Silazane-modified phosphorus-containing molecular sieve catalysts, methods for making and using the same

Abstract

This invention provides a silazane-modified phosphorus-containing molecular sieve catalyst, its preparation method, and its application, relating to the field of molecular sieve catalysts. The catalyst preparation method includes the following steps: Step 1: Obtaining a mixture containing a silicon source, an aluminum source, sodium hydroxide, water, and a phosphate ester, followed by crystallization treatment to obtain a phosphorus-containing Na-type molecular sieve; Step 2: Ion-exchanging the phosphorus-containing Na-type molecular sieve obtained in Step 1 with an ammonium salt solution to obtain a phosphorus-containing ZSM-5 molecular sieve; Step 3: Obtaining a mixture of silazane and the phosphorus-containing ZSM-5 molecular sieve obtained in Step 2 to obtain a silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst. The catalyst preparation method provided by this invention first directly hydrothermally synthesizes a phosphorus-containing ZSM-5 molecular sieve in an amine-free system, and then uses silazane to surface-modify the molecular sieve, improving the conversion rate of naphthalene and the selectivity of 2,6-diisopropylnaphthalene.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve catalysts, specifically to a silazane-modified phosphorus-containing molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] Diisopropylnaphthalene (DIPN) is an important organic chemical raw material. 2,6-Diisopropylnaphthalene (2,6-DIPN), like 2,6-DMN (2,6-dimethylnaphthalene), can be used as a raw material for the preparation of polyethylene terephthalate (PEN) and thermally oriented liquid crystal polymers (LCPs). It can also be used as a high-value-added fine chemical product. 2,6-DIPN can be used in environmentally friendly pesticides, plant growth regulators, and preservatives for storing vegetables.

[0003] 2,6-DIPN can be directly prepared via the isopropylation of naphthalene. The unique steric hindrance of isopropyl groups significantly reduces the difficulty of subsequent product separation and purification processes, thus this synthetic route has gradually attracted widespread attention. The direct synthesis of 2,6-DIPN via alkylation of naphthalene and alcohols is a simple route with readily available and inexpensive raw materials and mild reaction conditions, hence its growing popularity. However, alkylation of naphthalene involves numerous substitution sites and complex byproducts; there are at least 10 isomers of disubstituted products alone, and the physicochemical properties of these disubstituted products are similar. In particular, the boiling point difference between 2,6-DIPN and 2,7-DIPN is around 2.6 °C, which is unfavorable for the purification of 2,6-DIPN. Therefore, the key to this process route is the preparation of a catalyst with high selectivity for 2,6-DIPN.

[0004] Traditional catalysts for the synthesis of diisopropylnaphthalene mainly include anhydrous aluminum chloride (AlCl3), porous molecular sieves of silica-alumina compounds, and emerging ionic liquid catalysts. AlCl3 exhibits very high activity for monosubstituted products, but its selectivity for disubstituted products, especially 2,6-DIPN, is relatively low, around 20%. Furthermore, the reaction conditions for anhydrous AlCl3 catalysts are harsh, and the separation of catalyst and product after the reaction is difficult. Most importantly, this reaction generates a large amount of toxic and hazardous waste that is difficult to treat. While emerging ionic liquid catalysts overcome the low selectivity of 2,6-DIPN, the conversion rate of the naphthalene feedstock is not high, and the recovery loss after recycling is significant. Molecular sieve catalysts, on the other hand, have tunable acidic sites, an ordered pore structure, simple separation of solid catalyst and liquid product, easy catalyst regeneration, and low environmental pollution. However, the acidic sites on the surface of molecular sieve catalysts contribute to the low selectivity for 2,6-DIPN.

[0005] Therefore, all of the above methods suffer from problems such as low conversion rate of raw materials and low selectivity of 2,6-DIPN. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a silazane-modified phosphorus-containing molecular sieve catalyst, its preparation method and application, to solve at least one of the following existing problems: improving the conversion rate of naphthalene and improving the selectivity of 2,6-DIPN.

[0007] The objective of this invention is mainly achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a silazane-modified phosphorus-containing molecular sieve catalyst, comprising the following steps:

[0009] Step 1: Obtain a mixture containing silicon source, aluminum source, sodium hydroxide, water and phosphate ester, and then perform crystallization treatment to obtain phosphorus-containing Na-type molecular sieve;

[0010] Step 2: The phosphorus-containing Na-type molecular sieve obtained in Step 1 is subjected to ion exchange with an ammonium salt solution to obtain phosphorus-containing ZSM-5 molecular sieve;

[0011] Step 3: Obtain a mixture of silazane and the phosphorus-containing ZSM-5 molecular sieve obtained in Step 2 to obtain a silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst.

[0012] Preferably, in step 1, the mass ratio of silicon source, aluminum source, sodium hydroxide, water and phosphate ester is (50-100):(2-4):(8-17):(2000-3500):(2-5), and more preferably (60-100):(2.5-4):(10-17):(2500-3500):(2.5-5).

[0013] Preferably, in step 1, the temperature of the crystallization treatment is 160-200℃, and more preferably 180-190℃.

[0014] Preferably, in step 1, the silicon source includes at least one of silica sol, tetraethyl orthosilicate, and tetraalkyl silicate; the aluminum source includes at least one of sodium aluminate, aluminum triisopropoxy, aluminum isopropoxide, and aluminum hydroxide; and the phosphate ester includes at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, and tri(butoxyethyl) phosphate.

[0015] Preferably, in step 2, the concentration of the ammonium salt solution is 0.5-1.5 mol / L, and more preferably 1-1.2 mol / L.

[0016] Preferably, in step 2, the ammonium salt includes at least one of ammonium chloride, ammonium sulfate, ammonium nitrate, and ammonium phosphate.

[0017] Preferably, in step 3, the mass ratio of silazane to the phosphorus-containing ZSM-5 molecular sieve is (1-10):(90-99); the silazane includes at least one of hexamethyldisilazane and 1,3-bis(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane.

[0018] Secondly, the present invention provides a silazane-modified phosphorus-containing molecular sieve catalyst prepared by the aforementioned preparation method.

[0019] Preferably, the mass percentage of silazane is 1-10 wt% based on the total weight of the catalyst.

[0020] Thirdly, the present invention provides the application of a silazane-modified phosphorus-containing molecular sieve catalyst in the preparation method of 2,6-diisopropylnaphthalene.

[0021] Fourthly, the present invention provides a method for preparing 2,6-diisopropylnaphthalene, characterized by comprising the steps of: obtaining a mixture comprising naphthalene and isopropanol, adding the silazane-modified phosphorus-containing molecular sieve catalyst, and reacting to obtain 2,6-diisopropylnaphthalene.

[0022] Preferably, in the method for preparing 2,6-diisopropylnaphthalene, the amount of silazane-modified phosphorus-containing molecular sieve catalyst added is 1-15% of the total mass of naphthalene and isopropanol, preferably 1-10%.

[0023] Preferably, in the method for preparing 2,6-diisopropylnaphthalene, the molar ratio of naphthalene to isopropanol is 1:(2-2.2).

[0024] Preferably, in the method for preparing 2,6-diisopropylnaphthalene, the reaction temperature is 220-300℃, more preferably 230-280℃, and the reaction pressure is 1-2 MPa.

[0025] Beneficial effects:

[0026] The catalyst preparation method provided by this invention firstly involves the direct hydrothermal synthesis of phosphorus-containing ZSM-5 molecular sieves in an amine-free system. The phosphorus-aluminum structure prepared by the condensation reaction of phosphate ester and Al-OH is more stable, and the phosphorus species are not easily washed away, exhibiting better hydrothermal stability. After hydrothermal treatment, more microporous structures and strong acid sites of the molecular sieve are retained, improving the conversion rate of naphthalene. Then, the surface of the molecular sieve is modified with silazane, changing the surface of the molecular sieve from hydrophilic to lipophilic, which greatly reduces the adsorption reaction of isopropanol on the catalyst surface and improves the selectivity of 2,6-diisopropylnaphthalene. Detailed Implementation

[0027] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0028] In a first aspect, the present invention provides a method for preparing a silazane-modified phosphorus-containing molecular sieve catalyst, comprising the following steps:

[0029] Step 1: Obtain a mixture containing silicon source, aluminum source, sodium hydroxide, water and phosphate ester, then heat to crystallize, wash, dry and calcine to obtain phosphorus-containing Na-type molecular sieve;

[0030] Step 2: The phosphorus-containing Na-type molecular sieve obtained in Step 1 is subjected to ion exchange with ammonium salt solution, dried and calcined to obtain phosphorus-containing ZSM-5 molecular sieve;

[0031] Step 3: Obtain a mixture of silazane and phosphorus-containing ZSM-5 molecular sieve, react it, wash, filter and dry it to obtain silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst.

[0032] In a specific embodiment of the present invention, in step 1, the silicon source is at least one of silica sol, tetraethyl orthosilicate, and tetraalkyl silicate, preferably silica sol.

[0033] In a specific embodiment of the present invention, in step 1, the aluminum source is at least one of sodium aluminate, aluminum triisopropoxy, aluminum isopropoxide, and aluminum hydroxide, preferably sodium aluminate.

[0034] In one specific embodiment of the present invention, in step 1, the phosphate ester is at least one selected from trimethyl phosphate, triethyl phosphate, tributyl phosphate, and tri(butoxyethyl) phosphate. It should be noted that the present invention uses a phosphate ester as the phosphorus source. If a non-phosphate ester compound is used, phosphorus cannot be fixed into the molecular sieve structure, thus failing to improve the conversion rate of naphthalene and the selectivity of 2,6-diisopropylnaphthalene.

[0035] In a specific embodiment of the present invention, in step 1, the mass ratio of silicon source, aluminum source, sodium hydroxide, water and phosphate ester is (50-100):(2-4):(8-17):(2000-3500):(2-5), preferably (60-100):(2.5-4):(10-17):(2500-3500):(2.5-5).

[0036] In a specific embodiment of the present invention, in step 1, the temperature of the crystallization treatment is 160-200℃, such as 170, 180, 190℃, etc., preferably 180-190℃, and the crystallization treatment time is 24-48h, preferably 40-48h.

[0037] In one specific embodiment of the present invention, in step 1, the drying temperature is 100-120℃ and the drying time is 8-12h.

[0038] In one specific embodiment of the present invention, in step 1, the calcination temperature is 500-550℃, preferably 530-550℃, and the calcination time is 6-10h, preferably 8-10h.

[0039] In one specific embodiment of the present invention, in step 2, the concentration of the ammonium salt aqueous solution is 0.5-1.5 mol / L, preferably 1-1.2 mol / L.

[0040] In one specific embodiment of the present invention, in step 2, the ammonium salt is selected from at least one of ammonium chloride, ammonium sulfate, ammonium nitrate, and ammonium phosphate.

[0041] In one specific embodiment of the present invention, in step 3, the silazane is selected from at least one of hexamethyldisilazane (HMDS) and 1,3-bis(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane.

[0042] In one specific embodiment of the present invention, in step 3, the reaction time is 2-8 hours, preferably 5-7 hours, and the reaction temperature is room temperature (20℃±5℃).

[0043] In a specific embodiment of the present invention, in step 3, the mass ratio of silazane to the phosphorus-containing ZSM-5 molecular sieve is (1-10):(90-99).

[0044] It should be noted that the catalyst preparation method provided by this invention firstly involves the direct hydrothermal synthesis of phosphorus-containing ZSM-5 molecular sieves in an amine-free system. The phosphorus-aluminum structure prepared by the condensation reaction of phosphate ester and Al-OH is more stable, and the phosphorus species are not easily washed away, exhibiting better hydrothermal stability. After hydrothermal treatment, more microporous structures and strong acid sites of the molecular sieve are retained, improving the conversion rate of naphthalene. Then, the surface of the molecular sieve is modified with silazane, changing the surface of the molecular sieve from hydrophilic to lipophilic, which greatly reduces the adsorption reaction of isopropanol on the catalyst surface and improves the selectivity of 2,6-diisopropylnaphthalene.

[0045] As a specific embodiment of the present invention, the preparation method of the silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst provided by the present invention may specifically include the following steps:

[0046] Step 1: Mix silica sol, sodium aluminate, phosphate ester, and deionized water. After stirring evenly, place the mixture in a high-pressure reactor and crystallize at 160-200℃ for 24-48 hours. After crystallization, allow the reactor to cool to room temperature, transfer the resulting product to a centrifuge bottle, centrifuge and wash several times until the pH is close to 7, then dry at 100-120℃ for 8-12 hours and calcine at 500-550℃ for 6-10 hours to obtain phosphorus-containing Na-type molecular sieves.

[0047] Step 2: The Na-type molecular sieve is subjected to ion exchange three times with ammonium chloride aqueous solution at 80℃, dried at 100-120℃ for 8-12 hours, and calcined at 500-550℃ for 6-10 hours. This yields phosphorus-containing ZSM-5 molecular sieve.

[0048] Step 3: Add liquid hexamethyldisilazane solution to phosphorus-containing ZSM-5 molecular sieve and react at room temperature with rapid stirring for 2-8 hours. After the reaction is completed, place the reactants in dichloromethane solution, wash 3 times, filter and dry to obtain a silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst.

[0049] Secondly, the present invention provides a silazane-modified phosphorus-containing molecular sieve catalyst prepared by the above-mentioned preparation method.

[0050] The catalyst provided by this invention enhances the acidic sites within the molecular sieve pores through phosphorus modification, thereby increasing the conversion rate of naphthalene. Simultaneously, the acidic sites on the outer surface of the molecular sieve are removed using silazane, causing the surface of the molecular sieve to change from hydrophilic to lipophilic. This significantly reduces the adsorption reaction of isopropanol on the catalyst surface and improves the selectivity of 2,6-diisopropylnaphthalene.

[0051] As a specific embodiment of the present invention, the mass percentage of silazane in the total weight of the phosphorus-containing ZSM-5 molecular sieve catalyst modified with silazane is 1-10 wt%, such as 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, etc.

[0052] Thirdly, the present invention provides the application of a silazane-modified phosphorus-containing molecular sieve catalyst in the preparation method of 2,6-diisopropylnaphthalene.

[0053] Fourthly, the present invention provides a method for preparing 2,6-diisopropylnaphthalene, comprising the steps of: obtaining a mixture comprising naphthalene and isopropanol, adding a phosphorus-containing ZSM-5 molecular sieve catalyst modified with silazane, introducing pressurized gas, heating to carry out the reaction, and obtaining 2,6-diisopropylnaphthalene.

[0054] It should be noted that the preparation method of 2,6-diisopropylnaphthalene provided by this invention uses a silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst. This catalyst directly synthesizes phosphorus-containing ZSM-5 molecular sieves via hydrothermal modification in an amine-free system, resulting in a more stable phosphorus-aluminum structure for the molecular sieve. Phosphorus species are less easily washed away, exhibiting better hydrothermal stability. After hydrothermal treatment, more microporous structures and strong acid sites of the molecular sieve are retained, maintaining the catalyst's activity. Utilizing silazane for surface modification of the molecular sieve catalyst significantly reduces the adsorption reaction of isopropanol on the catalyst surface.

[0055] In a specific embodiment of the present invention, the reaction temperature in the preparation method of 2,6-diisopropylnaphthalene is 220-300℃, preferably 230-280℃, the reaction pressure is 1-2MPa, and the reaction time is 4-7h, preferably 4-6h.

[0056] As a specific embodiment of the present invention, in the preparation method of 2,6-diisopropylnaphthalene, the amount of phosphorus-containing ZSM-5 molecular sieve catalyst modified with silazane added is 1-15% of the total mass of naphthalene and isopropanol, preferably 1-10%.

[0057] In one specific embodiment of the present invention, in the preparation method of 2,6-diisopropylnaphthalene, the molar ratio of naphthalene to isopropanol is 1:(2-2.2).

[0058] In one specific embodiment of the present invention, in the method for preparing 2,6-diisopropylnaphthalene, the pressurized gas is at least one of nitrogen and argon.

[0059] The following detailed description of preferred embodiments of the present invention illustrates the principles of the invention and is not intended to limit the scope of the invention.

[0060] Qualitative and quantitative analysis of the product was performed using a gas chromatograph (model: Yimeng A90) from Shanghai Yimeng Electronic Technology Co., Ltd.

[0061] The formula for calculating the conversion rate of naphthalene is: Naphthalene conversion rate = (Number of moles of naphthalene converted / Total number of moles of naphthalene) * 100%

[0062] The formula for calculating the selectivity of 2,6-diisopropylnaphthalene (2,6-DIPN) is: 2,6-DIPN selectivity = molar amount of 2,6-DIPN in the product / total molar amount of the product.

[0063] Example 1

[0064] (1) A method for preparing a silazane-modified phosphorus-containing ZSM-5 molecular sieve, comprising the following steps:

[0065] Step 1: Silica sol, sodium aluminate, sodium hydroxide, deionized water, and tributyl phosphate were mixed in a mass ratio of 80:3:10:3000:3. After thorough mixing, the mixture was placed in a high-pressure reactor and crystallized at 180°C for 48 hours. After crystallization, the reactor was allowed to cool to room temperature, and the resulting product was transferred to a centrifuge bottle. The product was centrifuged and washed several times until the pH approached 7, then dried at 120°C for 12 hours and calcined at 550°C for 10 hours to obtain phosphorus-containing Na-type molecular sieves.

[0066] Step 2: The phosphorus-containing Na-type molecular sieve is subjected to ion exchange three times with a 1 mol / L ammonium chloride solution at 80℃, dried at 120℃ for 12 h, and calcined at 550℃ for 8 h. This yields the phosphorus-containing ZSM-5 molecular sieve.

[0067] Step 3: Based on the assumption that the mass content of hexamethyldisilazane (HMDS) in the silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst is 1% and the mass content of phosphorus-containing ZSM-5 molecular sieve is 99%, liquid hexamethyldisilazane is added to the phosphorus-containing ZSM-5 molecular sieve, and the reaction is carried out at room temperature with rapid stirring for 6 hours. After the reaction is completed, the reactants are placed in dichloromethane solution, washed 3 times, filtered and dried to obtain silazane-modified phosphorus-containing ZSM-5 molecular sieve with a mass percentage of HMDS of 1%.

[0068] (2) Preparation of 2,6-diisopropylnaphthalene from phosphorus-containing ZSM-5 molecular sieve modified with silazane

[0069] The reaction of naphthalene with isopropanol was carried out in a reaction vessel. Naphthalene and isopropanol were added to the reaction vessel at a molar ratio of 1:2.1. A catalyst with a mass fraction of 10% of the total raw material mass was added. The reaction temperature was 270℃, and nitrogen gas was introduced to adjust the pressure to 2 MPa. The reaction time was 6 h. After the reaction was completed, the obtained 2,6-diisopropylnaphthalene was extracted and analyzed by gas chromatography. The data results are recorded in Table 1.

[0070] Example 2

[0071] Example 2 is basically the same as Example 1, except that: in the silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst, the mass content of HMDS is 3% and the mass content of phosphorus-containing ZSM-5 molecular sieve is 97%.

[0072] Example 3

[0073] Example 3 is basically the same as Example 1, except that: in the silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst, the mass content of HMDS is 5% and the mass content of phosphorus-containing ZSM-5 molecular sieve is 95%.

[0074] Example 4

[0075] Example 4 is basically the same as Example 1, except that: in the silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst, the mass content of HMDS is 8% and the mass content of phosphorus-containing ZSM-5 molecular sieve is 92%.

[0076] Example 5

[0077] Example 5 is basically the same as Example 1, except that: in the silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst, the mass content of HMDS is 10% and the mass content of phosphorus-containing ZSM-5 molecular sieve is 90%.

[0078] Example 6

[0079] Example 6 is basically the same as Example 1, except that in step 1, silica sol, sodium aluminate, sodium hydroxide, deionized water and tributyl phosphate are mixed in a mass ratio of 80:6:10:3000:3.

[0080] Example 7

[0081] Example 7 is basically the same as Example 1, except that in step 1, silica sol, sodium aluminate, sodium hydroxide, deionized water and tributyl phosphate are mixed in a mass ratio of 80:6:10:3000:6.

[0082] Example 8

[0083] Example 8 is basically the same as Example 1, except that HMDS is replaced with 1,3-bis(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane.

[0084] Example 9

[0085] Example 9 is basically the same as Example 1, except that HMDS is replaced with 1,3-diphenyltetramethyldisilazane.

[0086] Comparative Example 1

[0087] Comparative Example 1 is basically the same as Example 1, except that step 3 is not included in the catalyst preparation method, that is, the catalyst does not include HMDS.

[0088] Comparative Example 2

[0089] Comparative Example 2 is basically the same as Example 1, except that: in the preparation method of the catalyst, tributyl phosphate is not added in step 1, and steps 2 and 3 are continued, that is, the catalyst does not contain phosphorus.

[0090] Table 1. Performance of the catalysts prepared in the examples and comparative examples for the preparation of 2,6-diisopropylnaphthalene

[0091]

[0092] As shown in Table 1, the silazane-modified phosphorus-containing ZSM-5 molecular sieve catalysts prepared in Examples 1-9 can be used to synthesize 2,6-diisopropylnaphthalene, with naphthalene conversion rates all above 90% and target product selectivity above 50%.

[0093] The catalyst used in Comparative Example 1 had a low selectivity of only 20.3% for the target product because its surface was not modified with silazane. This indicates that silazane surface modification of the molecular sieve changes the surface of the molecular sieve from hydrophilic to lipophilic, which greatly reduces the adsorption reaction of isopropanol on the catalyst surface and improves the selectivity of 2,6-diisopropylnaphthalene.

[0094] The catalyst used in Comparative Example 2 was modified with silazane, but the molecular sieve did not contain phosphorus, which led to a decrease in the conversion rate of naphthalene and a reduction in the selectivity of 2,6-diisopropylnaphthalene to 12.1%.

[0095] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing a silazane-modified phosphorus-containing molecular sieve catalyst, characterized in that, Includes the following steps: Step 1: Obtain a mixture containing silicon source, aluminum source, sodium hydroxide, water and phosphate ester, and then perform crystallization treatment to obtain phosphorus-containing Na-type molecular sieve; Step 2: The phosphorus-containing Na-type molecular sieve obtained in Step 1 is subjected to ion exchange with an ammonium salt solution to obtain phosphorus-containing ZSM-5 molecular sieve; Step 3: Obtain a mixture of silazane and the phosphorus-containing ZSM-5 molecular sieve obtained in Step 2 to obtain a silazane-modified phosphorus-containing ZSM-5 molecular sieve catalyst.

2. The preparation method according to claim 1, characterized in that, In step 1, the mass ratio of silicon source, aluminum source, sodium hydroxide, water and phosphate ester is (50-100):(2-4):(8-17):(2000-3500):(2-5), preferably (60-100):(2.5-4):(10-17):(2500-3500):(2.5-5).

3. The preparation method according to any one of claims 1-2, characterized in that, In step 1, the temperature of the crystallization treatment is 160-200℃, preferably 180-190℃.

4. The preparation method according to any one of claims 1-3, characterized in that, In step 1, The silicon source includes at least one of silica sol, tetraethyl orthosilicate, and tetraalkyl silicate. And / or, the aluminum source includes at least one of sodium aluminate, aluminum triisopropoxy, aluminum isopropoxide, and aluminum hydroxide; And / or, the phosphate ester includes at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, and tri(butoxyethyl) phosphate.

5. The preparation method according to any one of claims 1-4, characterized in that, In step 2, the concentration of the ammonium salt solution is 0.5-1.5 mol / L, preferably 1-1.2 mol / L; And / or, in step 2, the ammonium salt includes at least one of ammonium chloride, ammonium sulfate, ammonium nitrate, and ammonium phosphate.

6. The preparation method according to any one of claims 1-5, characterized in that, In step 3, the mass ratio of silazane to the phosphorus-containing ZSM-5 molecular sieve is (1-10):(90-99); And / or, the silazane includes at least one of hexamethyldisilazane and 1,3-bis(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane.

7. A silazane-modified phosphorus-containing molecular sieve catalyst prepared by the method according to any one of claims 1-6, Preferably, the mass percentage of silazane is 1-10 wt% based on the total weight of the catalyst.

8. The application of the silazane-modified phosphorus-containing molecular sieve catalyst of claim 7 in the preparation method of 2,6-diisopropylnaphthalene.

9. A method for preparing 2,6-diisopropylnaphthalene, characterized in that, The steps include: obtaining a mixture comprising naphthalene and isopropanol, adding the silazane-modified phosphorus-containing molecular sieve catalyst as described in claim 7, and reacting to obtain 2,6-diisopropylnaphthalene; Preferably, in the method for preparing 2,6-diisopropylnaphthalene, the amount of silazane-modified phosphorus-containing molecular sieve catalyst added is 1-15% of the total mass of naphthalene and isopropanol, preferably 1-10%. Preferably, in the method for preparing 2,6-diisopropylnaphthalene, the molar ratio of naphthalene to isopropanol is 1:(2-2.2).

10. The preparation method according to claim 9, characterized in that, In the method for preparing 2,6-diisopropylnaphthalene, The reaction temperature is 220-300℃, preferably 230-280℃. And / or, the reaction pressure is 1-2 MPa.

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