A modified hydrogen-type silicoaluminate molecular sieve and a method for preparing the same

Abstract

A modified hydrogen type silico-aluminate molecular sieve, characterized in that (1) the A value is 4.0-6.0 and the B value is not less than 1.4, in the formula: the Q4, Q3, Q2, Q1 and Q0 respectively correspond to the SiO4 tetrahedron structure of the molecular sieve MAS NMR 29 The peak area of five distinguishable peaks appearing in the Si spectrum corresponds to the SiO4 tetrahedron structure of the species, and the peaks from high field to low field are in turn corresponding to Si(4Si, 0Al), Si(3Si, 1Al), Si(2Si, 2Al), Si(1Si, 3Al) and Si(0Si, 4Al) resonance peaks; (2) the surface silicon aluminum molar ratio is 0.9-2.0; (3) the bulk silicon aluminum molar ratio is 2.0-4.0.

Description

Technical Field

[0001] This invention relates to the field of molecular sieves, specifically to modified hydrogen-form aluminosilicate molecular sieves and their preparation methods. Background Technology

[0002] Acid-catalyzed reactions commonly use liquid acid catalysts such as concentrated sulfuric acid, phosphoric acid, hydrofluoric acid, and concentrated hydrochloric acid, which easily pollute the environment and corrode equipment. Aluminosilicate molecular sieves, as a green catalyst, are widely used in acid catalysis due to their abundant acidic sites and unique pore structure. Commonly used aluminosilicate molecular sieves include X, Y, ZSM-5, MOR, and Beta, which possess different acid properties and regular pore structures, enabling them to effectively catalyze acid reactions. Numerous experiments have shown that acid-catalyzed reactions place high demands on the catalytic activity, i.e., the acid properties, of the molecular sieves; therefore, acid modification of molecular sieves is particularly important.

[0003] Aluminosilicate molecular sieves are mainly composed of [SiO4]. 0 and [AlO4] - It is composed of tetrahedra, where the cation sites, or acidic sites, are formed from [AlO4] in the molecular sieve. - The number of tetrahedra determines the silica-to-alumina ratio of the molecular sieve, which is closely related to its acidic properties. Secondly, the aluminum distribution of the molecular sieve is also an important factor; molecular sieves with aluminum-rich surfaces have a significant effect on enhancing their acidic catalytic performance.

[0004] Currently, the main methods for modifying the silicon-to-aluminum ratio of aluminosilicate molecular sieves are direct synthesis and post-treatment methods. Direct synthesis methods include hydrothermal, solvothermal, ionothermal, and directing agent synthesis methods, which are implemented by changing the types of silicon and aluminum sources, altering synthesis conditions, and employing directing agent synthesis technology. Direct synthesis is a relatively mature technology and is currently the main method used; however, its cumbersome steps and high cost of directing agents limit its widespread industrial application. Post-treatment methods primarily aim to reduce the total acid content of the molecular sieve and increase its acid strength. Research reports on post-treatment modifications for reducing the silicon-to-aluminum ratio of aluminosilicate molecular sieves are limited.

[0005] CN104556102A discloses a method for preparing a low silica-to-alumina ratio molecular sieve, comprising mixing a high silica-to-alumina ratio molecular sieve with a seed crystal directing agent and an aluminum-containing compound, and molding the mixture. The molded molecular sieve is then kept at 200-800℃ for 2-120 hours to obtain the low silica-to-alumina ratio molecular sieve. The seed crystal directing agent is prepared by mixing solid powdered silica, a template agent, and water. This method can supplement the framework of a synthesized molecular sieve with aluminum to obtain a molecular sieve with an even lower silica-to-alumina ratio, thereby improving catalytic activity. However, this method involves controlling the silica-to-alumina ratio of the molded molecular sieve catalyst and cannot obtain a purely low silica-to-alumina ratio molecular sieve.

[0006] CN108927207B discloses a porous catalytic material with a surface rich in aluminum and its preparation method. The main body of the material has a pseudo-boehmite crystal phase structure with trace amounts of FAU crystal phase structure. The method includes secondary crystallization of NaY molecular sieve, addition of silicon source and aluminum source, obtaining a solid precipitate, and then removing impurities by ammonium exchange to obtain a catalytic material with a sodium oxide content of less than 0.3%. This method can obtain a surface-rich aluminum catalytic material, but it is not a molecular sieve alone, which limits its acid properties.

[0007] CN110540214A discloses a surface-enriched NaY molecular sieve and its preparation method. By adjusting the molecular sieve synthesis ratio and crystallization method, a surface-enriched Na-type molecular sieve is obtained. Similarly, CN109516471A discloses a method for synthesizing a surface-enriched ZSM-23 molecular sieve. This method is simple and time-saving, but it yields a Na-type molecular sieve, which also requires Na removal treatment before it can be used in catalytic reactions. Summary of the Invention

[0008] The inventors discovered that by hydrothermal treatment of a solution containing four-coordinated aluminum species with a finished molecular sieve, followed by acid treatment and calcination, aluminum can be easily added to the framework of the molecular sieve, resulting in aluminosilicate molecular sieves with physicochemical characteristics different from those of existing technologies. Based on this, the present invention was formed.

[0009] Therefore, the purpose of this invention is to provide a modified hydrogen aluminosilicate molecular sieve with different physicochemical characteristics from existing hydrogen aluminosilicate molecular sieves used in acid catalytic reactions, and to provide a method for its preparation.

[0010] To achieve the objectives of this invention, a first aspect of this invention provides a modified hydrogen-form aluminosilicate molecular sieve, characterized in that...

[0011] (1) The value of A is 4.0-6.0 and the value of B is not less than 1.4, as stated above. The aforementioned In the formula: Q4, Q3, Q2, Q1 and Q0 respectively correspond to molecular sieve MAS NMR. 29 The peak areas of the five resolvable peaks appearing in the Si spectrum correspond to the possible SiO4 tetrahedral structure of the species. From high field to low field, they are the resonance peaks corresponding to Si(4Si,0Al)), Si(3Si,1Al), Si(2Si,2Al), Si(1Si,3Al)), and Si(0Si,4Al). (This method comes from "Research Methods for Solid Catalysts", edited by Xin Qin, Beijing: Science Press, 2004, p. 435).

[0012] (2) The surface silicon-aluminum molar ratio is 0.9-2.0, and the surface elemental distribution is determined by X-ray photoelectron spectroscopy analysis;

[0013] (3) The bulk silicon-aluminum molar ratio is 1.0-4.0, and the bulk elemental distribution of the sample is determined by X-ray fluorescence spectroscopy.

[0014] The A value represents the molar silica-alumina ratio of the aluminosilicate molecular sieve framework, and the B value represents the ratio of Q3 to Q4 species within the aluminosilicate molecular sieve, indicating the degree of aluminum enrichment of the molecular sieve.

[0015] The molecular sieve of the present invention contains no more than 0.5 wt% sodium oxide, preferably no more than 0.2 wt%.

[0016] Furthermore, the molecular sieve of the present invention has a specific surface area greater than 650 m². 2 Furthermore, the NH3-TPD acidity of the molecular sieve of the present invention is greater than 2000 μg / g. Preferably, the A value is 5.0-5.8 and the B value is 1.4-1.8.

[0017] To achieve the objectives of this invention, a second aspect of this invention provides a method for preparing modified aluminosilicate molecular sieves, characterized in that the method comprises the following steps:

[0018] (1) Alumina or its precursor reacts with an organic amine to obtain a solution containing a tetracoordinated aluminum species.

[0019] (2) The aluminosilicate molecular sieve is mixed with the solution containing tetracoordinated aluminum species described in step (1) and then subjected to a hydrothermal reaction in a crystallization kettle. The crystallization product is filtered, washed and dried to obtain the first molecular sieve.

[0020] (3) The first molecular sieve in step (2) is mixed with an acid solution and heated. The product is filtered, washed and dried to obtain the second molecular sieve.

[0021] (4) The second molecular sieve described in step (3) is roasted to obtain a modified hydrogen-type aluminosilicate molecular sieve.

[0022] In the preparation method of this invention, the alumina precursor in step (1) is selected from one or more of boehmite, aluminum hydroxide, and aluminum sol. The organic amine has a wide selection range; preferably, it is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide. The mass ratio of alumina or its precursor to the organic amine is 0.01-2:1, preferably 0.04-1:1, and the alumina precursor is calculated as alumina. The contact reaction in step (1) is not particularly limited by conditions, as long as a stable and homogeneous solution can be obtained. For example, the conditions include: a temperature of 60-150℃, preferably 100-150℃, and a time of 1-10h, preferably 2-6h. The concentration of the solution containing the tetracoordinated aluminum species is 0.4-20wt% based on aluminum.

[0023] In the preparation method of the present invention, the aluminosilicate molecular sieve in step (2) has a wide selection range. Preferably, the hydrogen-form aluminosilicate molecular sieve is selected from one of Y-type molecular sieve, X-type molecular sieve, β-type molecular sieve, MOR-type molecular sieve, and ZSM-5 type molecular sieve. The silica-to-alumina ratio of the hydrogen-form aluminosilicate molecular sieve is 5-100, preferably 5-20. To facilitate the entry of tetracoordinated aluminum species into the molecular sieve framework, the mass ratio of the hydrogen-form aluminosilicate molecular sieve to the solution containing tetracoordinated aluminum species in step (2) is 100-1:1, preferably 25-5:1, wherein the aluminosilicate molecular sieve is on a dry basis, and the solution containing tetracoordinated aluminum species is based on aluminum. The hydrothermal reaction conditions include: temperature 100-150℃, time 1-20h, preferably 2-10h.

[0024] In the preparation method of this invention, through step (2), the four-coordinated aluminum species in the solution containing the four-coordinated aluminum species can enter the vacancies in the aluminosilicate molecular sieve framework, completing the molecular sieve framework and playing a role in finely adjusting the silica-alumina ratio of the molecular sieve. The solution containing the four-coordinated aluminum species refers to the solution capable of forming Al(OH)4 under the above mixing conditions. - The solution of the substance. The filtration, washing, and drying conditions are not particularly limited and can be any washing and drying conditions existing in the art. The washing is preferably performed by rinsing with hot water until neutral. Preferably, the drying conditions include: a temperature of 100-200°C, more preferably 100-150°C; and a time of 1-12 hours, more preferably 4-8 hours.

[0025] In the preparation method of the present invention, steps (1) and (2) are preferably carried out in a homogeneous reactor after mixing in a crystallization kettle. The present invention does not have any particular limitation on the equipment for achieving the rotation conditions, and can be a conventional choice in the field. Those skilled in the art can select the rotation speed of the stirring equipment according to actual needs.

[0026] In the preparation method of this invention, step (3) involves using an acid solution to clean the pore structure and remove non-framework aluminum species. The acid can be selected from a wide range, as long as it can provide H+ in the presence of water. +The acid solution can be an organic acid or an inorganic acid, and can be a strong acid, a weak acid, or a moderately strong acid. Preferably, the organic acid is a C2-C4 organic acid. The acid solution is selected from one or more of hydrochloric acid, nitric acid, lactic acid, oxalic acid, hydrofluoric acid, and fluorosilicic acid. The concentration of the acid solution is 0.1-20 wt%, preferably 0.5-5 wt%. The acid solution is not particularly limited, as long as a homogeneous and stable solution can be obtained. Considering the need to save preparation costs, the solvent in the acid solution is preferably water, more preferably deionized water. The mass ratio of the acid solution to the second molecular sieve is 2-20:1, preferably 3-8:1. The reaction conditions include: a temperature of 40-95℃, preferably 50-70℃, and a time of 0.1-10h, preferably 0.5-5h. Most preferably, the acid solution is mixed with the first molecular sieve by dropwise addition at room temperature (25℃); the total dropwise addition time is 0.1-10h, preferably 0.5-2h. Under preferred conditions, it is more conducive to the structural repair and regulation of molecular sieves, thereby obtaining modified molecular sieves with better diffusion performance. The mixing and heating treatment in step (3) is preferably carried out under stirring conditions. The present invention does not have any particular limitation on the equipment for achieving the stirring conditions, and can be a conventional choice in the field. Those skilled in the art can select the stirring rate of the stirring equipment according to actual needs.

[0027] The preparation method of the present invention allows for a wide range of calcination atmospheres in step (4), including air, nitrogen, and steam. The calcination conditions include: a temperature of 400-650℃, preferably 500-600℃; and a time of 0.5-4h, preferably 1-3h.

[0028] The preparation method provided by this invention involves post-treatment modification of hydrogen-form aluminosilicate molecular sieves, achieving secondary aluminum replenishment of the molecular sieves through hydrothermal treatment without introducing Na ions, eliminating the need for subsequent ion exchange, and removing residual organic amines through subsequent acid treatment and calcination. This method achieves the preparation of surface-rich aluminum-form hydrogen molecular sieves and is simple and easy to operate.

[0029] The present invention further provides a modified aluminosilicate molecular sieve obtained by the above preparation method. Detailed Implementation

[0030] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0031] The framework silicon-to-aluminum ratio and the chemical states of silicon and aluminum in the molecular sieves were determined using solid-state nuclear magnetic resonance (MAS NMR). The specific surface area of ​​the molecular sieve samples was determined using the BET method with low-temperature N2 adsorption-desorption. The acidity of the molecular sieve samples was determined using NH3-programmed temperature desorption (NH3-TPD). The elemental distribution on the surface of the molecular sieve samples was determined by X-ray photoelectron spectroscopy (XPS). The elemental distribution in the bulk phase of the molecular sieve samples was determined by X-ray fluorescence spectroscopy (XRF).

[0032] Example 1

[0033] (1) Boehmite and 25wt% tetramethylamine hydroxide solution were mixed at a mass ratio of 0.125:1 and transferred into a crystallization vessel. The mixture was reacted for 4 hours at a reaction temperature of 120℃ to obtain a homogeneous and stable solution.

[0034] (2) Mix the HY type molecular sieve (sample number HY) with the above solution at a mass ratio of 25:1 (based on the dry basis weight of the molecular sieve and the Al(OH)4 content in the solution). - The mass ratio of the two liquids was used to transfer the mixed liquid into a crystallization vessel and react for 4 hours at a reaction temperature of 120°C. Then the mixture was filtered, washed, and dried at 110°C for 4 hours to obtain the first molecular sieve.

[0035] (3) At room temperature (25°C), a 1 wt% fluorosilicic acid solution is added dropwise into the first molecular sieve over 1 hour, wherein the mass ratio of the fluorosilicic acid solution to the first molecular sieve is 5:1. Then, the mixture is stirred at 65°C for 1 hour, filtered, washed, and dried at 110°C for 4 hours to obtain the second molecular sieve.

[0036] (4) The second molecular sieve was calcined at 550°C for 3 hours in an air atmosphere to obtain a modified aluminosilicate molecular sieve, sample number MY-1.

[0037] Example 2

[0038] The molecular sieve was modified using the same method as in Example 1, except that in step (2), the HY-type molecular sieve was reacted with Al(OH)4 (calculated as Al). - The mass ratio was changed to 12:1; a modified molecular sieve was obtained, and the sample number was MY-2.

[0039] Example 3

[0040] The molecular sieve was modified using the same method as in Example 1, except that in step (2), the mass ratio of the HY type molecular sieve to the solution (calculated as Al) was changed to 5:1; the modified molecular sieve was obtained, and the sample number was MY-3.

[0041] Example 4

[0042] The molecular sieve was modified using the same method as in Example 1, except that in step (2), the reaction temperature was changed to 150°C to obtain the modified molecular sieve, which was numbered MY-4.

[0043] Comparative Example 1

[0044] The method is the same as in Example 1, except that steps (1), (2), and (3) are not included, and step (4) is retained. Specifically, the HY type molecular sieve is calcined at 550°C for 3 hours in an air atmosphere to obtain a modified molecular sieve, and the sample number is HY-C.

[0045] Comparative Example 2

[0046] Following the same method as in Example 1, except that step (3) is omitted, while steps (1), (2), and (4) are retained, a modified molecular sieve is obtained, with the sample number HY-A.

[0047] Comparative Example 3

[0048] The method is the same as in Example 1, except that steps (1) and (2) are not included, while steps (3) and (4) are retained. Specifically, the HY type molecular sieve is calcined at 550°C for 3 hours in an air atmosphere to obtain a modified molecular sieve, and the sample number is HY-G.

[0049] Comparative Example 4

[0050] The molecular sieve was modified using the same method as in Example 1, except that in step (2), the mass ratio of the HY type molecular sieve to the solution (calculated as Al) was changed to 1:1; the modified molecular sieve was obtained, and the sample number was MY-5.

[0051] Comparative Example 5

[0052] The molecular sieve was modified using the same method as in Example 1, except that in step (2), the reaction temperature was changed to 90°C to obtain the modified molecular sieve, which was numbered MY-6.

[0053] The specific physicochemical properties of the samples obtained from the above embodiments and comparative examples are listed in Table 1.

[0054] Table 1

[0055]

Claims

1. A modified hydrogen-form aluminosilicate molecular sieve, characterized in that, (1) The value of A is 4.0-6.0 and the value of B is not less than 1.4, the aforementioned The aforementioned In the formula: Q4, Q3, Q2, Q1 and Q0 respectively correspond to molecular sieve MAS NMR. 29 The peak areas of the five resolvable peaks in the Si spectrum correspond to the SiO4 tetrahedral structure of the species, and from high field to low field, they correspond to the resonance peaks of Si (4Si, 0Al)), Si (3Si, 1Al), Si (2Si, 2Al), Si (1Si, 3Al)) and Si (0Si, 4Al). (2) The surface silicon-aluminum molar ratio is 0.9-2.0, and the elemental distribution on the sample surface is determined by X-ray photoelectron spectroscopy analysis; (3) The bulk silicon-aluminum molar ratio is 2.0-4.0, and the elemental distribution of the bulk phase of the sample is determined by X-ray fluorescence spectroscopy.

2. The molecular sieve according to claim 1, characterized in that, The sodium oxide content does not exceed 0.5 wt%.

3. The molecular sieve according to claim 2, characterized in that, The sodium oxide content does not exceed 0.2 wt%.

4. The molecular sieve according to claim 1, characterized in that, Specific surface area greater than 650 m² 2 / g.

5. The molecular sieve according to claim 1, characterized in that, The NH3-TPD acidity of the molecular sieve is greater than 2000 μg / g.

6. The molecular sieve according to claim 1, characterized in that, The value of A is 5.0-5.8 and the value of B is 1.4-1.

8.

7. The method for preparing the modified hydrogen-form aluminosilicate molecular sieve of claim 1, characterized in that, The preparation method includes the following steps: (1) Alumina or its precursor reacts with an organic amine to yield a solution containing a tetracoordinated aluminum species; (2) The hydrogen-type aluminosilicate molecular sieve is mixed with the solution containing tetracoordinated aluminum species described in step (1) and then subjected to a hydrothermal reaction in a crystallization kettle. The crystallization product is filtered, washed, and dried to obtain the first molecular sieve. (3) The first molecular sieve in step (2) is mixed with an acid solution and heated. The product is then filtered, washed and dried to obtain the second molecular sieve. (4) Calcination step (3) The second molecular sieve is used to obtain modified hydrogen-type aluminosilicate molecular sieve.

8. The preparation method according to claim 7, characterized in that, The precursor of alumina in step (1) is selected from one or more of boehmite, aluminum hydroxide and aluminum sol.

9. The preparation method according to claim 7, characterized in that, The organic amine in step (1) is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

10. The preparation method according to claim 7, characterized in that, The mass ratio of alumina or its precursor to organic amine in step (1) is 0.01-2:1, and the precursor of alumina is calculated as alumina.

11. The preparation method according to claim 10, characterized in that, The mass ratio of alumina or alumina precursor to organic amine in step (1) is 0.04-1:

1.

12. The preparation method according to claim 7, characterized in that, The contact reaction described in step (1) is subject to the following conditions: temperature of 60-150℃ and time of 1-10 h.

13. The preparation method according to claim 12, characterized in that, The contact reaction described in step (1) is subject to the following conditions: temperature of 100-150℃ and time of 2-6 h.

14. The preparation method according to claim 7, characterized in that, The solution containing tetracoordinated aluminum species described in step (1) has a concentration of 0.4-20 wt% based on aluminum.

15. The preparation method according to claim 7, characterized in that, The hydrogen-type aluminosilicate molecular sieve in step (2) is selected from one of the hydrogen-type Y-type molecular sieve, X-type molecular sieve, β-type molecular sieve, MOR-type molecular sieve and ZSM-5-type molecular sieve.

16. The preparation method according to claim 7, characterized in that, The silicon-to-aluminum ratio of the hydrogen-type aluminosilicate molecular sieve in step (2) is 5-100.

17. The preparation method according to claim 16, characterized in that, The silicon-to-aluminum ratio of the hydrogen-type aluminosilicate molecular sieve in step (2) is 5-20.

18. The preparation method according to claim 7, characterized in that, In step (2), the mass ratio of the hydrogen-form aluminosilicate molecular sieve to the solution containing four-coordinated aluminum species is 100-1:1, wherein the hydrogen-form aluminosilicate molecular sieve is on a dry basis and the solution containing four-coordinated aluminum species is based on aluminum.

19. The preparation method according to claim 18, characterized in that, In step (2), the mass ratio of the hydrogen-type aluminosilicate molecular sieve to the solution containing tetracoordinated aluminum species is 25-5:

1.

20. The preparation method according to claim 7, characterized in that, The hydrothermal reaction in step (2) is subject to the following conditions: temperature of 100-150℃ and time of 1-20 h.

21. The preparation method according to claim 20, characterized in that, The time required for step (2) is 2-10 hours.

22. The preparation method according to claim 7, characterized in that, The acid solution in step (3) is selected from one or more of hydrochloric acid, nitric acid, lactic acid, oxalic acid, hydrofluoric acid and fluorosilicic acid.

23. The preparation method according to claim 7, characterized in that, The acid solution described in step (3) has a concentration of 0.1-20 wt%.

24. The preparation method according to claim 23, characterized in that, The acid solution described in step (3) has a concentration of 0.5-5 wt%.

25. The preparation method according to claim 7, characterized in that, The mass ratio of the acid solution to the first molecular sieve in step (3) is 2-20:

1.

26. The preparation method according to claim 25, characterized in that, The mass ratio of the acid solution to the first molecular sieve in step (3) is 3-8:

1.

27. The preparation method according to claim 7, characterized in that, The heating treatment described in step (3) includes the following conditions: temperature of 40-95℃ and time of 0.1-10 h.

28. The preparation method according to claim 27, characterized in that, The heating treatment described in step (3) includes the following conditions: temperature of 50-70℃ and time of 0.5-5 h.

29. The preparation method according to claim 7, characterized in that, The roasting process described in step (4) includes the following conditions: temperature of 400-650℃ and time of 0.5-4h.

30. The preparation method according to claim 29, characterized in that, The roasting process described in step (4) includes the following conditions: temperature of 500-600℃ and time of 1-3h.

31. Modified hydrogen-type aluminosilicate molecular sieve obtained by the preparation method according to any one of claims 7-30.

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