CN111569935A

CN111569935A - Catalyst for preparing p-xylene, preparation method and application thereof

Info

Publication number: CN111569935A
Application number: CN202010443581.1A
Authority: CN
Inventors: 李孝国; 侯章贵; 郭新闻; 张安峰; 常洋; 齐美美; 李永恒; 曹辉; 韩国栋; 张永坤
Original assignee: Dalian University of Technology; China National Offshore Oil Corp CNOOC; CNOOC Oil and Petrochemicals Co Ltd; CNOOC Research Institute of Refining and Petrochemicals Beijing Co Ltd; CNOOC Qingdao Heavy Oil Processing Engineering Technology Research Center Co Ltd
Current assignee: Dalian University of Technology; China National Offshore Oil Corp CNOOC; CNOOC Oil and Petrochemicals Co Ltd; CNOOC Research Institute of Refining and Petrochemicals Beijing Co Ltd; CNOOC Qingdao Heavy Oil Processing Engineering Technology Research Center Co Ltd
Priority date: 2020-05-22
Filing date: 2020-05-22
Publication date: 2020-08-25
Anticipated expiration: 2040-05-22
Also published as: CN111569935B

Abstract

The invention relates to a catalyst for preparing paraxylene, a preparation method and application thereof, wherein the catalyst is a molecular sieve with a core-shell structure, and comprises a core molecular sieve and a shell molecular sieve coated on the surface of the core molecular sieve, the core molecular sieve is a ZSM-5 molecular sieve, the shell molecular sieve is an S-1 molecular sieve, and hydrogenation metal is encapsulated in the core molecular sieve; the catalyst has high conversion rate and selectivity to a product p-xylene in the process of catalyzing the toluene methanol alkylation reaction, and the carbon deposition rate of the catalyst is obviously reduced in the catalysis process, so that the catalyst has high stability.

Description

Catalyst for preparing p-xylene, preparation method and application thereof

Technical Field

The invention belongs to the technical field of catalysis, and relates to a catalyst for preparing paraxylene, and a preparation method and application thereof.

Background

Para-xylene (PX) is an important organic chemical raw material, and is mainly used for producing polyester. In recent years, the polyester industry has been rapidly developed, and thus the demand for p-xylene has been increasing. The typical method for producing the paraxylene is naphtha catalytic reforming, only a thermodynamic equilibrium xylene mixture can be obtained, and the high-concentration paraxylene needs to be obtained through further cryogenic crystallization or a simulated moving bed adsorption separation technology, so that the cost is high and the energy consumption is high.

At present, isomerization of mixed xylene, transalkylation of C9 aromatics and selective disproportionation of toluene are the main methods for increasing the yield of p-xylene in industrial production. In addition, because of the development of C1 chemistry, the yield of methanol is increased, the cost is reduced, a large amount of excess toluene resources in petrochemical industry and cheap methanol resources in coal chemical industry are utilized to produce high-concentration p-xylene, separation procedures and isomerization processes are reduced, and the economic benefit is considerable, so that the research on the selective synthesis of p-xylene by toluene methanol alkylation reaction is concerned.

At present, one of the obstacles of the fixed bed process for toluene methanol alkylation that has not been industrialized is the deactivation of the catalyst. It was found that carbon deposition is the main cause of catalyst deactivation in the toluene methanol alkylation reaction. The methanol is activated by acid sites, is easy to dehydrate to generate dimethyl ether, is further converted to generate low-carbon olefin, and the low-carbon olefin is easy to generate alkylation reaction with aromatic hydrocarbon in a system to generate polyalkylbenzene, so that channels are blocked to cover acid centers, and the catalyst is inactivated. Therefore, to suppress the occurrence of side reactions, the zeolite is usually modified or post-treated to improve the selectivity to p-xylene.

The ZSM-5 molecular sieve and the Silicalite-1 molecular sieve are typical molecular sieves with MFI structures, and both have two sets of mutually crossed pore channel structures, one set is an elliptical pore channel parallel to a unit cell b, the diameter of the pore channel is 0.53 multiplied by 0.56nm, the other set is a Z-shaped pore channel parallel to an a axis of the unit cell, and the diameter of the pore channel is 0.51 multiplied by 0.55 nm. The ZSM-5 molecular sieve has excellent shape selectivity and is widely applied to reactions such as aromatic alkylation, methanol-to-aromatic hydrocarbon preparation, aromatic isomerization and the like, and the Silicalite-1 molecular sieve is an all-silica molecular sieve, does not have an acid site and is usually used as a carrier or an adsorbent.

Currently, molecular sieves of composite structure are attracting attention because of their excellent properties. The earliest synthesis of ZSM-5@ Silicalite-1 molecular sieves by Rollmann (see literature: Rollmann LD. US 4088605.1978); nishiyama et al coat a polycrystalline S-1 molecular sieve shell layer on hydrogen type ZSM-5 with different particle sizes (5-30 μm), and find that when ZSM-5 molecular sieve crystal grains with the particle size of 5 μm are taken as a core, the prepared core-shell structure catalyst has higher stability and selectivity to dimethylbenzene; the core-shell structure catalyst prepared with the increased crystal grains not only reduces the selectivity OF the product to xylene because large crystal grains are difficult to completely coat, but also rapidly deactivates the catalyst with larger crystal grains (see the literature, "Van Vu D., Miyamoto M., Nishiyama N., et al. selected formation OF para-xylene over H-ZSM-5coated with polycrystalline silica crystals. JOURNAL OF CATALYSIS [ J ] (2):389 394"). In addition, Nishiyama et al also adopt a repeated hydrothermal synthesis method to prepare a ZSM-5 catalyst with polycrystalline silicalite-1 as a coating, the catalyst is applied to toluene/methanol 1, the reaction is carried out at 400 ℃ for 60min, the selectivity of the product to xylene is more than 99.9 percent, and the selectivity of an uncoated catalyst parent body can only reach about 40 percent (see the literature: Van Vu D., Miyamoto M., Nishiyama N., et al, catalytic activities and structural reactions of silicalite-1/H-ZSM-5zeolite ").

The Mesoporous Silica-coated ZSM-5 core-shell structure catalyst is prepared by adopting a cationic surfactant template method by Jiyongjun and the like, the shell thickness can be effectively adjusted, when the Mesoporous Silica-coated ZSM-5 core-shell structure catalyst is applied to a toluene methanol alkylation reaction, compared with a matrix with the selectivity of 28.8% for a product p-xylene, when the shell-core mass ratio is 3, the selectivity of the synthesized Mesoporous core-shell structure catalyst for the product p-xylene is improved to 41.1%, and after the Mesoporous Silica-shell structure catalyst is further subjected to dry glue conversion and aging for 12h, the selectivity for the product p-xylene is improved to 54.6% (see the literature: preparation of ZSM-5@ meso pore Silica core-shell composite structure molecular sieve and research of toluene methanol alkylation shape-selective performance thereof, the chemical report [ J ].2013,71(03):371-380. ").

Therefore, the development of a catalyst with high selectivity and excellent catalytic stability to the product p-xylene and a preparation method thereof still have important significance.

Disclosure of Invention

The invention aims to provide a catalyst for preparing p-xylene, a preparation method and application thereof, wherein the catalyst is a core-shell structure molecular sieve and comprises an inner core molecular sieve and a shell layer molecular sieve coated on the surface of the inner core molecular sieve, the inner core molecular sieve is a ZSM-5 molecular sieve, the shell layer molecular sieve is an S-1 molecular sieve, hydrogenation metal is encapsulated in the inner core molecular sieve, the catalyst has high conversion rate and selectivity on a product p-xylene in the process of catalyzing a toluene methanol alkylation reaction, the carbon deposition rate of the catalyst in the catalysis process is obviously reduced, and the catalyst has high stability.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a catalyst for preparing paraxylene, wherein the catalyst is a core-shell structure molecular sieve, and comprises a core molecular sieve and a shell layer molecular sieve coated on the surface of the core molecular sieve, the core molecular sieve is a ZSM-5 molecular sieve, the shell layer molecular sieve is an S-1 molecular sieve, and hydrogenation metal is encapsulated in the core molecular sieve.

The catalyst takes a ZSM-5 molecular sieve encapsulated with hydrogenation metal as a core, and the surface of the catalyst is coated with an S-1 molecular sieve; the S-1 molecular sieve is an all-silicon molecular sieve, and the surface of the molecular sieve does not have an acid site, so that the secondary isomerization side reaction of paraxylene generated in a catalyst pore channel in a toluene methanol alkylation reaction at the acid site on the surface of the catalyst is avoided, the selectivity of a product paraxylene in a catalytic process is effectively improved, and the selectivity of the catalyst on the paraxylene in the using process can reach 98%.

The hydrogenation metal encapsulated in the ZSM-5 molecular sieve in the catalyst can convert a carbon deposition precursor generated in the reaction process into alkane, so that the carbon deposition rate in the catalytic reaction is reduced, the inactivation of the catalyst is slowed, and the stability of the catalyst is improved; in the catalyst, the hydrogenation metal is encapsulated in the ZSM-5 molecular sieve instead of being positioned on the surface of the molecular sieve, so that the hydrogenation metal is not easy to migrate or agglomerate, and the stability of the catalyst is improved.

The catalyst of the invention has no agglomeration phenomenon of hydrogenation metal in the regeneration process, is relatively stable and can be recycled.

The S-1 molecular sieve is a Silicalite-1 molecular sieve, is an all-silicon molecular sieve and does not have an acid site.

Preferably, the ZSM-5 molecular sieve is an H-type ZSM-5 molecular sieve.

The ZSM-5 molecular sieve has two sets of mutually crossed pore channel systems, namely a Z-shaped pore channel and an oval straight pore channel, and the pore channel sizes are respectively

And

wherein the kinetic diameter of paraxylene is 0.58nm, the kinetic diameters of ortho-xylene and meta-xylene are about 0.63nm, and the diffusion rate of paraxylene in pore channels is 10 of that of ortho-xylene and meta-xylene³Or even 10⁴And the ZSM-5 molecular sieve has obvious shape-selective advantage.

Preferably, the hydrogenation metal has a particle size of 1 to 10nm, such as 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm or 9nm, etc., preferably 4 to 5 nm.

Preferably, the mass ratio of the ZSM-5 molecular sieve to the S-1 molecular sieve is 1 (0.3-10), such as 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9, etc., preferably 1 (0.5-5).

The mass ratio of the ZSM-5 molecular sieve to the S-1 molecular sieve in the catalyst is in the range, so that the core can be well coated by a shell layer, the selectivity of paraxylene can be improved, the conversion rate of toluene cannot be greatly lost, and when the mass ratio of the ZSM-5 molecular sieve to the S-1 molecular sieve is less than 1:10, the ratio of silicon to aluminum is too high, so that the conversion rate of toluene is reduced; when the mass ratio of the ZSM-5 molecular sieve to the S-1 molecular sieve is more than 1:0.3, the coating is difficult to be uniform, and the selectivity of the paraxylene is not effectively improved.

Preferably, the hydrogenation metal comprises any one of Pt, Pd or Ni or a combination of at least two thereof, which illustratively comprises a combination of Pt and Pd, a combination of Ni and Pt, or a combination of Pd and Ni, and the like, preferably Pt.

Preferably, the hydrogenation metal is present in an amount of 0.001 to 1% by mass, for example 0.001%, 0.0015%, 0.002%, 0.004%, 0.01%, 0.012%, 0.014%, 0.018%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or 0.9%, etc., preferably 0.004 to 0.02% by mass, based on 100% by mass of the catalyst.

Preferably, the ZSM-5 molecular sieve has a silica to alumina molar ratio of 40 to 500, such as 50, 100, 150, 200, 250, 300, 350, 400, 450, etc., preferably 100-.

The molar ratio of silicon to aluminum is defined herein as SiO₂Calculated as Al, Al₂O₃In terms of Si/Al molar ratio, i.e. SiO₂/Al₂O₃。

Preferably, the S-1 molecular sieve is obtained by one-time epitaxial growth.

In a second aspect, the present invention provides a process for the preparation of a catalyst as described in the first aspect, the process comprising the steps of:

(1) preparing a ZSM-5 molecular sieve encapsulating hydrogenation metal;

(2) and (2) taking the ZSM-5 molecular sieve encapsulated with the hydrogenation metal obtained in the step (1) as a core, and carrying out primary epitaxial growth on the surface of the core to form the S-1 molecular sieve to obtain the catalyst.

In the preparation process of the catalyst, the ZSM-5 molecular sieve encapsulated with the hydrogenation metal is taken as a core, the S-1 molecular sieve serving as a shell layer is obtained by one-time epitaxial growth, and the coverage of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal can reach 98%, so that the catalyst can keep high selectivity on the product p-xylene in the process of being used for the toluene methanol alkylation reaction, and the selectivity on the product p-xylene can reach 98%.

Preferably, the preparation method of the ZSM-5 molecular sieve encapsulating the hydrogenation metal in the step (1) comprises adding a hydrogenation metal source in the preparation process of the ZSM-5 molecular sieve.

In the preparation process of the catalyst, the hydrogenation metal source is added in the preparation process of the ZSM-5 molecular sieve, compared with the traditional impregnation method, the obtained catalyst has better dispersity and excellent hydrogenation performance of the hydrogenation metal particles, and the agglomeration phenomenon of the hydrogenation metal does not occur in the regeneration process of the catalyst, so that the catalyst has a stable structure and can be recycled; the hydrogenation metal generated in situ in the preparation process of the ZSM-5 molecular sieve by adopting the method has the characteristics of uniform dispersion and small particle size of the hydrogenation metal particles, and the hydrogenation metal particles are dispersed in the catalyst but not on the surface; meanwhile, in the preparation process, the added hydrogenation metal enables the carbon deposition precursor low-carbon olefin generated by the reaction to be converted into alkane, so that the inactivation of the catalyst is slowed down, the carbon deposition rate is reduced, and the stability of the catalyst is improved.

Preferably, the preparation method of the ZSM-5 molecular sieve encapsulating hydrogenation metal in the step (1) comprises the following steps:

(a) mixing a silicon source, a template agent, an aluminum source and water to obtain a mixed solution;

(b) and (b) mixing the mixed solution in the step (a) with an aqueous solution of a hydrogenation metal source to obtain primary crystallization mother liquor, and then carrying out primary crystallization and roasting to obtain the ZSM-5 molecular sieve encapsulated with the hydrogenation metal.

In the preparation process, the silicon source, the template agent, the aluminum source and the water are mixed and then the hydrogenation metal is added, so that the uniform dispersion of the hydrogenation metal in the ZSM-5 molecular sieve is facilitated, and the activity and the stability of the catalyst are further improved.

Preferably, the method of mixing in step (a) comprises the steps of:

(a') dissolving a silicon source and a template agent in water to obtain a first solution;

(b') dissolving an aluminum source in water to obtain a second solution;

(c ') mixing the first solution of step (a ') and the second solution of step (b ') to obtain the mixed solution.

Preferably, the silicon source in step (a) includes any one of or a combination of at least two of tetraethoxysilane, silica sol or water glass, and the combination exemplarily includes a combination of tetraethoxysilane and silica sol, a combination of water glass and tetraethoxysilane, or a combination of silica sol and water glass, and the like.

Preferably, the templating agent of step (a) comprises any one or a combination of at least two of TPAOH, TPABr, n-butylamine, or hexamethylenamine bromide; exemplary combinations include a combination of TPAOH and TPABr or a combination of n-butylamine and hexamethylamine bromide, and the like.

Preferably, the aluminium source of step (a) comprises any one of, or a combination of at least two of, aluminium sulphate, aluminium chloride, aluminium hydroxide or aluminium isopropoxide; the combination illustratively includes a combination of aluminum sulfate and aluminum chloride or a combination of aluminum hydroxide and aluminum isopropoxide, or the like.

Preferably, the method further comprises stirring the mixed solution in step (a) for 0.5-5h, such as 1h, 2h, 3h or 4h, before performing step (b).

Preferably, the hydrogenation metal source of step (b) is a soluble salt of the hydrogenation metal.

Preferably, the molar ratio of the silicon source, the aluminum source, the template agent, the water and the hydrogenation metal source in the primary crystallization mother liquor in the step (b) is 1 (0.0025-0.025): (0.1-5): 30-50): 0.0003-0.006; for example, 1:0.0025:0.1:30:0.0003, 1:0.005:0.5:35:0.001, 1:0.01:0.1:40:0.003, 1:0.02:2:45:0.004, or 1:0.025:3.5:50:0.005, etc.

Preferably, the temperature of the first crystallization in step (b) is 150-.

In the preparation process of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal, the temperature of the first crystallization is controlled to be 150-180 ℃, which is beneficial to the crystallization of the ZSM-5, when the temperature is less than 150 ℃, the crystallization speed is low, the time for completely crystallizing the sample is too long, and when the temperature is more than 180 ℃, the metal particles are not easy to be coated in the ZSM-5;

the first crystallization time is controlled to be 60-80h in the preparation process of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal, so that the molecular sieve with higher crystallinity and good crystallization can be formed, when the time is less than 60h, incomplete crystallization can be caused due to shorter crystallization time, the crystallinity is lower, when the time is more than 80h, the molecular sieve basically grows and finishes at the later stage of crystallization, the influence of the time extension on the crystallization is weaker, the energy consumption is higher, and the synthesis cost of the catalyst is increased.

Preferably, the temperature of the calcination in step (b) is 540-560 ℃, such as 545 ℃, 550 ℃ or 555 ℃, and the like, and the time is 6-8h, such as 6.5h, 7h or 7.5h, and the like.

In the preparation process of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal, the roasting temperature is controlled within the range, so that the template agent can be completely burnt out, and good hydrogenation performance can be ensured; when the temperature is less than 540 ℃, the roasting of the template agent is incomplete; when the temperature is higher than 560 ℃, the sintering and agglomeration of metal are easily caused, and the hydrogenation effect of the catalyst is influenced.

In the preparation process of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal, the roasting time is controlled within the range, so that the template agent can be roasted cleanly within effective time; when the time is less than 6 hours, the problem of incomplete roasting of the template exists; when the time is more than 8 hours, the overlong roasting time not only can easily cause the agglomeration of metals, but also prolongs the time cost of the catalyst.

Preferably, after the first crystallization in step (b), solid-liquid separation and drying are further included before calcination.

Preferably, the method of solid-liquid separation is centrifugation.

Preferably, the method for primary epitaxial growth in step (2) comprises the following steps:

(1') dissolving a silicon source and a template agent in water to obtain secondary crystallization mother liquor;

(2') hydrolyzing the secondary crystallization mother liquor in the step (1'), adding the ZSM-5 molecular sieve which is packaged with hydrogenation metal in the step (1), and carrying out secondary crystallization and roasting to form the S-1 molecular sieve.

The preparation of the conventional ZSM-5@ Silicalite-1 core-shell structure molecular sieve can form a compact molecular sieve shell layer only by repeated growth, the preparation process can cause serious waste of a silicon source, water, a template agent and energy consumption, the synthesis period is long, and the cost is high; the conventional ZSM-5@ Silicalite-1 core-shell structure molecular sieve is coated for many times and then is subjected to reaction evaluation, so that the conversion rate is obviously reduced, the selectivity is improved, but the stability is poor, the inactivation is rapid, and the industrial value is not high; and the repeated coating prolongs the pore channel of the catalyst, increases the probability of side reaction, generates polycyclic aromatic hydrocarbon to cover the active center, improves the carbon deposition rate of the catalyst and accelerates the inactivation.

In the preparation process of the catalyst, the S-1 molecular sieve serving as the shell layer is obtained by one-step epitaxial growth, the steps are adopted in the preparation process, the higher coverage can be achieved by one-step epitaxial growth, and compared with multiple coatings, the preparation process of the catalyst can be simplified, and the preparation time of the catalyst is shortened.

Preferably, the molar ratio of templating agent to silicon source in step (1') is (0.05-0.15: 1, e.g., 0.06:1, 0.08:1, 0.1:1, or 0.13:1, etc.

In the process of forming the S-1 molecular sieve by one-time epitaxial growth, the core can be well coated by adopting the molar ratio of the template agent to the silicon source; when the molar ratio of the two is less than 0.05, the template dosage is too low, and the secondary crystallization liquid crystallization speed is slow; when the molar ratio of the two is more than 0.15, the high content of the template agent can cause the self-nucleation of the secondary crystallization liquid, and the good coating is difficult to carry out.

Preferably, the molar ratio of water in step (1') to the ZSM-5 molecular sieve with the hydrogenation metal encapsulated therein in step (2') is 100 to 250:1, such as 130:1, 150:1, 180:1, 200:1, 220:1 or 240:1, etc., wherein the molar mass of the ZSM-5 molecular sieve is 60g/mol as the molar mass of silica.

Preferably, the molar ratio of the silicon source in step (1') to the ZSM-5 molecular sieve encapsulated with hydrogenation metal in step (2') is 0.5 to 3, such as 1, 1.5, 2, 2.5, etc. Wherein the molecular mass of the ZSM-5 molecular sieve is taken as the molar mass of silica in terms of 60 g/mol.

Preferably, the hydrolysis method in step (2') is stirring.

Preferably, the second crystallization of step (2') is a spin crystallization.

Preferably, the rotation speed of the rotary crystallization is 10-30r/min, such as 15r/min, 20r/min or 25 r/min.

Preferably, the temperature of the second crystallization in step (2') is 150-.

In the process of forming S-1 by one-time epitaxial growth, the crystallization temperature and the crystallization time are adopted, so that the S-1 molecular sieve in the prepared catalyst forms high coverage on the surface of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal, the coverage can reach 98 percent, and when the crystallization temperature is lower than 150 ℃, the molecular sieve is easy to form additional nucleation instead of growing on the surface of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal; when the crystallization temperature is higher than 180 ℃, the molecular sieve is easy to be crystallized, and the crystallinity is reduced; when the crystallization time is less than 60 hours, the secondary growth is incomplete; when the crystallization time is more than 80h, the synthesized material is not significantly changed.

Preferably, the temperature of the calcination in step (2') is 540-560 ℃, such as 545 ℃, 550 ℃ or 555 ℃, and the like, and the time is 6-8h, such as 6.5h, 7h or 7.5h, and the like.

Preferably, after the second crystallization in step (2'), solid-liquid separation and drying are further included before the calcination.

Preferably, the method of solid-liquid separation is centrifugation.

As a preferred technical scheme of the invention, the preparation method of the catalyst comprises the following steps:

(1') preparing a ZSM-5 molecular sieve encapsulating hydrogenation metal, wherein the preparation process comprises the following steps:

(a ") dissolving a silicon source and a template agent in water to obtain a first solution;

(b ") dissolving an aluminum source in water to obtain a second solution;

(c ") mixing the first solution of step (a") and the second solution of step (b ") to obtain a mixed solution;

(d ') mixing the mixed solution in the step (c') with an aqueous solution of a hydrogenation metal source to obtain a primary crystallization mother liquor, then crystallizing at 150-;

(2') taking the ZSM-5 molecular sieve encapsulated with the hydrogenation metal obtained in the step (1') as a core, and carrying out primary epitaxial growth on the surface of the core to form an S-1 molecular sieve; the method for primary epitaxial growth comprises the following steps:

(2') stirring and hydrolyzing the secondary crystallization mother liquor in the step (1') for 0.5-10 h, then adding the ZSM-5 molecular sieve which is packaged with hydrogenation metal in the step (1'), crystallizing for 60-80h at the temperature of 150-.

In a third aspect, the present invention provides the use of a catalyst as described in the first aspect for the production of paraxylene.

Preferably, the catalyst is used for catalyzing the alkylation reaction of toluene and methanol to prepare paraxylene.

Compared with the prior art, the invention has the following beneficial effects:

(1) the catalyst is of a core-shell structure, a ZSM-5 molecular sieve which is packaged with hydrogenation metal is used as a core, an S-1 molecular sieve which is full silicon is used as a shell, the catalyst has high stability in the process of catalyzing the toluene methanol alkylation reaction, and the hydrogenation metal in the core can convert carbon deposition precursor low-carbon olefin into alkane, reduce the carbon deposition rate and slow down the inactivation of the catalyst; the hydrogenation metal encapsulated in the ZSM-5 molecular sieve is not easy to agglomerate in the catalyst regeneration process, has stable property and can be recycled;

(2) the shell layer of the catalyst is an all-silicon S-1 molecular sieve, and the surface of the shell layer does not contain an acid site, so that the occurrence of secondary isomerization reaction of paraxylene generated in a catalyst pore channel in an acid center on the surface of the catalyst is avoided, and the selectivity of the catalyst is obviously improved;

(3) the preparation method of the ZSM-5 molecular sieve with the hydrogenation metal encapsulated in the catalyst adopts the step of adding the hydrogenation metal source in the preparation process of the ZSM-5 molecular sieve so as to generate the hydrogenation metal in situ, the hydrogenation metal of the obtained catalyst is positioned in the catalyst but not on the surface, and the hydrogenation metal has high dispersity and small particle size, is not easy to migrate and agglomerate in the roasting process, and is further favorable for prolonging the service life of the catalyst;

(4) the preparation of the S-1 molecular sieve in the catalyst adopts a one-time epitaxial growth method, the S-1 molecular sieve has obvious growth tendency by taking ZSM-5 encapsulated with hydrogenation metal as a core in a crystallization synthesis system, high coverage can be obtained through one-time epitaxial growth, high selectivity can be realized without multiple coating, the production efficiency is further improved, and the production cost of the catalyst is saved.

Drawings

FIG. 1 is an X-ray diffraction pattern of a core-shell structured molecular sieve obtained in examples 1-5 of the present invention and Pt @ ZSM-5 obtained in example 1;

FIG. 2 is a graph of the activity and selectivity of the catalyst of comparative example 1 of the present invention for catalyzing toluene methylation;

FIG. 3 is a graph of the core-shell molecular sieves of examples 1-5 of the present invention and Pt @ ZSM-5 of example 1 used to catalyze toluene conversion, xylene selectivity, and p-xylene selectivity during the toluene methanol alkylation reaction;

FIG. 4 is a plot of toluene conversion, xylene selectivity and p-xylene selectivity for the catalytic toluene methanol alkylation process using fresh and regenerated Pt @ ZSM-5 obtained in example 1 of the present invention.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

In the embodiment, the mass ratio of the core shell to the shell is 1:0.51, the hydrogenation metal is Pt, and the mass percentage content of the hydrogenation metal Pt in the catalyst is 0.016%; the preparation method of the catalyst comprises the following steps:

(1) preparing a nuclear phase Pt @ ZSM-5 molecular sieve, wherein the preparation process comprises the following steps:

(a) adding 10g of ethyl orthosilicate and 26g of tetrapropyl ammonium hydroxide into 10g of deionized water, stirring at 35 ℃ for 10min, and marking as a solution A;

(b) 0.1332g of aluminum sulfate (silica to alumina molar ratio of 400) was dissolved in 10g of deionized water, labeled as solution B;

(c) slowly dripping the solution B into the solution A, and continuously stirring for 6 hours to obtain a mixed solution;

(d) dissolving 0.0095g of platinum tetraammine nitrate in 10.8g of deionized water to obtain a hydrogenation metal source aqueous solution;

(e) slowly dripping the hydrogenation metal source aqueous solution in the step (d) into the mixed solution in the step (c), stirring for 30min, transferring the mixed solution into a 100mL crystallization kettle with a polytetrafluoroethylene lining, crystallizing for 72H at 170 ℃, centrifugally separating the crystallized suspension, washing the suspension to be neutral by deionized water, drying for 12H at 120 ℃, and roasting for 6H at 540 ℃ to obtain H-type ZSM-5 which is marked as Pt @ ZSM-5.

The mass percentage content of Pt in the Pt @ ZSM-5 prepared in the embodiment is 0.034%;

(2) one-time epitaxial growth to form S-1 molecular sieve

(a') mixing 1.74g of ethyl orthosilicate, 0.34g of tetrapropylammonium hydroxide and 52g of water, stirring at 35 ℃ and hydrolyzing for 7 hours to obtain a mixed solution;

(b ') adding 1g of Pt @ ZSM-5 powder prepared in the step (1) into the mixed solution in the step (a'), continuously stirring for 1H, transferring into a 100mL crystallization kettle with a polytetrafluoroethylene lining, crystallizing for 72H at 170 ℃ in a rotary crystallization oven at the rotating speed of 20r/min, centrifugally separating the obtained suspension, washing with deionized water to be neutral, drying at 120 ℃ for 12H, roasting at 540 ℃ for 6H to obtain H-type ZSM-5@ Silicalite-1 with the core-shell mass ratio of 1:0.51, wherein the mark is Pt @ ZSM-5@ (0.5) S-1.

Example 2

The mass ratio of the core shell to the shell of the catalyst is 1:1.08, the hydrogenation metal is Pt, and the mass percentage content of the hydrogenation metal Pt in the catalyst is 0.014%;

in the preparation process of the catalyst, the nuclear phase Pt @ ZSM-5 molecular sieve prepared in the example 1 is used as a raw material, and the nuclear phase Pt @ ZSM-5 molecular sieve is subjected to primary epitaxial growth to form an S-1 molecular sieve, so that the catalyst is obtained; the preparation method comprises the following steps:

(a') mixing 3.47g of ethyl orthosilicate, 0.68g of tetrapropylammonium hydroxide and 52g of water, stirring at 35 ℃ and hydrolyzing for 7 hours to obtain a mixed solution;

(b ') adding 1g of Pt @ ZSM-5 powder prepared in example 1 into the mixed solution obtained in the step (a'), continuously stirring for 1H, transferring into a 100mL crystallization kettle with a polytetrafluoroethylene lining, crystallizing for 72H at 170 ℃ in a rotary crystallization oven at the rotating speed of 20r/min, centrifugally separating the obtained suspension, washing with deionized water to be neutral, drying at 120 ℃ for 12H, and roasting at 540 ℃ for 6H to obtain H-type ZSM-5@ Silicalite-1 with the core-shell mass ratio of 1:1.08, wherein the H-type ZSM-5@ Silicalite-1 is marked as Pt @ ZSM-5@ S-1.

Example 3

The mass ratio of the core shell to the shell of the catalyst is 1:1.51, the hydrogenation metal is Pt, and the mass percentage content of the hydrogenation metal Pt in the catalyst is 0.011%;

(a') mixing 5.21g of ethyl orthosilicate, 1.02g of tetrapropylammonium hydroxide and 52g of water, stirring at 35 ℃ and hydrolyzing for 7 hours to obtain a mixed solution;

(b ') adding 1g of Pt @ ZSM-5 powder prepared in example 1 into the mixed solution obtained in the step (a'), continuously stirring for 1H, transferring the mixture into a 100mL crystallization kettle with a polytetrafluoroethylene lining, crystallizing the mixture for 72H at a rotating crystallization oven at 170 ℃ and at a rotating speed of 20r/min, centrifugally separating the obtained suspension, washing the suspension to be neutral by deionized water, drying the suspension at 120 ℃ for 12H, and roasting the suspension at 540 ℃ for 6H to obtain H-type ZSM-5@ Silicalite-1 with the core-shell mass ratio of 1:1.51, wherein the H-type ZSM-5@ Silicalite-1 is marked as Pt @ ZSM-5@ S-1 (1.5).

Example 4

The mass ratio of the core shell to the shell of the catalyst is 1:2.01, the hydrogenation metal is Pt, and the mass percentage content of the hydrogenation metal Pt in the catalyst is 0.008%;

(a') mixing 6.94g of ethyl orthosilicate, 1.36g of tetrapropylammonium hydroxide and 52g of water, stirring at 35 ℃ and hydrolyzing for 7 hours to obtain a mixed solution;

(b ') adding 1g of Pt @ ZSM-5 powder prepared in example 1 into the mixed solution obtained in the step (a'), continuously stirring for 1H, transferring the mixture into a 100mL crystallization kettle with a polytetrafluoroethylene lining, crystallizing the mixture for 72H at a rotating crystallization oven at 170 ℃ and at a rotating speed of 20r/min, centrifugally separating the obtained suspension, washing the suspension to be neutral by deionized water, drying the suspension at 120 ℃ for 12H, and roasting the suspension at 540 ℃ for 6H to obtain H-type ZSM-5@ Silicalite-1 with the core-shell mass ratio of 1:2.01, wherein the H-type ZSM-5@ Silicalite-1 is marked as Pt @ ZSM-5@ S-1.

Example 5

The mass ratio of the core shell to the shell of the catalyst is 1:3.01, the hydrogenation metal is Pt, and the mass percentage content of the hydrogenation metal Pt in the catalyst is 0.004%;

(a') mixing 10.42g of ethyl orthosilicate, 2.03g of tetrapropylammonium hydroxide and 52g of water, stirring at 35 ℃ and hydrolyzing for 7 hours to obtain a mixed solution;

(b ') adding 1g of Pt @ ZSM-5 powder prepared in example 1 into the mixed solution obtained in the step (a'), continuously stirring for 1H, transferring into a 100mL crystallization kettle with a polytetrafluoroethylene lining, crystallizing for 72H at 170 ℃ in a rotary crystallization oven at a rotating speed of 20r/min, centrifugally separating the obtained suspension, washing with deionized water to be neutral, drying at 120 ℃ for 12H, and roasting at 540 ℃ for 6H to obtain H-type ZSM-5@ Silicalite-1 with the core-shell mass ratio of 1:3.01, wherein the mark is Pt @ ZSM-5@ S-1.

ICP analysis was performed on the Pt @ ZSM-5 prepared in example 1 and the catalysts prepared in examples 1 to 5, and the physicochemical parameters thereof are shown in Table 1;

TABLE 1

From the above table, it can be seen that Pt is present in all of the above catalysts, and the silica-alumina ratio is continuously increased as the coating amount increases.

The X-ray diffraction analysis of Pt @ ZSM-5 prepared in example 1 and the catalysts prepared in examples 1 to 5 showed that the diffraction peaks of the samples prepared as described above were consistent with those of the MFI crystal structure, and no other diffraction peaks were observed, and the crystallization was good, as shown in fig. 1.

Example 6

In the embodiment, the mass ratio of the core shell to the shell is 1:7, the hydrogenation metal is Pt, and the mass percentage content of the hydrogenation metal Pt in the catalyst is 0.002%;

the catalyst of this example was prepared in a manner different from that of example 1 in that the mass of tetraethoxysilane in the mixed solution of step (a') was 24.36g and the mass of tetrapropylammonium hydroxide was 4.76g, under the same conditions as those of example 1.

The catalyst obtained in this example was evaluated for 30 hours under the performance test conditions as described in the performance evaluation section, with a toluene conversion of 9.2% and a selectivity to the product p-xylene of 98%.

Example 7

This example is different from example 1 in that the crystallization time in step (b') was replaced with 50h, and other conditions were completely the same as in example 1.

The catalyst obtained in this example was evaluated for 30 hours under the performance test conditions as described in the performance evaluation section, with a toluene conversion of 11.5% and a selectivity to the product, p-xylene, of 48.6%.

Example 8

This example is different from example 1 in that the crystallization time in step (b') was replaced with 90h, and other conditions were completely the same as in example 1.

The catalyst obtained in this example was evaluated for 30 hours under the performance test conditions as described in the performance evaluation section, with a toluene conversion of 11.3% and a selectivity to the product, p-xylene, of 56.3%.

Example 9

This example differs from example 1 in that the amount of aluminium sulphate in step (b) was replaced by 1.066g, the silica to alumina molar ratio of the prepared nuclear ZSM-5 was 50 and the other conditions were exactly the same as in example 1.

The catalyst obtained in this example was evaluated for 30 hours under the performance test conditions as described in the performance evaluation section, with a conversion of toluene of 12.3% and a selectivity to the product, p-xylene, of 50.3%.

Comparative example 1

The catalyst in the comparative example is a hydrogen type core-shell molecular sieve (the reference document is that the core-shell ZSM-5/Silicalite-1 molecular sieve with shape selective function is synthesized by a Koujin, Liuqin, Houding industry and an epitaxial growth method [ J ] catalytic report, 2009,30(09): 885-:

(1) tetrapropylammonium hydroxide, ethyl orthosilicate and water are mixed according to the formula n (SiO)₂):n(TPAOH):n(H₂Mixing O) at the ratio of 1:0.1:50, and stirring for 3h to obtain a shell layer growth solution;

(2) mixing with SiO in the shell layer growth liquid in the step (1)₂Molecular sieve ZSM-5(n (SiO) of equivalent mass₂)/n(Al₂O₃) 30, Shanghai catalyst division) as a core, adding the core into the shell growth solution in the step (1), putting the shell growth solution into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, sealing, heating to 180 ℃, performing hydrothermal crystallization for 1 day, quenching when crystallization is finished, filtering a solid product, washing until the pH of a washing solution is 7, and drying at 110 ℃ to obtain a once-grown core-shell molecular sieve (marked as CS1 (p));

(3) adding the core-shell molecular sieve CS1(p) obtained in the step (2) into the shell layer growth solution obtained in the step (1) for hydrothermal crystallization growth for the second time to obtain a core-shell molecular sieve (marked as CS2(p)) for the second growth;

(4) roasting the core-shell molecular sieve CS2(p) in the step (3) at 550 ℃ for 6h, marking the roasted sample as CS2, and adding CS2 to 10% NH₄NO₃In the solution, ion exchange is carried out for 3 hours under the stirring of 95 ℃, filtering and washing are carried out, the ion exchange process is repeated for 3 times, drying is carried out, and roasting is carried out for 6 hours at 550 ℃, thus obtaining the hydrogen type core-shell molecular sieve HCS2 which is the catalyst of the comparative example.

Carrying out catalytic performance evaluation on the catalyst, wherein the reaction evaluation is carried out on a fixed bed continuous micro reaction device; 2.0g of catalyst (20-40 meshes) is filled in the reactor, and the catalyst is roasted and activated at 550 ℃ in advance; toluene methylation reaction conditions: toluene and methanol are used as raw materials (n (PhCH)₃)/n(CH₃OH)＝2)，H₂Carrier gas, temperature 420 ℃, pressure 0.5MPa, space velocity 4h^–1，n(H₂)/n(HC)＝3。

The evaluation data is shown in fig. 2, the toluene conversion rate is continuously reduced after 5 hours of reaction, the inactivation is obvious, and meanwhile, the selectivity of the p-xylene is continuously improved and kept above 35 percent, and the highest selectivity reaches 56 percent.

Comparative example 2

The catalyst in the comparative example is a ZSM-5/Silicalite-1 core-shell molecular sieve (see the literature: Jajuan, Liu Shicheng, high brightness. the synthesis and shape-selective catalytic performance of the ZSM-5/Silicalite-1 core-shell molecular sieve [ J ]. chemical reaction engineering and process, 2012,28(06):519-524.), and the preparation method of the catalyst comprises the following steps:

(1) mixing tetrapropylammonium hydroxide (TPAOH, 25 wt%, Yixing Da Hua chemical plant) water solution, tetraethoxysilane (TEOS, Shanghai reagent company of national drug group) and water at a certain ratio (wherein TPAOH, TEOS and H₂The mass ratio of O is 1:25:1500), stirring for 6h at 35 ℃ to obtain a shell layer growth solution;

(2) adding a ZSM-5 molecular sieve ((n (SiO) into the shell layer growth solution in the step (1))₂)/n(Al₂O₃) 150, particle size 0.3 μm, catalyst division of south kyo, china petrochemical) as the core, and the relative amounts of the core and shell growth liquids were calculated as the theoretical core-shell ratio (all based on SiO)₂Measured by the amount of the components), the core-shell ratio is 1:3, then the components are put into a stainless steel crystallization kettle with a polytetrafluoroethylene lining for sealing, the temperature is raised to 180 ℃, hydrothermal crystallization is carried out for 6 hours, then quenching is carried out, the solid product is filtered, washed until the pH value is 7, and dried at 110 ℃, and the product is marked as CS;

(3) the CS obtained in step (2) was calcined at 550 ℃ for 6h to produce a catalyst, which was designated as CSP and used for reaction evaluation.

The evaluation conditions were: toluene and methanol were mixed in a certain ratio (molar ratio 6:1, i.e. nT/nM 6) with N₂As carrier gas, the reaction temperature is 380 ℃, the pressure is 0.2MPa, and the space velocity is 3h^-1The evaluation was carried out for 200 hours, and the specific reaction data are shown in Table 2.

TABLE 2

Sample (I)	Toluene conversion (%)	P-xylene selectivity (%)	Yield of p-xylene (%)
				CSP	11.1	30.1	3.3

Comparative example 3

The comparative example is different from example 1 in that the core of the core-shell structure molecular sieve does not contain hydrogenation metal; namely, no hydrogenation metal source is added in the preparation process of the ZSM-5 molecular sieve, other conditions are completely the same as those of the example 1, and the obtained catalyst is marked as ZSM-5@ (0.5) S-1.

The catalyst obtained in the comparative example was evaluated for 30 hours under the performance test conditions as described in the performance evaluation section, the conversion of toluene was 11.4%, and the selectivity to the product, p-xylene, was 51.2%.

Comparative example 4

In the comparative example, the catalyst in the comparative example 3 was used as a carrier, and was immersed in an aqueous solution of tetraammine platinum nitrate, followed by drying and calcination at 550 ℃ for 4 hours, to obtain the catalyst, wherein the mass percentage of Pt in the obtained catalyst was 0.02%, and the catalyst was labeled as ZSM-5@ (0.5) S-1/Pt.

The catalyst obtained in the comparative example was evaluated for 30 hours under the performance test conditions as described in the performance evaluation section, the conversion of toluene was 10.8%, and the selectivity to the product, p-xylene, was 49.6%.

And (3) performance testing:

the catalysts prepared in the examples and comparative examples were subjected to the catalytic performance test under the following test conditions;

adding a proper amount of the prepared catalyst powder into a tablet press, pressurizing to 20.1MPa, keeping for 2-3min, taking out the pressed tablet, crushing to solid particles with the size of 10-20 meshes by using a sieve, and weighing 0.6g for subsequent catalytic reaction performance evaluation.

Evaluation conditions for catalytic reaction performance: the performance evaluation of the catalyst adopts a small fixed bed, and the reaction is carried out in a constant-temperature reaction tube; toluene (T) and methanol (M) were mixed at a certain ratio (molar ratio 6:1, i.e., nT/nM ═ 6), and the raw material liquid was mixed with a certain amount of water (molar ratio of water to raw material 2, i.e., nH)₂O/(nT + nM) ═ 2) is simultaneously fed into the reaction tube; hydrogen is used as carrier gas, the pressure is normal, and the reaction temperature is 460 ℃; before reaction, reducing the catalyst at 500 ℃ for 2h under the reducing atmosphere of hydrogen at the flow rate of 50mL/min, then activating for 1h, evaluating the reaction, filling 0.6g of the catalyst, and controlling the mass space velocity (WHSV) of the raw material to be 6h^-1。

The evaluation indexes are as follows: toluene Conversion (CT) and p-xylene Selectivity (SPX); the specific definition is as follows:

CT ═ 100% (1-moles of toluene in the product/total moles of aromatics in the product);

SPX ═ 100% moles of para-xylene in the product/total moles of xylene in the product;

the evaluation data of the catalytic reaction are shown in fig. 3, and the average value of the exhaust gas composition data corresponding to the liquid phase sampling time is shown in table 3 (unit, mole percentage);

TABLE 3

As can be seen by combining FIG. 3 and Table 3, in the molecular sieve catalyst with the core-shell structure, the catalyst still maintains higher activity with the increase of the ratio of the shell to the core, the conversion rate of the toluene is above 10%, and the selectivity of the product p-xylene is improved from 38% of Pt @ ZSM-5 to 96% of Pt @ ZSM-5@ (3) S-1. Meanwhile, due to the addition of hydrogenation metal, the catalyst has excellent hydrogenation performance, the compositions of low-carbon olefin and alkane in tail gas are shown in table 3, the values of ethylene/ethane and propylene/propane of Pt @ ZSM-5 are only 0.06 and 0.57 respectively, and are very low, which shows that the catalyst has excellent hydrogenation performance, the ethylene/ethane value in the tail gas of the core-shell structure molecular sieve catalyst is less than 3, and the value of propylene/propane is less than 14.1, so that the carbon deposition rate in the catalytic reaction process is reduced, and the stability of the catalyst is improved.

Stability testing of the catalyst:

regenerating the catalyst, namely reacting Pt @ ZSM-5, Pt @ ZSM-5@ (0.5) S-1 and ZSM-5@ (0.5) S-1/Pt catalysts for 30h, then roasting the reaction product in a muffle furnace at 540 ℃ for 6h for regeneration, and evaluating the performances of the fresh catalyst and the regenerated catalyst again under the same device and reaction conditions to compare the performances of the fresh catalyst and the regenerated catalyst, wherein the regenerated catalyst is marked as Pt @ ZSM-5-R, Pt @ ZSM-5@ (0.5) S-1-R and ZSM-5@ (0.5) S-1/Pt-R; the results of the evaluation of the exhaust gas are shown in Table 4; the results of the selectivity test for fresh and regenerated Pt @ ZSM-5 on product p-xylene are shown in FIG. 4;

TABLE 4

As can be seen by combining FIG. 4 and Table 4, the regenerated Pt @ ZSM-5 catalyst has slightly higher toluene conversion and p-xylene selectivity than the fresh catalyst, and the analysis on the gas phase product shows that Pt particles in the Pt @ ZSM-5-R are not easy to agglomerate and still have good hydrogenation performance, and ethylene/ethane and propylene/propane are at lower levels, and the Pt @ ZSM-5@ (0.5) S-1 catalyst has high hydrogenation performance before and after regeneration, and has high structural stability, and the hydrogenation performance of the ZSM-5@ (0.5) S-1/Pt catalyst prepared by an impregnation method is obviously reduced after the regeneration of the ZSM-5@ (0.5) S-1/Pt-R catalyst.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims

1. The catalyst for preparing paraxylene is characterized by being a core-shell structure molecular sieve and comprising a core molecular sieve and a shell molecular sieve coated on the surface of the core molecular sieve, wherein the core molecular sieve is a ZSM-5 molecular sieve, the shell molecular sieve is an S-1 molecular sieve, and hydrogenation metal is encapsulated in the core molecular sieve.

2. The catalyst of claim 1, wherein the ZSM-5 molecular sieve is an H-type ZSM-5 molecular sieve;

preferably, the mass ratio of the ZSM-5 molecular sieve to the S-1 molecular sieve is 1 (0.3-10), and preferably 1 (0.5-5).

3. The catalyst of claim 1 or 2, wherein the hydrogenation metal comprises any one or a combination of at least two of Pt, Pd, or Ni;

preferably, the mass percentage of the hydrogenation metal is 0.001-1%, preferably 0.004-0.02%, based on 100% of the mass of the catalyst.

4. The catalyst as claimed in any one of claims 1 to 3, wherein the ZSM-5 molecular sieve has a silica to alumina molar ratio of 40 to 500, preferably 100 to 400.

5. Catalyst according to any one of claims 1 to 4, characterized in that the S-1 molecular sieve is obtained by one epitaxial growth.

6. A process for preparing a catalyst according to any one of claims 1 to 5, characterized in that it comprises the following steps:

(1) preparing a ZSM-5 molecular sieve encapsulating hydrogenation metal;

7. The method of claim 6, wherein the step (1) of preparing the ZSM-5 molecular sieve encapsulating the hydrogenation metal comprises adding a source of the hydrogenation metal during the preparation of the ZSM-5 molecular sieve;

(b) mixing the mixed solution in the step (a) with an aqueous solution of a hydrogenation metal source to obtain primary crystallization mother liquor, then carrying out primary crystallization, and roasting to obtain the ZSM-5 molecular sieve encapsulated with the hydrogenation metal;

preferably, the method of mixing in step (a) comprises the steps of:

(b') dissolving an aluminum source in water to obtain a second solution;

(c ') mixing the first solution of step (a ') with the second solution of step (b ') to obtain the mixed solution;

preferably, the silicon source of step (a) comprises any one of or a combination of at least two of tetraethoxysilane, silica sol or water glass;

preferably, the templating agent of step (a) comprises any one or a combination of at least two of TPAOH, TPABr, n-butylamine, or hexamethylenamine bromide;

preferably, the aluminium source of step (a) comprises any one of, or a combination of at least two of, aluminium sulphate, aluminium chloride, aluminium hydroxide or aluminium isopropoxide;

preferably, the method further comprises stirring the mixed solution in the step (a) for 0.5-5h before the step (b);

preferably, the hydrogenation metal source of step (b) is a soluble salt of a hydrogenation metal;

preferably, the molar ratio of the silicon source, the aluminum source, the template agent, the water and the hydrogenation metal source in the primary crystallization mother liquor in the step (b) is 1 (0.0025-0.025): (0.1-5): 30-50): 0.0003-0.006;

preferably, the temperature of the first crystallization in the step (b) is 150-;

preferably, the temperature for the roasting in the step (b) is 540-560 ℃, and the time is 6-8 h;

preferably, after the first crystallization in the step (b), before roasting, solid-liquid separation and drying are further included;

preferably, the method of solid-liquid separation is centrifugation.

8. The method according to claim 6 or 7, wherein the method of primary epitaxial growth of step (2) comprises the steps of:

(2') hydrolyzing the secondary crystallization mother liquor in the step (1'), adding the ZSM-5 molecular sieve which is packaged with hydrogenation metal in the step (1), and carrying out secondary crystallization and roasting to form an S-1 molecular sieve;

preferably, the molar ratio of the template agent to the silicon source in step (1') is (0.05-0.15): 1;

preferably, the molar ratio of the water in the step (1') to the ZSM-5 molecular sieve encapsulated with the hydrogenation metal in the step (2') is 100-250: 1;

preferably, the molar ratio of the silicon source in the step (1') to the ZSM-5 molecular sieve encapsulated with the hydrogenation metal in the step (2') is 0.5-3;

preferably, the hydrolysis method in step (2') is stirring;

preferably, the second crystallization of step (2') is a spin crystallization;

preferably, the rotating speed of the rotary crystallization is 10-30 r/min;

preferably, the temperature of the second crystallization in the step (2') is 150-;

preferably, the roasting temperature in the step (2') is 540-560 ℃, and the time is 6-8 h;

preferably, after the second crystallization in step (2'), before roasting, solid-liquid separation and drying are further included;

preferably, the method of solid-liquid separation is centrifugation.

9. Method according to any of claims 6-8, characterized in that the method comprises the steps of:

(b ") dissolving an aluminum source in water to obtain a second solution;

10. Use of a catalyst according to any one of claims 1 to 5, wherein the catalyst is used for the production of para-xylene;