Preparation method of nano titanium silicalite molecular sieve

Abstract

The invention discloses a preparation method of a nano titanium silicalite molecular sieve, and belongs to the technical field of nano molecular sieve preparation, the preparation method comprises the following steps: adding a titanium source, a silicon source and a template agent into a supercritical crystallization reaction kettle, heating, stirring, and carrying out a melting reaction on the raw materials to obtain a seed crystal mixed material; introducing absolute ethyl alcohol into the seed crystal mixed material obtained by the melting reaction, heating, stirring, and carrying out crystallization reaction to obtain a reaction product; and cooling, washing, drying and roasting the crystallization reaction product to obtain the nano titanium silicalite molecular sieve. According to the invention, a melting reaction technology and a supercritical crystallization reaction technology are introduced into the preparation of the nano titanium silicalite molecular sieve for the first time. The method disclosed by the invention has the advantages of short crystallization time, no generation of wastewater and high content of framework tetra-coordinated titanium atoms, and the prepared nano titanium silicalite molecular sieve is small in grain size, uniform in dispersion and large in specific surface area.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanometer molecular sieve preparation, and particularly relates to a preparation method of nanometer titanium-silicon molecular sieve. BACKGROUND

[0002] Titanium-silicon molecular sieve is a very important catalyst in catalytic oxidation reaction, and its catalytic activity mainly comes from the four-coordinated titanium atoms in the skeleton. The nanometer titanium-silicon molecular sieve has the advantages of small crystal grain size and large specific surface area, and exhibits more efficient catalytic performance in oxidation reaction. However, the current patent preparation method of nanometer titanium-silicon molecular sieve has problems of long crystallization period, large production wastewater amount, and low content of four-coordinated titanium atoms in the active center skeleton. SUMMARY

[0003] The application aims to solve the problems of long crystallization period, large production wastewater amount, and low content of four-coordinated titanium atoms in the active center skeleton in the current preparation method of nanometer titanium-silicon molecular sieve, and provides a preparation method of nanometer titanium-silicon molecular sieve with short crystallization period, no wastewater generation, and high content of four-coordinated titanium atoms in the skeleton. The nanometer titanium-silicon molecular sieve prepared by the application has the advantages of small crystal grain size, uniform dispersion, and large specific surface area.

[0004] Technical scheme: A preparation method of nanometer titanium-silicon molecular sieve, comprising the following steps:

[0005] Step (1), adding a titanium source, a silicon source, and a template agent into a supercritical crystallization reactor, heating, stirring, and making the raw materials undergo a melting reaction to obtain a crystal seed mixture;

[0006] Step (2), introducing anhydrous ethanol into the crystal seed mixture obtained by the melting reaction, heating, stirring, and performing a crystallization reaction to obtain a reaction product;

[0007] Step (3), cooling, washing, drying, and calcining the reaction product of step (2) to obtain nanometer titanium-silicon molecular sieve.

[0008] Further, in steps (1) and (2), the amounts of the titanium source and the silicon source are calculated based on TiO2 and SiO2, and the molar ratio of TiO2, SiO2, the template agent, and anhydrous ethanol is 1:(0.2-0.5):(0.03-0.08):(5-15).

[0009] Further, in step (1), the template agent is N-hexanoyl-N-propylhexadecylammonium, and its structure is as follows:

[0010]

[0011] Further, in step (1), the titanium source is titanium oxalate.

[0012] Further, in step (1), the silicon source is silicic acid.

[0013] Further, in step (1), the melting reaction temperature is 150-180℃, the stirring rate is 300-500n / min, and the reaction time is 1-5h.

[0014] Further, in step (2), the crystallization reaction temperature is 200-250℃, the stirring rate is 50-100n / min, the pressure in the kettle is 5-7MPa, and the reaction time is 6-12h.

[0015] Further, in step (3), the reaction product of step (2) is cooled to room temperature, then washed with deionized water until the pH of the filtrate is 7.0, and finally dried and calcined to obtain the nano-titanium silicate molecular sieve;

[0016] Further, in step (3), the drying temperature is 100-120℃, and the time is 12-24h.

[0017] Further, in step (3), the calcination temperature is 500-550℃, and the time is 3-5h.

[0018] Beneficial effects:

[0019] (2) The present application introduces the melting reaction and supercritical crystallization reaction technology into the preparation of nano-titanium silicate molecular sieve for the first time.

[0020] The present application uses the melting reaction to regulate the condensation rate of the titanium source and the silicon source, so that they are more matched, thereby increasing the content of four-coordinated titanium atoms entering the framework, and generating a mixture material containing a large amount of crystal seeds.

[0021] When the crystallization reaction temperature is 200-250℃ and the pressure in the kettle is 5-7MPa, ethanol is in a supercritical state, and the present application uses the high solubility and high diffusivity of supercritical ethanol, as well as the regulation performance on the crystal growth rate and morphology, so that the crystal seed mixture material is fully contacted and reacted in the supercritical crystallization kettle, the crystallization reaction time is short, and it is beneficial to form a large amount of molecular sieve precursor with small crystal size, and finally the nano-titanium silicate molecular sieve has small crystal size, uniform distribution, large specific surface area, high content of four-coordinated titanium atoms in the framework, and high yield.

[0022] (2) The method of the present application does not need to use water as a solvent, avoids the generation of wastewater, and uses N-hexanoyl-N-propylhexadecylammonium as a template agent. This substance is alkaline, and it plays the role of a template agent and an alkali at the same time, avoiding the addition of inorganic alkali. The ammonium ion (NH4 + ) in the template agent can play the role of alkali metal ions (Na + or K +The role of the balancing ions in the molecular sieve structure, the decomposition after drying and calcination, the direct obtaining of the titanium-silicon molecular sieve without the operation of removing the alkali metal ions, and the simplification of the preparation process. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 XRD patterns of the samples prepared in Example 4 and Comparative Examples 2 and 3;

[0024] Figure 2 SEM patterns of the samples prepared in Example 4 and Comparative Examples 2 and 3;

[0025] Figure 3 UV-Vis patterns of the samples prepared in Example 4 and Comparative Examples 2 and 3. DETAILED DESCRIPTION

[0026] The technical solutions of the present application will be clearly and completely explained in combination with the drawings and specific examples, so that the present application can be better understood.

[0027] The calculation formula of the yield of the nano titanium-silicon molecular sieve is as follows:

[0028]

[0029] Wherein, m1 is the total mass of the actually used titanium source and silicon source, and m2 is the mass of the actually obtained titanium-silicon molecular sieve.

[0030] Example 1

[0031] A preparation method of a nano titanium-silicon molecular sieve, comprising the following steps:

[0032] Step (1), 11.7 g of titanium source titanium oxalate, 0.78 g of silicon source silicic acid and 0.64 g of template agent N-hexanoyl-N-propyl hexadecyl ammonium are added into a supercritical crystallization reactor, the temperature is raised to 150℃, the stirring rate is 300n / min, the melt reaction is carried out for 1 h, and the seed mixture is obtained.

[0033] Step (2), 23 g of anhydrous ethanol is introduced into the seed mixture obtained by the melt reaction, the temperature is raised to 220℃, the pressure in the reactor is 5.5 MPa, the stirring rate is 50n / min, the crystallization reaction is carried out for 6 h, and the reaction product is obtained.

[0034] Wherein, the amount of the titanium source and the silicon source is calculated based on TiO2 and SiO2 respectively, and the molar ratio of TiO2, SiO2, template agent and anhydrous ethanol is 1:0.2:0.03:10.

[0035] Step (3), the reaction product of step (2) is cooled to room temperature, then washed with deionized water until the filtrate pH is 7.0, and finally dried at 120°C for 12h and calcined at 500°C for 3h to obtain the nano-titanium silicate molecular sieve with a yield of 95.8%.

[0036] Example 2

[0037] A method for preparing a nano-titanium silicate molecular sieve, comprising the following steps:

[0038] Step (1), 11.7g of titanium source titanium oxalate, 1.95g of silicon source silicic acid and 1.71g of template agent N-hexanoyl-N-propyl hexadecyl ammonium acetate are added to a supercritical crystallization reactor, heated to 180°C, stirred at a rate of 500n / min, and melt reacted for 3h to obtain a crystal seed mixture.

[0039] Step (2), 11.5g of anhydrous ethanol is introduced into the crystal seed mixture obtained by melt reaction, heated to 250°C, the pressure in the reactor is 7MPa, stirred at a rate of 100n / min, and crystallized for 12h to obtain a reaction product.

[0040] The amount of titanium source and silicon source is calculated based on TiO2 and SiO2, respectively, and the molar ratio of TiO2, SiO2, template agent and anhydrous ethanol is 1:0.5:0.08:5.

[0041] Step (3), the reaction product of step (2) is cooled to room temperature, then washed with deionized water until the filtrate pH is 7.0, and finally dried at 100°C for 24h and calcined at 550°C for 5h to obtain the nano-titanium silicate molecular sieve with a yield of 98.1%.

[0042] Example 3

[0043] A method for preparing a nano-titanium silicate molecular sieve, comprising the following steps:

[0044] Step (1), 11.7g of titanium source titanium oxalate, 1.95g of silicon source silicic acid and 1.71g of template agent N-hexanoyl-N-propyl hexadecyl ammonium acetate are added to a supercritical crystallization reactor, heated to 180°C, stirred at a rate of 500n / min, and melt reacted for 3h to obtain a crystal seed mixture.

[0045] Step (2), 11.5g of anhydrous ethanol is introduced into the crystal seed mixture obtained by melt reaction, heated to 250°C, the pressure in the reactor is 7MPa, stirred at a rate of 100n / min, and crystallized for 12h to obtain a reaction product.

[0046] Wherein, the amount of titanium source and silicon source is calculated by TiO2 and SiO2 respectively, the molar ratio of TiO2, SiO2, template agent and anhydrous ethanol is 1:0.3:0.05:15.

[0047] Step (3), the reaction product of step (2) is cooled to room temperature, then washed with deionized water until the pH of the filtrate is 7.0, and finally dried at 110°C for 18h and calcined at 530°C for 4h to obtain the nano-titanium silicon molecular sieve with a yield of 97.7%.

[0048] Example 4

[0049] A method for preparing a nano-titanium silicon molecular sieve, comprising the following steps:

[0050] Step (1), 11.7g of titanium source titanium oxalate, 1.95g of silicon source silicic acid and 0.86g of template agent N-hexanoyl-N-propyl hexadecyl ammonium are added to a supercritical crystallization reactor, heated to 180°C, stirred at a rate of 450n / min, and melt reacted for 3h to obtain a crystal seed mixture.

[0051] Step (2), 25.3g of anhydrous ethanol is introduced into the crystal seed mixture obtained by melt reaction, heated to 240°C, the pressure in the reactor is 6.8MPa, stirred at a rate of 55n / min, and crystallized for 10h to obtain a reaction product.

[0052] Wherein, the amount of titanium source and silicon source is calculated by TiO2 and SiO2 respectively, the molar ratio of TiO2, SiO2, template agent and anhydrous ethanol is 1:0.5:0.04:11.

[0053] Step (3), the reaction product of step (2) is cooled to room temperature, then washed with deionized water until the pH of the filtrate is 7.0, and finally dried at 120°C for 12h and calcined at 500°C for 3h to obtain the nano-titanium silicon molecular sieve with a yield of 98.9%.

[0054] Example 5

[0055] A method for preparing a nano-titanium silicon molecular sieve, comprising the following steps:

[0056] Step (1), 11.7g of titanium source titanium oxalate, 1.56g of silicon source silicic acid and 1.28g of template agent N-hexanoyl-N-propyl hexadecyl ammonium are added to a supercritical crystallization reactor, heated to 170°C, stirred at a rate of 450n / min, and melt reacted for 2h to obtain a crystal seed mixture.

[0057] Step (2), 18.4 g of anhydrous ethanol was introduced into the seed mixture obtained from the melt reaction, the temperature was raised to 220 °C, the pressure in the reactor was 6.5 MPa, and the stirring rate was 60 n / min, and the crystallization reaction was carried out for 7 h to obtain a reaction product.

[0058] The amounts of the titanium source and the silicon source are calculated based on TiO2 and SiO2, respectively, and the molar ratio of TiO2, SiO2, the template agent and anhydrous ethanol is 1:0.4:0.06:8.

[0059] Step (3), the reaction product of Step (2) was cooled to room temperature, then washed with deionized water until the pH of the filtrate was 7.0, and finally dried at 120 °C for 12 h and calcined at 500 °C for 5 h to obtain the nanometer titanium silicate molecular sieve with a yield of 98.5%.

[0060] Example 6

[0061] A method for preparing a nanometer titanium silicate molecular sieve comprises the following steps:

[0062] Step (1), 11.7 g of titanium source titanium oxalate, 0.78 g of silicon source silicic acid and 1.50 g of template agent N-hexanoyl-N-propylhexadecylammonium were introduced into a supercritical crystallization reactor, the temperature was raised to 160 °C, the stirring rate was 350 n / min, and the melt reaction was carried out for 5 h to obtain a seed mixture.

[0063] Step (2), 13.8 g of anhydrous ethanol was introduced into the seed mixture obtained from the melt reaction, the temperature was raised to 210 °C, the pressure in the reactor was 5 MPa, the stirring rate was 70 n / min, and the crystallization reaction was carried out for 12 h to obtain a reaction product.

[0064] The amounts of the titanium source and the silicon source are calculated based on TiO2 and SiO2, respectively, and the molar ratio of TiO2, SiO2, the template agent and anhydrous ethanol is 1:0.2:0.07:6.

[0065] Step (3), the reaction product of Step (2) was cooled to room temperature, then washed with deionized water until the pH of the filtrate was 7.0, and finally dried at 100 °C for 24 h and calcined at 550 °C for 3 h to obtain the nanometer titanium silicate molecular sieve with a yield of 97.9%.

[0066] Comparative Example 1

[0067] A titanium silicate molecular sieve was prepared according to the molar ratio of the raw materials in Example 4, but without melt reaction, by directly carrying out a crystallization reaction, and the specific preparation steps were as follows:

[0068] Step (1) 11.7 g of titanium source titanium oxalate, 1.95 g of silicon source silicic acid, 0.86 g of template agent N-hexanoyl-N-propylhexadecylammonium and 25.3 g of anhydrous ethanol (molar ratio of TiO2, SiO2, template agent and anhydrous ethanol is 1:0.5:0.04:11) were added into a supercritical crystallization reactor, heated to 240 °C, the pressure in the reactor was 6.8 MPa, and the stirring rate was 55 n / min. The crystallization reaction was carried out for 10 h to obtain a reaction product.

[0069] Step (2) The reaction product of step (1) was cooled to room temperature, then washed with deionized water until the pH of the filtrate was 7.0, and finally dried at 120 °C for 12 h and calcined at 500 °C for 3 h to obtain a solid product with a yield of 30.6%.

[0070] Comparative Example 2

[0071] A titanium silicalite was prepared according to the molar ratio of each raw material in Example 4, but without adding anhydrous ethanol during the crystallization reaction, and the specific preparation steps were as follows:

[0072] Step (1) 11.7 g of titanium source titanium oxalate, 1.95 g of silicon source silicic acid and 0.86 g of template agent N-hexanoyl-N-propylhexadecylammonium (molar ratio of TiO2, SiO2, template agent is 1:0.5:0.04) were added into a supercritical crystallization reactor, heated to 180 °C, and stirred at a rate of 450 n / min for 3 h of melt reaction to obtain a seed mixture.

[0073] Step (2) The reactor was heated to 240 °C, and the pressure in the reactor was atmospheric pressure. The stirring rate was 55 n / min, and the crystallization reaction was carried out for 10 h to obtain a reaction product.

[0074] Step (3) The reaction product of step (2) was cooled to room temperature, then washed with deionized water until the pH of the filtrate was 7.0, and finally dried at 120 °C for 12 h and calcined at 500 °C for 3 h to obtain a solid product with a yield of 99.3%.

[0075] Comparative Example 3

[0076] A titanium silicalite was prepared according to the molar ratio of each raw material in Example 4, but the crystallization reaction was carried out in a supercritical carbon dioxide state, and the specific preparation steps were as follows:

[0077] Step (1) 11.7 g of titanium source titanium oxalate, 1.95 g of silicon source silicic acid and 0.86 g of template agent N-hexanoyl-N-propylhexadecylammonium (molar ratio of TiO2, SiO2, template agent is 1:0.5:0.04) were added into a supercritical crystallization reactor, heated to 180 °C, and stirred at a rate of 450 n / min for 3 h of melt reaction to obtain a seed mixture.

[0078] Step (2), carbon dioxide was introduced into the seed mixture obtained from the melting reaction, and the temperature was raised to 240°C, so that the pressure in the kettle was 7.4 MPa, and the stirring rate was 55 n / min. The crystallization reaction was carried out for 10 h to obtain a reaction product.

[0079] Step (3), the reaction product of step (2) was cooled to room temperature, then washed with deionized water until the pH of the filtrate was 7.0, and finally dried at 120°C for 12 h and calcined at 500°C for 3 h to obtain a solid product with a yield of 99.0%.

[0080] The XRD pattern of the sample prepared in Example 4 and Comparative Examples 2 and 3 is shown in FIG. 1, the SEM pattern of the sample prepared in Example 4 and Comparative Examples 2 and 3 is shown in FIG. 2, and the grain size, crystallinity, and specific surface area of the sample prepared in Example 4 and Comparative Examples 2 and 3 are shown in Table 1. Figure 1 Figure 2 The XRD pattern of the sample prepared in Example 4 and Comparative Examples 2 and 3 is shown in FIG. 1, the SEM pattern of the sample prepared in Example 4 and Comparative Examples 2 and 3 is shown in FIG. 2, and the grain size, crystallinity, and specific surface area of the sample prepared in Example 4 and Comparative Examples 2 and 3 are shown in Table 1.

[0081] Table 1

[0082]

[0083]

[0084] Comparing with Example 4, in Comparative Example 1, because the seed mixture was not formed by the melting reaction, and there was anhydrous ethanol, the crystal growth was slowed down, and the crystals were not easy to form, so most of the titanium oxalate and silicic acid did not undergo crystallization reaction, and the titanium oxalate was easy to dissolve in water, so it was removed by filtration during the washing process, so the yield of the finally generated solid product was extremely low.

[0085] In Comparative Example 2, although the yield was high, but because high temperature easily led to sintering of the crystal grains, and the crystal grew too fast, the morphology was irregular, the grain size of the titanium silicalite molecular sieve obtained was large (210 nm), the stacking was serious, the crystallinity was low (54%), and the specific surface area was small (251 m 2 / g).

[0086] In Example 4, the crystallization reaction was carried out in supercritical ethanol, which had high solubility, high diffusion, and regulation performance on the crystal growth rate and morphology, so the grain size of the titanium silicalite molecular sieve obtained was small (45 nm), the crystallinity was high (100%), the dispersibility was good, and the specific surface area was large (625 m 2 / g).

[0087] ​In Comparative Example 3, although supercritical carbon dioxide also has high solubility and high diffusion properties, it does not have the regulatory properties of supercritical ethanol on crystal growth rate and morphology, so the obtained titanium silicon molecular sieve grain size (92nm) is larger than that in Example 4 (45nm).

[0088] The UV-Vis images of the samples prepared in Example 4 and Comparative Examples 2 and 3 are as follows: Figure 3 As shown, from Figure 3 The UV-visible absorption spectra of each sample show that the absorption peak of the tetracoordinated titanium atoms in the skeleton is at 210 nm. The peak area shows the content of the tetracoordinated titanium atoms in the skeleton. Figure 3 The peak area in Example 4 is significantly larger than the peak areas of Comparative Examples 2 and 3, indicating that the melting reaction and supercritical ethanol crystallization reaction technology in the present invention can regulate the condensation rate of the titanium source and the silicon source, making the two more matched, which is beneficial to increase the content of tetracoordinated titanium atoms in the skeleton and improve the catalytic performance of the nano-titanium silicon molecular sieve.

[0089] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to the form and details without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing nano titanium silicon molecular sieve, characterized in that: The steps include: Step (1), adding a titanium source, a silicon source and a template into a supercritical crystallization reactor, heating, stirring, and causing the raw materials to undergo a melting reaction to obtain a seed crystal mixture material; the melting reaction conditions are: temperature 150-180° C., reaction time 1-5 hours; Step (2), adding anhydrous ethanol to the seed mixture obtained by the melt reaction, heating, stirring, and performing a crystallization reaction to obtain a reaction product; the crystallization reaction conditions are: temperature 200-250° C., pressure in the autoclave 5-7 MPa, and reaction time 6-12 h; Step (3), cooling, washing, drying and calcining the reaction product of step (2) to obtain nano titanium silicon molecular sieve.

2. The preparation method according to claim 1, characterized in that The amounts of the titanium source and the silicon source are calculated as TiO2 and SiO2, respectively. The molar ratio of TiO2, SiO2, template and anhydrous ethanol is 1:(0.2-0.5):(0.03-0.08):(5-15).

3. The preparation method according to claim 1, characterized in that In the step (1), the template is N-hexanoyl-N-propyl ammonium hexadecanoate, the titanium source is titanium oxalate, and the silicon source is silicic acid.

4. The preparation method according to claim 1, characterized in that In the step (1), during the melting reaction, the stirring rate is 300 to 500 n / min.

5. The preparation method according to claim 1, characterized in that During the crystallization reaction, the stirring rate is 50-100 n / min.

6. The preparation method according to claim 1, characterized in that In step (3), the reaction product of step (2) is cooled to room temperature, then washed with deionized water until the pH of the filtrate is 7.0, and finally dried and calcined to obtain nano-titanium silicon molecular sieve.

7. The preparation method according to claim 1, characterized in that In step (3), the drying temperature is 100-120° C. and the drying time is 12-24 hours.

8. The preparation method according to claim 1, characterized in that In step (3), the calcination temperature is 500-550° C. and the calcination time is 3-5 hours.

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