A Ti-MWW molecular sieve catalyst, preparation method and application thereof in the preparation of epoxy compounds by direct epoxidation of hydrogen peroxide with olefins

Abstract

The present invention discloses a Ti-MWW molecular sieve catalyst, a preparation method, and its application in the direct epoxidation of hydrogen peroxide with olefins to prepare epoxy compounds, primarily relating to the field of molecular sieve catalyst technology. Compared with the prior art, the Ti-MWW molecular sieve catalyst prepared by the present invention can simultaneously improve epoxy compound selectivity and hydrogen peroxide conversion rate, and can be applied in the direct epoxidation reaction of hydrogen peroxide with olefins. The present invention optimizes the solvent, crystallization step, and organic amine during the preparation process to better guide crystal growth during the molecular sieve formation process, forming a pore structure and acidic environment that is more conducive to the epoxidation reaction of olefins, ultimately enhancing the catalytic activity and selectivity for the target reaction, and improving the selectivity of epoxy compounds and the hydrogen peroxide conversion rate.

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 and application thereof in preparing epoxy compounds by direct epoxidation of hydrogen peroxide with olefins. Background Art

[0002] Ti-MWW molecular sieve catalyst, a porous titanium silicate material, exhibits excellent catalytic performance in the direct oxidation of olefins in hydrogen peroxide. It provides suitable diffusion pathways and active sites for the reactants, the olefins, and the hydrogen peroxide oxidant, selectively promoting the epoxidation of the olefins. CN113880111A discloses a Ti-MWW molecular sieve, its preparation method, and applications. This invention obtains the Ti-MWW molecular sieve through the steps of preparing a B-MWW molecular sieve precursor, deboronizing and titaniumizing it, acid solution post-treatment, and calcination. The Ti-MWW molecular sieve provided by this invention has the advantages of high titanium content, suitable hydrophilicity, and good catalytic oxidation performance, and can be used in the industrial production of epoxides.

[0003] CN114225961A discloses a method for preparing a catalyst for synthesizing propylene oxide, the catalyst, and its application. The method comprises the steps of preparing a boron-containing molecular sieve precursor, preparing a B-MWW molecular sieve, acid washing, and preparing a titanium silicalite molecular sieve Ti-MWW, which is the catalyst for synthesizing propylene oxide. The catalyst prepared by this method is used in the HPPO process for synthesizing propylene oxide, improving propylene conversion and propylene oxide selectivity. 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 simultaneously improve the selectivity of epoxy compounds and the conversion rate of hydrogen peroxide using a Ti-MWW molecular sieve catalyst, which can directly react with olefins in hydrogen peroxide for epoxidation.

[0005] To achieve the above objectives, the present invention provides a Ti-MWW molecular sieve catalyst, a preparation method and its application in the preparation of epoxy compounds by direct epoxidation of hydrogen peroxide with olefins.

[0006] The preparation method of the Ti-MWW molecular sieve catalyst comprises the following steps, calculated in parts by weight:

[0007] (1) 20-40 parts of fumed silica and 0.1-1.5 parts of titanium dioxide are mixed and ground for 24 hours, 4-6 parts of seed crystals and 10-30 parts of boric acid are added and ground for 2 hours to obtain a dry gel; 40-80 parts of dry gel, 30-50 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 5-8 days to obtain a molecular sieve precursor;

[0008] Alternatively, 20-40 parts of fumed silica and 0.1-1.5 parts of titanium dioxide are mixed and ground for 24 hours, 4-6 parts of seed crystals and 10-30 parts of boric acid are added, and grinding is continued for 2 hours to obtain a dry gel; 40-80 parts of 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, and 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;

[0009] (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.

[0010] The seed crystal is molecular sieve raw powder with MWW structure.

[0011] The organic amine is one of piperidine, 3,5-dimethylpiperidine, 4-aminopiperidine, N-hydroxyethylpiperidine, and modified N-hydroxyethylpiperidine.

[0012] More preferably, the organic amine is one of 3,5-dimethylpiperidine, 4-aminopiperidine, N-hydroxyethylpiperidine, and modified N-hydroxyethylpiperidine.

[0013] The preparation method of the modified N-hydroxyethyl piperidine is as follows, in parts by weight:

[0014] 20-40 parts of N-hydroxyethylpiperidine are added to 140-180 parts of dichloromethane, and 25-35 parts of triethylamine and 1-2 parts of 4-pyrrolidinylpyridine are added in sequence. The mixture is stirred at 0-5°C for 0.5-1 hour, and 50-60 parts of p-toluenesulfonyl chloride are added. The mixture is stirred at room temperature for 3-5 hours. 140-180 parts of a saturated aqueous sodium bicarbonate solution is added for quenching. The mixture is extracted with dichloromethane 1-3 times, each time using 80-120 parts. The organic phases are combined. 100-150 parts of dilute hydrochloric acid is added to the organic phase, the mixture is stirred for 10-30 minutes, and the mixture is allowed to stand for separation. 100-150 parts of a saturated aqueous sodium chloride solution is added to the organic phase, the mixture is stirred for 10-30 minutes, and the mixture is allowed to stand for separation. The organic phase is concentrated to obtain modified N-hydroxyethylpiperidine.

[0015] An application of a Ti-MWW molecular sieve catalyst is as follows: hydrogen peroxide is directly epoxidized with olefins to prepare epoxy compounds under the action of the Ti-MWW molecular sieve catalyst;

[0016] The specific application method is as follows: add solvent, hydrogen peroxide, and Ti-MWW molecular sieve catalyst into a reactor, add olefin, and maintain the reaction at 40-60°C and 2-3 MPa for 1-3 hours; the olefin is one of ethylene, propylene, butene, pentene, hexene, heptene, and octene.

[0017] The solvent used in the application is one of water, acetonitrile, methanol, ethanol, tert-butanol, ethyl acetate, dichloromethane and benzene; preferably acetonitrile.

[0018] 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.

[0019] The hydrogen peroxide in the application is 20-50 wt% hydrogen peroxide.

[0020] The Ti-MWW molecular sieve catalyst prepared by the present invention can simultaneously improve the selectivity of epoxy compounds and the conversion rate of hydrogen peroxide, and can directly epoxidize hydrogen peroxide with olefins to prepare epoxy compounds under the action of the Ti-MWW molecular sieve catalyst. The addition of seed crystals guides the growth direction of the crystals, helps to accelerate the crystallization process, and at the same time ensures the uniformity and integrity of the crystal structure, shortens the crystallization time, and improves the preparation efficiency. In the application, a variety of solvents are also screened, preferably acetonitrile, because the by-products involved in acetonitrile in the overall reaction system are small, which improves the selectivity of the target product. In the preparation, a crystallization step is also screened, and an organic amine is added after pre-crystallization for secondary crystallization to promote the formation of crystal nuclei and the incorporation of titanium into the skeleton structure during the skeleton formation process. The present invention also screens organic amines, and 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 electronic effects, which affect the pore structure and acid site distribution of the Ti-MWW molecular sieve during the crystallization stage of catalyst synthesis, thereby affecting the application effect. Furthermore, the present invention also modifies N-hydroxyethylpiperidine, and the modified N-hydroxyethylpiperidine can be improved by introducing a tosyl group into the N-hydroxyethylpiperidine. The pore environment and active centers of the molecular sieve are optimized, thereby better guiding the crystal growth during the formation of the molecular sieve and constructing a pore structure and acidic environment that is more suitable for the synthesis of propylene oxide. The introduction of the tosyl 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 tosyl group can adjust the pore size distribution of the molecular sieve, making 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.

[0021] Beneficial effects of the present invention:

[0022] 1. Compared with the prior art, the Ti-MWW molecular sieve catalyst of the present invention screens a variety of solvents in its application, preferably acetonitrile, because acetonitrile produces fewer by-products in the overall reaction system, thereby improving the selectivity of the target product.

[0023] 2. Compared with the prior art, the Ti-MWW molecular sieve catalyst of the present invention further includes a crystallization step during preparation. After pre-crystallization, organic amine is added for secondary crystallization to promote the formation of crystal nuclei and the incorporation of titanium into the skeleton structure during the skeleton formation process.

[0024] 3. Compared with the prior art, the Ti-MWW molecular sieve catalyst of the present invention screens organic amines during preparation. 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 electronic effects, which affect the pore structure and acid site distribution of the Ti-MWW molecular sieve during the crystallization stage of catalyst synthesis, thereby affecting the application effect. Furthermore, the present invention also modifies N-hydroxyethylpiperidine. The groups 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, and construct a pore structure and acidic environment that are more suitable for the synthesis of propylene oxide, thereby simultaneously improving the selectivity of propylene oxide and the conversion rate of hydrogen peroxide. DETAILED DESCRIPTION

[0025] The parameters of the specific chemical substances used in the examples are derived from the following sources:

[0026] Seed crystal: commercially available molecular sieve with MWW structure, manufactured by Zhejiang Taide New Materials Co., Ltd.

[0027] Fumed silica: Specific surface area is 200m 2 / g, the manufacturer is Hubei Huifu Nanomaterials Co., Ltd., and the model is HL-200.

[0028] Titanium dioxide: Specific surface area is 50m 2 / g, the manufacturer is Hubei Huifu Nanomaterials Co., Ltd., and the model is NT-50.

[0029] Example 1

[0030] A method for preparing a Ti-MWW molecular sieve catalyst comprises the following steps:

[0031] (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 dry gel, 38 g of piperidine, and 250 g of water were added to a crystallization kettle and statically crystallized at 170 ° C for 7 days to obtain a molecular sieve precursor;

[0032] (2) The molecular sieve precursor was treated with a 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.

[0033] Example 2

[0034] A method for preparing a Ti-MWW molecular sieve catalyst comprises the following steps:

[0035] (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, 38 g of 3,5-dimethylpiperidine, and 250 g of water were added to a crystallization kettle and statically crystallized at 170 ° C for 7 days to obtain a molecular sieve precursor;

[0036] (2) The molecular sieve precursor was treated with a 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.

[0037] Example 3

[0038] A method for preparing a Ti-MWW molecular sieve catalyst comprises the following steps:

[0039] (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, 38 g of 4-aminopiperidine, and 250 g of water were added to a crystallization kettle and statically crystallized at 170 ° C for 7 days to obtain a molecular sieve precursor;

[0040] (2) The molecular sieve precursor was treated with a 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.

[0041] Example 4

[0042] A method for preparing a Ti-MWW molecular sieve catalyst comprises the following steps:

[0043] (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, 38 g of N-hydroxyethylpiperidine, and 250 g of water were added to a crystallization kettle and statically crystallized at 170 ° C for 7 days to obtain a molecular sieve precursor;

[0044] (2) The molecular sieve precursor was treated with a 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.

[0045] Example 5

[0046] A method for preparing a Ti-MWW molecular sieve catalyst comprises the following steps:

[0047] (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 dry gel, 25 g of N-hydroxyethylpiperidine, and 250 g of water were added to a crystallization kettle, and statically crystallized at 170 ° C for 4 days, and then 13 g of N-hydroxyethylpiperidine was added and statically crystallized at 170 ° C for 3 days to obtain a molecular sieve precursor;

[0048] (2) The molecular sieve precursor was treated with a 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.

[0049] Example 6

[0050] A method for preparing a Ti-MWW molecular sieve catalyst comprises the following steps:

[0051] (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 dry gel, 25 g of modified N-hydroxyethylpiperidine, and 250 g of water were added to a crystallization kettle, and statically crystallized at 170 ° C for 4 days, and then 13 g of modified N-hydroxyethylpiperidine was added and statically crystallized at 170 ° C for 3 days to obtain a molecular sieve precursor;

[0052] (2) treating the molecular sieve precursor with a 2.5 mol / L nitric acid aqueous solution for 14 hours, centrifuging, drying at 77° C. for 12 hours, and calcining at 600° C. for 10 hours to obtain the Ti-MWW molecular sieve catalyst;

[0053] The preparation method of the modified N-hydroxyethyl piperidine is as follows:

[0054] 30 g of N-hydroxyethylpiperidine was added to 150 g of dichloromethane, followed by the addition of 28 g of triethylamine and 1.5 g of 4-pyrrolidinylpyridine. The mixture was stirred at 0°C for 0.5 hour, and 55 g of p-toluenesulfonyl chloride was added. The mixture was stirred at room temperature for 4 hours. 150 g of saturated aqueous sodium bicarbonate solution was added to quench the mixture, and the mixture was extracted twice with dichloromethane, each time using 100 g of the mixture. The organic phases were combined. 120 g of 0.5 mol / L dilute hydrochloric acid was added to the organic phase, and the mixture was stirred for 20 minutes, followed by standing to separate the liquids. 120 g of saturated aqueous sodium chloride solution was added to the organic phase, and the mixture was stirred for 20 minutes, followed by standing to separate the liquids. The organic phase was concentrated to obtain modified N-hydroxyethylpiperidine.

[0055] Test Example 1

[0056] The Ti-MWW molecular sieve catalyst prepared in Examples 1-6 of the present invention was directly epoxidized with propylene in hydrogen peroxide to produce 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 the Ti-MWW molecular sieve catalyst were added to a reactor, followed by 2.5 g of propylene. The reaction was maintained at 45°C and 2.5 MPa for 2 hours. A sample of the mixed raw materials was taken before the reaction. After the 2-hour reaction, the hydrogen peroxide content was determined by titration using the cerium sulfate method. Other organic compounds were determined by gas chromatography. The propylene oxide selectivity was calculated as follows: (amount of H₂O₂ consumed in PO production / initial amount of H₂O₂) × 100%; a summary is shown in Table 1.

[0057] Table 1 Propylene oxide selectivity data

[0058] 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%

[0059] There are differences in the data of different embodiments in Test Example 1. The reason is that the types and usage of organic amines are different during the preparation of the Ti-MWW molecular sieve catalyst. Examples 1-4 respectively use piperidine, 3,5-dimethylpiperidine, 4-aminopiperidine, and N-hydroxyethylpiperidine as organic amines. Different organic amines have different molecular structures and electronic effects. They affect the pore structure and acid site distribution of the Ti-MWW molecular sieve during the crystallization stage of catalyst synthesis. The pore structure is directly related to whether the reactants can smoothly contact the active center. The acid site will affect the intermediate steps of the reaction, which will eventually affect the selectivity of propylene oxide. Example 4 uses N-hydroxyethylpiperidine. The hydroxyethyl group in its molecule gives unique hydrophilicity and steric hindrance, which can better adjust the surface properties of the molecular sieve and promote the adsorption and reaction of the reactants. Therefore, the selectivity of propylene oxide is better than that of Examples 1-3. Example 5, based on Example 4, adopts the method of adding N-hydroxyethylpiperidine in stages during the crystallization process to make the molecular sieve crystal growth more orderly, and the pore structure is more conducive to the propylene oxide generation reaction, thereby improving the selectivity. In Example 6, N-hydroxyethylpiperidine is modified on the basis of Example 5 by introducing a toluenesulfonyl group into N-hydroxyethylpiperidine, thereby enhancing the hydrophobicity and electronic effect of the molecular sieve. This helps to improve the adsorption and activation ability of the catalyst for hydrogen peroxide while reducing the occurrence of side reactions. The steric hindrance effect of the toluenesulfonyl group is then used to adjust the pore size distribution of the molecular sieve, making it more suitable for the diffusion and reaction of propylene molecules, thereby enhancing the catalytic activity and selectivity for the target reaction. Its propylene oxide selectivity is better than that of Examples 1-5.

[0060] Test Example 2

[0061] The Ti-MWW molecular sieve catalyst prepared in Examples 1-6 of the present invention was directly epoxidized with ethylene in hydrogen peroxide to produce ethylene 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 the Ti-MWW molecular sieve catalyst were added to a reactor, followed by 2.5 g of ethylene. The reaction was maintained at 45°C and 2.5 MPa for 2 hours. A sample of the mixed raw materials was taken before the reaction. After the 2-hour reaction, the hydrogen peroxide content was determined by titration using the cerium sulfate method. Other organic compounds were determined by gas chromatography. The hydrogen peroxide conversion rate was calculated as (H₂O₂ consumption / initial H₂O₂ amount) × 100%. A summary is shown in Table 2.

[0062] Table 2 Hydrogen peroxide conversion rate data

[0063] 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%

[0064] The reason for the data difference in Test Example 2 is that in the preparation process of the Ti-MWW molecular sieve catalyst, the use of different organic amine templates will affect the structure and performance of the Ti-MWW molecular sieve catalyst. Examples 1-4 use piperidine, 3,5-dimethylpiperidine, 4-aminopiperidine, and N-hydroxyethylpiperidine as templates, respectively. During the crystallization process, the pore structure and acid site distribution of the molecular sieve will be affected. By comparison, it is found that the improvement effect of Example 4 on the conversion of hydrogen peroxide is significantly higher than that of Example 1-3, indicating that the difference in molecular structure and properties leads to differences in the structure of the molecular sieve precursor formed, thereby affecting the activity and selectivity of the final catalyst. Example 5 changes the primary crystallization to secondary crystallization on the basis of Example 4, so the first crystallization is pre-crystallization, and N-hydroxyethylpiperidine is continued to be added to the molecular sieve after pre-crystallization for secondary crystallization, which promotes the entry of titanium into the skeleton structure during the formation of crystal nuclei and skeleton, and its hydrogen peroxide conversion is better than that of Example 4 of the primary crystallization. Example 6: Based on Example 5, N-hydroxyethylpiperidine was modified. 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 improving the hydrogen peroxide conversion rate.

[0065] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a Ti-MWW molecular sieve catalyst, characterized in that: The method comprises the following steps, in parts by weight: (1) 20-40 parts of fumed silica and 0.1-1.5 parts of titanium dioxide are mixed and ground for 24 hours, 4-6 parts of seed crystals and 10-30 parts of boric acid are added and ground for 2 hours to obtain a dry gel; 40-80 parts of dry gel, 30-50 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 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, 4-6 parts of seed crystals and 10-30 parts of boric acid are added, and grinding is continued for 2 hours to obtain a dry gel; 40-80 parts of 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, and 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) treating the molecular sieve precursor with a 2-4 mol / L nitric acid aqueous solution for 12-16 hours, centrifuging, drying at 70-80° C. for 12 hours, and calcining at 550-650° C. for 6-12 hours to obtain the Ti-MWW molecular sieve catalyst; The organic amine is modified N-hydroxyethylpiperidine; The preparation method of the modified N-hydroxyethyl piperidine is as follows, in parts by weight: 20-40 parts of N-hydroxyethylpiperidine are added to 140-180 parts of dichloromethane, and 25-35 parts of triethylamine and 1-2 parts of 4-pyrrolidinylpyridine are added in sequence. The mixture is stirred at 0-5°C for 0.5-1 hour, and 50-60 parts of p-toluenesulfonyl chloride are added. The mixture is stirred at room temperature for 3-5 hours. 140-180 parts of saturated sodium bicarbonate solution is added to quench the mixture. The mixture is extracted with dichloromethane 1-3 times, each time using 80-120 parts. The organic phases are combined. 100-150 parts of dilute hydrochloric acid is added to the organic phase, the mixture is stirred for 10-30 minutes, and the mixture is allowed to stand for separation. 100-150 parts of saturated sodium chloride aqueous solution is added to the organic phase, the mixture is stirred for 10-30 minutes, and the mixture is allowed to stand for separation. The organic phase is concentrated to obtain modified N-hydroxyethylpiperidine.

2. A Ti-MWW molecular sieve catalyst, characterized in that: Prepared by the preparation method according to claim 1.

3. An application of the Ti-MWW molecular sieve catalyst as claimed in claim 2, characterized in that: Application of hydrogen peroxide in direct epoxidation of olefins over Ti-MWW molecular sieve catalyst; The specific application method is as follows: add solvent, hydrogen peroxide, and Ti-MWW molecular sieve catalyst into a reactor, add olefin, and react at 40-60°C and 2-3 MPa for 1-3 hours; the olefin is one of ethylene, propylene, butene, pentene, hexene, heptene, and octene.

4. The use of the Ti-MWW molecular sieve catalyst as claimed in claim 3, characterized in that: The solvent used in the application is one of water, acetonitrile, methanol, ethanol, tert-butanol, ethyl acetate, dichloromethane and benzene.

5. The use of the Ti-MWW molecular sieve catalyst as claimed in claim 3, characterized in that: The weight ratio of the solvent, olefin, hydrogen peroxide and Ti-MWW molecular sieve catalyst used in the application is 4-6:1-4:0.2-2:0.1-0.

5.

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

3.

7. Use of the Ti-MWW molecular sieve catalyst as claimed in claim 3, characterized in that: The hydrogen peroxide in the application is 20-50 wt% hydrogen peroxide.