Titanium silicalite molecular sieve, its preparation method and application

Abstract

The present invention relates to the technical field of titanium silicalite molecular sieves, and discloses a titanium silicalite molecular sieve, a preparation method thereof and an application thereof. The method comprises the following steps: (1) providing titanium silicalite seeds, wherein, based on the total amount of titanium element in the titanium silicalite seeds, the content of non-framework titanium is 70-80% by weight; (2) mixing the titanium silicalite seeds with a solution containing a mesoporous template agent and an alkali, and then performing crystallization and calcination to obtain a titanium silicalite molecular sieve. The titanium silicalite molecular sieve prepared by the method of the present invention has a low content of non-framework titanium, hardly contains non-framework titanium, reduces the acidity of the titanium silicalite molecular sieve, and the obtained titanium silicalite molecular sieve has a hierarchical pore structure.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium silicalite molecular sieves, and particularly relates to a titanium silicalite molecular sieve, a preparation method thereof and an application thereof. Background Art

[0002] Propylene oxide (PO), as the second largest organic chemical product after polypropylene in the production of propylene derivatives, is widely used in the preparation of derivatives such as polyurethane and polyester resins. At present, the main methods for producing PO in industry are the chlorohydrin method and the co-oxidation method. However, the chlorohydrin method has a large corrosion to equipment, produces a large amount of wastewater and chlorine-containing by-products during the production process, and does not meet the requirements of current green environmental protection. And the economy of the co-oxidation method is restricted by a large number of by-products. In recent years, the emerging H 2 O 2 The liquid-phase oxidation method has received extensive attention from the scientific and industrial circles at home and abroad because of its green production raw materials, wide supply, mild production conditions, and the by-products can be reused. This method uses titanium silicalite molecular sieve as a catalyst. Titanium silicalite TS-1 has advantages in terms of energy saving, environmental protection and economy in the oxidation reaction, and has good application prospects in the olefin epoxidation reaction. Enichem Company first announced the titanium silicalite TS-1 with MFI structure in 1983, and then people have successively developed titanium silicalite molecular sieves with different framework structures. For example, TS-2 with MEL structure, Ti-beta with BEA structure, Ti-ZSM-12 with MTW structure and Ti-MCM-22 with MWW structure.

[0003] Generally, the morphology of titanium silicalite molecular sieve synthesized by traditional methods is ellipsoidal, the internal pore channels are micropores, the pore diameter of the crystal grains is about 0.5 nm, and the crystal grains contain more non-framework titanium, resulting in stronger acidity of the molecular sieve; the larger crystal grain size, micropore channels and stronger acidity lead to greater diffusion resistance of reactants when used in catalytic reactions, increasing the desorption difficulty of products, causing blockage of the molecular sieve pore channels and reducing the catalytic activity and service life of the catalyst.

[0004] CN107265474A discloses a synthesis method of a honeycomb hexagonal titanium silicalite molecular sieve. By mixing isopropanol with a titanium source and controlling an appropriate feeding sequence and heating rate, a titanium silicalite molecular sieve in the shape of a quasi-hexagonal prism or a hexagonal prism can be prepared. The molecular sieve has a morphology in the shape of a quasi-hexagonal prism or a hexagonal prism, and the ratio of the height of the quasi-hexagon or hexagon to the longest diagonal of the hexagonal bottom surface is 0.8-1.2. Although this titanium silicalite molecular sieve can improve the catalytic activity of the propylene epoxidation reaction, its service life is short. Summary of the Invention

[0005] The object of the present invention is to overcome the problem of short service life of titanium silicalite in the prior art, and a titanium silicalite, a preparation method and an application thereof are provided. The titanium silicalite has the advantages of high stability and long service life.

[0006] As is well known to those skilled in the art, the mesopore aperture of the titanium silicalite synthesized from a titanium source, a silicon source and a mesoporous template agent after primary crystallization and primary calcination is in the range of 2-3 nm. However, the inventors found in the research process that recrystallizing the titanium silicalite seed with an alkaline solution of the mesoporous template agent can not only rearrange the non-framework titanium in the titanium silicalite seed to form framework titanium, but also form a mesoporous cavity with an aperture in the range of 10-45 nm after calcination. When used for liquid-phase epoxidation of propylene, the propylene conversion rate is high and the service life is long.

[0007] In the present invention, "non-framework titanium" refers to titanium atoms not in the framework, which exist in the form of TiO 2 ; "framework titanium" refers to titanium atoms in the framework, and the titanium atoms with a coordination number of 4.

[0008] To achieve the above object, in the first aspect of the present invention, a titanium silicalite is provided. Based on the total amount of titanium element in the titanium silicalite, the content of non-framework titanium is not higher than 0.01% by weight.

[0009] In the second aspect of the present invention, a method for preparing a titanium silicalite is provided. The method includes the following steps:

[0010] (1) Providing a titanium silicalite seed, wherein, based on the total amount of titanium element in the titanium silicalite seed, the content of non-framework titanium is 70-80% by weight;

[0011] (2) Mixing the titanium silicalite seed with a solution containing a mesoporous template agent and an alkali, and then performing crystallization and calcination to obtain a titanium silicalite.

[0012] In the third aspect of the present invention, a titanium silicalite prepared by the above method is provided.

[0013] In the fourth aspect of the present invention, an application of the above titanium silicalite in the liquid-phase epoxidation reaction of propylene is provided.

[0014] Through the above technical solutions, the present invention has achieved the following beneficial effects:

[0015] (1) The titanium silicalite prepared by the dissolution-recrystallization method of the present invention has a low content of non-framework titanium and almost no non-framework titanium, reducing the acidity of the titanium silicalite.

[0016] (2) The titanium silicalite molecular sieve prepared by the method of the present invention has an MFI structure and a microporous-mesoporous hierarchical pore structure, wherein the mesopores include first mesopores and second mesopores. The pore diameter of the first mesopores ranges from 2 to 3 nm, and the pore diameter of the second mesopores ranges from 10 to 45 nm.

[0017] (3) The surface of the titanium silicalite molecular sieve prepared by the method of the present invention has a bumpy structure similar to that of blackberries, and has a pore structure similar to that of wormholes inside.

[0018] (4) When the titanium silicalite molecular sieve of the present invention is used in the propylene epoxidation reaction, the propylene conversion rate is relatively high, the carbon deposition content of the catalyst is significantly reduced, and the service life of the catalyst is relatively long. Description of the Drawings

[0019] Figure 1 SEM image of the titanium silicalite molecular sieve prepared in Example 1;

[0020] Figure 2 SEM image of the titanium silicalite molecular sieve prepared in Example 1;

[0021] Figure 3 TEM image of the titanium silicalite molecular sieve prepared in Example 1;

[0022] Figure 4 TEM image of the titanium silicalite molecular sieve prepared in Example 1;

[0023] Figure 5 XRD spectrum of the titanium silicalite molecular sieve prepared in Example 1;

[0024] Figure 6 UV-Vis spectrum of the titanium silicalite molecular sieve prepared in Example 1;

[0025] Figure 7 SEM image of the titanium silicalite molecular sieve prepared in Comparative Example 1;

[0026] Figure 8 TEM image of the titanium silicalite molecular sieve prepared in Comparative Example 1;

[0027] Figure 9 TEM image of the titanium silicalite molecular sieve prepared in Example 7;

[0028] Figure 10 TEM image of the titanium silicalite molecular sieve prepared in Example 8;

[0029] Figure 11 TEM image of the titanium silicalite molecular sieve prepared in Comparative Example 3;

[0030] Figure 12TEM image of the titanium silicalite molecular sieve prepared in Example 10;

[0031] Figure 13 TEM image of the titanium silicalite molecular sieve prepared in Example 11; Detailed implementation manners

[0032] In the ranges disclosed herein, the endpoints and any values are not limited to the exact 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, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0033] In the present invention, unless otherwise stated, "titanium-silicon ratio" means the molar ratio between titanium element and silicon element.

[0034] In the first aspect of the present invention, a titanium silicalite molecular sieve is provided. Based on the total amount of titanium element in the titanium silicalite molecular sieve, the content of non-framework titanium is not higher than 0.01% by weight.

[0035] The content test method of "non-framework titanium" is to pickle the titanium silicalite molecular sieve seeds or the titanium silicalite molecular sieve with a nitric acid solution (mass fraction of 10 wt%), and the reduced mass of the titanium silicalite molecular sieve seeds or the titanium silicalite molecular sieve is the mass of non-framework titanium.

[0036] According to the present invention, preferably, the particle size of the titanium silicalite molecular sieve is 80 - 150 nm, the specific surface area is 320 - 500 m 2 / g, the pore volume of mesopores is 0.18 - 0.35 cm 3 / g, and the pore volume of micropores is 0.15 - 0.21 cm 3 / g. The pore volume of mesopores refers to the total pore volume of pores with pore diameters in the range of 2 - 50 nm. The pore volume of micropores refers to the total pore volume of pores with pore diameters less than 2 nm.

[0037] According to the present invention, preferably, the titanium silicalite molecular sieve has a microporous-mesoporous hierarchical pore structure. More preferably, the titanium silicalite molecular sieve has micropores with pore diameters in the range of 0.4 - 0.8 nm, and the titanium silicalite molecular sieve has a first mesopore and a second mesopore.

[0038] According to the present invention, preferably, the pore diameter of the first mesopore is in the range of 2 - 3 nm, and the pore diameter of the second mesopore is in the range of 10 - 45 nm.

[0039] According to the present invention, preferably, the titanium-silicon ratio in the titanium silicalite molecular sieve is 1:40 - 200.

[0040] The second aspect of the present invention provides a method for preparing titanium silicalite molecular sieve, which method comprises the following steps:

[0041] (1) Providing titanium silicalite molecular sieve seeds, wherein, based on the total amount of titanium element in the titanium silicalite molecular sieve seeds, the content of non-framework titanium is 70-80% by weight;

[0042] (2) Mixing the titanium silicalite molecular sieve seeds with a solution containing a mesoporous template agent and an alkali, and then subjecting the mixture to crystallization and calcination to obtain a titanium silicalite molecular sieve.

[0043] According to the present invention, preferably, in step (1), the method for preparing the titanium silicalite molecular sieve seeds comprises: contacting a titanium source, a silicon source and a microporous template agent, and then subjecting the mixture to aging, crystallization and calcination to obtain the titanium silicalite molecular sieve seeds; the molar ratio of the titanium source, the silicon source and the microporous template agent is 1:40-200:100-200, the amount of the titanium source is calculated as Ti, and the amount of the silicon source is calculated as Si.

[0044] According to the method for preparing the titanium silicalite molecular sieve seeds of the present invention, the conditions of the aging are not particularly limited and may be the commonly used aging conditions in the art. Preferably, the conditions of the aging include: the aging temperature is 15-40°C, and the aging time is 1-24 h.

[0045] According to the method for preparing the titanium silicalite molecular sieve seeds of the present invention, the conditions of the crystallization may be the commonly used conditions in the art; preferably, the conditions of the crystallization include: the crystallization temperature is 150-200°C, and the crystallization time is 24-72 h.

[0046] According to the method for preparing the titanium silicalite molecular sieve seeds of the present invention, the equipment for the crystallization is not particularly limited. Preferably, the equipment for the crystallization is an autoclave.

[0047] According to the method for preparing the titanium silicalite molecular sieve seeds of the present invention, preferably, before calcining the crystallization product, it further comprises first washing and first drying the crystallization product. The number of times of the first washing is 3-5 times, and distilled water or deionized water can be used for washing; the temperature of the first drying is 90-120°C, and the time is 12-24 h.

[0048] According to the method for preparing the titanium silicalite molecular sieve seeds of the present invention, the conditions of the calcination are not particularly limited. Preferably, the conditions of the calcination include: the calcination temperature is 480-600°C, and the calcination time is 3-8 h.

[0049] According to the method for preparing the titanium silicalite molecular sieve seeds of the present invention, the atmosphere of the calcination is not particularly limited and may be at least one of an air atmosphere, a nitrogen atmosphere and a helium atmosphere. Further preferably, the calcination is carried out in an air atmosphere.

[0050] According to the present invention, the titanium silicalite seeds described in step (1) can be prepared by the conventional methods of titanium silicalite in the art, and the present invention does not particularly limit this. For example, the method disclosed in patent CN107265474A can be referred to for preparation.

[0051] According to a preferred embodiment, the titanium silicalite seeds are prepared by the following method: mixing a titanium source and isopropanol to obtain solution A, mixing a silicon source and a microporous template agent to obtain solution B, adding solution B to solution A at a rate of 0.01 mL / min, and then aging, crystallizing, and calcining to obtain titanium silicalite seeds.

[0052] According to the present invention, preferably, in step (2), the mass ratio of the titanium silicalite seeds, the mesoporous template agent, and the base is 1:0.1 - 0.5:50 - 100. Limiting the mass ratio of the titanium silicalite seeds, the mesoporous template agent, and the base within the above range can obtain titanium silicalite with good crystal form and low content of non-framework titanium.

[0053] According to the present invention, preferably, in step (2), the crystallization conditions can be the commonly used conditions in the art; the crystallization conditions include: the crystallization temperature is 100 - 150 °C, and the crystallization time is 24 - 72 h.

[0054] According to the present invention, in step (2), there is no particular limitation on the crystallization equipment. Preferably, the crystallization equipment is an autoclave.

[0055] According to the present invention, in step (2), preferably, before calcining the crystallization product, it further includes performing a second washing and a second drying. The number of second washings is 3 - 5 times, and distilled water or deionized water can be used for washing; the temperature of the second drying is 90 - 120 °C, and the time is 12 - 24 h.

[0056] According to the present invention, in step (2), there is no particular limitation on the calcination conditions. Preferably, the calcination conditions include: the calcination temperature is 480 - 600 °C, and the calcination time is 5 - 10 h.

[0057] According to the present invention, in step (2), there is no particular limitation on the calcination atmosphere, and it can be at least one of an air atmosphere, a nitrogen atmosphere, and a helium atmosphere. Further preferably, the calcination is carried out in an air atmosphere.

[0058] According to the present invention, the silicon source can be a commonly used substance in the art that can provide silicon element. Preferably, the silicon source is a silicate ester, and more preferably at least one of tetraethyl orthosilicate, tetramethyl orthosilicate, and tetraethyl orthosilicate.

[0059] According to the present invention, the titanium source may be a substance common in the art that can provide titanium elements. Preferably, the titanium source is a titanium source containing alkoxy groups, and more preferably tetrabutyl titanate.

[0060] According to the present invention, preferably, the microporous template agent is at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0061] According to the present invention, preferably, the mesoporous template agent is a quaternary ammonium salt, and more preferably at least one of cetyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, decyltrimethylammonium bromide, and octyltrimethylammonium bromide.

[0062] According to the present invention, preferably, the base is at least one of ammonia, alkali metal hydroxides, and organic amines, and further preferably at least one of ammonia, sodium hydroxide, potassium hydroxide, urea, and ethylenediamine.

[0063] According to the present invention, there is no particular limitation on the method for preparing the solution containing the mesoporous template agent and the base. Preferably, the solution containing the mesoporous template agent and the base is obtained by mixing the mesoporous template agent with an aqueous solution of the base.

[0064] According to the present invention, the aqueous solution of the base can be obtained by purchase or can be prepared by itself according to the mass concentration.

[0065] According to the present invention, preferably, the mass fraction of the aqueous solution of the base is 20 - 30 wt%.

[0066] According to the present invention, in order to further promote the formation of a mesoporous structure in the titanium silicalite molecular sieve. Preferably, the crystallization temperature in step (1) is higher than the crystallization temperature in step (2), and further preferably, the crystallization temperature in step (1) is 40 - 50 °C higher than the crystallization temperature in step (2).

[0067] According to the present invention, when using quaternary ammonium salts with different alkyl chain lengths as the mesoporous template agent, titanium silicalite molecular sieves containing mesopores with different pore sizes can be obtained.

[0068] The third aspect of the present invention provides the titanium silicalite molecular sieve prepared by the above method.

[0069] The fourth aspect of the present invention provides the application of the above titanium silicalite molecular sieve in the liquid-phase epoxidation reaction of propylene.

[0070] According to the present invention, preferably, the conditions for the liquid-phase epoxidation reaction of propylene using the titanium silicalite molecular sieve include: the temperature is 30 - 50 °C, the pressure is 2 - 3 MPa, relative to 100 g of propylene, the amount of the titanium silicalite molecular sieve used is 4 - 10 g, and the molar ratio of hydrogen peroxide to propylene is 1:1 - 3.

[0071] According to the present invention, the form of addition of the hydrogen peroxide is not particularly limited, and hydrogen peroxide can be directly added, or an aqueous hydrogen peroxide solution can be added. Preferably, the mass fraction of the aqueous hydrogen peroxide solution is 20-40% by weight.

[0072] According to the present invention, preferably, the propylene epoxidation reaction uses methanol as a solvent. Further preferably, the molar ratio of hydrogen peroxide to methanol is 1:1-3.

[0073] The present invention will be described in detail below through examples. In the following examples,

[0074] "Room temperature" refers to "25°C".

[0075] The pore structure and specific surface area of the silico-titanium molecular sieve were characterized by BET. The instrument used for the BET test was the ASAP2020 model of Micromeritics, USA. The pore structure test method was as follows: A certain amount of sample, about 0.10 g, was degassed at 200°C and 1 mmHg vacuum for 6 hours, and the nitrogen adsorption and desorption curves of the sample were measured in liquid nitrogen (-196°C); then the pore size and distribution of the mesopores in the pore size distribution were calculated by NLDFT. The specific surface area test method was as follows: A certain amount of sample, about 0.10 g, was evacuated at 30°C for 10 h, and the vacuum degree was <6.67×10 2 Pa, and then the adsorption line data in the BET equation was used to calculate the specific surface area of the sample.

[0076] The crystal structure of the silico-titanium molecular sieve was characterized by XRD. The instrument used for the XRD test was the D / Max2550VB / PC type X-ray diffractometer of Rigaku Corporation. The test conditions were: the incident light source was a Cu target, K α rays, the tube current was 100 mA, the tube voltage was 40 kV, and the scanning rate was 12 scanning rate 40; before the test, the powder sample was pressed into a sheet on a sample holder and then tested.

[0077] The internal mesopore distribution of the silico-titanium molecular sieve was characterized by TEM. The instrument used for the TEM test was the JEM 2100F model of JEOL, Japan. The test conditions were: the acceleration voltage was 200 kV, the point resolution of the instrument was 0.23 nm, and the line resolution was 0.14 nm. Before the test, the sample was crushed and ground to 300 mesh and placed in ethanol to form a suspension. After ultrasonic dispersion at room temperature for 5-10 min, the upper suspension was sucked with a dropper and dropped on a copper grid, and after the ethanol evaporated, HRTEM (high-resolution transmission electron microscopy) characterization was carried out.

[0078] The morphology and particle size of the silico-titanium molecular sieve were characterized by SEM. The instrument used for the SEM test was the JSM360LVJOEL model, and the test voltage was 20 kV.

[0079] The carbon deposition content of the catalyst was tested by thermogravimetry (TGA), and the instrument used was a Perkin-Elmer Pyris1 thermogravimetric analyzer from Perkin-Elmer Company in the United States.

[0080] The coordination state of titanium in the titanium silicalite molecular sieve was characterized by an ultraviolet-visible spectrophotometer. The instrument model used was a Shimadzu UV-2700 ultraviolet spectrophotometer in Japan. The test conditions were: the detection wavelength range λ = 200 - 700 nm, and BaSO 4 was used as a reference. The ultraviolet-visible diffuse reflectance spectrum discriminates the coordination state of heteroatoms by comparing the transfer absorption of framework heteroatoms and their corresponding oxide electrons. Among them, the characteristic peak at a wavelength of 220 nm corresponds to tetracoordinated framework Ti, and the characteristic peak at a wavelength of 330 nm corresponds to non-framework Ti.

[0081] The mass fraction of ammonia water was 25 wt%.

[0082] The titanium-silicon ratio in the titanium silicalite molecular sieve was measured by an elemental analyzer (ICP).

[0083] Example 1

[0084] (1) Take 3.6 g of isopropanol and 0.368 g of tetrabutyl titanate and mix them evenly to obtain solution A. Take 27.9 g of tetrapropylammonium hydroxide and place it in a beaker. Add 22.58 g of tetraethyl orthosilicate and 6.93 g of H 2 O, stir for 30 min to obtain solution B. Add solution B to solution A at a rate of 0.01 mL / min, stir for 3 h to obtain a mixed solution C, then age at room temperature for 3 h, and then heat up to 90 °C at a heating rate of 5 °C / min. Remove the alcohol at 90 °C for 12 h until a transparent gel liquid is obtained. Put the transparent gel liquid into an autoclave, crystallize at 170 °C for 36 h, take it out and wash it with water 3 times, then dry it at 100 °C for 15 h, and then calcine it in an air atmosphere at 550 °C for 6 h to obtain titanium silicalite molecular sieve TS-1 seeds.

[0085] (2) Take 1.4 g of cetyltrimethylammonium bromide, add it to 260 g of ammonia water and stir for 30 min to obtain solution D. Put 4 g of titanium silicalite molecular sieve TS-1 seeds into solution D and stir for 3 h. Put solution D and the seeds into an autoclave, crystallize at 130 °C for 48 h, take it out and wash it with water 5 times, then dry it at 100 °C for 15 h, and then calcine it in an air atmosphere at 550 °C for 6 h to obtain micro-mesoporous composite titanium silicalite molecular sieve TS-1. The test results are shown in Table 1 and Table 2.

[0086] The morphology and particle size of the micro-mesoporous composite titanium silicalite molecular sieve TS-1 prepared in Example 1 were observed by SEM, and the results are as follows Figure 1 andFigure 2 As shown, it can be seen from the figure that the morphology of the micro-mesoporous composite silico-titanium molecular sieve TS-1 is blackberry-like, with small protrusions covering the surface, and the particle size is between 80 - 150 nm.

[0087] The internal mesopore distribution of the micro-mesoporous composite silico-titanium molecular sieve TS-1 prepared in Example 1 was observed by TEM, and the results are as Figure 3 and Figure 4 shown. It can be seen from the figure that the micro-mesoporous composite silico-titanium molecular sieve TS-1 has mesopores with pore diameters in the range of 10 - 45 nm inside the crystal.

[0088] The crystal form of the micro-mesoporous composite silico-titanium molecular sieve TS-1 prepared in Example 1 was observed by XRD, and the results are as Figure 5 shown. It can be seen from the figure that characteristic diffraction peaks of the MFI structure appear near 2θ of 7.96°, 8.83°, 23.18°, 23.99°, and 24.45°, proving that the silico-titanium molecular sieve prepared in Example 1 has the MFI structure.

[0089] The existence form of titanium in the micro-mesoporous composite silico-titanium molecular sieve TS-1 prepared in Example 1 was observed by UV-Vis, and the results are as Figure 6 shown. It can be seen from the figure that only the characteristic peak with a wavelength of 220 nm appears, indicating that all the titanium in the micro-mesoporous composite silico-titanium molecular sieve TS-1 exists in the form of framework Ti.

[0090] Example 2

[0091] (1) Mix 3.6 g of isopropanol and 0.368 g of tetrabutyl titanate evenly to obtain solution A. Place 32.65 g of tetrapropylammonium hydroxide in a beaker, add 30.21 g of tetraethyl orthosilicate and 9.05 g of H 2 O, stir for 30 min to obtain solution B, add solution B to A at a rate of 0.01 mL / min, stir for 3 h to obtain a mixed solution C. Age at room temperature for 7 h, then heat up to 90 °C at a heating rate of 6 °C / min, and remove alcohol at 90 °C for 12 h until a transparent gel liquid is obtained. Put the transparent gel liquid into an autoclave, crystallize at 160 °C for 50 h, take it out and wash it with water 3 times, then dry it at 100 °C for 15 h, and then calcine it in an air atmosphere at 500 °C for 8 h to obtain the silico-titanium molecular sieve TS-1 seed crystal.

[0092] (2) 1.6 g of cetyltrimethylammonium bromide was taken and added to 300 g of ammonia water, and after stirring for 30 min, solution D was obtained. 4 g of titanium silicalite TS-1 seeds were put into solution D and stirred for 3 h. Solution D and the seeds were placed in an autoclave and crystallized at 120 °C for 60 h, taken out and washed with water 5 times, then dried at 100 °C for 15 h, and calcined in an air atmosphere at 500 °C for 8 h to obtain micro-mesoporous composite titanium silicalite TS-1. The test results are shown in Tables 1 and 2. The XRD characterization results are similar to Figure 5 and are not shown here again.

[0093] Example 3

[0094] (1) 3.6 g of isopropanol and 0.368 g of tetrabutyl titanate were mixed evenly to obtain solution A. 37.25 g of tetrapropylammonium hydroxide was placed in a beaker, 33.79 g of tetraethyl orthosilicate and 10.12 g of H 2 O were added, and after stirring for 30 min, solution B was obtained. Solution B was added to A at a rate of 0.01 mL / min and stirred for 3 h to obtain a mixed solution C. It was aged at room temperature for 10 h, then heated to 90 °C at a heating rate of 6 °C / min, and the alcohol was removed at 90 °C for 12 h until a transparent gel liquid was obtained. The transparent gel liquid was placed in an autoclave and crystallized at 180 °C for 30 h, taken out and washed with water 3 times, then dried at 100 °C for 15 h, and calcined in an air atmosphere at 580 °C for 5 h to obtain titanium silicalite TS-1 seeds.

[0095] (2) 1.2 g of cetyltrimethylammonium bromide was taken and added to 340 g of ammonia water, and after stirring for 30 min, solution D was obtained. 4 g of titanium silicalite TS-1 seeds were put into solution D and stirred for 3 h. Solution D and the seeds were placed in an autoclave and crystallized at 140 °C for 30 h, taken out and washed with water 5 times, then dried at 100 °C for 15 h, and calcined in an air atmosphere at 580 °C for 5 h to obtain micro-mesoporous composite titanium silicalite TS-1. The test results are shown in Tables 1 and 2. The XRD characterization results are similar to Figure 5 and are not shown here again.

[0096] Example 4

[0097] (1) 3.6 g of isopropanol and 0.368 g of tetrabutyl titanate were mixed evenly to obtain solution A. 22 g of tetrapropylammonium hydroxide was placed in a beaker, 18.04 g of tetraethyl orthosilicate and 5.42 g of H 2O, stir for 30 min to obtain solution B. Add solution B to A at a rate of 0.01 mL / min, stir for 3 h to obtain a mixed solution C. Age at room temperature for 24 h, then heat up to 90 °C at a heating rate of 6 °C / min, and remove alcohol at 90 °C for 12 h until a transparent gel liquid is obtained. Put the transparent gel liquid into an autoclave, crystallize at 150 °C for 72 h, take it out, wash it with water 3 times, then dry it at 100 °C for 15 h, and then calcine it in an air atmosphere at 600 °C for 3 h to obtain the TS-1 zeolite seed crystal.

[0098] (2) Take 0.4 g of cetyltrimethylammonium bromide, add it to 400 g of ammonia water and stir for 30 min to obtain solution D. Put 4 g of the TS-1 zeolite seed crystal into solution D and stir for 3 h. Put solution D and the seed crystal into an autoclave, crystallize at 100 °C for 72 h, take it out, wash it with water 5 times, then dry it at 100 °C for 15 h, and then calcine it in an air atmosphere at 600 °C for 5 h to obtain the micro-mesoporous composite TS-1 zeolite. The test results are shown in Table 1 and Table 2. The XRD characterization results are similar to Figure 5 those, which are not shown here.

[0099] Example 5

[0100] (1) Mix 3.6 g of isopropanol and 0.368 g of tetrabutyl titanate evenly to obtain solution A. Put 43.96 g of tetrapropylammonium hydroxide in a beaker, add 45.05 g of tetraethyl orthosilicate and 13.51 g of H 2 O, stir for 30 min to obtain solution B. Add solution B to A at a rate of 0.01 mL / min, stir for 3 h to obtain a mixed solution C. Age at room temperature for 1 h, then heat up to 90 °C at a heating rate of 6 °C / min, and remove alcohol at 90 °C for 12 h until a transparent gel liquid is obtained. Put the transparent gel liquid into an autoclave, crystallize at 200 °C for 24 h, take it out, wash it with water 3 times, then dry it at 100 °C for 15 h, and then calcine it in an air atmosphere at 480 °C for 8 h to obtain the TS-1 zeolite seed crystal.

[0101] (2) Take 2 g of cetyltrimethylammonium bromide, add it to 200 g of ammonia water and stir for 30 min to obtain solution D. Put 4 g of the TS-1 zeolite seed crystal into solution D and stir for 3 h. Put solution D and the seed crystal into an autoclave, crystallize at 150 °C for 24 h, take it out, wash it with water 5 times, then dry it at 100 °C for 15 h, and then calcine it in an air atmosphere at 480 °C for 8 h to obtain the micro-mesoporous composite TS-1 zeolite. The test results are shown in Table 1 and Table 2. The XRD characterization results are similar to Figure 5 those, which are not shown here.

[0102] Example 6

[0103] The molecular sieve was prepared according to the method of Example 1, except that in step (2), the amount of cetyltrimethylammonium bromide was 4 g and the amount of ammonia water was 500 g. The test results are shown in Table 1 and Table 2.

[0104] Example 7

[0105] The molecular sieve was prepared according to the method of Example 1, except that in step (2), the crystallization conditions included: temperature was 250 °C and time was 12 h. The test results are shown in Table 1 and Table 2. The internal pore distribution of the molecular sieve prepared in Example 7 was observed by TEM, and the results are as Figure 9 shown. It can be seen from the figure that there are no obvious mesopores in the molecular sieve.

[0106] Example 8

[0107] The molecular sieve was prepared according to the method of Example 1, except that in step (2), tetrapropylammonium hydroxide was used to replace cetyltrimethylammonium bromide. The test results are shown in Table 1 and Table 2. The internal pore distribution of the molecular sieve prepared in Example 8 was observed by TEM, and the results are as Figure 10 shown. It can be seen from the figure that hollow molecular sieves appear in the molecular sieve.

[0108] Example 9

[0109] The molecular sieve was prepared according to the method of Example 1, except that in step (2), ammonia water was replaced by calcium hydroxide. The test results are shown in Table 1 and Table 2.

[0110] Example 10

[0111] The molecular sieve was prepared according to the method of Example 1, except that in step (2), dodecyltrimethylammonium bromide was used to replace cetyltrimethylammonium bromide. The test results are shown in Table 1 and Table 2. The internal pore distribution of the molecular sieve prepared in Example 10 was observed by TEM, and the results are as Figure 12 shown. It can be seen from the figure that the micro-mesoporous composite silicotitanium molecular sieve TS-1 crystals have mesopores with pore diameters in the range of 20 - 30 nm inside.

[0112] Example 11

[0113] The molecular sieve was prepared according to the method of Example 1, except that in step (2), octyltrimethylammonium bromide was used to replace cetyltrimethylammonium bromide. The test results are shown in Table 1 and Table 2. The internal pore distribution of the molecular sieve prepared in Example 11 was observed by TEM, and the results are as Figure 13 shown. It can be seen from the figure that the micro-mesoporous composite silicotitanium molecular sieve TS-1 crystals have mesopores with pore diameters in the range of 5 - 10 nm inside.

[0114] Comparative Example 1

[0115] The titanium silicalite TS-1 was synthesized by the conventional method described in the prior art (zeolites, 1992, vol.12943-12950). The specific process was as follows: First, 2 g of Tween 20 was mixed with 28.6 g of water and 22.6 g of the template tetrapropylammonium hydroxide and stirred for 1 h until it became clear; 40.5 g of the silicon source tetraethyl orthosilicate was slowly added to the above solution and stirred for 1 h until the solution became clear; the solution obtained by fully mixing 0.66 g of tetrabutyl titanate and 3.6 g of isopropanol was slowly added dropwise to the above mixed solution and stirred for 2 h, and then the alcohol was removed at 80 °C for 6 h. Finally, the alcohol-removed mixture was transferred into a crystallization kettle and crystallized at 180 °C for 40 h. After the crystallization, the sample was taken out, centrifuged, washed, and calcined in a muffle furnace at 550 °C for 6 h.

[0116] The morphology and particle size of the silicon-titanium molecular sieve prepared in Comparative Example 1 were observed by SEM, and the results were as Figure 7 shown. It can be seen from the figure that the morphology of the silicon-titanium molecular sieve is blackberry-like, the surface is covered with small protrusions, and the particle size is between 100-500 nm.

[0117] The internal structure of the silicon-titanium molecular sieve TS-1 prepared in Comparative Example 1 was observed by TEM, and the results were as Figure 8 shown. It can be seen from the figure that the silicon-titanium molecular sieve does not have a mesoporous structure.

[0118] Comparative Example 2

[0119] The molecular sieve was prepared according to the method of Example 1, except that the ammonia water in step (2) was replaced with hydrochloric acid (mass fraction 25 wt%). The test results are shown in Table 1 and Table 2. Since the hydrochloric acid dissolved all the seeds of the silicon-titanium molecular sieve TS-1, the generated molecular sieve did not have a crystal form.

[0120] Comparative Example 3

[0121] The molecular sieve was prepared according to the method of Example 1, except that the one-pot method was used to prepare the molecular sieve. 3.6 g of isopropanol, 0.368 g of tetrabutyl titanate, 27.9 g of tetrapropylammonium hydroxide, 22.58 g of tetraethyl orthosilicate, 6.9 g of H 2 O, 1.4 g of cetyltrimethylammonium bromide, and 260 g of ammonia water were directly mixed, aged at room temperature for 3 h, then heated to 90 °C at a heating rate of 5 °C / min, and the alcohol was removed at 90 °C for 12 h until a transparent gel liquid was obtained. The transparent gel liquid was placed in an autoclave and crystallized at 130 °C for 48 h. After taking out, washing, and drying, it was calcined in an air atmosphere at 550 °C for 6 h to obtain a silicon-titanium molecular sieve. The test results are shown in Table 1 and Table 2. The internal pore distribution of the molecular sieve prepared in Comparative Example 3 was observed by TEM, and the results were as Figure 11As shown, it can be seen from the figure that there is no mesoporous structure in the molecular sieve.

[0122] Table 1

[0123]

[0124]

[0125] Table 2

[0126]

[0127] Test Example 1

[0128] The silico-titanium molecular sieves prepared in the above examples and comparative examples were used in the propylene epoxidation reaction. The reaction conditions for propylene epoxidation included: in a batch reactor, the temperature was 40 °C, the pressure was 3 MPa, relative to 100 g of propylene, the mass of the silico-titanium molecular sieve was 4 g, the molar ratio of hydrogen peroxide to propylene was 1:2, the molar ratio of hydrogen peroxide to methanol was 1:2, and hydrogen peroxide was added in the form of an aqueous hydrogen peroxide solution (mass fraction 30 wt%). The reaction products were monitored and analyzed using a gas chromatograph. The results are shown in Table 3.

[0129] The propylene conversion rate and the selectivity of propylene oxide in Table 3 are the average values during the reaction time.

[0130] Table 3

[0131] Reaction time Propylene conversion rate Selectivity of propylene oxide Example 1 1000h 99.3％ 99.5％ Example 2 1000h 99％ 99.1％ Example 3 1000h 98.8％ 98.2％ Example 4 604h 86.5％ 85％ Example 5 568h 80.3％ 78％ Example 6 500h 79.3％ 67％ Example 7 30h 73.2％ 65％ Example 8 389h 70.9％ 62％ Example 9 1h 20％ 50％ Example 10 652h 85.1％ 83.7％ Example 11 584h 83.4％ 80.6％ Comparative example 1 10h 50％ 89％ Comparative example 2 1h 5％ 36％ Comparative example 3 8h 63％ 81％

[0132] From the results in Table 3, it can be seen that the micro-mesoporous composite silico-titanium molecular sieve TS-1 prepared by the method of the present invention has a high conversion rate, and still has a high conversion rate during a long reaction time, indicating that the catalyst has a long service life.

[0133] Test Example 2

[0134] The carbon deposition amount of the catalyst after the reaction in Test Example 1 was characterized. The catalyst after the reaction was heated at a rate of 5 °C / min in a carrier gas (nitrogen) at 50 mL / min and the carbon deposition amount was analyzed. The results are shown in Table 4.

[0135] Table 4

[0136]

[0137]

[0138] From the results in Table 4, it can be seen that the micro-mesoporous composite silico-titanium molecular sieve TS-1 prepared by the method of the present invention has a low carbon deposition content, indicating that the catalyst has a long service life.

[0139] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing titanium silicalite molecular sieve, characterized in that, the method comprises the following steps: (1) Providing titanium silicalite molecular sieve seeds, wherein, based on the total amount of titanium element in the titanium silicalite molecular sieve seeds, the content of non-framework titanium is 70 - 80 wt%; (2) Mixing the titanium silicalite molecular sieve seeds with a solution containing a mesoporous template agent and an alkali, and then performing crystallization and calcination to obtain a titanium silicalite molecular sieve; Wherein, in step (1), the preparation method of the titanium silicalite molecular sieve seeds comprises: contacting a titanium source, a silicon source and a microporous template agent, and then performing aging, crystallization and calcination to obtain titanium silicalite molecular sieve seeds; the molar ratio of the titanium source, the silicon source and the microporous template agent is 1:40 - 200:100 - 200, the dosage of the titanium source is calculated as Ti, and the dosage of the silicon source is calculated as Si; the conditions of the aging include: the aging temperature is 15 - 40 °C, and the aging time is 1 - 24 h; In step (2), the mass ratio of the titanium silicalite molecular sieve seeds, the mesoporous template agent and the alkali is 1:0.1 - 0.5:50 - 100; The particle size of the titanium silicalite molecular sieve is 80 - 150 nm, the specific surface area is 320 - 500 m 2 / g, the pore volume of the mesopores is 0.18 - 0.35 cm 3 / g, and the pore volume of the micropores is 0.15 - 0.21 cm 3 / g; the titanium - silicon ratio in the titanium silicalite molecular sieve is 1:50 - 75.

2. The method according to claim 1, wherein, in step (1), the conditions of the crystallization include: the crystallization temperature is 150 - 200 °C, and the crystallization time is 24 - 72 h.

3. The method according to claim 1, wherein, in step (1), the conditions of the calcination include: the calcination temperature is 480 - 600 °C, and the calcination time is 3 - 8 h.

4. The method according to claim 1, wherein, in step (2), the conditions of the crystallization include: the crystallization temperature is 100 - 150 °C, and the crystallization time is 24 - 72 h.

5. The method according to claim 1, wherein, in step (2), the conditions of the calcination include: the calcination temperature is 480 - 600 °C, and the calcination time is 5 - 10 h.

6. The method according to claim 1, wherein, the silicon source is silicate ester; and / or, the titanium source is a titanium source containing an alkoxy group; and / or, the microporous template agent is at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

7. The method according to claim 1, wherein, the silicon source is at least one of tetraethyl orthosilicate, methyl orthosilicate and tetraethyl orthosilicate; and / or, the titanium source is tetrabutyl titanate.

8. The method according to claim 1, wherein, the mesoporous template agent is a quaternary ammonium salt; and / or, the alkali is at least one of ammonia, alkali metal hydroxide and organic amine.

9. The method according to claim 1, wherein, the mesoporous template agent is at least one of cetyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, decyltrimethylammonium bromide and octyltrimethylammonium bromide.

10. The method according to claim 1, wherein, the alkali is at least one of ammonia, sodium hydroxide, potassium hydroxide, urea and ethylenediamine.

11. Titanium silicalite molecular sieve prepared by the method according to any one of claims 1 - 10.

12. Application of the titanium silicalite molecular sieve according to claim 11 in the liquid-phase epoxidation reaction of propylene.

13. According to the application described in claim 12, Among them, the conditions for the liquid-phase epoxidation reaction of propylene with the titanium silicalite include: the temperature is 30-50 °C, the pressure is 2-3 MPa, the amount of the titanium silicalite is 4-10 g relative to 100 g of propylene, and the molar ratio of hydrogen peroxide to propylene is 1:1-3.

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