium hydroxide as a template, ZSM-5 molecular sieves are synthesized. The product is then subjected to exfoliation to obtain ZSM-5 molecular sieve crystals. The intercalation process expands the interlayer spacing while maintaining a certain distance to prevent fusion. During crystallization, the growth rate is controlled to allow the molecular sieve to nucleate and grow along the layers of the material. After the reaction, the template and polar molecules are removed, ultimately obtaining the molecular sieve while preserving the two-dimensional structure of the layered material. This significantly improves the accessibility of macromolecular reactants to the active acid centers, thus enhancing the reaction performance. CN97100145.6 provides a method for synthesizing ZSM-5 molecular sieves. The method involves heating water glass to 40°C to its boiling point, then adding an acidified aluminum salt solution to the heated water glass. Molecular sieve seed crystals may or may not be added. The resulting reaction mixture conforms to a molar ratio of (3-11)Na₂O:Al₂O₃:(20-100)SiO₂:(500-1500)H₂O. The reaction mixture is then hydrothermally crystallized using conventional methods. This method can increase the single-boiler yield of ZSM-5 molecular sieve synthesis by more than 100%, and the resulting product has higher crystallinity and specific surface area than products obtained by conventional inorganic methods but is close to products obtained by organic template methods. CN200910169617.5 describes a method for synthesizing ZSM-5 zeolite, which includes mixing amorphous silica solid silicon source, aluminate aluminum source, water, and ZSM-5 synthesis mother liquor, and then crystallizing at a temperature of 110-200℃ for 8-24 hours. The crystallized mixture is filtered, washed, and dried to obtain ZSM-5 zeolite. This method is simple, has a high single-reactor yield, short crystallization time, can reduce mother liquor discharge or achieve zero mother liquor discharge, and has low synthesis and operation costs. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a method for preparing mesoporous molecular sieves and the resulting mesoporous molecular sieve. This method not only integrates the aging and crystallization processes but also shortens the aging and crystallization times. By pumping two solutions into a rotating bed at a specific feed rate and circulating them multiple times, a new type of mesoporous molecular sieve is obtained. When used to synthesize molecular sieves, this method requires very little template agent, reducing environmental pollution. The synthesis steps are simple and easy to industrialize. Furthermore, the aging and crystallization times are significantly shortened, the crystallization temperature is significantly reduced, and the crystallization efficiency is high. The resulting molecular sieve exhibits mesoporous characteristics.

[0005] The first aspect of this invention provides a method for preparing mesoporous molecular sieves, comprising the following steps:

[0006] (1) Solution a is prepared by using a silicon source and water; solution b is prepared by using an aluminum source, template agent B and water.

[0007] (2) The solutions a and b are simultaneously fed into the integrated ultragravity aging and crystallization device to mix and obtain the initial gel. Then, the solution is premixed under pressure to form the initial gel circulation system. Then, the solution is directly crystallized. After exiting the device, the solution is washed, dried, and calcined to prepare the molecular sieve.

[0008] Further, in step (1), the template agent B is at least one of tetrapropylammonium bromide, tetrapropylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, n-propylamine, n-butylamine, n-hexylamine, methylamine, ethylamine, ethylenediamine, diethanolamine, hexamethylene diisocyanate, hexamethylenediamine, hexamethylenetetramine and its derivatives (urotropine and its derivatives). The silicon source is at least one of silica sol, tetraethyl orthosilicate, and silicate, and the aluminum source is at least one of aluminum sulfate, aluminum isopropoxide, and aluminate. The water can be deionized water.

[0009] Further, in step (1), the molar ratio of silicon source, aluminum source, template agent B, and water in solution a and solution b is H2O / SiO2 = 5-1000; Si / Al = 0.5-∞; B / SiO2 = 0-0.6.

[0010] Furthermore, in step (2), the integrated ultragravity aging and crystallization device includes a feeding system, a reaction system, and a discharging system.

[0011] Further, in step (2), the integrated ultragravity aging and crystallization device simultaneously feeds two solutions, solution a and solution b, into the integrated ultragravity aging and crystallization device through the feeding system. The two solutions, solution a and solution b, are mixed in the reaction system to obtain an initial gel. Then, they are pressurized and premixed to form an initial gel circulation system, which is then directly crystallized. Finally, the reacted material is sent out of the device through the discharge system.

[0012] Further, in step (2), the two solutions, solution a and solution b, are pumped into the high gravity rotating bed, with a feed rate ratio of 1:0.1 to 1-10.

[0013] Further, in step (2), the initial gel is discharged into the premixing tank through the liquid outlet of the rotating packed bed in the hypergravity device to form an initial gel circulation system. After more than 2 cycles, preferably 3 to 5 cycles, hypergravity crystallization is carried out directly, and then the reaction is stopped.

[0014] Furthermore, in step (2), the pressure in the initial gel circulation system is increased by 0.1-7 MPa on top of the initial pressure of the circulation system.

[0015] Furthermore, in step (2), the reaction time of pressurized premixing in the initial gel circulation system is more than 10 min, preferably 30 min to 12 h.

[0016] Furthermore, in step (2), during the premixing cycle of the initial gel entering the reaction system through the hypergravity device, the hypergravity rotation speed is maintained at 500-3000 rpm, preferably 1200-2000 rpm, for a time of 5 min-48 h.

[0017] Further, in step (2), the crystallization conditions are: based on the pressure of the supergravity device circulation system, increase the pressure by 0.01-7MPa, preferably 0.1-3MPa, and crystallize at 180-200℃ for 0.5-72h.

[0018] Furthermore, in step (2), the crystallization is circulated in the integrated ultragravity aging and crystallization device, which is dynamic crystallization with a rotation speed of 1500rpm-2000rpm.

[0019] Further, in step (2), the washing adopts conventional technical methods in the art, preferably washing and centrifuging with water 2-3 times; the drying conditions are: temperature of 50-120℃, time of 3-12h; the calcination conditions are 500-600℃, time of 2-6h.

[0020] A second aspect of the present invention also provides a mesoporous molecular sieve prepared by the above method, wherein the mesoporous molecular sieve is one or more composite molecular sieves selected from ZSM-5, ZSM-11, and SAPO-34.

[0021] Furthermore, the specific surface area of ​​the mesoporous molecular sieve is 400-500 cm². 2 / g, micropore volume is 0.06-0.1cm³ 3 / g, mesopore volume is 0.1-0.3cm 3 / g, the proportion of mesopore volume to total pore volume is 15%-90%.

[0022] The third aspect of the present invention provides the molecular sieve described in the second aspect for use in butene pyrolysis reactions.

[0023] Furthermore, the reaction is carried out at a reaction temperature of 500-600℃ and a reaction pressure of 0.01-0.3MPa.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The preparation method provided by this invention utilizes a supergravity reactor to crystallize in one step to obtain mesoporous molecular sieves. The preparation method is simple, easy to operate, and has stable performance.

[0026] The mesoporous molecular sieve obtained by the method provided in this invention has a specific surface area as high as 400-500 cm². 2 The yield per g is 30-50% higher than that of molecular sieves obtained by traditional methods. Furthermore, the proportion of mesopore volume to total pore volume is higher. This overcomes the challenge that molecular sieves prepared using traditional methods generally lack mesopores or have very few mesopores, while mesoporous molecular sieves are more conducive to diffusion and improved catalytic reaction performance. Attached Figure Description

[0027] Figure 1 The XRD pattern of the molecular sieve obtained in Example 1;

[0028] Figure 2 The graphs show the nitrogen adsorption-desorption curves of the molecular sieves obtained in Example 1 and Comparative Example 1. Detailed Implementation

[0029] The following embodiments will further illustrate the molecular sieve synthesis method provided by the present invention, but the scope of protection of the present invention is not limited to these embodiments.

[0030] In this invention, the scanning electron microscope (SEM) images of the samples were taken on a Hitachi S-4800II scanning electron microscope.

[0031] In this invention, the XRD testing conditions were as follows: molecular sieve phase analysis was performed using a Rigaku-Ultima X-ray diffractometer (Japan). CuKα radiation was used, with a wavelength λ = 0.15432 nm. The X-ray diffraction pattern scanning range 2θ was 5-50°, and the scanning speed was 10° / min.

[0032] In this specification, the specific surface area, micropore volume, and mesopore volume of the molecular sieve are measured using the nitrogen physical adsorption-desorption method (BET method): the nitrogen physical adsorption-desorption isotherm of the molecular sieve is measured using a physical adsorption instrument (such as the Micromeretic ASAP2020M physical adsorption instrument), and then calculated using the BET equation and t-plot equation. The experimental conditions for ZSM-5 molecular sieve are: measurement temperature -169℃, and before measurement, the molecular sieve is heat-treated at 550℃ in air for 6 hours, followed by vacuum pretreatment at 350℃ for 4 hours.

[0033] Example 1

[0034] Silica sol solution A was prepared according to a ratio of H2O / SiO2 = 30, and aluminum sulfate and template agent tetrapropylammonium hydroxide solution B was prepared according to a ratio of H2O / Al = 500 and T / SiO2 = 0.02. The two solutions were pumped into a rotating bed at a feed rate ratio of 1. The initial gel was discharged into a premixing tank through the liquid outlet of the rotating bed, forming an initial gel circulation system. The rotation speed was adjusted to 1500 rpm, the pressure increased by 0.7 MPa, and after 5 cycles (approximately 30 minutes), the mixture was directly crystallized at 180℃ under a further increased pressure of 1.7 MPa for 12 hours. The reaction was then stopped at 1500 rpm. After the reaction, the mixture was cooled to room temperature, washed with deionized water and centrifuged three times, dried at 80℃ for 12 hours, and calcined at 550℃ for 4 hours. Nitrogen adsorption-desorption results showed that the obtained ZSM-5 molecular sieve was a mesoporous molecular sieve with a specific surface area as high as 420 cm². 2 / g. The micropore volume is 0.1cm³. 3 / g mesopore volume is 0.2cm 3 / g, accounting for 60% of the total pore volume.

[0035] The XRD pattern of Example 1 is shown below. Figure 1 ,according to Figure 1 It can be determined that it is a ZSM-5 molecular sieve.

[0036] Example 2

[0037] A solution of tetraethyl orthosilicate (H₂O / SiO₂ = 30) was prepared, and a solution of aluminum sulfate and tetrapropylammonium bromide (T / SiO₂ = 0.03) was prepared. The two solutions were pumped into a rotating bed at a feed rate ratio of 1. The initial gel was discharged into a premixing tank through the liquid outlet of the rotating bed, forming an initial gel circulation system. The rotation speed was adjusted to 1500 rpm, the pressure was increased by 0.7 MPa, and after 5 cycles (approximately 40 min), the mixture was directly crystallized at 170℃ under a further increased pressure of 1.7 MPa for 12 h. The reaction was then stopped at 1700 rpm. After the reaction, the mixture was cooled to room temperature, washed with deionized water, centrifuged three times, dried at 80℃ for 12 h, and calcined at 550℃ for 4 h. Nitrogen adsorption-desorption results showed that the obtained ZSM-5 molecular sieve was a mesoporous molecular sieve with a specific surface area as high as 450 cm⁻². 2 / g. The micropore volume is 0.09 cm³. 3 / g, mesopore volume is 0.1cm 3 / g, accounting for 50% of the total pore volume.

[0038] XRD pattern of Example 2 and Figure 1 They are similar, both being ZSM-5 molecular sieves.

[0039] Example 3

[0040] Silica sol solution A was prepared according to a ratio of H2O / SiO2 = 30, and aluminum isopropoxide and template agent n-propylamine solution B was prepared according to a ratio of H2O / Al = 500 and T / SiO2 = 0.01. The two solutions were pumped into a rotating bed at a feed rate ratio of 1. The initial gel was discharged into a premixing tank through the liquid outlet of the rotating bed, forming an initial gel circulation system. The rotation speed was adjusted to 1400 rpm, the pressure was increased by 0.7 MPa, and after 5 cycles (approximately 6 hours), the mixture was directly crystallized at 170℃ under a further increased pressure of 2.3 MPa for 12 hours. The reaction was then stopped at 2000 rpm. After the reaction, the mixture was cooled to room temperature, washed with deionized water and centrifuged three times, dried at 80℃ for 12 hours, and calcined at 550℃ for 4 hours. Nitrogen adsorption-desorption results showed that the obtained ZSM-5 molecular sieve was a mesoporous molecular sieve with a specific surface area as high as 410 cm². 2 / g. The micropore volume is 0.07cm³. 3 / g, mesopore volume is 0.2cm³ 3 / g, accounting for 40% of the total pore volume.

[0041] XRD pattern of Example 3 and Figure 1 They are similar, both being ZSM-5 molecular sieves.

[0042] Comparative Example 1

[0043] Silica sol solution A was prepared according to a ratio of H2O / SiO2 = 30, and aluminum source and template agent tetrapropylammonium hydroxide solution B was prepared according to a ratio of H2O / Al = 500 and T / SiO2 = 0.02. The two solutions were pumped into a rotating bed at a feed rate ratio of 1. The initial gel was discharged into a premixing tank through the liquid outlet of the rotating bed, forming an initial gel circulation system. The rotating bed speed was adjusted to 1500 rpm, and after 5 cycles (approximately 30 minutes) without additional pressure, the mixture was directly crystallized at 180℃ for 12 hours under high gravity, and then the reaction was stopped at 1500 rpm. After the reaction, the mixture was cooled to room temperature, washed with deionized water and centrifuged three times, dried at 80℃ for 12 hours, and calcined at 550℃ for 4 hours. Nitrogen adsorption-desorption results showed that the obtained molecular sieve was a microporous molecular sieve with a specific surface area of ​​260 cm². 2 / g. The micropore volume is 0.08cm³. 3 / g, without mesoporous structures.

[0044] Compare the XRD pattern of Example 1 with Figure 1 They are similar, both being ZSM-5 molecular sieves. Additionally, Figure 2 The nitrogen adsorption-desorption curves were obtained by... Figure 2 It can be seen that the molecular sieve obtained in Comparative Example 1 does not have mesopores.

[0045] Comparative Example 2

[0046] Silica sol solution A was prepared according to a ratio of H2O / SiO2 = 30, and aluminum source and template agent tetrapropylammonium hydroxide solution B was prepared according to a ratio of H2O / Al = 500 and T / SiO2 = 0.02. The two solutions were pumped into a rotating bed at a feed rate ratio of 1. The initial gel was discharged into a premixing tank through the liquid outlet of the rotating bed, forming an initial gel circulation system. The rotation speed was adjusted to 1500 rpm, and the pressure was increased by 0.7 MPa. After 5 cycles and approximately 30 minutes, the mixture was directly crystallized at 180℃ under high gravity for 12 hours. The reaction was then stopped at 1500 rpm. After the reaction, the mixture was cooled to room temperature, washed with deionized water, centrifuged three times, dried at 80℃ for 12 hours, and calcined at 550℃ for 4 hours. Nitrogen adsorption-desorption results showed that the obtained molecular sieve was a microporous molecular sieve with a specific surface area as high as 255 cm². 2 / g, micropore volume is 0.07cm³ 3 / g, without mesoporous structures.

[0047] Compare the XRD patterns of Example 2 with Figure 1 They are similar, both being ZSM-5 molecular sieves.

[0048] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a mesoporous molecular sieve, comprising the following steps: (1) Prepare solution a, which is a silicon source and water; Solution b consists of an aluminum source, template agent B, and water; (2) The solutions a and b are simultaneously fed into the integrated device for ultragravity aging and crystallization to mix and obtain the initial gel. Then, the solution is premixed under pressure to form the initial gel circulation system. Then, the solution is directly crystallized. After exiting the device, the solution is washed, dried, and calcined to prepare the molecular sieve. In step (2), the pressure of the initial gel circulation system is increased by 0.1-7 MPa on top of the initial pressure of the circulation system; In step (2), the crystallization process involves increasing the pressure by 0.01-7 MPa based on the pressure of the circulation system of the hypergravity device. In step (2), during the premixing and circulation process of the initial gel entering the reaction system through the hypergravity device, the hypergravity rotation speed is maintained at 500-3000 rpm for 5 min-48 h. In step (2), the crystallization is carried out at 180-200℃ for 0.5-72h. The crystallization is circulated in the integrated ultra-gravity aging and crystallization device, which is dynamic crystallization with a rotation speed of 1500rpm-2000rpm.

2. The preparation method according to claim 1, characterized in that, In step (1), the template agent B is at least one of tetrapropylammonium bromide, tetrapropylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, n-propylamine, n-butylamine, n-hexylamine, methylamine, ethylamine, ethylenediamine, diethanolamine, hexamethylene diisocyanate, hexamethylenediamine, hexamethylenetetramine and its derivatives; the silicon source is at least one of silica sol, tetraethyl orthosilicate and silicate, and the aluminum source is at least one of aluminum sulfate, aluminum isopropoxide and aluminate.

3. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of silicon source, aluminum source, template agent B and water in solution a and solution b is H2O / SiO2=5-1000; Si / Al=0.5-∞; B / SiO2=0-0.

6.

4. The preparation method according to claim 1, characterized in that, In step (2), the integrated ultragravity aging and crystallization device includes a feeding system, a reaction system, and a discharging system.

5. The preparation method according to claim 4, characterized in that, In step (2), the integrated ultragravity aging and crystallization device simultaneously feeds solutions a and b into the device through the feeding system. Solutions a and b are mixed in the reaction system to obtain an initial gel. Then, they are pressurized and premixed to form an initial gel circulation system, which is then directly crystallized. Finally, the reacted material is sent out of the device through the discharge system.

6. The mesoporous molecular sieve obtained by the preparation method according to any one of claims 1-5, wherein the mesoporous molecular sieve is one or more composite molecular sieves selected from ZSM-5, ZSM-11, and SAPO-34.

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