CN111569935B

CN111569935B - Catalyst for preparing paraxylene and preparation method and application thereof

Info

Publication number: CN111569935B
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: 2023-12-12
Anticipated expiration: 2040-05-22
Also published as: CN111569935A

Abstract

The invention relates to a catalyst for preparing paraxylene, a preparation method and application thereof, 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 has high conversion rate and selectivity to p-xylene in the process of catalyzing toluene methanol alkylation reaction, and the carbon deposition rate of the catalyst in the catalytic process is obviously reduced, so that the catalyst has high stability.

Description

Catalyst for preparing paraxylene and preparation method and application thereof

Technical Field

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

Background

Para-xylene (PX) is an important organic chemical raw material, mainly used for producing polyesters. In recent years, the polyester industry has progressed rapidly, and the demand for paraxylene has also increased. Typical processes for producing para-xylene are catalytic reforming of naphtha to obtain only a thermodynamically balanced mixture of xylenes, requiring further cryogenic crystallization or simulated moving bed adsorptive separation techniques to obtain high concentrations of para-xylene, at high cost and with significant energy consumption.

At present, the isomerization of mixed xylenes, the transalkylation technology of C9 aromatic hydrocarbon and the selective disproportionation of toluene are the main methods for increasing the yield of paraxylene 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 paraxylene, and the separation procedure and the isomerization process are reduced, so that the economic benefit is considerable, and therefore, the research on the selective synthesis of paraxylene by toluene-methanol alkylation reaction is attracting attention.

At present, one of the barriers to industrialization of the fixed bed process for toluene methanol alkylation is the deactivation of the catalyst. It was found that carbon deposition is a major cause of catalyst deactivation in toluene methanol alkylation reactions. The methanol is activated by acid sites, is easy to dehydrate to generate dimethyl ether, is further converted to generate low-carbon olefin, and is extremely easy to generate alkylation reaction with aromatic hydrocarbon in a system to generate polyalkylbenzene, so that a pore canal is blocked to cover an acid center, and the catalyst is deactivated. Therefore, in order to suppress the occurrence of side reactions, zeolite is generally modified or post-treated to increase the selectivity of paraxylene.

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

Currently, molecular sieves of composite structure are of great interest because of their excellent properties. The earliest synthesis of ZSM-5@Silicalite-1 molecular sieve by Rollmann (see: rollmann LD. US 4 088 605.1978); the Nishiyama et al coats hydrogen ZSM-5 with different particle sizes (5-30 mu m) with a polycrystalline S-1 molecular sieve shell, and the prepared core-shell catalyst has higher stability and paraxylene selectivity when ZSM-5 molecular sieve crystal grains with the particle size of 5 mu m are taken as cores; the core-shell catalyst prepared with the increase of the crystal grains not only has reduced selectivity to the p-xylene of the product because the large crystal grains are difficult to completely coat, but also has more rapid deactivation as the crystal grains are larger (see the literature: van Vu D., miyamoto M., nishima N., et al, selective formation of para-xylene over H-ZSM-5coated with polycrystalline silicalite crystals.JOURNAL OF CATALYSIS[J ].2006,243 (2): 389-394 "). In addition, nishiyama et al also used a ZSM-5 catalyst coated with polysilicalite-1 prepared by repeated hydrothermal synthesis to react for 60min at 400 ℃ with toluene/methanol=1, the selectivity to p-xylene of the product being greater than 99.9%, whereas the selectivity can only reach about 40% without the coated catalyst matrix (see literature: "Van Vu D., miyamoto M., nishiyama N., et al, catalytic activities and structures of silicalite-1/H-ZSM-5 zeolite").

Ji Yongjun and the like, a cationic surfactant template method is adopted to prepare a mesoporous silica coated ZSM-5 core-shell structure catalyst, the shell thickness can be effectively regulated, and compared with the selectivity of a parent to p-xylene product which is 28.8%, the selectivity of the synthesized mesoporous core-shell structure catalyst to p-xylene product is improved to 41.1% when the shell-core mass ratio is 3, and the selectivity of the synthesized mesoporous core-shell structure catalyst to p-xylene product is improved to 54.6% after the catalyst is further aged for 12 hours through dry gel conversion (see documents: ji Yongjun, zhang, zhang Kun, and the like; the preparation of ZSM-5@Mesoporous Silica core-shell composite structure molecular sieve and the research of the toluene methanol alkylation shape selective catalytic performance of the ZSM-5@Mesoporous Silica, chemistry report [ J ].2013,71 (03): 371-380) ".

Therefore, development of a catalyst with high selectivity and excellent catalytic stability for p-xylene product and a preparation method thereof are of great significance.

Disclosure of Invention

The invention aims to provide a catalyst for preparing paraxylene, a preparation method and application thereof, wherein the catalyst is a core-shell structure molecular sieve, the catalyst 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, hydrogenation metal is encapsulated in the core molecular sieve, the catalyst has high conversion rate and selectivity to the paraxylene in the process of catalyzing toluene methanol alkylation reaction, the carbon deposition rate of the catalyst in the catalytic process is obviously reduced, and the catalyst has high stability.

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

in a first aspect, the invention provides a catalyst for preparing paraxylene, which is a core-shell structure molecular sieve, and comprises 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.

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

The hydrogenation metal encapsulated in the ZSM-5 molecular sieve in the catalyst can convert the carbon deposition precursor generated in the reaction process into alkane, thereby reducing the carbon deposition rate in the catalytic reaction, slowing down the deactivation of the catalyst and further improving the stability of the catalyst; the hydrogenation metal in the catalyst is encapsulated in the ZSM-5 molecular sieve, but not 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 disclosed by the invention has the advantages that the agglomeration phenomenon of hydrogenation metal does not occur in the regeneration process, the catalyst is relatively stable, and the catalyst can be regenerated and utilized.

The S-1 molecular sieve is Silicalite-1 molecular sieve, is an all-silicon molecular sieve, and has no acid sites.

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 canal systems, namely Z-shaped pore canal and elliptic straight pore canal with the pore canal sizes of respectivelyAnd->Wherein the kinetic diameter of the paraxylene is 0.58nm, the kinetic diameters of the ortho-xylene and the meta-xylene are about 0.63nm, and the diffusion rate of the paraxylene in the pore canal is 10 percent of that of the ortho-xylene and the meta-xylene ³ Even 10 ⁴ The ZSM-5 molecular sieve has obvious shape-selective advantages.

Preferably, the particle size of the hydrogenation metal is 1-10nm, e.g. 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm or 9nm, etc., preferably 4-5nm.

Preferably, the mass ratio of ZSM-5 molecular sieve to S-1 molecular sieve is 1 (0.3-10), for example 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, which is favorable for the shell layer to carry out good cladding on the core, so that the selectivity of paraxylene can be improved, the conversion rate of toluene can not 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 silicon-aluminum ratio 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 paraxylene is not effectively improved.

Preferably, the hydrogenation metal includes any one or a combination of at least two of Pt, pd, and Ni, and the combination includes, for example, a combination of Pt and Pd, a combination of Ni and Pt, or a combination of Pd and Ni, and the like, and Pt is preferred.

Preferably, the hydrogenation metal is present in an amount of 0.001 to 1% by mass, based on 100% by mass of the catalyst, 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% by mass, etc., preferably 0.004 to 0.02%.

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

The silicon in the silicon-aluminum molar ratio is expressed herein as SiO ₂ Calculated as Al ₂ O ₃ The molar ratio of silicon to aluminum is referred to as SiO ₂ /Al ₂ O ₃ 。

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

In a second aspect, the present invention provides a process for the preparation of a catalyst according to the first aspect, the process comprising the steps of:

(1) Preparing ZSM-5 molecular sieve encapsulated with hydrogenation metal;

(2) And (3) taking the ZSM-5 molecular sieve which is obtained in the step (1) and is encapsulated with hydrogenation metal as a core, and carrying out one-time epitaxial growth on the surface of the ZSM-5 molecular sieve to form the S-1 molecular sieve, thereby obtaining the catalyst.

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

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

In the preparation process of the catalyst, a hydrogenation metal source is added in the preparation process of the ZSM-5 molecular sieve, compared with the traditional impregnation method, the catalyst obtained by the preparation method has better dispersibility and excellent hydrogenation performance of hydrogenation metal particles, and the agglomeration phenomenon of 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 of the hydrogenation metal particles and small particle size, and the hydrogenation metal particles are dispersed in the catalyst instead of the surface, compared with the traditional impregnation method, the hydrogenation metal particles in the catalyst cannot migrate or agglomerate due to high-temperature roasting; meanwhile, the addition of hydrogenation metal in the preparation process of the invention enables the carbon deposition precursor low-carbon olefin generated by the reaction to be converted into alkane, thereby slowing down the deactivation of the catalyst, reducing the carbon deposition rate and improving the stability of the catalyst.

Preferably, the preparation method of the ZSM-5 molecular sieve encapsulated with 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) 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 hydrogenation metal is added after the silicon source, the template agent, the aluminum source and the water are mixed, so that the hydrogenation metal is uniformly dispersed in the ZSM-5 molecular sieve, and the activity and the stability of the catalyst are improved.

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

(a') dissolving a silicon source and a templating 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 in step (a ') with the second solution in step (b ') to obtain the mixed solution.

Preferably, the silicon source in step (a) comprises any one or at least two of ethyl orthosilicate, silica sol or water glass, and the combination exemplarily comprises a combination of ethyl orthosilicate and silica sol, a combination of water glass and ethyl orthosilicate, or a combination of silica sol and water glass, etc.

Preferably, the template of step (a) comprises any one or a combination of at least two of TPAOH, TPABr, n-butylamine, or hexamethylamine bromide; the combination illustratively includes a combination of TPAOH and TPABr or a combination of n-butylamine and hexamethylenebromide, etc.

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

Preferably, step (b) is preceded by stirring the mixed solution of step (a) for a period of time ranging from 0.5 to 5 hours, for example 1 hour, 2 hours, 3 hours or 4 hours, etc.

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; 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 150-180 ℃, e.g. 155 ℃, 160 ℃, 165 ℃, 170 ℃ or 175 ℃, etc., for a period of 60-80 hours, e.g. 65 hours, 70 hours or 75 hours, etc.

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

the preparation process of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal is controlled to be 60-80 hours in the first crystallization time, which is favorable for forming the molecular sieve with higher crystallinity and good crystallization, when the time is less than 60 hours, the crystallization time is shorter, the incomplete crystallization can be possibly caused, the crystallinity is lower, the time is more than 80 hours, the molecular sieve basically grows to be finished in the later stage of crystallization, the influence of the time extension on the crystallization is weaker, the energy consumption is larger, and the synthesis cost of the catalyst is increased.

Preferably, the temperature of the calcination in step (b) is 540-560 ℃, e.g. 545 ℃, 550 ℃ or 555 ℃, etc., for a period of 6-8 hours, e.g. 6.5 hours, 7 hours or 7.5 hours, etc.

The calcination temperature is controlled within the range in the preparation process of the ZSM-5 molecular sieve encapsulated with hydrogenation metal, so that the template agent can be burnt out cleanly and good hydrogenation performance can be ensured; when the temperature is less than 540 ℃, the template agent is incompletely baked; when the temperature is more than 560 ℃, sintering and agglomeration of metal are easy to cause, and the hydrogenation effect of the catalyst is affected.

The preparation process of the ZSM-5 molecular sieve encapsulated with the hydrogenation metal controls the roasting time within the range, which is beneficial to roasting the template agent in an effective time; when the time is less than 6 hours, the problem of incomplete roasting of the template agent exists; when the time is more than 8 hours, the too long roasting time can not only cause agglomeration of metals more easily, but also prolong the time cost of the catalyst.

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

Preferably, the solid-liquid separation method is centrifugation.

Preferably, the method for one epitaxial growth of step (2) comprises the steps of:

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

and (2 ') hydrolyzing the secondary crystallization mother liquor in the step (1'), adding the ZSM-5 molecular sieve packaged with hydrogenation metal in the step (1), crystallizing for the second time, and roasting to form the S-1 molecular sieve.

The conventional ZSM-5@Silicalite-1 core-shell structure molecular sieve can form a compact molecular sieve shell layer through repeated growth, and the preparation process can cause serious waste of silicon sources, water, templates and energy consumption, and has the advantages of longer synthesis period and higher cost; the conventional ZSM-5@Silicalite-1 core-shell structure molecular sieve is subjected to reaction evaluation after being coated for a plurality of times, so that the conversion rate is obviously reduced, the selectivity is improved, the stability is poor, the deactivation is rapid, and the high industrial value is not realized; and the pore canal of the catalyst is prolonged by multiple coating, the probability of side reaction is increased, aromatic hydrocarbon generating condensed rings covers the active center, so that the carbon deposition rate of the catalyst is increased, and the deactivation is accelerated.

In the preparation process of the catalyst, the S-1 molecular sieve serving as a shell layer is obtained through one-step epitaxial growth, the steps are adopted in the preparation process, and high coverage can be achieved through one-step epitaxial growth.

Preferably, the molar ratio of template 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 through one-time epitaxial growth, the template agent and the silicon source are adopted in the molar ratio, so that the core can be well coated; when the molar ratio of the two is less than 0.05, the template dosage is too low, and the crystallization speed of the secondary crystallization liquid is slower; 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 ZSM-5 molecular sieve encapsulating hydrogenation metal in step (2') is from 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 ZSM-5 molecular sieve is taken as the molar mass of silica in 60 g/mol.

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

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

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

Preferably, the rotational speed of the rotary crystallization is 10-30r/min, for example 15r/min, 20r/min or 25r/min, etc.

Preferably, the temperature of the second crystallization in step (2') is 150 to 180 ℃, such as 155 ℃, 160 ℃, 165 ℃, 170 ℃, 175 ℃, etc., and the time is 60 to 80 hours, such as 65 hours, 70 hours, 75 hours, etc.

In the process of forming the 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 packaged 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 nucleate in addition and does not grow on the surface of the ZSM-5 molecular sieve packaged with the hydrogenation metal; when the crystallization temperature is higher than 180 ℃, the molecular sieve is easy to rotate, 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 80 hours, the synthesized material is not significantly changed.

Preferably, the temperature of the calcination in step (2') is 540-560 ℃, e.g. 545 ℃, 550 ℃ or 555 ℃, etc., and the time is 6-8 hours, e.g. 6.5 hours, 7 hours or 7.5 hours, etc.

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

Preferably, the solid-liquid separation method is centrifugation.

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

(1') preparing a ZSM-5 molecular sieve encapsulated with hydrogenation metal, the preparation process comprising the steps of:

(a ") dissolving a silicon source and a templating 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 in step (a") with the second solution in 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 solution, crystallizing at 150-180 ℃ for 60-80h, centrifuging, drying, and roasting at 540-560 ℃ for 6-8h to obtain the ZSM-5 molecular sieve encapsulated with the hydrogenation metal;

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

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

(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 packaged with hydrogenation metal in the step (1 '), crystallizing for 60-80h at 150-180 ℃, centrifuging, drying, and roasting for 6-8h at 540-560 ℃ to form the S-1 molecular sieve, thereby obtaining the catalyst.

In a third aspect, the present invention provides the use of a catalyst according to the first aspect for the preparation of para-xylene.

Preferably, the catalyst is used to catalyze toluene and methanol alkylation reactions to produce para-xylene.

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

(1) The catalyst is of a core-shell structure, takes a ZSM-5 molecular sieve encapsulated with hydrogenation metal as a core and takes an S-1 molecular sieve of all silicon as a shell, has high stability in the process of catalyzing toluene methanol alkylation reaction, and the hydrogenation metal in the core can convert carbon deposition precursor low-carbon olefin into alkane, so that the carbon deposition rate is reduced, and the deactivation of the catalyst is slowed down; 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 regenerated and utilized;

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

(3) According to the preparation method of the ZSM-5 molecular sieve with the hydrogenation metal encapsulated in the catalyst, a hydrogenation metal source is added in the preparation process of the ZSM-5 molecular sieve, so that the hydrogenation metal is generated in situ, the hydrogenation metal of the catalyst is positioned in the catalyst instead of on the surface, the dispersity of the hydrogenation metal is high, the particle size is small, migration and agglomeration are not easy to occur in the roasting process, and the service life of the catalyst is prolonged;

(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 trend by taking ZSM-5 encapsulated with hydrogenation metal as a core in a crystallization synthesis system, the high coverage is obtained through one-time epitaxial growth, the high selectivity can be realized without multiple coating, the production efficiency is improved, and the production cost of the catalyst is saved.

Drawings

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

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

FIG. 3 is a graph showing toluene conversion, xylene selectivity, and para-xylene selectivity during the catalytic toluene methanol alkylation reaction of the core-shell structured molecular sieves obtained in examples 1-5 of the present invention and Pt@ZSM-5 obtained in example 1;

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

Detailed Description

The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.

Example 1

In the embodiment, the mass ratio of the core shell to the hydrogenation metal is 1:0.51, and the mass percentage 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 of:

(a) 10g of ethyl orthosilicate and 26g of tetrapropylammonium hydroxide are added into 10g of deionized water and stirred for 10min at 35 ℃, and marked as solution A;

(b) 0.1332g of aluminum sulfate (400 silica to alumina mole ratio) was dissolved in 10g of deionized water and 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) 0.0095g of tetramine platinum nitrate is dissolved in 10.8g of deionized water to obtain a hydrogenation metal source water solution;

(e) Slowly dripping the aqueous solution of the hydrogenation metal source 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 at 170 ℃ for 72H, centrifugally separating the crystallized suspension, washing the suspension with deionized water to be neutral, drying at 120 ℃ for 12H, and roasting at 540 ℃ for 6H to obtain H-type ZSM-5, wherein the mark is Pt@ZSM-5.

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

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

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

and (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 a rotating speed of 20r/min by a rotary crystallization oven at 170 ℃, centrifuging, washing the suspension obtained after the completion of the crystallization, drying at 120 ℃ for 12H by deionized water, and roasting at 540 ℃ for 6H to obtain H-type ZSM-5@Silicalite-1 with a core-shell mass ratio of 1:0.51, wherein the H-type ZSM-5@Silicalite-1 is marked as Pt@ZSM-5@0.5S-1.

Example 2

The mass ratio of the core shell to the hydrogenation metal of the catalyst is 1:1.08, and the mass percentage 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 embodiment 1 is used as a raw material, and the S-1 molecular sieve is formed by one-time epitaxial growth, so that the catalyst is obtained; the preparation method comprises the following steps:

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

and (b ') adding 1g of Pt@ZSM-5 powder prepared in the embodiment 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 a rotating speed of 20r/min by a rotary crystallization oven at 170 ℃, centrifuging and separating the suspension obtained after the completion, washing with deionized water to neutrality, drying at 120 ℃ for 12H, and roasting at 540 ℃ for 6H to obtain H-type ZSM-5@Silicalite-1 with a core-shell mass ratio of 1:1.08, wherein the H-type ZSM-5@1S-1 is marked as Pt@ZSM-5@1.

Example 3

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

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

and (b ') adding 1g of Pt@ZSM-5 powder prepared in the embodiment 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 a rotating speed of 20r/min by a rotary crystallization oven at 170 ℃, centrifuging and separating the suspension obtained after the completion, 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 a core-shell mass ratio of 1:1.51, wherein the H-type ZSM-5@1.5@S-1 is marked by Pt@ZSM-5.

Example 4

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

(a') after 6.94g of tetraethyl orthosilicate, 1.36g of tetrapropylammonium hydroxide and 52g of water are mixed and stirred at 35 ℃ for hydrolysis for 7 hours, a mixed solution is obtained;

and (b ') adding 1g of Pt@ZSM-5 powder prepared in the embodiment 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 a rotating speed of 20r/min in a rotary crystallization oven at 170 ℃, centrifuging and separating the suspension obtained after the completion, 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 a core-shell mass ratio of 1:2.01, wherein the H-type ZSM-5@2S-1 is marked by Pt@ZSM-5@2.

Example 5

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

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

And (b ') adding 1g of Pt@ZSM-5 powder prepared in the embodiment 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 a rotating speed of 20r/min by a rotary crystallization oven at 170 ℃, centrifuging and separating the suspension obtained after the completion, washing with deionized water to neutrality, drying at 120 ℃ for 12H, and roasting at 540 ℃ for 6H to obtain H-type ZSM-5@Silicalite-1 with a core-shell mass ratio of 1:3.01, wherein the H-type ZSM-5@3S-1 is marked by Pt@ZSM-5@3.

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

TABLE 1

It can be seen from the above table that Pt was present in the above catalyst, and the silicon to aluminum ratio was continuously increased as the coating amount was increased.

The analysis results of the X-ray diffraction analysis of Pt@ZSM-5 prepared in example 1 and the catalysts prepared in examples 1 to 5 are shown in FIG. 1, and it can be seen from FIG. 1 that the diffraction peaks of the prepared samples are consistent with those of the MFI crystal structure, no other diffraction peaks appear, and crystallization is good.

Example 6

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

The catalyst preparation method of this example was different from example 1 in that the mass of tetraethyl orthosilicate in the mixed solution of step (a') was 24.36g, the mass of tetrapropylammonium hydroxide was 4.76g, 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 described in the performance evaluation section, with a toluene conversion of 9.2% and a selectivity to p-xylene of 98% for the product.

Example 7

The difference between this example and example 1 is that the crystallization time in step (b') was replaced with 50h, and the other conditions were exactly the same as those in example 1.

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

Example 8

The difference between this example and example 1 is that the crystallization time in step (b') was replaced with 90h, and the other conditions were exactly the same as those in example 1.

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

Example 9

This example differs from example 1 in that the amount of aluminum sulfate in step (b) was replaced with 1.066g and the core ZSM-5 prepared had a silica to alumina molar ratio of 50, with the other conditions being exactly the same as in example 1.

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

Comparative example 1

The catalyst of the comparative example is a hydrogen type core-shell molecular sieve (reference documents: kong Dejin, liu Zhicheng, houding industry, epitaxial growth method for synthesizing a shape-selective core-shell ZSM-5/Silicalite-1 molecular sieve [ J ]. Catalytic school report, 2009,30 (09): 885-890), the preparation method comprises the following steps:

(1) Tetrapropylammonium hydroxide, tetraethyl orthosilicate and water were combined according to n (SiO ₂ ):n(TPAOH):n(H ₂ Mixing in a ratio of O) =1:0.1:50, and stirring for 3 hours to obtain a shell growth solution;

(2) Will be equal to SiO in the shell layer growth liquid in the step (1) ₂ Molecular sieve ZSM-5 of comparable mass (n (SiO) ₂ )/n(Al ₂ O ₃ ) =30, shanghai catalyst division company) as a core, adding the core into the shell growth solution in the step (1), filling the core into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, sealing, heating to 180 ℃, carrying out hydrothermal crystallization for 1 day, quenching after the crystallization is finished, filtering a solid product, washing to a washing solution pH=7, and drying at 110 ℃ to obtain a core-shell molecular sieve (marked as CS1 (p)) growing once;

(3) Adding the core-shell molecular sieve CS1 (p) obtained in the step (2) into the shell growth liquid of the step (1) for secondary hydrothermal crystallization growth, and obtaining a secondarily grown core-shell molecular sieve (CS 2 (p));

(4) Roasting the core-shell molecular sieve CS2 (p) in the step (3) at 550 ℃ for 6 hours, marking a roasted sample as CS2, and adding the CS2 into 10% NH ₄ NO ₃ And (3) in the solution, carrying out ion exchange for 3 hours at 95 ℃ under stirring, filtering, washing, repeating the ion exchange process for 3 times, drying, and roasting at 550 ℃ for 6 hours to obtain the hydrogen type core-shell molecular sieve HCS2, namely the catalyst in the comparative example.

The catalyst is subjected to catalytic performance evaluation, and the reaction evaluation is performed on a fixed bed continuous micro-reaction device; 2.0g of catalyst (20-40 meshes) is filled in the reactor, and the catalyst is baked and activated at 550 ℃ in advance; toluene methylation reaction conditions: toluene and methanol were used as starting materials (n (PhCH) ₃ )/n(CH ₃ OH)＝2)，H ₂ Carrier gas at 420 deg.c, pressure of 0.5MPa and airspeed of 4 hr ^–1 ，n(H ₂ )/n(HC)＝3。

As shown in the evaluation data in FIG. 2, the toluene conversion rate is continuously reduced and the inactivation is obvious after 5 hours of reaction, and meanwhile, the selectivity of the paraxylene is continuously improved, and the selectivity is kept above 35% and reaches 56% at most.

Comparative example 2

The catalyst of this comparative example is a ZSM-5/Silicalite-1 core-shell molecular sieve (see documents: gu Yinjuan, liu Zhicheng, gao Huanxin. Synthesis and shape selective catalytic performance of ZSM-5/Silicalite-1 core-shell molecular sieve [ J ]. Chemical reaction engineering and Process, 2012,28 (06): 519-524.), the method of preparing the catalyst comprises the steps of:

(1) Mixing aqueous solution of tetrapropylammonium hydroxide (TPAOH, mass fraction of which is 25%, yixing Dahua chemical plant), ethyl orthosilicate (TEOS, shanghai reagent company of national medicine group) and water at a certain ratio (wherein, TPAOH, TEOS and H) ₂ The mass ratio of the O is 1:25:1500), and stirring for 6 hours at 35 ℃ to obtain a shell growth solution;

(2) Adding ZSM-5 molecular sieve ((n (SiO)) into the shell growth solution in the step (1) ₂ )/n(Al ₂ O ₃ ) =150, particle size 0.3 μm, south-Beijing catalyst division, petrochemical, china) as a core, and the relative addition amount of the core and shell growth liquids was calculated by theoretical core-shell ratio (all of SiO ₂ The ratio of the core to the shell is 1:3, then the mixture is put into a stainless steel crystallization kettle with a polytetrafluoroethylene lining for sealing, the mixture is heated to 180 ℃ for hydrothermal crystallization for 6 hours and then quenched, the solid product is filtered, washed to pH value of 7, dried at 110 ℃ and recorded as CS;

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

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

TABLE 2

Sample of	Toluene conversion (%)	Para-xylene selectivity (%)	Para-xylene yield (%)
				CSP	11.1	30.1	3.3

Comparative example 3

The comparative example differs from example 1 in that the core of the core-shell structured 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 identical to those of the embodiment 1, and the obtained catalyst is marked as ZSM-5@0.5S-1.

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

Comparative example 4

The catalyst in comparative example 3 is taken as a carrier, immersed in a tetramine platinum nitrate aqueous solution, dried and roasted for 4 hours at 550 ℃ to obtain the catalyst, wherein the mass percent of Pt in the catalyst is 0.02%, and the catalyst is marked as ZSM-5@0.5S-1/Pt.

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

Performance test:

the catalysts prepared in examples and comparative examples were subjected to catalytic performance tests under the following 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 the tablet into solid particles with the size of 10-20 meshes by using a sieve, and weighing 0.6g for subsequent catalytic reaction performance evaluation.

Catalytic reaction performance evaluation conditions: 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 in a certain ratio (molar ratio of 6:1, i.e., nT/nm=6), and the raw material liquid and a certain amount of water (molar ratio of water to raw material: 2, i.e., nH ₂ O/(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 the reaction, the catalyst is reduced for 2 hours at 500 ℃, the reducing atmosphere is hydrogen, the flow is 50mL/min, then the catalyst is activated for 1 hour, when the reaction is evaluated, the catalyst is filled with 0.6g, and the mass space velocity (WHSV) of the raw materials is controlled to be 6 hours ^-1 。

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

ct= (1-moles of toluene in product/total moles of aromatic hydrocarbon in product) ×100%;

SPX = moles of para-xylene in product/total moles of xylenes in product x 100%;

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 percent);

TABLE 3 Table 3

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As can be seen from the combination of FIG. 3 and Table 3, in the core-shell structured molecular sieve catalyst, the catalyst still maintains higher activity along with the increase of the shell-core ratio, the conversion rate of p-toluene is over 10 percent, and the selectivity of p-xylene as a product is improved from 38 percent of Pt@ZSM-5 to 96 percent of Pt@ZSM-5@3S-1. Meanwhile, the catalyst has excellent hydrogenation performance due to the addition of hydrogenation metal, the composition of low-carbon olefin and alkane in tail gas is shown in table 3, and the values of ethylene/ethane and propylene/propane of Pt@ZSM-5 are only 0.06 and 0.57 respectively, which indicates that the catalyst has excellent hydrogenation performance, the value of ethylene/ethane 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 test of catalyst:

regenerating the catalyst, namely, after the Pt@ZSM-5, pt@ZSM-5@ (0.5) S-1 and ZSM-5@ (0.5) S-1/Pt catalyst react for 30 hours, roasting in a muffle furnace at 540 ℃ for 6 hours for regeneration, evaluating again in the same device and reaction conditions, and comparing 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 tail gas evaluation results are shown in table 4; the results of the selectivity test for fresh and regenerated Pt@ZSM-5 to p-xylene product are shown in FIG. 4;

TABLE 4 Table 4

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

The applicant declares that the above is only a specific embodiment of the present application, but the scope of the present application is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present application disclosed by the present application fall within the scope of the present application and the disclosure.

Claims

1. The catalyst for preparing the paraxylene is characterized by comprising a core-shell 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, hydrogenation metal is encapsulated in the core molecular sieve, and the hydrogenation metal is Pt and/or Pd; the mass ratio of the ZSM-5 molecular sieve to the S-1 molecular sieve is 1 (0.5-5); the mass percentage of the hydrogenation metal is 0.004-0.02% based on 100% of the mass of the catalyst; the silicon-aluminum mole ratio of the ZSM-5 molecular sieve is 300-400;

The catalyst for preparing paraxylene is prepared by a method comprising the steps of:

(1) Preparing ZSM-5 molecular sieve encapsulated with hydrogenation metal, the preparation process comprises the following steps:

(a) Mixing a silicon source, a template agent, an aluminum source and water to obtain a mixed solution; the aluminum source is aluminum sulfate and/or aluminum chloride;

(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;

controlling the hydrogenation metal to be Pt and/or Pd, wherein the silicon-aluminum molar ratio of the ZSM-5 molecular sieve is 300-400; controlling the mass percentage content of the hydrogenation metal to be 0.004-0.02% based on 100% of the mass of the catalyst;

(2) Taking the ZSM-5 molecular sieve which is obtained in the step (1) and is encapsulated with hydrogenation metal as a core, and carrying out primary epitaxial growth on the surface of the ZSM-5 molecular sieve to form an S-1 molecular sieve, so that the mass ratio of the ZSM-5 molecular sieve to the S-1 molecular sieve is 1 (0.5-5), and the catalyst is obtained.

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

3. The catalyst of claim 1, wherein the S-1 molecular sieve is obtained by one epitaxial growth.

4. A method for preparing a catalyst according to any one of claims 1 to 3, characterized in that it comprises the steps of:

5. The method of claim 4, wherein the method of mixing in step (a) comprises the steps of:

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

6. The method of claim 4, wherein the silicon source of step (a) comprises any one or a combination of at least two of ethyl orthosilicate, silica sol, or water glass.

7. The method of claim 4, wherein the templating agent of step (a) comprises any one or a combination of at least two of TPAOH, TPABr, n-butylamine, or hexamine bromide.

8. The method of claim 4, further comprising stirring the mixed solution of step (a) for a period of 0.5 to 5 hours prior to performing step (b).

9. The method of claim 4, wherein the hydrogenation metal source of step (b) is a soluble salt of a hydrogenation metal.

10. The method of claim 4 wherein the molar ratio of silicon source, aluminum source, templating agent, water and hydrogenation metal source in the primary crystallization mother liquor of step (b) is 1 (0.0025-0.025): 0.1-5): 30-50): 0.0003-0.006.

11. The method of claim 4, wherein the first crystallization in step (b) is performed at a temperature of 150 to 180 ℃ for a time of 60 to 80 hours.

12. The method of claim 4, wherein the firing in step (b) is at a temperature of 540 to 560 ℃ for a period of 6 to 8 hours.

13. The method of claim 4, wherein after the first crystallization in step (b), solid-liquid separation and drying are further included before the firing.

14. The method of claim 13, wherein the method of solid-liquid separation is centrifugation.

15. The method of claim 4, wherein the one-time epitaxial growth method of step (2) comprises the steps of:

16. The method of claim 15, wherein the molar ratio of template to silicon source in step (1') is from (0.05 to 0.15): 1.

17. The process of claim 15 wherein the molar ratio of water in step (1 ') to ZSM-5 molecular sieve encapsulated with hydrogenation metal in step (2') is from 100 to 250:1.

18. The method of claim 15, wherein the molar ratio of the silicon source in step (1 ') to the ZSM-5 molecular sieve encapsulated with the hydrogenation metal in step (2') is between 0.5 and 3.

19. The method of claim 15, wherein the method of hydrolysis of step (2') is agitation.

20. The method of claim 15, wherein the second crystallization of step (2') is rotary crystallization.

21. The method according to claim 20, wherein the rotational speed of the rotary crystallization is 10-30r/min.

22. The method of claim 15, wherein the second crystallization in step (2') is performed at a temperature of 150-180 ℃ for a time of 60-80h.

23. The method of claim 15, wherein the firing in step (2') is performed at a temperature of 540 to 560 ℃ for a period of 6 to 8 hours.

24. The method of claim 15, wherein after the second crystallization in step (2'), solid-liquid separation and drying are further included before the firing.

25. The method of claim 24, wherein the solid-liquid separation method is centrifugation.

26. The method according to claim 4, characterized in that it comprises the steps of:

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

27. Use of a catalyst according to any of claims 1-3, characterized in that the catalyst is used for the preparation of para-xylene.

28. Use of the catalyst according to claim 27 for catalyzing the alkylation of toluene with methanol to produce para-xylene.