A zsm-5 zeolite with adjustable crystal size, and a preparation method and application thereof

Abstract

The application relates to the technical field of molecular sieve preparation, in particular to a preparation method and application of ZSM-5 zeolite with adjustable crystal grain size, which comprises the following steps: adding a silicon source, an aluminum source, a structure directing agent and a mineralizing agent into distilled water, adjusting the pH to neutral, stirring uniformly and obtaining an initial gel; microwave treating the initial gel; adding a template agent into the microwave-treated product and drying to obtain a solid gel; grinding the solid gel into powder, placing the powder in an autoclave and carrying out steam phase conversion; and carrying out washing, filtering, drying and calcining on the steam phase conversion product in sequence to obtain the ZSM-5 zeolite with adjustable crystal grain size. The growth and nucleation rate of the ZSM-5 zeolite can be controlled by changing the adding amount of the template agent, the classic and non-classic construction of the ZSM-5 zeolite is further controlled, and the effective control of the ZSM-5 zeolite crystal grain is realized. Compared with the traditional hydrothermal synthesis method, the yield of the ZSM-5 zeolite is improved, and the controllability of the ZSM-5 zeolite crystal grain size is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve preparation, and particularly relates to a preparation method of ZSM-5 zeolite with adjustable grain size and application. BACKGROUND

[0002] ZSM-5 zeolite is widely used as a solid acid catalyst and an adsorption separation material due to its unique regular pore structure, adjustable acidity and good hydrothermal stability, but the narrow pore structure of the zeolite limits its application in catalysis and separation of macromolecules. Reducing the grain size of the zeolite helps to improve the external surface area, and the accessibility of acid sites is greatly improved. At the same time, due to the small grain size, the micropore channel is effectively shortened, the diffusion limitation of reactant molecules in the material pore channel is greatly reduced, the diffusion rate of molecules in the material internal pore channel is effectively improved, and the release rate of reaction products in the zeolite material pore channel is faster, and the probability of secondary reaction is reduced.

[0003] At present, the synthesis methods for adjusting the grain size of ZSM-5 zeolite mainly include the following two methods: adding a growth inhibitor and adding seeds. Deng et al. successfully prepared ZSM-5 zeolite with a grain size controllable in the range of 50-450 nm by controlling the amount of added lysine in the synthesis system of ZSM-5. It is found that in the cyclohexanone oxime to caprolactam reaction, the grain size of the zeolite significantly affects the catalytic activity of the reactants and the selectivity of the target product, and with the decrease of the grain size, the catalytic performance of the reaction can be significantly improved. Tang et al. successfully prepared ZSM-5 zeolite with a grain size of 270-1100 nm by using the seed method and elucidated the growth process and crystallization mechanism of the zeolite.

[0004] However, these methods still have some problems. First, these adjustment methods are mainly based on the traditional hydrothermal synthesis method for preparing ZSM-5 zeolite, which has the disadvantages of large amount of template agent, low utilization efficiency, low zeolite yield, and more wastewater discharge; second, adding seeds greatly increases the production cost, and the complicated synthesis steps seriously restrict the industrial application of the zeolite material.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of ZSM-5 zeolite with adjustable grain size, which not only improves the yield of ZSM-5 zeolite, but also realizes the controllability of the grain size of ZSM-5 zeolite.

[0007] In a first aspect, the present application provides a preparation method of ZSM-5 zeolite with adjustable grain size, comprising the following steps:

[0008] S1, add a silicon source, an aluminum source, a structure-directing agent, a mineralizing agent to distilled water, adjust pH to neutral, stir uniformly, and obtain an initial gel;

[0009] S2, microwave treat the initial gel;

[0010] S3, add a template agent to the microwave-treated product, and dry to obtain a solid gel;

[0011] S4, grind the solid gel into powder, and place in an autoclave to perform steam phase conversion;

[0012] S5, after sequentially performing washing, filtering, drying, and calcination treatment on the steam phase conversion product, obtain ZSM-5 zeolite with adjustable grain size.

[0013] In the preparation of ZSM-5 zeolite, first, a silicon source, an aluminum source, a structure-directing agent, a mineralizing agent, and distilled water are stirred uniformly, and pH is adjusted to neutral to prepare a silicon-aluminum gel; then, the obtained silicon-aluminum gel is microwave treated to form a large number of primary units and secondary structural units of ZSM-5 zeolite in a short time; subsequently, the microwave-treated product is added to a template agent solution, stirred fully, and dried; finally, steam phase conversion is performed, and drying and calcination treatment are performed, and ZSM-5 zeolite is obtained. The microwave treatment of the zeolite precursor is a key step for subsequent regulation of the grain size of ZSM-5 zeolite. After microwave treatment, the growth and nucleation rate of ZSM-5 zeolite can be regulated by changing the amount of template agent added, and the classic and non-classic construction of ZSM-5 zeolite is regulated to effectively regulate the grain size of ZSM-5 zeolite. Compared with the traditional synthesis method, the yield of ZSM-5 zeolite is improved, and the controllability of the grain size of ZSM-5 zeolite is realized.

[0014] As preferred in the technical solution, in step S1, the molar ratio of silicon dioxide in the silicon source, aluminum oxide in the aluminum source, the structure-directing agent, the mineralizing agent, and distilled water in the initial gel is (0.3-1.2):(0.003-0.012):(0.02-0.14):(0.2-1.6):(50.8-250.3).

[0015] Specifically, the aluminum source includes any one or more of aluminum oxide, sodium aluminate, aluminum hydroxide, and pseudo-boehmite; the silicon source includes any one or more of tetraethyl orthosilicate, fumed silica, and silica sol; the structure-directing agent includes any one or more of tetrapropylammonium hydroxide, n-butylamine, tetrapropylammonium bromide, and diethylamine; the mineralizing agent includes any one or more of ammonium fluoride, sodium hydroxide, and potassium hydroxide; and the pH adjusting agent used for adjusting pH includes any one or more of hydrogen fluoride, hydrochloric acid, and nitric acid.

[0016] In step S2, the obtained initial gel is subjected to microwave treatment. Its main function is to form a large number of primary and secondary structural units of ZSM-5 zeolite in a short time, without further forming zeolite crystals, thus facilitating the induction of subsequent zeolite crystallization. Specifically, during microwave treatment, the temperature is controlled at 140-180℃, preferably 150-170℃, and the time is 1-7 hours, preferably 3-5 hours.

[0017] The microwave-treated product is further mixed with template agents such as tetrapropylammonium hydroxide, tetrapropylammonium bromide, and n-butylamine, and then thoroughly stirred before drying. The drying temperature is preferably 90-120℃, and the drying time is 12-24 hours. The template agent is preferably tetrapropylammonium hydroxide, and the amount of template agent added depends on the size of the ZSM-5 zeolite crystals to be prepared. Specifically, the mass ratio of the microwave-treated product to the template agent is 1:(2-3.5).

[0018] As a preferred embodiment of this technical solution, in step S4, the solid powder obtained above is placed in a high-pressure reactor with a polytetrafluoroethylene liner and distilled water is added (note: the dry gel powder is separated from the water) for vapor phase conversion. Specifically, during vapor phase conversion, the mass ratio of solid gel to distilled water is preferably 1:(2.5-7.0), the crystallization temperature is controlled at 140-180℃, and the time is 24-72h.

[0019] In a preferred embodiment of this technical solution, during step S5, the drying process is controlled at a temperature of 90-120℃ for 24-48 hours; during the calcination process, the temperature is controlled at 500-650℃ for 4-12 hours.

[0020] Secondly, the present invention also discloses a ZSM-5 zeolite with adjustable grain size prepared according to the above method, which should also fall within the protection scope of the present invention. Specifically, the grain size of the ZSM-5 zeolite with adjustable grain size can be arbitrarily adjusted within the range of 0.2-15μm.

[0021] Thirdly, the present invention also provides the application of the above-mentioned ZSM-5 zeolite with adjustable grain size in macromolecular pyrolysis reactions, which should also fall within the protection scope of the present invention.

[0022] Studies have shown that when the ZSM-5 molecular sieve with adjustable crystal size prepared in this invention is used as a solid acid catalyst in the cracking reaction of triisopropylbenzene, the catalytic activity of triisopropylbenzene gradually increases as the zeolite crystal size decreases, and the selectivity of the deep cracking products cumene and benzene also gradually increases. Furthermore, its catalytic performance is optimal when the crystal size is reduced to the nanoscale.

[0023] The method for preparing ZSM-5 zeolite with adjustable grain size according to the present invention has at least the following beneficial effects:

[0024] 1. In the preparation method of ZSM-5 zeolite with adjustable grain size of the present invention, firstly, silicon source, aluminum source, structure directing agent, mineralizing agent and distilled water are stirred evenly and the pH is adjusted to neutral to obtain a silica-alumina gel; then, the obtained silica-alumina gel is microwave-treated to form a large number of primary and secondary structural units of ZSM-5 zeolite in a short time; subsequently, the microwave-treated product is added to a template agent solution, stirred thoroughly and dried; finally, vapor phase conversion is performed, followed by drying and calcination to obtain ZSM-5 zeolite. During the preparation process, the growth and nucleation rate of ZSM-5 zeolite can be controlled by changing the amount of template agent added, thereby controlling the classical and non-classical structures of ZSM-5 zeolite to achieve effective control of ZSM-5 zeolite grain size. Compared with traditional synthesis methods, this method not only improves the yield of ZSM-5 zeolite but also achieves controllability of ZSM-5 zeolite grain size.

[0025] 2. The preparation conditions of this invention are relatively mild and the process is simple, which can realize the preparation of ZSM-5 zeolite with different grain sizes and is easy to promote and apply in industrial applications;

[0026] 3. The ZSM-5 zeolite crystal size prepared by this invention can be arbitrarily controlled within a wide range of 0.2-15 μm. The reduction in crystal size can effectively shorten the diffusion path of reactants and products. Therefore, the ZSM-5 zeolite prepared by this invention exhibits excellent catalytic performance in macromolecular cracking reactions. Compared with conventional microporous ZSM-5 zeolite, its catalytic activity and selectivity of deep cracking products (cumene and benzene) can be significantly improved, which has guiding significance in solving the problem of crude oil heavyification. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram illustrating the principle of the two-step method for preparing ZSM-5 zeolite using microwave treatment and steam phase transformation according to the present invention.

[0029] Figure 2 The XRD pattern of the product after microwave treatment in Example 1 of this invention is shown below. Figure 2 A) and infrared spectrum ( Figure 2 B);

[0030] Figure 3XRD pattern of the sample after the steam phase conversion of Example 1 of the present application;

[0031] Figure 4 SEM pattern of the sample after the steam phase conversion of Example 1 of the present application;

[0032] Figure 5 XRD pattern of the sample after the steam phase conversion of Comparative Example 1 of the present application without microwave treatment;

[0033] Figure 6 SEM pattern of the sample after the steam phase conversion of Comparative Example 1 of the present application without microwave treatment. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed description is merely exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0035] It is also important to note that the terms "comprises", "comprising", "includes", "including", "contains", "containing" or variations thereof herein, do not specify an exhaustive or complete list of components or features as used by those skilled in the art. Unless otherwise expressed, the terms "comprises", "comprising", "includes", "including", "contains", "containing" or variations thereof herein, are intended to be inclusive or open-ended and not exclude additional, unrecited components, features, steps, devices, or the like.

[0036] The technical solutions of the present application will be described clearly and completely in combination with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0037] Example 1

[0038] S1, 20.8 g of tetraethyl orthosilicate, 0.1 g of sodium aluminate, 1.86 g of tetrapropylammonium bromide, and 1.32 g of ammonium fluoride were sequentially added to 144 g of distilled water, and stirred to obtain a clear solution. Then, the pH was adjusted to neutral with hydrogen fluoride, and the mixture was stirred to obtain an initial gel;

[0039] S2, the initial gel was transferred to a microwave reactor, and the temperature was set to 160°C and the time was set to 2 h for microwave treatment;

[0040] S3, 8 g of tetrapropylammonium hydroxide solution (25 wt.%) was added to the microwave treated product, and the mixture was stirred to obtain a solid gel. The solid gel was placed in an oven, and the temperature was controlled at 100°C for drying treatment for 24 h.

[0041] S4, after the solid gel is ground into powder, it is transferred into an autoclave with a polytetrafluoroethylene liner and a certain amount of distilled water is added (note: the solid powder is separated from the distilled water) for vapor phase transformation, wherein the mass ratio of the solid powder to the distilled water is 1:3;

[0042] S5, the vapor phase transformation product is sequentially washed, filtered, dried at 100°C overnight, and then calcined at 550°C for 4h to obtain a ZSM-5 zeolite with adjustable crystal size.

[0043] Example 2

[0044] The amount of tetrapropylammonium hydroxide solution (25wt.%) is 10g;

[0045] The other steps and parameters are basically the same as those in Example 1.

[0046] Example 3

[0047] The amount of tetrapropylammonium hydroxide solution (25wt.%) is 12g;

[0048] The other steps and parameters are basically the same as those in Example 1.

[0049] Example 4

[0050] The amount of tetrapropylammonium hydroxide solution (25wt.%) is 16g;

[0051] The other steps and parameters are basically the same as those in Example 1.

[0052] Example 5

[0053] S1, 6.5g of fumed SiO2, 0.08g of aluminum hydroxide, 1.55g of tetrapropylammonium bromide, and 1.0g of sodium hydroxide are sequentially added to 144g of distilled water, stirred uniformly to obtain a clear solution, and then the pH is adjusted to neutral with hydrochloric acid, and stirred uniformly to obtain an initial gel;

[0054] S2, the initial gel is transferred into a microwave reactor, and the temperature is set to 170°C and the time is set to 1h for microwave treatment;

[0055] S3, 6g of tetrapropylammonium hydroxide solution (25wt.%) is added to the product after microwave treatment for uniform mixing, and then placed in an oven for drying treatment at a temperature of 100°C for 24h to obtain a solid gel;

[0056] S4, after the solid gel is ground into powder, it is transferred into an autoclave with a polytetrafluoroethylene liner and a certain amount of distilled water is added (note: the solid powder is separated from the distilled water) for vapor phase transformation, wherein the mass ratio of the solid powder to the distilled water is 1:3.5;

[0057] S5, the vapor phase transformation product is sequentially washed, filtered, dried at 100°C overnight, and then calcined at 550°C for 6h to obtain ZSM-5 zeolite with adjustable crystal size.

[0058] Example 6

[0059] The amount of tetrapropylammonium hydroxide solution (25wt.%) is 8g;

[0060] The other steps and parameters are basically the same as those in Example 5.

[0061] Example 7

[0062] The amount of tetrapropylammonium hydroxide solution (25wt.%) is 12g;

[0063] The other steps and parameters are basically the same as those in Example 5.

[0064] Example 8

[0065] The amount of tetrapropylammonium hydroxide solution (25wt.%) is 16g;

[0066] The other steps and parameters are basically the same as those in Example 5.

[0067] Example 9

[0068] S1, 16g of silica sol (40wt.%) is sequentially added to 165g of distilled water, 0.11g of alumina, 0.51g of tetrapropylammonium bromide, 1.0g of sodium hydroxide, and stirred uniformly to obtain a clear solution, and then the pH is adjusted to neutral with hydrochloric acid, and stirred uniformly to obtain an initial gel;

[0069] S2, the initial gel is transferred to a microwave reactor, and the temperature is set to 140°C and the time is set to 4h for microwave treatment;

[0070] S3, 6g of tetrapropylammonium hydroxide solution (25wt.%) is added to the product after microwave treatment and mixed uniformly, and then placed in an oven and controlled at a temperature of 100°C for 24h of drying treatment to obtain a solid gel;

[0071] S4, the solid gel is ground into powder and transferred to a high-pressure kettle with a polytetrafluoroethylene liner and a certain amount of distilled water (note: the solid powder and distilled water are separated) for vapor phase transformation, wherein the mass ratio of the solid powder to distilled water is 1:3;

[0072] S5, the vapor phase transformation product is sequentially washed, filtered, dried at 100°C overnight, and then calcined at 600°C for 4h to obtain ZSM-5 zeolite with adjustable crystal size.

[0073] Example 10

[0074] The amount of tetrapropylammonium hydroxide solution (25 wt.%) is 8 g;

[0075] Other steps and parameters are basically the same as those in Example 9.

[0076] Example 11

[0077] The amount of tetrapropylammonium hydroxide solution (25 wt.%) is 12 g;

[0078] Other steps and parameters are basically the same as those in Example 9.

[0079] Example 12

[0080] The amount of tetrapropylammonium hydroxide solution (25 wt.%) is 16 g;

[0081] Other steps and parameters are basically the same as those in Example 9.

[0082] Example 13

[0083] S1, 14 g of silica sol (40 wt.%), 0.15 g of alumina, 0.73 g of tetrapropylammonium bromide, and 0.89 g of potassium hydroxide were sequentially added to 180 g of distilled water, and stirred to obtain a clear solution, followed by adjusting the pH to neutral with hydrogen fluoride, and stirring to obtain an initial gel;

[0084] S2, the initial gel was transferred to a microwave reactor, and the temperature was set to 150°C and the time was set to 6 h for microwave treatment;

[0085] S3, 6 g of tetrapropylammonium hydroxide solution (25 wt.%) was added to the microwave-treated product, and the mixture was stirred to obtain a solid gel;

[0086] S4, the solid gel was ground into a powder, and then transferred to a high-pressure kettle with a polytetrafluoroethylene liner and a certain amount of distilled water (note: the solid powder and distilled water were separated) for vapor phase transformation, wherein the mass ratio of the solid powder to distilled water was 1:2.5;

[0087] S5, the vapor phase transformation product was sequentially washed, filtered, dried at 100°C overnight, and then calcined at 580°C for 6 h to obtain a ZSM-5 zeolite with adjustable crystal size.

[0088] Example 14

[0089] The amount of tetrapropylammonium hydroxide solution (25 wt.%) is 8 g;

[0090] Other steps and parameters are basically the same as those in Example 13.

[0091] Example 15

[0092] The amount of tetrapropylammonium hydroxide solution (25 wt.%) used was 12 g;

[0093] The other steps and parameters were basically the same as in Example 13.

[0094] Example 16

[0095] The amount of tetrapropylammonium hydroxide solution (25 wt.%) used was 16 g;

[0096] The other steps and parameters were basically the same as in Example 13.

[0097] Example 17

[0098] S1, 14 g of silica sol (40 wt.%) was added to 148 g of distilled water, followed by the addition of 0.07 g of sodium aluminate, 1.50 g of tetrapropylammonium bromide, and 0.95 g of potassium hydroxide, and the mixture was stirred until uniform, to obtain an initial gel; S2, the initial gel was transferred to a microwave reactor, and the temperature was set to 180°C and the time was set to 6 h, and the gel was subjected to microwave treatment;

[0099] S2, the initial gel was transferred to a microwave reactor, and the temperature was set to 180°C and the time was set to 6 h, and the gel was subjected to microwave treatment;

[0100] S3, 6 g of tetrapropylammonium hydroxide solution (25 wt.%) was added to the product after microwave treatment, and the mixture was stirred until uniform, and then the mixture was placed in an oven, the temperature was controlled at 100°C, and the mixture was subjected to drying treatment for 24 h, to obtain a solid gel;

[0101] S4, the solid gel was ground into a powder, and then the powder was transferred to an autoclave with a polytetrafluoroethylene liner and a certain amount of distilled water (note: the solid powder and the distilled water were separated) was added to perform vapor phase transformation, wherein the mass ratio of the solid powder to the distilled water was 1:4.5;

[0102] S5, the vapor phase transformation product was sequentially subjected to washing, filtration, drying at 100°C overnight, and then calcination at 600°C for 4 h, to obtain a ZSM-5 zeolite with adjustable crystal size.

[0103] Example 18

[0104] The amount of tetrapropylammonium hydroxide solution (25 wt.%) used was 8 g;

[0105] The other steps and parameters were basically the same as in Example 17.

[0106] Example 19

[0107] The amount of tetrapropylammonium hydroxide solution (25 wt.%) used was 10 g;

[0108] Other steps and parameters are basically the same as those in Example 17.

[0109] Example 20

[0110] The amount of tetrapropylammonium hydroxide solution (25 wt.%) is 16 g;

[0111] Other steps and parameters are basically the same as those in Example 17.

[0112] Example 21

[0113] S1, 18 g of silica sol (40 wt.%) is sequentially added to 160 g of distilled water, 0.07 g of sodium aluminate, 8.5 g of tetrapropylammonium hydroxide, 0.85 g of sodium hydroxide, and stirred uniformly to obtain a clear solution, and then the pH is adjusted to neutral with hydrochloric acid, and stirred uniformly to obtain an initial gel;

[0114] S2, the initial gel is transferred to a microwave reactor, and the temperature is set to 180℃ and the time is set to 5h, and microwave treatment is performed;

[0115] S3, 6 g of tetrapropylammonium hydroxide solution (25 wt.%) is added to the product after microwave treatment, and is uniformly mixed, and is placed in an oven, and the temperature is controlled at 100℃, and is dried for 24 h to obtain a solid gel;

[0116] S4, the solid gel is ground into powder, and is transferred to an autoclave with a polytetrafluoroethylene liner and a certain amount of distilled water (note: the solid powder and distilled water are separated) for vapor phase transformation, wherein the mass ratio of the solid powder to distilled water is 1:5.0;

[0117] S5, the vapor phase transformation product is sequentially washed, filtered, dried at 100℃ overnight, and then calcined at 580℃ for 4h to obtain a ZSM-5 zeolite with adjustable crystal size.

[0118] Example 22

[0119] The amount of tetrapropylammonium hydroxide solution (25 wt.%) is 8 g;

[0120] Other steps and parameters are basically the same as those in Example 21.

[0121] Example 23

[0122] The amount of tetrapropylammonium hydroxide solution (25 wt.%) is 10 g;

[0123] Other steps and parameters are basically the same as those in Example 21.

[0124] Example 24

[0125] The amount of tetrapropylammonium hydroxide solution (25 wt.%) is 14 g;

[0126] Other steps and parameters are substantially the same as in Example 21.

[0127] Comparative Example 1

[0128] The initial gel was not subjected to microwave treatment, but was added with 8 g of tetrapropylammonium hydroxide solution (25 wt.%) and was subjected to drying treatment after being mixed well, and was further subjected to vapor phase transformation treatment.

[0129] Other steps and parameters are substantially the same as in Example 1.

[0130] Comparative Example 1

[0131] The initial gel was not subjected to microwave treatment, but was added with 8 g of tetrapropylammonium hydroxide solution (25 wt.%) and was subjected to drying treatment after being mixed well, and was further subjected to vapor phase transformation treatment.

[0132] Other steps and parameters are substantially the same as in Example 1.

[0133] Comparative Example 2

[0134] The initial gel was not subjected to microwave treatment, but was added with 10 g of tetrapropylammonium hydroxide solution (25 wt.%) and was subjected to drying treatment after being mixed well, and was further subjected to vapor phase transformation treatment.

[0135] Other steps and parameters are substantially the same as in Example 1.

[0136] Comparative Example 3

[0137] The initial gel was not subjected to microwave treatment, but was added with 12 g of tetrapropylammonium hydroxide solution (25 wt.%) and was subjected to drying treatment after being mixed well, and was further subjected to vapor phase transformation treatment.

[0138] Other steps and parameters are substantially the same as in Example 1.

[0139] Comparative Example 4

[0140] The initial gel was not subjected to microwave treatment, but was added with 16 g of tetrapropylammonium hydroxide solution (25 wt.%) and was subjected to drying treatment after being mixed well, and was further subjected to vapor phase transformation treatment.

[0141] Other steps and parameters are substantially the same as in Example 1.

[0142] Comparative Example 5

[0143] According to the method disclosed in Example 1 of the Chinese invention patent with the publication number CN105293522A,

[0144] Mix 30 g of deionized water, 0.2 g of sodium aluminate, 17.6 g of tetrapropylammonium hydroxide and 16 mL of tetraethyl orthosilicate in sequence, stir at room temperature for 5 h, crystallize at 180℃ for 48 h, and then filter, wash, dry at 120℃, and calcine at 550℃ for 5 h.

[0145] Comparative Example 6

[0146] According to the method disclosed in Example 1 of the Chinese invention patent with the publication number CN113830788A,

[0147] (1) 25 mL of concentrated desilication liquid was measured, 10.8 g of silica sol was added, after stirring uniformly, 0.368 g of sodium hydroxide and 3.5 g of n-butylamine were added as a silica solution, then 0.34 g of Al2(SO4)3·18H2O was weighed, water was added and stirred to dissolve as an aluminum solution, the aluminum solution was added dropwise into the silica solution, stirred uniformly, and 0.29 g of ZSM-5 molecular sieve seed was added to obtain a precursor;

[0148] The molar ratio of each substance in the precursor is SiO2:Al2O3:water:Na2O:n-butylamine = 1:0.005:30:0.2:0.4, and the mass of the ZSM-5 molecular sieve seed is 4% of the mass of the ZSM-5 molecular sieve;

[0149] (2) After stirring the above precursor for 0.5 h, it was transferred to a reaction kettle and crystallized in a microwave reactor at 180℃ for 4 h under a microwave power of 800 W. The crystallized suspension was filtered, washed with water until the pH was neutral, then dried at 110℃ for 12 h, and the dried sample was sintered in a muffle furnace at 550℃ for 6 h to remove the template to obtain ZSM-5 molecular sieve;

[0150] (3) 6 g of ZSM-5 molecular sieve was taken and tableted on an electric tablet press, then the formed ZSM-5 molecular sieve was ground and sieved with a sieve to obtain a molecular sieve of 40-60 mesh, namely a ZSM-5 molecular sieve of 40-60 mesh.

[0151] Figure 1 The principle diagram for preparing ZSM-5 zeolite by the two-step method of microwave treatment and vapor phase transformation of the present application. As can be seen, before vapor phase transformation, microwave treatment is performed on the initial gel to form a large number of primary and secondary structural units of ZSM-5, and further vapor phase transformation can realize accurate regulation of the zeolite crystal grains by changing the addition amount of tetrapropylammonium hydroxide.

[0152] Figure 2 The XRD spectrum of the product after microwave treatment in Example 1 of the present application Figure 2A) and infrared spectrum (2B). From the XRD spectrum, it can be seen that the product after microwave treatment appears characteristic diffraction peaks of (NH4)2SiF6 and structure-directing agent (TPABr), and no characteristic diffraction peaks of ZSM-5 are detected. In the infrared spectrum, a clear vibration peak appears at wave number 546 cm -1 which belongs to the vibration peak of five-membered ring structure unit in zeolite, further indicating that the gel after microwave treatment contains a large amount of primary and secondary structure units of ZSM-5 zeolite.

[0153] Figure 3 XRD patterns of the samples obtained after steam phase conversion of Examples 1-4 of the present application. From the figures, it can be seen that during the steam phase conversion, by adjusting the addition amount of tetrapropylammonium hydroxide (8 g, 10 g, 12 g and 16 g), pure-phase ZSM-5 zeolite can be obtained, and no other crystal phase is generated. Moreover, with the increase of the addition amount of tetrapropylammonium hydroxide, the broadening phenomenon of the characteristic peaks of ZSM-5 becomes more and more obvious, indicating that the zeolite crystal grain size of ZSM-5 presents a gradually decreasing trend.

[0154] Figure 4 SEM images of the samples obtained after steam phase conversion of Examples 1-4 of the present application. From the figures, it can be seen that with the increase of the addition amount of tetrapropylammonium hydroxide, the morphology and crystal grain size of ZSM-5 change obviously, from the "coffin board" morphology of single-crystal micron-level ZSM-5 zeolite to the morphology of nano-polycrystal aggregate of ZSM-5, further indicating that by adjusting the amount of tetrapropylammonium hydroxide, the crystal grain size of zeolite can be effectively adjusted.

[0155] Figure 5 XRD patterns of the samples obtained after steam phase conversion of Comparative Examples 1-4 of the present application without microwave treatment. From the figures, it can be seen that the initial gel product without microwave treatment, after steam phase conversion, can also obtain pure-phase ZSM-5 zeolite. However, by changing the amount of tetrapropylammonium hydroxide, the characteristic diffraction peaks of ZSM-5 do not change obviously.

[0156] Figure 6 SEM images of the samples obtained after steam phase conversion of Comparative Examples 1-4 of the present application without microwave treatment. From the figures, it can be seen that the morphology and crystal grain size of the sample do not change obviously with the increase of the amount of tetrapropylammonium hydroxide, further indicating that the microwave treatment is a necessary step for adjusting the crystal grain size of ZSM-5 zeolite.

[0157] In order to study the performance of ZSM-5 zeolite with different crystal grain sizes, the above-prepared samples are used as catalysts for triisopropylbenzene cracking reaction, and the catalytic performance is tested and investigated, and the test method is as follows:

[0158] The triisopropyl benzene cracking reaction was carried out in a normal pressure micro fixed bed reactor, and the catalyst loading was 0.2 g.

[0159] Firstly, N2 was introduced into the reactor at a flow rate of 50 mL / min, and the temperature was raised from room temperature to 550℃ at a heating rate of 5℃ / min, and the activation time was 2 h, and then the temperature was reduced to 400℃;

[0160] Then, triisopropyl benzene was introduced by using a micro metering pump, and the feeding amount was controlled to be 1.5 mL / h;

[0161] The products after the reaction were analyzed on a gas chromatograph equipped with a hydrogen flame ionization detector (FID). Table 1 shows the catalytic performance data of different ZSM-5 zeolites.

[0162] Table 1 shows the catalytic performance data

[0163]

[0164]

[0165] As can be seen from the data of Comparative Examples 1-4, the catalytic performance of the ZSM-5 zeolites with different crystal grain sizes prepared by the two-step method of microwave treatment and steam phase conversion on triisopropyl benzene has a significant influence, and as the crystal grain size decreases, the catalytic activity on triisopropyl benzene can be significantly improved. For example, when the crystal grain size is reduced to the nanometer level (Example 4), the conversion rate of triisopropyl benzene is as high as 78.8%, which is significantly better than the ZSM-5 zeolites prepared in Examples 1-3. In addition, the selectivity of the deep cracking product (benzene + cumene) is as high as 49.3%, and the catalytic performance is significantly better than the ZSM-5 zeolites prepared by direct steam phase conversion in Comparative Examples 1-4 (for example, in Comparative Example 1, the initial conversion rate of triisopropyl benzene is 7.6%, and the average selectivity of the deep cracking product is 5.9%).

[0166] However, the zeolites synthesized in Comparative Examples 5 and 6 have a single morphology, a large crystal grain size, a small external surface area, and cannot be flexibly adjusted according to the reaction requirements, and the application range is narrow. Further, in the macromolecular cracking reaction, it can be seen that triisopropyl benzene is difficult to pre-crack on the surface of the zeolite, which further prevents the deep cracking reaction, thereby showing very low catalytic activity and product selectivity.

[0167] In conclusion, the ZSM-5 zeolite is prepared by the two-step method of microwave treatment and vapor phase transformation, in the preparation process, the growth and nucleation rate of the ZSM-5 zeolite can be regulated by changing the adding amount of the template tetrapropylammonium hydroxide solution, and then the classical and non-classical construction of the ZSM-5 zeolite is regulated to realize the effective regulation of the ZSM-5 zeolite grain. The prepared ZSM-5 zeolite shows excellent catalytic performance in the macromolecular cracking reaction, compared with the conventional microporous ZSM-5 zeolite, the catalytic activity and the selectivity of the deep cracking product (cumene and benzene) can be obviously improved, which has guiding significance in solving the problem of crude oil heavy.

[0168] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a ZSM-5 zeolite with adjustable crystal size, characterized in that, The method comprises the following steps: S1, adding a silicon source, an aluminum source, a structure-directing agent, and a mineralizing agent into distilled water, adjusting the pH to neutral, stirring uniformly to obtain an initial gel; S2, microwave treating the initial gel; S3, adding a template agent to the microwave-treated product and drying to obtain a solid gel; S4, grinding the solid gel into powder and placing it in an autoclave for steam phase conversion; S5, after the steam phase conversion product is sequentially subjected to washing, filtering, drying, and calcining, a ZSM-5 zeolite with adjustable crystal grain size is obtained; By changing the amount of the template agent added, the crystal grain size of the ZSM-5 zeolite can be adjusted in the range of 0.2-15 μm; In step S2, the microwave treatment is controlled at a temperature of 140-180 ℃ for 1-7 h; In step S3, the template agent comprises any one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, and n-butylamine; The mass ratio of the microwave-treated product to the template agent is 1:(2-3.5); In step S4, the steam phase conversion is controlled at a temperature of 140-180 ℃ for 24-72 h with a mass ratio of the solid gel to distilled water of 1:(2.5-7.0).

2. The production method according to claim 1, characterized by, In step S1, the molar ratio of silica, alumina, the structure-directing agent, the mineralizing agent, and distilled water in the initial gel is (0.3-1.2):(0.003-0.012):(0.02-0.14):(0.2-1.6):(50.8-250.3).

3. The preparation method according to claim 1, characterized in that, In step S1, the aluminum source comprises any one or more of alumina, sodium aluminate, aluminum hydroxide, and pseudo-boehmite; The silicon source comprises any one or more of tetraethyl orthosilicate, fumed silica, and silica sol; The structure-directing agent comprises any one or more of tetrapropylammonium hydroxide, n-butylamine, tetrapropylammonium bromide, and diethylamine; The mineralizing agent comprises any one or more of ammonium fluoride, sodium hydroxide, and potassium hydroxide; The adjusting agent used for adjusting the pH comprises any one or more of hydrogen fluoride, hydrochloric acid, and nitric acid.

4. The preparation method according to claim 1, characterized in that, In step S3, the drying is controlled at a temperature of 90-120 ℃ for 12-24 h.

5. The preparation method according to claim 1, characterized in that, In step S5, the drying is controlled at a temperature of 90-120 ℃ for 24-48 h; The calcining is controlled at a temperature of 500-650 ℃ for 4-12 h.

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