Preparation method of nano HZSM-5 molecular sieve

Abstract

The invention discloses a preparation method of a nano HZSM-5 molecular sieve, and belongs to the technical field of nano molecular sieve preparation, the preparation method comprises the following steps: 1, adding a silicon source, an aluminum 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 obtained reaction product to obtain the nano HZSM-5 molecular sieve. According to the present invention, the melting reaction and the supercritical ethanol crystallization reaction technology are introduced into the preparation of the nanometer HZSM-5 molecular sieve for the first time, and the prepared nanometer HZSM-5 molecular sieve has advantages of small grain size, uniform distribution, large specific surface area and high yield.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of nano zeolites, and particularly relates to a preparation method of nano HZSM-5 zeolite. Background Art

[0002] Nano HZSM-5 zeolite has short diffusion channels, a large specific surface area, and abundant acidic catalytic active sites, with small diffusion and mass transfer resistance, and excellent catalytic performance. It plays an extremely important role in catalytic reactions such as catalytic cracking, isomerization, alkylation, methanol to olefins, and biomass conversion.

[0003] Among the preparation methods of nano HZSM-5 zeolite, the relatively traditional one is the hydrothermal synthesis method. However, its operation process is complex, the preparation cycle is long, a large amount of water is required as a solvent, a large amount of expensive organic template agent is used, and inorganic alkali is used in the raw materials. A large amount of strong alkali waste liquid will be generated during the preparation process, resulting in problems such as high preparation cost and environmental pollution; according to the common knowledge in this field, since the zeolite prepared with inorganic alkali in the raw materials, it is also necessary to use ammonium chloride or ammonium nitrate solution to perform ion exchange, secondary washing, drying, and calcination on the ZSM-5 zeolite to convert it into HZSM-5 zeolite, and a large amount of waste liquid and high energy consumption problems will be generated during the operation process. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing nano HZSM-5 zeolite with a short crystallization time, no wastewater generation, and a simple preparation process, aiming at the problems of long crystallization time, large amount of production wastewater, and cumbersome preparation process in the current method for preparing nano HZSM-5 zeolite. The nano HZSM-5 zeolite prepared by the method of the present invention has small crystal grain size, uniform dispersion, and a large specific surface area.

[0005] Technical Solution: A method for preparing nano HZSM-5 zeolite, comprising the following steps:

[0006] Step 1: Add a silicon source, an aluminum source, and a template agent into a supercritical crystallization reaction kettle, heat up and stir to make the raw materials undergo a melting reaction at 115-125°C for 1-5 h to obtain a seed mixed material;

[0007] Step 2: Pass anhydrous ethanol into the seed mixed material obtained by the melting reaction, heat up and stir to carry out a crystallization reaction to obtain a reaction product; Crystallization reaction conditions: temperature is 200-250°C, pressure is 5-7 MPa, and reaction time is 6-12 h;

[0008] Step 3: Cool, wash, dry, and calcine the reaction product obtained in Step 2 to obtain nano HZSM-5 zeolite.

[0009] Further, in Step 1 and Step 2, the dosages of the silicon source and the aluminum source are calculated based on SiO2 and Al2O3 respectively, and the molar ratio of SiO2, Al2O3, the template agent and absolute ethanol is 1:(0.04 - 0.1):(0.01 - 0.05):(10.5 - 14.3);

[0010] Further, in Step 1, the silicon source is tetraethoxysilane; the aluminum source is aluminum isopropoxide; the template agent is dioctyl sulfosuccinate ammonium, and its structure is as follows:

[0011]

[0012] Further, in Step 1, during the melting reaction, the stirring rate is 300 - 500 r / min.

[0013] Further, in Step 2, during the crystallization reaction, the stirring rate is 50 - 100 r / min.

[0014] Further, in Step 3, the reaction product obtained in Step 2 is cooled to room temperature, then washed with deionized water until the pH of the filtrate is 7.0, and then dried and calcined.

[0015] Further, in Step 3, the drying temperature is 100 - 120 °C and the time is 12 - 24 h; the calcination temperature is 500 - 550 °C and the time is 3 - 5 h.

[0016] Beneficial effects:

[0017] The present invention creatively introduces the melting reaction and supercritical ethanol crystallization reaction technologies into the preparation of nano HZSM-5 molecular sieve. The present invention uses the melting reaction to regulate the condensation rate of the silicon source and the aluminum source, making them more compatible, so as to promote the entry of silicon and aluminum atoms into the framework and generate a mixed material containing a large number of crystal seeds. In the preparation method of the present invention, the crystallization reaction temperature is 200 - 250 °C and the pressure is 5 - 7 MPa, making ethanol in a supercritical state. The present invention utilizes the high solubility, high diffusivity of supercritical ethanol, as well as the regulation performance on the crystal growth rate and morphology, enabling the crystal seed mixed material to fully contact and react in the supercritical crystallization kettle. The crystallization reaction time is short and it is beneficial to form a large number of molecular sieve precursors with small grain sizes. The final nano HZSM-5 molecular sieve has small grain sizes, uniform distribution, large specific surface area and high yield.

[0018] The method of the present invention does not need to use water as a solvent, avoiding the generation of waste water, and uses dioctyl sulfosuccinate ammonium as the template agent. This substance is alkaline, which not only plays the role of the template agent, but also plays the role of a base, avoiding the addition of inorganic bases. The ammonium ion (NH4 + ) in the template agent can play the role of the alkali metal ion (Na+ or K + ) After drying and calcination, the ammonium ions decompose into NH3 and H under the action of the balance ions in the molecular sieve structure + , directly obtaining the HZSM-5 molecular sieve without the need for ion exchange and secondary washing, drying, and calcination, simplifying the process. Description of the Drawings

[0019] Figure 1 XRD patterns of the samples prepared in Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4;

[0020] Figure 2 SEM images of the samples prepared in Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4. Detailed Description of the Invention

[0021] The technical solution of the present invention will be described in detail below with reference to the drawings, but the protection scope of the present invention is not limited to the described embodiments. The technical solution of the present invention will be clearly and completely described below in combination with the drawings and specific embodiments, so that the present invention can be better understood.

[0022] The calculation formula for the yield of nano-HZSM-5 molecular sieve is:

[0023]

[0024] Wherein, m1 is the total mass of the silicon source and aluminum source actually used, and m2 is the mass of the actually obtained HZSM-5 molecular sieve.

[0025] Example 1

[0026] A method for preparing nano-HZSM-5 molecular sieve, comprising the following steps:

[0027] Step (1): Add 10.4 g of silicon source tetraethoxysilane, 0.2 g of aluminum source aluminum isopropoxide, and 0.22 g of template agent dioctyl ammonium sulfosuccinate to a supercritical crystallization reactor, heat up to 115 °C, stir at a rate of 500 r / min, and carry out a melting reaction for 3 h to obtain a seed mixture.

[0028] Step (2): Introduce 24.2 g of absolute ethanol into the seed mixture obtained by the melting reaction, heat up to 200 °C, the pressure in the reactor is 5 MPa, stir at a rate of 50 r / min, and carry out a crystallization reaction for 12 h to obtain a reaction product.

[0029] The dosages of the silicon source and aluminum source are calculated based on SiO2 and Al2O3 respectively, and the molar ratio of SiO2, Al2O3, template agent, and absolute ethanol is 1:0.04:0.01:10.5.

[0030] Step (3): Cool the reaction product of step (2) to room temperature, then wash it with deionized water until the pH of the filtrate is 7.0. Finally, dry it at 120 °C for 24 h and calcine it at 550 °C for 3 h to obtain nano-HZSM-5 molecular sieve with a yield of 98.8%.

[0031] Example 2

[0032] A preparation method of nano-HZSM-5 molecular sieve includes the following steps:

[0033] Step (1): Add 10.4 g of silicon source tetraethyl orthosilicate, 0.51 g of aluminum source aluminum isopropoxide, and 1.1 g of template dioctyl ammonium sulfosuccinate (the molar ratio of SiO2, Al2O3, template and absolute ethanol is 1:0.1:0.05:14.3) into a supercritical crystallization reactor, heat it up to 120 °C, stir at a rate of 300 r / min, and carry out a melting reaction for 5 h to obtain a seed mixture;

[0034] Step (2): Introduce 32.9 g of absolute ethanol into the seed mixture obtained from the melting reaction, heat it up to 230 °C, the pressure in the reactor is 7 MPa, stir at a rate of 100 r / min, and carry out a crystallization reaction for 12 h to obtain a reaction product;

[0035] The dosages of the silicon source and aluminum source are calculated based on SiO2 and Al2O3 respectively, and the molar ratio of SiO2, Al2O3, template and absolute ethanol is 1:0.1:0.05:14.3.

[0036] Step (3): Cool the reaction product of step (2) to room temperature, then wash it with deionized water until the pH of the filtrate is 7.0. Finally, dry it at 100 °C for 12 h and calcine it at 500 °C for 5 h to obtain nano-HZSM-5 molecular sieve with a yield of 99.3%.

[0037] Example 3

[0038] A preparation method of nano-HZSM-5 molecular sieve includes the following steps:

[0039] Step (1): Add 10.4 g of silicon source tetraethyl orthosilicate, 0.41 g of aluminum source aluminum isopropoxide, and 0.88 g of template dioctyl ammonium sulfosuccinate into a supercritical crystallization reactor, heat it up to 120 °C, stir at a rate of 350 r / min, and carry out a melting reaction for 4 h to obtain a seed mixture;

[0040] Step (2): Introduce 31.1 g of absolute ethanol into the seed mixture obtained from the melting reaction, heat it up to 240 °C, the pressure in the reactor is 6.5 MPa, stir at a rate of 80 r / min, and carry out a crystallization reaction for 10 h to obtain a reaction product;

[0041] The amounts of the silicon source and the aluminum source are calculated based on SiO2 and Al2O3 respectively, and the molar ratio of SiO2, Al2O3, the templating agent and absolute ethanol is 1:0.08:0.04:13.5.

[0042] Step (3): Cool the reaction product of step (2) to room temperature, then wash it with deionized water until the pH of the filtrate is 7.0, and finally dry it at 110 °C for 20 h and calcine it at 530 °C for 4 h to obtain the nano HZSM-5 molecular sieve, with a yield of 99.0%.

[0043] Example 4

[0044] A preparation method of nano HZSM-5 molecular sieve, comprising the following steps:

[0045] Step (1): Add 10.4 g of silicon source tetraethyl orthosilicate, 0.31 g of aluminum source aluminum isopropoxide and 0.66 g of templating agent dioctyl ammonium sulfosuccinate into a supercritical crystallization reactor, heat up to 118 °C, stir at a rate of 450 r / min, and carry out a melting reaction for 2 h to obtain a seed mixture.

[0046] Step (2): Introduce 27.1 g of absolute ethanol into the seed mixture obtained from the melting reaction, heat up to 250 °C, the pressure in the reactor is 7 MPa, stir at a rate of 70 r / min, and carry out a crystallization reaction for 8 h to obtain a reaction product.

[0047] The amounts of the silicon source and the aluminum source are calculated based on SiO2 and Al2O3 respectively, and the molar ratio of SiO2, Al2O3, the templating agent and absolute ethanol is 1:0.06:0.03:11.8.

[0048] Step (3): Cool the reaction product of step (2) to room temperature, then wash it with deionized water until the pH of the filtrate is 7.0, and finally dry it at 120 °C for 12 h and calcine it at 550 °C for 3 h to obtain the nano HZSM-5 molecular sieve, with a yield of 99.1%.

[0049] Example 5

[0050] A preparation method of nano HZSM-5 molecular sieve, comprising the following steps:

[0051] Step (1): Add 10.4 g of silicon source tetraethyl orthosilicate, 0.36 g of aluminum source aluminum isopropoxide and 1.1 g of templating agent dioctyl ammonium sulfosuccinate into a supercritical crystallization reactor, heat up to 125 °C, stir at a rate of 500 r / min, and carry out a melting reaction for 5 h to obtain a seed mixture.

[0052] Step (2): 29.0 g of absolute ethanol was introduced into the seed mixture obtained by the melting reaction, and the temperature was raised to 200 °C. The pressure in the autoclave was 5.8 MPa, and stirring was carried out at a rate of 60 r / min for 12 h of crystallization reaction to obtain a reaction product.

[0053] The amounts of the silicon source and the aluminum source are calculated based on SiO2 and Al2O3 respectively. The molar ratio of SiO2, Al2O3, the template agent, and absolute ethanol is 1:0.07:0.05:12.6.

[0054] 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 10 h and calcined at 550 °C for 3 h to obtain nano-HZSM-5 molecular sieve with a yield of 98.9%.

[0055] Comparative Example 1

[0056] According to the molar ratio of each raw material in Example 2, but without undergoing the melting reaction, the crystallization reaction was directly carried out:

[0057] Step (1): 10.4 g of silicon source tetraethoxysilane, 0.51 g of aluminum source aluminum isopropoxide, 1.1 g of template agent dioctyl ammonium sulfosuccinate, and 32.9 g of absolute ethanol (the molar ratio of SiO2, Al2O3, the template agent, and absolute ethanol is 1:0.1:0.05:14.3) were added to the supercritical crystallization autoclave, the temperature was raised to 230 °C, the pressure in the autoclave was 7 MPa, and stirring was carried out at a rate of 100 r / min for 12 h of crystallization reaction to obtain a reaction product;

[0058] 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 100 °C for 12 h and calcined at 500 °C for 5 h to obtain a solid product with a yield of 58.5%.

[0059] Comparative Example 2

[0060] According to the molar ratio of each raw material in Example 2, but absolute ethanol was not added during the crystallization reaction:

[0061] Step (1): 10.4 g of silicon source tetraethoxysilane, 0.51 g of aluminum source aluminum isopropoxide, and 1.1 g of template agent dioctyl ammonium sulfosuccinate (the molar ratio of SiO2, Al2O3, and the template agent is 1:0.1:0.05) were added to the supercritical crystallization autoclave, the temperature was raised to 120 °C, and stirring was carried out at a rate of 300 r / min for 5 h of melting reaction to obtain a seed mixture;

[0062] Step (2): Heat the reaction kettle to 230°C, keep the pressure in the kettle at atmospheric pressure, stir at a rate of 100 r / min, and carry out a crystallization reaction for 12 h to obtain a reaction product;

[0063] Step (3): Cool the reaction product in step (2) to room temperature, then wash it with deionized water until the pH of the filtrate is 7.0, and finally dry it at 100°C for 12 h and calcine it at 500°C for 5 h to obtain a solid product, with a yield of 99.1%.

[0064] Comparative Example 3

[0065] According to the molar ratio of each raw material in Example 2, but the crystallization reaction is carried out under supercritical carbon dioxide conditions:

[0066] Step (1): Add 10.4 g of silicon source tetraethyl orthosilicate, 0.51 g of aluminum source aluminum isopropoxide, and 1.1 g of template dioctyl sulfosuccinate ammonium (the molar ratio of SiO2, Al2O3, and template is 1:0.1:0.05) to a supercritical crystallization reaction kettle, heat it to 120°C, stir at a rate of 300 r / min, and carry out a melting reaction for 5 h to obtain a seed mixture;

[0067] Step (2): Introduce carbon dioxide into the seed mixture obtained from the melting reaction, heat it to 230°C, keep the pressure in the kettle at 7.5 MPa, stir at a rate of 100 r / min, and carry out a crystallization reaction for 12 h to obtain a reaction product;

[0068] Step (3): Cool the reaction product in step (2) to room temperature, then wash it with deionized water until the pH of the filtrate is 7.0, and finally dry it at 100°C for 12 h and calcine it at 500°C for 5 h to obtain a solid product, with a yield of 99.5%.

[0069] Comparative Example 4

[0070] According to the molar ratio of each raw material in Example 2, but the grinding method and supercritical carbon dioxide crystallization method are adopted:

[0071] Step (1): Grind (the rotation speed of the grinder is 200 r / min) and mix 10.4 g of silicon source tetraethyl orthosilicate, 0.51 g of aluminum source aluminum isopropoxide, and 1.1 g of template dioctyl sulfosuccinate ammonium (the molar ratio of SiO2, Al2O3, and template is 1:0.1:0.05) for 20 min to obtain a solid-phase reaction mixture;

[0072] Step (2): Place the solid-phase reaction mixture in a supercritical crystallization reaction kettle, introduce carbon dioxide gas, heat it to 230°C, keep the pressure in the kettle at 7.5 MPa, stir at a rate of 100 r / min, and carry out a crystallization reaction for 12 h to obtain a reaction product;

[0073] Step (3): Cool the reaction product of step (2) to room temperature, then wash it with deionized water until the pH of the filtrate is 7.0, and finally dry it at 100 °C for 12 h and calcine it at 500 °C for 5 h to obtain a solid product with a yield of 98.5%.

[0074] The XRD patterns of the samples prepared in Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are as Figure 1 shown; the SEM images of the samples prepared in Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are as Figure 2 shown. The crystallinity of the samples can be obtained from the XRD characterization results, the grain size can be obtained from the SEM characterization, and the specific surface area can be obtained from the BET characterization. The grain size, crystallinity, and specific surface area of the samples prepared in Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are shown in Table 1:

[0075] Table 1

[0076] sample Grain size (nm) Crystallinity (%) <![CDATA[Specific surface area (m 2 / g)]]> Example 2 37 100 592 Comparative Example 2 110 32 270 Comparative Example 3 48 43 558 Comparative Example 4 55 40 521

[0077] Compared with Example 2, in Comparative Example 1, since the seed mixture was not formed through a melting reaction and anhydrous ethanol was present, which had the effect of slowing down crystal growth and making it difficult for crystals to form, most of the tetraethoxysilane and aluminum isopropoxide did not undergo crystallization reactions. Moreover, tetraethoxysilane and aluminum isopropoxide are soluble in ethanol, so they were removed during the washing and filtration processes. Therefore, the yield of the final solid product is relatively low.

[0078] In Comparative Example 2, although the yield was relatively high, because high temperature easily caused the grains to sinter and the crystal growth was too fast, the morphology was irregular. The obtained molecular sieve had a relatively large grain size (110 nm), serious stacking, a relatively low crystallinity (32%), and a small specific surface area (270 m 2 / g). In Example 2, the crystallization reaction was carried out in supercritical ethanol. Supercritical ethanol has high solubility, high diffusivity, and the ability to regulate the crystal growth rate and morphology. Therefore, the obtained molecular sieve had a relatively small grain size (38 nm), high crystallinity (100%), good dispersibility, and a large specific surface area (592 m 2 / g).

[0079] In Comparative Example 3, although supercritical carbon dioxide also has high solubility and high diffusivity, it does not have the ability to regulate the crystal growth rate and morphology of supercritical ethanol. Therefore, the grain size of the obtained molecular sieve (48 nm) is larger than that in Example 2.

[0080] Comparative Example 4 and Comparative Example 3 were also subjected to a crystallization reaction under supercritical carbon dioxide conditions. However, in Comparative Example 4, a solid-phase reaction mixture was first obtained by a grinding method, while in Comparative Example 3, a seed mixture was obtained by the melting reaction in the examples of the present invention. The raw materials contacted and reacted more fully in the molten state, which was conducive to the generation of a large number of seeds. Under the condition of the same amount of raw materials, the more the number of seeds, the smaller the final grain size of the crystal. Therefore, the grain size of the molecular sieve obtained in Comparative Example 3 (48 nm) was smaller than that of the molecular sieve obtained in Comparative Example 4 (55 nm), and the yield of the molecular sieve obtained in Comparative Example 3 was higher than that in Comparative Example 4.

[0081] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation of the present invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the present invention.

Claims

1. A preparation method of nano HZSM-5 molecular sieve, characterized in that, It includes the following steps: Step 1: Add a silicon source, an aluminum source, and a template agent into a supercritical crystallization reactor, raise the temperature, and stir to cause the raw materials to undergo a melting reaction at 115 - 125°C for 1 - 5 h to obtain a seed mixture; Step 2: Pass anhydrous ethanol into the seed mixture obtained from the melting reaction, raise the temperature, and stir to carry out a crystallization reaction to obtain a reaction product; The crystallization reaction conditions are: temperature is 200 - 250°C, pressure is 5 - 7 MPa, and reaction time is 6 - 12 h; Step 3: Cool, wash, dry, and calcine the reaction product obtained in Step 2 to obtain a nano HZSM-5 molecular sieve.

2. The preparation method according to claim 1, characterized in that, The dosages of the silicon source and the aluminum source are calculated based on SiO2 and Al2O3 respectively, and the molar ratio of SiO2, Al2O3, the template agent, and anhydrous ethanol is 1:(0.04 - 0.1):(0.01 - 0.05):(10.5 - 14.3).

3. The preparation method according to claim 1, characterized in that, In Step 1, the silicon source is tetraethyl orthosilicate; the aluminum source is aluminum isopropoxide; the template agent is dioctyl sulfosuccinate ammonium.

4. The preparation method according to claim 1, characterized in that, In Step 1, during the melting reaction, the stirring rate is 300 - 500 r / min.

5. The preparation method according to claim 1, characterized in that, In Step 2, during the crystallization reaction, the stirring rate is 50 - 100 r / min.

6. The preparation method according to claim 1, wherein In Step 3, cool the reaction product obtained in Step 2 to room temperature, then wash it with deionized water until the pH of the filtrate is 7.0, and then carry out drying and calcination.

7. The preparation method according to claim 1, characterized in that In Step 3, the drying temperature is 100 - 120°C and the time is 12 - 24 h; the calcination temperature is 500 - 550°C and the time is 3 - 5 h.

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