CN107032366B - Method for preparing titanium silicalite TS-1 with high framework titanium content - Google Patents

Method for preparing titanium silicalite TS-1 with high framework titanium content Download PDF

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CN107032366B
CN107032366B CN201610651670.9A CN201610651670A CN107032366B CN 107032366 B CN107032366 B CN 107032366B CN 201610651670 A CN201610651670 A CN 201610651670A CN 107032366 B CN107032366 B CN 107032366B
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starch
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CN107032366A (en
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左轶
郭新闻
刘民
张�廷
刘准
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Dalian University of Technology
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    • C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
    • C01B39/06—Preparation of isomorphous zeolites characterised by measures to replace the aluminium or silicon atoms in the lattice framework by atoms of other elements, i.e. by direct or secondary synthesis
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Abstract

The invention provides a method for preparing a titanium silicalite TS-1 with high framework titanium content, which comprises the following steps: mixing a silicon source and a titanium source in proportion, and adding a quaternary ammonium alkali aqueous solution to obtain a mixed solution; hydrolyzing the mixed solution to remove alcohol, adding a starch solution, and crystallizing to obtain a crystallized product; and drying and roasting the crystallized product to obtain the titanium silicalite TS-1 with high framework titanium content. According to the method, a starch solution is added in the synthesis process, and a silicon source and a titanium source are bridged by using a large amount of hydroxyl contained in the starch, so that the silicon source and the titanium source are more easily combined, and more titanium can enter a TS-1 framework. The titanium-silicon molecular sieve prepared by the method has high framework titanium content, almost does not contain non-framework titanium, and the mother solution can be recycled.

Description

Method for preparing titanium silicalite TS-1 with high framework titanium content
Technical Field
The invention relates to the technical field of catalyst synthesis, in particular to a synthesis method of a titanium silicalite TS-1 with high framework titanium content.
Background
Since the synthesis of a titanium silicalite TS-1 was first reported in 1983, an oxidation system consisting of the titanium silicalite TS-1 and hydrogen peroxide shows high activity on olefin epoxidation, aromatic hydrocarbon hydroxylation, ketone ammoxidation and other reactions, and a byproduct is water, which belongs to an environment-friendly process, so that the titanium silicalite TS-1 attracts wide attention.
The main catalytic oxidation active center on the titanium-silicon molecular sieve is four-coordination framework titanium, however, the content of the titanium species cannot be increased at will because lattice expansion is caused when the titanium enters, so that more titanium is inhibited from entering the framework, and the titanium species which do not enter the framework can form six-coordination non-framework titanium or anatase titanium dioxide. Hexadentate non-framework titanium is generally considered inert to catalytic oxidation, whereas anatase titanium dioxide tends to cause H2O2Ineffective decomposition into O2This not only reduces H2O2The effective utilization rate of the method and the safety of the production process can be seriously damaged. Therefore, researchers always try to synthesize the titanium-silicon molecular sieveThe figure synthesizes a molecular sieve with high framework titanium content and no non-framework titanium and anatase titanium dioxide.
The synthesis method of the titanium silicalite molecular sieve disclosed by the U.S. Pat. No. 4,430,01 is characterized in that tetraethoxysilane is used as a silicon source, tetraethyl titanate is used as a titanium source, tetrapropylammonium hydroxide (TPAOH) is used as a template agent, and crystallization is carried out for 6-30 days in a hydrothermal system, wherein the method is generally called as a classical method. The preferred molar composition of the raw materials is as follows:
SiO2:TiO2:TPAOH:H2O＝1:(0.01～0.025):(0.4～1.0):(20～200)
from the above composition, it can be seen that in order to reduce the generation of non-framework titanium, the titanium content in the raw material is low, which only can obtain a molecular sieve with low framework titanium content, and is not favorable for catalytic oxidation reaction. Second, the synthesis process needs to be carried out in a moisture-tight glove box to prevent excessively rapid hydrolysis of the titanium source.
For many years, researchers have made various improvements to the synthesis of TS-1, including the replacement of the silicon source, titanium source, and templating agent. It is generally believed that the hydrolysis rates of the silicon source and the titanium source are greatly different, and the hydrolysis rate of the titanium source is much greater than that of the silicon source, which causes the titanium to be rapidly hydrolyzed before entering the framework and form anatase titanium dioxide, which is unfavorable for the catalytic oxidation reaction. The matching of the two hydrolysis rates can enable more titanium to enter the framework to form the titanium active center of the framework. Therefore, researchers hydrolyze the silicon source and the titanium source respectively, dissolve the titanium source in alcohol to form a complex, inhibit the over-rapid hydrolysis of titanium, and mix and crystallize the two after completing the hydrolysis process at the same time. Such as Chinese patents CN1089274, CN1234458, and the journal of catalysis (2001,22(6): 513-514).
According to the literature (J.Am.chem.Soc.2008,130,10150-10164), the alkalinity of the system can be reduced by adding different ammonium salts into the synthesis system, so that the crystallization rate of TS-1 is slowed, the crystallization mechanism is changed, more titanium can enter the molecular sieve framework, and the ammonium salts have many difficulties in practical operation due to the characteristics of odor, easy decomposition and the like. In addition, the mother liquor synthesized by the molecular sieve contains ammonium salt with an undeterminable content, which causes great obstacles to the post-treatment and recycling of the mother liquor.
Disclosure of Invention
The invention aims to solve the problems that the content of framework titanium in the titanium silicalite TS-1 in the prior art is low, the generation of non-framework titanium in the hydrothermal synthesis process is difficult to avoid, and the like.
In order to solve the problems, the invention provides a method for preparing a titanium silicalite TS-1 with high framework titanium content, which comprises the following steps:
s1, mixing a silicon source and a titanium source in proportion, and adding 20-40 wt% of quaternary ammonium alkaline water solution to obtain a mixed solution;
the molar ratio of each substance in the mixed solution is as follows:
SiO2:TiO2quaternary ammonium base H2O＝1:(0.0251～0.0333):(0.0501～0.4499):(20.01～54.99)；
Further optimizing, the molar ratio of each substance in the mixed solution is as follows:
SiO2:TiO2quaternary ammonium base H2O＝1:(0.0251～0.0333):(0.0501～0.3999):(20.01～54.99)；
In a preferable mode, the silicon source in step S1 is at least one of methyl orthosilicate, ethyl orthosilicate, silica sol, and white carbon black; the titanium source is at least one of tetraethyl titanate, tetrabutyl titanate, isopropyl titanate, titanium trichloride and titanium tetrachloride; the quaternary ammonium hydroxide is at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.
S2, hydrolyzing the mixed solution obtained in the step S1 at 30-60 ℃ for 0-5 h, and removing alcohol at 90 ℃ for 0-1 h;
s3, adding a starch solution with the concentration of 0.1-20 wt% into the product obtained in the step S2, uniformly stirring, filling into a crystallization kettle, and crystallizing at the temperature of 140-170 ℃ for 24-72 hours to obtain a crystallized product;
the starch in the added starch solution is one or a mixture of amylose and amylopectin; amylose is preferred. The mass of the starch and SiO contained in the silicon source added in step S12The mass ratio of (A) to (B) is 0.0101-1.9999: 1(ii) a Further optimization, the quality of starch in the added starch solution is equal to that of the SiO added in step S12The mass ratio of (1) to (0.301-1.001) is 1.
S4, drying the crystallized product obtained in the step S3 at 80-120 ℃ for 3-8 hours; roasting for 3-6 h at 500-600 ℃ to obtain the titanium silicalite TS-1 with high framework titanium content.
Preferably, when the silicon source and the titanium source are both non-ester compounds, the hydrolysis time and the alcohol removal time in step S2 in step S2 are both 0 h; namely, hydrolysis treatment is not needed, so alcohol removal treatment is not needed; in other cases, it is desirable to have adequate hydrolysis and alcohol removal times.
Compared with the prior art, the synthesis method of the titanium silicalite molecular sieve provided by the invention has the following advantages:
1. the method of the invention is characterized in that soluble starch is added in the synthesis process, and a silicon source and a titanium source are bridged by utilizing a large amount of hydroxyl contained in the starch, so that the silicon source and the titanium source are more easily combined, and more titanium can enter a TS-1 framework. The titanium silicalite TS-1 prepared by the invention has high content of active center framework titanium and hardly contains non-framework titanium, so that the titanium silicalite prepared by the invention has excellent catalytic activity, main product selectivity and H-shaped catalyst for selective oxidation reactions such as alkane selective oxidation, olefin epoxidation, aromatic hydrocarbon hydroxylation, ketone/aldehyde ammoxidation and the like2O2The effective utilization rate.
2. The titanium silicalite TS-1 prepared by the invention adopts cheap and edible starch to replace inorganic ammonium salt and the like as additives, is nontoxic and harmless, and reduces the synthesis cost of the TS-1; moreover, the starch has stable structure under the alkaline and hydrothermal treatment conditions, and basically does not have chemical change in the crystallization process of the molecular sieve, and the alkalinity of the mother liquor is also basically kept unchanged, so that the recycling of the mother liquor is not adversely affected. On the other hand, the recycling of the mother liquor can further control the production cost of TS-1, and meanwhile, the cost input for avoiding the harm of the mother liquor discharge to the environment is reduced, and a foundation is laid for green chemical production.
3. All the methods of the present invention adoptContaining Na+、K+、Mg2+And the TS-1 is synthesized by the raw materials of alkali metal or alkaline earth metal ions, so that titanium can enter a framework more favorably, the generation of non-framework titanium is inhibited, and the high catalytic activity TS-1 with high framework titanium content and low non-framework titanium content is obtained. Meanwhile, the ion exchange step required by removing the ions can be omitted, and the preparation period is shortened.
4. The method has simple and convenient operation, does not need to slow down the hydrolysis rate of the titanium source intentionally in the synthesis process, and does not need to introduce aging operation, so the synthesis energy consumption is lower, the preparation period is shorter, the yield of the molecular sieve in unit time is high, and the relative cost is lower.
In conclusion, the TS-1 framework prepared by the method provided by the invention has high titanium content, almost does not contain non-framework titanium, and has excellent catalytic performance on selective oxidation reactions such as alkane selective oxidation, olefin epoxidation, aromatic hydrocarbon hydroxylation, ketone/aldehyde ammoxidation and the like. Compared with the existing catalyst preparation process, the method provided by the invention has the advantages that no additional equipment investment is added, the method can be directly applied to the existing titanium silicalite molecular sieve preparation process, and the industrial production can be conveniently and rapidly realized; the mother liquor in the preparation process of the method can be recycled, so that the production cost is reduced, and the environmental protection cost is saved.
Drawings
FIG. 1 is a scanning electron micrograph of a titanium silicalite TS-1-B prepared in comparative example 2;
FIG. 2 is a scanning electron micrograph of a titanium silicalite TS-1-D prepared in comparative example 4;
FIG. 3 is a SEM photograph of the Ti-Si molecular sieve TS-1-E prepared in example 1;
FIG. 4 is a SEM photograph of the Ti-Si molecular sieve TS-1-F prepared in example 2;
FIG. 5 is a graph of the diffuse reflectance of UV and visible light of the Ti-Si molecular sieve prepared in each comparative example;
FIG. 6 is an X-ray diffraction pattern of the titanium silicalite molecular sieves prepared in the respective comparative examples;
Detailed Description
Comparative example 1
According to the method provided by the patent US4410501, 45.5g of ethyl orthosilicate is added into a jacketed three-neck flask, 1.5g of tetraethyl titanate is added under the protection of nitrogen, 80g of 25% tetrapropyl ammonium hydroxide solution is added, the mixture is stirred for 1h at normal temperature, and then the temperature is raised to 80 ℃, and alcohol is removed for 5 h. And (3) supplementing the volume of the synthesized gel to 150mL by using deionized water, filling the obtained solution into a crystallization kettle, crystallizing for 10d at 175 ℃, washing and drying a crystallized product, and roasting for 6h at 550 ℃ to obtain TS-1, wherein the TS-1 is numbered as TS-1-A.
Comparative example 2
According to the method provided by patent CN1401569, 50g of tetraethoxysilane is added into a three-neck flask with a jacket, 45g of TPAOH aqueous solution and 40g of water are added under magnetic stirring at 25 ℃, and the tetraethoxysilane is hydrolyzed for 90 min; adding 15g of isopropanol into 2g of tetrabutyl titanate, adding 17g of TPAOH solution and 20g of water in sequence under stirring, and hydrolyzing at room temperature for 30min to obtain tetrabutyl titanate hydrolysate. Mixing silicon ester and titanium ester hydrolysate, removing alcohol at 85 deg.C for 6h, placing the obtained clear solution into a crystallization kettle, crystallizing at 170 deg.C for 24h, washing and drying the crystallized product, and calcining at 540 deg.C for 5h to obtain TS-1, which is numbered TS-1-B.
FIG. 1 is a scanning electron micrograph of the titanium silicalite TS-1-B prepared in comparative example 2, which shows that the sample prepared in this comparative example is ellipsoidal, the particle size is very uneven, the distribution is wide, and the particle size is about 50-250 nm.
FIG. 5 is a graph of the diffuse reflectance of UV and visible light of the Ti-Si molecular sieve prepared in each comparative example; in the figure, the absorption peak at 210nm is the characteristic peak of framework titanium, the absorption peak at 260nm is the characteristic peak of six-coordination non-framework titanium, and the absorption peak at 330nm is anatase TiO2As can be seen from the figure, TS-1-B synthesized according to comparative example 2 contains a large amount of anatase TiO2The synthesis system is proved to be easy to produce anatase type TiO2。
FIG. 6 is an X-ray diffraction pattern of the titanium silicalite molecular sieves prepared in the respective comparative examples; as can be seen from the figure, the TS-1-B samples prepared by the comparative example have characteristic diffraction peaks of typical MFI structures at 7.8, 8.8, 23.0, 23.9 and 24.4 degrees.
Comparative example 3
29.6g of ethyl orthosilicate was charged in a jacketed three-necked flask, 1.60g of tetrabutyl titanate and 33.6g of 25 wt% tetrapropylammonium hydroxide solution were sequentially added, and the three-necked flask was immersed in a water bath at 50 ℃ to hydrolyze for 3 hours. Dealcoholizing the hydrolysate at 90 deg.c for 1 hr, adding 90mL deionized water, stirring, crystallizing at 170 deg.c for 60 hr in a crystallizing kettle, washing and drying the crystallized product, and roasting at 540 deg.c for 5 hr to obtain TS-1, which is numbered TS-1-C.
Comparative example 4
29.6g of ethyl orthosilicate was charged in a jacketed three-necked flask, 1.60g of tetrabutyl titanate and 33.6g of 25 wt% tetrapropylammonium hydroxide solution were sequentially added, and the three-necked flask was immersed in a water bath at 50 ℃ to hydrolyze for 3 hours. Removing alcohol from the hydrolysate at 90 deg.C for 1h, adding 100mL of 5 wt% ammonium carbonate aqueous solution, stirring, placing the mixed solution into a crystallization kettle, crystallizing at 170 deg.C for 60h, washing and drying the crystallized product, and calcining at 540 deg.C for 5h to obtain TS-1, which is numbered TS-1-D.
FIG. 2 is a SEM photograph of the Ti-Si molecular sieve TS-1-D prepared in comparative example 4. it can be seen that the morphology of the sample prepared in this example is very similar to that of FIG. 1, and the sample is ellipsoidal and has a particle size of about 200 nm.
As can be seen from FIG. 5, anatase type TiO in TS-1-D synthesized according to comparative example 42The amount of the ammonium carbonate is obviously reduced, which indicates that the ammonium carbonate can inhibit anatase type TiO2And (4) generating.
As can be seen from FIG. 6, TS-1-D synthesized according to comparative example 4 also has a typical MFI structure.
The following non-limiting examples are presented to enable those of ordinary skill in the art to more fully understand the present invention and are not intended to limit the invention in any way.
Example 1
20.3g of methyl orthosilicate was charged in a jacketed three-necked flask, 0.78g of tetraethyl titanate and 42.1g of a 25 wt% tetrapropylammonium hydroxide solution were sequentially added, and the three-necked flask was immersed in a water bath at 40 ℃ to hydrolyze for 1.5 hours. Removing alcohol from the hydrolysate at 90 ℃ for 1h, adding 180mL of starch solution with the concentration of 5 wt%, uniformly stirring, filling the mixed solution into a crystallization kettle, crystallizing at 160 ℃ for 48h, washing and drying the crystallized product, and roasting at 540 ℃ for 6h to obtain TS-1, wherein the TS-1 is numbered as TS-1-E.
FIG. 3 is a SEM photograph of the Ti-Si molecular sieve TS-1-E prepared in example 1. it can be seen that the sample prepared in this example has a shape very similar to that of FIG. 1, and is ellipsoidal with a particle size of about 200 nm.
As can be seen from FIG. 5, the sample TS-1-E synthesized according to example 1 contained only skeletal titanium, and did not contain hexacoordinated non-skeletal titanium and anatase TiO2。
As can be seen from FIG. 6, TS-1-E synthesized according to example 1 also has a typical MFI structure and the sample crystallinity is high, indicating that the addition of starch does not adversely affect the crystallization of TS-1.
Example 2
29.6g of ethyl orthosilicate was charged in a jacketed three-necked flask, 1.60g of tetrabutyl titanate and 33.6g of 25 wt% tetrapropylammonium hydroxide solution were sequentially added, and the three-necked flask was immersed in a water bath at 50 ℃ to hydrolyze for 3 hours. Removing alcohol from the hydrolysate at 90 deg.C for 1h, adding 100mL of starch solution with concentration of 5 wt%, stirring, placing the mixed solution into a crystallization kettle, crystallizing at 170 deg.C for 60h, washing and drying the crystallized product, and calcining at 540 deg.C for 5h to obtain TS-1, which is numbered TS-1-F.
FIG. 4 is a SEM photograph of the Ti-Si molecular sieve TS-1-F prepared in example 2. it can be seen that the sample prepared in this example has a shape very similar to that of FIG. 1, and is ellipsoidal with a particle size of about 200 nm.
As can be seen from FIG. 5, the sample TS-1-F synthesized according to example 2 contained only skeletal titanium, and did not contain hexacoordinated non-skeletal titanium and anatase TiO2。
As can be seen from FIG. 6, TS-1-F synthesized according to example 1 also has a typical MFI structure and the sample crystallinity is high, indicating that the addition of starch does not adversely affect the crystallization of TS-1.
Example 3
20.8g of ethyl orthosilicate was charged in a jacketed three-necked flask, 0.96g of tetrabutyl titanate and 9.8g of a 40 wt% tetraethylammonium hydroxide solution were sequentially added, and the three-necked flask was immersed in a water bath at 50 ℃ to hydrolyze for 1 hour. Dealcoholizing the hydrolysate at 90 deg.c for 0.5 hr, adding 8 wt% concentration starch solution in 90mL, stirring, crystallizing in a crystallizing kettle at 150 deg.c for 72 hr, washing and drying the crystallized product, and roasting at 540 deg.c for 3 hr to obtain TS-1, which is numbered TS-1-G.
As can be seen from FIG. 5, the sample TS-1-G synthesized according to example 3 contained only skeletal titanium, and did not contain hexacoordinated non-skeletal titanium and anatase TiO2。
As can be seen from FIG. 6, TS-1-G synthesized according to example 1 also had a typical MFI structure and the sample was very crystalline, indicating that the addition of starch did not adversely affect the crystallization of TS-1.
Example 4
30.0g of 25 wt% silica sol was put into a jacketed three-necked flask, 1.12g of tetrabutyl titanate, 4.5g of 20 wt% tetrapropylammonium hydroxide solution and 5.0g of 20 wt% tetrabutylammonium hydroxide solution were sequentially added, and the three-necked flask was immersed in a water bath at 50 ℃ to hydrolyze for 0.2 h. Dealcoholizing the hydrolysate at 90 deg.c for 0.5 hr, adding 5 wt% starch solution in 15mL, stirring, crystallizing at 170 deg.c for 48 hr, washing and drying the crystallized product, and roasting at 540 deg.c for 5 hr to obtain TS-1, TS-1-H.
As can be seen from FIG. 5, the sample TS-1-H synthesized according to example 4 contained only skeletal titanium, and did not contain hexacoordinated non-skeletal titanium and anatase TiO2。
Example 5
31.2g of ethyl orthosilicate was charged in a jacketed three-necked flask, 0.84g of titanium tetrachloride, 10.7g of a 25 wt% tetrapropylammonium hydroxide solution and 7.5g of a 25% tetramethylammonium hydroxide solution were sequentially added, and the three-necked flask was immersed in a water bath at 40 ℃ to hydrolyze for 3 hours. Removing alcohol from the hydrolysate at 90 ℃ for 1h, adding 81mL of 20 wt% starch solution, stirring uniformly, placing the mixed solution into a crystallization kettle, crystallizing at 140 ℃ for 64h, washing and drying the crystallized product, and roasting at 540 ℃ for 5h to obtain TS-1, wherein the TS-1 is numbered as TS-1-I.
Example 6
31.2g of ethyl orthosilicate was charged in a jacketed three-necked flask, 0.75g of tetrabutyl titanate, 0.42g of titanium tetrachloride, 10.7g of a 25 wt% tetrapropylammonium hydroxide solution and 7.5g of a 25 wt% tetramethylammonium hydroxide solution were sequentially added, and the three-necked flask was immersed in a water bath at 40 ℃ to hydrolyze for 3 hours. Removing alcohol from the hydrolysate at 90 deg.C for 1h, adding 20 wt% starch solution 45mL, stirring, placing the mixed solution into a crystallization kettle, crystallizing at 140 deg.C for 64h, washing and drying the crystallized product, and calcining at 540 deg.C for 5h to obtain TS-1, which is numbered TS-1-J.
Based on the spectra and electron micrographs of the samples, the TS-1 molecular sieves prepared in examples 1-6 above have typical MFI structures with particle sizes of about 200nm, and more importantly, the samples contain almost no non-framework titanium but only framework titanium.
Application example 1
0.2g of titanium silicalite molecular sieve is added into a 400mL stainless steel batch reactor, and then 34mL3.0mol/L H is added2O2Introducing 0.5MPa propylene into methanol solution, heating to 40 deg.C, reacting for 1 hr, cooling to room temperature, taking out product, centrifuging to separate catalyst, collecting upper layer liquid, and performing iodometry to titrate H2O2The concentrations and the chromatographic analysis of the product contents are shown in Table 1.
TABLE 1
Figure BDA0001074404950000071
Figure BDA0001074404950000081
Note: x (H)2O2) Represents H2O2S (PO) represents the selectivity for Propylene Oxide (PO), U (H)2O2) Represents H2O2The effective utilization rates of (a) are respectively calculated by the following formulas:
X(H2O2)＝1–n(H2O2)/n0(H2O2) (1)
S(PO)＝n(PO)/(n(PO)+n(MME)+n(PG)) (2)
U(H2O2)＝(n(PO)+n(MME)+n(PG))/(n0(H2O2)·X(H2O2)) (3)
in the formula, n0(H2O2) And n (H)2O2) Respectively represent before and after the reaction H2O2N (PO), n (MME) and n (PG) represent the amounts of PO, propylene glycol monomethyl ether (MME) and Propylene Glycol (PG), respectively.
Application example 2
0.1g of titanium silicalite molecular sieve is added into a 200mL stainless steel batch reactor, and then 34mL1.1mol/L H is added2O2Introducing 0.25MPa of butylene into a methanol solution, heating to 50 ℃, reacting for 1H, cooling to room temperature, taking out a product, centrifugally separating out the catalyst, taking the upper layer liquid, and carrying out iodometry H titration2O2The concentrations and the chromatographic analysis of the product contents are shown in Table 2.
TABLE 2
Figure BDA0001074404950000082
Note: x (H)2O2) Represents H2O2(ii) S (BO) represents the selectivity to Butylene Oxide (BO), U (H)2O2) Represents H2O2The effective utilization rates of (a) are respectively calculated by the following formulas:
X(H2O2)＝1–n(H2O2)/n0(H2O2) (1)
S(BO)＝n(BO)/(n(BO)+n(MME)+n(BG)) (2)
U(H2O2)＝(n(BO)+n(MME)+n(BG))/(n0(H2O2)·X(H2O2)) (3)
in the formula, n0(H2O2) And n (H)2O2) Respectively represent before and after the reaction H2O2N (BO), n (MME) and n (BG) respectively represent the quantitative concentrations of BO, butanediol monomethyl ether (MME) and propylene glycol (BG).
In summary, the invention relates to a synthesis method of a titanium silicalite TS-1 with high catalytic oxidation activity. The titanium silicalite molecular sieve prepared by the method has high framework titanium content, almost does not contain non-framework titanium, and the mother liquor can be recycled. The method is characterized in that soluble starch is added in the synthesis process, and a silicon source and a titanium source are bridged by using a large amount of hydroxyl contained in the starch, so that the silicon source and the titanium source are more easily combined, and more titanium can enter a TS-1 framework. The titanium-silicon molecular sieve prepared by the invention has excellent catalytic performance on selective oxidation reactions such as olefin epoxidation, aromatic hydrocarbon hydroxylation, ketone/aldehyde ammoxidation and the like.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical solutions and the inventive concepts of the present invention within the technical scope of the present invention.

Claims (4)

1. A method for preparing a titanium silicalite TS-1 with high framework titanium content is characterized by comprising the following specific steps:
s1, mixing a silicon source and a titanium source in proportion, and adding 20-40 wt% of quaternary ammonium alkaline water solution to obtain a mixed solution;
the molar ratio of each substance in the mixed solution is as follows:
SiO2:TiO2quaternary ammonium base H2O＝1:(0.0251～0.0333):(0.0501～0.4499):(20.01～54.99)；
S2, hydrolyzing the mixed solution obtained in the step S1 at 30-60 ℃ for 0-5 h, and removing alcohol at 90 ℃ for 0-1 h;
s3, adding a starch solution with the concentration of 0.1-20 wt% into the product obtained in the step S2, uniformly stirring, filling into a crystallization kettle, and crystallizing at the temperature of 140-170 ℃ for 24-72 hours to obtain a crystallized product;
the starch in the added starch solution is one or a mixture of amylose and amylopectin; the mass of starch in the added starch solution is equal to the SiO added in step S12The mass ratio of (0.301-1.001) to (1);
s4, drying the crystallized product obtained in the step S3 at 80-120 ℃ for 3-8 hours; roasting for 3-6 h at 500-600 ℃ to obtain the titanium silicalite TS-1 with high framework titanium content.
2. The method for preparing the titanium silicalite molecular sieve TS-1 with high framework titanium content according to claim 1, wherein the silicon source in step S1 is at least one of methyl orthosilicate, ethyl orthosilicate, silica sol and white carbon black;
the titanium source is at least one of tetraethyl titanate, tetrabutyl titanate, isopropyl titanate, titanium trichloride and titanium tetrachloride;
the quaternary ammonium hydroxide is at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.
3. The method of claim 1, wherein the starch in the starch solution added in step S3 is amylose.
4. The method of claim 1, wherein the hydrolysis time and the alcohol removal time of step S2 are both 0h when the silicon source and the titanium source are both non-ester compounds.
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