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

[0002] Molecular sieves are a kind of inorganic microporous crystalline materials 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), which contains a titanium framework. TS-1 has the same pore structure as ZSM-5 molecular sieves, and both have MFI structures, but ZSM-5 is composed of silicon, aluminum, and oxygen, while TS-1 is composed of silicon, titanium, and oxygen. TS-1 is an orthorhombic crystal system consisting of "Z"-shaped channels and intersecting elliptical straight channels, with an average pore size of 0.54-0.56 nm.

[0003] Titanium-silicon molecular sieves can catalyze various types of oxidation reactions of organic matter, such as epoxidation of alkenes, partial oxidation of alkanes, oxidation of alcohols, hydroxylation of phenols, ammoxidation of cyclic ketones, etc. In the oxidation reaction of organic matter, titanium-silicon molecular sieves can use low-concentration hydrogen peroxide as an oxidant that does not cause pollution, which avoids the complex oxidation process and the problem of environmental pollution, and has the advantages of energy saving, economical, and environmental friendliness that are incomparable with traditional oxidation systems, as well as good reaction selectivity.

[0004] The catalytic activity of titanium-silicon molecular sieves is significantly affected by the microenvironment of the titanium active center on their surface, so adjusting the Ti-OH concentration on the surface of titanium-silicon molecular sieves is an important measure to improve their product selectivity. Methods for adjusting the Ti-OH concentration on the surface of titanium-silicon molecular sieves include surface silane treatment, construction of core-shell structure, etc., but on the one hand, these methods use surfactants and silanizing reagents, which not only cause serious pollution problems, but also the complexity and strict requirements of the synthesis process greatly increase the time cost of industrial synthesis, and on the other hand, these methods cannot recognize the Ti-OH sites on the surface of titanium-silicon molecular sieves in a directional manner, so they cannot realize accurate control of the surface Ti-OH concentration. Therefore, how to provide titanium-silicon molecular sieves that can solve the above problems has been continuously paid attention by those skilled in the art. Summary of the Invention

[0005] The present application provides a use of a titanium-silicon molecular sieve with silicon islands on its surface in catalysis of the epoxidation reaction of 1-hexene, where the isoelectric point of the titanium-silicon molecular sieve surface can be adjusted without adding any surfactant or silanizing agent, and the silicon islands can be deposited on the target Ti-OH sites on the surface of the titanium-silicon molecular sieve to precisely adjust 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 reaction 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 catalysis of an epoxidation reaction of 1-hexene, the titanium-silicon molecular sieve having silicon islands on its surface comprising: 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, the mass ratio of HO to SiO in the first concentrated liquid being 0.1-10, performing a first crystallization process on the first concentrated liquid, and obtaining a first crystallization product after the process is completed; 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. 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.

[0007] In the process of producing titanium-silicon molecular sieve, the present application achieves precise adjustment of the Ti-OH concentration on the surface of titanium-silicon molecular sieve by adjusting the isoelectric point of the surface of titanium-silicon molecular sieve without adding surfactant or silanizing agent, and depositing silicon islands on the target Ti-OH sites on the surface of titanium-silicon molecular sieve. Therefore, the titanium-silicon molecular sieve provided by the present application can be used as a catalyst for the epoxidation reaction of 1-hexene to obtain the catalytic product 1,2-epoxyhexane, and the selectivity to the catalytic product 1,2-epoxyhexane can be improved. In addition, the present application simplifies the synthesis steps and synthesis conditions, reduces the production cost of titanium-silicon molecular sieve, and improves the economical, green and efficient synthesis process.

[0008] In a specific embodiment, the titanium-silicon molecular sieve is specifically prepared by the following preparation 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 an inorganic silicon source and an organic silicon source, where the inorganic silicon source is one or two of silica and silica sol, 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] In addition, the ratio of the amount of the silicon source to the amount of the titanium source is (30~1000):1, and the ratio of the amount of the silicon source to the amount of the organic template agent is (0.1~50):1. In addition, the mixing ratio of the raw materials affects the rate of titanium entering the framework, so finally, the titanium content of the molecular sieve is different. In addition, within a certain range, with the increase of the titanium content, the reaction conversion rate increases, so it can be specifically mixed according to actual needs.

[0010] The organic template agent, the silicon source, and the titanium source are mixed in a predetermined ratio, and when the mixture is stirred to be homogenous, a first mixed solution is obtained. However, the stirring time is shorter than the time required for forming a large amount of non-titanium skeletons, specifically, the stirring time is 0.5 to 6 hours, and furthermore, the stirring time is 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, it has been 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 crystallization process of the molecular sieve and obtain a precursor of titanium-silicon molecular sieve with excellent performance, and is ready for the manufacture of titanium-silicon molecular sieve. For this purpose, in the concentrating process of the first mixed solution, the temperature of the concentrating process is 50-200°C; further, the temperature of the concentrating process is T, which is 50°C or less; <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 completion of the treatment, a first crystallization product is obtained. The first crystallization treatment may be carried out in a crystallization vessel, and the temperature of the first crystallization treatment is 100-200°C. The temperature of the first crystallization treatment is 140-180°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, and the cooling method includes water cooling or natural cooling, and further, the cooling method is water cooling.

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

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

[0019] Furthermore, in 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 is 1-10°C / min and the roasting time is 4-8 hours, and further, the heating rate is 4-6°C / min and the roasting time is 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, so that the first crystallization product is mixed with a silicon source for crystallization, and the isoelectric point of the surface of the titanium-silicon molecular sieve is adjusted, thereby realizing the precise adjustment of the Ti-OH concentration on the surface of the titanium-silicon molecular sieve 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 further, 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 25-120°C during the process of mixing the first crystallization product and the silica sol, and further, the temperature is 35-60°C.

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

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

[0026] The titanium-silicon molecular sieve produced by the above manufacturing method can be used as a catalyst to catalyze the epoxidation reaction of 1-hexene. Specifically, in the epoxidation reaction, 1-hexene and hydrogen peroxide are used as raw materials, and the titanium-silicon molecular sieve produced by the above manufacturing method is used as a catalyst to carry out the epoxidation reaction at 30-80°C. After reacting for 1-5 hours, 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 the present application can catalyze the epoxidation reaction of 1-hexene to produce 1,2-epoxyhexane, and improve the reaction selectivity to 1,2-epoxyhexane while ensuring the conversion of the reaction raw materials. Effect of the Invention

[0028] The implementation of this application provides at least the following advantages: 1. The titanium-silicon molecular sieve catalyst provided by the present application can catalyze the epoxidation reaction of 1-hexene to produce 1,2-epoxyhexane, and improve the reaction selectivity to 1,2-epoxyhexane while ensuring the conversion of the reaction raw materials.

[0029] 2. The preparation method of titanium-silicon molecular sieve provided by the present application achieves precise adjustment of the Ti-OH concentration on the surface of titanium-silicon molecular sieve by adjusting the isoelectric point of the surface of titanium-silicon molecular sieve without adding surfactant or silanization reagent, and depositing silicon islands on the target Ti-OH sites on the surface of titanium-silicon molecular sieve, and simplifies the synthesis steps and synthesis conditions, reduces the production cost of titanium-silicon molecular sieve, and improves the economical, green and efficient synthesis process. [Brief description of the drawings]

[0030] In order to make the description of the technical solutions in the embodiments of the present application or 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 creative labor. [Figure 1] FIG. 1 is a UV-Vis spectrum of the titanium-silicon molecular sieve provided in Example 1 of the present application. [Diagram 2] FIG. 2 is an XRD pattern of the titanium-silicon molecular sieve provided in Example 1 of the present application. [Diagram 3] FIG. 3 is an SEM image of the titanium-silicon molecular sieve provided by Example 1 of the present application. [Figure 4] FIG. 4 is a TEM image of the titanium-silicon molecular sieve provided by Example 1 of the present application. [Diagram 5] FIG. 5 is a 1H MAS NMR spectrum of the titanium-silicon molecular sieve provided in Example 1 of the present application. [Figure 6] FIG. 6 is an SEM image of the titanium-silicon molecular sieve provided by Comparative Example 1 of the present application. [Figure 7] FIG. 7 is an SEM image of the titanium-silicon molecular sieve provided by Comparative Example 2 of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] In order to make the objectives, technical solutions and advantages of the present application clearer, the following uses the embodiments of the present application to clearly and completely describe the technical solutions 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 creative labor 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 with a mass fraction of tetrapropylammonium hydroxide of 25 wt %, and the mass fraction of SiO2 in the silica sol is 30%.

[0033] Example 1 The preparation method of 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 10g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

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

[0035] FIG. 1 is a UV-Vis spectrum of the titanium-silicon molecular sieve provided by Example 1 of the present application. As shown in FIG. 1, the UV spectrum of the molecular sieve shows a peak at 220 nm of the 4-coordinate titanium framework, suggesting that the titanium framework is in a good form. FIG. 2 is an XRD pattern of the titanium-silicon molecular sieve provided by Example 1 of the present application. As shown in FIG. 2, the titanium-silicon molecular sieve was successfully synthesized and had a typical MFI structure. FIG. 3 is an SEM image of the titanium-silicon molecular sieve provided by Example 1 of the present application. FIG. 4 is a TEM image of the titanium-silicon molecular sieve provided by Example 1 of the present application. As shown in FIG. 3 and FIG. 4, the surface of the titanium-silicon molecular sieve is covered with silicon islands, and the silicon islands are 2-10 nm in size and uniformly distributed. FIG. 5 is an XRD pattern of the titanium-silicon molecular sieve provided by Example 1 of the present application. 1 H MAS NMR spectrum, as shown in FIG. 5, in which no Ti-OH peak appeared around 7.5 ppm, indicating that the silicon islands effectively covered most of the titanium hydroxyls on the surface of the molecular sieve.

[0036] Example 2 The preparation method of 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 subjected to a high concentration treatment at 60° C. for 24 hours to obtain a first concentrated liquid, in which the mass ratio of H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 10g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 6 hours to obtain titanium-silicon molecular sieve.

[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, the silicon islands were 2-10 nm in size and showed a uniform distribution, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0038] Example 3 The preparation method of 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 10g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[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, the silicon islands were 2-10 nm in size and showed a uniform distribution, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0040] Example 4 The preparation method of 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 5g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 9±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and cooled to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[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, the silicon islands were 2-10 nm in size and showed a uniform distribution, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0042] Example 5 The preparation method of 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 10g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[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, the silicon islands were 2-10 nm in size and showed a uniform distribution, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0044] Example 6 The preparation method of 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 20g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[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, the silicon islands were 2-10 nm in size and showed a uniform distribution, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0046] Example 7 The preparation method of 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 10g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[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, the silicon islands were 2-10 nm in size and showed a uniform distribution, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0048] Example 8 The preparation method of 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 10g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[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, the silicon islands were 2-10 nm in size and showed a uniform distribution, and the silicon islands effectively covered most of the titanium hydroxyls on the surface.

[0050] Comparative Example 1 The preparation method of titanium-silicon molecular sieve provided by 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 naturally cooled to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 10g of silica sol to obtain the second mixed solution, NaOH solution was added to the second mixed solution, and the pH of the second mixed solution was kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[0051] The titanium-silicon molecular sieve provided in this comparative example was observed under a scanning electron microscope. The observation result is shown in FIG. 6. It can be seen that the titanium-silicon molecular sieve does not have a uniform distribution of silicon islands on its surface.

[0052] Comparative Example 2 The preparation method of titanium-silicon molecular sieve provided by 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization product was mixed with 10g of silica sol to obtain the second mixed solution, and 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 placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[0053] The titanium-silicon molecular sieve provided in this comparative example was observed under a scanning electron microscope. The observation result is shown in FIG. 7. It can be seen that no silicon islands appear on the surface of the titanium-silicon molecular sieve.

[0054] Comparative Example 3 The preparation method of titanium-silicon molecular sieve provided by 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 H2O to SiO2 was 0.9. The first concentrated liquid was put into a crystallization vessel and crystallized at 170℃ 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. The solid product was dried at 80℃ and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[0055] Comparative Example 4 The preparation method of titanium-silicon molecular sieve provided by 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 H2O to SiO2 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 naturally to room temperature. The solid product was collected by centrifugation. The solid product was dried at 80°C and then roasted at 550°C for 8 hours to obtain a first crystallized product. 0.5g of the first crystallization 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 kept at 8±0.5 and stirred for 24 hours. The second mixed solution was placed in a crystallization vessel and crystallized at 170℃ for 72 hours. After the crystallization was completed, the crystallization product was taken out and allowed to cool to room temperature. The solid product was collected by centrifugation, dried at 80℃, and then roasted at 550℃ for 8 hours to obtain titanium-silicon molecular sieve.

[0056] Using 1-hexene and hydrogen peroxide as raw materials and the titanium-silicon molecular sieves prepared in Examples 1-8 and Comparative Examples 1-4 as catalysts, the epoxidation reaction was carried out at 60°C. After reacting for 3 hours, the upper layer liquid was taken out and analyzed, and the conversion rate 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 by Examples 1-8 can not only catalyze the epoxidation reaction, but also improve the selectivity to 1,2-epoxyhexane. In addition, the method provided by the present application avoids the use of surfactants, thereby reducing the production cost of titanium-silicon molecular sieves and improving the economics, greening 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 island appears 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, and the catalytic activity of the titanium-silicon molecular sieve is further affected.

[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 that the catalytic activity of the titanium-silicon molecular sieve is improved compared to Comparative Examples 1-3, but the effect is inferior to that of Examples 1-8.

[0060] It should be noted that the above embodiments are for illustrating the technical solutions of the present application, and are not intended to be limiting. 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 title "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 titanium silicon molecular sieve having silicon islands on its surface in catalysis of 1-hexene epoxidation reaction, 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 and the mass ratio of the first concentrated liquid to the first crystallization treatment is 0.1 to 10. After completion of the treatment, 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 7-11, 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 a silica sol are mixed to obtain the second mixed solution, and the first crystallization product and the 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 from 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 tetrabutyl orthotitanate, tetraethyl orthotitanate, tetraisopropyl orthotitanate, titanium(III) chloride, titanium(IV) chloride.

7. The use according to any one of claims 1 to 6, 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 6, wherein the ratio of the amounts of the silicon source and the organic template agent is (0.1-50):

1.

9. The use according to any one of claims 1 to 8, wherein the first crystallization treatment and the second crystallization treatment are carried out at a temperature of 100 to 200°C for a time of 5 hours or more.

10. The use according to any one of claims 1 to 9, 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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