Method for preparing amine-free high-silicon zsm-5 molecular sieve with variable basicity

Abstract

The application discloses a method for preparing amine-free high-silicon ZSM-5 molecular sieves with variable alkalinity, which comprises the following steps: mixing a silicon source, an aluminum source, an alkali source, water and seeds to obtain a first mixture, and then performing a first hydrothermal reaction to obtain a first hydrothermal reaction product; mixing the first hydrothermal reaction product with additional water or mixing the first hydrothermal reaction product with additional water and ethanol to obtain a second mixture, and then performing a second hydrothermal reaction. Small crystal nuclei are formed under high alkalinity, and the second step of adding water or further adding ethanol is performed, and then the ZSM-5 molecular sieves with a high crystallinity and a silicon-aluminum molar ratio of 35-60 can be prepared under low alkalinity.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation and application of molecular sieve, more particularly, the present application relates to a method for preparing high-silicon ZSM-5 molecular sieve without amine and the application of the obtained molecular sieve in catalytic cracking of light hydrocarbon. BACKGROUND

[0002] ZSM-5 molecular sieve has a unique three-dimensional cross-pore system and MFI topological structure, and has two kinds of cross-linked ten-membered ring pores. Due to the strong selective adsorption performance, good thermal stability and hydrothermal stability, and moderate acidity, it is suitable for various catalytic reactions of hydrocarbons, such as catalytic cracking, isomerization, aromatization, alkylation, etc., and is widely used in the field of petroleum chemical industry and industrial catalysis.

[0003] The traditional hydrothermal synthesis method must add quaternary ammonium cations or other organic amine molecules as a template, i.e. amine method. At present, the synthesis of high-silicon aluminum ratio ZSM-5 molecular sieve is mostly synthesized by amine method. Although the organic amine molecules with strong structure guiding effect are used as the template, ZSM-5 molecular sieve with uniform particle size, regular pore and crystal shape can be synthesized under relatively wide conditions, but the synthesized ZSM-5 molecular sieve has small crystal grain and low stability in harsh reaction environment of catalytic cracking. In addition, the organic amine template has high toxicity, a large amount of organic wastewater is generated in the synthesis process, and the air will be polluted and the performance of the molecular sieve will be affected when the template is calcined and decomposed. The large amount of use of expensive template will greatly increase the production cost of the molecular sieve.

[0004] The method for synthesizing ZSM-5 molecular sieve without organic amine template system, i.e. the amine-free method, has the characteristics of environmental friendliness and low cost, and has been favored by researchers in recent years. More and more amine-free methods for synthesizing ZSM-5 molecular sieve have emerged. However, compared with the traditional synthesis method, the amine-free method needs a longer crystallization time, because the absence of the guiding effect of the organic amine molecules leads to the increase of the nucleation activation energy and the growth activation energy. In addition, the absence of the guiding effect of the organic amine molecules makes it more difficult to form crystal nuclei, and the transformation phenomenon is prone to occur, so the synthesis phase region of the ZSM-5 molecular sieve by the amine-free method is relatively narrow. If seeds containing formed crystal nuclei are added to the synthesis solution, a large number of specific crystal nuclei can be induced to form in a short time, which not only shortens the crystallization time but also widens the synthesis phase region, and greatly avoids the co-crystallization and transformation phenomenon, i.e. the seed method. The seed method for preparing ZSM-5 molecular sieve with a silicon-aluminum ratio of about 25 has been realized industrial application, but the ZSM-5 molecular sieve with a silicon-aluminum ratio of about 25 has a relatively high acidity and has the disadvantage of a high degree of hydrogen transfer reaction. It is found that the ZSM-5 molecular sieve with a silicon-aluminum ratio of 35-50 is more suitable for catalyzing cracking to produce more low-carbon olefins. However, it is a difficult problem to synthesize ZSM-5 molecular sieve with a high silicon-aluminum ratio by the amine-free method, because although the seed guiding effect can guide the synthesis of ZSM-5 molecular sieve with a low silicon-aluminum ratio, when the seed guiding effect is used to synthesize ZSM-5 molecular sieve with a high silicon-aluminum ratio, the activation energy of nucleation and growth is relatively high, and it is relatively difficult to form crystal nuclei in a short time. Therefore, even if seeds are added to synthesize ZSM-5 molecular sieve with a high silicon-aluminum ratio, the crystallinity of the ZSM-5 molecular sieve is still relatively low.

[0005] For the synthesis of ZSM-5 molecular sieve by the amine-free method, CN105621451A and CN105692652A disclose a preparation method for synthesizing ZSM-5 molecular sieve without using a template agent. The preparation method mixes a silicon source, an alkali source, an aluminum source, seeds and deionized water, and prepares ZSM-5 molecular sieve through two-stage crystallization. The preparation method synthesizes the molecular sieve without using a template agent, under the conditions of low water-silicon ratio and controlled heating rate and two-stage crystallization. Although the preparation method has relatively high crystallinity when synthesizing ZSM-5 molecular sieve with a silicon-aluminum ratio of 20-25, the crystallinity of the molecular sieve is relatively low when synthesizing ZSM-5 molecular sieve with a silicon-aluminum ratio of 35-60 or higher. CN108190913A discloses a method for synthesizing a silicon-rich ZSM-5 zeolite molecular sieve by a seed guiding method. The method introduces methanol or ethanol as a pore filling agent to obtain a molecular sieve with completely open pores. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the existing amine-free method, and to provide a method for preparing ZSM-5 molecular sieve with a silicon-aluminum ratio of 35-60 and high crystallinity and to provide an application thereof.

[0007] To achieve the above object, the first aspect of the present application provides a method for preparing an amine-free high-silicon ZSM-5 molecular sieve with variable alkalinity, comprising:

[0008] S1, a first mixture obtained by mixing a silicon source, an aluminum source, an alkali source, water and seeds is subjected to a first hydrothermal reaction to obtain a first hydrothermal reaction product, wherein the molar ratio of the silicon source, the aluminum source, the alkali source and the water is (40-70):1:(1-5):(400-700), and the amount of the seeds is 1-10% by weight of the amount of the silicon source;

[0009] S2, the first hydrothermal reaction product is mixed with additional water or the first hydrothermal reaction product is mixed with additional water and ethanol to obtain a second mixture for a second hydrothermal reaction;

[0010] Wherein, the total amount of water in step S1 and the additional water in step S2 is in a molar ratio of 720-1000:1 to the aluminum source, the molar ratio of the ethanol to the silicon source is 0.1-1, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the alkali source is calculated as alkali metal oxide, and the seeds are calculated as SiO2.

[0011] In step S1, the first hydrothermal reaction has a temperature of 160-180℃ and a time of 1-8 hours; in step S2, the second hydrothermal reaction has a temperature of 160-180℃ and a time of 4-11 hours. The total crystallization time is 10-16 hours.

[0012] In step S1, the molar ratio of the amount of the silicon source, the aluminum source, the alkali source and the water is (55-65):1:(4-5):(500-700), and the amount of the seeds is 8-10% by weight of the amount of the silicon source.

[0013] In step S2, when the first hydrothermal reaction product is mixed with additional water and ethanol, the molar ratio of the ethanol to the silicon source is 0.1-1, preferably 0.1-0.5.

[0014] In the method provided by the present application, the total amount of water in step S1 and the additional water in step S2 is in a molar ratio of 720-1000:1, preferably 800-1000:1, to the aluminum source.

[0015] The silicon source is selected from one or more of silica gel, water glass, silicon dioxide and white carbon black; the aluminum source is selected from one or more of sodium metaaluminate, SB powder, aluminum oxide, aluminum hydroxide and aluminum sulfate; the alkali source is independently selected from one or more of sodium hydroxide and potassium hydroxide; the ethanol is anhydrous ethanol;

[0016] The seed crystal is ZSM-5 molecular sieve with a molar ratio of silicon oxide to aluminum oxide of 25-50.

[0017] Optionally, the method further comprises a step S3 of collecting the product obtained from the second hydrothermal reaction, and sequentially performing filtration, washing, ammonium exchange, drying and calcination on the product. The calcination is performed under conditions of a temperature of 400-800 ℃, a time of 0.5-8 h, and an air atmosphere or a water vapor atmosphere.

[0018] To achieve the above-mentioned purpose, the second aspect of the present application provides an amine-free high-silicon ZSM-5 molecular sieve prepared by the method of the first aspect of the present application. The amine-free high-silicon ZSM-5 molecular sieve has a molar ratio of SiO2 to Al2O3 of 35-60, a relative crystallinity of 80-95%, and a specific surface area of 240-360 m 2 / g.

[0019] To achieve the above-mentioned purpose, the third aspect of the present application provides a light hydrocarbon catalytic cracking reaction method, characterized in that the amine-free high-silicon ZSM-5 molecular sieve provided by the second aspect of the present application is used as a catalyst.

[0020] The method for preparing a high-silicon aluminum ratio ZSM-5 molecular sieve with variable alkalinity and without amine provided by the present application adopts a method of forming a small crystal nucleus initial product at a high alkalinity in a first-stage crystallization, and then performing a second-stage crystallization by supplementing water or supplementing water and ethanol, so that the small crystal nucleus continues to grow at a low alkalinity in the second-stage crystallization. In addition, the method further crystallizes the unused silicon source at a low alkalinity to further improve the crystallinity, and can prepare a ZSM-5 molecular sieve with a silicon aluminum ratio of 35-60 and high crystallinity. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is an X-ray diffraction spectrum of the ZSM-5 molecular sieve sample A1 prepared in Example 1;

[0022] Figure 2 is an X-ray diffraction spectrum of the ZSM-5 molecular sieve sample A2 prepared in Example 2;

[0023] Figure 3 is a scanning electron microscope photo of the ZSM-5 molecular sieve sample A2 prepared in Example 2;

[0024] Figure 4 is an X-ray diffraction spectrum of the ZSM-5 molecular sieve sample A3 prepared in Example 3;

[0025] Figure 5 is a scanning electron microscope photo of the ZSM-5 molecular sieve sample A3 prepared in Example 3;

[0026] Figure 6X-ray diffraction spectrum of comparative sample D1 of ZSM-5 molecular sieve prepared in Comparative Example 1;

[0027] Figure 7 Scanning electron microscope photograph of comparative sample D1 of ZSM-5 molecular sieve prepared in Comparative Example 1;

[0028] Figure 8 X-ray diffraction spectrum of comparative samples D3 and D4 of ZSM-5 molecular sieve prepared in Comparative Examples 3 and 4;

[0029] Figure 9 X-ray diffraction spectrum of ZSM-5 molecular sieve samples A7 and A8 prepared in Examples 7 and 8.

[0030] Figure 10 Scanning electron microscope photograph of ZSM-5 molecular sieve sample A7 prepared in Example 7.

[0031] Figure 11 Scanning electron microscope photograph of ZSM-5 molecular sieve sample A8 prepared in Example 8.

[0032] Figure 12 X-ray diffraction spectrum of comparative sample D5 of ZSM-5 molecular sieve prepared in Comparative Example 5.

[0033] Figure 13 X-ray diffraction spectrum of comparative sample D6 of ZSM-5 molecular sieve prepared in Comparative Example 6.

[0034] Figure 14 Scanning electron microscope photograph of comparative sample D6 of ZSM-5 molecular sieve prepared in Comparative Example 6. DETAILED DESCRIPTION

[0035] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0036] The first aspect of the present application provides a method for preparing an amine-free high-silicon ZSM-5 molecular sieve with variable alkalinity, which comprises:

[0037] S1, a first mixture obtained by mixing a silicon source, an aluminum source, an alkali source, water and seeds is subjected to a first hydrothermal reaction to obtain a first hydrothermal reaction product, wherein the molar ratio of the silicon source, the aluminum source, the alkali source and the water is (40-70):1:(1-5):(400-700), and the amount of the seeds is 1-10% by weight of the amount of the silicon source;

[0038] S2, subjecting the second mixture obtained by mixing the first hydrothermal reaction product with additional water and ethanol to a second hydrothermal reaction, the molar ratio of the ethanol to the silicon source being 0.1-1;

[0039] The total amount of water, including the water in step S1 and the additional water in step S2, and the aluminum source has a molar ratio of 720-1000:1, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the alkali source is calculated as alkali metal oxide, and the seed crystal is calculated as SiO2.

[0040] The present application adopts a two-stage crystallization secondary water supply scheme or a water supply and ethanol supply scheme, that is, small crystal nuclei are formed under high alkalinity, the alkalinity is diluted by adding water after one-stage crystallization, and a more favorable environment for crystal growth is formed to improve the crystallinity; or on the basis of adding water to dilute the alkalinity, further adding ethanol, in addition to forming a more favorable environment for crystal growth, and promoting the further crystallization and growth of the silicon source that is not fully utilized after one-stage crystallization, further improving the crystallinity. The method provided by the present application is simple to operate and has no ammonia-nitrogen wastewater discharge. Compared with the prior art method of one-stage crystallization with one-time feeding, the ZSM-5 molecular sieve prepared by the method has a higher silicon-aluminum ratio and a higher relative crystallinity, and is more suitable for catalytic cracking of light hydrocarbons.

[0041] In one specific embodiment of the present application, the conditions of the first hydrothermal reaction include a temperature of 160-180℃ and a time of 1-8 hours, preferably a temperature of 165-175℃ and a time of 5-8 hours; the conditions of the second hydrothermal reaction include a temperature of 160-180℃ and a time of 4-11h, preferably a temperature of 165-175℃ and a time of 4-7 hours. Preferably, the total hydrothermal reaction time of step S1 and step S2 is 10-16 hours.

[0042] The hydrothermal reaction is well known to those skilled in the art, and the first hydrothermal reaction and the second hydrothermal reaction can be carried out in a device commonly used by those skilled in the art, for example, in a heat-resistant sealed container, preferably a high-pressure reaction kettle. The present application does not make specific limitations on the reaction pressure of the first hydrothermal reaction and the second hydrothermal reaction, for example, it can be the autogenous pressure of the reaction system, or it can be carried out under an external pressure, preferably under the autogenous pressure of the reaction system.

[0043] The molar ratio of the amount of the silicon source, the aluminum source, the alkali source and the water in step S1 of the present application can be varied in a wide range. In one embodiment of step S1, the molar ratio of the amount of the silicon source, the aluminum source, the alkali source and the water is (40-70):1:(1-5):(400-700), preferably (50-65):1:(4-5):(500-700), and the amount of the seed crystal is 1-10 wt% of the amount of the silicon source, preferably 8-10 wt%.

[0044] In step S2 of the present application, the molar ratio of the ethanol and the silicon source is 0.1-0.5.

[0045] The total amount of the water in step S1 and the additional water in step S2 of the present application has a molar ratio of 720-1000:1, preferably 800-1000:1, to the amount of the aluminum source.

[0046] The silicon source, the aluminum source and the alkali source are well known to those skilled in the art. Preferably, the silicon source is selected from one or more of silica gel, water glass, silicon dioxide and white carbon black, the alkali source is selected from one or more of sodium hydroxide and potassium hydroxide, preferably the alkali source is sodium hydroxide, and the aluminum source is selected from one or more of sodium metaaluminate, SB powder, aluminum oxide, aluminum hydroxide and aluminum sulfate. The ethanol is anhydrous ethanol. The seed crystal can be ZSM-5 molecular sieve with a silicon to aluminum ratio of 25-50.

[0047] The method of the present application further comprises step S3: collecting the product obtained from the second hydrothermal reaction, and sequentially subjecting the product to collection, washing, ammonium exchange, drying and calcination. For example, the product can be collected by filtration, centrifugal separation or the like. The liquid used for washing can be any kind of liquid that does not react with the solid product, such as deionized water to wash the solid product to neutral. The ammonium exchange, drying and calcination are well known to those skilled in the art, and will not be described here. The calcination can be carried out in a tube furnace, a muffle furnace or the like. Preferably, the calcination conditions can include a temperature of 400-800°C and a time of 0.5-8 hours, and the calcination can be carried out in an air atmosphere or a water vapor atmosphere.

[0048] The second aspect of the present application provides an amine-free high-silicon ZSM-5 molecular sieve prepared by the method of the first aspect of the present application. The ZSM-5 molecular sieve of the present application has a high molar ratio of silicon to aluminum and a relatively high crystallinity.

[0049] In one embodiment of the present application, the amine-free high-silicon ZSM-5 molecular sieve has a molar ratio of SiO2 to Al2O3 of 35-60, a relative crystallinity of 80-95%, and a specific surface area of 280-360 m 2(g). The molar ratio of SiO2 to Al2O3 can be determined by X-ray fluorescence spectroscopy. The relative crystallinity is determined by Siemens D5005 X-ray diffractometer, with the ZSM-5 molecular sieve standard sample of the Research Institute of Petroleum Processing as the reference (i.e. the relative crystallinity of the ZSM-5 molecular sieve standard sample of the Research Institute of Petroleum Processing is 100%). The specific surface area can be determined by a specific surface area tester according to the N2 adsorption principle and the BJH calculation method (see Petroleum Chemical Analysis Method (RIPP Test Method), RIPP 151-90, published by Science Press in 1990).

[0050] The third aspect of the present application provides the use of the high-silica-to-alumina ratio ZSM-5 molecular sieve prepared by the amine-free method of the second aspect of the present application in a light hydrocarbon catalytic cracking reaction.

[0051] According to the present application, the light hydrocarbon catalytic cracking reaction can be carried out in a fixed bed reactor, and the reaction conditions of the light hydrocarbon catalytic cracking reaction can include a temperature of 600-650°C, a reaction mass space velocity of 20-40h-1, and a reaction pressure of 0.8-1.2 MPa. -1

[0052] The present disclosure is further illustrated by the following examples, but the present disclosure is not limited in any way by the following examples. The raw materials used in the following examples and comparative examples are commercially available unless otherwise specified.

[0053] Examples 1-5 illustrate the scheme in which the first hydrothermal reaction product in step S2 is only supplemented with water.

[0054] Example 1

[0055] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, and 2.01 g of ZSM-5 crystal seeds (wherein the molar amount of the silica gel in terms of SiO2: the molar amount of the sodium metaaluminate in terms of Al2O3: the molar amount of the sodium hydroxide in terms of Na2O: the molar amount of the deionized water = 60: 1: 4.5: 660, and the amount of the ZSM-5 crystal seeds in terms of SiO2 is 10% by weight of the silica gel in terms of SiO2) were sequentially added under stirring, and stirred until uniform; transferred to a stainless steel kettle, and subjected to a first hydrothermal reaction at 190°C for 3 h to obtain a first hydrothermal reaction product;

[0056] ​S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water was added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water = 60:1:4.5:840, the total amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the total amount of silica gel calculated based on SiO2), and stirred until uniform; it was transferred again to a stainless steel kettle, a second hydrothermal reaction was carried out at 170°C for 9h, filtered, washed until pH = 7-8, after ammonium exchange, dried at 120°C for 12h, and then calcined at 550°C for 4h in an air atmosphere to obtain ZSM-5 molecular sieve, denoted as A1, the X-ray diffraction spectrum of which is shown in Figure 1. Figure 1 .

[0057] The specific surface area S BET (m 2 / g) of A1, the total pore volume V total (cm 3 ·g -1 ), the micropore volume V micro (cm 3 ·g -1 ), and the mesopore volume V meso (cm 3 ·g -1 ) data are shown in Table 1.

[0058] Example 2

[0059] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, and 2.01 g of ZSM-5 seeds were added under stirring (the molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the molar amount of sodium hydroxide calculated based on Na2O: the molar amount of deionized water = 60:1:4.5:660, the amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the silica gel calculated based on SiO2), and stirred until uniform; it was transferred to a stainless steel kettle, a first hydrothermal reaction was carried out at 190°C for 5h to obtain a first hydrothermal reaction product;

[0060] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water was added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water = 60: 1: 4.5: 840, the total amount of ZSM-5 crystal seeds calculated based on SiO2was 10% of the total amount of silica gel calculated based on SiO2by weight), and stirred uniformly; then transferred to a stainless steel kettle again, and a second hydrothermal reaction was carried out at 170℃ for 7h, filtered, washed until pH = 7-8, dried at 120℃ for 12h after ammonium exchange, and then calcined at 550℃ in an air atmosphere for 4h to obtain a ZSM-5 molecular sieve, denoted as A2, the X-ray diffraction spectrum of which is shown in Figure 2 , and the scanning electron microscope image is Figure 3 .

[0061] Example 3

[0062] S1, 20g of silica gel, 5.99g of sodium metaaluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 0.81g of sodium hydroxide, 50.69g of deionized water, and 2.01g of ZSM-5 crystal seeds were added under stirring (the molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the molar amount of sodium hydroxide calculated based on Na2O: the molar amount of deionized water = 60: 1: 4.5: 660, the amount of ZSM-5 crystal seeds calculated based on SiO2was 10% of the amount of silica gel calculated based on SiO2by weight), and stirred uniformly; then transferred to a stainless steel kettle, and a first hydrothermal reaction was carried out at 190℃ for 8h to obtain a first hydrothermal reaction product;

[0063] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water was added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water = 60: 1: 4.5: 840, the total amount of ZSM-5 crystal seeds calculated based on SiO2was 10% of the total amount of silica gel calculated based on SiO2by weight), and stirred uniformly; then transferred to a stainless steel kettle again, and a second hydrothermal reaction was carried out at 170℃ for 4h, filtered, washed until pH = 7-8, dried at 120℃ for 12h after ammonium exchange, and then calcined at 550℃ in an air atmosphere for 4h to obtain a ZSM-5 molecular sieve, denoted as A3, the X-ray diffraction spectrum of which is shown in Figure 4 , and the scanning electron microscope image is Figure 5 .

[0064] Example 4

[0065] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, 2.01 g of ZSM-5 seed crystals (wherein the molar amount of silica gel: the molar amount of sodium metaaluminate: the molar amount of sodium hydroxide: the molar amount of deionized water = 60: 1: 4.5: 660, the amount of ZSM-5 seed crystals in terms of SiO2 is 10% by weight of the silica gel in terms of SiO2) were added in sequence under stirring, and stirred uniformly; transferred to a stainless steel kettle, and a first hydrothermal reaction was performed at 190°C for 6 h to obtain a first hydrothermal reaction product;

[0066] S2, the first hydrothermal reaction product was transferred to a beaker, 21.12 g of deionized water was added in sequence under stirring (wherein the total molar amount of silica gel: the molar amount of sodium metaaluminate: the total molar amount of sodium hydroxide: the total molar amount of deionized water = 60: 1: 4.5: 900, the total amount of ZSM-5 seed crystals in terms of SiO2 is 10% by weight of the total amount of silica gel in terms of SiO2), and stirred uniformly; again transferred to a stainless steel kettle, and a second hydrothermal reaction was performed at 170°C for 6 h, filtered, washed to pH = 7-8, after ammonium exchange, dried at 120°C for 12 h, and then calcined at 550°C for 4 h in an air atmosphere to obtain a ZSM-5 molecular sieve, recorded as A4.

[0067] Example 5

[0068] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, 2.01 g of ZSM-5 seed crystals (wherein the molar amount of silica gel: the molar amount of sodium metaaluminate: the molar amount of sodium hydroxide: the molar amount of deionized water = 60: 1: 4.5: 660, the amount of ZSM-5 seed crystals in terms of SiO2 is 10% by weight of the silica gel in terms of SiO2) were added in sequence under stirring, and stirred uniformly; transferred to a stainless steel kettle, and a first hydrothermal reaction was performed at 190°C for 6 h to obtain a first hydrothermal reaction product;

[0069] S2, the first hydrothermal reaction product was transferred into a beaker, 21.12 g of deionized water was added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water = 60: 1: 4.5: 900, and the total amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the total amount of silica gel calculated based on SiO2), and stirred until uniform; it was then transferred into a stainless steel kettle and subjected to a second hydrothermal reaction at 170℃ for 3 h, filtered, washed until the pH was 7-8, dried at 120℃ for 12 h after ammonium exchange, and then calcined at 550℃ for 4 h in an air atmosphere to obtain ZSM-5 molecular sieves, which were labeled as A5.

[0070] Comparative Example 1

[0071] Under stirring, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, and 2.01 g of ZSM-5 seeds (the molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the molar amount of sodium hydroxide calculated based on Na2O: the molar amount of deionized water = 60: 1: 4.5: 660, and the amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the silica gel calculated based on SiO2) were added in sequence and stirred until uniform; it was then transferred into a stainless steel kettle and subjected to a first hydrothermal reaction at 190℃ for 12 h to obtain a first hydrothermal reaction product; the product was filtered, washed until the pH was 7-8, dried at 120℃ for 12 h after ammonium exchange, and then calcined at 550℃ for 4 h in an air atmosphere to obtain ZSM-5 molecular sieves, which were labeled as D1. The X-ray diffraction spectrum thereof is shown in Figure 6 , and the scanning electron microscope image thereof is shown in Figure 7 .

[0072] Comparative Example 2

[0073] In comparison with Example 2, it was shown that the first-stage crystallization time cannot be too short, and the crystallinity will not be improved too much if it is too short.

[0074] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, 2.01 g of ZSM-5 seed crystals (wherein the molar amount of silica gel in terms of SiO2: the molar amount of sodium metaaluminate in terms of Al2O3: the molar amount of sodium hydroxide in terms of Na2O: the molar amount of deionized water = 60: 1: 4.5: 660, and the amount of ZSM-5 seed crystals in terms of SiO2is 10% by weight of the silica gel in terms of SiO2) were added in sequence under stirring, and stirred uniformly; transferred to a stainless steel kettle, and a first hydrothermal reaction was performed at 190°C for 1 h to obtain a first hydrothermal reaction product;

[0075] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water was added in sequence under stirring (wherein the total molar amount of silica gel in terms of SiO2: the molar amount of sodium metaaluminate in terms of Al2O3: the total molar amount of sodium hydroxide in terms of Na2O: the total molar amount of deionized water = 60: 1: 4.5: 840, and the total amount of ZSM-5 seed crystals in terms of SiO2is 10% by weight of the total amount of silica gel in terms of SiO2), and stirred uniformly; again transferred to a stainless steel kettle, and a second hydrothermal reaction was performed at 170°C for 11 h, filtered, washed until pH = 7-8, dried at 120°C for 12 h after ammonium exchange, and then calcined at 550°C for 4 h in an air atmosphere to obtain a ZSM-5 molecular sieve, denoted as D2.

[0076] Comparative Example 3

[0077] In comparison with Example 2, it is illustrated that the first-stage water amount cannot be too small, and too small amount will result in lower crystallinity.

[0078] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, 2.01 g of ZSM-5 seed crystals (wherein the molar amount of silica gel in terms of SiO2: the molar amount of sodium metaaluminate in terms of Al2O3: the molar amount of sodium hydroxide in terms of Na2O: the molar amount of deionized water = 60: 1: 4.5: 660, and the amount of ZSM-5 seed crystals in terms of SiO2is 10% by weight of the silica gel in terms of SiO2) were added in sequence under stirring, and stirred uniformly; transferred to a stainless steel kettle, and a first hydrothermal reaction was performed at 190°C for 1 h to obtain a first hydrothermal reaction product;

[0079] S2, the first hydrothermal reaction product was transferred to a beaker, 10.56 g of deionized water was added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium aluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water = 60: 1: 4.5: 660, the total amount of ZSM-5 crystal seeds calculated based on SiO2was 10% of the total amount of silica gel calculated based on SiO2by weight), and stirred uniformly; it was transferred to a stainless steel kettle again, and a second hydrothermal reaction was carried out at 170℃ for 7h, filtered, washed until pH = 7-8, dried at 120℃ for 12h after ammonium exchange, and then calcined at 550℃ in an air atmosphere for 4h to obtain a ZSM-5 molecular sieve, denoted as D3, and the X-ray diffraction spectrum thereof is shown in Figure 8 .

[0080] Comparative Example 4

[0081] Compared with Example 3, the temperature rising process was the same, and the difference was still the water amount in the first stage, which was 540 in the comparative example and 660 in the example. The crystallinity was low when the water amount in the first stage was too small.

[0082] S1, 20g of silica gel, 5.99g of sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 0.81g of sodium hydroxide, 40.13g of deionized water, and 2.01g of ZSM-5 crystal seeds were added under stirring (the molar amount of silica gel calculated based on SiO2: the molar amount of sodium aluminate calculated based on Al2O3: the molar amount of sodium hydroxide calculated based on Na2O: the molar amount of deionized water = 60: 1: 4.5: 540, the amount of ZSM-5 crystal seeds calculated based on SiO2was 10% of the amount of silica gel calculated based on SiO2by weight), and stirred uniformly; it was transferred to a stainless steel kettle, and a first hydrothermal reaction was carried out at 190℃ for 8h to obtain a first hydrothermal reaction product;

[0083] S2, the first hydrothermal reaction product was transferred to a beaker, 10.56 g of deionized water was added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium aluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water = 60: 1: 4.5: 660, the total amount of ZSM-5 crystal seeds calculated based on SiO2was 10% of the total amount of silica gel calculated based on SiO2by weight), and stirred uniformly; it was transferred to a stainless steel kettle again, and a second hydrothermal reaction was carried out at 170℃ for 4h, filtered, washed until pH = 7-8, dried at 120℃ for 12h after ammonium exchange, and then calcined at 550℃ in an air atmosphere for 4h to obtain a ZSM-5 molecular sieve, denoted as D4, and the X-ray diffraction spectrum thereof is shown in Figure 8 .

[0084] The specific surface area S of samples A1-A5 and comparative samples D1-D4 BET (m 2 / g), total pore volume V total / (cm 3 ·g -1 ), micropore volume V micro / (cm 3 ·g -1 ), mesopore volume V meso / (cm 3 ·g -1 ), silica-alumina molar ratio and relative crystallinity data are shown in Table 1.

[0085] Comparative Example 1 is compared with Example 1, Example 1 is two-step water replenishment preparation, 190℃ for 3 hours + 170℃ for 9 hours, and Comparative Example 1 is one-step, 190℃ for 12 hours. It can be seen that the one-step crystallinity of Comparative Example 1 is 80.1%, and the crystallinity of the two-step water replenishment of Example 1 is higher, which is 84.9%

[0086] Comparative Example 2 is compared with Example 2, Example 2 is two-step water replenishment preparation, 190℃ for 5 hours + 170℃ for 7 hours, and Comparative Example 2 is also two-step water replenishment, but 190℃ for 1 hour + 170℃ for 11 hours. The first period of time cannot be too short, and the crystallinity will not be improved too much if it is too short. It can be seen that the crystallinity, the first crystallization time of Comparative Example 2 is too short, and the crystallinity is low.

[0087] Comparative Example 3 is compared with Example 2, Example 2 is two-step water replenishment preparation, 190℃ for 5 hours + 170℃ for 7 hours, and the water is replenished from 660 to 840; Comparative Example 3 is also two-step water replenishment, 190℃ for 5 hours + 170℃ for 7 hours, but the water is replenished from 540 to 660. It shows that the first water amount cannot be too small, and too small will lead to low crystallinity.

[0088] Comparative Example 4 and Example 3 are compared, and the temperature rising process is the same, and the difference is still the first water amount, Comparative Example 4 is 540, and Example 3 is 660. The first water amount is too small, and the crystallinity is low.

[0089] Test Example 1

[0090] The molecular sieves prepared in Examples 1-5 and Comparative Examples 1-4 are used as catalysts in light hydrocarbon catalytic cracking reactions, and the catalytic cracking reaction of n-tetradecane is carried out, and the specific method is as follows: The influence of molecular sieves in light hydrocarbon catalytic cracking on low carbon olefin yield and conversion rate is evaluated by pure hydrocarbon micro-reaction. The reaction is carried out in a fixed bed reactor, the raw material oil is n-tetradecane, the carrier gas is nitrogen, the flow rate is 30 mL / min, the reaction temperature is 550℃, the regeneration temperature is 600℃, the weight hourly space velocity is 20h -1The ZSM-5 molecular sieve is sieved into 20-40 mesh particles after tabletting, the loading amount is 2.0 g, the volume ratio of the catalyst to oil is 1.28, and the sample is analyzed after reaction for 900 s, and the product distribution is shown in Table 1.

[0091] The micro-reverse conversion rate X of the raw material and the yield Y of the product are calculated by using the following formula i :

[0092] X = 100% - (the content of n-tetradecane in the oil phase - the feeding amount of n-tetradecane) * 100%;

[0093] Y i = the weight of component i in the product / the feeding amount of n-tetradecane * 100%, and i represents ethylene, propylene, butylene or a component with C5 or above.

[0094] Table 1

[0095]

[0096] As shown in Table 1, the ZSM-5 molecular sieve prepared by the variable alkalinity method has a silicon-aluminum ratio of 35-55, a relatively high relative crystallinity (the highest relative crystallinity can reach 87.8%), and a relatively large specific surface area (333 cm 2 / g). When the ZSM-5 molecular sieve is used in a light hydrocarbon catalytic cracking reaction, a relatively high yield of low-carbon olefins can be obtained, and propylene can be produced in large amounts.

[0097] Examples 6-11 illustrate the scheme of supplementing water and ethanol to the first hydrothermal reaction product in step S2.

[0098] Example 6

[0099] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water and 2.01 g of ZSM-5 crystal seeds (the molar amount of the silica gel in terms of SiO2: the molar amount of the sodium metaaluminate in terms of Al2O3: the molar amount of the sodium hydroxide in terms of Na2O: the molar amount of the deionized water = 60:1:4.5:660, and the amount of the ZSM-5 crystal seeds in terms of SiO2 is 10% by weight of the silica gel) are sequentially added under stirring, and the mixture is fully stirred and uniformly mixed; the mixture is transferred to a stainless steel kettle, and a first hydrothermal reaction is performed at 190 ℃ for 5 h to obtain a first hydrothermal reaction product;

[0100] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water and 1.8 g of anhydrous ethanol were added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water: the total molar amount of anhydrous ethanol = 60: 1: 4.5: 840: 6, the total amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the total amount of silica gel calculated based on SiO2), and stirred uniformly; it was transferred to a stainless steel kettle again, a second hydrothermal reaction was carried out at 170℃ for 7h, filtered, washed to pH = 7-8, after ammonium exchange, dried at 120℃ for 12h, then calcined at 550℃ for 4h in air atmosphere, to obtain ZSM-5 molecular sieve, recorded as A6.

[0101] Example 7

[0102] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, and 2.01 g of ZSM-5 seeds were added under stirring (the molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the molar amount of sodium hydroxide calculated based on Na2O: the molar amount of deionized water = 60: 1: 4.5: 660, the amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the silica gel calculated based on SiO2), and stirred uniformly; it was transferred to a stainless steel kettle, a first hydrothermal reaction was carried out at 190℃ for 5h, to obtain a first hydrothermal reaction product;

[0103] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water and 1.8 g of anhydrous ethanol were added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water: the total molar amount of anhydrous ethanol = 60: 1: 4.5: 840: 6, the total amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the total amount of silica gel calculated based on SiO2), and stirred uniformly; it was transferred to a stainless steel kettle again, a second hydrothermal reaction was carried out at 170℃ for 7h, filtered, washed to pH = 7-8, after ammonium exchange, dried at 120℃ for 12h, then calcined at 550℃ for 4h in air atmosphere, to obtain ZSM-5 molecular sieve, recorded as A6. Figure 9 Figure 10

[0104] ​​Example 6 and Example 7 have the same feeding as Example 2, the only difference is that ethanol is further added, wherein the alcohol-silicon ratio of Example 6 is 0.1, and the alcohol-silicon ratio of Example 7 is 0.3. The addition of ethanol further improves the crystallinity of the synthesized molecular sieve, and the morphology presents a long strip shape.

[0105] Example 8

[0106] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, and 2.01 g of ZSM-5 seeds (wherein the molar amount of silica gel in terms of SiO2: the molar amount of sodium metaaluminate in terms of Al2O3: the molar amount of sodium hydroxide in terms of Na2O: the molar amount of deionized water = 60:1:4.5:660, and the amount of ZSM-5 seeds in terms of SiO2 is 10% by weight of the silica gel) were added in sequence under stirring, and stirred uniformly; transferred to a stainless steel kettle, and subjected to a first hydrothermal reaction at 190°C for 8 h to obtain a first hydrothermal reaction product;

[0107] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water and 1.8 g of anhydrous ethanol were added in sequence under stirring (wherein the total molar amount of silica gel in terms of SiO2: the molar amount of sodium metaaluminate in terms of Al2O3: the total molar amount of sodium hydroxide in terms of Na2O: the total molar amount of deionized water: the total molar amount of anhydrous ethanol = 60:1:4.5:840:6, and the total amount of ZSM-5 seeds in terms of SiO2 is 10% by weight of the total amount of silica gel), and stirred uniformly; again transferred to a stainless steel kettle, and subjected to a second hydrothermal reaction at 170°C for 4 h, filtered, washed to pH = 7-8, subjected to ammonium exchange, dried at 120°C for 12 h, and then calcined at 550°C for 4 h in an air atmosphere to obtain a ZSM-5 molecular sieve, denoted as A8, the X-ray diffraction spectrum of which is shown in Figure 9 , and the scanning electron microscope photograph is shown in Figure 11 .

[0108] Example 9

[0109] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, 2.01 g of ZSM-5 seed crystals (wherein the molar amount of silica gel: the molar amount of sodium metaaluminate: the molar amount of sodium hydroxide: the molar amount of deionized water = 60: 1: 4.5: 660, and the amount of ZSM-5 seed crystals in terms of SiO2 is 10% by weight of the silica gel in terms of SiO2) were added in sequence under stirring, and stirred uniformly; transferred to a stainless steel kettle, and a first hydrothermal reaction was performed at 190°C for 8 h to obtain a first hydrothermal reaction product;

[0110] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water and 5.4 g of anhydrous ethanol were added in sequence under stirring (wherein the total molar amount of silica gel: the molar amount of sodium metaaluminate: the total molar amount of sodium hydroxide: the total molar amount of deionized water: the total molar amount of anhydrous ethanol = 60: 1: 4.5: 840: 18, and the total amount of ZSM-5 seed crystals in terms of SiO2 is 10% by weight of the total amount of silica gel in terms of SiO2), and stirred uniformly; again transferred to a stainless steel kettle, and a second hydrothermal reaction was performed at 170°C for 4 h, filtered, washed until pH = 7-8, dried at 120°C for 12 h after ammonium exchange, and then calcined at 550°C for 4 h in an air atmosphere to obtain a ZSM-5 molecular sieve, denoted as A9.

[0111] Example 10

[0112] S1, 20 g of silica gel, 5.99 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 0.81 g of sodium hydroxide, 50.69 g of deionized water, 2.01 g of ZSM-5 seed crystals (wherein the molar amount of silica gel: the molar amount of sodium metaaluminate: the molar amount of sodium hydroxide: the molar amount of deionized water = 60: 1: 4.5: 660, and the amount of ZSM-5 seed crystals in terms of SiO2 is 10% by weight of the silica gel in terms of SiO2) were added in sequence under stirring, and stirred uniformly; transferred to a stainless steel kettle, and a first hydrothermal reaction was performed at 190°C for 8 h to obtain a first hydrothermal reaction product;

[0113] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water and 5.4 g of anhydrous ethanol were added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water: the total molar amount of anhydrous ethanol = 75: 1: 4.5: 840: 18, the total amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the total amount of silica gel calculated based on SiO2), and stirred uniformly; it was transferred to a stainless steel kettle again, and a second hydrothermal reaction was carried out at 170°C for 7h, filtered, washed to pH = 7-8, dried at 120°C for 12h after ammonium exchange, and then calcined at 550°C for 4h in an air atmosphere to obtain a ZSM-5 molecular sieve, denoted as A10.

[0114] Example 11

[0115] S1, 20 g of silica gel, 4.79 g of sodium metaaluminate (Na2O: 156.3 g / L, Al2O3: 103.8 g / L), 1.01 g of sodium hydroxide, 50.53 g of deionized water, and 2.01 g of ZSM-5 seeds were added under stirring (the molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the molar amount of sodium hydroxide calculated based on Na2O: the molar amount of deionized water = 75: 1: 4.5: 660, the amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the silica gel calculated based on SiO2), and stirred uniformly; it was transferred to a stainless steel kettle, and a first hydrothermal reaction was carried out at 190°C for 5h to obtain a first hydrothermal reaction product;

[0116] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water and 5.4 g of anhydrous ethanol were added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metaaluminate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water: the total molar amount of anhydrous ethanol = 75: 1: 4.5: 840: 18, the total amount of ZSM-5 seeds calculated based on SiO2was 10% by weight of the total amount of silica gel calculated based on SiO2). It was transferred to a stainless steel kettle for the third time, and a second hydrothermal reaction was carried out at 170°C for 4h. It was filtered, washed to pH = 7-8, dried at 120°C for 12h after ammonium exchange, and then calcined at 550°C for 4h in an air atmosphere to obtain a ZSM-5 molecular sieve, denoted as A11.

[0117] Comparative Example 5

[0118] The conditions of Comparative Example 5 are a one-step synthesis, 190°C for 12h, with less water (540) and with a certain amount of ethanol (6).

[0119] S1, 20g of silica gel, 5.99g of sodium metaaluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 0.81g of sodium hydroxide, 48.9g of deionized water, 1.8g of anhydrous ethanol, 2.01g of ZSM-5 seeds (wherein the molar amount of silica gel in terms of SiO2: the molar amount of sodium metaaluminate in terms of Al2O3: the molar amount of sodium hydroxide in terms of Na2O: the molar amount of deionized water = 60: 1: 4.5: 540: 6, and the amount of ZSM-5 seeds in terms of SiO2is 10wt% of the silica gel in terms of SiO2) were added in sequence under stirring, and stirred thoroughly; transferred to a stainless steel kettle, and subjected to a first hydrothermal reaction at 190°C for 12h to obtain a first hydrothermal reaction product; filtered, washed until pH = 7-8, subjected to ammonium exchange, dried at 120°C for 12h, and then calcined at 550°C for 4h in an air atmosphere to obtain ZSM-5 molecular sieves, denoted as D5, and the X-ray diffraction spectrum thereof is shown in Figure 1. Figure 12 .

[0120] Comparative Example 6

[0121] This comparative example is compared with Example 6, and the conditions such as the temperature rising process are the same as those of Example 6, but the amount of ethanol is significantly increased, the amount of ethanol in Example 6 is 6, and the alcohol-silicon ratio is 0.1; the amount of ethanol in Comparative Example 6 is 90, and the alcohol-silicon ratio is 1.5.

[0122] S1, 20g of silica gel, 5.99g of sodium metaaluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 0.81g of sodium hydroxide, 48.9g of deionized water, 1.8g of anhydrous ethanol, 2.01g of ZSM-5 seeds (wherein the molar amount of silica gel in terms of SiO2: the molar amount of sodium metaaluminate in terms of Al2O3: the molar amount of sodium hydroxide in terms of Na2O: the molar amount of deionized water = 60: 1: 4.5: 540: 6, and the amount of ZSM-5 seeds in terms of SiO2is 10wt% of the silica gel in terms of SiO2) were added in sequence under stirring, and stirred thoroughly; transferred to a stainless steel kettle, and subjected to a first hydrothermal reaction at 190°C for 12h to obtain a first hydrothermal reaction product; filtered, washed until pH = 7-8, subjected to ammonium exchange, dried at 120°C for 12h, and then calcined at 550°C for 4h in an air atmosphere to obtain ZSM-5 molecular sieves, denoted as D5, and the X-ray diffraction spectrum thereof is shown in Figure 1.

[0123] S2, the first hydrothermal reaction product was transferred to a beaker, 15.84 g of deionized water and 1.8 g of anhydrous ethanol were added under stirring (the total molar amount of silica gel calculated based on SiO2: the molar amount of sodium metasilicate calculated based on Al2O3: the total molar amount of sodium hydroxide calculated based on Na2O: the total molar amount of deionized water: the total molar amount of anhydrous ethanol = 60: 1: 4.5: 840: 90, the amount of ZSM-5 seed crystal calculated based on SiO2was 10% by weight of the silica gel calculated based on SiO2), and stirred uniformly; it was transferred to a stainless steel kettle, and a first hydrothermal reaction was carried out at 170℃ for 7h to obtain a first hydrothermal reaction product; it was filtered, washed until pH = 7-8, subjected to ammonium exchange, dried at 120℃ for 12h, and then calcined at 550℃ for 4h in an air atmosphere to obtain ZSM-5 molecular sieve, which is denoted as D6, and the X-ray diffraction spectrum thereof is shown in Figure 13 , and the scanning electron microscope image thereof is shown in Figure 14 .

[0124] The specific surface area S BET (m 2 / g) of samples A6-A11 and comparative samples D5-D6, the total pore volume V total / (cm 3 ·g -1 ), the micropore volume V micro / (cm 3 ·g -1 ), the mesopore volume V meso / (cm 3 ·g -1 ), the silicon-aluminum molar ratio and the relative crystallinity data are shown in Table 2.

[0125] Test Example 2

[0126] The molecular sieves prepared in Examples 6-11 and Comparative Examples 5 and 6 were used as catalysts in a light hydrocarbon catalytic cracking reaction, and a catalytic cracking reaction of n-tetradecane was carried out.

[0127] The product distribution is shown in Table 2 under the same conditions as in Test Example 1.

[0128] Table 2

[0129]

[0130] As can be seen from Table 2, the silicon-aluminum ratio of the ZSM-5 molecular sieve prepared by the method of the present application is between 35 and 60, Examples 6-9 show that the relative crystallinity is higher when the water and ethanol addition scheme is used than when only water is added (the highest relative crystallinity can reach 90.8%), and Examples 10 and 11 show that when the water and ethanol addition scheme is used, the relative crystallinity can also exceed 80 even when the higher feed silicon-aluminum ratio (75) is used. When used in a light hydrocarbon catalytic cracking reaction, it has a relatively high yield of low-carbon olefins, and can produce more propylene.

Claims

1. A method for preparing amine-free high-silica ZSM-5 molecular sieves by varying alkalinity, the method comprising the steps of: S1, subjecting a first mixture obtained by mixing a silicon source, an aluminum source, an alkali source, water, and seed crystals to a first hydrothermal reaction to obtain a first hydrothermal reaction product; S2, mixing the first hydrothermal reaction product with additional water, or mixing the first hydrothermal reaction product with additional water and ethanol to obtain a second mixture for a second hydrothermal reaction; wherein, The molar ratio of the silicon source, aluminum source, alkali source and water is (50-65):1:(4-5):(500-700), the amount of the seed crystal is 1-10% by weight of the amount of the silicon source, the total amount of water mentioned in step S1 and the additional water mentioned in step S2 is in a molar ratio of 720-1000:1 to the aluminum source, the molar ratio of the ethanol and the silicon source is 0.1-1, the silicon source is SiO2, the aluminum source is Al2O3, the alkali source is alkali metal oxide, and the seed crystal is SiO2. The conditions for the first hydrothermal reaction include: a temperature of 160-180℃ and a time of 1-8 hours; the conditions for the second hydrothermal reaction include: a temperature of 160-180℃ and a time of 4-7 hours.

2. The method according to claim 1, wherein, In step S1, the amount of the seed crystal is 8-10% by weight of the amount of the silicon source.

3. The method according to claim 1, wherein, The total amount of water mentioned in step S1 and the additional water mentioned in step S2, in a molar ratio to the aluminum source, is 800-1000:

1.

4. The method according to claim 1, wherein, The molar ratio of ethanol to silicon source in S2 is 0.1-0.

5.

5. The method according to claim 1, wherein, The silicon source is selected from one or more of silica gel, water glass, silica and fumed silica; the aluminum source is selected from one or more of sodium aluminate, SB powder, alumina, aluminum hydroxide and aluminum sulfate; the alkali source is selected from one or more of sodium hydroxide and potassium hydroxide; the seed crystal is industrial ZSM-5 molecular sieve with a molar ratio of silica to alumina of 25 to 50.

6. The method according to claim 1, characterized in that, The method further includes step S3: collecting the product obtained from the second hydrothermal reaction, and subjecting the product to sequential filtration, washing, ammonium exchange, drying and calcination.

7. The method according to claim 6, wherein, The calcination conditions include: a temperature of 400-800℃, a time of 0.5-8h, and an atmosphere of air or water vapor.

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