Preparation method of hierarchical pore TS-1 molecular sieve with high content of active titanium species

Abstract

The invention relates to the field of preparation of molecular sieve materials, and discloses a preparation method of a hierarchical pore TS-1 molecular sieve with high content of active titanium species, and the hierarchical pore TS-1 molecular sieve with high content of active titanium species is synthesized by combining aging and vapor phase assistance. According to the method, the content of TS-1 molecular sieve skeleton titanium can be effectively increased, and meanwhile, TO6 skeleton external active titanium species can be effectively generated; the content of the active titanium species is effectively increased, and meanwhile, the nano hierarchical pore TS-1 molecular sieve rich in mesopores can be obtained under the condition that a pore forming agent is not added; besides, the synthesis temperature range of the TS-1 molecular sieve can be carried out at a high temperature of 120-180 DEG C, and also can be carried out at a low temperature of 100-120 DEG C; the crystallization time of the TS-1 molecular sieve is short at high temperature, the TS-1 molecular sieve with higher crystallinity can be obtained within 5 hours at the soonest, and the high-temperature and high-pressure synthesis conditions can be effectively avoided by the latter, so that the production energy consumption of the molecular sieve is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and particularly relates to a method for preparing a multi-level porous TS-1 molecular sieve with a high content of active titanium species. Background Art

[0002] TS-1 molecular sieve is a heteroatom molecular sieve with MFI topology. The synthesis of this type of molecular sieve was first reported by Taramasso et al. in 1983 (US4410501). TS-1 molecular sieve exhibits good catalytic performance in many important oxidation reactions such as olefin epoxidation, oxidative desulfurization, and phenol hydroxylation. Therefore, this type of molecular sieve has attracted much attention from researchers since its first report.

[0003] However, since titanium atoms have a larger atomic size than silicon atoms, when they are introduced into the MFI molecular sieve framework, the lattice of the MFI molecular sieve will expand, which will lead to the instability of the MFI molecular sieve framework structure. In addition, the silicon source used in the synthesis process often has a slower hydrolysis rate than the titanium source. The rate at which titanium enters the molecular sieve framework is difficult to match the rate of molecular sieve crystallization. Therefore, non-framework TiO2 phase titanium species are easily generated, further inhibiting titanium from entering the molecular sieve framework. At present, the skeleton titanium content in TS-1 obtained by conventional hydrothermal synthesis is usually less than 1.5wt%. The low content of skeleton titanium limits the application development of TS-1 molecular sieve to a certain extent. Therefore, effectively increasing the content of skeleton titanium in TS-1 molecular sieve is of great significance for the development of practical applications. In previous syntheses, pH modulation is often used to inhibit the formation of non-framework titanium, such as adding different ammonium salts (J.Am.Chem.Soc.2008,130,10150-10164), aromatic acids (CN114920262B) and other acidic substances to reduce the pH value of the synthesis system, thereby reducing the hydrolysis rate of the titanium source so that the rate at which titanium enters the molecular sieve framework matches the rate of molecular sieve crystallization, thereby inhibiting the formation of non-framework titanium. Although this method can effectively avoid the formation of non-framework titanium, due to the low alkalinity of the synthesis system (usually pH <10.5), the synthesis system lacks a certain mineralizer, which leads to a limited total content of titanium entering the framework. Therefore, further increasing the framework titanium content is still an extremely challenging task in the field of TS-1 molecular sieve synthesis.

[0004] In addition, recent studies have shown that non-framework titanium also has titanium species (TiO6) with high catalytic activity. Such titanium species are often constructed through post-synthesis methods, such as alkali treatment or recrystallization to effectively generate TiO6 titanium species (Appl. Catal. A. 2013, 453, 272-279; Chem. Commun. 2016, 52, 8679-8682). However, such methods are often more complicated, and the post-treatment process will also cause the loss of molecular sieve quality and the reduction of molecular sieve crystallinity. Therefore, while ensuring the generation of high-content framework titanium, how to effectively introduce additional highly active TiO6 species is also a research that has attracted much attention.

[0005] For the traditional TS-1 molecular sieve, due to the existence of a single microporous channel and a long diffusion pore path, the diffusion of reactants and products in and out of the channel is blocked during the actual catalytic process, which in turn affects the activity and selectivity of the catalyst. The accessibility of the active center of the traditional microporous TS-1 molecular sieve is often low, so it is also subject to certain restrictions in applications involving macromolecular catalysis. In recent years, some corresponding solutions have been developed for the above problems, which mainly involve the modulation of the morphology of the molecular sieve and the modification of the pore structure. For example: reducing the crystal size of the molecular sieve to the nanometer level (CN107500310B; CN110294484B; CN116161673A), introducing mesopores or macropores into the molecular sieve channel to synthesize multi-level pore molecular sieves (CN110330025B; CN103818923B). Among them, the synthesis of multi-level pore TS-1 molecular sieve has attracted much attention from researchers because it can significantly improve the application performance of this type of molecular sieve.

[0006] At present, the synthesis of multi-level pore TS-1 molecular sieves is mainly divided into bottom-up method and top-down method. The former mainly constructs multi-level pores in in-situ synthesis, and the latter prepares multi-level pore molecular sieves by acid-base or fluoride etching method on the basis of synthesizing titanium silicon molecular sieve. The latter is difficult to control in synthesis, and often causes problems such as reduced crystallinity of molecular sieves and blockage of molecular sieve channels, so there are still certain problems in practical applications. In contrast, the former has attracted much attention from researchers because it can directly construct multi-level pore molecular sieves in situ. At present, the soft and hard template method is the most commonly used synthesis strategy in the bottom-up method. Multi-level pore molecular sieves can be effectively constructed by introducing effective pore-forming agents. However, since this method often requires the addition of a certain amount of pore-forming agents in the synthesis system, its synthesis cost is relatively high. Based on this, we proposed a simple synthesis method to prepare multi-level pore TS-1 molecular sieves with high content of active titanium species to solve the above problems. Summary of the invention

[0007] In view of the above situation, the purpose of the present invention is to provide a method for preparing a multi-level porous TS-1 molecular sieve with a high content of active titanium species, which can effectively increase the content of active titanium species (framework titanium and TiO6 titanium species) in the TS-1 molecular sieve by combining aging and steam phase assisted synthesis of a multi-level porous TS-1 molecular sieve with a high framework titanium content.

[0008] To achieve the above object, the technical solution adopted by the present invention is: to provide a preparation method of a multi-level porous TS-1 molecular sieve with a high content of active titanium species, which effectively prepares a multi-level porous TS-1 molecular sieve with a high content of active titanium species in the range of 100-180°C by combining aging and steam-assisted synthesis; the preparation method comprises the following specific steps: Step 1, weighing the required organic structure directing agent, silicon source and water according to the synthesis ratio, and mixing and stirring the synthetic raw materials to form a synthetic sol; Step 2, weighing the required titanium source and adding it to the synthetic sol obtained in the above step 1, and then stirring the synthetic sol at 25 to 100° C. for 1 to 120 hours to obtain a synthetic precursor; Step 3, heating the synthetic precursor obtained in step 2 at a certain temperature of 50 to 100° C. to completely remove the solvent in the synthetic precursor to obtain a completely dried synthetic precursor; Step 4, placing the completely dried synthetic precursor obtained in step 3 in a tray of a homemade reactor, adding a certain amount of water under the tray, and then sealing the reactor at 100-180° C. for crystallization for 5-120 hours; Step 5, separating the crystallized mixture into solid and liquid, and drying the obtained solid phase product to obtain TS-1 molecular sieve.

[0009] The preparation method can also effectively construct a multi-level pore structure by combining aging and steam phase-assisted method. The synthesis temperature range is 120-180°C. The crystallization time is short at high temperature, and TS-1 molecular sieve with high crystallinity can be obtained within 5 hours at the fastest. The synthesis temperature range is 100-120°C. Low temperature and high pressure synthesis conditions are avoided.

[0010] The silicon source is at least one of silica sol, tetraethyl orthosilicate, amorphous silicon dioxide, white carbon black and silicate.

[0011] The structure directing agent is at least one of ethylenediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrapropylammonium bromide.

[0012] The titanium source is an organic or inorganic compound containing heteroatoms, and is at least one of tetraethyl titanate, tetrabutyl titanate, tetrapentyl titanate, tetrahexyl titanate, titanium isopropoxide, titanium tetrachloride, and titanium acetylacetonate.

[0013] The present invention mainly utilizes a vapor phase synthesis method to prepare a multi-level pore molecular sieve. The vapor phase synthesis mainly completes the crystallization of the molecular sieve. At the same time, this special synthesis method can effectively introduce mesopores to prepare a multi-level pore molecular sieve. More importantly, this step can also introduce TO6 active titanium species.

[0014] The beneficial effects of the present invention are that a high-framework titanium content multi-level pore TS-1 molecular sieve can be prepared within the range of 100 to 180°C; at the same time, the content of active titanium species in the TS-1 molecular sieve, namely, framework titanium and TiO6 titanium species, can be effectively increased; wherein the framework titanium content can be as high as 2.0wt%, and the proportion of TiO6 can be as high as 23%; in particular, in a low-temperature synthesis system of 100°C, a multi-level pore TS-1 molecular sieve can still be effectively prepared, and the framework titanium content can still be as high as 1.6wt% at low temperatures, and the proportion of TiO6 can be as high as 11%; the preparation method of the present invention has simple steps and has the advantages of good parallelism, repeatability, operability, practicality and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The XRD spectrum of the sample obtained in Example 1; Figure 2 This is the SEM image of the sample obtained in Example 1; Figure 3 The XRD spectrum of sample 3 obtained in Example 2; Figure 4 This is a TEM photo of sample 3 obtained in Example 2; Figure 5 is the UV-vis spectrum of sample 3 obtained in Example 2; Figure 6 is the FTIR spectrum of sample 3 obtained in Example 2; Figure 7 It is the N2 isothermal adsorption and desorption diagram of sample 3 obtained in Example 2; Figure 8 This is the XRD picture of the sample obtained in Example 4; Fig. 9 This is a SEM photograph of the sample obtained in Example 4. DETAILED DESCRIPTION

[0016] The specific implementation of the present invention is described in detail below. The specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0017] The endpoints and any values ​​of the ranges involved in this patent are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this patent.

[0018] Technical terms in the present invention are defined according to their definitions, and are understood according to the common meanings in the art if not defined. The organic structure directing agent in the present invention is also called a template agent in the art.

[0019] The technical solution provided by the present invention aims to solve the following technical problems: the non-framework titanium TiO2 phase is easily generated in the existing TS-1 molecular sieve synthesis, and the framework titanium content in the TS-1 molecular sieve synthesis is difficult to increase; at the same time, the problem that the additional use of pore-forming agents in the existing bottom-up synthesis method makes the synthesis cost higher is solved.

[0020] The present invention provides a method for preparing a multi-level porous TS-1 molecular sieve with a high content of active titanium species, and the specific steps are as follows: Step 1, weighing the required organic structure directing agent, silicon source and water according to the synthesis ratio, and mixing and stirring the synthetic raw materials to form a synthetic sol; Step 2, weighing the required titanium source and adding it to the synthetic sol obtained in the above step 1, and then stirring the synthetic sol at 25 to 100° C. for 1 to 120 hours to obtain a synthetic precursor; Step 3, heating the synthetic precursor obtained in step 2 at 50-100° C. to completely remove the solution in the synthetic precursor to obtain a completely dry synthetic precursor; Step 4, placing the completely dried synthetic precursor obtained in step 3 in a tray of a homemade reactor, adding a certain amount of water under the tray, and then sealing the reactor at 100-180° C. for crystallization for 5-120 hours; Step 5, separating the crystallized mixture into solid and liquid, and drying the obtained solid phase product to obtain TS-1 molecular sieve.

[0021] According to the method of the present invention, the silicon source is calculated as SiO2, the titanium source is calculated as TiO2, and the structure directing agent is calculated as R. The molar ratio of the silicon source, the titanium source, the structure directing agent and water in the aging step is as follows: SiO2:xTiO2:yR:zH2O, wherein: R is an organic structure directing agent, x=0.02~0.04, y=0.05~0.5, z=5~100.

[0022] The present invention has no particular limitation on the types of silicon source, structure directing agent and heteroatom precursor, and any of them can be conventionally selected.

[0023] Generally, the silicon source is at least one of silica sol, tetraethyl orthosilicate, amorphous silica, white carbon black, and silicate; the structure directing agent is at least one of ethylenediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide; the heteroatom precursor is an organic or inorganic compound containing heteroatoms, which can be at least one of tetraethyl titanate, tetrabutyl titanate, tetrapentyl titanate, tetrahexyl titanate, titanium isopropoxide, titanium tetrachloride, and titanium acetylacetonate.

[0024] The present invention is further described in detail and completely below in conjunction with specific embodiments. Example 1

[0025] A preparation method of a multi-level porous TS-1 molecular sieve with a high content of active titanium species, the synthesis method is as follows: first, 9g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 30mL of water are stirred and mixed uniformly at room temperature, then 0.55g of tetrabutyl titanate is added, the obtained solution is stirred at 25°C for 6h, and then evaporated at 80°C; after evaporation, the obtained dry precursor is placed in a tray of a homemade reactor, 1ml of water is placed under the tray, and then the reactor is sealed and transferred to a 170°C oven for crystallization for 12h, and after crystallization, the reactor is cooled to room temperature, the obtained molecular sieve catalyst is washed with deionized water, and dried at 80°C overnight to obtain the final product.

[0026] Figure 1 This is the XRD spectrum of the obtained product. It can be seen that the product has the characteristic diffraction peak of the MFI structure and has a high degree of crystallinity; Figure 2 The SEM image of the obtained sample shows that the obtained sample is nanoparticles with a crystal size of about 200 nm. Example 2

[0027] A preparation method of a multi-level porous TS-1 molecular sieve with a high content of active titanium species, the synthesis method is as follows: first, 15g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 30mL of water are stirred and mixed evenly at room temperature, then 0.66g of tetrabutyl titanate is added, the resulting solution is stirred at 25°C for 6h, 12h, 24h, 48h and 72h respectively, and then evaporated at 80°C; after evaporation, the resulting dried precursor is placed in a tray of a homemade reactor, 1ml of water is placed under the tray, and then the reactor is sealed and transferred to a 170°C oven for crystallization for a certain period of time, and after crystallization, the reactor is cooled to room temperature, the molecular sieve catalyst is washed with deionized water, and the final product is obtained at 80°C overnight. The results show that the obtained samples are all TS-1 molecular sieves, as shown in Table 1.

[0028] Table 1 Effect of aging time on TS-1 molecular sieve

[0029] Figure 3 This is the XRD pattern of the obtained sample 3. It can be seen that the product has the characteristic diffraction peak of the MFI structure and has a high crystallinity; Figure 4 This is the TEM image of the obtained sample 3. The obtained sample is a nanoparticle with a crystal size of about 50nm; Figure 5 The UV-Vis spectrum of sample 3 shows an obvious absorption peak at 220nm, corresponding to the framework titanium species; in addition, there is an absorption peak at about 270nm, which corresponds to the TO6 titanium species. The existence of the TiO2 phase corresponding to the extra-framework titanium species was not observed in the UV-Vis spectrum, indicating that this method can effectively avoid the formation of the TiO2 phase. Table 1 shows that the titanium content in sample 3 can be as high as 2.6%, of which the framework titanium content is as high as 2%, and the proportion of TiO6 can be as high as 23%. Figure 6 FTIR spectrum of sample 3, 960 cm -1 The Si-O-Ti vibration peak at 1000 nm once again proves the existence of Ti element in the molecular sieve framework, that is, the obtained sample is an MFI molecular sieve containing heteroatoms. Figure 7 The N2 isothermal adsorption and desorption diagram of sample 3 is shown in Figure 1. Figure 7 It can be seen that sample 3 is at 0.5 <p / p 0 There is an obvious hysteresis loop in the range of <0.9, and the appearance of this hysteresis loop indicates that there are certain mesopores in sample 3. Example 3

[0030] A preparation method of a multi-level porous TS-1 molecular sieve with a high content of active titanium species, the synthesis method is as follows: first, 18g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 25mL of water are stirred and mixed at room temperature, then 0.66g of tetrabutyl titanate is added, the resulting solution is stirred at 25°C for 24h, and then evaporated at 80°C; after evaporation, the resulting dried precursor is placed in a tray of a homemade reactor, 1ml of water is placed under the tray, and then the reactor is sealed and transferred to an oven at 100°C, 120°C, 150°C and 180°C for crystallization for a certain period of time, and after crystallization, the reactor is cooled to room temperature, the molecular sieve catalyst is washed with deionized water, and the final product is obtained by drying at 80°C overnight. The results show that the obtained samples are all TS-1 molecular sieves, as shown in Table 2.

[0031] Table 2 Effect of crystallization temperature on TS-1 molecular sieve Example 4

[0032] A preparation method of a multi-level porous TS-1 molecular sieve with a high content of active titanium species, the synthesis method is as follows: first, 20g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 20mL of water are stirred and mixed uniformly at room temperature, then 0.66g of tetrabutyl titanate is added, the obtained solution is stirred at 25°C for 24h, and then evaporated at 80°C; after evaporation, the obtained dry precursor is placed in a tray of a homemade reactor, 0ml of water is respectively loaded under the tray, and then the reactor is sealed and transferred to a 170°C oven for crystallization for a certain time, and after crystallization, the reactor is cooled to room temperature, the obtained molecular sieve catalyst is washed with deionized water, and dried at 80°C overnight to obtain the final product.

[0033] Figure 8 This is the XRD spectrum of sample 4. The results show that when there is no water in the synthesis system, the evaporated dry glue cannot crystallize; Fig. 9 is the SEM image of sample 4, which further shows that the obtained sample 4 is in an amorphous state. Example 5

[0034] A preparation method of a multi-level porous TS-1 molecular sieve with a high content of active titanium species, the synthesis method is as follows: first, 20g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 20mL of water are stirred and mixed uniformly at room temperature, then 0.66g of tetrabutyl titanate is added, the obtained solution is stirred at 25°C for 24h, and then evaporated at 80°C; after evaporation, the obtained dry precursor is placed in a tray of a homemade reactor, 0.5ml of water is respectively loaded under the tray, and then the reactor is sealed and transferred to a 170°C oven for crystallization for a certain time, and after crystallization, the reactor is cooled to room temperature, the obtained molecular sieve catalyst is washed with deionized water, and dried at 80°C overnight to obtain the final product. The results show that the obtained sample is a TS-1 molecular sieve with good crystallinity. The sample is still a nano-multi-level pore TS-1 molecular sieve with a crystal size of about 60nm. The titanium content in the sample is 2.1%, the skeleton titanium content is about 1.8%, the TiO6 accounts for 14%, and the mesopore volume is 0.24cm 3 / g. Example 6

[0035] A preparation method of a multi-level porous TS-1 molecular sieve with a high content of active titanium species, the synthesis method is as follows: first, 20g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 20mL of water are stirred and mixed evenly at room temperature, then 0.66g of tetrabutyl titanate is added, the resulting solution is stirred at 25°C for 24h, and then evaporated at 80°C. After evaporation, the resulting dried precursor is placed in a tray of a homemade reactor, 5ml of water is placed under the tray, and then the reactor is sealed and transferred to a 170°C oven for crystallization for a certain period of time. After crystallization, the reactor is cooled to room temperature, the molecular sieve catalyst is washed with deionized water, and dried at 80°C overnight to obtain the final product. The results show that the obtained sample is a TS-1 molecular sieve with good crystallinity. The sample is still a nano-multi-level pore TS-1 molecular sieve with a crystal size of about 120nm. The titanium content of the sample is 2.1%, the skeleton titanium content is about 1.9%, the TiO6 accounts for 8%, and the mesopore volume is 0.13cm 3 / g. Example 7

[0036] A preparation method of a multi-level porous TS-1 molecular sieve with a high content of active titanium species, the synthesis method is as follows: first, 15g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 30mL of water are stirred and mixed evenly at room temperature, then 0.66g of tetrabutyl titanate is added, the resulting solution is stirred at 50°C for 24h, and then evaporated at 80°C. After evaporation, the resulting dried precursor is placed in a tray of a homemade reactor, 1ml of water is placed under the tray, and then the reactor is sealed and transferred to a 170°C oven for crystallization for a certain period of time. After crystallization, the reactor is cooled to room temperature, the molecular sieve catalyst is washed with deionized water, and dried at 80°C overnight to obtain the final product. The results show that the obtained sample is a TS-1 molecular sieve with good crystallinity. The sample is still a nano-multi-level pore TS-1 molecular sieve with a crystal size of about 55nm. The titanium content in the sample is 2.3%, the skeleton titanium content is about 1.9%, the TiO6 accounts for 17%, and the mesopore volume is 0.23cm 3 / g. Example 8

[0037] Synthesis method: First, 15g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 30mL of water were stirred and mixed at room temperature, and then 0.66g of tetrabutyl titanate was added. The resulting solution was stirred at 80°C for 24h, and then evaporated at 80°C. After evaporation, the dried precursor was placed in a tray of a homemade reactor, and 1ml of water was placed under the tray. The reactor was then sealed and transferred to a 170°C oven for crystallization for a certain period of time. After crystallization, the reactor was cooled to room temperature, and the molecular sieve catalyst was washed with deionized water. It was dried at 80°C overnight to obtain the final product. The results show that the obtained sample is a TS-1 molecular sieve with good crystallinity. The sample is still a nano-multi-level pore TS-1 molecular sieve with a crystal size of about 75nm. The titanium content in the sample is 2.1%, the skeleton titanium content is about 1.8%, the TiO6 accounts for 14%, and the mesopore volume is 0.21cm 3 / g.

[0038] Through the analysis of the experimental results of the above examples, it can be seen that by changing the synthesis temperature, the framework titanium content of the obtained molecular sieve can be maintained at 1.6-2.0%. The main reasons are: (1) the framework titanium content in the synthesis of TS-1 molecular sieve has a certain upper limit (<2%); (2) the effects of aging and evaporation in the synthesis system can promote the acquisition of higher framework titanium in the low-temperature synthesis system, so the framework titanium content does not change much when the synthesis temperature is adjusted. Comparative Example 1

[0039] Synthesis method: First, 15g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 25mL of water were stirred and mixed at room temperature, and then 0.66g of tetrabutyl titanate was added. The resulting solution was stirred at 25°C for 3h, and then the synthetic solution was transferred into a reactor and crystallized in an oven at 170°C for 5h. After crystallization, the reactor was cooled to room temperature, and the molecular sieve catalyst was washed with deionized water and dried at 80°C overnight to obtain the final product. The results show that the obtained sample is still an amorphous sample. Comparative Example 2

[0040] Synthesis method: First, 15g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 30mL of water were stirred and mixed at room temperature, and then 0.66g of tetrabutyl titanate was added. The resulting solution was stirred at room temperature for 3h, and then the synthetic solution was transferred to the reactor and crystallized in an oven at 170℃ for 48h. After crystallization, the reactor was cooled to room temperature, and the molecular sieve catalyst was washed with deionized water and dried at 80℃ overnight to obtain the final product. The results show that the obtained sample is a TS-1 molecular sieve with good crystallinity. The crystal size of the sample is about 500nm, the titanium content in the sample is 2.1%, the skeleton titanium content is about 1.4%, the TiO6 accounts for 5%, and the mesopore volume is 0.06cm3 / g. Comparative Example 3

[0041] Synthesis method: First, 15g of tetrapropylammonium hydroxide (25%), 20g of tetraethyl orthosilicate and 30mL of water were stirred and mixed at room temperature, and then 0.66g of tetrabutyl titanate was added. The resulting solution was stirred at 25°C for 24h, and then the synthetic solution was transferred to the reactor and crystallized in a 170°C oven for 12h. After crystallization, the reactor was cooled to room temperature, and the molecular sieve catalyst was washed with deionized water and dried at 80°C overnight to obtain the final product. The results show that the obtained sample is a TS-1 molecular sieve with good crystallinity. The sample crystal size is about 200nm, the titanium content in the sample is 2.2%, the skeleton titanium content is about 1.6%, the TiO6 accounts for 7%, and the mesopore volume is 0.10cm 3 / g.

[0042] As shown in the technical solution given in Comparative Example 2, if the titanium content in the molecular sieve sample obtained without aging and evaporation is 2.1%, the skeleton titanium content is about 1.4%, and TO6 accounts for 5%, while the titanium content in the molecular sieve sample obtained by aging for 24 hours without evaporation is 2.2%, the skeleton titanium content is about 1.6%, and TO6 accounts for 7%. This result proves to a certain extent that the content of active titanium can be increased to a certain extent by the aging step. Secondly, the titanium content in the molecular sieve sample obtained by the combination of aging and evaporation steps can be as high as 2.6%, of which the skeleton titanium content is as high as 2%, and the TO6 accounted for as high as 23%. This result proves to a certain extent that the evaporation step can effectively increase the content of active titanium in the molecular sieve. In addition, the temperature modulation also shows to a certain extent that the titanium content in the molecular sieve sample obtained at low temperature (100°C) is 1.8%, the skeleton titanium content is about 1.6%, and TO6 accounts for 11%. Therefore, it can be seen from the above that the aging step, evaporation and temperature play an important role in the modulation of the active titanium content in the molecular sieve.

Claims

1. A method for preparing a multi-level porous TS-1 molecular sieve with a high content of active titanium species, characterized in that: The vapor phase synthesis is carried out using organic structure directing agent, silicon source and titanium source as raw materials, as follows: Step 1, weighing the required organic structure directing agent, silicon source and water according to the synthesis ratio, and mixing and stirring the synthetic raw materials to form a synthetic sol; Step 2, weighing the required titanium source and adding it to the synthetic sol obtained in the above step 1, and then stirring the synthetic sol at 25 to 100° C. for 1 to 120 hours to obtain a synthetic precursor; Step 3, heating the synthetic precursor obtained in step 2 at a certain temperature of 50 to 100° C. to completely remove the solvent in the synthetic precursor to obtain a completely dried synthetic precursor; Step 4, placing the completely dried synthetic precursor obtained in step 3 in a tray of a homemade reactor, adding a certain amount of water under the tray, and then sealing the reactor at 100-180° C. for crystallization for 5-120 hours; Step 5, after the reaction is completed, the reactor is cooled to room temperature, the mixture obtained by crystallization is filtered / centrifuged, washed, solid-liquid separated, and the obtained solid phase product is dried to obtain TS-1 molecular sieve; The ratio of the reactant raw materials is: SiO2:TiO2:R:H2O=1:x:y:z, wherein: R is an organic structure directing agent, x=0.02-0.04, y=0.05-0.5, z=5-100.

2. The method for preparing a multi-level porous TS-1 molecular sieve with a high content of active titanium species according to claim 1, characterized in that This method can also effectively construct a multi-level pore structure by combining aging and steam-assisted method. The synthesis temperature range is 120-180℃. The crystallization time is short at high temperature, and TS-1 molecular sieve with high crystallinity can be obtained within 5 hours at the fastest. The synthesis temperature range is 100-120℃, which avoids high temperature and high pressure synthesis conditions.

3. The method for preparing a multi-level porous TS-1 molecular sieve with a high content of active titanium species according to claim 1, characterized in that: The silicon source is at least one of silica sol, tetraethyl orthosilicate, amorphous silica, white carbon black, and silicate; the structure directing agent is at least one of ethylenediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide; the titanium source is an organic or inorganic compound containing heteroatoms, and is at least one of tetraethyl titanate, tetrabutyl titanate, tetrapentyl titanate, tetrahexyl titanate, titanium isopropoxide, titanium tetrachloride, and titanium acetylacetonate.

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