A multi-level pore titanosilicate molecular sieve, a synthesis method and application thereof

Abstract

This invention discloses a hierarchical porous titanium-silicon molecular sieve, its synthesis method, and its applications, belonging to the field of molecular sieve material preparation. An initial sol is obtained by mixing a silicon source, a titanium source, a template agent, and water. Alcohols are removed, and a polyquaternary ammonium salt is added. The mixture is then hydrothermally crystallized, filtered, washed, dried, and calcined to obtain the hierarchical porous titanium-silicon molecular sieve. This invention uses a polyquaternary ammonium salt as an additive to achieve the construction of a mesoporous structure. After hydrothermal synthesis, the template agent and additive can be removed simultaneously by calcination. The construction of the micro-mesoporous composite structure can reduce mass transfer resistance and decrease carbon deposition. Therefore, the synthesis of hierarchical porous titanium-silicon molecular sieves using polyquaternary ammonium salt as an additive has significant implications for improving catalyst lifetime and reducing production costs.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve material preparation, and relates to a method for synthesizing hierarchical porous titanium-silicon molecular sieves using polyquaternary ammonium salts as additives and its application in the hydroxylation reaction of phenol. Background Technology

[0002] Titanium silicate molecular sieve TS-1 belongs to the orthorhombic crystal system and has the same MFI topology as ZSM-5 molecular sieve. The introduction of the transition metal titanium gives TS-1 unique catalytic oxidation properties. TS-1 is widely used in catalytic oxidation reactions such as olefin epoxidation, hydroxylation of phenols and benzenes, oxidative desulfurization, and oxime conversion of ketones.

[0003] Mass transfer efficiency is a core parameter determining the catalytic performance and separation efficiency of molecular sieves. Traditional microporous TS-1 molecular sieves (pore size < 2 nm) exhibit significant diffusion limitations in reactions involving macromolecules, leading to hindered reactant / product mass transfer, increased side reactions, and rapid catalyst deactivation. Diffusion kinetic studies have shown that shortening the diffusion path is an effective strategy to improve mass transfer efficiency, prompting the development of hierarchical porous molecular sieve systems. These materials, by integrating a hierarchical pore network of micropores, mesopores, and macropores, significantly improve mass transport efficiency and demonstrate important application value in industrial catalysis. Based on pore construction methods, the synthesis of hierarchical porous molecular sieves can be divided into two main technical routes: in-situ synthesis and post-synthesis. The former involves the simultaneous construction of hierarchical channels during molecular sieve crystallization, while the latter modifies the pore structure of the formed molecular sieve through post-processing.

[0004] Chinese invention patent CN201510149191.2 discloses a method for preparing a hierarchical porous titanium-silicon molecular sieve: (1) a silicon source, a structure-directing agent, a titanium source, and water are mixed evenly in a certain proportion, and then a silanizing agent and a surfactant are added, or the mixture is pre-crystallized at 30~90℃ for 0.5~48 hours before adding the silanizing agent and the surfactant to obtain a mixture containing the silanizing agent and the surfactant; (2) the mixture obtained in step (1) is crystallized in a pressure-resistant sealed container at a temperature of 110~230℃ and under autogenous pressure for 1~240 hours to obtain a crystallized product; (3) the crystallized product obtained in step (2) is recovered. According to this technical solution, a hierarchical porous titanium-silicon molecular sieve with large mesopore volume, adjustable pore structure, and good macromolecular reaction performance can be prepared.

[0005] Chinese invention patent CN106276958B discloses an ordered macroporous-mesoporous hierarchical porous titanium-silicon molecular sieve TS-1 single crystal with an opal structure and its synthesis method. The ordered macroporous-mesoporous hierarchical porous titanium-silicon molecular sieve TS-1 single crystal is composed of interconnected molecular sieve nanostructure units arranged in a highly ordered face-centered cubic close-packed manner. This invention combines the hard template method and the dry gel method, successfully introducing both macropores and mesopores into TS-1 molecular sieve single crystals for the first time. The synthesized ordered macroporous-mesoporous hierarchical porous titanium-silicon molecular sieve TS-1 single crystal possesses the advantages of both hierarchical pore structure and single crystal structure, exhibiting ultra-large pore volume, high specific surface area, catalytic activity, catalytic oxidation performance, and structural stability.

[0006] In summary, both the soft template method and the hard template method can construct hierarchical porous structures within the crystals of TS-1 molecular sieves. However, the silanizing reagents are expensive, and the hard template method faces problems such as poor pore connectivity and structural shrinkage after calcination. Summary of the Invention

[0007] This invention provides a method for synthesizing hierarchical porous titanium-silicon molecular sieves using polyquaternary ammonium salts as additives. The synthesized TS-1 has the same catalytic performance as the hierarchical porous TS-1 synthesized using silanizing reagents as templates. This method can reduce the synthesis cost of hierarchical porous titanium-silicon molecular sieves and is of certain significance.

[0008] To achieve the above objectives and effects, the following plan is adopted: This invention provides a method for synthesizing hierarchical porous titanium-silicon molecular sieves. The method involves mixing a silicon source, a titanium source, a template agent, and water to obtain an initial sol, removing alcohols, adding additives, hydrothermal crystallizing, filtering, washing, drying, and calcining to obtain the hierarchical porous titanium-silicon molecular sieve. The additive is a polyquaternary ammonium salt.

[0009] Further, the polyquaternary ammonium salt is selected from at least one of the following: poly[bis(2-chloroethyl) ether-alt-1,3-bis[3-(dimethylamino)propyl]urea]quaternization (polyquaternary ammonium salt-2, CAS: 68555-36-2), dimethyl diallyl ammonium chloride and acrylamide copolymer (polyquaternary ammonium salt-7, CAS: 26590-05-6), and vinylpyrrolidone / N,N-dimethylaminomethyl methacrylate cationic polymer (polyquaternary ammonium salt-11, CAS: 53633-54-8); The degree of polymerization of the polyquaternary ammonium salt is 20 to 10,000.

[0010] Furthermore, the degree of polymerization of the polyquaternary ammonium salt is 50 to 7000.

[0011] Furthermore, the degree of polymerization of the polyquaternary ammonium salt is 500 to 3000.

[0012] Furthermore, the degree of polymerization of the polyquaternary ammonium salt is 1000~2000.

[0013] The degree of polymerization is the average degree of polymerization of the polyquaternary ammonium salt, which is the average number of repeating units on the polymer molecular chain.

[0014] Furthermore, the silicon source is selected from at least one of tetraethyl orthosilicate, methyl orthosilicate, and silica sol; the titanium source is selected from at least one of tetrabutyl titanate and tetraethyl titanate; and the template agent is tetrapropylammonium hydroxide.

[0015] Furthermore, the molar ratio of each material is as follows: silicon source (calculated as SiO2): titanium source (calculated as TiO2): template agent: water = 1 : 0.015~0.025 : 0.15~0.3 : 20~30, and the mass ratio of silicon source (calculated as SiO2) to polyquaternary ammonium salt is (15~1):1, preferably (12~2.4):1.

[0016] Furthermore, it includes the following steps: (1) After mixing the titanium source and silicon source, stir for the first time, add the template agent aqueous solution, and stir for the second time to obtain sol A; (2) Add deionized water to sol A and distill to remove alcohol to obtain sol B; (3) Add polyquaternary ammonium salt to sol B, stir for the third time, and then perform hydrothermal crystallization, filter, wash, dry and calcinate the mixture.

[0017] Furthermore, the conditions for the first stirring are stirring at 30℃~35℃ for 30~35 min, the conditions for the second stirring are stirring at 30℃~40℃ for 1~2 h, and the conditions for the third stirring are stirring at 30℃~35℃ for 0.5~1 h.

[0018] Furthermore, the concentration of the template agent aqueous solution is 20-25 wt%.

[0019] Furthermore, the distillation to remove alcohol includes subjecting the sol to programmed heating to remove alcohols produced during hydrolysis at a rate of 10-15°C / h until the temperature reaches 75-80°C. Deionized water is then added, followed by re-distillation. The fraction is collected, and when the ethanol content is less than 1 wt% as determined by GC, the water addition and re-distillation operation is stopped. Distillation continues or water is added until the water-silica ratio is 20-30, at which point heating is stopped and the mixture is cooled.

[0020] Furthermore, the hydrothermal crystallization is segmented crystallization, with the first segment crystallization condition being crystallization at 80~90℃ for 12~24h, and the second segment crystallization condition being crystallization at 160~170℃ for 12~48h.

[0021] Furthermore, the drying conditions are drying at 80~100℃ for 8~12h, and the calcination conditions are calcination at 500~600℃ for 5~6h.

[0022] This invention also provides a hierarchical porous titanium-silica molecular sieve prepared by the above synthesis method, wherein the specific surface area of ​​the hierarchical porous titanium-silica molecular sieve is 430~565 m². 2 / g, with a specific surface area excluding micropores of 220~270 m² / g. 2 / g, pore size 2.5~3.0nm, pore volume 0.2~0.36 cm³ 3 / g.

[0023] The present invention also provides an application of the above-mentioned hierarchical porous titanium-silicon molecular sieve in the hydroxylation reaction of phenol.

[0024] Furthermore, in the phenol hydroxylation reaction, the molar ratio of phenol to H2O2 is 2:(0.6~1.5), preferably 2:1, the mass ratio of water to phenol is (0.5~1.2):1, preferably 1:1, and the reaction temperature is 70~75℃.

[0025] The present invention has the following beneficial effects: This invention synthesizes hierarchical porous titanium-silicon molecular sieves using polyquaternary ammonium salts as additives, thereby achieving the construction of a mesoporous structure. After hydrothermal synthesis, the template agent and additives can be removed simultaneously by calcination. The construction of the micro-mesoporous composite structure can reduce mass transfer resistance, decrease carbon deposition, and improve the accessibility of active sites, resulting in a higher probability of collision between reactants and active sites, thus improving conversion and selectivity. Therefore, the synthesis of hierarchical porous titanium-silicon molecular sieves using polyquaternary ammonium salts as additives has significant implications for improving catalyst lifetime and reducing production costs. Attached Figure Description

[0026] Figure 1 The XRD pattern of titanium silicate molecular sieve A-1 is shown. Figure 2 SEM image of titanium silicate molecular sieve A-1; Figure 3 The XRD pattern of titanium silicate molecular sieve A-2 is shown. Figure 4 SEM image of titanium silicate molecular sieve A-2; Figure 5 XRD pattern of titanium silicate molecular sieve A-3; Figure 6 The image shows the SEM spectrum of titanium silicate molecular sieve A-3. Figure 7 XRD pattern of titanium silicate molecular sieve B-1; Figure 8 The image shows the SEM spectrum of titanium silicate molecular sieve B-1. Figure 9 XRD pattern of titanium silicate molecular sieve B-2; Figure 10 SEM image of titanium silicate molecular sieve B-2; Figure 11 This is a SEM image of titanium silicate molecular sieve B-3. Detailed Implementation

[0027] The following embodiments will further illustrate the present invention, but do not limit the scope of the invention.

[0028] The purity of the materials used in the examples is not less than 99%.

[0029] Polyquaternium-2 (P871975), polyquaternium-7 (P815472), and polyquaternium-11 (P815440) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0030] This invention provides a method for synthesizing hierarchical porous titanium silicate molecular sieves, comprising: (1) Add tetrabutyl titanate dropwise into tetraethyl orthosilicate and stir at 35°C for 30-35 min; (2) Add 25% tetrapropylammonium hydroxide aqueous solution to the solution in (1), control the temperature inside the reactor to be below 40℃, stir for 1~2h after the addition is complete, and add deionized water; (3) The sol in (2) is heated in a programmed manner to remove the alcohols produced during the hydrolysis process. The temperature is increased by 10℃ / h until it reaches 75℃. Deionized water is added to it, and then it is distilled again. The fraction is collected. When the ethanol content is less than 1% by GC detection, the water addition is stopped. Distillation continues until the water-silicon ratio is 20. Heating is stopped and the temperature is cooled to below 35℃. (4) Add polyquaternary ammonium salt to the sol in (3) and stir for 0.5~1 h; (5) The mixture in (4) is loaded into a stainless steel high-pressure reactor and crystallized at 90°C for 12-24 hours, then crystallized at 170°C for 12-48 hours. After cooling, the mixture is filtered, washed, dried at 80-100°C, and calcined at 500-600°C to obtain a multi-level porous titanium silicon molecular sieve.

[0031] The hierarchical porous titanium silicate molecular sieve synthesized in this invention is used in a batch reactor reaction for the hydroxylation of phenol. 30g of phenol and 30g of water are added to the reactor, and the mixture is heated to 60°C and stirred for 1 hour to dissolve the phenol. Then, 20g of 30% hydrogen peroxide is added dropwise over 30 minutes, with the temperature gradually increased to 75°C during the addition. Product analysis is performed periodically, and the reaction index is the phenol conversion rate (X). PhOH ) and hydroquinone selectivity (S Dihydroxybenzene The calculation method for the reaction index is as follows: Phenol conversion rate (X)PhOH = (Number of moles of PhOH in the reaction / Total number of moles of PhOH) * 100%; Hydroquinone selectivity (S) Dihydroxybenzene = (Number of moles of hydroquinone and catechol produced in the reaction) / (Number of phenols produced in the reaction) * 100%.

[0032] The catalyst was characterized by XRD analysis using an X-ray diffraction analyzer (Shimadzu 6100 X-ray diffractometer).

[0033] Catalyst N2 adsorption-desorption (BET) characterization was performed using a MicroActive for ASAP 2460 2.02 nitrogen adsorption analyzer.

[0034] The contents of ethanol, phenol, hydroquinone and catechol were determined by Agilent 7820A gas chromatograph. Example 1

[0035] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silica ratio to 20. After cooling to room temperature, 1 g of polyquaternium-2 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 24 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as A-1-1. Example 2

[0036] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silica ratio to 20. After cooling to room temperature, 3 g of polyquaternium-2 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 24 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as A-1-2. Example 3

[0037] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silica ratio to 20. After cooling to room temperature, 5 g of polyquaternium-2 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 24 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as A-1.

[0038] The XRD pattern and SEM image of titanium silicate molecular sieve A-1 are attached. Figure 1 and attached Figure 2 . Example 4

[0039] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silica ratio to 20. After cooling to room temperature, 5 g of polyquaternium-7 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 24 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as A-2.

[0040] The XRD pattern and SEM image of titanium silicate molecular sieve A-2 are attached. Figure 3 and attached Figure 4 . Example 5

[0041] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silicon ratio to 20. After cooling to room temperature, 5 g of polyquaternium-11 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 24 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as A-3.

[0042] The XRD pattern and SEM image of titanium-silicon molecular sieve A-3 are attached. Figure 5 and attached Figure 6 . Example 6

[0043] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silica ratio to 20. After cooling to room temperature, 5 g of polyquaternium-7 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 36 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as A-4. Example 7

[0044] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silica ratio to 20. After cooling to room temperature, 5 g of polyquaternium-7 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 48 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as A-5. Example 8

[0045] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silica ratio to 20. After cooling to room temperature, 5 g of polyquaternium-7 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 24 h, followed by crystallization at 170 °C for 24 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as A-6. Comparative Example 1

[0046] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silicon ratio to 20. After cooling to room temperature, 5 g of N-phenyl-3-aminopropyltrimethoxysilane was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 24 h. The mixture was cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, denoted as B-1.

[0047] The XRD pattern and SEM image of titanium silicate molecular sieve B-1 are attached. Figure 7 and attached Figure 8 . Comparative Example 2

[0048] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled off. The fraction was collected, and the ethanol content was analyzed by GC to be <1 wt%. The mixture was cooled to room temperature, and the resulting gel was transferred to a hydrothermal reactor and crystallized at 90 °C for 12 h, followed by crystallization at 170 °C for 24 h. The mixture was then cooled, filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, designated B-2.

[0049] The XRD pattern and SEM image of titanium silicate molecular sieve B-2 are attached. Figure 9 and attached Figure 10 . Comparative Example 3

[0050] 1.7 g of tetrabutyl titanate was added dropwise to 41.6 g of tetraethyl orthosilicate and stirred at 35 °C for 30 min. 24.8 g of 25% tetrapropylammonium hydroxide aqueous solution was added dropwise, keeping the temperature inside the reactor below 40 °C. After the addition was complete, the mixture was stirred for 2 h, and then 75 g of deionized water was added. The temperature was increased by 10 °C / h until it reached 75 °C. Ethanol was removed, and when the mass of the distilled liquid was 75 g, 75 g of water was added. Distillation continued until 54.8 g of liquid was distilled. The fraction was collected, and when the ethanol content was <1 wt% by GC analysis, distillation was stopped. Water was added to bring the water-to-silica ratio to 20. After cooling to room temperature, 5 g of polyquaternium-2 was added. The resulting gel was transferred to a hydrothermal reactor and crystallized at 170 °C for 36 h. After cooling, the gel was filtered, washed until neutral, dried at 80 °C, and calcined at 550 °C for 6 h to obtain a hierarchical porous titanium silicate molecular sieve, designated B-3.

[0051] SEM images of titanium-silicon molecular sieve B-3 are attached. Figure 11 As shown in the figure, the crystal size of the molecular sieve obtained by a single crystallization is much larger than that of the molecular sieve in this application, which significantly reduces the utilization rate of active sites.

[0052] The BET data for all titanium silicate molecular sieves are shown in Table 1.

[0053] Table 1. BET data for catalysts of each sample Application examples

[0054] The phenol hydroxylation performance of the catalyst samples obtained in the comparative example and the embodiment was evaluated. The phenol hydroxylation reaction was carried out in a three-necked flask reactor. 1.5 g of catalyst was packed into the reactor, and the reaction temperature was maintained at 75 °C in a constant temperature oil bath. 30 g of phenol was dissolved in 30 g of solvent water, and 20 g of 27.5 wt% hydrogen peroxide was added dropwise over 30 min. The molar ratio of phenol to H2O2 was 2. Samples were taken for analysis after the reaction had proceeded for 4 h.

[0055] The performance evaluation results of the samples obtained from the comparative examples and the embodiments are listed in Table 2.

[0056] As can be seen from the table below, the hierarchical porous TS-1 synthesized with polyquaternary ammonium salt as an additive has the same catalytic performance as the hierarchical porous TS-1 synthesized with silanizing reagent as a template agent.

[0057] Table 2. Catalytic performance evaluation results of each sample catalyst

Claims

1. A method for synthesizing a hierarchical porous titanium-silicon molecular sieve, characterized in that, The initial sol was obtained by mixing silicon source, titanium source, template agent and water, removing alcohols, adding additives, hydrothermal crystallization, filtering, washing, drying and calcining to obtain multi-level porous titanium silicon molecular sieve. The additive is a polyquaternary ammonium salt.

2. The synthesis method according to claim 1, characterized in that, The polyquaternary ammonium salt is selected from at least one of polyquaternary ammonium salt-2, polyquaternary ammonium salt-7, and polyquaternary ammonium salt-11; The degree of polymerization of the polyquaternary ammonium salt is 20-10000, preferably 50-7000, more preferably 500-3000, and most preferably 1000-2000.

3. The synthesis method according to claim 1 or 2, characterized in that, The silicon source is selected from at least one of tetraethyl orthosilicate, methyl orthosilicate, and silica sol; the titanium source is selected from at least one of tetrabutyl titanate and tetraethyl titanate; and the template agent is tetrapropylammonium hydroxide.

4. The synthesis method according to any one of claims 1 to 3, characterized in that, The molar ratio of each material is as follows: silicon source (calculated as SiO2): titanium source (calculated as TiO2): template agent: water = 1 : 0.015~0.025 : 0.15~0.3 : 20~30. The mass ratio of silicon source (calculated as SiO2) to polyquaternary ammonium salt is (15~1):1, preferably (12~2.4):

1.

5. The synthesis method according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) After mixing the titanium source and silicon source, stir for the first time, add the template agent aqueous solution, and stir for the second time to obtain sol A; (2) Add deionized water to sol A and distill to remove alcohol to obtain sol B; (3) Add polyquaternary ammonium salt to sol B, stir for the third time, and then perform hydrothermal crystallization, filter, wash, dry and calcinate the mixture.

6. The synthesis method according to claim 5, characterized in that, The conditions for the first stirring are 30℃~35℃ for 30~35 min, the conditions for the second stirring are 30℃~40℃ for 1~2 h, and the conditions for the third stirring are 30℃~35℃ for 0.5~1 h. And / or, the concentration of the template agent aqueous solution is 20~25wt%; And / or, the distillation to remove alcohol includes subjecting the sol to programmed heating to remove alcohols produced during hydrolysis at a rate of 10-15°C / h until the temperature reaches 75-80°C, adding deionized water, re-distilling, collecting the fraction, and stopping the water replenishment and re-distillation operation when the ethanol content is less than 1 wt% as determined by GC. The distillation or water replenishment is continued until the water-silica ratio is 20-30, at which point heating is stopped and cooling is performed.

7. The synthesis method according to claim 5 or 6, characterized in that, The hydrothermal crystallization is segmented crystallization. The first stage crystallization is carried out at 80~90℃ for 12~24h, and the second stage crystallization is carried out at 160~170℃ for 12~48h. And / or, the drying conditions are drying at 80~100℃ for 8~12h, and the calcination conditions are calcination at 500~600℃ for 5~6h.

8. A hierarchical porous titanium-silicon molecular sieve prepared by the synthesis method according to any one of claims 1 to 7, characterized in that, The specific surface area of ​​the hierarchical porous titanium-silicon molecular sieve is 430~565 m². 2 / g, with a specific surface area excluding micropores of 220~270 m² / g. 2 / g, pore size 2.5~3.0 nm, pore volume 0.2~0.36 cm³ 3 / g.

9. The application of the hierarchical porous titanium-silicon molecular sieve of claim 8 in the hydroxylation reaction of phenol.

10. The application according to claim 9, characterized in that, In the hydroxylation reaction of phenol, the molar ratio of phenol to H2O2 is 2:(0.6~1.5), preferably 2:1, the mass ratio of water to phenol is (0.5~1.2):1, preferably 1:1, and the reaction temperature is 70~75℃.

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