Preparation method and preparation system for para-xylene

Abstract

Provided is a preparation method for para-xylene, comprising: (1) feeding a naphtha feedstock to a first reaction zone, and performing a first catalytic reaction in the presence of a first catalyst to obtain a first material stream comprising benzene, toluene, para-xylene, and a by-product; (2) feeding benzene, toluene, and methanol to a second reaction zone, and performing a second catalytic reaction in the presence of a second catalyst to obtain a second material stream comprising benzene, toluene, p-xylene, and a by-product; (3) feeding the first material stream and / or the second material stream into a separation system for separation, so as to obtain a benzene-rich fraction, a toluene-rich fraction, and a para-xylene-rich fraction serving as a product and a by-product-rich fraction serving as a product; and (4) returning the separated benzene-rich fraction and toluene-rich fraction to step (2) as a source of benzene and toluene. A corresponding preparation system is also provided. The preparation method and preparation system utilize a naphtha feedstock and methanol to prepare para-xylene, thereby adjusting product distribution and significantly increasing para-xylene selectivity.

Description

Preparation method and system of p-xylene

[0001] This application claims priority to Chinese Patent Application No. 2024115077777, filed on October 28, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of chemical engineering, and specifically relates to a method and system for preparing para-xylene. Background Technology

[0003] Aromatic hydrocarbons, represented by benzene, toluene, and xylene (BTX), are fundamental petrochemical chemicals. Paraxylene (PX) is the most closely watched product among aromatics. As a key link between oil refining and chemical processing, it is not only the most important of the three xylene isomers but also a major raw material for the polyester industry. Downstream products of paraxylene (PX) are primarily purified terephthalic acid (PTA), which is then used to produce polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polypropylene terephthalate (PTT). A smaller portion is used in other fields such as the pharmaceutical intermediate dimethyl terephthalate (DMT) and coatings. In recent years, the extensive application of polyester in textiles, apparel, and beverage packaging has driven rapid growth in the production and consumption of purified terephthalic acid (PTA) and its upstream product, paraxylene (PX). Taking the chemical fiber industry as an example, synthetic fibers currently account for 70% of my country's textile fiber production, of which polyester fibers produced using paraxylene (PX) account for more than 80% of the total synthetic fiber production.

[0004] Industrially, para-xylene (PX) is primarily produced from naphtha via a catalytic reforming / aromatics complex. First, naphtha catalytic reforming yields a mixture of aromatics, which are then separated to obtain benzene, toluene, and a mixture of xylenes. The mixed xylenes are then separated from the mixture of xylene isomers with extremely similar boiling points using multi-stage cryogenic crystallization or molecular sieve-simulated moving bed adsorption separation technology. Due to thermodynamic equilibrium limitations, the para-xylene (PX) content in the xylene mixture is relatively low (~24%). With the increasing demand for para-xylene (PX), direct extraction and separation from reformate and cracked gasoline can no longer meet the demand. Toluene disproportionation and alkyl transfer, and xylene isomerization technologies are commonly used to increase para-xylene (PX) production. However, the insufficient number of methyl groups in reformed naphtha feedstock and the thermodynamic equilibrium distribution of the produced xylene (PX of only about 24 wt%) remain major factors hindering the significant increase in para-xylene (PX) production and the simplification of the process flow in traditional catalytic reforming / aromatics complexes. Therefore, developing new para-xylene preparation technologies is particularly important to address these issues. Summary of the Invention

[0005] The first objective of this invention is to provide a method for preparing para-xylene that improves the selectivity of para-xylene during the preparation process, thereby increasing the yield of para-xylene.

[0006] A second objective of the present invention is to provide a preparation system for the aforementioned preparation method.

[0007] To achieve the first objective of this invention, the following technical solution is adopted:

[0008] A method for preparing p-xylene, the method comprising:

[0009] (1) The naphtha feedstock is sent to the first reaction zone and undergoes a first catalytic reaction in the presence of a first catalyst to obtain a first stream; wherein the first stream contains benzene, toluene, p-xylene and byproducts;

[0010] (2) Benzene, toluene and methanol are sent to the second reaction zone and a second catalytic reaction is carried out in the presence of a second catalyst to obtain a second stream; wherein the second stream contains benzene, toluene, p-xylene and byproducts;

[0011] (3) Send the first stream obtained in step (1) and / or the second stream obtained in step (2) to a separation system for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component as the product, and a by-product-rich component, respectively.

[0012] (4) The benzene-rich and toluene-rich components separated in step (3) are returned to step (2) as sources of benzene and toluene.

[0013] In the preferred embodiment of the preparation method of the present invention, step (3) involves sending the first stream obtained in step (1) and the second stream obtained in step (2) to a separation system for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component, and a by-product-rich component.

[0014] The preparation method of the present invention preferably includes a first separation system and a second separation system in the separation system.

[0015] In step (3), the first stream obtained in step (1) is sent to the first separation system for separation to obtain a first benzene-rich component, a first toluene-rich component, a first p-xylene-rich component, and a first by-product-rich component; and the second stream obtained in step (2) is sent to the second separation system for separation to obtain a second benzene-rich component, a second toluene-rich component, a second p-xylene-rich component, and a second by-product-rich component; wherein,

[0016] The benzene-rich component obtained in step (3) includes a first benzene-rich component and a second benzene-rich component;

[0017] The toluene-rich component obtained in step (3) comprises a first toluene-rich component and a second toluene-rich component;

[0018] The p-xylene-rich component obtained in step (3) comprises a first p-xylene-rich component and a second p-xylene-rich component;

[0019] The rich byproduct component obtained in step (3) includes a first rich byproduct component and a second rich byproduct component.

[0020] In the preferred embodiment of the preparation method of the present invention, in step (3), the first stream obtained in step (1) is sent to a first separation system for separation to obtain a first benzene-rich component, a first toluene-rich component, a first p-xylene-rich component and a first by-product component; and the first p-xylene-rich component, the first by-product component and the second stream obtained in step (2) are sent to a second separation system for separation to obtain a second benzene-rich component, a second toluene-rich component, a second p-xylene-rich component and a second by-product component.

[0021] In the preferred embodiment of the preparation method of the present invention, step (3) involves sending the second stream obtained in step (2) to a separation system for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component, and a by-product-rich component.

[0022] Preferably, the preparation method of the present invention further includes step (5), in which the first stream obtained in step (1) is sent to step (2) as a source of benzene and toluene.

[0023] The preparation method of the present invention, preferably, wherein in the first catalyst and the second catalyst, the first catalyst is selected from any one or more combinations of metal-modified ZSM-5 molecular sieve catalysts; and / or

[0024] The second catalyst is selected from any one or a combination of ZSM-5 molecular sieve catalysts modified by silanization and metal modification; preferably, the second catalyst is selected from any one or a combination of ZSM-5 molecular sieve catalysts modified by metal modification and silanization in sequence.

[0025] In the preparation method of the present invention, preferably, the metal modification is bimetallic modification, wherein the first metal is selected from any one of La, Ce, Mg and Ca, and the second metal is selected from any one of Ga and Zn.

[0026] The preparation method of the present invention, preferably, includes metal modification comprising: (i) preparing an aqueous solution of a soluble metal salt; (ii) impregnating a ZSM-5 molecular sieve in the aqueous solution of the soluble metal salt obtained in step (i) to obtain an impregnated molecular sieve; and (iii) drying and calcining the impregnated molecular sieve obtained in step (ii) to obtain a ZSM-5 molecular sieve catalyst of the metal.

[0027] In the preferred embodiment of the preparation method of the present invention, in step (ii), the impregnation conditions include: an impregnation time of 2 to 10 hours and / or an impregnation temperature of 60 to 90°C; in step (iii), the drying conditions include: an air atmosphere and a temperature of 110 to 150°C; and / or the calcination conditions include: an air atmosphere and a temperature of 500 to 700°C.

[0028] In the preparation method of the present invention, preferably, the silanizing agent used for silanization modification is selected from at least one compound with the structure shown in Formula I:

[0029] Formula I;

[0030] R1, R2, R3 and R4 are each independently selected from any one of C1 to C10 alkyl groups and C1 to C10 alkoxy groups; preferably, in Formula I, at least one of R1, R2, R3 and R4 is selected from any one of C1-10 alkoxy groups.

[0031] In the preparation method of the present invention, preferably, the silicon-to-aluminum ratio in the ZSM-5 molecular sieve, calculated on an atomic basis, is Si / Al = 10 to 200.

[0032] In the preparation method of the present invention, preferably, in step (1), the conditions for the first catalytic reaction include:

[0033] The reaction temperature is 350–650℃; and / or,

[0034] The reaction pressure is 0.1–0.5 MPa; and / or,

[0035] The feed weight hourly space velocity (WHSV) of the naphtha feedstock I is 0.1–10 h⁻¹. -1 .

[0036] In the preparation method of the present invention, preferably, in step (2), the conditions for the second catalytic reaction include:

[0037] The reaction temperature is 350–650℃; and / or,

[0038] The reaction pressure is 0.1–0.5 MPa; and / or,

[0039] The weight hourly space velocity (WHSV) of the mixed feed of benzene, toluene, and methanol is 0.1–8 h⁻¹. -1 ; and / or,

[0040] The molar ratio of methanol to the total amount of benzene and toluene used is 0.2 to 2.

[0041] In the preferred embodiment of the preparation method of the present invention, the second catalyst is prepared in situ in the second reaction zone.

[0042] The preparation method of the present invention, preferably, is an in-situ preparation method as follows: the first catalyst is loaded into the second reaction zone, then a silanizing agent is introduced to contact it, and the mixture is heated and calcined to obtain the second catalyst in situ.

[0043] In the preparation method of the present invention, preferably, the calcination temperature is 500-700℃; and / or the calcination time is 2-8h.

[0044] In the preparation method of the present invention, preferably, after calcination, the second reaction zone is directly cooled to its reaction temperature to carry out the second catalytic reaction.

[0045] To achieve the second objective of the present invention, a preparation system for the aforementioned preparation method is provided.

[0046] The beneficial effects of this invention are as follows:

[0047] (1) The method for preparing para-xylene of the present invention uses naphtha and methanol as raw materials to prepare para-xylene, and by adding methanol, the product distribution is adjusted, which significantly improves the selectivity of para-xylene.

[0048] (2) The method for preparing para-xylene of the present invention uses naphtha and methanol as raw materials to prepare para-xylene. Since methanol is added to the raw materials and benzene and toluene contained in the first and / or second streams obtained from the catalytic reaction are returned to the second reaction zone, the material recycling is realized, the yield of para-xylene is improved, and the economic benefits are improved.

[0049] (3) The preparation method of para-xylene of the present invention is simple, highly feasible, and can greatly improve the selectivity and yield of para-xylene. It provides a new way to efficiently produce para-xylene from naphtha and has important application value.

[0050] (4) In the preparation method of p-xylene of the present invention, the second catalyst can be prepared in situ in the second reaction zone. After the calcination of the in situ preparation process, the second reaction zone can be directly cooled to its reaction temperature to carry out the second catalytic reaction, thereby avoiding heat loss. Compared with the inherent production methods in the chemical industry, the in situ preparation of the second catalyst in the second reaction zone of the present invention saves the washing and separation process after catalyst modification, the catalyst cooling process after calcination to room temperature, the catalyst transportation step, the catalyst loading step, and the step of high-temperature pre-activation after the catalyst is loaded into the reactor, which greatly improves production efficiency and avoids the safety problems that may occur in the above-mentioned saved steps. More importantly, the second catalytic reaction can start as soon as the second reaction zone is cooled from the calcination temperature to its reaction temperature, and the thermal energy is fully utilized, which greatly saves energy consumption in production. Attached Figure Description

[0051] Figure 1 is a schematic flowchart of the method for preparing p-xylene according to the present invention in the first embodiment;

[0052] Figure 2 is a schematic flowchart of the method for preparing p-xylene according to the present invention in the second embodiment;

[0053] Figure 3 is a schematic flowchart of the method for preparing p-xylene according to the present invention in the third embodiment;

[0054] Figure 4 is a schematic flowchart of the preparation method of p-xylene in Comparative Example 1. Detailed Implementation

[0055] The technical solution and its effects of the present invention will be further described below with reference to specific embodiments / examples and accompanying drawings. The following embodiments / examples are only for illustrating the content of the present invention, and the invention is not limited to the following embodiments or examples. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0056] This invention provides a method for preparing p-xylene, as shown in Figures 1-3, the method comprising:

[0057] (1) The naphtha feedstock is sent to the first reaction zone and undergoes a first catalytic reaction in the presence of a first catalyst to obtain a first stream; wherein the first stream contains benzene, toluene, p-xylene and byproducts;

[0058] (2) Benzene, toluene and methanol are sent to the second reaction zone and a second catalytic reaction is carried out in the presence of a second catalyst to obtain a second stream; wherein the second stream contains benzene, toluene, p-xylene and byproducts;

[0059] (3) Send the first stream obtained in step (1) and / or the second stream obtained in step (2) to a separation system for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component as the product, and a by-product-rich component, respectively.

[0060] (4) The benzene-rich and toluene-rich components separated in step (3) are returned to step (2) as sources of benzene and toluene.

[0061] The present invention provides a method for preparing p-xylene using naphtha and methanol as raw materials. By adding methanol, the product distribution is adjusted, significantly improving the selectivity of p-xylene. The yield of p-xylene is effectively improved by further selectively alkylating benzene and toluene in the first stream obtained from naphtha conversion with methanol. The addition of methanol to supplement methyl groups overcomes the inherent problem of insufficient methyl groups in naphtha.

[0062] In this invention, the methanol feedstock includes methanol and / or dimethyl ether. Unless otherwise specified, the methanol feedstock in this application can be wholly or partially replaced by dimethyl ether. The amount of methanol feedstock can also be calculated by converting dimethyl ether into methanol with the same number of carbon atoms.

[0063] In one embodiment, as shown in Figure 1, in step (3), the first stream obtained in step (1) and the second stream obtained in step (2) are sent to a separation system for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component and a by-product-rich component.

[0064] In one embodiment, as shown in FIG2, the separation system includes a first separation system and a second separation system;

[0065] In step (3), the first stream obtained in step (1) is sent to the first separation system for separation to obtain a first benzene-rich component, a first toluene-rich component, a first p-xylene-rich component, and a first by-product-rich component; and the second stream obtained in step (2) is sent to the second separation system for separation to obtain a second benzene-rich component, a second toluene-rich component, a second p-xylene-rich component, and a second by-product-rich component; wherein,

[0066] The benzene-rich component obtained in step (3) includes a first benzene-rich component and a second benzene-rich component;

[0067] The toluene-rich component obtained in step (3) comprises a first toluene-rich component and a second toluene-rich component;

[0068] The p-xylene-rich component obtained in step (3) comprises a first p-xylene-rich component and a second p-xylene-rich component;

[0069] The rich byproduct component obtained in step (3) includes a first rich byproduct component and a second rich byproduct component.

[0070] In a preferred embodiment, as shown in FIG2, in step (3), the first stream obtained in step (1) is sent to the first separation system for separation to obtain the first benzene-rich component, the first toluene-rich component, the first p-xylene-rich component and the first by-product component; and the first p-xylene-rich component, the first by-product component and the second stream obtained in step (2) are sent to the second separation system for separation to obtain the second benzene-rich component, the second toluene-rich component, the second p-xylene-rich component and the second by-product component.

[0071] In one embodiment, as shown in Figure 3, in step (3), the second stream obtained in step (2) is sent to a separation system for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component, and a by-product-rich component.

[0072] In a preferred embodiment, as shown in FIG3, the preparation method further includes step (5), in which the first stream obtained in step (1) is sent to step (2) as a source of benzene and toluene.

[0073] The present invention provides a method for preparing para-xylene using naphtha and methanol as feedstocks. By adding methanol to the feedstocks and returning benzene and toluene contained in the first and / or second streams obtained from the catalytic reaction to the second reaction zone, material recycling is achieved, improving economic efficiency. Furthermore, the process is simple, highly feasible, and can significantly improve the selectivity and yield of para-xylene, providing a new and efficient route for producing para-xylene from naphtha, and has significant application value.

[0074] In one embodiment, the first catalyst is selected from any one or a combination of metal-modified ZSM-5 molecular sieve catalysts. That is, the first catalyst is obtained by metal modification of ZSM-5 molecular sieve.

[0075] In one embodiment, the second catalyst is selected from any one or a combination of ZSM-5 molecular sieve catalysts modified by silanization and metal modification; preferably, the second catalyst is selected from any one or a combination of ZSM-5 molecular sieve catalysts modified by metal modification and silanization in sequence, that is, the ZSM-5 molecular sieve is first modified by metal, and then the ZSM-5 molecular sieve obtained by metal modification is modified by silanization.

[0076] In one embodiment, in the first catalyst and the second catalyst, the metal modification is bimetallic modification, wherein the first metal is selected from any one of La, Ce, Mg and Ca, and the second metal is selected from any one of Ga and Zn.

[0077] This invention improves the selectivity of para-xylene (PX) in xylene products by using a selective catalyst, which can significantly reduce the throughput of the xylene isomerization unit and simplify the xylene separation process, thus developing a new route for the preparation of para-xylene.

[0078] In one embodiment, the metal modification is performed using an impregnation method.

[0079] In one embodiment, ZSM-5 molecular sieve is modified with metal by impregnation, specifically including the following steps:

[0080] (i) Prepare an aqueous solution of a soluble metal salt;

[0081] (ii) Impregnate the ZSM-5 molecular sieve in the aqueous solution of the soluble metal salt obtained in step (i) to obtain the impregnated molecular sieve;

[0082] (iii) The impregnated molecular sieve obtained in step (ii) is dried and calcined to obtain the metal-modified ZSM-5 molecular sieve catalyst.

[0083] In one embodiment, the impregnation conditions in step (ii) include:

[0084] The immersion time is 2 to 10 hours, such as 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, and 10h, and any value and range within this range; and / or, the immersion temperature is 60 to 90°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, and any value and range within this range.

[0085] In one implementation, in step (iii),

[0086] Drying conditions include: an air atmosphere, a temperature of 110–150°C, such as 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, and 150°C, and any values ​​and ranges within this range; and / or,

[0087] The roasting conditions include: an air atmosphere and a temperature of 500–700°C, such as 500°C, 525°C, 550°C, 575°C, 600°C, 625°C, 650°C, 675°C and 700°C, and any value and range within this range.

[0088] In one embodiment, the silanizing agent used for the silanization modification is selected from at least one compound with the structure shown in Formula I:

[0089] R1, R2, R3 and R4 are each independently selected from any one of C1 to C10 alkyl groups and C1 to C10 alkoxy groups.

[0090] In one embodiment, optionally, in Formula I, at least one of R1, R2, R3 and R4 is selected from any of the C1-10 alkoxy groups.

[0091] In this invention, "C1 to C10" refers to the number of carbon atoms contained in the group;

[0092] The term "alkyl" refers to a group formed by losing any hydrogen atom from an alkane compound molecule; the alkane compound includes straight-chain alkanes, branched alkanes, cycloalkanes, and branched cycloalkanes.

[0093] The term "alkoxy group" refers to a group formed by the loss of a hydrogen atom from a hydroxyl group in an alkyl alcohol molecule.

[0094] In one embodiment, the silanizing agent is optionally tetraethyl silicate and / or tetramethyl silicate.

[0095] In one embodiment, optionally, the ZSM-5 molecular sieve is a shaped ZSM-5 molecular sieve formed according to the reactor type; the shaped ZSM-5 molecular sieve is composed of ZSM-5 molecular sieves; or the shaped ZSM-5 molecular sieve contains ZSM-5 molecular sieves and a binder.

[0096] In one embodiment, the shaped ZSM-5 molecular sieve is optionally prepared by one of the following methods: ZSM-5 molecular sieve pressing and crushing, mixing ZSM-5 molecular sieve with a binder and extruding and then cutting into strips, or mixing ZSM-5 molecular sieve with a binder and spray drying to form the shaped ZSM-5 molecular sieve.

[0097] In one embodiment, the silicon-to-aluminum ratio in the ZSM-5 molecular sieve, measured in atomic ratios, is Si / Al = 10 to 200, such as 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, and 200, and any value or range within that range.

[0098] In one embodiment, to further synergistically improve the conversion rate of reactants and the selectivity of products, in step (1), the conditions of the first catalytic reaction include:

[0099] The reaction temperature is 350–650℃, such as 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, and 650℃, and any value and range within this range; and / or,

[0100] The reaction pressure is 0.1–0.5 MPa, for example, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, and 0.5 MPa; and / or,

[0101] The feed weight hourly space velocity (WHSV) of the naphtha feedstock I is 0.1–10 h⁻¹. -1 For example, 0.1h -1 0.5h -1 1h -1 2h -1 3h -1 4h -1 5h -1 6h -1 7h -1 8h -1 9h -1 and 10h -1 and any value within that range and the range of values.

[0102] In one embodiment, to significantly improve catalytic efficiency and product yield, and to optimize the distribution of the obtained product, the conditions for the second catalytic reaction in step (2) include:

[0103] The reaction temperature is 350–650℃, such as 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, and 650℃, and any value and range within this range; and / or,

[0104] The reaction pressure is 0.1–0.5 MPa, for example, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, and 0.5 MPa; and / or,

[0105] The weight hourly space velocity (WHSV) of the mixed feed of benzene, toluene, and methanol is 0.1–8 h⁻¹. -1 For example, 0.1h -1 0.5h -1 1h -1 2h -1 3h -1 4h -1 5h -1 6h -1 7h -1 and 8h -1 and any value and range of values ​​within that range; and / or,

[0106] The molar ratio of methanol to the total amount of benzene and toluene is 0.2 to 2, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 and 2, and any value and range within this range.

[0107] In one embodiment, the second catalyst is prepared in situ in the second reaction zone;

[0108] Preferably, the in-situ preparation method is as follows: the first catalyst is packed into the second reaction zone, then a silanizing agent is introduced to contact it, and the mixture is heated and calcined to obtain the second catalyst in situ.

[0109] In one embodiment, in order to obtain a second catalyst with stronger selectivity, the calcination temperature during the in-situ preparation process is 500–700°C, such as 500°C, 525°C, 550°C, 575°C, 600°C, 625°C, 650°C, 675°C, and 700°C, and any value and range within this range; and / or, the calcination time is 2–8 h, such as 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, and 8 h, and any value and range within this range.

[0110] In one embodiment, during the in-situ preparation process, after calcination, the second reaction zone is directly cooled to its reaction temperature to carry out the second catalytic reaction.

[0111] In the method for preparing p-xylene of the present invention, the second catalyst can be prepared in situ in the second reaction zone. Therefore, after the calcination process in the in-situ preparation is completed, the second reaction zone can be directly cooled to its reaction temperature to carry out the second catalytic reaction, thus avoiding heat loss. Compared with conventional production methods in the chemical industry, the in-situ preparation of the second catalyst in the second reaction zone of the present invention saves the steps of washing and separating the catalyst after modification, cooling the catalyst to room temperature after calcination, catalyst transportation, catalyst loading, and high-temperature pre-activation after the catalyst is loaded into the reactor, significantly improving production efficiency and avoiding potential safety issues in the aforementioned saved steps. More importantly, the second catalytic reaction can begin as soon as the second reaction zone is cooled from the calcination temperature to its reaction temperature, making full use of thermal energy and significantly saving energy consumption in production.

[0112] In this invention, the first catalytic reaction carried out in the first reaction zone is a naphtha conversion reaction, and the second catalytic reaction carried out in the second reaction zone is a shape-selective alkylation reaction.

[0113] The present invention also provides a preparation system for the aforementioned preparation method, as shown in Figures 1, 2, and 3.

[0114] In one embodiment, as shown in Figures 1, 2, and 3, the preparation system includes a first reaction zone 1, a second reaction zone 2, and a separation system 3; wherein,

[0115] The inlet of the first reaction zone 1 is connected to a naphtha feedstock pipeline, and the outlet is connected to the inlet of the second reaction zone 2. The naphtha feedstock is introduced and undergoes a first catalytic reaction in the presence of a first catalyst to obtain a first stream containing benzene, toluene, paraxylene and byproducts, which is then sent to the second reaction zone 2.

[0116] The inlet of the second reaction zone 2 is connected to the methanol feed pipeline, the benzene feed pipeline and the toluene feed pipeline, and the outlet is connected to the inlet of the separation system 3, which is used to introduce methanol feed, benzene and toluene and to carry out a second catalytic reaction in the presence of a second catalyst to obtain a second stream containing benzene, toluene, paraxylene and by-products and send it to the separation system 3.

[0117] The benzene-rich component outlet of the separation system 3 is connected to the benzene feed pipeline of the second reaction zone 2, and the toluene-rich component outlet is connected to the toluene feed pipeline of the second reaction zone 2, which is used to return the benzene-rich component and toluene-rich component output by the separation system 3 to the second reaction zone 2 as the source of benzene and toluene.

[0118] The product outlet of the separation system 3 is connected to the paraxylene product line for outputting the paraxylene product from the separation system 3.

[0119] In one embodiment, as shown in FIG1, the outlet of the first reaction zone 1 is connected to the inlet of the separation system 3, and is connected to the inlet of the second reaction zone 2 through the benzene-rich component outlet and the toluene-rich component outlet of the separation system 3.

[0120] Specifically, in one embodiment, as shown in FIG1, the preparation system includes a first reaction zone 1, a second reaction zone 2, and a separation system 3; wherein,

[0121] The inlet of the first reaction zone 1 is connected to a naphtha feedstock pipeline, and the outlet is connected to the inlet of the separation system 3. The naphtha feedstock is introduced and undergoes a first catalytic reaction in the presence of a first catalyst to obtain a first stream containing benzene, toluene, paraxylene and byproducts, which is then sent to the separation system 3.

[0122] The inlet of the second reaction zone 2 is connected to the methanol feed pipeline, the benzene feed pipeline and the toluene feed pipeline, and the outlet is connected to the inlet of the separation system 3, which is used to introduce methanol feed, benzene and toluene and to carry out a second catalytic reaction in the presence of a second catalyst to obtain a second stream containing benzene, toluene, paraxylene and by-products and send it to the separation system 3.

[0123] The benzene-rich component outlet of the separation system 3 is connected to the benzene feed pipeline of the second reaction zone 2, and the toluene-rich component outlet is connected to the toluene feed pipeline of the second reaction zone 2, which is used to return the benzene-rich component and toluene-rich component output by the separation system 3 to the second reaction zone 2 as the source of benzene and toluene.

[0124] The product outlet of the separation system 3 is connected to the paraxylene product line for outputting paraxylene products from the separation system 3.

[0125] In the preparation system shown in Figure 1, the first reaction zone 1 first undergoes a first catalytic reaction, and after being connected to the separation system 3 for the first stream separation, the separated benzene-rich and toluene-rich components enter the inlet of the second reaction zone 2 together with the methanol feedstock for the second catalytic reaction. The second stream enters the separation system 3 for product separation again, and the separated benzene-rich and toluene-rich components then enter the inlet of the second reaction zone 2 for recycling.

[0126] Specifically, in one embodiment, as shown in FIG2, the preparation system includes a first reaction zone 1, a second reaction zone 2, and a separation system 3, wherein the separation system 3 includes a first separation system 301 and a second separation system 302; wherein,

[0127] The inlet of the first reaction zone 1 is connected to a naphtha feedstock pipeline, and the outlet is connected to the inlet of the first separation system 301. The naphtha feedstock is introduced and undergoes a first catalytic reaction in the presence of a first catalyst to obtain a first stream containing benzene, toluene, paraxylene and byproducts, which is then sent to the first separation system 301 and separated and output as a first benzene-rich component, a first toluene-rich component, a first paraxylene-rich component and a first byproduct-rich component.

[0128] The inlet of the second reaction zone 2 is connected to a methanol feed pipeline, a benzene feed pipeline, and a toluene feed pipeline. The benzene feed pipeline is connected to the first benzene-rich component outlet of the first separation system 301, and the toluene feed pipeline is connected to the first toluene-rich component outlet of the first separation system 301. The outlet of the second reaction zone 2, the first p-xylene-rich component outlet and the first by-product-rich component outlet of the first separation system 301 are respectively connected to the inlet of the second separation system 302. This is used to introduce methanol feed, benzene, and toluene into the second reaction zone 2, and to return the first benzene-rich component and the first toluene-rich component output from the first separation system 301 to the second reaction zone 2 as the source of benzene and toluene. In the presence of the second catalyst, a second catalytic reaction occurs to obtain a second stream containing benzene, toluene, p-xylene, and by-products, which is then sent to the second separation system 302. The second benzene-rich component, the second toluene-rich component, the second p-xylene-rich component, and the second by-product-rich component are then separated and output.

[0129] The second benzene-rich component outlet of the second separation system 302 is connected to the benzene feed pipeline of the second reaction zone 2, and the second toluene-rich component outlet is connected to the toluene feed pipeline of the second reaction zone 2, for returning the second benzene-rich component and the second toluene-rich component output from the second separation system 302 to the second reaction zone 2 as the source of benzene and toluene;

[0130] The product outlet of the second separation system 302 is connected to the paraxylene product line for outputting the paraxylene product from the second separation system 302.

[0131] In the preparation system shown in Figure 2, the first stream from the first catalytic reaction in the first reaction zone 1 undergoes a first separation in the first separation system 301. The separated first benzene-rich component and first toluene-rich component, together with the methanol feedstock, enter the inlet of the second reaction zone 2 for a second catalytic reaction. The separated first p-xylene-rich component and first by-product component are sent to the second separation system 302. The second stream from the reaction in the second reaction zone 2 is then connected to the second separation system 302 and also sent to the second separation system 302 for separation. The separated second benzene-rich component and second toluene-rich component are returned to the inlet of the second reaction zone 2 for recycling. The separated second p-xylene-rich component is output as the p-xylene product.

[0132] Specifically, in one embodiment, as shown in FIG3, the preparation system includes a first reaction zone 1, a second reaction zone 2, and a separation system; wherein,

[0133] The inlet of the first reaction zone 1 is connected to a naphtha feedstock pipeline, and the outlet is connected to the inlet of the second reaction zone 2. The naphtha feedstock is introduced and undergoes a first catalytic reaction in the presence of a first catalyst to obtain a first stream containing benzene, toluene, paraxylene and byproducts, which is then sent to the second reaction zone 2.

[0134] The inlet of the second reaction zone 2 is connected to the methanol feed pipeline, the benzene feed pipeline and the toluene feed pipeline, and the outlet is connected to the inlet of the separation system 3, which is used to introduce methanol feed, benzene and toluene and to carry out a second catalytic reaction in the presence of a second catalyst to obtain a second stream containing benzene, toluene, paraxylene and by-products and send it to the separation system 3.

[0135] The benzene-rich component outlet of the separation system 3 is connected to the benzene feed pipeline of the second reaction zone 2, and the toluene-rich component outlet is connected to the toluene feed pipeline of the second reaction zone 2, which is used to return the benzene-rich component and toluene-rich component output by the separation system 3 to the second reaction zone 2 as the source of benzene and toluene.

[0136] The product outlet of the separation system 3 is connected to the paraxylene product line for outputting the paraxylene product from the separation system 3.

[0137] In the preparation system shown in Figure 3, the first stream from the first catalytic reaction in the first reaction zone 1 is not separated by the separation system 3, but directly enters the second reaction zone 2 to undergo a second catalytic reaction with the introduced methanol feedstock. The second stream from the second reaction zone 2 is then connected to the separation system 3 and sent to the separation system 3 for separation. The benzene-rich component and toluene-rich component separated by the separation system 3 are then recycled into the inlet of the second reaction zone 2. The p-xylene-rich component separated is output as the p-xylene product.

[0138] In one embodiment, the first reaction zone 1 includes one reactor or multiple reactors connected in series and / or in parallel.

[0139] In one embodiment, the second reaction zone 2 includes one or more reactors connected in series and / or in parallel.

[0140] In one embodiment, the reactor is at least one of a fixed bed, a fluidized bed, or a moving bed.

[0141] In one embodiment, the first reaction zone 1 and the second reaction zone 2 are located in the same reactor.

[0142] The present invention discloses a method and system for preparing para-xylene, which utilizes naphtha and methanol as feedstocks. By adding methanol, the product distribution is adjusted, significantly improving the selectivity of para-xylene. Because methanol is added to the feedstock, and benzene and toluene contained in the first and / or second streams obtained from the catalytic reaction are returned to the second reaction zone, material recycling is achieved, increasing the yield of para-xylene and improving economic efficiency. The process is simple, highly feasible, and can significantly improve the selectivity and yield of para-xylene, providing a new and efficient route for producing para-xylene from naphtha, and has significant application value.

[0143] Raw materials used in the following examples / comparative examples:

[0144] Unless otherwise specified, all raw materials and reagents used in this invention are commercially available and used directly without processing.

[0145] In the embodiments of the present invention, the naphtha feedstock is coal direct liquefaction full-fraction naphtha, and its specific composition is shown in Table 1.

[0146] Table 1. Composition of naphtha from direct coal liquefaction.

[0147] In the examples, the catalyst wear index was measured using an MS-C type wear index tester from Shenyang Hexing Machinery & Electronics Co., Ltd.

[0148] In the embodiments, the inner diameter of the fixed bed reactor is 1.5 cm; the inner diameter of the fixed fluidized bed reactor is 3 cm; and the inner diameter of the circulating fluidized bed reactor is 12 cm.

[0149] Preparation system and preparation method

[0150] Example a1 (Sa1)

[0151] The p-xylene product was prepared using the preparation system and process shown in Figure 1, as detailed below:

[0152] (1) The naphtha feedstock is sent to the first reaction zone 1 and a first catalytic reaction is carried out in the presence of a first catalyst to obtain a first stream; wherein the first stream contains benzene, toluene, p-xylene and by-products;

[0153] (2) Benzene, toluene and methanol are sent to the second reaction zone 2 and a second catalytic reaction is carried out in the presence of a second catalyst to obtain a second stream; wherein the second stream contains benzene, toluene, p-xylene and byproducts;

[0154] (3) The first stream obtained in step (1) and the second stream obtained in step (2) are sent to the separation system 3 for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component as a p-xylene product, and a by-product-rich component.

[0155] (4) The benzene-rich and toluene-rich components separated in step (3) are returned to step (2) as sources of benzene and toluene.

[0156] Example a2 (Sa2)

[0157] The p-xylene product was prepared using the preparation system and process shown in Figure 2, as detailed below:

[0158] (1) The naphtha feedstock is sent to the first reaction zone 1 and a first catalytic reaction is carried out in the presence of a first catalyst to obtain a first stream; wherein the first stream contains benzene, toluene, p-xylene and by-products;

[0159] (2) Benzene, toluene and methanol are sent to the second reaction zone 2 and a second catalytic reaction is carried out in the presence of a second catalyst to obtain a second stream; wherein the second stream contains benzene, toluene, p-xylene and byproducts;

[0160] (3) The first stream obtained in step (1) is sent to the first separation system 301 for separation to obtain the first benzene-rich component, the first toluene-rich component, the first p-xylene-rich component and the first by-product component; and the second stream obtained in step (2) is sent to the second separation system 302 for separation to obtain the second benzene-rich component, the second toluene-rich component, the second p-xylene-rich component as a p-xylene product and the second by-product component.

[0161] (4) The first benzene-rich component and the first toluene-rich component separated by the first separation system 301 in step (3), and the second benzene-rich component and the second toluene-rich component separated by the second separation system 302 are returned to step (2) as the source of benzene and toluene.

[0162] Example a3 (Sa3)

[0163] The p-xylene product was prepared using the preparation system and process shown in Figure 3, as detailed below:

[0164] (1) The naphtha feedstock is sent to the first reaction zone 1 and a first catalytic reaction is carried out in the presence of a first catalyst to obtain a first stream; wherein the first stream contains benzene, toluene, p-xylene and by-products;

[0165] (2) Benzene, toluene and methanol are sent to the second reaction zone 2 and a second catalytic reaction is carried out in the presence of a second catalyst to obtain a second stream; wherein the second stream contains benzene, toluene, p-xylene and byproducts;

[0166] (3) The second stream obtained in step (2) is sent to the separation system 3 for separation to obtain benzene-rich component, toluene-rich component, para-xylene-rich component and by-product-rich component as para-xylene product;

[0167] (4) The benzene-rich and toluene-rich components separated in step (3) are returned to step (2) as sources of benzene and toluene.

[0168] Comparative example a1 (Da1)

[0169] The p-xylene product was prepared using the preparation system and process shown in Figure 4, as detailed below:

[0170] (1) The naphtha feedstock is sent to the first reaction zone 1 and a first catalytic reaction is carried out in the presence of a first catalyst to obtain a first stream; wherein the first stream contains benzene, toluene, p-xylene and by-products;

[0171] (2) The first stream obtained in step (1) is sent to the separation system 3 for separation to obtain a benzene-rich component, a toluene-rich component, a para-xylene-rich component as a para-xylene product, and a by-product-rich component.

[0172] Catalyst preparation

[0173] Example b1 (Sb1) Lanthanum-gallium modified ZSM-5 molecular sieve for fixed bed

[0174] ZSM-5 molecular sieves were modified by impregnation to prepare [10% La 5% Ga]ZSM-5 (i.e., the first catalyst C1) and FX-[10% La 5% Ga]ZSM-5 (i.e., the first catalyst C1). 颗粒 The specific steps include the following:

[0175] (i) Prepare an aqueous solution of soluble metal salts of lanthanum nitrate and gallium nitrate, such that the La content is 10% of the amount of ZSM-5 molecular sieve used, the Ga content is 5% of the amount of ZSM-5 molecular sieve used, and the water content is the saturated water absorption of the ZSM-5 molecular sieve used.

[0176] (ii) 100g of ZSM-5 molecular sieve (from Nankai University Catalyst Factory, with a silicon-to-aluminum ratio of Si / Al = 20 based on atomic ratio) is impregnated in the soluble metal salt aqueous solution obtained in step (i) to obtain the impregnated molecular sieve; wherein,

[0177] The impregnation conditions include: an impregnation temperature of 80℃ and an impregnation time of 6 hours;

[0178] (iii) The impregnated molecular sieve obtained in step (ii) is dried and calcined to obtain the metal-modified ZSM-5 molecular sieve catalyst - [10% La 5% Ga] ZSM-5 (i.e., the first catalyst C1). Then, it is pressed into tablets, crushed, and sieved to obtain shaped molecular sieve catalyst particles with a particle size of 40-60 mesh, denoted as FX-[10% La 5% Ga] ZSM-5 (i.e., the first catalyst C1). 颗粒 );in,

[0179] Drying conditions include: drying at 120°C for 4 hours in air atmosphere;

[0180] The roasting conditions included roasting at 550°C for 4 hours in an air atmosphere.

[0181] Example b2 (Sb2) Lanthanum-gallium modified ZSM-5 molecular sieve for fixed bed applications

[0182] [10% La 10% Ga]ZSM-5 (i.e., the first catalyst C2) and FX-[10% La 10% Ga]ZSM-5 (i.e., the first catalyst C2) were prepared according to the method of Example b1 (Sb1). 颗粒 The difference between this and embodiment b1 (Sb1) is only that:

[0183] In step (i), a soluble aqueous solution of lanthanum nitrate and gallium nitrate is prepared, such that the La content is 10% of the amount of ZSM-5 molecular sieve used, the Ga content is 10% of the amount of ZSM-5 molecular sieve used, and the water content is the saturated water absorption of the ZSM-5 molecular sieve used.

[0184] Example b3 (Sb3) Lanthanum-zinc modified ZSM-5 molecular sieve for fixed bed applications

[0185] [10% La 5% Zn]ZSM-5 (i.e., the first catalyst C3) and FX-[10% La 5% Zn]ZSM-5 (i.e., the first catalyst C3) were prepared according to the method of Example b1 (Sb1). 颗粒 The difference between this and embodiment b1 (Sb1) is only that:

[0186] In step (i), a soluble metal salt aqueous solution of lanthanum nitrate and zinc nitrate is prepared, such that the La content is 10% of the amount of ZSM-5 molecular sieve used, the Zn content is 5% of the amount of ZSM-5 molecular sieve used, and the water content is the saturated water absorption of the ZSM-5 molecular sieve used.

[0187] Example b4 (Sb4) Lanthanum-zinc modified ZSM-5 molecular sieve for fixed bed applications

[0188] [5% La 5% Zn]ZSM-5 (i.e., the first catalyst C4) and FX-[5% La 5% Zn]ZSM-5 (i.e., the first catalyst C4) were prepared according to the method of Example b1 (Sb1). 颗粒 The difference between this and embodiment b1 (Sb1) is only that:

[0189] In step (i), a soluble metal salt aqueous solution of lanthanum nitrate and zinc nitrate is prepared, such that the La content is 5% of the amount of ZSM-5 molecular sieve used, the Zn content is 5% of the amount of ZSM-5 molecular sieve used, and the water content is the saturated water absorption of the ZSM-5 molecular sieve used.

[0190] Example b5 (Sb5) Lanthanum-zinc modified ZSM-5 molecular sieve for fluidized bed applications

[0191] The [10% La 5% Zn] ZSM-5 (i.e., the first catalyst C3) prepared in Example b3 (Sb3) was mixed with an aluminum- or silicon-containing amorphous binder and spray-dried to form a mold. The specific steps are as follows:

[0192] [10% La5% Zn]ZSM-5 (i.e., the first catalyst C3), kaolin, pseudoboehmite, silica sol, alumina sol, xanthan gum (i.e., bio-gum) and water were mixed evenly, and the mixture was pulped, ground, and defoamed to obtain a slurry; the weight parts of each component in the slurry were as follows:

[0193] The obtained slurry was spray-dried and shaped to obtain microsphere samples with a particle size distribution of 20-100 μm;

[0194] After calcining the obtained microsphere sample in a muffle furnace at 550°C for 4 hours, a [10%La5%Zn]ZSM-5 shaped molecular sieve with an abrasion index of 0.9 was obtained, denoted as FL-[10%La5%Zn]ZSM-5 (i.e., the first catalyst C5).

[0195] Preparation and reaction evaluation of p-xylene

[0196] Example c1 (Sc1)

[0197] The first catalyst C1 prepared using the preparation system and process of Example a1 (Sa1) and Example b1 (Sb1) 颗粒 (i.e., FX-[10% La5% Ga]ZSM-5) is used to prepare p-xylene P1, as follows:

[0198] (1) The naphtha feedstock is sent to the first reaction zone 1 and a first catalytic reaction is carried out in the presence of a first catalyst to obtain a first stream; wherein the first stream contains benzene, toluene, p-xylene and by-products;

[0199] (2) Benzene, toluene and methanol are sent to the second reaction zone 2 and a second catalytic reaction is carried out in the presence of a second catalyst to obtain a second stream; wherein the second stream contains benzene, toluene, p-xylene and byproducts;

[0200] (3) The first stream obtained in step (1) and the second stream obtained in step (2) are sent to the separation system 3 for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component as p-xylene product P1, and a by-product-rich component.

[0201] (4) The benzene-rich and toluene-rich components separated in step (3) are returned to step (2) as sources of benzene and toluene; wherein,

[0202] In step (1), after the first catalyst is loaded into the first reaction zone 1, it is first treated with nitrogen at 550°C for 1 hour at a rate of 50 mL / min, and then cooled to 525°C under a nitrogen atmosphere.

[0203] The first catalyst is the first catalyst C1 prepared in Example b1 (Sb1). 颗粒 The dosage is 5g;

[0204] Naphtha feedstock is fed using a micro-feed pump, with a weight hourly space velocity (WHSV) of 4.0 h⁻¹. -1 The reaction pressure is 0.1 MPa.

[0205] In step (2), after the first catalyst (5g) is loaded into the second reaction zone 2, it is first treated with nitrogen at 550℃ for 1 hour at a nitrogen atmosphere of 50mL / min, and then cooled to 400℃ under nitrogen atmosphere; then tetraethyl silicate is fed in using a micro-feed pump, and the weight hourly space velocity of tetraethyl silicate is 0.1h. -1 Under normal pressure, after feeding for 60 minutes, the feed was stopped, nitrogen was purged, the temperature was raised to 550℃, and calcined in air for 4 hours to obtain FX-[10%La5%Ga]ZSM-5-T, i.e., the second catalyst, in situ; then the temperature was lowered to 450℃ to carry out the second catalytic reaction.

[0206] The molar ratio of methanol to the total amount of benzene and toluene is 0.5.

[0207] Response evaluation:

[0208] The second stream from the second reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 minutes of reaction. The product distribution after deducting the benzene and toluene components (benzene and toluene feedstocks from the second reaction zone) is shown in Table 2.

[0209] The first stream from the first reaction zone and the second stream from the second reaction zone were mixed and analyzed by an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction. The product distribution after deducting benzene and toluene components is shown in Table 3.

[0210] Table 2 Product Distribution of the Second Logistics Stream

[0211] Table 3. Product distribution after the first and second logistics are combined.

[0212] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0213] Example c2 (Sc2)

[0214] The first catalyst C2 was prepared using the preparation system and process of Example a1 (Sa1) and Example b2 (Sb2). 颗粒 (i.e., FX-[10% La10% Ga]ZSM-5) to prepare p-xylene product P2; its difference from Example c1 (Sc1) is only that:

[0215] In step (1), the first catalyst is the first catalyst C2 prepared in Example b2 (Sb2). 颗粒 The dosage is 5g;

[0216] In step (2), the first catalyst is the first catalyst C2 prepared in Example b2 (Sb2). 颗粒 The dosage was 5g; the first catalyst was prepared in situ to obtain FX-[10%La10%Ga]ZSM-5-T, which is the second catalyst.

[0217] Response evaluation:

[0218] The second stream from the second reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 minutes of reaction. The product distribution after deducting the benzene and toluene components (benzene and toluene feedstocks from the second reaction zone) is shown in Table 4.

[0219] The first stream from the first reaction zone and the second stream from the second reaction zone were mixed and analyzed by an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction. The product distribution after deducting benzene and toluene components is shown in Table 5.

[0220] Table 4. Product Distribution of the Second Logistics Stream

[0221] Table 5. Product distribution after the first and second logistics are combined.

[0222] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0223] Example c3 (Sc3)

[0224] The first catalyst C3 was prepared using the preparation system and process of Example a1 (Sa1) and Example b3 (Sb3). 颗粒 (i.e., FX-[10% La 5% Zn] ZSM-5) to prepare p-xylene product P3; its difference from Example c1 (Sc1) is only that:

[0225] In step (1), the first catalyst is the first catalyst C3 prepared in Example b3 (Sb3). 颗粒 The dosage is 5g;

[0226] In step (2), the first catalyst is the first catalyst C3 prepared in Example b3 (Sb3). 颗粒 The dosage was 5g; the first catalyst was prepared in situ to obtain FX-[10%La5%Zn]ZSM-5-T, which is the second catalyst.

[0227] Response evaluation:

[0228] The second stream from the second reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 minutes of reaction. The product distribution after deducting the benzene and toluene components (benzene and toluene feedstocks from the second reaction zone) is shown in Table 6.

[0229] The first stream from the first reaction zone and the second stream from the second reaction zone were mixed and analyzed by an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction. The product distribution after deducting benzene and toluene components is shown in Table 7.

[0230] Table 6 Product Distribution of Second Logistics

[0231] Table 7. Product Distribution After the Combination of First and Second Logistics

[0232] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0233] Example c4 (Sc4)

[0234] The p-xylene product P4 was prepared using the preparation system and process of Example a1 (Sa1) and the first catalyst C5 (i.e., FL-[10% La5% Zn] ZSM-5) obtained in Example b5 (Sb5); the only difference between it and Example c1 (Sc1) is:

[0235] In step (1), the first catalyst is the first catalyst C5 prepared in Example b5 (Sb5), and the amount used is 5g;

[0236] In step (2), the first catalyst is the first catalyst C5 prepared in Example b5 (Sb5), with an amount of 5g; the first catalyst is used to prepare FL-[10%La5%Zn]ZSM-5-T in situ, which is the second catalyst.

[0237] Response evaluation:

[0238] The second stream from the second reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 minutes of reaction. The product distribution after deducting the benzene and toluene components (benzene and toluene feedstocks from the second reaction zone) is shown in Table 8.

[0239] The first stream from the first reaction zone and the second stream from the second reaction zone were mixed and analyzed by an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction. The product distribution after deducting benzene and toluene components is shown in Table 9.

[0240] Table 8 Product Distribution of Second Logistics

[0241] Table 9. Product Distribution After the Combination of First and Second Logistics

[0242] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0243] Example c5 (Sc5)

[0244] The first catalyst C4 was prepared using the preparation system and process of Example a1 (Sa1) and Example b4 (Sb4). 颗粒 (i.e., FX-[5% La 5% Zn] ZSM-5) to prepare p-xylene product P5; its difference from Example c1 (Sc1) is only that:

[0245] In step (1), the first catalyst is the first catalyst C4 prepared in Example b4 (Sb4). 颗粒 The dosage is 5g;

[0246] In step (2), the first catalyst is the first catalyst C4 prepared in Example b4 (Sb4).颗粒 The dosage was 5g; the first catalyst was prepared in situ to obtain FX-[5%La5%Zn]ZSM-5-T, which is the second catalyst.

[0247] Response evaluation:

[0248] The second stream from the second reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction. The product distribution after deducting the benzene and toluene components (benzene and toluene feedstocks from the second reaction zone) is shown in Table 10.

[0249] The first stream from the first reaction zone and the second stream from the second reaction zone were mixed and analyzed by an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction. The product distribution after deducting benzene and toluene components is shown in Table 11.

[0250] Table 10 Product Distribution of the Second Logistics Stream

[0251] Table 11. Product distribution after the first and second logistics are mixed.

[0252] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0253] Comparative example c1 (Dc1)

[0254] The first catalyst C1 prepared using the preparation system and process of Comparative Example a1 (Da1) and Example b1 (Sb1) 颗粒 (i.e., FX-[10% La5% Ga]ZSM-5) is used to prepare p-xylene P1', as follows:

[0255] (1) The naphtha feedstock is sent to the first reaction zone 1 and a first catalytic reaction is carried out in the presence of a first catalyst to obtain a first stream; wherein the first stream contains benzene, toluene, p-xylene and by-products;

[0256] (2) The first stream obtained in step (1) is sent to separation system 3 for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component as the p-xylene product P1', and a by-product-rich component; wherein...

[0257] In step (1), after the first catalyst is loaded into the first reaction zone 1, it is first treated with nitrogen at 550°C for 1 hour at a rate of 50 mL / min, and then cooled to 525°C under a nitrogen atmosphere.

[0258] The first catalyst is the first catalyst C1 prepared in Example b1 (Sb1). 颗粒The dosage is 5g;

[0259] Naphtha feedstock is fed using a micro-feed pump, with a weight hourly space velocity (WHSV) of 4.0 h⁻¹. -1 The reaction pressure is 0.1 MPa.

[0260] Response evaluation:

[0261] The first stream from the first reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction, and the product distribution is shown in Table 12.

[0262] Table 12 Product Distribution of the First Logistics Stream

[0263] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0264] Comparative example c2 (Dc2)

[0265] The first catalyst C2 was prepared using the preparation system and process of Comparative Example a1 (Da1) and Example b2 (Sb2). 颗粒 (i.e., FX-[10% La10% Ga]ZSM-5) to prepare p-xylene P2'; its difference from comparative example c1 (Dc1) is only in that:

[0266] In step (1), the first catalyst is the first catalyst C2 prepared in Example b2 (Sb2). 颗粒 The dosage is 5g.

[0267] Response evaluation:

[0268] The first stream from the first reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction, and the product distribution is shown in Table 13.

[0269] Table 13 Product Distribution of the First Logistics Stream

[0270] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0271] Comparative example c3 (Dc3)

[0272] The first catalyst C3 was prepared using the preparation system and process of Comparative Example a1 (Da1) and Example b3 (Sb3). 颗粒 (i.e., FX-[10% La5% Zn]ZSM-5) to prepare p-xylene P3'; its difference from comparative example c1 (Dc1) is only in that:

[0273] In step (1), the first catalyst is the first catalyst C3 prepared in Example b3 (Sb3). 颗粒 The dosage is 5g.

[0274] Response evaluation:

[0275] The first stream from the first reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction, and the product distribution is shown in Table 14.

[0276] Table 14 Product Distribution of the First Logistics Stream

[0277] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0278] Comparative example c4 (Dc4)

[0279] p-Xylene P4' was prepared using the preparation system and process of Comparative Example a1 (Da1) and the first catalyst C5 (i.e., FL-[10% La5% Zn] ZSM-5) prepared in Example b5 (Sb5); its difference from Comparative Example c1 (Dc1) is only that:

[0280] In step (1), the first catalyst is the first catalyst C5 prepared in Example b5 (Sb5), and the amount used is 5g.

[0281] Response evaluation:

[0282] The first stream from the first reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction, and the product distribution is shown in Table 15.

[0283] Table 15 Product Distribution of the First Logistics Stream

[0284] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0285] Comparative example c5 (Dc5)

[0286] The first catalyst C4 was prepared using the preparation system and process of Comparative Example a1 (Da1) and Example b4 (Sb4). 颗粒 (i.e., FX-[5% La5% Zn]ZSM-5) to prepare p-xylene P5'; its difference from comparative example c1 (Dc1) is only:

[0287] In step (1), the first catalyst is the first catalyst C4 prepared in Example b4 (Sb4). 颗粒 The dosage is 5g.

[0288] Response evaluation:

[0289] The first stream from the first reaction zone was analyzed using an online Agilent 7890 gas chromatograph. Samples were taken for analysis after 30 min of reaction, and the product distribution is shown in Table 16.

[0290] Table 16 Product Distribution of the First Logistics Stream

[0291] a Aliphatic hydrocarbons with more than 4 carbon atoms in the product after the reaction are used as naphtha feedstock.

[0292] A comparison of the embodiments and comparative examples shows that:

[0293] Under otherwise identical conditions, compared with existing preparation processes, the preparation method of the present invention can significantly improve the selectivity of PX in the product and the selectivity of PX in the xylene product.

Claims

1. A method for preparing p-xylene, characterized in that, The preparation method includes: (1) The naphtha feedstock is sent to the first reaction zone and undergoes a first catalytic reaction in the presence of a first catalyst to obtain mixed aromatics as the first stream; wherein the first stream contains benzene, toluene, p-xylene and by-products; (2) Benzene, toluene and methanol are sent to the second reaction zone and a second catalytic reaction is carried out in the presence of a second catalyst to obtain a second stream; wherein the second stream contains benzene, toluene, p-xylene and byproducts; (3) Send the first stream obtained in step (1) and / or the second stream obtained in step (2) to a separation system for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component as the product, and a by-product-rich component, respectively. (4) The benzene-rich and toluene-rich components separated in step (3) are returned to step (2) as sources of benzene and toluene.

2. The preparation method according to claim 1, characterized in that, In step (3), the first stream obtained in step (1) and the second stream obtained in step (2) are sent to the separation system for separation to obtain a benzene-rich component, a toluene-rich component, a p-xylene-rich component and a by-product-rich component.

3. The preparation method according to claim 1, characterized in that, The separation system includes a first separation system and a second separation system; In step (3), the first stream obtained in step (1) is sent to the first separation system for separation to obtain the first benzene-rich component, the first toluene-rich component, the first p-xylene-rich component and the first by-product-rich component; The second stream obtained in step (2) is then sent to the second separation system for separation to obtain a second benzene-rich component, a second toluene-rich component, a second p-xylene-rich component, and a second byproduct-rich component; wherein, The benzene-rich component obtained in step (3) includes a first benzene-rich component and a second benzene-rich component; The toluene-rich component obtained in step (3) comprises a first toluene-rich component and a second toluene-rich component; The p-xylene-rich component obtained in step (3) comprises a first p-xylene-rich component and a second p-xylene-rich component; The rich byproduct component obtained in step (3) includes a first rich byproduct component and a second rich byproduct component.

4. The preparation method according to claim 3, characterized in that, In step (3), the first stream obtained in step (1) is sent to the first separation system for separation to obtain the first benzene-rich component, the first toluene-rich component, the first p-xylene-rich component and the first by-product-rich component; The first p-xylene-rich component, the first by-product-rich component, and the second stream obtained in step (2) are sent to the second separation system for separation to obtain the second benzene-rich component, the second toluene-rich component, the second p-xylene-rich component, and the second by-product-rich component.

5. The preparation method according to claim 1, characterized in that, In step (3), the second stream obtained in step (2) is sent to the separation system for separation to obtain benzene-rich components, toluene-rich components, para-xylene-rich components and by-product-rich components respectively. Preferably, the preparation method further includes step (5), in which the first stream obtained in step (1) is sent to step (2) as a source of benzene and toluene.

6. The preparation method according to any one of claims 1-5, characterized in that, The first catalyst is selected from any one or more combinations of metal-modified ZSM-5 molecular sieve catalysts; and / or The second catalyst is selected from any one or a combination of ZSM-5 molecular sieve catalysts modified by silanization and metal modification; preferably, the second catalyst is selected from any one or a combination of ZSM-5 molecular sieve catalysts modified by metal modification and silanization in sequence. Preferably, in the first catalyst and the second catalyst, the metal modification is bimetallic modification, and the first metal is selected from any one of La, Ce, Mg and Ca, and the second metal is selected from any one of Ga and Zn.

7. The preparation method according to claim 6, characterized in that, The metal modification includes: (i) Prepare an aqueous solution of a soluble metal salt; (ii) The ZSM-5 molecular sieve is impregnated in the aqueous solution of the soluble metal salt obtained in step (i) to obtain an impregnated molecular sieve; (iii) The impregnated molecular sieve obtained in step (ii) is dried and calcined to obtain the metal-modified ZSM-5 molecular sieve catalyst.

8. The preparation method according to claim 7, characterized in that, In step (ii), The immersion conditions include: immersion time of 2 to 10 hours, and / or immersion temperature of 60 to 90°C; In step (iii), Drying conditions include: an air atmosphere at a temperature of 110–150°C; and / or, The roasting conditions include: an air atmosphere and a temperature of 500–700°C.

9. The preparation method according to claim 6, characterized in that, The silanizing agent used in the silanization modification is selected from at least one of the compounds with the structure shown in Formula I: R1, R2, R3 and R4 are each independently selected from any one of C1 to C10 alkyl groups and C1 to C10 alkoxy groups; Preferably, in Formula I, at least one of R1, R2, R3 and R4 is selected from any of the C1-10 alkoxy groups.

10. The preparation method according to claim 6, characterized in that, The silicon-aluminum ratio in the ZSM-5 molecular sieve, measured in atomic ratios, is Si / Al = 10–200.

11. The preparation method according to any one of claims 1-10, characterized in that, In step (1), the conditions for the first catalytic reaction include: The reaction temperature is 350–650℃; and / or, The reaction pressure is 0.1–0.5 MPa; and / or, The feed weight hourly space velocity (WHSV) of the naphtha feedstock I is 0.1–10 h⁻¹. -1 .

12. The preparation method according to any one of claims 1-11, characterized in that, In step (2), the conditions for the second catalytic reaction include: The reaction temperature is 350–650℃; and / or, The reaction pressure is 0.1–0.5 MPa; and / or, The weight hourly space velocity (WHSV) of the mixed feed of benzene, toluene, and methanol is 0.1–8 h⁻¹. -1 ; and / or, The molar ratio of methanol to the total amount of benzene and toluene used is 0.2 to 2.

13. The preparation method according to any one of claims 1-12, characterized in that, The second catalyst was prepared in situ in the second reaction zone; Preferably, the in-situ preparation method is as follows: the first catalyst is packed into the second reaction zone, then a silanizing agent is introduced to contact it, and the mixture is heated and calcined to obtain the second catalyst in situ; Preferably, the calcination temperature is 500–700°C; and / or the calcination time is 2–8 hours. Preferably, after calcination, the second reaction zone is directly cooled to its reaction temperature to carry out the second catalytic reaction.

14. A preparation system for use in the preparation method according to any one of claims 1-13.

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