Use of titanium-silicon molecular sieves with silicon islands on their surfaces in catalysis of 1-hexene epoxidation reaction

Abstract

The present application provides a use of a titanium-silicon molecular sieve with silicon islands on its surface in catalysis of 1-hexene epoxidation reaction, the titanium-silicon molecular sieve with silicon islands on its surface is prepared by mixing an organic template agent, a titanium source, and a silicon source to obtain a first mixed solution, concentrating the first mixed solution to obtain a first concentrated liquid, carrying out a first crystallization process on the first concentrated liquid, obtaining a first crystallization product after the process, mixing the first crystallization product and a silicon source to obtain a second mixed solution, carrying out a second crystallization process on the second mixed solution, obtaining a titanium-silicon molecular sieve after the process. The present application realizes precise adjustment of the Ti-OH concentration on the surface of the titanium-silicon molecular sieve, which is helpful in improving the selectivity of 1-hexene epoxidation reaction.

Description

[Technical Field]

[0001] This application relates to the technical field of catalysis and relates to the use of titanium-silicon molecular sieves with silicon islands on their surface in catalyzing the epoxidation reaction of 1-hexene. [Background technology]

[0002] Molecular sieves are a type of inorganic microporous crystalline material that not only play an important role in sustainable development, which is closely related to energy and the environment, but also have a wide range of applications as reaction catalysts. In the 1980s, Enichem, an Italian company, developed a new type of heteroatomic molecular sieve, titanium-silicon molecular sieve (TS-1), containing a titanium framework. TS-1 has the same pore structure as ZSM-5 molecular sieves, and both have an MFI structure. However, ZSM-5 is composed of silicon, aluminum, and oxygen, while TS-1 is composed of silicon, titanium, and oxygen. TS-1 has a rectangular crystal structure consisting of "Z"-shaped channels and intersecting elliptical linear channels, with an average pore diameter of 0.54–0.56 nm.

[0003] Titanium-silicon molecular sieves can catalyze various types of important oxidation reactions of organic compounds, such as epoxidation of alkenes, partial oxidation of alkanes, oxidation of alcohols, hydroxylation of phenols, and ammoxidation of cyclic ketones. In the oxidation reactions of organic compounds, titanium-silicon molecular sieves can use low-concentration, non-polluting hydrogen peroxide as an oxidant, thereby avoiding the complex oxidation process and environmental pollution issues. This not only offers energy-saving, economical, and environmentally friendly advantages that are unmatched by conventional oxidation systems, but also offers good reaction selectivity.

[0004] Because the catalytic activity of titanium-silicon molecular sieves is significantly affected by the microenvironment of their surface titanium active centers, adjusting the surface Ti-OH concentration of titanium-silicon molecular sieves is an important strategy for improving their product selectivity. Methods for adjusting the surface Ti-OH concentration of titanium-silicon molecular sieves include surface silanization and core-shell structure construction. However, these methods not only pose serious contamination problems due to the use of surfactants and silanization reagents, but also significantly increase the time and cost of industrial synthesis due to the complexity and stringent requirements of the synthetic process. Furthermore, these methods lack the ability to target the Ti-OH sites on the surface of titanium-silicon molecular sieves in a directional manner, making it difficult to precisely control the surface Ti-OH concentration. Therefore, researchers in the field have been continuously researching how to provide titanium-silicon molecular sieves that can address these issues. Summary of the Invention

[0005] This application provides a method for using a titanium-silicon molecular sieve with silicon islands on its surface to catalyze the epoxidation of 1-hexene. The isoelectric point of the titanium-silicon molecular sieve can be adjusted without the addition of surfactants or silanizing reagents, and the silicon islands can be deposited on the Ti-OH sites on the surface of the titanium-silicon molecular sieve, thereby enabling precise adjustment of the Ti-OH concentration on the surface of the titanium-silicon molecular sieve. The titanium-silicon molecular sieve produced by this method can be used as a catalyst for the epoxidation of 1-hexene to improve the selectivity to the catalytic product, 1,2-epoxyhexane.

[0006] The present application provides a use of a titanium-silicon molecular sieve having silicon islands on its surface in catalyzing the epoxidation reaction of 1-hexene, the titanium-silicon molecular sieve having silicon islands on its surface comprising: An organic template agent, a titanium source, and a silicon source are mixed to obtain a first mixed solution, the first mixed solution is concentrated to obtain a first concentrated liquid, and the mass ratio of HO to SiO in the first concentrated liquid is 0.1 to 10. The first concentrated liquid is subjected to a first crystallization treatment, and after the treatment is completed, a first crystallization product is obtained; The first crystallization product and a silicon source are mixed to obtain a second mixed solution, and the pH of the second mixed solution is maintained at 7 to 11, and the second mixed solution is subjected to a second crystallization treatment. After the treatment, a titanium-silicon molecular sieve having silicon islands on the surface is obtained.

[0007] In the process for producing titanium-silicon molecular sieves, the isoelectric point of the surface of the titanium-silicon molecular sieve is adjusted without adding surfactants or silanizing reagents, and silicon islands are deposited on the targeted Ti-OH sites on the surface of the titanium-silicon molecular sieve, thereby achieving precise adjustment of the Ti-OH concentration on the surface of the titanium-silicon molecular sieve. Therefore, the titanium-silicon molecular sieve provided by the present invention can be used as a catalyst for the epoxidation of 1-hexene to obtain the catalytic product 1,2-epoxyhexane, and the selectivity to the catalytic product 1,2-epoxyhexane can be improved. Furthermore, the present invention simplifies the synthesis steps and synthesis conditions, reduces the production cost of titanium-silicon molecular sieves, and improves the economical, green, and efficient synthesis process.

[0008] In a specific embodiment, the titanium-silicon molecular sieve is specifically produced by the following production method: In step 1, an organic template agent, a titanium source, and a silicon source are mixed to obtain a first mixed solution. An organic template agent, a titanium source, and a silicon source are dissolved in water as a solvent to obtain a first mixed solution, wherein the organic template agent is one or more selected from the group consisting of ethylenediamine, tetraethylammonium hydroxide, n-butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide. The silicon source refers to a silicon-containing compound that is soluble in water, and may be one or two selected from inorganic silicon sources and organic silicon sources, where the inorganic silicon source is one or two of silica and silica sol, and the silica sol may be one or more of alkaline silica sol, neutral silica sol, and acidic silica sol, and the organic silicon source includes one or more of tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, and dimethoxydiethoxysilane. The titanium source refers to a titanium-containing compound that is soluble in water, and specifically, is one or more selected from tetrabutyl orthotitanate, tetraethyl orthotitanate, tetraisopropyl orthotitanate, titanium(III) chloride, and titanium(IV) chloride.

[0009] Furthermore, the molar ratio of the silicon source to the titanium source is (30-1000):1, and the molar ratio of the silicon source to the organic template agent is (0.1-50):1. Since the blending of raw materials affects the rate at which titanium is introduced into the framework, the titanium content of the molecular sieve will ultimately vary. Within a certain range, the reaction conversion rate will increase with the increase in titanium content. Therefore, the blending can be specifically tailored to meet actual needs.

[0010] The organic template agent, silicon source, and titanium source are mixed in a predetermined ratio and stirred until homogenized to obtain a first mixed solution. The stirring time is shorter than the time required to form a large amount of non-titanium skeletons, specifically, 0.5 to 6 hours, and more specifically, 0.5 to 3 hours. The stirring is then terminated to obtain the first mixed solution.

[0011] In step 2, the first mixed solution is concentrated to obtain a first concentrated solution. Through research, we have found that concentrating the first mixed solution to evaporate the water in the first mixed solution to form a highly concentrated system can help grow crystals during the molecular sieve crystallization process and obtain a precursor of titanium-silicon molecular sieve with excellent performance, and is ready for the production of titanium-silicon molecular sieve. For this purpose, the concentration temperature for the first mixed solution is 50-200°C, and the concentration temperature is T, which is 50°C. <T≦70℃とする。

[0012] After the concentration treatment, a first concentrated liquid is obtained, and in the first concentrated liquid, the mass ratio of H2O to SiO2 is 0.1-10, and further, the mass ratio of H2O to SiO2 is 0.5-3.

[0013] In step 3, the first concentrated liquid is subjected to a first crystallization treatment, and after the treatment is completed, a first crystallized product is obtained. The first crystallization treatment may be carried out in a crystallization vessel, and the temperature of the first crystallization treatment is 100 to 200°C, and further, the temperature of the first crystallization treatment is 140 to 180°C, and the crystallization temperature is higher than the growth temperature of the molecular sieve and lower than the allowable temperature of the molecular sieve skeleton.

[0014] Furthermore, the duration of the first crystallization treatment is greater than 5 hours, and further, the duration of the first crystallization treatment is 72 hours.

[0015] The first crystallization process may be static crystallization and / or rotational crystallization, and the specific operation may be carried out according to conventional technical means in the art, and further, the first crystallization process is rotational crystallization.

[0016] After the first crystallization treatment is completed, the system needs to be cooled. The cooling method includes water cooling or natural cooling, and the cooling method is water cooling.

[0017] After cooling to room temperature, the crystallized product is subjected to solid-liquid separation, and the solid product is collected and dried. The drying temperature should be lower than the decomposition temperature of the organic template agent, specifically, the drying temperature is 40 to 120°C, and more specifically, the drying temperature is 70 to 90°C.

[0018] The dried first solid product may be subjected to a roasting treatment to remove the organic template and form a molecular sieve with unblocked pores. Specifically, the roasting temperature should be higher than the decomposition temperature of the organic template but lower than the allowable temperature of the molecular sieve skeleton. Specifically, the roasting temperature is 500-700°C, and preferably 550-600°C.

[0019] Furthermore, during the roasting process, the heating rate of the roasting treatment should be lower than the allowable heating rate of the molecular sieve skeleton, and the roasting time should be shorter than the allowable roasting time of the molecular sieve skeleton, specifically, the heating rate should be 1-10°C / min and the roasting time should be 4-8 hours, or the heating rate should be 4-6°C / min and the roasting time should be 5-7 hours.

[0020] In step 4, the first crystallization product and a silicon source are mixed to obtain a second mixed solution, and the pH of the second mixed solution is maintained at 7-11. The first crystallization product prepared in step 3 is mixed with silica sol to obtain a second mixed solution, and an alkaline solution is added to the second mixed solution to control the pH of the mixed solution. The first crystallization product is mixed with a silicon source for crystallization, and the isoelectric point of the titanium-silicon molecular sieve surface is adjusted, thereby achieving precise adjustment of the Ti-OH concentration on the titanium-silicon molecular sieve surface by silicon islands.

[0021] Furthermore, the pH of the second mixed solution is maintained at 8 to 10. The alkaline solution may be a common alkaline solution in the art, such as ammonia water, NaOH, or KOH.

[0022] Furthermore, the first crystallization product and silica sol are mixed to obtain a second mixed solution, and the mass ratio of the first crystallization product to the SiO2 in the silica sol is 0.1 to 10, and the mass ratio of the first crystallization product to the SiO2 in the silica sol is 0.5 to 3.

[0023] Furthermore, the temperature is controlled to be 25 to 120°C during the process of mixing the first crystallization product and the silica sol, and further, the temperature is 35 to 60°C.

[0024] In step 5, the second mixed solution is subjected to a second crystallization treatment, and after the treatment is completed, the titanium-silicon molecular sieve is obtained.

[0025] The second crystallization process is the same as the first crystallization process. After the crystallization process is completed, the solid product may be dried and roasted to obtain titanium-silicon molecular sieve. The specific requirements for the drying and roasting processes are as described above.

[0026] The titanium-silicon molecular sieve prepared by the above method can be used as a catalyst to catalyze the epoxidation of 1-hexene. Specifically, the epoxidation reaction is carried out using 1-hexene and hydrogen peroxide as raw materials at 30-80°C using the titanium-silicon molecular sieve prepared by the above method as a catalyst. After 1-5 hours of reaction, the catalyst is centrifuged and the reaction liquid is collected to obtain the catalytic product, 1,2-epoxyhexane.

[0027] The titanium-silicon molecular sieve catalyst provided by this application can catalyze the epoxidation reaction of 1-hexene to produce 1,2-epoxyhexane, improving the reaction selectivity to 1,2-epoxyhexane while ensuring the conversion of the reaction raw materials. [Effects of the Invention]

[0028] By implementing this application, at least the following advantages can be obtained: 1. The titanium-silicon molecular sieve catalyst provided by this application can catalyze the epoxidation reaction of 1-hexene to produce 1,2-epoxyhexane, improving the reaction selectivity to 1,2-epoxyhexane while ensuring the conversion of the reaction raw materials.

[0029] 2. The method for preparing titanium-silicon molecular sieves provided by the present application does not require the addition of surfactants or silanizing reagents, but rather adjusts the isoelectric point of the surface of the titanium-silicon molecular sieve and deposits silicon islands on the target Ti-OH sites on the surface of the titanium-silicon molecular sieve, thereby achieving precise adjustment of the Ti-OH concentration on the surface of the titanium-silicon molecular sieve. Furthermore, the synthesis steps and conditions are simplified, reducing the production cost of titanium-silicon molecular sieves and improving the economical, green and efficient synthesis process. [Brief explanation of the drawings]

[0030] In order to make the description of the embodiments of the present application or the technical solutions of the prior art clearer, the drawings used in the description of the embodiments or the prior art will be briefly described below. It goes without saying that the drawings in the following description are some embodiments of the present application, and those skilled in the art can derive other drawings from these drawings without any creative work. [Figure 1] Figure 1 shows the UV-Vis spectrum of the titanium-silicon molecular sieve provided in Example 1 of the present application. [Figure 2] Figure 2 shows the XRD pattern of the titanium-silicon molecular sieve provided in Example 1 of the present application. [Figure 3] Figure 3 is an SEM image of the titanium-silicon molecular sieve provided by Example 1 of the present application. [Figure 4] Figure 4 is a TEM image of the titanium-silicon molecular sieve provided by Example 1 of the present application. [Figure 5] Figure 5 shows the 1H MAS NMR spectrum of the titanium-silicon molecular sieve provided in Example 1 of the present application. [Figure 6] Figure 6 is an SEM image of the titanium-silicon molecular sieve provided by Comparative Example 1 of the present application. [Figure 7] Figure 7 is an SEM image of the titanium-silicon molecular sieve provided by Comparative Example 2 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0031] In order to make the purpose, technical solution and advantages of the present application clearer, the following uses the embodiments of the present application to clearly and completely describe the technical solution of the embodiments of the present application. Needless to say, the described embodiments are not all the embodiments, but only some of the embodiments of the present application. All other embodiments that a person skilled in the art can obtain based on the embodiments of the present application without any creative work shall fall within the scope of protection of the present application.

[0032] In the following examples, the tetrapropylammonium hydroxide is an aqueous solution of tetrapropylammonium hydroxide in which the mass fraction of tetrapropylammonium hydroxide is 25 wt %, and the mass fraction of SiO2 in the silica sol is 30%.

[0033] Example 1 The method for preparing titanium-silicon molecular sieve provided in this embodiment includes the following steps: 28 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 1.1954 g of tetrabutyl orthotitanate, and 30 g of tetraethyl orthosilicate were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 60°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.9. The first concentrated liquid was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0034] The titanium-silicon molecular sieve obtained in this example was analyzed and characterized.

[0035] Figure 1 shows the UV-Vis spectrum of the titanium-silicon molecular sieve prepared in Example 1 of the present application. As shown in Figure 1, the UV spectrum of the molecular sieve shows a peak at 220 nm, which is due to the tetrahedral titanium framework, suggesting that the titanium framework has a good morphology. Figure 2 shows the XRD pattern of the titanium-silicon molecular sieve prepared in Example 1 of the present application. As shown in Figure 2, the titanium-silicon molecular sieve was successfully synthesized and had a typical MFI structure. Figure 3 shows an SEM image of the titanium-silicon molecular sieve prepared in Example 1 of the present application. Figure 4 shows a TEM image of the titanium-silicon molecular sieve prepared in Example 1 of the present application. As shown in Figures 3 and 4, the surface of the titanium-silicon molecular sieve is covered with silicon islands, which are 2-10 nm in size and uniformly distributed. Figure 5 shows the XRD pattern of the titanium-silicon molecular sieve prepared in Example 1 of the present application. 1 The H MAS NMR spectrum, as shown in Figure 5, showed that the silicon islands effectively covered most of the titanium hydroxyls on the surface of the molecular sieve, since the Ti-OH peak at around 7.5 ppm did not appear.

[0036] Example 2 The method for preparing titanium-silicon molecular sieve provided in this embodiment includes the following steps: 28 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 1.0954 g of tetrabutyl orthotitanate, and 60 g of silica sol were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 60°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 1.8. The first concentrated liquid was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 6 hours to obtain titanium-silicon molecular sieves.

[0037] The molecular sieve prepared in this example was analyzed and characterized in the same manner as in Example 1. As a result, it was found that the synthesized molecular sieve had a good titanium skeleton and a typical MFI structure, and the silicon islands were 2 to 10 nm in size and uniformly distributed, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0038] Example 3 The method for preparing titanium-silicon molecular sieve provided in this embodiment includes the following steps: 20 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 1.2936 g of tetrabutyl orthotitanate, and 30 g of tetraethyl orthosilicate were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 70°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.9. The first concentrated liquid was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0039] The molecular sieve prepared in this example was analyzed and characterized in the same manner as in Example 1. As a result, it was found that the synthesized molecular sieve had a good titanium skeleton and a typical MFI structure, and the silicon islands were 2 to 10 nm in size and uniformly distributed, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0040] Example 4 The method for preparing titanium-silicon molecular sieve provided in this embodiment includes the following steps: 20 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 1.2936 g of tetrabutyl orthotitanate, and 30 g of tetraethyl orthosilicate were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 70°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.8. The first concentrated liquid was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 5g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 9±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0041] The molecular sieve prepared in this example was analyzed and characterized in the same manner as in Example 1. As a result, it was found that the synthesized molecular sieve had a good titanium skeleton and a typical MFI structure, and the silicon islands were 2 to 10 nm in size and uniformly distributed, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0042] Example 5 The method for preparing titanium-silicon molecular sieve provided in this embodiment includes the following steps: 40 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 0.7956 g of tetrabutyl orthotitanate, and 100 g of silica sol were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 60°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 3. The first concentrated liquid was placed in a crystallization vessel and crystallized at 140°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0043] The molecular sieve prepared in this example was analyzed and characterized in the same manner as in Example 1. As a result, it was found that the synthesized molecular sieve had a good titanium skeleton and a typical MFI structure, and the silicon islands were 2 to 10 nm in size and uniformly distributed, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0044] Example 6 The method for preparing titanium-silicon molecular sieve provided in this embodiment includes the following steps: 32 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 0.7956 g of tetrabutyl orthotitanate, and 60 g of silica sol were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 60°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.9. The first concentrated liquid was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 20g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0045] The molecular sieve prepared in this example was analyzed and characterized in the same manner as in Example 1. As a result, it was found that the synthesized molecular sieve had a good titanium skeleton and a typical MFI structure, and the silicon islands were 2 to 10 nm in size and uniformly distributed, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0046] Example 7 The method for preparing titanium-silicon molecular sieve provided in this embodiment includes the following steps: 32 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 1.1956 g of tetrabutyl orthotitanate, and 30 g of silica sol were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 60°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.9. The first concentrated liquid was placed in a crystallization vessel and crystallized at 140°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0047] The molecular sieve prepared in this example was analyzed and characterized in the same manner as in Example 1. As a result, it was found that the synthesized molecular sieve had a good titanium skeleton and a typical MFI structure, and the silicon islands were 2 to 10 nm in size and uniformly distributed, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0048] Example 8 The method for preparing titanium-silicon molecular sieve provided in this embodiment includes the following steps: 32 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 0.5956 g of tetrabutyl orthotitanate, and 30 g of tetraethyl orthosilicate were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 70°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.9. The first concentrated liquid was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0049] The molecular sieve prepared in this example was analyzed and characterized in the same manner as in Example 1. As a result, it was found that the synthesized molecular sieve had a good titanium skeleton and a typical MFI structure, and the silicon islands were 2 to 10 nm in size and uniformly distributed, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0050] (Comparative Example 1) The method for preparing titanium-silicon molecular sieve provided in this comparative example includes the following steps: 28 g of tetrapropylammonium hydroxide (25 wt %), 5 g of water, 1.1954 g of tetrabutyl orthotitanate, and 30 g of tetraethyl orthosilicate were mixed and stirred at 30° C. for 30 minutes to obtain a first mixed solution. The first mixed solution was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80°C, and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of silica sol to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0051] The titanium-silicon molecular sieve provided in this comparative example was observed under a scanning electron microscope. The observation results are shown in FIG. 6, and it was found that the surface of the titanium-silicon molecular sieve did not have a uniform distribution of silicon islands.

[0052] (Comparative Example 2) The method for preparing titanium-silicon molecular sieve provided in this comparative example includes the following steps: 28 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 1.1954 g of tetrabutyl orthotitanate, and 30 g of tetraethyl orthosilicate were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 60°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.8. The first concentrated liquid was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of silica sol to obtain a second mixed solution. Hydrochloric acid solution was added to maintain the pH of the second mixed solution at 3±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0053] The titanium-silicon molecular sieve provided in this comparative example was observed under a scanning electron microscope. The observation results are shown in FIG. 7, which show that no silicon islands appeared on the surface of the titanium-silicon molecular sieve.

[0054] (Comparative Example 3) The method for preparing titanium-silicon molecular sieve provided in this comparative example includes the following steps: 28 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 1.0954 g of tetrabutyl orthotitanate, and 30 g of silica sol were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 60°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.9. The first concentrate was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieve.

[0055] Comparative Example 4 The method for preparing titanium-silicon molecular sieve provided in this comparative example includes the following steps: 28 g of tetrapropylammonium hydroxide (25 wt%), 5 g of water, 1.1954 g of tetrabutyl orthotitanate, and 30 g of tetraethyl orthosilicate were mixed and stirred at 30°C for 30 minutes to obtain a first mixed solution, which was then highly concentrated at 60°C for 24 hours to obtain a first concentrated liquid, in which the mass ratio of HO to SiO was 0.9. The first concentrated liquid was placed in a crystallization vessel and crystallized at 170°C for 72 hours. After the crystallization was completed, the crystallized product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. The solid product was then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallized product was mixed with 10g of cetyltrimethylammonium bromide to obtain a second mixed solution. NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was maintained at 8±0.5 and stirred for 24 hours. The second mixed solution was then placed in a crystallization vessel and crystallized at 170°C for 72 hours. After crystallization, the crystallized product was removed and allowed to cool to room temperature. The solid product was collected by centrifugation and dried at 80°C. It was then roasted at 550°C for 8 hours to obtain titanium-silicon molecular sieves.

[0056] Using 1-hexene and hydrogen peroxide as raw materials and the titanium-silicon molecular sieves prepared in Examples 1 to 8 and Comparative Examples 1 to 4 as catalysts, an epoxidation reaction was carried out at 60°C. After 3 hours of reaction, the upper liquid layer was taken out and analyzed, and the conversion rates of 1-hexene and hydrogen peroxide, as well as the selectivity to 1,2-epoxyhexane, were calculated. The calculation results are shown in Table 1. [Table 1]

[0057] As can be seen from Table 1, the titanium-silicon molecular sieve catalysts provided in Examples 1 to 8 can not only catalyze the epoxidation reaction, but also improve the selectivity to 1,2-epoxyhexane. Furthermore, the method provided herein avoids the use of surfactants, thereby reducing the production cost of the titanium-silicon molecular sieve and improving the economics, greenness, and efficiency of the synthesis process.

[0058] As can be seen from Comparative Examples 1 to 3, without concentration, pH adjustment or second crystallization treatment, no silicon islands appear on the surface of the titanium-silicon molecular sieve, so the Ti-OH concentration on the surface of the titanium-silicon molecular sieve cannot be effectively adjusted, which will further affect the catalytic activity of the titanium-silicon molecular sieve.

[0059] As can be seen from Comparative Example 4, cetyltrimethylammonium bromide, as a cationic surfactant, can adjust the Ti-OH concentration on the surface of the titanium-silicon molecular sieve, so the catalytic activity of the titanium-silicon molecular sieve is improved compared to Comparative Examples 1 to 3, but the effect is inferior to Examples 1 to 8.

[0060] It should be noted that the above embodiments are for illustrating the technical solutions of the present application, and are not intended to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art can still understand that the technical solutions described in the above embodiments may be modified or some or all of the technical features may be replaced with equivalents, and such modifications or replacements will not cause the spirit of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present application.

[0061] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to a Chinese patent application bearing application number 202211736091.6 and entitled "Titanium-silicon molecular sieve, its manufacturing method and use" filed with the State Intellectual Property Office of the People's Republic of China on December 30, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. 1. Use of a titanium-silicon molecular sieve having silicon islands on its surface in catalyzing the epoxidation reaction of 1-hexene, comprising: The titanium-silicon molecular sieve having silicon islands on its surface is An organic template agent, a titanium source, and a silicon source are mixed to obtain a first mixed solution, the first mixed solution is concentrated to obtain a first concentrated solution, and H ２ O and SiO ２ the mass ratio of the first concentrate to the first crystallization treatment is 0.1 to 10, and after the treatment is completed, a first crystallization product is obtained, The first crystallization product is mixed with a silicon source to obtain a second mixed solution, and the pH of the second mixed solution is maintained at 7 to 11, and the second mixed solution is subjected to a second crystallization treatment, and after the treatment, a titanium-silicon molecular sieve having silicon islands on the surface is obtained.

2. The first crystallization product and silica sol are mixed to obtain the second mixed solution, and the first crystallization product and SiO in the silica sol are mixed to obtain the second mixed solution. ２ The use according to claim 1, wherein the mass ratio of

3. The use according to claim 1, wherein the temperature of the concentration is 50 to 200°C.

4. The use according to any one of claims 1 to 3, wherein the organic template agent is one or more selected from the group consisting of ethylenediamine, tetraethylammonium hydroxide, n-butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide.

5. The use according to any one of claims 1 to 3, wherein the silicon source is one or two selected from an inorganic silicon source and an organic silicon source, the inorganic silicon source being one or two selected from silica and silica sol, and the organic silicon source being one or more selected from tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, and dimethoxydiethoxysilane.

6. The use according to any one of claims 1 to 3, wherein the titanium source is one or more selected from the group consisting of tetrabutyl orthotitanate, tetraethyl orthotitanate, tetraisopropyl orthotitanate, titanium(III) chloride, and titanium(IV) chloride.

7. The use according to any one of claims 1 to 3, wherein the ratio of the amounts of the silicon source and the titanium source is (30-1000):

1.

8. The use according to any one of claims 1 to 3, wherein the ratio of the amount of the silicon source to the amount of the organic template agent is (0.1-50):

1.

9. The use according to any one of claims 1 to 3, wherein the first crystallization treatment and the second crystallization treatment are carried out at a temperature of 100 to 200°C for a period of 5 hours or more.

10. The use according to any one of claims 1 to 3, wherein the epoxidation reaction is carried out at a temperature of 30 to 80°C for a time of 1 to 5 hours.

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