A nano-BETA molecular sieve and its synthesis method

Abstract

The present invention discloses a nano-BETA molecular sieve and its synthesis method. The nano-BETA molecular sieve has a crystal size of 10 to 100 nm and exists as individual crystals within a 10 to 100 nm crystal size range. The product has a high relative crystallinity. The synthesis method first involves uniformly mixing an alkali source, a silicon source, an aluminum source, a template, and water to conduct a crystallization reaction. Then, lignin sulfonate is added to continue the crystallization reaction. After the reaction is complete, the nano-BETA molecular sieve is separated, dried, and calcined to obtain the nano-BETA molecular sieve. This method solves the problem that the nano-BETA molecular sieve synthesized by existing methods primarily forms nano-aggregates, which affects its performance.

Description

Technical Field

[0001] The present invention relates to a molecular sieve synthesis method, belongs to the field of molecular sieve synthesis, and particularly relates to a BETA molecular sieve and a synthesis method thereof. Background Art

[0002] Molecular sieves are porous solid materials with high specific surface area, good hydrothermal stability, moderate acidity, abundant and uniform micropores, and adjustable surface properties. They can be widely used in the preparation of catalysts, adsorbents, ion exchangers and other materials. With the continuous development of the industry, the requirements for the pore properties of molecular sieves are becoming increasingly higher, and the development of nanomolecular sieves has received widespread attention. When the particle size of molecular sieves is reduced from micron to nanometer, its mass transfer, heat transfer and other properties related to molecular sieve adsorption and catalysis will change. As the size of molecular sieve particles decreases, the ratio of the number of atoms on its outer surface to the inner surface increases rapidly. Therefore, nanomolecular sieves have a larger outer surface and higher surface activity, playing an increasingly important role in industry.

[0003] CN102092741A discloses a nano-mesoporous molecular sieve and a synthesis method thereof. The invention uses a silicon source, an aluminum source and a surfactant cetyltrimethylammonium bromide, which are commonly used to synthesize mesoporous molecular sieves, as raw materials, and uses ammonia water to adjust the pH value of the reaction mixture to synthesize the nano-mesoporous molecular sieve through a hydrothermal synthesis method.

[0004] CN102464330A discloses a method for synthesizing nano-Beta zeolite. The method comprises the following steps: first, mixing a silicon source, an aluminum source, an alkali, a composite template, and water; then, crystallizing the mixture at a temperature of 110 to 200° C. for 5 to 100 hours to obtain a crystallization solution; then, adding an acidic compound to the crystallization solution to adjust the pH value of the crystallization solution to less than 11; and obtaining the nano-Beta zeolite after separation, washing, and drying.

[0005] CN110668459A discloses a nano-Beta molecular sieve with a wide silicon-to-aluminum ratio range and a preparation method thereof. Raw materials containing a silicon source, an alkali source, an aluminum source, a template, an amino acid, and water are mixed to obtain an initial gel; the initial gel is then placed in a reactor and subjected to a first stage crystallization and a second stage crystallization in sequence; and then the nano-Beta molecular sieve is obtained through washing, drying, and calcination.

[0006] CN106698455A discloses a method for synthesizing a nano-Beta molecular sieve. The method comprises mixing an inorganic base, water, a template, an aluminum source, and a silicon source to obtain a gel. The gel is mixed with macroporous carbon and then ultrasonically treated. The mixture is then stirred at 50-100°C until it becomes viscous. The mixture is then dried until the water is completely evaporated. The mixture is then loaded into a reactor and a certain amount of water is added to the closed reactor for crystallization. The obtained solid product is filtered, washed, dried, and then calcined in an oxygen or air atmosphere to obtain a nano-Beta molecular sieve. Summary of the Invention

[0007] In response to the deficiencies in the prior art, the main purpose of the present invention is to provide a nano-BETA molecular sieve and a synthesis method thereof, which can synthesize nano-sized BETA molecular sieves, and the molecular sieve crystals exist in the form of independent crystals, solving the problem that the nano-BETA molecular sieves synthesized by the existing methods are mainly nano-aggregates, which affect the use effect.

[0008] In order to achieve the above object, the present invention first provides a method for synthesizing nano-BETA molecular sieve, which comprises the following steps:

[0009] (1) Under contact conditions, the alkali source, silicon source, aluminum source, template and water are mixed and the first stage crystallization reaction is carried out after the mixture is evenly mixed;

[0010] (2) After the first stage crystallization reaction is completed and the temperature drops to 10-30°C, lignin sulfonate is added to carry out the second stage crystallization reaction. After the reaction is completed, nano-BETA molecular sieve is obtained after separation, drying and roasting.

[0011] Furthermore, as a specific embodiment, the alkali source in step (1) is an inorganic base, and the inorganic base can be specifically selected from one or more of sodium hydroxide and potassium hydroxide.

[0012] Furthermore, as a specific embodiment, the aluminum source in step (1) can be selected from one or more of sodium aluminate, aluminum sulfate, aluminum chloride, and aluminum nitrate, preferably aluminum chloride and / or aluminum nitrate.

[0013] Furthermore, as a specific embodiment, the silicon source in step (1) can be selected from one or more of white carbon black, silica gel, silica sol, and water glass.

[0014] Furthermore, as a specific embodiment, the template agent in step (1) can be selected from one or more of tetraethylammonium hydroxide and tetraethylammonium bromide.

[0015] Furthermore, as a specific embodiment, the lignin sulfonate can be selected from one or more of sodium lignin sulfonate and potassium lignin sulfonate, preferably sodium lignin sulfonate.

[0016] Furthermore, as a specific embodiment, an alkali metal chloride is introduced simultaneously with the introduction of the lignin sulfonate in step (2). The alkali metal chloride can be selected from one or more of sodium chloride, potassium chloride, and lithium chloride, preferably sodium chloride and / or potassium chloride. The molar ratio of the alkali metal chloride to the aluminum source is 0.8 to 2.1:1, preferably 1 to 2:1.

[0017] Furthermore, as a specific embodiment, the molar ratio of materials in step (1) is 4-11Na2O:24-110SiO2:Al2O3:550-2500H2O:3-25 M, preferably 5-10Na2O:25-100SiO2:Al2O3:600-2000H2O:5-20 M, where M represents a template.

[0018] Furthermore, as a specific embodiment, alcohol is further added in step (1), wherein the alcohol is a low molecular weight alcohol having 1 to 4 carbon atoms, specifically one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, 1,2-propylene glycol, glycerol, and butanediol, and the mass ratio of the alcohol to water is 0.8 to 1.6:1, preferably 1 to 1.5:1. Furthermore, the alcohol is added after the alkali source, silicon source, aluminum source, template, and water are uniformly mixed.

[0019] Furthermore, as a specific embodiment, the reaction temperature of the first stage crystallization reaction in step (1) is 100-160° C., preferably 110-150° C.; the first stage crystallization reaction time is 2-7 h, preferably 3-6 h.

[0020] Furthermore, as a specific embodiment, in step (2), the mass ratio of lignin sulfonate to silicon source is 0.03-0.15:1, preferably 0.05-0.1:1.

[0021] Furthermore, as a specific embodiment, the reaction temperature of the second stage crystallization reaction in step (2) is 90 to 150° C., preferably 100 to 140° C.; the second stage reaction time is 15 to 55 hours, preferably 20 to 50 hours.

[0022] Furthermore, as a specific embodiment, the reaction temperature of the second stage crystallization reaction in step (2) is 5 to 25° C. lower than the reaction temperature of the first stage crystallization reaction in step (1), preferably 10 to 15° C. lower.

[0023] Furthermore, as a specific embodiment, the separation in step (2) can be performed by filtration, which usually includes multiple filtrations, generally 1 to 10 times.

[0024] Furthermore, as a specific embodiment, the drying in step (2) is performed at 100-150° C. for 1-10 hours.

[0025] Furthermore, as a specific embodiment, the calcination in step (2) is a high-temperature calcination treatment at 400-600° C. for 1-10 hours, and the calcination is carried out in air or oxygen atmosphere.

[0026] The second aspect of the present invention provides a nano-BETA molecular sieve obtained by the above-mentioned synthesis method, wherein the nano-BETA molecular sieve has a crystal size of 10 to 100 nm and exists as a single crystal; the product has a high relative crystallinity; and a total specific surface area of ​​300 to 700 m 2 / g, pore volume of 0.2~0.5cm 3 / g.

[0027] The nano-BETA molecular sieve provided by the present invention has good macromolecular substance transmission ability and can be used as the acid component of the catalyst or the adsorption separation agent of gas and liquid; it can be widely used in the petrochemical industry or other chemical industry production processes.

[0028] Compared with existing methods, the nano-BETA molecular sieve and its synthesis method of the present invention have the following advantages:

[0029] During the research process, the applicant discovered that for the synthesis of BETA molecular sieves, the nucleation stage in the early stage of molecular sieve synthesis is very critical, which directly determines the final structure of the synthetic product. The general molecular sieve synthesis system consists of water, an alkali source, a silicon source, an aluminum source and a template. However, with the increasing requirements for the properties of molecular sieves, it is usually necessary to introduce some specific additives during the synthesis process to adjust certain properties of the molecular sieve. However, when additives are added to the molecular sieve synthesis system, the additives can easily affect the growth of the molecular sieve crystal nucleus. Especially when the introduced additives and the synthesis system do not match, it will prevent the molecular sieve from nucleating and the target product cannot be synthesized. Lignin sulfonate is an unfavorable factor for the synthesis of Beta molecular sieves. If lignin sulfonate is directly added to the synthesis system, it will result in the inability to synthesize Beta molecular sieves. The present invention discloses a method for synthesizing nano-BETA molecular sieves using a two-stage crystallization process. The first stage is primarily used for molecular sieve nucleation; in the second stage, a lignin sulfonate additive is added. The temperature and time of the crystallization reactions in the first and second stages are controlled. During the molecular sieve crystal growth stage, the added lignin sulfonate adsorbs on the high-energy crystal faces of the molecular sieve, preventing further growth and aggregation of the molecular sieve, thereby facilitating the production of a nano-BETA molecular sieve product. Furthermore, the addition of the lignin sulfonate in the second stage can prevent its effect on molecular sieve nucleation, thereby preventing the failure to synthesize a BETA molecular sieve product. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a TEM photo of the nano-BETA molecular sieve obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions and effects of the present invention are further illustrated below with reference to the following examples, but are not limited to the following examples. In the present invention, wt% refers to mass fraction.

[0032] Pore ​​structure parameters such as specific surface area of ​​the samples used in this invention were measured using low-temperature nitrogen adsorption, using an ASAP2400 physical adsorption instrument produced by Micromeritics Instruments. Prior to measurement, the samples were vacuum-treated at 300°C for at least 4 hours. The total specific surface area was calculated using the BET isotherm equation, the micropore specific surface area and mesopore specific surface area were calculated using the t-plot method, and the pore size distribution was calculated using the BJH method.

[0033] The microscopic morphology of the samples was characterized by high-resolution electron microscopy. A JEM-2100LaB6 high-resolution transmission electron microscope (TEM) from JEOL, Japan, was used for sample morphology observation and electron diffraction analysis. An 832 CCD camera from Gatan, USA, was used to capture images and electron diffraction spectra.

[0034] The crystal structure of the sample in the present invention was characterized by an X-ray diffractometer, using a Japanese Rigaku D / max2500 X-ray diffractometer with a Cu target, a Kα radiation source, a graphite monochromator, a tube voltage of 40 kV, a tube current of 80 mA, a scanning range of 5° to 40°, a step size of 0.1°, and a scanning speed of 1° / min.

[0035] Example 1

[0036] 1.3g sodium hydroxide, 12g white carbon black, 1.0g aluminum chloride, 7.6g tetraethylammonium bromide, and 85g distilled water were mixed evenly, and then 102g propanol was added and the mixture was reacted at 140℃ for 8h. After the reaction, the temperature was lowered to 25℃, and then 0.84g sodium lignin sulfonate and 0.43g potassium chloride were added and the mixture was reacted at 130℃ for 35h. The obtained sample was filtered 5 times, and then dried in an oven at 130℃ for 10h, and calcined in a high-temperature furnace at 600℃ for 3h. The obtained sample was numbered M1. The properties of the sample are shown in Table 1, and its TEM photo is shown in Figure 1 .

[0037] Example 2

[0038] 0.75 g potassium hydroxide, 22.5 g silica gel, 1.0 g aluminum chloride, 4 g tetraethylammonium bromide, and 135 g distilled water were mixed evenly, and then 135 g propanol was added and the mixture was reacted at 110°C for 5 h. After the reaction, the temperature was lowered to 20°C, and then 1.13 g sodium lignin sulfonate and 0.28 g potassium chloride were added and the mixture was reacted at 100°C for 20 h. The obtained sample was filtered six times, dried in an oven at 120°C for 10 h, and calcined in a high-temperature furnace at 550°C for 4 h. The obtained sample was numbered M2, and the sample properties are shown in Table 1.

[0039] Example 3

[0040] 1.5 g of sodium hydroxide, 5.7 g of white carbon black, 1.0 g of aluminum chloride, 15.5 g of tetraethylammonium bromide, and 41 g of distilled water were mixed evenly, and then 61.5 g of propanol was added, and the mixture was reacted at 150°C for 15 h. After the reaction, the temperature was lowered to 25°C, and then 0.57 g of sodium lignin sulfonate and 0.56 g of potassium chloride were added, and the mixture was reacted at 140°C for 50 h. The obtained sample was filtered five times, and then dried in an oven at 125°C for 10 h, and calcined in a high-temperature furnace at 510°C for 5 h. The obtained sample was numbered M3, and the sample properties are shown in Table 1.

[0041] Example 4

[0042] 1 g of potassium hydroxide, 8.6 g of silica gel, 1.0 g of aluminum chloride, 28 g of tetraethylammonium hydroxide (25 wt%), and 70 g of distilled water were mixed evenly, and then 84 g of propanol was added. The mixture was reacted at 135°C for 10 h. After the reaction, the temperature was lowered to 22°C, and then 0.6 g of sodium lignin sulfonate and 0.36 g of sodium chloride were added. The mixture was reacted at 120°C for 40 h. The obtained sample was filtered six times, dried in an oven at 110°C for 10 h, and calcined in a high-temperature furnace at 540°C for 5 h. The obtained sample was numbered M4, and the sample properties are shown in Table 1.

[0043] Example 5

[0044] 1.2 g of sodium hydroxide, 9 g of white carbon black, 1.0 g of aluminum chloride, 32 g of tetraethylammonium hydroxide (25 wt%), and 75 g of distilled water were mixed evenly, and then 90 g of propanol was added. The mixture was reacted at 140°C for 7 h. After the reaction, the temperature was lowered to 25°C, and then 0.63 g of sodium lignin sulfonate and 0.41 g of sodium chloride were added. The mixture was reacted at 125°C for 45 h. The obtained sample was filtered several times, dried in an oven at 110°C for 10 h, and calcined in a high-temperature furnace at 550°C for 5 h. The obtained sample was numbered M5, and the sample properties are shown in Table 1.

[0045] Example 6

[0046] 1.3 g of sodium hydroxide, 12 g of white carbon black, 1.0 g of aluminum chloride, 7.6 g of tetraethylammonium bromide, and 85 g of distilled water were mixed evenly and reacted at 140°C for 8 h. After the reaction, the temperature was lowered to 25°C, and then 0.84 g of sodium lignin sulfonate and 0.43 g of potassium chloride were added and reacted at 130°C for 35 h. The obtained sample was filtered five times, dried in an oven at 130°C for 10 h, and calcined in a high-temperature furnace at 600°C for 3 h. The obtained sample was numbered M6, and the sample properties are shown in Table 1.

[0047] Example 7

[0048] 0.75 g potassium hydroxide, 22.5 g white carbon black, 1.0 g aluminum chloride, 4 g tetraethylammonium bromide, and 135 g distilled water were mixed evenly, and then 135 g propanol was added, and the mixture was reacted at 110°C for 5 h. After the reaction, the temperature was lowered to 20°C, and then 1.13 g sodium lignin sulfonate and 0.28 g potassium chloride were added, and the mixture was reacted at 110°C for 20 h. The obtained sample was filtered 6 times, and then dried in an oven at 120°C for 10 h, and calcined in a high-temperature furnace at 550°C for 4 h. The obtained sample was numbered M7, and the sample properties are shown in Table 1.

[0049] Example 8

[0050] 1.5 g of sodium hydroxide, 5.7 g of white carbon black, 1.0 g of aluminum chloride, 15.5 g of tetraethylammonium bromide, and 41 g of distilled water were mixed evenly, and then 61.5 g of propanol was added and reacted at 150°C for 15 h. After the reaction, the temperature was lowered to 25°C, and then 0.57 g of sodium lignin sulfonate was added and reacted at 140°C for 50 h. The obtained sample was filtered five times, and then dried in an oven at 125°C for 10 h, and calcined in a high-temperature furnace at 510°C for 5 h. The obtained sample was numbered M8, and the sample properties are shown in Table 1.

[0051] Comparative Example 1

[0052] Referring to the raw material ratios in Example 1, 1.3 g of sodium hydroxide, 12 g of white carbon black, 1.0 g of aluminum chloride, 7.6 g of tetraethylammonium bromide, 0.84 g of sodium lignin sulfonate, and 85 g of distilled water were mixed uniformly, and then 102 g of propanol was added. The mixture was reacted at 130° C. for 43 h. After the reaction, the obtained sample was filtered five times and then dried in an oven at 110° C. for 10 h. It was then calcined in a high-temperature furnace at 550° C. for 5 h. The obtained sample was numbered M9 and was an intangible substance, indicating that the direct addition of lignin would affect the nucleation of the molecular sieve and prevent the raw material from crystallizing. The sample properties are shown in Table 1.

[0053] Comparative Example 2

[0054] 1.3 g of sodium hydroxide, 12 g of white carbon black, 1.0 g of aluminum chloride, 7.6 g of tetraethylammonium bromide, and 85 g of distilled water were mixed evenly, and then 102 g of propanol was added and reacted at 140°C for 8 h. After the reaction, the temperature was lowered to 25°C and then raised to 130°C for 35 h. After the reaction, the temperature was lowered to 25°C, and then 0.84 g of sodium lignin sulfonate and 0.43 g of potassium chloride were added and stirred evenly. The obtained sample was filtered 5 times, and then placed in an oven to dry at 130°C for 10 h, and calcined in a high-temperature furnace at 600°C for 3 h. The obtained sample was numbered M10, and the sample properties are shown in Table 1.

[0055] Table 1 Properties of Examples and Comparative Examples

[0056]

[0057] Note: In the present invention, the crystallinity of the molecular sieve in Example 1 is taken as 100%, and the crystallinity of all samples is obtained by comparing with the crystallinity of this sample.

[0058] By comparing the examples and comparative examples, it can be seen that the method of the present invention can not only synthesize nano-molecular sieves, but also the molecular sieve crystals exist in a non-aggregated state, which is conducive to fully exerting their nano-characteristics.

[0059] The pore structure of the molecular sieve material of the present invention is characterized by N2 adsorption-desorption, and the crystal size and state are characterized by transmission electron microscopy.

Claims

1. A method for synthesizing nano-BETA molecular sieves, comprising the following steps: (1) Under contact conditions, the alkali source, silicon source, aluminum source, template and water are mixed and the first stage crystallization reaction is carried out after the mixture is evenly mixed; (2) After the first stage crystallization reaction is completed and the temperature drops to 10-30°C, lignin sulfonate is added to carry out the second stage crystallization reaction. After the reaction is completed, the nano-BETA molecular sieve is obtained after separation, drying and roasting; wherein the reaction temperature of the second stage crystallization reaction is 5-25°C lower than the reaction temperature of the first stage crystallization reaction in step (1).

2. The synthesis method according to claim 1, wherein The alkali source in step (1) is an inorganic base, and the inorganic base is selected from one or both of sodium hydroxide and potassium hydroxide.

3. The synthesis method according to claim 1, wherein The aluminum source in step (1) is selected from one or more of sodium aluminate, aluminum sulfate, aluminum chloride, and aluminum nitrate.

4. The synthesis method according to claim 1 or 3, wherein The aluminum source in step (1) is aluminum chloride and / or aluminum nitrate.

5. The synthesis method according to claim 1, wherein The silicon source in step (1) is selected from one or more of white carbon black, silica gel, silica sol, and water glass.

6. The synthesis method according to claim 1, wherein The template agent in step (1) is selected from one or both of tetraethylammonium hydroxide and tetraethylammonium bromide.

7. The synthesis method according to claim 1, wherein The lignin sulfonate is selected from one or both of sodium lignin sulfonate and potassium lignin sulfonate.

8. The synthesis method according to claim 1 or 7, wherein The lignin sulfonate is selected from sodium lignin sulfonate.

9. The synthesis method according to claim 1, wherein When the lignin sulfonate is introduced in step (2), an alkali metal chloride is introduced at the same time, and the alkali metal chloride is selected from one or more of sodium chloride, potassium chloride and lithium chloride.

10. The synthesis method according to claim 1 or 9, wherein When the lignin sulfonate is introduced in step (2), an alkali metal chloride is introduced at the same time, and the alkali metal chloride is sodium chloride and / or potassium chloride.

11. The synthesis method according to claim 9, wherein The molar ratio of the alkali metal chloride to the aluminum source is 0.8 to 2.1:

1.

12. The synthesis method according to claim 9 or 11, wherein The molar ratio of the alkali metal chloride to the aluminum source is 1 to 2:

1.

13. The synthesis method according to claim 1, wherein The material molar ratio in step (1) is 4-11 Na2O: 24-110 SiO2: Al2O3: 550-2500 H2O: 3-25M, where M is a template.

14. The synthesis method according to claim 1, wherein The material molar ratio in step (1) is 5-10Na2O:25-100SiO2:Al2O3:600-2000H2O:5-20M, where M is the template.

15. The synthesis method according to claim 1, wherein In step (1), alcohol is added, wherein the alcohol is a low molecular weight alcohol having 1 to 4 carbon atoms.

16. The synthesis method according to claim 15, wherein The low molecular alcohol is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, 1,2-propylene glycol, glycerol, and butanediol, and the mass ratio of alcohol to water is 0.8 to 1.6:

1.

17. The synthesis method according to claim 16, wherein The mass ratio of alcohol to water is 1 to 1.5:

1.

18. The synthesis method according to claim 1, wherein The reaction temperature of the first stage crystallization reaction in step (1) is 100-160° C., and the first stage crystallization reaction time is 2-7 h.

19. The synthesis method according to claim 1, wherein The reaction temperature of the first stage crystallization reaction in step (1) is 110-150° C., and the first stage crystallization reaction time is 3-6 h.

20. The synthesis method according to claim 1, wherein In step (2), the mass ratio of lignin sulfonate to silicon source is 0.03-0.15:

1.

21. The synthesis method according to claim 1 or 20, wherein: In step (2), the mass ratio of lignin sulfonate to silicon source is 0.05-0.1:

1.

22. The synthesis method according to claim 1, wherein The reaction temperature of the second stage crystallization reaction in step (2) is 90-150° C., and the reaction time of the second stage is 15-55 h.

23. The synthesis method according to claim 1 or 22, wherein: The reaction temperature of the second stage crystallization reaction in step (2) is 100-140° C., and the second stage reaction time is 20-50 h.

24. The synthesis method according to claim 1 or 22, wherein: The reaction temperature of the second stage crystallization reaction in step (2) is 10 to 15° C. lower than the reaction temperature of the first stage crystallization reaction in step (1).

25. The synthesis method according to claim 1, wherein The drying in step (2) is carried out at 100-150° C. for 1-10 hours.

26. The synthesis method according to claim 1, wherein The calcination in step (2) is carried out at a high temperature of 400 to 600° C. for 1 to 10 hours, and the calcination is carried out in air or oxygen atmosphere.

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