Preparation method and application of nanoscale H-ZSM-5 with low silica-alumina ratio

Abstract

The invention discloses a preparation method of nanoscale H-ZSM-5 with a low silica-alumina ratio and an application of the nanoscale H-ZSM-5. Comprising the following steps: (1) mixing a silicon source with water to obtain a solution A; (2) mixing an aluminum source with water to obtain a solution B; (3) mixing tetraethylammonium bromide with water to obtain a solution C; and (4) adding the solution B into the solution A, then adding the solution C, stirring, crystallizing, separating, washing, drying and roasting to obtain the nanoscale H-ZSM-5 with the low silica-alumina ratio, the silica-alumina ratio is 32-60, the raw materials are cheap, the use amount of the organic template agent is small, the synthesis time is short, the yield is high, the product morphology is nanocrystalline, and the nanoscale H-ZSM-5 has a good application prospect in the fields of petrochemical engineering and fine chemical engineering.

Description

Technical Field

[0001] The present application relates to a preparation method and application of nano-scale H-ZSM-5 with a low silicon-aluminum ratio, and belongs to the field of molecular sieve synthesis. Background Art

[0002] Since ZSM-5 was first synthesized by Mobil in 1972, it has been widely used in catalytic cracking, aromatic alkylation, aromatization and other reactions due to its unique three-dimensional channel structure and selectable acid strength distribution. Due to its unique pore structure, it not only provides a space confinement effect for shape-selective catalysis, but also provides rich access channels for reactants and products, and also provides a crystal structure basis for the preparation of industrial catalysts with high selectivity, high activity and strong anti-coking deactivation performance. Therefore, ZSM-5 molecular sieve has been widely used in the oil refining industry, mainly in: increasing the octane number of gasoline, hydrodewaxing of diesel, reducing olefins in catalytic cracking gasoline, catalytic dewaxing of lubricating oil, selective conversion of methanol and selective conversion of aromatics. In addition, nano-scale crystalline ZSM-5 molecular sieve has attracted wide attention. Compared with conventional molecular sieves, nano-scale crystalline ZSM-5 molecular sieve has a large external surface area, which can expose more active centers. At the same time, it has short pore channels and many pore mouths, which can reduce carbon deposition and extend the service life of the catalyst. Therefore, nano-scale crystalline ZSM-5 molecular sieve shows superior performance in improving the efficiency of the catalyst, the ability to convert macromolecules, selectivity and extending the service life of the catalyst. ZSM-5 molecular sieve has good application prospects in the petroleum industry, and its research has important practical value.

[0003] The catalytic reaction activity of ZSM-5 zeolite molecular sieve depends on its shape selectivity and acidity, where the acidity includes the nature of acid sites (B acid / L acid), acid site concentration, acid site strength, distribution and the position of acid sites. Most catalytic reactions rely on the concentration of B acid sites, and for a specific zeolite molecular sieve structure, the concentration of B acid sites can be changed by adjusting its framework composition, that is, adjusting the framework silicon-aluminum ratio of the zeolite molecular sieve. For special catalytic reactions, ZSM-5 molecular sieve catalysts with a high B acid concentration, that is, a low silicon-aluminum ratio, are often required.

[0004] There are many synthesis methods for ZSM-5 zeolite molecular sieves, and the raw materials and ratios are also different. The raw materials are compounds containing silicon and aluminum, and ratios ranging from low silicon-aluminum ratios to all-silicon can be synthesized. CN110885089A describes that sodium hydroxide, aluminum sulfate, silicon dioxide, tetrapropylammonium bromide, and ZSM-5 seeds are added in an aqueous environment, and a temperature environment is provided according to a preset temperature curve. Thus, ZSM-5 molecular sieves with a silicon-aluminum ratio less than 23 can be prepared; CN101898767A describes that a silicon source, an aluminum source, sulfuric acid or hydrochloric acid, an organic template agent, and a guiding gel are added to synthesize high-silicon ZSM-5 zeolite with a silicon-aluminum ratio greater than 100. CN107055568A describes that a silicon source, an aluminum source, sulfuric acid, and seeds are added to synthesize conventional ZSM-5 molecular sieves under variable temperature conditions of 80-130 °C. The basic synthesis methods all add seeds or guiding gels, increasing the synthesis steps and costs. In addition, the synthesized samples are micron-sized crystals. There are few reports on low-silicon-aluminum ratio nanoscale crystals without adding seeds in the synthesis method. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method and application of nanoscale H-ZSM-5 with a low silicon-aluminum ratio. To provide a synthesis method with a simple process, environmental friendliness, and low cost. The raw materials used are inexpensive, simple to operate, have no special requirements for equipment, and are suitable for industrial production and application. Nanoscale ZSM-5 has characteristics such as strong reaction activity, strong anti-coking ability, good hydrothermal stability, and high dispersion of supported metal components. The prepared ZSM-5 molecular sieve can be used in the cracking reaction of n-heptane and the aromatization reaction of n-hexane coupling with methanol.

[0006] According to one aspect of the present application, a preparation method of nanoscale H-ZSM-5 with a low silicon-aluminum ratio is provided, including the following steps:

[0007] (1) Mix the silicon source with water to obtain solution A;

[0008] (2) Mix the aluminum source with water to obtain solution B;

[0009] (3) Mix tetraethylammonium bromide with water to obtain solution C;

[0010] (4) Add solution B to solution A, then add solution C, stir, crystallize, separate, wash, dry, and calcine to obtain the nanoscale H-ZSM-5 with a low silicon-aluminum ratio.

[0011] The silicon source is selected from at least one of water glass, silica sol, white carbon black, and tetraethyl orthosilicate;

[0012] The aluminum source is selected from at least one of aluminum sulfate, pseudo-boehmite, and sodium aluminate;

[0013] The molar ratio of each substance is silicon source: aluminum source: water: tetraethylammonium bromide = 38 - 75:1:1400 - 2500:3 - 20;

[0014] Among them, the molar amount of the silicon source is calculated based on the molar amount of SiO2 therein;

[0015] The molar amount of the aluminum source is calculated based on the molar amount of Al2O3 therein.

[0016] The temperature of the crystallization is 140 - 190 °C;

[0017] Optionally, the temperature of the crystallization is any value among 140, 150, 160, 170, 180, 190 or the range value between any two of them.

[0018] The time of the crystallization is 24 - 48 h.

[0019] Optionally, the time of the crystallization is any value among 24 h, 36 h, 42 h, 48 h or the range value between any two of them.

[0020] The temperature of the drying is 80 - 120 °C;

[0021] Optionally, the temperature of the drying is any value among 80 °C, 90 °C, 100 °C, 110 °C, 120 °C or the range value between any two of them.

[0022] The time of the drying is 12 - 48 h;

[0023] Optionally, the time of the drying is any value among 12 h, 24 h, 36 h, 48 h or the range value between any two of them.

[0024] The temperature of the first calcination is 550 - 650 °C;

[0025] Optionally, the temperature of the first calcination is any value among 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C, 610 °C, 620 °C, 630 °C, 640 °C, 650 °C or the range value between any two of them.

[0026] The time of the first calcination is 3 - 6 h;

[0027] Optionally, the time of the first calcination is any value among 3 h, 4 h, 5 h, 6 h or the range value between any two of them.

[0028] Optionally, it includes the following steps:

[0029] S1, Mix water glass and water to form solution A;

[0030] S2, Dissolve aluminum sulfate and sulfuric acid in water to form solution B;

[0031] S3, tetraethylammonium bromide and water are mixed to form solution C; and

[0032] S4, solution B is added to solution A, and then solution C is added to form a ZSM-5 molecular sieve gel system. The mixture is stirred evenly, crystallized, the lower-layer solid is collected, centrifugally washed with deionized water until the pH is neutral, dried, and calcined to obtain Na-type ZSM-5 molecular sieve. Then it is soaked in ammonium chloride solution for ion exchange, the lower-layer solid is collected, centrifugally washed with deionized water until the pH is neutral, dried, and calcined to obtain the H-type ZSM-5 molecular sieve powder.

[0033] The modulus of the water glass is 2.3 - 3.3, and optionally, the modulus of the water glass is 2.6.

[0034] The molar ratio of each substance is 15 - 25Na2O:38 - 75SiO2:Al2O3:1400 - 2500H2O:9 - 13.6H2SO4:3 - 20tetraethylammonium bromide.

[0035] The concentration of the ammonium chloride solution is 0.1 - 1 mol / L.

[0036] According to another aspect of the present application, there is provided a low-silica-alumina ratio nano-sized H-ZSM-5 prepared by the above preparation method, and the silica-alumina ratio of the low-silica-alumina ratio nano-sized H-ZSM-5 is 32 - 60;

[0037] The particle size of the low-silica-alumina ratio nano-sized H-ZSM-5 is 4 - 30 μm;

[0038] The specific surface area of the low-silica-alumina ratio nano-sized H-ZSM-5 is 330 - 350 m 2 / g;

[0039] The pore volume of the low-silica-alumina ratio nano-sized H-ZSM-5 is 0.2 - 0.4 cm 3 / g.

[0040] According to another aspect of the present application, there is provided an application of the above low-silica-alumina ratio nano-sized H-ZSM-5 in the cracking reaction of n-heptane.

[0041] According to another aspect of the present application, there is provided an application of the above low-silica-alumina ratio nano-sized H-ZSM-5 in the aromatization reaction of n-hexane coupling with methanol.

[0042] The beneficial effects that the present application can produce include:

[0043] The technical solution of this application can synthesize low-silica H-ZSM-5 molecular sieve, with less template agent consumption, short synthesis time, low raw material price, simple operation process, and easy production control. The prepared ZSM-5 molecular sieve is in the form of nanocrystals and is applicable to the petrochemical field. Description of the Drawings

[0044] Figure 1 SEM image of the H-ZSM-5 molecular sieve in Example 1.

[0045] Figure 2 SEM image of the H-ZSM-5 molecular sieve in Example 2.

[0046] Figure 3 SEM image of the H-ZSM-5 molecular sieve in Example 3.

[0047] Figure 4 SEM image of the H-ZSM-5 molecular sieve in Example 4.

[0048] Figure 5 SEM image of the H-ZSM-5 molecular sieve in Example 5.

[0049] Figure 6 Flow chart of the preparation method of a nano-scale H-ZSM-5 with a low silica-to-alumina ratio according to the present invention. Detailed Description of the Invention

[0050] The following describes this application in detail with reference to the examples, but this application is not limited to these examples.

[0051] Unless otherwise specified, the raw materials in the examples of this application are all purchased through commercial channels.

[0052] Example 1

[0053] 1) Add 21.00 g of deionized water and 20.10 g of water glass (modulus 2.6) to a 100 mL stainless steel synthesis kettle and stir for 30 min;

[0054] 2) Add 1.10 g of aluminum sulfate, 10 g of water, and 2.20 g of sulfuric acid (98%) to beaker A and stir evenly;

[0055] 3) Add 2.20 g of tetraethylammonium bromide and 10 g of deionized water to beaker B and stir evenly;

[0056] 4) Slowly drip the solution in beaker A into the kettle while stirring, and then drip the solution in beaker B into the kettle;

[0057] 5) Continue stirring for 2 hours to obtain the initial reaction gel. After sealing, heat up to 180 °C and carry out dynamic crystallization for 36 hours.

[0058] 6) After crystallization, centrifuge, and wash the filter cake 4 times at room temperature, with each pulping for 10 minutes, until the pH value of the centrifugate is 7-8.

[0059] 7) Dry the filter cake at 100 °C and calcine it at 550 °C for 3 hours to obtain Na-ZSM-5 molecular sieve.

[0060] 8) Add Na-ZSM-5 molecular sieve to the flask, then add 52.00 g of 0.2 mol / L ammonium chloride solution, and stir at 90 °C for 2 h.

[0061] 9) Centrifuge, and wash the filter cake 3 times at room temperature, with each pulping for 10 minutes, and use silver nitrate solution for the identification of Cl - .

[0062] 10) Dry the filter cake at 100 °C and calcine it at 550 °C for 3 hours to obtain H-ZSM-5 molecular sieve. The silica-aluminum ratio (SiO2 / Al2O3) mol / mol of the H-ZSM-5 molecular sieve is 43, the specific surface area is 344.51 m 2 / g, the pore volume is 0.21 cm 3 / g, the particle size is 10.1 μm, and its SEM image is as Figure 1 shown.

[0063] Example 2

[0064] 1) Add 19.00 g of deionized water and 17.50 g of water glass (modulus 2.6) to a 100 mL stainless steel synthesis kettle and stir for 30 min;

[0065] 2) Add 1.30 g of aluminum sulfate, 10 g of water, and 1.90 g of sulfuric acid (98%) to beaker A and stir evenly;

[0066] 3) Add 2.00 g of tetraethylammonium bromide and 10 g of deionized water to beaker B and stir evenly;

[0067] 4) Slowly drip the solution in beaker A into the kettle while stirring, and then drip the solution in beaker B into the kettle;

[0068] 5) Continue to stir for 2 hours to obtain the initial reaction gel. After sealing, heat up to 180 °C and carry out dynamic crystallization for 36 hours.

[0069] 6) After crystallization, centrifuge, and wash the filter cake 4 times at room temperature, with each pulping for 10 minutes, until the pH value of the centrifugate is 7-8.

[0070] 7) Dry the filter cake at 100 °C and calcine it at 550 °C for 3 hours to obtain Na-ZSM-5 molecular sieve.

[0071] 8) Add Na-ZSM-5 molecular sieve into the flask, and then add 49.00 g of 0.25 mol / L ammonium chloride solution. Stir for 2 h at 90 °C.

[0072] 9) Centrifuge, wash the filter cake 3 times at room temperature, and beat the pulp for 10 minutes each time. The identification of Cl can be carried out using silver nitrate solution. - identification.

[0073] 10) Dry the filter cake at 100 °C and calcine it at 550 °C for 3 hours to obtain H-ZSM-5 molecular sieve. The silicon-aluminum ratio (SiO2 / Al2O3) mol / mol of H-ZSM-5 molecular sieve is 34, the specific surface area is 340.82 m 2 / g, the pore volume is 0.23 cm 3 / g, the particle size is 4.83 μm, and its SEM image is as Figure 2 shown.

[0074] Example 3

[0075] On the basis of Example 2, adjust 1.90 g of sulfuric acid (98%) to 2.10 g, and keep the amounts of the remaining raw materials and conditions unchanged. The silicon-aluminum ratio (SiO2 / Al2O3) mol / mol of -ZSM-5 molecular sieve is 35, the specific surface area is 333.64 m 2 / g, the pore volume is 0.34 cm 3 / g, the particle size is 6.80 μm, and its SEM image is as Figure 3 shown.

[0076] Example 4

[0077] 1) Add 25.00 g of deionized water and 25.20 g of water glass (modulus 3.2) into a 100 mL stainless steel synthesis kettle and stir for 30 min;

[0078] 2) Add 1.10 g of aluminum sulfate, 10 g of water, and 2.00 g of sulfuric acid (98%) into beaker A and stir evenly;

[0079] 3) Add 2.00 g of tetraethylammonium bromide and 10 g of deionized water into beaker B and stir evenly;

[0080] 4) Slowly drip the solution in beaker A into the kettle while stirring, and then drip the solution in beaker B into the kettle;

[0081] 5) Continue to stir for 2 hours to obtain the initial reaction gel. After sealing, heat up to 180 °C and carry out dynamic crystallization for 36 hours.

[0082] 6) After crystallization, centrifuge, wash the filter cake 4 times at room temperature, and beat the pulp for 10 minutes each time until the pH value of the centrifugate is 7 - 8.

[0083] 7) The filter cake is dried at 100 °C and calcined at 550 °C for 3 hours to obtain Na-ZSM-5 molecular sieve.

[0084] 8) Add Na-ZSM-5 molecular sieve to the flask, and then add 49.50 g of 0.25 mol / L ammonium chloride solution, and stir at 90 °C for 2 h.

[0085] 9) Centrifuge, wash the filter cake 3 times at room temperature, and beat the pulp for 10 minutes each time. The identification of Cl can be carried out using silver nitrate solution. - The identification of.

[0086] 10) The filter cake is dried at 100 °C and calcined at 550 °C for 3 hours to obtain H-ZSM-5 molecular sieve. The silica-alumina ratio (SiO2 / Al2O3) mol / mol of H-ZSM-5 molecular sieve is 54, the specific surface area is 346.25 m 2 / g, the pore volume is 0.25 cm 3 / g, the particle size is 13.00 μm, and its SEM image is as Figure 4 shown.

[0087] Example 5

[0088] 1) Add 19.20 g of silica sol (SiO2 content 25%), 6.9 g of 10% sodium hydroxide solution, and 7.7 g of deionized water to a 100 mL stainless steel synthesis kettle, and stir for 30 min;

[0089] 2) Add 7.7 g of deionized water and 0.34 g of sodium aluminate to beaker A, and stir evenly;

[0090] 3) Add 2.00 g of tetraethylammonium bromide and 10 g of deionized water to beaker B, and stir evenly;

[0091] 4) Slowly drip the solution in beaker A into the kettle while stirring, and then drip the solution in beaker B into the kettle;

[0092] 5) Continue to stir for 2 hours to obtain an initial reaction gel. After sealing, heat up to 190 °C and carry out dynamic crystallization for 24 hours.

[0093] 6) After crystallization, centrifuge, wash the filter cake 4 times at room temperature, and beat the pulp for 10 minutes each time until the pH value of the centrifugate is 7-8.

[0094] 7) The filter cake is dried at 110 °C and calcined at 650 °C for 3 hours to obtain Na-ZSM-5 molecular sieve.

[0095] 8) Add Na-ZSM-5 molecular sieve to the flask, and then add 49.50 g of 0.5 mol / L ammonium chloride solution, and stir at 90 °C for 2 h.

[0096] 9) Centrifuge, wash the filter cake at room temperature 3 times, each time for 10 minutes of pulping, and silver nitrate solution can be used for the identification of Cl - .<

[0097] 10) Dry the filter cake at 100 °C and calcine it at 650 °C for 3 hours to obtain H-ZSM-5 molecular sieve. The silica-alumina ratio (SiO2 / Al2O3) mol / mol of the H-ZSM-5 molecular sieve is 32, the specific surface area is 348.8 m 2 / g, the pore volume is 0.20 cm 3 / g, the particle size is 11.10 μm, and its SEM image is as shown Figure 5 .

[0098] Example 6

[0099] The n-heptane cracking reaction is carried out on an atmospheric pressure micro fixed-bed reaction device. The ZSM-5 molecular sieve raw powder obtained in Example 1 is pressed into tablets with a tablet press, then ground, and then screened with a sieve. Take 0.1 g of the 40-60 mesh screened sample and fill it into the fixed-bed reactor. The inner diameter of the reactor is 6 mm, and then in an argon atmosphere at a heating rate of 5 °C·min -1 heat up to 550 °C for pretreatment for 30 min, and then turn on the n-heptane feed pump to start the reaction. The weight hourly space velocity (WHSV) is 3.4 h -1 . The reaction products are introduced into an on-line gas chromatograph through heat preservation throughout the process. The chromatograph is equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). After the reaction starts, ethylene, propylene, and butene can be clearly observed in the gas chromatograph. -1 .

[0100] As described above, only several embodiments of the present application are shown, and the present application is not limited in any form. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A preparation method of nano - scale H - ZSM - 5 with a low silica - alumina ratio, characterized in that, it comprises the following steps: (1) Mix a silicon source with water to obtain solution A; (2) Mix an aluminum source with water to obtain solution B; (3) Mix tetraethylammonium bromide with water to obtain solution C; (4) Add solution B to solution A, then add solution C, stir, crystallize, separate, wash, dry, and calcine to obtain the nano - scale H - ZSM - 5 with a low silica - alumina ratio.

2. The preparation method according to claim 1, characterized in that, the silicon source is selected from at least one of water glass, silica sol, white carbon black, and tetraethyl orthosilicate; the aluminum source is selected from at least one of aluminum sulfate, pseudo - boehmite, and sodium metaaluminate.

3. The preparation method according to claim 1, characterized in that, the molar ratio of each substance is silicon source: aluminum source: water: tetraethylammonium bromide = 38 - 75:1:1400 - 2500:3 - 20; wherein, the molar amount of the silicon source is calculated based on the molar amount of SiO₂ therein; the molar amount of the aluminum source is calculated based on the molar amount of Al₂O₃ therein.

4. The preparation method according to claim 1, characterized in that, the temperature of the crystallization is 140 - 190 °C; the time of the crystallization is 24 - 48 h.

5. The preparation method according to claim 1, characterized in that, the temperature of the drying is 80 - 120 °C; the time of the drying is 12 - 48 h.

6. The preparation method according to claim 1, characterized in that, the temperature of the first calcination is 550 - 650 °C; the time of the first calcination is 3 - 6 h.

7. A nano - scale H - ZSM - 5 with a low silica - alumina ratio prepared by the preparation method according to any one of claims 1 - 6, characterized in that, the silica - alumina ratio of the nano - scale H - ZSM - 5 with a low silica - alumina ratio is 32 - 60; the particle size of the nano - scale H - ZSM - 5 with a low silica - alumina ratio is 4 - 30 μm; The specific surface area of the nano-scale H-ZSM-5 with a low silicon-aluminum ratio is 330 to 350 m 2 / g; The pore volume of the nano-sized H-ZSM-5 with a low silica-alumina ratio is 0.2 to 0.4 cm 3 / g.

8. An application of the nano - scale H - ZSM - 5 with a low silica - alumina ratio according to claim 7, characterized in that, it is used for the cracking reaction of n - heptane.

9. An application of the nano - scale H - ZSM - 5 with a low silica - alumina ratio according to claim 7, characterized in that, it is used for the aromatization reaction of n - hexane coupling with methanol.

Images