Preparation of lamellar Ti-MWW titanium silicalite molecular sieve and application of lamellar Ti-MWW titanium silicalite molecular sieve in epoxidation reaction

Abstract

The invention discloses preparation of a lamellar Ti-MWW titanium silicalite molecular sieve and application of the lamellar Ti-MWW titanium silicalite molecular sieve in epoxidation reaction, and belongs to the technical field of synthesis of inorganic chemicals. According to the method, polycyclic aliphatic amines are added in the Ti-MWW molecular sieve synthesis process, the crystallization temperature is reduced in the initial crystallization stage of the molecular sieve to delay the growth speed of the C-axis of the molecular sieve, and the thin-layer Ti-MWW with the shorter C-axis is obtained, so that the diffusion performance of the Ti-MWW molecular sieve is greatly improved, the diffusion rate of reactant molecules in pore channels is increased, and the performance of the Ti-MWW molecular sieve is improved. Therefore, the catalytic performance of the molecular sieve is greatly improved, and the molecular sieve is suitable for catalyzing liquid-phase epoxidation reactions of propylene, butylene, hexene, cyclohexene and octene and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic chemical synthesis, and in particular relates to the preparation of a thin layer Ti-MWW titanium silicon molecular sieve and its application in epoxidation reaction. Background Art

[0002] In 1983, Taramasso successfully embedded the transition metal element Ti into the framework of all-silicon zeolite and developed the titanium silicate molecular sieve TS-1 (GB2071071A, USP4410501, 1983), which expanded the catalytic application of molecular sieves from the field of acid-base catalysis to the field of selective oxidation catalysis. Limited by the diffusion restriction of micropores, the TS-1 molecular sieve shows low activity in the catalytic oxidation of large molecular olefins. To solve this problem, the development of titanium silicate molecular sieves with larger pore systems has always been a top priority in research.

[0003] Ti-MWW molecular sieve has two independent pore systems: one is an elliptical 10-membered ring sinusoidal pore system, and the other is a 10-membered ring straight pore system connected to a 12-membered ring supercage with a diameter of about 0.7nm, and 12-membered ring cup holes are distributed on its crystal surface. This unique pore system enables Ti-MWW molecular sieve to show better catalytic performance than titanium silicalite TS-1 in a series of catalytic oxidation reactions, such as olefin epoxidation, aldehyde and ketone ammoxidation, and pyridine and thioether oxidation. 2 O 2 The catalytic system realized the industrial application of butanone ammoxidation to butanone oxime for the first time.

[0004] At present, the main synthesis method of Ti-MWW molecular sieve is to use single template cyclohexyl imine or piperidine as organic directing agent, use fumed silica or alkaline silica sol as silicon source, tetrabutyl titanate as titanium source, boric acid as crystallization aid to perform hydrothermal crystallization at a certain temperature. However, this method will cause a large amount of boric acid resources to be wasted. Subsequent researchers developed a method to prepare Ti-MWW molecular sieve using dual templates adamantane ammonium hydroxide and cyclohexyl imine as organic directing agents and potassium carbonate as crystallization aid. Regardless of the synthesis method used, although the prepared Ti-MWW has certain pore structure advantages over TS-1 molecular sieve, it still cannot achieve the ideal oxidation reaction activity in some macromolecular olefin epoxidation reactions.

[0005] In addition, selective regulation of the specific axial length of the molecular sieve can effectively optimize the catalytic performance of the molecular sieve; due to diffusion restrictions, some catalytic reactions involving large molecules are more likely to occur at the molecular sieve pores. Crystals with shorter lengths in a specific axial direction are more conducive to exposing more pore structures to participate in the reaction than block crystals, and also help the diffusion of molecules. Therefore, the design and synthesis of molecular sieve crystals with specific preferential orientations has become a research focus. From the perspective of industrial applications, the development of thin-layered Ti-MWW molecular sieves with shorter C axes is of great significance. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a preparation method of a thin layer Ti-MWW titanium silicon molecular sieve and its application in epoxidation reaction. The present invention innovatively adds polycyclic fatty amines during the synthesis process of Ti-MWW molecular sieve, and reduces the crystallization temperature in the early stage of molecular sieve crystallization to slow down the growth rate of the C axis of the molecular sieve, thereby obtaining a thin layer Ti-MWW with a shorter C axis. This method greatly improves the diffusion performance of Ti-MWW molecular sieve, increases the diffusion rate of reactant molecules in the pores, thereby greatly improving the catalytic performance of the molecular sieve, and is suitable for catalyzing liquid phase epoxidation reactions such as propylene, butene, hexene, cyclohexene, and octene.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a thin layer Ti-MWW titanium silicon molecular sieve, comprising the following steps:

[0009] (1) Mix the template and water evenly, add the titanium source dropwise, and stir evenly to obtain gel A;

[0010] (2) mixing the polycyclic fatty amine and water uniformly, adding a silicon source, and stirring uniformly to obtain gel B;

[0011] (3) Slowly add gel A to gel B, stir evenly, then add boric acid additive and stir evenly;

[0012] (4) stirring the reaction solution obtained in step (3) at 100-150° C. for crystallization for 5-36 hours, then stirring at 150-210° C. for 4-8 days, cooling, filtering the obtained mother liquor, washing, and drying to obtain a thin layer Ti-MWW molecular sieve raw powder;

[0013] (5) The Ti-MWW molecular sieve raw powder is dispersed in a nitric acid solution with a concentration of 1 to 5 mol / L and treated at 60 to 110° C. for 0.5 to 2 days, centrifuged, washed, dried, and calcined at 400 to 650° C. in an air atmosphere for 5 to 24 hours to obtain a Ti-MWW titanium silicon molecular sieve catalyst.

[0014] Based on the above technical solution, further, the template agent described in step (1) is one or a combination of two or more of piperidine, cycloheximide, and piperazine.

[0015] Based on the above technical solution, further, the titanium source described in step (1) is one or a combination of two or more of tetrabutyl titanate, tetraisopropyl titanate, titanium tetrachloride, titanium sulfate, hexafluorotitanic acid or ammonium hexafluorotitanate.

[0016] Based on the above technical solution, further, the mass ratio of the titanium source, template and water in step (1) is 1:5-10:10-20.

[0017] Based on the above technical solution, further, the silicon source described in step (2) is one or a combination of two or more of fumed silica, silica sol, tetraethyl orthosilicate and silicon powder.

[0018] Based on the above technical solution, further, the polycyclic aliphatic amines described in step (2) are one or a combination of two or more of dicyclohexylamine, N,N'-dimethylpiperazine, bicyclo[2.2.1]heptane-2-amine, bicyclo[2.2.2]octane-1-amine, adamantaneamine, and triethylenediamine.

[0019] Based on the above technical solution, further, the mass ratio of the polycyclic fatty amines, the silicon source and the water in step (2) is 1:1-5:3-15.

[0020] Based on the above technical solution, further, the mass ratio of gel A to gel B in step (3) is 1:2 to 2:1, and the mass percentage of added boric acid is 0.05 to 0.5%.

[0021] Based on the above technical scheme, further, the specific process of step (4) is to add the reaction solution obtained in step (3) into the synthesis kettle, stir and crystallize at 120-140°C for 10-14h, then stir at 150-190°C for 5-7 days, cool, filter the obtained mother liquor, wash, and dry to obtain the thin layer Ti-MWW molecular sieve raw powder.

[0022] Based on the above technical solution, further, the mass ratio of the Ti-MWW molecular sieve raw powder to the nitric acid solution described in step (5) is 1: (20-100), the concentration of the nitric acid solution is 1-3 mol / L; the roasting temperature is 500-600°C, and the roasting time is 5-12h.

[0023] In a second aspect, the present invention provides a thin layer Ti-MWW titanium silicon molecular sieve prepared by the above-mentioned preparation method.

[0024] In a third aspect, the present invention provides the use of the above-mentioned thin layer Ti-MWW titanium silicon molecular sieve in epoxidation reaction.

[0025] Based on the above technical solution, further, the epoxidation reaction is a liquid phase epoxidation reaction, the substrates of the epoxidation reaction are olefins and hydrogen peroxide, and the solvent includes methanol, ethanol, acetonitrile and dimethylformamide.

[0026] Based on the above technical solution, further, the olefins include propylene, butene, pentene, hexene, cyclohexene and octene.

[0027] Based on the above technical solution, further, the molar ratio of olefin, hydrogen peroxide and solvent is 1:1-2:10-50, the reaction temperature is 30-100°C, the reaction pressure is 0.1-3MPa, and the reaction time is 0.5-5h.

[0028] The beneficial effects of the present invention compared with the prior art are as follows:

[0029] The present invention adds polycyclic fatty amines during the preparation of titanium silicon molecular sieve Ti-MWW. The amines can prevent the growth of the C axis of the molecular sieve during the crystallization process to obtain a thin layer Ti-MWW molecular sieve. The synthesized Ti-MWW molecular sieve is particularly suitable for catalyzing liquid phase epoxidation of propylene, butene, hexene, cyclohexene, octene, and cyclohexanone amine oximation reactions, and in particular, exhibits good reaction activity in the epoxidation reaction of 1-hexene and hydrogen peroxide, and has very broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0031] Figure 1 This is a scanning electron microscope image of the conventional Ti-MWW molecular sieve in Comparative Example 1;

[0032] Figure 2 This is a scanning electron microscope image of the Ti-MWW molecular sieve catalyst-1 in Example 1. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0034] The 1-hexene conversion (x(1-Hexene), %) and the 1,2-epoxidehexane selectivity (s(1,2-Epoxidehexane), %) were calculated using formula (1) and formula (2).

[0035]

[0036] Where: n(1,2-Epoxide hexane) is the amount of 1,2-epoxide hexane, mol; n(Pentanal) is the amount of valeraldehyde, mol; n(1,2-Hexanediol) is the amount of 1,2-hexanediol, mol; n 0 (1-Hexene) is the amount of 1-hexene starting substance, mol.

[0037] Comparative Example 1: Traditional Ti-MWW molecular sieve

[0038] Synthesis of traditional Ti-MWW molecular sieve: The silicon source is fumed silica, tetrabutyl titanate is used as the titanium source, piperidine is used as the template, and boric acid is used as the crystallization aid. The specific feeding and synthesis steps are as follows: First, 11.9g piperidine is mixed and stirred evenly with 34.2g deionized water, then 1.2g tetrabutyl titanate solution is slowly added to the mixture, and finally, 8.2g boric acid and 6g fumed silica are added, and the titanium silica gel is obtained after mixing evenly. The titanium silica gel is transferred to a stainless steel static reactor, heated to 170°C, and crystallized for 168h. After crystallization, it is cooled to room temperature, filtered, dried at 110°C, and calcined at 540°C for 6h to obtain the Ti-MWW molecular sieve raw powder. The Ti-MWW molecular sieve raw powder was then mixed with 2 mol / L nitric acid solution at a mass ratio of 1:50, treated at 80°C for 1 day, centrifuged, washed, dried at 80°C for 12h, and calcined at 550°C in air atmosphere for 10h to finally obtain the Ti-MWW molecular sieve catalyst.

[0039] Figure 1 This is a scanning electron microscope image of the traditional Ti-MWW molecular sieve in Comparative Example 1.

[0040] Example 1: Ti-MWW molecular sieve catalyst-1

[0041] First, 11.9 g of piperidine and 17.1 g of water were mixed and stirred for 30 minutes, and then 1.2 g of tetrabutyl titanate was added dropwise, and the mixture was stirred for 2 hours to obtain gel A. 3.64 g of dicyclohexylamine and 17.1 g of water were mixed evenly, and then 6 g of fumed silica was added, and the mixture was stirred for 2 hours to obtain gel B. Then gel A was slowly added to gel B, mixed and stirred for 1 hour, and then 8.2g of boric acid was added, and the stirring was continued to be uniform. The stirred liquid was added to the synthesis kettle, stirred and crystallized at 130℃ for 12 hours at a speed of 20-100rpm, and then heated to 170℃ and stirred for 6 days. After cooling, the mother liquor was depressurized and extracted, and a thin layer of Ti-MWW molecular sieve raw powder was obtained after filtration, washing, and drying; the Ti-MWW molecular sieve raw powder was then mixed with 2mol / L nitric acid solution at a mass ratio of 1:50, treated at 80℃ for 1 day, centrifuged, washed, dried at 80℃ for 12 hours, and calcined at 550℃ in air atmosphere for 10 hours to finally obtain Ti-MWW molecular sieve catalyst-1. Among them, SiO 2 :TiO 2 :Piperidine:B 2 O 3 :Dicyclohexylamine:H 2 The molar ratio of O is: 1.0:0.038:1.2:0.67 : 0.2:19.

[0042] Figure 2 is a scanning electron microscope image of the Ti-MWW molecular sieve catalyst prepared in Example 1, and Figure 1 Compared with the traditional molecular sieve catalyst, the advantage of the molecular sieve prepared in Example 1 is that in the electron microscope image, it can be clearly observed that the molecular sieve presents a thinner layered structure, and the edges of the thinned layer structure are flat and smooth, without obvious uneven thickness or agglomeration.

[0043] Example 2: Ti-MWW molecular sieve catalyst-2

[0044] First, 11.9 g of piperidine and 17.1 g of water were mixed and stirred for 30 min, and then 1.2 g of tetrabutyl titanate was added dropwise, and the mixture was stirred for 2 h to obtain gel A. 2.3 g of N,N'-dimethylpiperazine and 17.1 g of water were mixed evenly, and then 6 g of fumed silica was added, and the mixture was stirred for 2 h to obtain gel B. Then gel A was slowly added to gel B, and after mixing and stirring for 1 hour, 8.2 g of boric acid was added and continued to be stirred evenly. The stirred liquid was added to a synthesis kettle, crystallized at 130°C for 12 hours at a rotation speed of 20-100 rpm, and then heated to 170°C and stirred for 6 days. After cooling, the pressure was released to extract the mother liquor, and a thin layer of Ti-MWW molecular sieve raw powder was obtained after filtration, washing and drying. The Ti-MWW molecular sieve raw powder was then mixed with 2 mol / L nitric acid solution in a mass ratio of 1:50, treated at 80°C for 1 day, centrifuged, washed, dried at 80°C for 12 hours, and calcined at 550°C in air atmosphere for 10 hours to finally obtain Ti-MWW molecular sieve catalyst-2.

[0045] Example 3: Ti-MWW molecular sieve catalyst-3

[0046] First, 11.9 g of piperidine and 17.1 g of water were mixed and stirred for 30 min, and then 1.2 g of tetrabutyl titanate was added dropwise, and the mixture was stirred for 2 h to obtain gel A. 2.22 g of bicyclo[2.2.1]heptane-2-amine and 17.1 g of water were mixed evenly, and then 6 g of silicon source was added, and the mixture was stirred for 2 h to obtain gel B. Then gel A was slowly added to gel B, and after mixing and stirring for 1 hour, 8.2 g of boric acid was added and continued to be stirred evenly. The stirred liquid was added to the synthesis kettle, stirred and crystallized at 130°C at a speed of 20-100 rpm for 12 hours, and then the temperature was raised to 170°C and stirred for 6 days. After cooling, the pressure was released to extract the mother liquor, and a thin layer of Ti-MWW molecular sieve raw powder was obtained after filtration, washing and drying. The Ti-MWW molecular sieve raw powder was then mixed with 2 mol / L nitric acid solution in a mass ratio of 1:50, treated at 80°C for 1 day, centrifuged, washed, dried at 80°C for 12 hours, and calcined at 550°C in air atmosphere for 10 hours to finally obtain Ti-MWW molecular sieve catalyst-3.

[0047] Example 4: Ti-MWW molecular sieve catalyst-4

[0048] First, 11.9g piperidine and 17.1g water were mixed and stirred for 30min, and then 1.2g tetrabutyl titanate was added dropwise, and the mixture was mixed and stirred for 2h to obtain gel A. 2.50g bicyclo[2.2.2]octane-1-amine and 17.1g water were mixed and evenly added, and then 6g fumed silica was added, and the mixture was stirred for 2h to obtain gel B. Then gel A was slowly added to gel B, and 8.2g boric acid was added after mixing and stirring for 1h, and the mixture was stirred evenly. The stirred solution was added to a synthesis reactor, and the mixture was stirred and crystallized at 130°C at a speed of 20 to 100rpm for 12h, and then the mixture was heated to 170°C and stirred for 6 days. After cooling, the mother liquor was depressurized and extracted, and the thin layer Ti-MWW molecular sieve raw powder was obtained after filtration, washing, and drying. The Ti-MWW molecular sieve raw powder was then mixed with 2 mol / L nitric acid solution at a mass ratio of 1:50, treated at 80°C for 1 day, centrifuged, washed, dried at 80°C for 12 hours, and calcined at 550°C in air atmosphere for 10 hours to finally obtain Ti-MWW molecular sieve catalyst-4.

[0049] Example 5: Ti-MWW molecular sieve catalyst-5

[0050] First, 11.9g piperidine and 17.1g water were mixed and stirred for 30min, and then 1.2g tetrabutyl titanate was added dropwise, and the mixture was mixed and stirred for 2h to obtain gel A. 3.02g adamantane amine and 17.1g water were mixed and evenly added, and then 6g fumed silica was added and stirred for 2h to obtain gel B. Then gel A was slowly added to gel B, and 8.2g boric acid was added after mixing and stirring for 1h, and the stirring was continued to be even, and the stirred liquid was added to the synthesis reactor, and the mixture was stirred and crystallized at 130°C at a speed of 20-100rpm for 12h, and then the temperature was raised to 170°C and stirred for 6 days. After cooling, the mother liquor was depressurized and extracted, and the thin layer Ti-MWW molecular sieve raw powder was obtained after filtration, washing and drying. The Ti-MWW molecular sieve raw powder was then mixed with 2 mol / L nitric acid solution at a mass ratio of 1:50, treated at 80°C for 1 day, centrifuged, washed, dried at 80°C for 12 hours, and calcined at 550°C in air atmosphere for 10 hours to finally obtain Ti-MWW molecular sieve catalyst-5.

[0051] Example 6: Ti-MWW molecular sieve catalyst-6

[0052] First, 11.9g piperidine and 17.1g water were mixed and stirred for 30min, and then 1.2g tetrabutyl titanate was added dropwise, and the mixture was mixed and stirred for 2 hours to obtain gel A. 1.82g dicyclohexylamine and 17.1g water were mixed and stirred, and then 6g fumed silica was added and stirred for 2 hours to obtain gel B. Then, gel A was slowly added to gel B, and 8.2g boric acid was added after mixing and stirring for 1 hour, and the stirring was continued to be uniform. The stirred liquid was added to the synthesis reactor, and the mixture was stirred and crystallized at 130°C at a speed of 20 to 100rpm for 12 hours, and then the temperature was raised to 170°C and stirred for 6 days. After cooling, the mother liquor was depressurized and extracted, and the thin layer Ti-MWW molecular sieve raw powder was obtained after filtering, washing and drying. The Ti-MWW molecular sieve raw powder was then mixed with 2 mol / L nitric acid solution at a mass ratio of 1:50, treated at 80°C for 1 day, centrifuged, washed, dried at 80°C for 12 hours, and calcined at 550°C in air atmosphere for 10 hours to finally obtain Ti-MWW molecular sieve catalyst-6.

[0053] Example 7: Ti-MWW molecular sieve catalyst-7

[0054] First, 11.9g piperidine and 17.1g water were mixed and stirred for 30min, and then 1.2g tetrabutyl titanate was added dropwise, and the mixture was mixed and stirred for 2h to obtain gel A. 5.47g dicyclohexylamine and 17.1g water were mixed and evenly added, and then 6g fumed silica was added and stirred for 2h to obtain gel B. Then gel A was slowly added to gel B, and 8.2g boric acid was added after mixing and stirring for 1h, and the stirring was continued to be even, and the stirred liquid was added to the synthesis reactor, and the mixture was stirred and crystallized at 130°C at a speed of 20-100rpm for 12h, and then the temperature was raised to 170°C and stirred for 6 days. After cooling, the mother liquor was depressurized and extracted, and the thin layer Ti-MWW molecular sieve raw powder was obtained after filtration, washing and drying. The Ti-MWW molecular sieve raw powder was then mixed with 2 mol / L nitric acid solution at a mass ratio of 1:50, treated at 80°C for 1 day, centrifuged, washed, dried at 80°C for 12h, and calcined at 550°C in air atmosphere for 15h to finally obtain the Ti-MWW molecular sieve catalyst.

[0055] Embodiment 8:

[0056] The weighed catalyst was placed in an intermittent reactor with an effective volume of 160 ml, and acetonitrile, 1-hexene and hydrogen peroxide were added in sequence. The molar ratio of the materials was n(1-hexene): n(H 2 O 2 ):n(acetonitrile)=1:1.05:20, the amount of catalyst is 10% of the mass fraction of 1-hexene. At a speed of 500r / min and a temperature of 40℃, the reaction is carried out at normal pressure for 4h, then cooled, centrifuged, and then sampled for analysis. The samples are analyzed by Agilent 7890A gas chromatograph, equipped with Innowax chromatographic column, and the product is quantitatively analyzed by area normalization method.

[0057] Table 1 Results of liquid phase epoxidation of 1-hexene with hydrogen peroxide catalyzed by the catalysts of Examples 1-7 and Comparative Example 1

[0058]

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a thin layer Ti-MWW titanium silicon molecular sieve, characterized in that: The steps include: (1) Mix the template and water evenly, add the titanium source dropwise, and stir evenly to obtain gel A; (2) mixing the polycyclic fatty amine and water uniformly, adding a silicon source, and stirring uniformly to obtain gel B; (3) Slowly add gel A to gel B, stir evenly, then add boric acid additive and stir evenly; (4) stirring the reaction solution obtained in step (3) at 100-150° C. for crystallization for 5-36 hours, then stirring at 150-210° C. for 4-8 days, cooling, filtering the obtained mother liquor, washing, and drying to obtain a thin layer Ti-MWW molecular sieve raw powder; (5) The Ti-MWW molecular sieve raw powder is dispersed in a nitric acid solution with a concentration of 1 to 5 mol / L and treated at 60 to 110° C. for 0.5 to 2 days, centrifuged, washed, dried, and calcined at 400 to 650° C. in an air atmosphere for 5 to 24 hours to obtain a Ti-MWW titanium silicon molecular sieve catalyst.

2. The preparation method according to claim 1, characterized in that: The template agent in step (1) is one or a combination of two or more selected from the group consisting of piperidine, cycloheximide, and piperazine; the titanium source is one or a combination of two or more selected from the group consisting of tetrabutyl titanate, tetraisopropyl titanate, titanium tetrachloride, titanium sulfate, hexafluorotitanic acid, and ammonium hexafluorotitanate; and the mass ratio of the titanium source, the template agent, and water is 1:5 to 10:10 to 20.

3. The preparation method according to claim 1, characterized in that: The silicon source described in step (2) is one or a combination of two or more selected from the group consisting of fumed silica, silica sol, tetraethyl orthosilicate and silicon powder; the polycyclic aliphatic amines are one or a combination of two or more selected from the group consisting of dicyclohexylamine, N,N'-dimethylpiperazine, bicyclo[2.2.1]heptane-2-amine, bicyclo[2.2.2]octane-1-amine, adamantaneamine and triethylenediamine; and the mass ratio of the polycyclic aliphatic amines, the silicon source and water is 1:1 to 5:3 to 15.

4. The preparation method according to claim 1, characterized in that: The mass ratio of gel A to gel B in step (3) is 1:2 to 2:1, and the mass percentage of added boric acid is 0.05 to 0.5%.

5. The preparation method according to claim 1, characterized in that: The specific process of step (4) is to add the reaction solution obtained in step (3) into the synthesis kettle, stir and crystallize at 120-140°C for 10-14h, then stir at 150-190°C for 5-7 days, cool, filter the obtained mother liquor, wash, and dry to obtain the thin layer Ti-MWW molecular sieve raw powder.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the Ti-MWW molecular sieve raw powder to the nitric acid solution described in step (5) is 1:(20-100), the concentration of the nitric acid solution is 1-3 mol / L; the roasting temperature is 500-600° C., and the roasting time is 5-12 h.

7. The thin layer Ti-MWW titanium silicon molecular sieve prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the thin layer Ti-MWW titanium silicon molecular sieve according to claim 7 in epoxidation reaction.

9. The use according to claim 8, characterized in that: The epoxidation reaction is a liquid phase epoxidation reaction, the substrates of the epoxidation reaction are olefins and hydrogen peroxide; the solvent includes methanol, ethanol, acetonitrile and dimethylformamide; the olefins include propylene, butene, pentene, hexene, cyclohexene and octene.

10. The use according to claim 9, characterized in that: The molar ratio of olefin, hydrogen peroxide and solvent is 1:1-2:10-50, the reaction temperature is 30-100°C, the reaction pressure is 0.1-3MPa, and the reaction time is 0.5-5h.

Images