MWW molecular sieve and preparation method thereof

Abstract

The invention discloses an MWW molecular sieve and a preparation method thereof, and the preparation method comprises the following steps: (a) mixing an alkali source, water, an aluminum source, a template agent and a silicon source to form a mixture A; (b) adding nano cellulose into the mixture A to form a mixture B, and pretreating, crystallizing and drying the mixture B to obtain the MWW molecular sieve. The preparation method disclosed by the invention is simple and convenient, easy to industrialize and wide in application prospect, and the MWW molecular sieve with the single-layer structure is prepared. The MWW molecular sieve with a single-layer structure can expose more active sites, promotes diffusion and mass transfer, shows excellent performance in many reaction processes, and particularly shows high activity and stability in a reaction with macromolecules as a substrate.

Description

Technical Field

[0001] This application relates to an MWW molecular sieve and its preparation method, belonging to the field of inorganic material chemical synthesis. Background Technology

[0002] MWW molecular sieves are layered molecular sieves with a crystal structure comprising two relatively independent pore systems: sinusoidal ten-membered ring pores within the layers and twelve-membered ring supercages between the layers, as well as semi-supercages with twelve-membered ring openings on the surface. They have wide commercial applications in many reaction processes, including alkylation, isomerization, and disproportionation. Common MWW molecular sieves are MCM-22 and MCM-49, with approximately 10-20 layers. The twelve-membered ring semi-supercages on the surface of MWW molecular sieves not only provide reaction sites for macromolecules, but the larger twelve-membered ring openings also allow for timely product diffusion, avoiding side reactions and improving reaction efficiency. Reducing the number of layers in MWW molecular sieves exposes more surface semi-supercage active sites, which helps enhance diffusion and mass transfer, improving the conversion rate and stability of various reaction processes.

[0003] A common method for preparing single-layer MWW molecular sieves (or ITQ-2 molecular sieves) involves delamination of multi-layer MWW molecular sieves (CN109908953B). This is achieved by swelling MCM-22(P) to increase the interlayer distance and disrupt the ordered stacking of its framework. Delamination is then performed using ultrasound or macromolecular organic amines, followed by calcination to obtain ITQ-2 molecular sieves. However, this process is complex, inevitably leads to quality loss, and carries the risk of damaging the framework integrity, making it unsuitable for large-scale production.

[0004] Direct synthesis of monolayer MWW molecular sieves has a narrow synthetic range and low crystallinity, requiring the use of numerous template agents and stringent synthetic conditions. Researchers have employed the introduction of second-structure directing agents (CN 112551539 B, CN 110615446B, CN 116947068A), such as organic amines, quaternary ammonium salts, and organosilanes, to prepare monolayer MWW molecular sieves under milder conditions. Summary of the Invention

[0005] This application provides a MWW molecular sieve and its preparation method. The preparation method includes: (a) mixing an alkali source, water, an aluminum source, a template agent, and a silicon source to form a mixture A; (b) then adding nanocellulose to the mixture A to form a mixture B, pretreating the mixture B, crystallizing it, and drying it to obtain the MWW molecular sieve. The monolayer structure of the MWW molecular sieve exposes more active sites, promotes diffusion and mass transfer, and exhibits excellent performance in many reaction processes, especially in reactions with macromolecules as substrates, demonstrating high activity and stability. The preparation method of this invention is simple, easy to industrialize, and has broad application prospects.

[0006] According to a first aspect of this application, a method for preparing MWW molecular sieves is provided, the method comprising:

[0007] (a) Mix the alkali source, water, aluminum source, template agent and silicon source to form mixture A;

[0008] (b) Then, nanocellulose is added to the mixture A to form mixture B. The mixture B is pretreated, crystallized, and dried to obtain the MWW molecular sieve.

[0009] Optionally, the MWW molecular sieve has a single-layer plate-like structure.

[0010] Optionally, the template agent is selected from at least one of hexamethyleneimine, piperidine, and cyclohexylamine.

[0011] Optionally, the alkali source is selected from at least one of hydroxides containing sodium and potassium.

[0012] Optionally, the silicon source is selected from at least one of solid silica gel, fumed silica, and silica sol.

[0013] Optionally, the aluminum source is selected from at least one of sodium aluminate, boehmite, aluminum chloride, and aluminum sulfate.

[0014] Optionally, in step (a), the molar ratios of the alkali source, water, aluminum source, template agent, and silicon source are: M2O / SiO2 = 0.05–0.5, H2O / SiO2 = 10–50, SiO2 / Al2O3 = 10–100, and template agent / SiO2 = 0.05–0.5; where M represents an alkali metal element; and the molar amount of the silicon source is calculated based on the molar amount of SiO2 contained therein.

[0015] Optionally, the upper limit of M2O / SiO2 is independently selected from 0.5, 0.3, and 0.1, and the lower limit is independently selected from 0.05, 0.3, and 0.1.

[0016] The upper limit of H2O / SiO2 is independently selected from 50, 40, and 30, and the lower limit is independently selected from 10, 40, and 30.

[0017] The upper limit of SiO2 / Al2O3 is independently selected from 100, 80, 60, 40, and 20, and the lower limit is independently selected from 10, 80, 60, 40, and 20.

[0018] The upper limit of the template agent / SiO2 is independently selected from 0.5, 0.3, and 0.1, and the lower limit is independently selected from 0.05, 0.3, and 0.1.

[0019] Preferably, in step (a), the alkali source, water, aluminum source, template agent and silicon source are mixed sequentially.

[0020] Optionally, in step (b), the mass ratio of the nanocellulose to the silicon source is 0.001 to 1;

[0021] The mass of the silicon source is measured by the mass of SiO2 contained therein.

[0022] Optionally, the upper limit of the mass ratio of nanocellulose to silicon source is independently selected from 1, 0.5, 0.1, 0.05, 0.01, and 0.005, and the lower limit is independently selected from 0.001, 0.5, 0.1, 0.05, 0.01, and 0.005.

[0023] Optionally, in step (b), the pretreatment conditions are: pretreatment at 60–120°C for 2–48 hours;

[0024] The crystallization conditions are: crystallization at 120–160°C for 24–120 hours;

[0025] The drying conditions are: drying at 80-120℃ for 6-12 hours.

[0026] According to a second aspect of this application, an MWW molecular sieve is provided, wherein the MWW molecular sieve is selected from at least one of the MWW molecular sieves prepared according to the above preparation method.

[0027] The beneficial effects that this application can produce include:

[0028] The preparation method of this invention is simple, easy to industrialize, and has broad application prospects. The prepared MWW molecular sieve has a monolayer structure. The monolayer structure of the MWW molecular sieve can expose more active sites, promote diffusion and mass transfer, and exhibit excellent performance in many reaction processes, especially in reactions with macromolecules as substrates, where it exhibits high activity and stability. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The X-ray diffraction pattern of product S1 from Example 1 is shown.

[0031] Figure 2 This is a scanning electron microscope image of product S1 from Example 1.

[0032] Figure 3 The X-ray diffraction pattern of product D1 in Comparative Example 1 is shown. Detailed Implementation

[0033] The present application is further illustrated below with reference to specific embodiments. The following descriptions are merely a few embodiments of the present application and are not intended to limit the present application in any way. Although the present application discloses preferred embodiments as follows, they are not intended to limit the present application. Any modifications or variations made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

[0034] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0035] Unless otherwise specified, the analytical methods in the embodiments all adopt conventional instrument or equipment settings and conventional analytical methods.

[0036] The specific composition of the raw materials used in this application embodiment is as follows:

[0037] Solid silica gel: 96% dry basis;

[0038] Silica: 96% on a dry basis;

[0039] Silica sol: 30.19 wt.% SiO2, 0.29 wt.% Na2O, 0.23 wt.% Al2O3, 69.29 wt.% H2O;

[0040] Sodium aluminate: 38 wt.% Na2O, 49 wt.% Al2O3, 13 wt.% H2O;

[0041] Phobospore: 95% on a dry basis;

[0042] Aluminum chloride: purity ≥ 99%;

[0043] Aluminum sulfate: purity ≥ 99%;

[0044] Hexamethyleneimine: Purity ≥ 99%;

[0045] Piperidine: Purity ≥ 99%;

[0046] Cyclohexylamine: Purity ≥ 99%;

[0047] Sodium hydroxide: content ≥96%;

[0048] Potassium hydroxide: content ≥96%.

[0049] Example 1

[0050] According to the molar ratio of 0.05Na₂O:0.01Al₂O₃:1.0SiO₂:0.5HMI:25H₂O, with an R / SiO₂ mass ratio of 0.5, 2.8g sodium hydroxide, 312.1g water, 1.1g solid sodium aluminate, 49.5g hexamethyleneimine, and 198.7g silica sol were first thoroughly stirred to obtain a homogeneous gel. Then, 30g of nanocellulose was added. The resulting gel was placed in a stainless steel reactor and pretreated at 60℃ for 12h, followed by dynamic crystallization at 150℃ for 48h. After washing with deionized water, centrifugation, and drying at 120℃ for 6h, solid product S1 was obtained.

[0051] like Figure 1 As shown, the X-ray diffraction (XRD) pattern of the product in this embodiment shows characteristic diffraction peaks of thin-layer MWW molecular sieves. Figure 2 As shown, the product of this embodiment is a single-layer MWW sheet-like crystal.

[0052] Comparative Example 1

[0053] The synthesis molar ratio and process were similar to those in Example 1, except that nanocellulose was not added, resulting in product D1. Figure 3 As shown, the X-ray diffraction (XRD) pattern of the product in this embodiment shows that D1 is a conventional multilayer MWW molecular sieve.

[0054] Comparative Example 2

[0055] The synthesis molar ratio and process were similar to those in Example 1. After the gel was mixed evenly, it was directly crystallized without any pretreatment to obtain product D2. Testing revealed that D2 was a conventional multilayer MWW molecular sieve.

[0056] Comparative Example 3

[0057] The synthesis molar ratio and process were similar to those in Example 1, except that the order of addition was adjusted so that nanocellulose was dissolved in a solution formed by sodium hydroxide and water, followed by the addition of an aluminum source, a template agent, and a silicon source, yielding product D3. Analysis showed that D3 was amorphous.

[0058] Example 2

[0059] According to the molar ratio of 0.05K₂O:0.01Al₂O₃:1.0SiO₂:0.05PI:10H₂O, with an R / SiO₂ mass ratio of 0.001, 5.5g potassium hydroxide, 177.5g water, 2.7g aluminum chloride, 4.25g piperidine, and 62.5g silica gel were first mixed evenly, and then 0.06g nanocellulose was added. The resulting gel was pretreated in a stainless steel reactor at 120℃ for 2h, followed by dynamic crystallization at 120℃ for 120h. The gel was washed with deionized water, centrifuged, and dried at 80℃ for 12h to obtain solid product S2. The properties of this product are similar to those of S1.

[0060] Example 3

[0061] According to the molar ratio of 0.05K₂O:0.01Al₂O₃:1.0SiO₂:0.5CHA:50H₂O, with an R / SiO₂ mass ratio of 1, 5.5g potassium hydroxide, 897.5g water, 1.7g aluminum sulfate, 49.5g cyclohexylamine, and 62.5g silica were first mixed evenly, and then 60g nanocellulose was added. The resulting gel was pretreated in a stainless steel reactor at 60℃ for 24h, and then dynamically crystallized at 160℃ for 24h. After washing with deionized water, centrifugation, and drying at 80℃ for 12h, solid product S3 was obtained. The properties of this product are similar to those of S1.

[0062] Example 4

[0063] According to the molar ratio of 0.5Na₂O:0.1Al₂O₃:1.0SiO₂:0.5CHA:20H₂O, with an R / SiO₂ mass ratio of 0.2, 41.7g sodium hydroxide, 355.2g water, 10.7g boehmite, 49.5g cyclohexylamine, and 62.5g silica were first mixed evenly, and then 12g nanocellulose was added. The resulting gel was pretreated in a stainless steel reactor at 80℃ for 12h, and then dynamically crystallized at 160℃ for 24h. The gel was washed with deionized water, centrifuged, and dried at 80℃ for 12h to obtain solid product S4. The properties of this product are similar to those of S1.

[0064] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing MWW molecular sieves, characterized in that, The preparation method includes: (a) Mix the alkali source, water, aluminum source, template agent and silicon source to form mixture A; (b) Then, nanocellulose is added to the mixture A to form mixture B. The mixture B is pretreated, crystallized, and dried to obtain the MWW molecular sieve.

2. The preparation method according to claim 1, characterized in that, The MWW molecular sieve has a single-layer plate-like structure.

3. The preparation method according to claim 1, characterized in that, The template agent is selected from at least one of hexamethyleneimine, piperidine, and cyclohexylamine.

4. The preparation method according to claim 1, characterized in that, The alkali source is selected from at least one of hydroxides containing sodium and potassium elements.

5. The preparation method according to claim 1, characterized in that, The silicon source is selected from at least one of solid silica gel, fumed silica, and silica sol.

6. The preparation method according to claim 1, characterized in that, The aluminum source is selected from at least one of sodium aluminate, boehmite, aluminum chloride, and aluminum sulfate.

7. The preparation method according to claim 1, characterized in that, In step (a), the molar ratios of the alkali source, water, aluminum source, template agent, and silicon source are: M2O / SiO2 = 0.05–0.5, H2O / SiO2 = 10–50, SiO2 / Al2O3 = 10–100, and template agent / SiO2 = 0.05–0.5; where M represents an alkali metal element. The molar amount of the silicon source is expressed as the molar amount of SiO2 contained therein; Preferably, in step (a), the alkali source, water, aluminum source, template agent and silicon source are mixed sequentially.

8. The preparation method according to claim 1, characterized in that, In step (b), the mass ratio of the nanocellulose to the silicon source is 0.001 to 1; The mass of the silicon source is measured by the mass of SiO2 contained therein.

9. The preparation method according to claim 1, characterized in that, In step (b), the pretreatment conditions are: 60–120°C for 2–48 hours. The crystallization conditions are: crystallization at 120–160°C for 24–120 hours; The drying conditions are: drying at 80-120℃ for 6-12 hours.

10. An MWW molecular sieve, characterized in that, The MWW molecular sieve is at least one of the MWW molecular sieves prepared according to any one of the preparation methods according to claims 1 to 9.

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