A Y-type molecular sieve and its synthesis method and application

Abstract

The present invention discloses a Y-type molecular sieve, a synthesis method, and applications thereof. The method comprises aging, crystallizing, washing, drying, and calcining a mixture containing an alkali source, a sodium source, an aluminum source, a tetramethylammonium template, a cationic surfactant, and a silicon source to obtain the Y-type molecular sieve. This method requires only a single crystallization step to produce Y-type molecular sieve nanoclusters with a high silicon-to-aluminum ratio, significantly reducing production processes and improving production efficiency, thus promising promising industrial applications.

Description

Technical Field

[0001] The invention belongs to the field of molecular sieve synthesis, and in particular relates to a Y-type molecular sieve and a synthesis method and application thereof. Background Art

[0002] As a large-pore molecular sieve, Y-type molecular sieve has been widely used in oil refining applications such as catalytic cracking, hydrocracking, and isomerization due to its unique acidic properties and pore structure, and has been used for over 50 years. The pores of Y-type molecular sieves are composed of twelve-membered rings with an effective pore diameter of 0.74 nm and an internal cavity volume of up to 50%, making them ideal as active components in cracking reactions. In recent years, the trend toward heavier and inferior crude oil has become increasingly pronounced. The limited pore size of traditional Y-type molecular sieves prevents large molecular reactants from entering the interior of the molecular sieve, forcing them to react only on the limited external surface, significantly reducing catalytic efficiency. Furthermore, due to the large crystal size and long pores of traditional Y-type molecular sieves, carbon deposits easily form during the reaction, which also shortens the catalyst life to a certain extent. Nanosizing Y-type molecular sieves can expose more acidic sites, which is an effective means of improving the diffusion efficiency of large molecules. Although nano Y molecular sieves solve the diffusion problem, there are still separation difficulties in actual industrial production. Self-assembling nano molecular sieves to form aggregates with cluster morphology not only retains the advantages of nano zeolites, but also overcomes the separation difficulties after synthesis. It has become a research direction in this field and has been reported in the literature.

[0003] Yu Jiao et al. reported a method for synthesizing a nano-self-assembled Y-type molecular sieve in "Nanocrystal zeolite Yassembly synthesized with CTAB under low gelling and aging temperature" in Volume 749 of Chemical Physics Letters. This paper used CTAB as a template to synthesize a molecular sieve with a specific surface area of ​​824 m 2 / g, and the external specific surface area is 163 m 2 / g, the grain size is 40nm, and the framework silicon-aluminum ratio is 4.4.

[0004] Ting Tang et al. reported a method for synthesizing nano-self-assembled Y molecular sieves under template-free conditions in RSC Advances Vol. 7, No. 13, P 7711-7717, “Organic template-free synthesis of zeolite Y nanoparticle assemblies and their application in the catalysis of the Ritter reaction”. This method was synthesized under high alkalinity, and the molecular sieve particles could be controlled at the nanoscale with a specific surface area of ​​647 m 2 / g, external specific surface area is 111m 2 / g, compared with traditional Y molecular sieve, it has better catalytic activity.

[0005] Patent CN 107055567 A discloses a method for preparing nano Y zeolite aggregates. The method uses water glass as a silicon source, dissolves it in a sodium hydroxide solution, then adds an aluminum source solution to the silicon source, stirs it evenly, and crystallizes it at 60-100°C for 12-36 hours to obtain nano Y zeolite aggregates. The specific surface area is 650-780m 2 / g, micropore volume 0.23-0.27ml / g, mesopore volume 0.16-0.25ml / g.

[0006] Patent CN 108046287 A discloses a method for synthesizing nano self-assembled zeolites using a long-chain alkyl trimethylammonium bromide surfactant as a template. This patent uses a relatively concentrated formulation system for gelation. By controlling the gelation, aging, and crystallization temperatures at low temperatures, the grain size can be reduced. However, the silicon and aluminum content of the product synthesized by this method is relatively low.

[0007] The nano Y molecular sieve synthesized by the existing technology has the problem of relatively low framework silicon and aluminum content, and has poor stability in practical applications. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention provides a Y-type molecular sieve, its synthesis method, and its application. This method requires only a single crystallization step to produce Y-type molecular sieve nanoclusters with a high silicon-to-aluminum ratio, significantly reducing production steps and improving production efficiency, thus promising promising industrial applications.

[0009] A Y-type molecular sieve synthesis method comprises the following steps: aging, crystallizing, washing, drying and calcining a mixture containing an alkali source, a sodium source, an aluminum source, a tetramethylammonium template, a cationic surfactant and a silicon source to obtain the Y-type molecular sieve.

[0010] In the method of the present invention, the concentration of the cationic surfactant in the mixture is 0.035-0.074 mol / L, preferably 0.046-0.062 mol / L, and more preferably 0.050-0.057 mol / L; the molar ratio of the tetramethylammonium template to the cationic surfactant is 50-120, preferably 60-102, and more preferably 70-90. By controlling the molar ratio of the tetramethylammonium template to the cationic surfactant in the solution, a nano-Y-type molecular sieve with a high silicon-to-aluminum ratio can be prepared.

[0011] In the method of the present invention, the molar ratio of materials in the mixed material is: Al2O3: (6.5-12.5)SiO2: (0.1-1.0)Na2O: (6.0-10.0)(TMA)2O: (160-310)H2O: (0.1-0.4) CTAB; preferably Al2O3: (7.2-10.0)SiO2: (0.3-0.7)Na2O: (7.7-9.0)(TMA)2O: (180-270)H2O: (0.15-0.30) CTAB.

[0012] In the method of the present invention, the alkali source is one or more of sodium hydroxide, tetramethylammonium hydroxide aqueous solution (TMAOH), and tetramethylammonium hydroxide pentahydrate.

[0013] In the method of the present invention, the aluminum source is one or more of aluminum isopropoxide, aluminum powder, sodium metaaluminate, and aluminum sulfate 18hydrate.

[0014] In the method of the present invention, the silicon source is one or more of silica sol, sodium silicate, ethyl orthosilicate, nano silicon dioxide and water glass.

[0015] In the method of the present invention, the sodium source is one or more of sodium hydroxide, sodium chloride and sodium bromide.

[0016] In the method of the present invention, the tetramethylammonium template agent is one or more of tetramethylammonium hydroxide aqueous solution, tetramethylammonium hydroxide pentahydrate, tetramethylammonium bromide and tetramethylammonium chloride.

[0017] In the method of the present invention, the cationic surfactant is one or more of dodecyltrimethylammonium bromide (DTAB), hexadecyltrimethylammonium bromide (CTAB), and octadecyltrimethylammonium bromide (STAB).

[0018] In the method of the present invention, the aging temperature is 25-35°C, preferably 28-31°C; the aging time is 20-40h, preferably 25-35h; the crystallization temperature is 100-120°C, preferably 105-115°C; and the crystallization time is 140-200h, preferably 160-180h.

[0019] A non-limiting method for synthesizing a Y-type molecular sieve employed in an embodiment of the present invention comprises the following steps:

[0020] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide template to water and stir for a period of time until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved. Then, under stirring, add hexadecyltrimethylammonium bromide to the solution to form an aluminum source solution.

[0021] (2) Add nano-silica to the aluminum source solution under stirring. After forming a gel, dynamically age it at a certain temperature, then dynamically crystallize it for a period of time. Then, take it out, wash it, dry it, and calcine it to obtain the final Y-type molecular sieve product.

[0022] A Y-type molecular sieve prepared by the above method is an aggregate formed by clustering nanocrystals, the nanocrystal size is 30-100nm, preferably 50-80nm; the aggregate size is 1.5-3.5μm, preferably 2.0-2.8μm, and the skeleton silicon-aluminum ratio (SiO2 / Al2O3) is 5.2-6.3, preferably 5.5-6.0.

[0023] The Y-type molecular sieve of the present invention has a specific surface area of ​​800-930m 2 / g, preferably 850-900m 2 / g, external specific surface area is 100-170m 2 / g, preferably 130-150m 2 / g.

[0024] The Y-type molecular sieve of the present invention has a hydrothermal stability of: after ammonium exchange, treatment at 700°C, 0.1 MPa high-temperature steam atmosphere for 2 hours, and calcination at 550°C for 3 hours. The crystallinity of the Y-type molecular sieve is 85-95%, preferably 89-93%, compared to the crystallinity of the Y-type molecular sieve before the hydrothermal treatment.

[0025] The above-mentioned Y-type molecular sieve is used as a hydrocracking acidic component.

[0026] In the method of the present invention, a cationic surfactant and tetramethylammonium ion (TMA + ) dual template system was used to synthesize Y-type molecular sieve nanoclusters. The cationic surfactant was distributed in the solution in the form of micelles, with the hydrophobic end facing inward and the positively charged hydrophilic end ammonium ion facing outward. + There is an electrostatic repulsive force between TMA + It will be easier to enter the micropores of the molecular sieve, and the synthesized molecular sieve has higher crystallinity and silicon-aluminum ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the XRD diffraction pattern of the Y-type molecular sieve prepared in Example 1. DETAILED DESCRIPTION

[0028] The Y-type molecular sieve described in this invention is characterized as follows: The hydrothermal stability test involves exchanging the sample three times with a 1.5 mol / L, 70°C ammonium chloride solution, maintaining a solid-to-liquid ratio of 1:10 for each exchange. The sample is then hydrothermally treated for two hours in a 700°C, 0.1 MPa steam atmosphere. The hydrothermally treated sample is then calcined at 550°C for three hours, and the crystallinity of the hydrothermally treated sample is determined by X-ray diffraction.

[0029] The specific surface area and pore volume of the molecular sieves were measured using the N2 adsorption-desorption method. The sample was first calcined at 550°C for 3 hours to remove the template. Prior to measurement, it was pretreated at 300°C for 3 hours and then tested by nitrogen adsorption at 77K. The specific surface area of ​​the molecular sieve was calculated using the BET method. The total pore volume was measured at p / p0 = 0.98. The external specific surface area was calculated using the t-Plot method.

[0030] The silicon-to-aluminum ratio of the molecular sieve framework was measured using X-ray diffraction. The unit cell parameter a0 was measured using the Chinese petrochemical industry standard SH / T0339-92 and then substituted into the Breck formula (Si / Al = ((192 × 0.00868) / (a0 − 24.191))–1) for calculation. The resulting silicon-to-aluminum ratio is expressed as the molar ratio SiO2 / Al2O3.

[0031] The crystallite size of the molecular sieves was measured using a scanning electron microscope (SEM).

[0032] The following examples and comparative examples further illustrate the effects and benefits of the method of the present invention, but the following examples do not limit the method of the present invention. In the preparation process of the Y-type molecular sieve of the present invention, the Y-type molecular sieve is dried at a temperature of 100°C for 10 hours and calcined at a temperature of 550°C for 3 hours.

[0033] Example 1

[0034] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide to water and stir for a while until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved. Then, add hexadecyltrimethylammonium bromide to the solution while stirring to form an aluminum source solution.

[0035] (2) Under stirring, nano-silica is added to the aluminum source solution, and the molar ratio of each material is Al2O3:9.0SiO2:0.55Na2O:8.5(TMA)2O:240H2O:0.26CTAB. The concentration of the cationic surfactant in the mixture is 0.06 mol / L; the molar ratio of the tetramethylammonium template agent to the cationic surfactant is 65. The mixture is dynamically aged at 30°C for 30 h and dynamically crystallized at 110°C for 170 h. The mixture is taken out, washed, dried, and calcined to obtain the final product.

[0036] Examples 2-5 are given with reference to Example 1.

[0037] Example 2

[0038] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide to water and stir for a while until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved. Then, add hexadecyltrimethylammonium bromide to the solution while stirring to form an aluminum source solution.

[0039] (2) While stirring, nano-silica was added to the aluminum source solution. The molar ratio of the materials after gel formation was Al2O3: 7.2SiO2: 0.3Na2O: 7.8(TMA)2O: 183H2O: 0.15DTAB. The concentration of the cationic surfactant in the mixture was 0.046 mol / L. The molar ratio of the tetramethylammonium template to the cationic surfactant was 10:4. The mixture was subjected to dynamic aging at 28°C for 35 h and dynamic crystallization at 105°C for 163 h. The mixture was then washed, dried, and calcined to obtain the final product.

[0040] Example 3

[0041] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide to water and stir for a while until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved. Then, add hexadecyltrimethylammonium bromide to the solution while stirring to form an aluminum source solution.

[0042] (2) While stirring, nano-silica was added to the aluminum source solution. The molar ratio of the materials after gel formation was Al2O3: 10.0SiO2: 0.66Na2O: 8.8(TMA)2O: 260H2O: 0.28STAB. The concentration of the cationic surfactant in the mixture was 0.06 mol / L; the molar ratio of the tetramethylammonium template to the cationic surfactant was 6:3. The mixture was subjected to dynamic aging at 31°C for 25 h and dynamic crystallization at 115°C for 176 h. The mixture was then washed, dried, and calcined to obtain the final product.

[0043] Example 4

[0044] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide to water and stir for a while until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved. Then, add hexadecyltrimethylammonium bromide to the solution while stirring to form an aluminum source solution.

[0045] (2) While stirring, nano-silica was added to the aluminum source solution. After gelation, the molar ratio of the materials was Al2O3: 6.8SiO2: 0.12Na2O: 6.0(TMA)2O: 160H2O: 0.10CTAB. The concentration of the cationic surfactant in the mixture was 0.035 mol / L. The molar ratio of the tetramethylammonium template to the cationic surfactant was 120. The mixture was subjected to dynamic aging at 25°C for 40 h and dynamic crystallization at 100°C for 200 h. The mixture was then washed, dried, and calcined to obtain the final product.

[0046] Example 5

[0047] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide to water and stir for a while until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved. Then, add hexadecyltrimethylammonium bromide to the solution while stirring to form an aluminum source solution.

[0048] (2) While stirring, nano-silica was added to the aluminum source solution. The molar ratio of the materials after gel formation was Al2O3: 12.5SiO2: 0.95Na2O: 10.0(TMA)2O: 300H2O: 0.4CTAB. The concentration of the cationic surfactant in the mixture was 0.074 mol / L. The molar ratio of the tetramethylammonium template to the cationic surfactant was 50. The mixture was subjected to dynamic aging at 35°C for 22 h and dynamic crystallization at 120°C for 144 h. The mixture was then washed, dried, and calcined to obtain the final product.

[0049] Comparative Example 1

[0050] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide to water and stir for a period of time until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved to form an aluminum source solution.

[0051] (2) While stirring, add nano-silica to the aluminum source solution. After gel formation, the molar ratio of the materials is Al2O3: 9.0SiO2: 0.55Na2O: 8.5(TMA)2O: 240H2O. Dynamic aging is performed at 30°C for 30 h and dynamic crystallization is performed at 110°C for 170 h. The product is then washed, dried, and calcined to obtain the final product.

[0052] Comparative Example 2

[0053] (1) Under stirring, sodium hydroxide is added to water, followed by aluminum powder, and stirred until the aluminum source is completely dissolved. Then, hexadecyltrimethylammonium bromide is added to the solution under stirring to form an aluminum source solution.

[0054] (2) While stirring, add nanosilica to the aluminum source solution. After gel formation, the molar ratio of the materials is Al2O3: 9.0SiO2: 0.55Na2O: 240H2O: 0.26CTAB. Dynamic aging is performed at 30°C for 30 h and dynamic crystallization is performed at 110°C for 170 h. The product is then washed, dried, and calcined to obtain the final product.

[0055] Comparative Example 3

[0056] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide to water and stir for a while until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved. Then, add hexadecyltrimethylammonium bromide to the solution while stirring to form an aluminum source solution.

[0057] (2) Under stirring, nano-silica is added to the aluminum source solution, and the molar ratio of each material is Al2O3:9.0SiO2:0.55Na2O:3.0(TMA)2O:240H2O:0.26CTAB. The concentration of the cationic surfactant in the mixture is 0.06 mol / L; the molar ratio of the tetramethylammonium template agent to the cationic surfactant is 23. The mixture is dynamically aged at 30°C for 30 h and dynamically crystallized at 110°C for 170 h. The mixture is taken out, washed, dried, and calcined to obtain the final product.

[0058] Comparative Example 4

[0059] (1) While stirring, add tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide to water and stir for a while until dissolved. Then add aluminum powder and stir until the aluminum source is completely dissolved. Then, add hexadecyltrimethylammonium bromide to the solution while stirring to form an aluminum source solution.

[0060] (2) Under stirring, nano-silica is added to the aluminum source solution, and the molar ratio of each material is Al2O3:9.0SiO2:0.55Na2O:19.0(TMA)2O:240H2O:0.26CTAB. The concentration of the cationic surfactant in the mixture is 0.06mol / L; the molar ratio of the tetramethylammonium template agent to the cationic surfactant is 23. The mixture is dynamically aged at 30°C for 30h and dynamically crystallized at 110°C for 170h. The mixture is taken out, washed, dried, and calcined to obtain the final product.

[0061] The product properties of the above examples and comparative examples are shown in Table 1.

[0062] Table 1

[0063]

Claims

1. A method for synthesizing a Y-type molecular sieve, characterized in that: The Y-type molecular sieve has a framework SiO2 / Al2O3 molar ratio of 5.2-6.3; the synthesis method comprises the following steps: aging, crystallizing, washing, drying, and calcining a mixture containing an alkali source, a sodium source, an aluminum source, a tetramethylammonium template, a cationic surfactant, and a silicon source to obtain the Y-type molecular sieve; The tetramethylammonium template is one or more of tetramethylammonium hydroxide aqueous solution, tetramethylammonium hydroxide pentahydrate, tetramethylammonium bromide, and tetramethylammonium chloride; The cationic surfactant is one or more of dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide; Wherein, the molar ratio of the tetramethylammonium template agent to the cationic surfactant is 50-120.

2. The synthesis method according to claim 1, wherein: The concentration of the cationic surfactant in the mixed material is 0.035-0.074 mol / L.

3. The synthesis method according to claim 2, wherein: The concentration of the cationic surfactant in the mixed material is 0.046-0.062 mol / L.

4. The synthesis method according to claim 3, wherein: The concentration of the cationic surfactant in the mixed material is 0.050-0.057 mol / L.

5. The synthesis method according to claim 1, wherein: The molar ratio of the tetramethylammonium template agent to the cationic surfactant is 60-102.

6. The synthesis method according to claim 5, characterized in that: The molar ratio of the tetramethylammonium template agent to the cationic surfactant is 70-90.

7. The synthesis method according to claim 1, wherein: The molar ratio of materials in the mixture is: Al2O3: (6.5-12.5) SiO2: (0.1-1.0) Na2O: (6.0-10.0) (TMA)2O: (160-310) H2O: (0.1-0.4) CTAB.

8. The synthesis method according to claim 7, wherein: The molar ratio of materials in the mixture is: Al2O3: (7.2-10.0) SiO2: (0.3-0.7) Na2O: (7.7-9.0) (TMA)2O: (180-270) H2O: (0.15-0.30) CTAB.

9. The synthesis method according to claim 1, wherein: The alkaline source is one or more of sodium hydroxide, tetramethylammonium hydroxide aqueous solution, and tetramethylammonium hydroxide pentahydrate.

10. The synthesis method according to claim 1, characterized in that: The aluminum source is one or more of aluminum isopropoxide, aluminum powder, sodium metaaluminate, and aluminum sulfate 18hydrate.

11. The synthesis method according to claim 1, characterized in that: The silicon source is one or more of silica sol, sodium silicate, ethyl orthosilicate, nano silicon dioxide and water glass.

12. The synthesis method according to claim 1, characterized in that: The sodium source is one or more of sodium hydroxide, sodium chloride and sodium bromide.

13. The synthesis method according to claim 1, characterized in that: The aging temperature is 25-35°C, and the aging time is 20-40h; the crystallization temperature is 100-120°C, and the crystallization time is 140-200h.

14. The synthesis method according to claim 13, characterized in that: The aging temperature is 28-31°C; the aging time is 25-35h; the crystallization temperature is 105-115°C; and the crystallization time is 160-180h.

15. The synthesis method according to claim 1, characterized in that: The specific steps include: (1) Under stirring, tetramethylammonium hydroxide pentahydrate, sodium hydroxide, and tetramethylammonium bromide template are added to water and stirred for a period of time until dissolved, followed by adding aluminum powder and stirring until the aluminum source is completely dissolved, and then, under stirring, cetyltrimethylammonium bromide is added to the solution to form an aluminum source solution; (2) Add nano-silica to the aluminum source solution under stirring. After forming a gel, dynamically age it at a certain temperature, then dynamically crystallize it for a period of time. Then, take it out, wash it, dry it, and calcine it to obtain the final Y-type molecular sieve product.

16. A Y-type molecular sieve prepared by the method according to any one of claims 1 to 15, characterized in that: The Y-type molecular sieve is an aggregate formed by clustering of nano-crystals, the size of the nano-crystals is 30-100 nm, and the size of the aggregates is 1.5-3.5 μm.

17. The Y-type molecular sieve according to claim 16, characterized in that: The Y-type molecular sieve is an aggregate formed by clustering nano-crystals, the size of the nano-crystals is 50-80 nm; the size of the aggregates is 2.0-2.8 μm, and the molar ratio of the framework SiO2 / Al2O3 is 5.5-6.

0.

18. The Y-type molecular sieve according to claim 16, characterized in that: The specific surface area of ​​the molecular sieve is 800-930m 2 / g, external specific surface area is 100-170m 2 / g.

19. The Y-type molecular sieve according to claim 18, characterized in that: The specific surface area of ​​the molecular sieve is 850-900m 2 / g, external specific surface area is 130-150m 2 / g.

20. Use of the Y-type molecular sieve according to any one of claims 16 to 19 as a hydrocracking acidic component.

Images