Silicalite-1 molecular sieve as well as preparation method and application thereof

Abstract

The invention provides a Silicalite-1 molecular sieve as well as a preparation method and application thereof. The Silicalite-1 molecular sieve is prepared from raw materials including tetrapropylammonium bromide and a silicon source water solution, and optionally, the Silicalite-1 molecular sieve also comprises an alkaline reagent; wherein the molar ratio of SiO2 to tetrapropylammonium bromide to OH <-> to H2O is 1: (0.06-5): (0-1): (1-200). The preparation method comprises the following steps: grinding tetrapropylammonium bromide into powder, optionally grinding the tetrapropylammonium bromide and an alkaline reagent into powder, then adding a silicon source aqueous solution, continuously grinding to uniformly mix all the raw materials, fully reacting, crystallizing, drying a solid product obtained after separation, and roasting to obtain the Silicalite-1 molecular sieve. When the Silicalite-1 molecular sieve is prepared, water does not need to be additionally added, the operation is simple, the preparation period is short, and less wastewater is generated.

Description

Technical Field

[0001] The present invention relates to the technical field of functional nanomaterials, and more particularly to a Silicalite-1 molecular sieve and a preparation method and application thereof. Background Art

[0002] Silicalite-1 was first successfully synthesized by EMFlanigen et al. of UCC in 1987 (Nature, 1978, 271 (5645): 512 5160). It is an all-silicon molecular sieve with MFI structure. Silicalite-1 has good hydrothermal stability, lipophilicity and hydrophobicity, and unique two-dimensional cross-ten-membered ring channels (straight channels with pore sizes of 0.51×0.55nm and sinusoidal channels with pore sizes of 0.54×0.56nm respectively). Its skeleton does not contain aluminum atoms and has weak acidic sites. Based on the above characteristics, Silicalite-1 has been widely used in the oxidation reaction of hydrocarbons below C6, catalytic cyclohexanone oxime Beckmann rearrangement reaction, gas separation, ethanol / water separation and other fields. Therefore, it is of great practical significance to seek a low-cost, simple to operate and environmentally friendly method for preparing Silicalite-1.

[0003] At present, most of the Silicalite-1 synthesis methods are hydrothermal methods, and the initial gel ratio is: SiO2: TPA: OH - :H2O=1:0.2:0.2:50(Microporous Mesoporous Mater,2012,155:56-64.),This method usually uses a large amount of water as a solvent, which will undoubtedly cause a large amount of wastewater discharge. Therefore, minimizing the amount of water added during the synthesis process has a positive significance for saving resources and reducing wastewater discharge. In addition, the steps for synthesizing the molecular sieve are cumbersome, and a large amount of expensive organic template agent tetrapropylammonium hydroxide and raw materials are required. The above multiple reasons limit its application in industry.

[0004] Chinese invention patent CN108002396A discloses a method for preparing Silicalite-1 molecular sieve using tetrapropylammonium bromide as a template. Compared with tetrapropylammonium hydroxide, tetrapropylammonium bromide has the advantages of being cheap and readily available. However, this method requires first making homemade seed crystals, and then using the homemade seed crystals to assist in the synthesis of Silicalite-1. The steps are cumbersome and complicated, and the preparation cycle is long. In addition, the relative amount of water used in this method is SiO2:H2O=80:1000-2000, and a lot of wastewater will be generated during the preparation process. Summary of the invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a Silicalite-1 molecular sieve and a preparation method and application thereof.

[0006] The preparation method of the Silicalite-1 molecular sieve of the present invention does not require the addition of additional water, is simple to operate, has a short preparation cycle, and uses relatively cheap tetrapropylammonium bromide as a template agent.

[0007] One of the objects of the present invention is to provide a Silicalite-1 molecular sieve.

[0008] The Silicalite-1 molecular sieve is prepared from raw materials including tetrapropylammonium bromide and a silicon source aqueous solution, and optionally, also includes an alkaline reagent; wherein SiO2, tetrapropylammonium bromide, OH - The molar ratio of H2O is 1:(0.06~5):(0~1):(1~200).

[0009] The Silicalite-1 molecular sieve of the present invention is a molecular sieve with an MFI structure, which is the same as the ZSM-5 structure, and both are MFI topological structures. The synthesis of molecular sieves often requires a lot of water as a solution, and the use of water can be greatly reduced by adopting a grinding method. The ratio between the various raw materials in the grinding method is different from that of the traditional hydrothermal method, and only a small amount of water is used during synthesis. At the same time, due to the small amount of water used, subsequent water treatment and other problems are avoided. There is no need to separate liquid or treat waste liquid after the reaction.

[0010] In a preferred embodiment of the present invention,

[0011] The alkaline agent is at least one of sodium hydroxide and potassium hydroxide, including but not limited to the above alkaline agents; in the reaction, Silicalite-1 molecular sieves with different crystallinity and different morphologies can be obtained by controlling the amount of alkaline agent added.

[0012] The silicon source aqueous solution is a mixture of a silicon source and water, preferably at least one of a mixed solution of silicon dioxide and water, silica sol, and a sodium silicate aqueous solution, including but not limited to the above silicon source aqueous solutions.

[0013] In a preferred embodiment of the present invention,

[0014] The silica sol is preferably alkaline silica sol, which is a colloidal solution of silica particles of varying sizes in water, with a pH value of 8 to 11 and a silica content of 15 to 40 wt%. The alkaline silica sol itself is alkaline, which can reduce or avoid the addition of alkaline reagents. At the same time, the solvent in the silica sol is used as a solvent in the raw material mixing process, which not only avoids the addition of additional solvents, but also can mix the raw materials evenly and react fully with grinding, and finally obtains Silicalite-1 molecular sieves of uniform size.

[0015] In a preferred embodiment of the present invention,

[0016] In the mixed raw materials, SiO2, tetrapropylammonium bromide, OH - The molar ratio of H2O is 1:(0.06~0.24):(2×10 -5 ~0.32):(5~19), preferably 1:(0.1~0.15):(2×10 -5 ~0.16):(7~8).

[0017] The second object of the present invention is to provide a method for preparing Silicalite-1 molecular sieve, comprising the following steps:

[0018] (1) grinding tetrapropylammonium bromide into powder, optionally grinding it together with an alkaline agent into powder, then adding a silicon source aqueous solution, continuing to grind so that all the raw materials are evenly mixed and fully reacted before crystallization, and separating to obtain a solid product;

[0019] (2) Drying and calcining the solid product obtained in step (1) to obtain Silicalite-1 molecular sieve.

[0020] In the absence of solvent, tetrapropylammonium bromide is firstly mixed alone or with an alkaline agent and then ground, and the raw material is fully ground until the granular state is converted into a fine and uniform powder. A silicon source aqueous solution is added to the reaction system, and the grinding is continued to make all the raw materials uniformly mixed and fully reacted. After the reaction system is in the state of a white lotion, it is put into a kettle for crystallization. After the crystallization is completed, a solid product is obtained by centrifugation or the like, and after drying, it is roasted to remove the template agent and other substances to obtain the Silicalite-1 molecular sieve.

[0021] In a preferred embodiment of the present invention,

[0022] In step (1),

[0023] The grinding time of tetrapropylammonium bromide and alkaline reagent is 5 to 60 minutes, preferably 5 to 10 minutes;

[0024] After adding the silicon source aqueous solution, the grinding time is 5 to 60 minutes, preferably 5 to 10 minutes;

[0025] The crystallization is carried out in an autoclave, preferably in a stainless steel hydrothermal autoclave lined with polytetrafluoroethylene;

[0026] The crystallization temperature is 140 to 220°C, preferably 160 to 180°C;

[0027] The crystallization time is 24 to 200 hours, preferably 24 to 48 hours;

[0028] The separation method is centrifugal washing.

[0029] In a preferred embodiment of the present invention,

[0030] In step (2),

[0031] Drying can be carried out by a common drying method in the art. Preferably, the drying temperature is 80 to 120° C. and the drying time is 2 to 8 hours.

[0032] The calcination temperature is 550-650°C, and the calcination time is 4-6 hours.

[0033] The third object of the present invention is to provide a Silicalite-1 molecular sieve obtained by the above preparation method.

[0034] A fourth object of the present invention is to provide an application of Silicalite-1 molecular sieve in a catalytic reaction, preferably in the hydrogenation of carbon dioxide to ethanol.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The initial gel is prepared by a simple grinding method, and the synthesis cycle is short;

[0037] (2) No additional water is required to be added to the reaction system, and the preparation process produces less wastewater, which is environmentally friendly;

[0038] (3) Using relatively cheap template agent tetrapropylammonium bromide and silicon source alkaline silica sol to save costs. Using alkaline silica sol as the silicon source is low in price and has little pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The X-ray diffraction pattern of the Silicalite-1 molecular sieve prepared in Example 1;

[0040] Figure 2 This is a scanning electron microscope image of the Silicalite-1 molecular sieve prepared in Example 1;

[0041] Figure 3 The X-ray diffraction pattern of the Silicalite-1 molecular sieve prepared in Example 2;

[0042] Figure 4 This is a scanning electron microscope image of the Silicalite-1 molecular sieve prepared in Example 2;

[0043] Figure 5 The X-ray diffraction pattern of the Silicalite-1 molecular sieve prepared in Example 3;

[0044] Figure 6 This is a scanning electron microscope image of the Silicalite-1 molecular sieve prepared in Example 3;

[0045] Figure 7 This is a scanning electron microscope image of the Silicalite-1 molecular sieve prepared in Comparative Example 1;

[0046] Figure 8 The X-ray diffraction patterns of the Silicalite-1 molecular sieves prepared in Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0047] The present invention is described in detail below in conjunction with specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0048] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0049] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0050] The raw materials used in the examples and comparative examples are all conventional commercially available raw materials.

[0051] Test method:

[0052] X-ray diffraction: D8 Advance X-ray diffractometer produced by Bruker, Germany; the sample powder was ground and spread flat in the sample slot and compacted, and then placed in the instrument for measurement. The working current was 40mA, the working voltage was 40kV, the radiation source was Kα radiation excited by Cu target, the radiation wavelength was 0.1542nm, and the scanning speed was 0.139s·step -1, the scanning step length is 0.0205°·step -1 .

[0053] Scanning electron microscope: JSM-7900F thermal field emission scanning electron microscope produced by JEOL Ltd.; the sample to be tested is evenly spread on the shooting table with conductive glue and the excess powder on the surface is blown off with compressed air, and then placed in a 110°C oven for drying for 30 minutes to remove the moisture and impurities adsorbed on the sample. After taking it out, the sample is loaded and photographed. In order to obtain a clearer SEM image, the test voltage and current can be appropriately adjusted according to the actual situation.

[0054] Example 1

[0055] In a mortar, add 3.14g of tetrapropylammonium bromide and 0.64g of sodium hydroxide, grind for about 10 minutes until the mixture is in a fine powder state, then pour in 20.02g of alkaline silica sol (30%wt), continue grinding for about 10 minutes until the mixture is in a white emollient state, transfer the resulting mixture into a stainless steel hydrothermal kettle lined with polytetrafluoroethylene, crystallize at 170°C for 24h, wash the product by centrifugation, dry at 100°C for 2h, and calcine at 550°C for 4h to obtain Silicalite-1 molecular sieve. During the reaction, tetrapropylammonium bromide: OH in the mixed raw materials - The molar ratio of SiO2:H2O is 0.12:0.16:1:7.78, and the yield of Silicalite-1 molecular sieve after the reaction is 68%.

[0056] Depend on Figures 1-2 It can be seen that the grinding method adopted in the present invention can successfully prepare Silicalite-1 molecular sieve.

[0057] Depend on Figure 1 It can be seen that the Silicalite-1 molecular sieve prepared by the method of the present invention has characteristic diffraction peaks of the MFI structure at 2θ=8.0°, 8.9°, 23.2°, 24.1°, and 24.7°, indicating that the Silicalite-1 molecular sieve was successfully synthesized using the grinding method.

[0058] Depend on Figure 2 It can be seen that the Silicalite-1 molecular sieve prepared by the method of the present invention is in the shape of irregular small spheres with an average size of about 4 μm.

[0059] Example 2

[0060] In a mortar, add 3.14g of tetrapropylammonium bromide, grind for about 10min until the tetrapropylammonium bromide is in fine powder form, then pour in 20.02g of alkaline silica sol (30%wt), continue grinding for about 10min until the mixture is a transparent viscous liquid, transfer the resulting mixture into a stainless steel hydrothermal kettle lined with polytetrafluoroethylene, crystallize at 170℃ for 24h, and after the product is centrifuged, washed, dried at 100℃ for 2h, and calcined at 550℃ for 4h, Silicalite-1 molecular sieve can be obtained. During the reaction, tetrapropylammonium bromide: OH in the mixed raw materials - :The molar ratio of SiO2:H2O is 0.12:2×10 -5 : 1:7.78, the yield of Silicalite-1 molecular sieve after the reaction was 63%.

[0061] Depend on Figures 3-4 It can be seen that the grinding method adopted in the present invention can adjust the structure of the Silicalite-1 molecular sieve by changing the amount of sodium hydroxide added.

[0062] Depend on Figure 3 It can be seen that the Silicalite-1 molecular sieve prepared by the method of the present invention has characteristic diffraction peaks of the MFI structure at 2θ=8.0°, 9.1°, 23.3°, 24.2°, and 24.7°, indicating that the Silicalite-1 molecular sieve was successfully synthesized using the grinding method.

[0063] Depend on Figure 4 It can be seen that the Silicalite-1 molecular sieve prepared by the method of the present invention is in the shape of long strips, and the average size is about 14 μm.

[0064] Example 3

[0065] In a mortar, add 3.14g of tetrapropylammonium bromide and 0.32g of sodium hydroxide, grind for about 10 minutes until the mixture is in a fine powder state, then pour in 20.02g of alkaline silica sol (30%wt), continue grinding for about 10 minutes until the mixture is in a white lotion state, transfer the resulting mixture into a stainless steel hydrothermal kettle lined with polytetrafluoroethylene, crystallize at 170°C for 24h, and after the product is centrifuged, washed, dried at 100°C for 2h, and calcined at 550°C for 4h, Silicalite-1 molecular sieve can be obtained. During the reaction, tetrapropylammonium bromide: OH in the mixed raw materials - The molar ratio of SiO2:H2O is 0.12:0.08:1:7.78, and the yield of Silicalite-1 molecular sieve after the reaction is 65%.

[0066] Depend on Figures 5-6 It can be seen that the grinding method adopted in the present invention can adjust the structure of the Silicalite-1 molecular sieve by changing the amount of sodium hydroxide added.

[0067] Depend on Figure 5 It can be seen that the Silicalite-1 molecular sieve prepared by the method of the present invention has characteristic diffraction peaks of the MFI structure at 2θ=7.8°, 8.7°, 22.9°, 23.8°, and 24.4°, indicating that the Silicalite-1 molecular sieve was successfully synthesized using the grinding method.

[0068] Depend on Figure 6 It can be seen that the Silicalite-1 molecular sieve prepared by the method of the present invention is ellipsoidal in shape, and the average size is about 14 μm.

[0069] Example 4

[0070] In a mortar, add 22g of tetrapropylammonium bromide and 0.67g of sodium hydroxide, grind for about 10 minutes until the mixture is in a fine powder state, then pour in 1g of silicon dioxide powder and 60g of water, and continue grinding for about 10 minutes until the mixture is in a white lotion state. The resulting mixture is transferred into a stainless steel hydrothermal kettle lined with polytetrafluoroethylene, and crystallized at 170°C for 24 hours. The product is centrifugally washed, dried at 100°C for 2 hours, and calcined at 550°C for 4 hours to obtain Silicalite-1 molecular sieve. During the reaction, tetrapropylammonium bromide: OH in the mixed raw materials - : The molar ratio of SiO2:H2O is 5:1:1:200, and the yield of Silicalite-1 molecular sieve after the reaction is 40%.

[0071] Example 5

[0072] In a mortar, add 1.6g of tetrapropylammonium bromide and 4g of sodium hydroxide, grind for about 10 minutes until the mixture is in a fine powder state, then pour in 6g of silicon dioxide powder and 1.8g of water, and continue grinding for about 10 minutes until the mixture is in a white lotion state. The resulting mixture is transferred into a stainless steel hydrothermal kettle lined with polytetrafluoroethylene, and crystallized at 170°C for 24 hours. The product is centrifugally washed, dried at 100°C for 2 hours, and calcined at 550°C for 4 hours to obtain Silicalite-1 molecular sieve. During the reaction, tetrapropylammonium bromide: OH in the mixed raw materials - : The molar ratio of SiO2:H2O is 0.06:1:1:1, and the yield of Silicalite-1 molecular sieve after the reaction is 30%.

[0073] Example 6

[0074] In a mortar, add 1.59g of tetrapropylammonium bromide and 0.32g of sodium hydroxide, grind for about 10 minutes until the mixture is in a fine powder state, then pour in 20.02g of alkaline silica sol (15%wt), continue grinding for about 10 minutes until the mixture is in a white lotion state, transfer the resulting mixture into a stainless steel hydrothermal kettle lined with polytetrafluoroethylene, crystallize at 170°C for 24h, and after the product is centrifuged, washed, dried at 100°C for 2h, and calcined at 550°C for 4h, Silicalite-1 molecular sieve can be obtained. During the reaction, tetrapropylammonium bromide: OH in the mixed raw materials - The molar ratio of SiO2:H2O is 0.06:0.16:1:19, and the yield of Silicalite-1 molecular sieve after the reaction is 58%.

[0075] Example 7

[0076] In a mortar, add 4.26g of tetrapropylammonium bromide and 0.85g of sodium hydroxide, grind for about 10 minutes until the mixture is in a fine powder state, then pour in 20.02g of alkaline silica sol (40%wt), continue grinding for about 10 minutes until the mixture is in a white emollient state, transfer the resulting mixture into a stainless steel hydrothermal kettle lined with polytetrafluoroethylene, crystallize at 170°C for 24h, and after the product is centrifuged, washed, dried at 100°C for 2h, and calcined at 550°C for 4h, Silicalite-1 molecular sieve can be obtained. During the reaction, tetrapropylammonium bromide: OH in the mixed raw materials - The molar ratio of SiO2:H2O is 0.12:0.16:1:5, and the yield of Silicalite-1 molecular sieve after the reaction is 57%.

[0077] Example 8

[0078] In a mortar, add 3.14g of tetrapropylammonium bromide and 0.64g of sodium hydroxide, grind for about 5min until the mixture is in the form of fine powder, then pour in 20.02g of alkaline silica sol (30%wt), continue grinding for about 5min until the mixture is in the form of white lotion, transfer the resulting mixture into a stainless steel hydrothermal autoclave lined with polytetrafluoroethylene, crystallize at 180°C for 24h, wash the product by centrifugation, dry at 80°C for 8h, and calcine at 550°C for 6h to obtain Silicalite-1 molecular sieve. During the reaction, the molar ratio of tetrapropylammonium bromide: OH-: SiO2: H2O in the mixed raw materials is 0.12: 0.16: 1: 7.78, and the yield of Silicalite-1 molecular sieve after the reaction is 65%.

[0079] Example 9

[0080] In a mortar, add 3.14g of tetrapropylammonium bromide and 0.64g of sodium hydroxide, grind for about 5min until the mixture is in the form of fine powder, then pour in 20.02g of alkaline silica sol (30%wt), continue grinding for about 10min until the mixture is in the form of white lotion, transfer the resulting mixture into a stainless steel hydrothermal autoclave lined with polytetrafluoroethylene, crystallize at 160°C for 48h, and after centrifugal washing, drying at 120°C for 4h, and calcining at 650°C for 4h, the Silicalite-1 molecular sieve can be obtained. During the reaction, the molar ratio of tetrapropylammonium bromide: OH-: SiO2: H2O in the mixed raw materials is 0.12: 0.16: 1: 7.78, and the yield of Silicalite-1 molecular sieve after the reaction is 60%.

[0081] Comparative Example 1

[0082] In a mortar, add 3.14g of tetrapropylammonium bromide and 0.64g of sodium hydroxide, then add 20.02g of alkaline silica sol (30%wt), stir the mixture slightly and move it into a stainless steel hydrothermal autoclave lined with polytetrafluoroethylene, crystallize it at 170°C for 24h, and after the product is centrifuged, washed, dried at 100°C for 2h, and calcined at 550°C for 4h, irregular morphology Silicalite-1 molecular sieve can be obtained.

[0083] Depend on Figure 7 It can be seen that whether the grinding method is used in the synthesis process of the present invention has a great influence on the structure of the Silicalite-1 molecular sieve.

[0084] Depend on Figure 8 It can be seen that the crystallinity of Comparative Example 1 is significantly lower than that of Example 1.

[0085] The Silicalite-1 molecular sieves prepared in Examples 1 to 9 have a yield of 30 to 68%; the Silicalite-1 molecular sieves prepared in Examples 1 to 3 have a yield of 63 to 68%, and the X-ray diffraction pattern shows the presence of characteristic diffraction peaks of the MFI structure, thereby proving that the Silicalite-1 molecular sieves have been successfully synthesized, and the obtained Silicalite-1 molecular sieves have regular morphologies, namely, irregular spheres with an average size of about 4 μm, long strips with an average size of about 14 μm, and ellipsoids with an average size of about 14 μm. The Silicalite-1 molecular sieve in Comparative Example 1 has an irregular morphology, and its crystallinity is significantly lower than that in Example 1.

[0086] Unlike the prior art which often requires a lot of water as a solution for synthesizing molecular sieves, the grinding method used in the present invention can greatly reduce the use of water. At the same time, due to the small amount of water used, subsequent water treatment and other problems can be avoided. There is no need to separate the liquid or treat the waste liquid after the reaction, which is more environmentally friendly.

[0087] Meanwhile, the preparation method of the present invention is simple to operate, has a short preparation cycle, uses relatively cheap template agent tetrapropylammonium bromide and silicon source alkaline silica sol, saves costs, and uses alkaline silica sol as the silicon source, which is low in price and has little pollution to the environment.

[0088] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0089] All publications, patent applications, patents and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of a conflict, the definition in this specification shall prevail.

[0090] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0091] In the context of the present specification, any matters or items not mentioned are directly applicable to those known in the art without any changes except those explicitly stated.

Claims

1. A Silicalite-1 molecular sieve prepared from raw materials including tetrapropylammonium bromide and a silicon source aqueous solution, and optionally, also including an alkaline agent; wherein: SiO2, tetrapropylammonium bromide, OH - The molar ratio of H2O is 1:(0.06~5):(0~1):(1~200).

2. The Silicalite-1 molecular sieve according to claim 1, characterized in that: The alkaline agent is at least one of sodium hydroxide and potassium hydroxide; and / or, The silicon source aqueous solution is a mixture of a silicon source and water, and is preferably at least one of a mixed solution of silicon dioxide and water, silica sol, and a sodium silicate aqueous solution.

3. The Silicalite-1 molecular sieve according to claim 2, characterized in that: The silica sol is preferably alkaline silica sol.

4. The Silicalite-1 molecular sieve according to claim 1, characterized in that: In the mixed raw materials, SiO2, tetrapropylammonium bromide, OH - The molar ratio of H2O is 1:(0.06~0.24):(2×10 -5 ~0.32):(5~19).

5. The Silicalite-1 molecular sieve according to claim 4, characterized in that: SiO2, tetrapropylammonium bromide, OH - The molar ratio of H2O is 1:(0.1~0.15):(2×10 -5 ~0.16):(7~8).

6. A method for preparing the Silicalite-1 molecular sieve according to any one of claims 1 to 5, comprising the following steps: (1) grinding tetrapropylammonium bromide into powder, optionally grinding it together with an alkaline agent into powder, then adding a silicon source aqueous solution, continuing to grind so that all the raw materials are evenly mixed and fully reacted before crystallization, and separating to obtain a solid product; (2) Drying and calcining the solid product obtained in step (1) to obtain Silicalite-1 molecular sieve.

7. The method for preparing the Silicalite-1 molecular sieve according to claim 6, characterized in that: In step (1), The grinding time of tetrapropylammonium bromide and alkaline agent is 5 to 60 minutes, preferably 5 to 10 minutes; and / or, After adding the silicon source aqueous solution, the grinding time is 5 to 60 minutes, preferably 5 to 10 minutes; and / or, The crystallization is carried out in an autoclave, preferably in a stainless steel hydrothermal autoclave lined with polytetrafluoroethylene; and / or, The crystallization temperature is 140 to 220° C., preferably 160 to 180° C.; and / or, The crystallization time is 24 to 200 hours, preferably 24 to 48 hours; and / or, The separation method is centrifugal washing.

8. The method for preparing the Silicalite-1 molecular sieve according to claim 6, characterized in that: In step (2), The drying temperature is 80 to 120°C and the drying time is 2 to 8 hours; and / or, The calcination temperature is 550-650°C, and the calcination time is 4-6 hours.

9. A Silicalite-1 molecular sieve obtained by the preparation method according to any one of claims 6 to 8.

10. Use of the Silicalite-1 molecular sieve according to any one of claims 1 to 5 and 9 in a catalytic reaction, preferably in the hydrogenation of carbon dioxide to ethanol.

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