Preparation method of titanium-containing heteroatom molecular sieve

Abstract

The invention discloses a preparation method of a titanium-containing heteroatom molecular sieve, and belongs to the technical field of catalytic synthesis. In the preparation process of the titanium silicalite molecular sieve TS-1, solid organic acid complexed titanium is used as a titanium source, so that introduction of an organic complexing agent is avoided, the pressure of alcohol removal in the preparation process is reduced, and the energy consumption is reduced; as the selected titanium source is dissolved in water, has certain acidity and slows down the hydrolysis speed of the titanium source, the hydrolysis speed of the silicon source is further matched, so that the titanium source better enters a molecular sieve framework, the TS-1 molecular sieve with more uniform framework titanium distribution and higher content is obtained, the catalytic activity of the molecular sieve is improved, and the conversion rate and selectivity of a product are greatly improved; and the method has a very good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic synthesis, and particularly relates to a method for preparing a titanium heteroatom-containing molecular sieve. Background Art

[0002] Titanium silicate molecular sieve TS-1 is a titanium heteroatom molecular sieve with unique performance and catalytic oxidation function. Since 1983, the synthesis of TS-1 molecular sieve was first reported in US4410501 patent. It has the same MFI topology as ZSM-5 molecular sieve. 4+ Ion substitution of Al in the framework of silica-alumina molecular sieve 3+ ions, Ti with six coordination capacity on the surface of the molecular sieve 4+ The ions can accept electron pairs and have unique adsorption and activation properties for H2O2. They can selectively oxidize a variety of organic compounds, among which the hydroxylation of phenol, the ammoxidation of cyclohexanone and the epoxidation of olefins are industrially applied.

[0003] The titanium sources used in the traditional method of preparing TS-1 molecular sieves are all liquid, such as tetrabutyl titanate or titanium chloride, which are first mixed evenly with a complexing agent during the preparation process and then added to the silicon source. Most of the complexing agents are organic solvents such as acetylacetone and diethanolamine. The purpose is to protect the titanium source through complexation and coordination so that it is not rapidly hydrolyzed into titanium dioxide, so that it reacts with the silicon source with a slow hydrolysis rate during the preparation of the molecular sieve to obtain the TS-1 molecular sieve. In recent years, with the increasing application of TS-1 in the field of selective oxidation, scientific researchers have conducted more in-depth and detailed research on its preparation. How to use a solid titanium source to produce a TS-1 molecular sieve with higher catalytic activity is a research difficulty in this field. Summary of the Invention

[0004] In order to make up for the deficiencies of the prior art, the present invention aims to provide a method for preparing a titanium heteroatom-containing molecular sieve.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a titanium heteroatom-containing molecular sieve, comprising the following steps:

[0007] (1) uniformly mixing a silicon source, a template, and water to obtain a silicon source hydrolyzate A;

[0008] (2) mixing the titanium source and water uniformly, adding the mixture dropwise to the silicon source hydrolyzate A, and stirring uniformly to obtain silicon-titanium hydrolyzate B; the titanium source is one or a mixture of two or more of titanium citrate, titanium hydroxyacetate, titanium tartrate, titanium oxalate, and titanium lactate;

[0009] (3) heating the silicon-titanium hydrolyzate B to remove alcohol, and then adding water to obtain silicon-titanium gel C, wherein the molar ratio of substances in the silicon-titanium gel C is SiO2:TiO2:template:H2O=1:(0.02-0.05):(0.25-0.4):(25-30);

[0010] (4) The titanium silicate gel C is placed in a crystallization kettle and crystallized at 130-210° C. for 20-120 h to obtain a crystallized product, which is filtered, dried, washed, and calcined to obtain titanium silicate molecular sieve TS-1.

[0011] Based on the above technical solution, further, the molar ratio of silicon to titanium in the molecular sieve is 20 to 50, preferably 35 to 45.

[0012] Based on the above technical solution, further, the silicon source in step (1) is one or a mixture of two or more of tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate and tetrabutyl orthosilicate, preferably tetraethyl orthosilicate.

[0013] Based on the above technical solution, further, the template agent in step (1) is tetrapropylammonium hydroxide (TPAOH).

[0014] Based on the above technical solution, further, the mass ratio of the silicon source, template and water described in step (1) is 1: (0.1-0.3): (0.5-1.5); the hydrolysis temperature of the silicon source is 35-45° C., and the hydrolysis time is 2-10 h.

[0015] Based on the above technical solution, further, the mass ratio of the titanium source to water in step (2) is 2 to 20, preferably 5 to 10.

[0016] Based on the above technical solution, further, the molar ratio of the substances in the silica-titanium gel C in step (3) is SiO2:TiO2:template:H2O=1:(0.022~0.033):(0.25~0.4):(25~30).

[0017] Based on the above technical solution, further, the temperature for removing alcohol in step (3) is 70-90° C., and the time for removing alcohol is 0.5-1.5 h.

[0018] Based on the above technical solution, further, in step (4), the crystallization temperature is 150-190° C., and the crystallization time is 20-60 h.

[0019] Based on the above technical solution, further, in step (4), the drying temperature is 80-120° C., the roasting is carried out in an air atmosphere, the roasting temperature is 500-650° C., and the roasting time is 2-10 h.

[0020] In a second aspect, the present invention provides a titanium heteroatom-containing molecular sieve prepared by the above preparation method.

[0021] In a third aspect, the present invention provides the use of the titanium heteroatom-containing molecular sieve in the hydroxylation reaction of phenol and anisole.

[0022] Based on the above technical solution, the specific process of the hydroxylation reaction is as follows: the titanium heteroatom molecular sieve catalyst is added to an intermittent reactor reaction device, an organic solvent solution containing 1 to 5.0 mol / L H2O2 and a reaction substrate is added, the reaction temperature is maintained at 50 to 100°C, the reaction pressure is 0.2 to 1 MPa, and the reaction time is 0.5 to 5 h.

[0023] Based on the above technical solution, further, the mass concentration of titanium heteroatom molecular sieve in the reaction system is 1-5%, the organic solvent includes acetone, hexane, and dichloromethane, and the molar concentration of the substrate in the reaction system is 1.1-2 times the molar concentration of hydrogen peroxide.

[0024] The present invention has the following beneficial effects compared to the prior art:

[0025] In the preparation process of titanium silicate molecular sieve TS-1, the present invention adopts solid organic acid complexed titanium as titanium source, avoids the introduction of organic complexing agent, reduces the pressure of alcohol removal in the preparation process, and reduces energy consumption; because the selected titanium source is soluble in water and has a certain acidity, hydrolysis occurs protonation to form Ti-OH, which reduces the electron cloud density around Ti and makes it react with H + Contact becomes difficult, thus further slowing down its hydrolysis rate; the weakly acidic conditions provided by the titanium source can play a role in reducing the pH value of the synthetic gel, thereby slowing down the crystallization process. The above two aspects work together to match the speed at which silicon and Ti enter the skeleton with the growth of the crystal; since low temperature and low pH value are conducive to complexation, high temperature and high pH value are conducive to hydrolysis, this combination ensures the stability of the titanium source during the early gel preparation period. During the later crystallization, as the temperature and pH value increase, the titanium source is hydrolyzed and enters the skeleton, obtaining a TS-1 molecular sieve with a more uniform skeleton titanium distribution and a higher content, further improving its catalytic activity; this titanium silicon molecular sieve has excellent epoxidation activity, and the conversion rate and selectivity of the product have been greatly improved, with very good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0027] Figure 1 This is a scanning electron microscope image of the titanium silicate molecular sieve TS-1-A prepared in Comparative Example 1.

[0028] Figure 2This is a scanning electron microscope image of the titanium silicate molecular sieve TS-1-B prepared in Example 1.

[0029] Figure 3 This is the UV-vis spectrum of TS-1-A.

[0030] Figure 4 This is the UV-vis spectrum of TS-1-C. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative work all fall within the scope of protection of the present invention.

[0032] Comparative Example 1

[0033] 47g of tetraethyl orthosilicate was added to a beaker and stirred, and then 45g of a 25wt% TPAOH aqueous solution and 36g of water were added, and the mixture was hydrolyzed at 40°C for 5h to obtain a silicon source hydrolysis mixture; 1.85g of tetrabutyl titanate was dissolved in 13.875g of isopropanol and stirred for 30min to obtain a titanium source hydrolysis mixture; the hydrolysis mixture of the titanium source and the silicon source was mixed, and the alcohol was removed at 80°C for 1.0h, 50.5g of water was added and stirred for 30min, and the obtained transparent glue was charged into a crystallization kettle for crystallization at 170°C for 36h. The obtained crystallized product was washed and dried, and then calcined in an air atmosphere at 550°C for 6h to obtain titanium silicon molecular sieve TS-1-A.

[0034] The Si / Ti ratio obtained by XRF test is 41.0. The SEM photo of the obtained sample is shown in Figure 1 , UV-vis spectrum see Figure 3 From the UV results, it can be seen that in addition to the skeleton titanium near 210nm, anatase exists near 325.

[0035] Example 1

[0036] 47g of tetraethyl orthosilicate was added to a beaker and stirred, and then 45g of a 25wt% TPAOH aqueous solution and 30g of water were added and hydrolyzed at 40°C for 5h to obtain a silicon source hydrolysis mixture; 0.92g of titanium tartaric acid (according to the literature: Yunnan Chemical Industry, 1996, No. 2, P 32-34The obtained product was dissolved in 5.25 g of water and then stirred for 30 min to obtain a titanium source hydrolysis mixture; the titanium source and the silicon source hydrolysis mixture were mixed and dealcoholized at 80 ° C for 1.2 h, 50.5 g of water was added and stirred for 30 min, and the obtained transparent glue was charged into a crystallization kettle for crystallization at 170 ° C for 36 h. The obtained crystallized product was washed and dried, and then calcined in an air atmosphere at 550 ° C for 6 h to obtain titanium silicon molecular sieve TS-1-B.

[0037] The Si / Ti ratio obtained by XRF test is 41.0. The SEM photo of the obtained sample is shown in Figure 2 , UV-vis spectrum see Figure 4 , it can be seen that the size and morphology of TS-1 particles are similar to those of the sample obtained in Comparative Example 1. From the UV spectrum results, it can be seen that the skeleton titanium content of the obtained sample is higher and does not contain anatase.

[0038] Example 2

[0039] The experimental procedure was identical to that of Example 1, except that the titanium tartrate in Example 1 was replaced with titanium oxalate, titanium hydroxyacetate, titanium lactate, and titanium citrate, respectively, in equal amounts. The resulting titanium silicate molecular sieve products were designated TS-1-C, TS-1-D, TS-1-E, and TS-1-F, respectively.

[0040] Example 3

[0041] Hydroxylation reaction of the titanium silicate TS-1 catalyst of Comparative Example 1 and Example 1-2: The hydroxylation reaction was carried out in an intermittent reactor reaction apparatus, and 2 g of titanium silicate TS-1 (TS-1-A, TS-1-B, TS-1-C, TS-1-D, TS-1-E, TS-1-F) was added to a stainless steel intermittent reactor as a catalyst, and 70 g of acetone reaction solution was added, wherein the H2O2 concentration was 2.5 mol / L, the substrate (phenol, anisole) concentration was 4.0 mol / L, the reaction temperature was maintained at 85°C, the pressure was 0.5 MPa, and the reaction time was 1 h; then the temperature was lowered and the liquid was taken to analyze the product composition, and the molar concentration of the remaining H2O2 was determined by titration. The reaction solution of the phenol hydroxylation reaction was analyzed using an Agilent 7890B gas chromatograph with an FID detector and an innowax polar column (60m*0.32μm*0.25μm). The column oven conditions for sample analysis were: 40°C for 10 min, then heating to 200°C at 10°C / min and holding for 5 min, then heating to 250°C at 50°C / min and holding for 18 min. The reaction solution of the anisole hydroxylation reaction was analyzed using an Agilent 7890B gas chromatograph with an FID detector and an innowax polar column (60m*0.32μm*0.25μm). The column oven conditions for sample analysis were: 40°C for 10 min, then heating to 200°C at 10°C / min and holding for 5 min, then heating to 250°C at 50°C / min and holding for 18 min.

[0042] The performance results of the titanium silicalite molecular sieves of Comparative Example 1 and Examples 1-2 in the hydroxylation reaction of different substrates are shown in Table 1-2.

[0043] Table 1 Performance data of phenol hydroxylation reaction of titanium silicalite molecular sieves of comparative example 1 and examples 1-2

[0044]

[0045]

[0046] Table 2 Performance data of anisole hydroxylation reaction of titanium silicalite molecular sieves of comparative example 1 and examples 1-2

[0047] Samples <![CDATA[C 苯甲醚 %]]> <![CDATA[S 对羟基苯甲醚 / %]]> <![CDATA[S 邻羟基苯甲醚 / %]]> <![CDATA[U 苯甲醚 %]]> TS-1-A 35.1 74.9 25.1 91.8 TS-1-B 45.9 75.0 25.0 94.4 TS-1-C 45.5 74.8 25.2 94.1 TS-1-D 45.7 75.1 24.9 94.3 TS-1-E 45.6 74.9 25.1 94.3 TS-1-F 45.8 75.1 24.9 94.2

[0048] Note: The formula for calculating the conversion rate, selectivity and effective utilization rate of anisole is as follows:

[0049]

[0050] no: amount of initial substance of anisole;

[0051] n: the amount of anisole after the reaction;

[0052]

[0053] n pairs: the amount of substance that generates p-hydroxyanisole;

[0054] n-o: the amount of substance that generates o-hydroxyanisole

[0055] S 邻 % = 100% - S 对 %.

[0056]

[0057] From the above reaction results, it can be seen that the catalytic performance of TS-1 prepared using solid titanium salt as the titanium source is significantly better than that of TS-1 prepared using the traditional titanium source.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a titanium heteroatom-containing molecular sieve, characterized in that: The following steps are involved: (1) uniformly mixing a silicon source, a template, and water to obtain a silicon source hydrolyzate A; (2) mixing the titanium source and water uniformly, adding the mixture dropwise to the silicon source hydrolyzate A, and stirring uniformly to obtain silicon-titanium hydrolyzate B; the titanium source is one or a mixture of two or more of titanium citrate, titanium hydroxyacetate, titanium tartrate, titanium oxalate, and titanium lactate; (3) heating the silicon-titanium hydrolyzate B to remove alcohol, and then adding water to obtain silicon-titanium gel C, wherein the molar ratio of substances in the silicon-titanium gel C is SiO2:TiO2:template:H2O=1:(0.02-0.05):(0.25-0.4):(25-30); (4) The titanium silicate gel C is placed in a crystallization kettle and crystallized at 130-210° C. for 20-120 h to obtain a crystallized product, which is filtered, dried, washed, and calcined to obtain titanium silicate molecular sieve TS-1.

2. The preparation method according to claim 1, characterized in that The molar ratio of silicon to titanium in the molecular sieve is 20 to 50, preferably 35 to 45.

3. The preparation method according to claim 1, characterized in that The silicon source in step (1) is one or a mixture of two or more of tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate and tetrabutyl orthosilicate, preferably tetraethyl orthosilicate; the template is tetrapropylammonium hydroxide (TPAOH); the mass ratio of the silicon source, template and water is 1:(0.1-0.3):(0.5-1.5); the hydrolysis temperature of the silicon source is 35-45°C, and the hydrolysis time is 2-10 hours.

4. The preparation method according to claim 1, characterized in that The mass ratio of the titanium source to water in step (2) is 2 to 20, preferably 5 to 10.

5. The preparation method according to claim 1, characterized in that The molar ratio of the substances in the silica-titanium gel C in step (3) is SiO2:TiO2:template:H2O=1:(0.022-0.033):(0.25-0.4):(25-30); the temperature for removing alcohol is 70-90°C, and the time for removing alcohol is 0.5-1.5h.

6. The preparation method according to claim 1, characterized in that In step (4), the crystallization temperature is 150-190° C., and the crystallization time is 20-60 h; the drying temperature is 80-120° C., and the calcination is carried out in an air atmosphere at a temperature of 500-650° C. and a calcination time of 2-10 h.

7. The titanium heteroatom-containing molecular sieve prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the titanium heteroatom-containing molecular sieve according to claim 7 in the hydroxylation reaction of phenol and anisole.

9. The use according to claim 8, characterized in that The specific process of the hydroxylation reaction is: adding the titanium heteroatom molecular sieve catalyst to an intermittent reactor reaction device, adding an organic solvent solution containing 1-5.0 mol / L H2O2 and a reaction substrate, maintaining the reaction temperature at 50-100°C, the reaction pressure at 0.2-1 MPa, and the reaction time at 0.5-5 h.

10. The use according to claim 9, characterized in that The mass concentration of the titanium heteroatom molecular sieve in the reaction system is 1-5%, the organic solvent includes acetone, hexane and dichloromethane, and the molar concentration of the substrate in the reaction system is 1.1-2 times the molar concentration of hydrogen peroxide.

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