Ti-MWW molecular sieve catalyst, preparation method and application of Ti-MWW molecular sieve catalyst in preparation of epoxy compound by direct epoxidation of hydrogen peroxide and olefin

Abstract

The invention discloses a Ti-MWW molecular sieve catalyst, a preparation method and application of the Ti-MWW molecular sieve catalyst in preparation of an epoxy compound through direct epoxidation of hydrogen peroxide and olefin, and mainly relates to the technical field of molecular sieve catalysts. Compared with the prior art, the Ti-MWW molecular sieve catalyst prepared by the invention can simultaneously improve the selectivity of epoxy compounds and the conversion rate of hydrogen peroxide, can be applied to direct epoxidation reaction of hydrogen peroxide and alkene, optimizes the solvent, crystallization step and organic amine in preparation, and can better guide crystal growth in the forming process of the molecular sieve; a pore structure and an acid environment which are more beneficial to olefin epoxidation reaction are formed, the catalytic activity and selectivity to target reaction are finally enhanced, and the selectivity of epoxy compounds and the hydrogen peroxide conversion rate are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve catalysts, and in particular to a Ti-MWW molecular sieve catalyst, a preparation method thereof, and an application thereof in the direct epoxidation of olefins with hydrogen peroxide to prepare epoxides. Background Art

[0002] As a titanium silicate porous material, the Ti-MWW molecular sieve catalyst exhibits excellent catalytic performance in the reaction of directly oxidizing olefins with hydrogen peroxide, providing a suitable diffusion path and active sites for the reactant olefins and hydrogen peroxide oxidant, and selectively promoting the epoxidation reaction of olefins. CN113880111A discloses a Ti-MWW molecular sieve and its preparation method and application. The invention obtains the Ti-MWW molecular sieve through steps such as the preparation of a B-MWW molecular sieve precursor, boron removal and titanium supplementation treatment, acid solution post-treatment, and calcination. The Ti-MWW molecular sieve provided by the invention has the advantages of high titanium content, suitable hydrophilicity, and good catalytic oxidation performance, and can be used in the industrial production process of epoxides.

[0003] CN114225961A discloses a preparation method, a catalyst, and an application of a catalyst for synthesizing propylene oxide. The preparation method includes the steps of preparing a boron-containing molecular sieve precursor, preparing a B-MWW molecular sieve, pickling, and preparing a titanium silicate molecular sieve Ti-MWW, which is the catalyst for synthesizing propylene oxide. The catalyst prepared by the method of the invention can improve the conversion rate of propylene and the selectivity of propylene oxide in the synthesis of propylene oxide by the HPPO method. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a Ti-MWW molecular sieve catalyst that can simultaneously improve the selectivity of epoxides and the conversion rate of hydrogen peroxide, and can be used in the direct epoxidation reaction of olefins with hydrogen peroxide.

[0005] To achieve the above object, the present invention provides a Ti-MWW molecular sieve catalyst, a preparation method thereof, and an application thereof in the direct epoxidation of olefins with hydrogen peroxide to prepare epoxides.

[0006] The preparation method of the Ti-MWW molecular sieve catalyst includes the following steps, in parts by weight: (1) Mix 20-40 parts of fumed silica and 0.1-1.5 parts of titanium dioxide, grind for 24 hours, add 4-6 parts of seeds and 10-30 parts of boric acid, and continue to grind for 2 hours to obtain a dry gel; add 40-80 parts of the dry gel, 30-50 parts of organic amine, and 200-300 parts of water to a reactor, and crystallize statically at 140-180°C for 5-8 days to obtain a molecular sieve precursor; Alternatively, 20 - 40 parts of fumed silica and 0.1 - 1.5 parts of titanium dioxide are mixed and ground for 24 hours, and then 4 - 6 parts of seeds and 10 - 30 parts of boric acid are added and ground for another 2 hours to obtain a dry gel. 40 - 80 parts of the dry gel, 20 - 30 parts of organic amine, and 200 - 300 parts of water are added to a reactor, and static crystallization is carried out at 140 - 180 °C for 3 - 6 days. Then 10 - 20 parts of organic amine are added, and static crystallization is carried out at 140 - 180 °C for 2 - 4 days to obtain a molecular sieve precursor. (2) The molecular sieve precursor is treated with a 2 - 4 mol / L nitric acid aqueous solution for 12 - 16 hours, centrifuged, dried at 70 - 80 °C for 12 hours, and calcined at 550 - 650 °C for 6 - 12 hours to obtain the Ti-MWW molecular sieve catalyst.

[0007] The seeds are molecular sieve raw powder with an MWW structure.

[0008] The organic amine is one of piperidine, 3,5-dimethylpiperidine, 4-aminopiperidine, N-hydroxyethylpiperidine, and modified N-hydroxyethylpiperidine.

[0009] More preferably, the organic amine is one of 3,5-dimethylpiperidine, 4-aminopiperidine, N-hydroxyethylpiperidine, and modified N-hydroxyethylpiperidine.

[0010] The preparation method of the modified N-hydroxyethylpiperidine is as follows, in parts by weight: 20 - 40 parts of N-hydroxyethylpiperidine are added to 140 - 180 parts of dichloromethane. 25 - 35 parts of triethylamine and 1 - 2 parts of 4-pyrrolidinopyridine are added in sequence, and the mixture is stirred at 0 - 5 °C for 0.5 - 1 hour. Then 50 - 60 parts of p-toluenesulfonyl chloride are added, and the mixture is stirred at room temperature for 3 - 5 hours. 140 - 180 parts of saturated sodium bicarbonate aqueous solution are added to quench the reaction, and the mixture is extracted with dichloromethane 1 - 3 times, with 80 - 120 parts used each time. The organic phases are combined. 100 - 150 parts of dilute hydrochloric acid are added to the organic phase and stirred for 10 - 30 minutes, and then left to stand for liquid separation. 100 - 150 parts of saturated sodium chloride aqueous solution are added to the organic phase and stirred for 10 - 30 minutes, and then left to stand for liquid separation. The organic phase is concentrated to obtain the modified N-hydroxyethylpiperidine.

[0011] The application of a Ti-MWW molecular sieve catalyst is as follows: Under the action of the Ti-MWW molecular sieve catalyst, hydrogen peroxide directly reacts with an olefin for epoxidation reaction to prepare an epoxide. The specific application method is as follows: A solvent, hydrogen peroxide, and the Ti-MWW molecular sieve catalyst are added to a reactor, and an olefin is added. The reaction is carried out at 40 - 60 °C and 2 - 3 MPa for 1 - 3 h. The olefin is one of ethylene, propylene, butene, pentene, hexene, heptene, and octene.

[0012] The solvent in the application is one of water, acetonitrile, methanol, ethanol, tert-butanol, ethyl acetate, dichloromethane, benzene; preferably acetonitrile.

[0013] The weight ratio of the solvent, olefin, hydrogen peroxide, and Ti-MWW molecular sieve catalyst in the application is 4-6:1-4:0.2-2:0.1-0.5; preferably 5-6:2-3:0.5-1.5:0.1-0.3.

[0014] The hydrogen peroxide in the application is 20-50wt% hydrogen peroxide.

[0015] The Ti-MWW molecular sieve catalyst prepared by the present invention can simultaneously improve the selectivity of epoxides and the conversion rate of hydrogen peroxide. Hydrogen peroxide can directly epoxidize olefins to prepare epoxides under the action of the Ti-MWW molecular sieve catalyst. Among them, seed crystals are added to guide the growth direction of the crystals, which helps to accelerate the crystallization process, while ensuring the uniformity and integrity of the crystal structure, shortening the crystallization time, and improving the preparation efficiency. In the application, a variety of solvents are also screened, preferably acetonitrile, because there are fewer by-products involved by acetonitrile in the overall reaction system, which improves the selectivity of the target product. In the preparation, the crystallization step is also screened. After pre-crystallization, an organic amine is added for secondary crystallization to promote the formation of crystal nuclei and the entry of titanium into the framework structure during the framework formation process. The present invention also screens the organic amine. The organic amine is one of piperidine, 3,5-dimethylpiperidine, 4-aminopiperidine, N-hydroxyethylpiperidine, and modified N-hydroxyethylpiperidine. Different organic amines have different molecular structures and different electronic effects, which affect the pore structure, acid site distribution, etc. of the Ti-MWW molecular sieve in the crystallization stage of catalyst synthesis, thus affecting the application effect; further, the present invention also modifies N-hydroxyethylpiperidine. The modified N-hydroxyethylpiperidine can optimize the pore environment and active center of the molecular sieve by introducing a toluenesulfonyl group onto N-hydroxyethylpiperidine, so as to better guide the crystal growth during the formation of the molecular sieve and construct a pore structure and acidic environment more suitable for the synthesis of propylene oxide reaction; the introduction of the toluenesulfonyl group enhances the hydrophobicity and electronic effect of the molecular sieve, which helps to improve the adsorption and activation ability of the catalyst for hydrogen peroxide, while reducing the occurrence of side reactions; in addition, the steric hindrance effect of the toluenesulfonyl group can adjust the pore size distribution of the molecular sieve to make it more suitable for the diffusion and reaction of propylene molecules, thereby improving the selectivity of propylene oxide and the conversion rate of hydrogen peroxide.

[0016] The beneficial effects of the present invention: 1. Compared with the prior art, the Ti-MWW molecular sieve catalyst of the present invention screens a variety of solvents in the application, preferably acetonitrile, because there are fewer by-products involved by acetonitrile in the overall reaction system, which improves the selectivity of the target product.

[0017] 2. Compared with the prior art, in the preparation of the Ti-MWW molecular sieve catalyst of the present invention, the crystallization step is also screened. After pre-crystallization, an organic amine is added for secondary crystallization to promote the formation of crystal nuclei and the entry of titanium into the framework structure during the framework formation process.

[0018] 3. Compared with the prior art, in the preparation of the Ti-MWW molecular sieve catalyst of the present invention, the organic amine is screened. The organic amine is one of piperidine, 3,5-dimethylpiperidine, 4-aminopiperidine, N-hydroxyethylpiperidine, and modified N-hydroxyethylpiperidine. Different organic amines have different molecular structures and different electronic effects, which affect the pore structure, acid site distribution, etc. of the Ti-MWW molecular sieve in the crystallization stage of catalyst synthesis, thus affecting the application effect. Further, the present invention also modifies N-hydroxyethylpiperidine. The group introduced by the modification can further optimize the pore environment and active center of the molecular sieve, better guide crystal growth during the formation of the molecular sieve, construct a pore structure and acidic environment more suitable for the synthesis of propylene oxide reaction, and finally improve the selectivity of propylene oxide and the conversion rate of hydrogen peroxide at the same time. Detailed implementation manners

[0019] The parameters of the specific chemical substances used in the examples are as follows: Seed crystal: commercially available molecular sieve with MWW structure, manufactured by Zhejiang Taide New Materials Co., Ltd.

[0020] Fumed silica: specific surface area is 200 m 2 / g, manufactured by Hubei Huifu Nano Materials Co., Ltd., model HL-200.

[0021] Titanium dioxide: specific surface area is 50 m 2 / g, manufactured by Hubei Huifu Nano Materials Co., Ltd., model NT-50.

[0022] Example 1 A preparation method of a Ti-MWW molecular sieve catalyst includes the following steps: (1) Mix 32 g of fumed silica and 1.0 g of titanium dioxide and grind for 24 hours, then add 5 g of seed crystal and 22 g of boric acid and continue to grind for 2 hours to obtain a dry gel; add 60 g of dry gel, 38 g of piperidine, and 250 g of water to a crystallization kettle, and crystallize statically at 170 °C for 7 days to obtain a molecular sieve precursor; (2) Treat the molecular sieve precursor with a 2.5 mol / L nitric acid aqueous solution for 14 hours, centrifuge, dry at 77 °C for 12 hours, and calcine at 600 °C for 10 hours to obtain the Ti-MWW molecular sieve catalyst.

[0023] Example 2 A preparation method of a Ti-MWW molecular sieve catalyst includes the following steps: (1) Mix 32 g of fumed silica and 1.0 g of titanium dioxide, grind for 24 hours, add 5 g of seed crystals and 22 g of boric acid, and continue grinding for 2 hours to obtain a dry gel; Add 60 g of the dry gel, 38 g of 3,5-dimethylpiperidine, and 250 g of water to a crystallization kettle, and carry out static crystallization at 170 °C for 7 days to obtain a molecular sieve precursor; (2) Treat the molecular sieve precursor with a 2.5 mol / L nitric acid aqueous solution for 14 hours, centrifuge, dry at 77 °C for 12 hours, and calcine at 600 °C for 10 hours to obtain the Ti-MWW molecular sieve catalyst.

[0024] Example 3 A preparation method of a Ti-MWW molecular sieve catalyst, comprising the following steps: (1) Mix 32 g of fumed silica and 1.0 g of titanium dioxide, grind for 24 hours, add 5 g of seed crystals and 22 g of boric acid, and continue grinding for 2 hours to obtain a dry gel; Add 60 g of the dry gel, 38 g of 4-aminopiperidine, and 250 g of water to a crystallization kettle, and carry out static crystallization at 170 °C for 7 days to obtain a molecular sieve precursor; (2) Treat the molecular sieve precursor with a 2.5 mol / L nitric acid aqueous solution for 14 hours, centrifuge, dry at 77 °C for 12 hours, and calcine at 600 °C for 10 hours to obtain the Ti-MWW molecular sieve catalyst.

[0025] Example 4 A preparation method of a Ti-MWW molecular sieve catalyst, comprising the following steps: (1) Mix 32 g of fumed silica and 1.0 g of titanium dioxide, grind for 24 hours, add 5 g of seed crystals and 22 g of boric acid, and continue grinding for 2 hours to obtain a dry gel; Add 60 g of the dry gel, 38 g of N-hydroxyethylpiperidine, and 250 g of water to a crystallization kettle, and carry out static crystallization at 170 °C for 7 days to obtain a molecular sieve precursor; (2) Treat the molecular sieve precursor with a 2.5 mol / L nitric acid aqueous solution for 14 hours, centrifuge, dry at 77 °C for 12 hours, and calcine at 600 °C for 10 hours to obtain the Ti-MWW molecular sieve catalyst.

[0026] Example 5 A preparation method of a Ti-MWW molecular sieve catalyst, comprising the following steps: (1) Mix 32 g of fumed silica and 1.0 g of titanium dioxide, grind for 24 hours, add 5 g of seed crystals and 22 g of boric acid, and continue grinding for 2 hours to obtain a dry gel; Add 60 g of the dry gel, 25 g of N-hydroxyethylpiperidine, and 250 g of water to a crystallization kettle, carry out static crystallization at 170 °C for 4 days, then add 13 g of N-hydroxyethylpiperidine, and carry out static crystallization at 170 °C for 3 days to obtain a molecular sieve precursor; (2) The molecular sieve precursor was treated with 2.5 mol / L nitric acid aqueous solution for 14 hours, centrifuged, dried at 77 °C for 12 hours, and calcined at 600 °C for 10 hours to obtain the Ti-MWW molecular sieve catalyst.

[0027] Example 6 A preparation method of a Ti-MWW molecular sieve catalyst, comprising the following steps: (1) 32 g of fumed silica and 1.0 g of titanium dioxide were mixed and ground for 24 hours, and 5 g of seed crystals and 22 g of boric acid were added and ground for another 2 hours to obtain a dry gel; 60 g of the dry gel, 25 g of modified N-hydroxyethylpiperidine, and 250 g of water were added to a crystallization kettle, statically crystallized at 170 °C for 4 days, then 13 g of modified N-hydroxyethylpiperidine was added, and statically crystallized at 170 °C for 3 days to obtain a molecular sieve precursor; (2) The molecular sieve precursor was treated with 2.5 mol / L nitric acid aqueous solution for 14 hours, centrifuged, dried at 77 °C for 12 hours, and calcined at 600 °C for 10 hours to obtain the Ti-MWW molecular sieve catalyst; The preparation method of the modified N-hydroxyethylpiperidine is as follows: 30 g of N-hydroxyethylpiperidine was added to 150 g of dichloromethane, 28 g of triethylamine and 1.5 g of 4-pyrrolidinopyridine were added in sequence, stirred at 0 °C for 0.5 hour, 55 g of p-toluenesulfonyl chloride was added, and stirred at room temperature for 4 hours; 150 g of saturated sodium bicarbonate aqueous solution was added to quench, extracted with dichloromethane twice, 100 g each time, and the organic phases were combined; 120 g of 0.5 mol / L dilute hydrochloric acid was added to the organic phase, stirred for 20 minutes and then left to stand for liquid separation; 120 g of saturated sodium chloride aqueous solution was added to the organic phase, stirred for 20 minutes and then left to stand for liquid separation; the organic phase was concentrated to obtain modified N-hydroxyethylpiperidine.

[0028] Test Example 1 The Ti-MWW molecular sieve catalysts prepared in Examples 1-6 of the present invention were used in the direct epoxidation of propylene with hydrogen peroxide to prepare propylene oxide; the specific application method was as follows: 5.6 g of acetonitrile, 1 g of 30 wt% hydrogen peroxide, and 0.2 g of Ti-MWW molecular sieve catalyst were added to a reactor, 2.5 g of propylene was added, and the reaction was carried out at 45 °C and 2.5 Mpa for 2 hours. Before the reaction, a mixed raw material sample was taken, and after 2 hours of reaction, the content of hydrogen peroxide was determined by cerium sulfate titration analysis, and other organic substances were determined by gas chromatography. The selectivity of propylene oxide was calculated, and the selectivity of propylene oxide = (the amount of H2O2 consumed for generating PO / the initial amount of H2O2) × 100%; the summary is shown in Table 1.

[0029] Table 1 Propylene oxide selectivity data Propylene oxide selectivity Example 1 95.4% Example 2 93.8% Example 3 94.2% Example 4 96.6% Example 5 99.2% Example 6 99.9% There are differences in the data of different examples in Test Example 1. The reason lies in the different types and usage methods of organic amines in the preparation process of the Ti-MWW molecular sieve catalyst. In Examples 1-4, piperidine, 3,5-dimethylpiperidine, 4-aminopiperidine, and N-hydroxyethylpiperidine are used as organic amines respectively. Different organic amines have different molecular structures and electronic effects, which affect the pore structure, acidic site distribution, etc. of the Ti-MWW molecular sieve in the crystallization stage of catalyst synthesis. The pore structure is directly related to whether the reactants can smoothly contact the active center, and the acidic sites will affect the intermediate steps of the reaction, ultimately affecting the selectivity of propylene oxide. In Example 4, N-hydroxyethylpiperidine is used, and the hydroxyethyl group in its molecule endows unique hydrophilicity and steric hindrance, which can better regulate the surface properties of the molecular sieve, promote the adsorption and reaction of reactants, so the selectivity of propylene oxide is better than that of Examples 1-3. On the basis of Example 4, in Example 5, N-hydroxyethylpiperidine is added in segments during the crystallization process, making the growth of the molecular sieve crystal more orderly and the pore structure more conducive to the propylene oxide formation reaction, improving the selectivity. On the basis of Example 5, in Example 6, N-hydroxyethylpiperidine is modified by introducing a toluenesulfonyl group onto N-hydroxyethylpiperidine, enhancing the hydrophobicity and electronic effect of the molecular sieve, which helps to improve the adsorption and activation ability of the catalyst for hydrogen peroxide, while reducing the occurrence of side reactions. Then, the pore size distribution of the molecular sieve is adjusted by using the steric hindrance effect of the toluenesulfonyl group, making it more suitable for the diffusion and reaction of propylene molecules, thereby enhancing the catalytic activity and selectivity for the target reaction, and its selectivity of propylene oxide is better than that of Examples 1-5.

[0030] Test Example 2 The Ti-MWW molecular sieve catalysts prepared in Examples 1-6 of the present invention are used in the direct epoxidation of ethylene with hydrogen peroxide to prepare ethylene oxide; the specific application method is as follows: 5.6 g of acetonitrile, 1 g of 30 wt% hydrogen peroxide, and 0.2 g of the Ti-MWW molecular sieve catalyst are added to the reactor, and 2.5 g of ethylene is added, and the reaction is carried out at 45 °C and 2.5 Mpa for 2 hours. Before the reaction, a mixed raw material sample is taken, and after 2 hours of reaction, the content of hydrogen peroxide is determined by cerium sulfate titration analysis, and other organic substances are determined by gas chromatography, and the hydrogen peroxide conversion rate is calculated. The hydrogen peroxide conversion rate = (consumption of H2O2 / initial amount of H2O2) × 100%; the summary is shown in Table 2.

[0031] Table 2 Hydrogen peroxide conversion rate data Hydrogen peroxide conversion rate Example 1 84.7% Example 2 82.5% Example 3 85.0% Example 4 88.0% Example 5 97.2% Example 6 99.0% The reason for the data difference in Test Example 2 is that during the preparation of the Ti-MWW molecular sieve catalyst, the use of different organic amine template agents will affect the structure and performance of the Ti-MWW molecular sieve catalyst. In Examples 1-4, piperidine, 3,5-dimethylpiperidine, 4-aminopiperidine, and N-hydroxyethylpiperidine were used as template agents respectively, which would affect the pore structure and acid site distribution of the molecular sieve during the crystallization process. It was found by comparison that the improvement effect of Example 4 on the conversion rate of hydrogen peroxide was significantly higher than that of Examples 1-3, indicating that the differences in the molecular structures and properties led to differences in the structures of the molecular sieve precursors formed, thereby affecting the activity and selectivity of the final catalyst. In Example 5, the primary crystallization was changed to secondary crystallization on the basis of Example 4. Therefore, the first crystallization was pre-crystallization. After pre-crystallization, N-hydroxyethylpiperidine was continuously added to the molecular sieve for secondary crystallization to promote the entry of titanium into the framework structure during the formation of crystal nuclei and the framework. Its hydrogen peroxide conversion rate was better than that of Example 4 with primary crystallization. In Example 6, N-hydroxyethylpiperidine was modified on the basis of Example 5. The introduction of the tosyl group enhanced the hydrophobicity and electronic effect of the molecular sieve, helped to improve the adsorption and activation ability of the catalyst for hydrogen peroxide, and reduced the occurrence of side reactions, thereby increasing the conversion rate of hydrogen peroxide.

[0032] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field according to the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A preparation method of a Ti-MWW molecular sieve catalyst, characterized in that, The following steps are included, by weight parts: (1) Mix 20 - 40 parts of fumed silica and 0.1 - 1.5 parts of titanium dioxide, grind for 24 hours, add 4 - 6 parts of seeds and 10 - 30 parts of boric acid, and continue to grind for 2 hours to obtain a dry gel; Add 40 - 80 parts of the dry gel, 30 - 50 parts of organic amine, and 200 - 300 parts of water into a reactor, and carry out static crystallization at 140 - 180 °C for 5 - 8 days to obtain a molecular sieve precursor; Or, mix 20 - 40 parts of fumed silica and 0.1 - 1.5 parts of titanium dioxide, grind for 24 hours, add 4 - 6 parts of seeds and 10 - 30 parts of boric acid, and continue to grind for 2 hours to obtain a dry gel; Add 40 - 80 parts of the dry gel, 20 - 30 parts of organic amine, and 200 - 300 parts of water into a reactor, carry out static crystallization at 140 - 180 °C for 3 - 6 days, then add 10 - 20 parts of organic amine, and carry out static crystallization at 140 - 180 °C for 2 - 4 days to obtain a molecular sieve precursor; (2) Treat the molecular sieve precursor with a 2 - 4 mol / L nitric acid aqueous solution for 12 - 16 hours, centrifuge, dry at 70 - 80 °C for 12 hours, and calcine at 550 - 650 °C for 6 - 12 hours to obtain the Ti - MWW molecular sieve catalyst; The organic amine is one of 3,5 - dimethylpiperidine, 4 - aminopiperidine, N - hydroxyethylpiperidine, and modified N - hydroxyethylpiperidine.

2. The preparation method of the Ti-MWW molecular sieve catalyst according to claim 1, characterized in that, The preparation method of the modified N - hydroxyethylpiperidine is as follows, by weight parts: Add 20 - 40 parts of N - hydroxyethylpiperidine into 140 - 180 parts of dichloromethane, successively add 25 - 35 parts of triethylamine and 1 - 2 parts of 4 - pyrrolidinopyridine, stir at 0 - 5 °C for 0.5 - 1 hour, add 50 - 60 parts of p - toluenesulfonyl chloride, and stir at room temperature for 3 - 5 hours; Add 140 - 180 parts of saturated sodium bicarbonate solution to quench, extract with dichloromethane for 1 - 3 times, with 80 - 120 parts used each time, and combine the organic phases; Add 100 - 150 parts of dilute hydrochloric acid to the organic phase, stir for 10 - 30 minutes, and then let it stand for liquid separation; Add 100 - 150 parts of saturated sodium chloride aqueous solution to the organic phase, stir for 10 - 30 minutes, and then let it stand for liquid separation; Concentrate the organic phase to obtain the modified N - hydroxyethylpiperidine.

3. A Ti-MWW molecular sieve catalyst, characterized in that, Prepared by the preparation method according to any one of claims 1 - 2.

4. Use of the Ti-MWW molecular sieve catalyst according to claim 3, characterized in that, Application in the direct epoxidation reaction of hydrogen peroxide with olefins under the action of the Ti - MWW molecular sieve catalyst; The specific application method is as follows: Add the solvent, hydrogen peroxide, and the Ti - MWW molecular sieve catalyst into a reactor, add olefin, and react at 40 - 60 °C and 2 - 3 Mpa for 1 - 3 h; The olefin is one of ethylene, propylene, butene, pentene, hexene, heptene, and octene.

5. Use of the Ti-MWW molecular sieve catalyst according to claim 4, characterized in that, The solvent in the application is one of water, acetonitrile, methanol, ethanol, tert - butanol, ethyl acetate, dichloromethane, and benzene.

6. The application of the Ti-MWW molecular sieve catalyst according to claim 4, characterized in that, The weight ratio of the solvent, olefin, hydrogen peroxide, and the Ti - MWW molecular sieve catalyst used in the application is 4 - 6:1 - 4:0.2 - 2:0.1 - 0.

5.

7. Use of the Ti-MWW molecular sieve catalyst according to claim 6, characterized in that, The weight ratio of the solvent, olefin, hydrogen peroxide, and Ti-MWW molecular sieve catalyst in the described application is 5-6:2-3:0.5-1.5:0.1-0.

3.

8. Use of the Ti-MWW molecular sieve catalyst according to claim 4, characterized in that, The hydrogen peroxide in the described application is 20-50 wt% hydrogen peroxide.