A process for the production of xylene by toluene disproportionation

Abstract

The application discloses a toluene disproportionation method for producing dimethylbenzene. The method is characterized in that, under hydrogenation condition, toluene raw material is contacted with a catalyst to generate benzene and dimethylbenzene through toluene disproportionation reaction; the catalyst comprises ZSM-5 molecular sieve with a SiO2 / Al2O3 molar ratio of 10-100 and a binder; wherein, in the ZSM-5 molecular sieve, the amount of external surface acid accounts for 5-40% of the total acid amount, and the external specific surface area accounts for 5-30% of the total specific surface area of the ZSM-5 molecular sieve. The method provided by the application is used for toluene disproportionation reaction, and has the characteristics of high toluene conversion rate, high selectivity of products (benzene+dimethylbenzene), low by-product C9 + A low selectivity.

Description

Technical Field

[0001] This invention relates to a toluene disproportionation method, particularly a toluene disproportionation method for producing xylene. Background Technology

[0002] p-Xylene is an important organic raw material, mainly used in the production of purified terephthalic acid (PTA), which is a raw material for polyester production. The main types of polyester include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyarylates, with applications spanning the chemical fiber industry, packaging industry, electronics, medical and health industries, and construction. Due to the surge in demand for polyester, the added value of p-xylene, as a raw material for polyester, has also increased. Industrially, the toluene disproportionation unit is one of the most important processes for producing xylene in aromatic hydrocarbon complexes. This technology uses toluene, which has a relatively low added value but a high yield, as a raw material. Under the action of a catalyst, toluene undergoes a disproportionation reaction to produce the main products, benzene and xylene, thus solving the problem of toluene overproduction and meeting market demand.

[0003] Currently, most catalysts used for toluene disproportionation are molecular sieve catalysts, including mordenite zeolite (MOR), ZSM-5, SSZ-33, and TNU-9 reported in the literature. During catalyst synthesis, they are typically bonded to inorganic oxides and selectively loaded with metal components to improve catalyst activity and lifespan.

[0004] It is well known that zeolite molecular sieves act as shape-selective catalysts, and toluene shape-selective catalysts are based on the small molecular size of p-xylene, targeting the shape of the product. In some literature reports, researchers have compared the reaction performance of different types of catalysts, and the results show that ZSM-5 zeolite molecular sieve has superior reaction performance in terms of xylene selectivity (Reference 1 Ind. Eng. Chem. Res, 2011, 50, 3169-3183; Reference 2 Chemical Engineering Transactions, 2017, 57: 907-912).

[0005] In a toluene disproportionation system under hydrogen conditions, the main reaction is the disproportionation of toluene to produce benzene and xylene, but side reactions also occur. These side reactions primarily include xylene disproportionation to produce trimethylbenzene and benzene, dealkylation of trimethylbenzene to produce benzene and lower hydrocarbons, hydrogenation of benzene to produce cyclohexane, and subsequent cracking to produce lower hydrocarbons such as methane, ethane, and propane. The presence of these side reactions reduces the yield and selectivity of xylene, decreases the purity of the benzene product, and generates relatively low-value-added heavy aromatics C9A and C6A. 10 +A (Reference 3 Current Catalysis, 2013, 2, 96-110). The yield and selectivity of xylene isomers vary considerably depending on the performance of the catalyst and the degree of toluene conversion.

[0006] Researchers typically load one or more modifiers onto existing molecular sieve zeolites or disproportionation catalysts, or employ different modification methods, to obtain toluene shape-selective catalysts with high para-xylene selectivity. The basic principles for improving para-selectivity include reducing diffusion rate and passivating acidic sites on the catalyst's outer surface. Major modification methods include: selective removal of aluminum from the zeolite's outer surface (e.g., hydrothermal treatment), selective poisoning of the zeolite's outer surface acid by macromolecular bases, pre-coking treatment, and silicone oil modification. In addition, oxides of elements such as magnesium, nickel, and phosphorus can be loaded onto the catalyst. These methods can reduce the acidity of the catalyst's outer surface, and the modifiers can penetrate into the zeolite channels, modifying some of the inner surface acidity. Modification using metal oxides is very simple to operate and can achieve good acid coverage in a single step.

[0007] Currently, Mobil's MSTDP-3 technology, UOP's PXplus technology, GTC's GT-STDPM technology, and Sinopec Shanghai Research Institute of Petrochemical Technology's SD shape-selective disproportionation technology are all technologies for producing para-xylene from toluene disproportionation, and all have been industrially applied. However, with increasingly stringent national environmental protection requirements, these mature disproportionation technologies have also revealed several disadvantages. For example, the use of organic solvents poses a risk of organic matter leakage during solvent evaporation. The numerous impregnations of modifiers result in large solvent consumption and the generation of substantial amounts of waste liquid to be treated. Furthermore, the disproportionation reaction involves low-carbon hydrocarbons, as well as C9A and C6A hydrocarbons. 10 + The large yield of byproducts such as A results in high reaction energy consumption and increased production costs for enterprises. In addition, as a basic organic raw material, OX and MX are increasingly being developed for their applications. Some oil refining companies are no longer simply seeking high para-selectivity, but are paying more attention to improving the yield of xylene, the main disproportionation product.

[0008] CN101124186A uses nickel-modified mordenite zeolite as a catalyst. The catalyst first requires moderate sulfidation to passivate the active nickel before being used in the toluene disproportionation reaction. This catalyst contains the precious metal platinum, increasing its production cost. Furthermore, to increase xylene production, a hydrogen-to-hydrocarbon ratio of 3:1 is required.

[0009] CN104607236A describes a method for loading barium oxide precursor onto microporous molecular sieves ZSM-5 or MCM-22 via grinding and calcination for the toluene disproportionation reaction. This catalyst preparation method is simple and energy-efficient, but the reaction space velocity is relatively low, only 1 h⁻¹. -1The toluene conversion rate was low, with a maximum of only 35.7%.

[0010] Therefore, there is an urgent need for a reaction condition that can be used under harsh conditions of high space velocity and low hydrogen-to-hydrocarbon ratio, with high toluene conversion, good xylene selectivity, and C9 byproduct. + A catalyst synthesis method with low selectivity is used for xylene production. Summary of the Invention

[0011] To address the shortcomings of existing toluene disproportionation technologies, such as the inability of catalysts to operate under demanding conditions of high space velocity and low hydrogen-to-hydrocarbon ratio, and the low selectivity of xylene due to side reactions and the presence of C9 byproducts, this technology aims to address these issues. + The high selectivity of xylene leads to technical problems such as low production capacity and high energy consumption of the target product. This invention provides a novel toluene disproportionation method for producing xylene. This method, used in the toluene disproportionation reaction, under conditions of high space velocity and low hydrogen-to-hydrocarbon ratio, also features high toluene conversion, high product (benzene + xylene) selectivity, and low byproduct C9. + A. Characteristic of low selectivity.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0013] A toluene disproportionation method for producing xylene involves contacting a toluene feedstock with a catalyst under hydrogen-containing conditions to produce benzene and xylene through a toluene disproportionation reaction.

[0014] The catalyst comprises a ZSM-5 molecular sieve with a SiO2 / Al2O3 molar ratio of 10 to 100 and a binder;

[0015] In the ZSM-5 molecular sieve, the acid content on the outer surface accounts for 5-40% of the total acid content, and the specific surface area on the outer surface accounts for 5-30% of the total specific surface area of ​​the ZSM-5 molecular sieve.

[0016] In the above technical solution, the catalyst, by weight, comprises 10 to 90 parts of ZSM-5 molecular sieve and 10 to 90 parts of binder.

[0017] In the above technical solution, the SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is preferably 20 to 40.

[0018] In the above technical solution, the ZSM-5 molecular sieve in the catalyst is 60 to 80 parts by weight.

[0019] In the above technical solution, the acid content on the outer surface of the ZSM-5 molecular sieve accounts for 10-25% of the total acid content.

[0020] In the above technical solution, the external specific surface area of ​​the ZSM-5 molecular sieve accounts for 10-25% of the total specific surface area.

[0021] In the above technical solution, the catalyst also includes a modified metal element, selected from at least one element in Group VIB of the periodic table; the weight of the modified metal element is 0.01 to 1 part by weight.

[0022] In the above technical solution, the binder in the catalyst is derived from boehmite and can be synthesized by carbonization. The binder has a biporous distribution, wherein the small pore size is distributed in the range of 1-7 nm and the large pore size is distributed in the range of 8-20 nm. Preferably, the small pore size is distributed in the range of 3-6 nm and the large pore size is distributed in the range of 9-16 nm.

[0023] In the above technical solution, the preparation method of the ZSM-5 molecular sieve includes the following steps:

[0024] (1) After mixing the alkali source, template agent, and modifier with water, add the silicon source and aluminum source and mix to obtain synthesis solution A;

[0025] (2) ZSM-5 seed crystals were added to synthesis solution A to obtain synthesis solution B, which underwent two-stage crystallization treatment;

[0026] (3) The solid after crystallization in step (2) is subjected to ammonium exchange to obtain ZSM-5 molecular sieve for toluene disproportionation reaction.

[0027] In the above technical solution, the alkali source in step (1) is an inorganic alkali; the inorganic alkali includes any one or more of NaOH, KOH, and ammonia water; the template agent is any one or more of n-butylamine, tetrapropylammonium hydroxide, and tetrapropylammonium bromide; the modifier is any one or more of imidazole, methylimidazolium, and ethylimidazolium; the aluminum source includes any one or more of sodium aluminate, aluminum hydroxide, aluminum sulfate, aluminum chloride, and aluminum nitrate; and the silicon source includes any one or more of silica sol, silica fume, tetraethyl orthosilicate, and water glass.

[0028] In the above technical solution, based on the total weight of silicon source, aluminum source, alkali source, template agent and water, the mass of the modifier in step (1) is 1 to 5% of the total weight; the mass of the ZSM-5 seed crystal in step (2) is 5 to 10% of the total weight.

[0029] In the above technical solution, in step (2), the composition of the synthesis liquid B is as follows: the silicon source is SiO2, and the alkali source is OH. - The molar ratio of the template agent, aluminum source (calculated as Al2O3), and water (calculated as H2O) is 15-150:5-10:0.1-2:1:50-200.

[0030] In the above technical solution, in step (2), the two-stage crystallization is as follows: the first stage crystallization is carried out at 80-120℃ for 10-24 hours, and the second stage crystallization is carried out at 160-180℃ for 24-48 hours. The two-stage crystallization is dynamic crystallization, and the stirring rate is 20-140 rpm.

[0031] In the above technical solution, in step (2), after the crystallization step is completed, the product can be obtained from the obtained mixture by any conventionally known separation method and drying process. As a separation method, for example, methods of filtering, washing, and drying the obtained mixture can be employed. Here, the filtration, washing, and drying can be carried out in any manner conventionally known in the art. Specifically, as the filtration, the obtained product mixture can be simply filtered by vacuum filtration. As the washing, washing can be performed using deionized water and / or ethanol. As the drying temperature, 40–250°C, preferably 60–150°C, can be used; and as the drying time, 8–30 hours, preferably 10–20 hours, can be used. This drying can be carried out under normal pressure or under reduced pressure.

[0032] In the above technical solution, during the ammonium exchange in step (3), the ammonium salt is selected from at least one of ammonium nitrate, ammonium chloride, and ammonium sulfate, and the mass concentration of the ammonium salt solution is 5% to 20%. The ammonium exchange temperature is 65 to 95°C, the ammonium exchange time is 1 to 10 hours, and the number of ammonium exchanges is 1 to 5 times. The ammonium salt solution is mixed with the solid obtained after crystallization in step (2) at a mass ratio of 1 to 10:1. After the ammonium exchange is completed, the sample is filtered, washed with deionized water, and dried. After the ammonium exchange step is completed, the drying temperature is 50 to 150°C, preferably 80 to 120°C, and the drying time is 10 to 24 hours. This drying can be carried out under normal pressure or under reduced pressure.

[0033] In the above technical solution, the method for preparing the catalyst includes:

[0034] The catalyst is obtained by mixing ZSM-5 molecular sieve, binder, inorganic acid, and optionally modified metal salt solution, molding, drying, and calcining.

[0035] In the above technical solution, the inorganic acid is at least one of nitric acid or hydrochloric acid.

[0036] In the above technical solution, the modified metal is a metal component selected from Group VIB, and the modified metal salt solution is a salt solution prepared from at least one soluble compound selected from Group VIB metal components.

[0037] In the above technical solution, the mass ratio of ZSM-5 molecular sieve to binder is (10-90):(10-90); the amount of inorganic acid added is based on the actual molding condition during catalyst preparation.

[0038] In the above technical solution, the drying conditions are as follows: drying is carried out in air, nitrogen or inert atmosphere, the processing temperature is 0 to 150°C, and the time is 1 to 24 hours.

[0039] In the above technical solution, the calcination conditions are: the calcination operation time is 1-6 hours, and the processing temperature is 400-600℃.

[0040] In the above technical solution, the reaction conditions are: reaction temperature 300-500℃, reaction pressure 0.1-5MPa, hydrogen / toluene molar ratio 0.2-4, and feed weight hourly space velocity 1-8h. -1 .

[0041] In the above technical solution, the preferred reaction conditions are: a reaction temperature of 430–480℃, a reaction pressure of 1–3 MPa, a hydrogen / toluene molar ratio of 0.5–2, preferably 0.5–1.5, and a feed weight hourly space velocity of 4–6 h⁻¹. -1 .

[0042] Compared with the prior art, the method of the present invention has the following advantages:

[0043] (1) Toluene disproportionation is an acid-sensitive reaction. The inventors unexpectedly discovered that the high external surface acidity and high external specific surface area of ​​molecular sieves expose more external surface acidic sites. These external surface acidic sites, lacking shape-selective catalytic effects, increase the production of heavy aromatics and reduce the selectivity of the catalyst (B+X). Through research, the inventors found that ZSM-5 is used as the catalyst modification substrate because ZSM-5 has a channel structure (straight and serrated) with an opening diameter of 0.55-0.57 nm, which is smaller than that of mordenite, thus promoting the production of xylene in the toluene disproportionation reaction. By controlling the appropriate external surface acidity and external specific surface area ratio of ZSM-5 molecular sieves, selectively adding modifying metals for modification, and cooperating with a dual-pore distributed binder, the catalyst as a whole exhibits high activity and high selectivity for the target product xylene, while reducing the byproduct C9. + The selective nature of A.

[0044] (2) Using the method of the present invention, under the harsh conditions of high space velocity and low hydrogen-to-hydrogen ratio, the toluene conversion rate is high, and the product (benzene + xylene) selectivity can be higher than 89 wt%, with C9 as a byproduct. + A selectivity of less than 6 wt% indicates unexpected technical effects. Attached Figure Description

[0045] Figure 1 SEM image of the ZSM-5 molecular sieve prepared in Example 1;

[0046] Figure 2 SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 1;

[0047] Figure 3 SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 2;

[0048] Figure 4 This is a pore structure distribution diagram of pseudoboehmite A in Example 1;

[0049] Figure 5 The pore structure distribution diagram of pseudoboehmite B in Comparative Example 3 is shown.

[0050] Figure 6 Here is a SEM image of pseudoboehmite A from Example 1;

[0051] Figure 7 The image shown is a SEM image of pseudoboehmite B, which is shown in Comparative Example 3. Detailed Implementation

[0052] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited by these specific embodiments, but is determined by the claims.

[0053] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0054] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application’s filing, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0055] It should be noted that the two or more aspects (or embodiments) disclosed in the context of this specification can be arbitrarily combined with each other, and the resulting technical solutions (such as methods or systems) are part of the original disclosure of this specification and also fall within the protection scope of this invention.

[0056] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless being based on weight would not be in accordance with the common understanding of those skilled in the art.

[0057] In this invention, the acid content on the outer surface of the molecular sieve is determined by tert-butylamine titration, the total acid content is determined by n-butylamine titration, and the acid content inside the molecular sieve channels is calculated using the difference between the two methods. The tests were performed on a ZDJ-5 potential titrator from Shanghai Leici Instruments Co., Ltd. Before testing, the sample was ground into powder, activated at high temperature, and dehydrated. The powder was dispersed in an acetonitrile solution and stirred until the potential stabilized. An organic amine solution was gradually added dropwise, and the potential change was recorded simultaneously. Titration continued until the potential remained essentially constant. The number of acidic sites added was calculated based on the amount of organic amine consumed.

[0058] In this invention, specific surface area includes external specific surface area and internal specific surface area. The specific surface area, external specific surface area, and pore structure in the embodiments and comparative examples of this invention were determined using nitrogen adsorption-desorption method. The tests were performed using an ASAP2020 automated physical adsorption instrument from Micromeritics Instruments, Inc., USA. High-purity nitrogen was used as the adsorbate, and the measurements were conducted at -196°C. A vacuum pretreatment at 350°C for 4 hours was required before the test. Specific surface area and external surface area were calculated using the BET formula, and pore structure analysis was performed using the BJH method.

[0059] In this invention, scanning electron microscopy (SEM) tests were performed on a Nova NanoSEM 450 from FEI Corporation in the United States, with an accelerating voltage of 30 kV.

[0060] In this invention, the conversion rate T in the toluene disproportionation reaction 转 (wt%), Benzene + Xylene Selectivity S B+X The formula for calculating (wt%) is as follows, where the amounts of reactants and products are calculated as mass fractions.

[0061]

[0062]

[0063] Example 1

[0064] First, ZSM-5 molecular sieve A was synthesized.

[0065] 16 g of sodium hydroxide, 26.6 g of tetrapropylammonium bromide, 21.4 g of methylimidazole, and 180 g of water were thoroughly mixed. Then, 528 g of tetraethyl orthosilicate and 8.3 g of sodium aluminate were added and thoroughly mixed to obtain synthesis solution A. Next, 75 g of ZSM-5 seed crystals were added and stirred thoroughly to obtain synthesis solution B. Synthesis solution B was crystallized at 120°C for 20 hours, then at 170°C for 40 hours, with a stirring rate of 60 rpm. It was then dried at 120°C for 8 hours to obtain ZSM-5 molecular sieve. The composition of the mixture B, with silicon source calculated as SiO2 and alkali source as OH... -The molar ratio of aluminum nitrate (calculated as Al2O3) to water (calculated as H2O) is 40:8:2:1:200. The resulting ZSM-5 molecular sieve requires ammonium exchange treatment. The mass concentration of the ammonium nitrate solution in the ammonium exchange is 10%, the solid-liquid ratio is 5:1, the temperature is 80℃, the exchange time is 6 hours, and the exchange is performed 4 times. After ammonium exchange, the molecular sieve needs to be dried at 120℃ for 8 hours to obtain ZSM-5 molecular sieve for toluene disproportionation.

[0066] SEM image of ZSM-5 molecular sieve A is shown below. Figure 1 As shown, the micron-sized blocky molecular sieve has a relatively small external surface area.

[0067] The synthesized ZSM-5 molecular sieve A had a SiO2 / Al2O3 molar ratio of 38. The acid content on the outer surface of ZSM-5 molecular sieve A was 105 μmol tert-butylamine / g, the total acid content was 678 μmol n-butylamine / g, and the acid content within the pores was 573 μmol tert-butylamine / g. The BET specific surface area of ​​ZSM-5 molecular sieve A was 354 m² / g. 2 / g, with an external specific surface area of ​​57m² 2 / g.

[0068] 70 g of ZSM-5 molecular sieve A was mixed evenly with 30 g of boehmite A. Then, 3 mL of pure nitric acid and 60 g of a 1.5% ammonium heptamolybdate tetrahydrate solution were added. After kneading until homogeneous, the mixture was extruded and shaped into strips. Catalyst A was obtained by drying at 120°C for 4 hours and calcining at 540°C for 3 hours. The pore size distribution diagram of boehmite A is shown below. Figure 4 It has a dual-pore distribution; see SEM image below. Figure 6 As can be seen from the SEM image, the structure of pseudoboehmite A is relatively loose and it is easy to produce macroporous distribution.

[0069] Example 2

[0070] First, ZSM-5 molecular sieve B was synthesized.

[0071] 16 g of sodium hydroxide, 26.6 g of tetrapropylammonium bromide, 53.5 g of methylimidazole, and 180 g of water were thoroughly mixed. Then, 528 g of tetraethyl orthosilicate and 8.3 g of sodium aluminate were added and thoroughly mixed to obtain synthesis solution A. Next, 75 g of ZSM-5 seed crystals were added and stirred thoroughly to obtain synthesis solution B. Synthesis solution B was crystallized at 120°C for 20 hours, then at 170°C for 40 hours, with a stirring rate of 60 rpm. After drying at 120°C for 8 hours, ZSM-5 molecular sieve was obtained. The composition of the mixture B is as follows: silicon source is SiO2, and alkali source is OH... -The molar ratio of aluminum nitrate (calculated as Al2O3) to water (calculated as H2O) is 40:8:2:1:200. The obtained ZSM-5 molecular sieve needs to undergo ammonium exchange treatment. The mass concentration of the ammonium nitrate solution in the ammonium exchange is 10%, the solid-liquid ratio is 5:1, the temperature is 80℃, the exchange time is 6 hours, and the exchange is performed 4 times. After ammonium exchange, the molecular sieve needs to be dried at 120℃ for 8 hours to obtain ZSM-5 molecular sieve for toluene disproportionation reaction.

[0072] SEM images of ZSM-5 molecular sieve B and Figure 1 resemblance.

[0073] The synthesized ZSM-5 molecular sieve B had a SiO2 / Al2O3 molar ratio of 38. The acid content on the outer surface of ZSM-5 molecular sieve B was 60 μmol tert-butylamine / g, the total acid content was 753 μmol n-butylamine / g, and the acid content within the pores was 693 μmol tert-butylamine / g. The BET specific surface area of ​​ZSM-5 molecular sieve B was 362 m² / g. 2 / g, with an external specific surface area of ​​59m² 2 / g.

[0074] Take 70g of ZSM-5 molecular sieve B, mix it evenly with 30g of pseudoboehmite A, add 3ml of pure nitric acid and 60g of 1.5% ammonium heptamolybdate tetrahydrate solution, knead evenly, extrude into strips, dry at 120℃ for 4 hours and calcine at 540℃ for 3 hours to obtain catalyst B.

[0075] Example 3

[0076] First, ZSM-5 molecular sieve C was synthesized.

[0077] 16 g of sodium hydroxide, 26.6 g of tetrapropylammonium bromide, 10.7 g of methylimidazole, and 180 g of water were thoroughly mixed. Then, 528 g of tetraethyl orthosilicate and 8.3 g of sodium aluminate were added and thoroughly mixed to obtain synthesis solution A. Next, 75 g of ZSM-5 seed crystals were added and stirred thoroughly to obtain synthesis solution B. Synthesis solution B was crystallized at 120°C for 20 hours, then at 170°C for 40 hours, with a stirring rate of 60 rpm. After drying at 120°C for 8 hours, ZSM-5 molecular sieve was obtained. The composition of the mixture B, with silicon source calculated as SiO2 and alkali source as OH... - The molar ratio of aluminum nitrate (calculated as Al2O3) to water (calculated as H2O) is 40:8:2:1:200. The obtained ZSM-5 molecular sieve needs to undergo ammonium exchange treatment. The mass concentration of the ammonium nitrate solution in the ammonium exchange is 10%, the solid-liquid ratio is 5:1, the temperature is 80℃, the exchange time is 6 hours, and the exchange is performed 4 times. After ammonium exchange, the molecular sieve needs to be dried at 120℃ for 8 hours to obtain ZSM-5 molecular sieve for toluene disproportionation reaction.

[0078] SEM image of ZSM-5 molecular sieve C and Figure 1 resemblance.

[0079] The synthesized ZSM-5 molecular sieve had a SiO2 / Al2O3 molar ratio of 38. The acid content on the outer surface of the ZSM-5 molecular sieve was 267 μmol tert-butylamine / g, the total acid content was 693 μmol n-butylamine / g, and the acid content within the pores was 426 μmol tert-butylamine / g. The BET specific surface area of ​​the ZSM-5 molecular sieve was 359 m² / g. 2 / g, with an external specific surface area of ​​62m² 2 / g.

[0080] Take 70g of ZSM-5 molecular sieve C, mix it evenly with 30g of pseudoboehmite A, add 3ml of pure nitric acid and 60g of 1.5% ammonium heptamolybdate tetrahydrate solution, knead evenly, extrude into strips, dry at 120℃ for 4 hours and calcine at 540℃ for 3 hours to obtain catalyst C.

[0081] Example 4

[0082] First, ZSM-5 molecular sieve D was synthesized.

[0083] 16 g of sodium hydroxide, 26.6 g of tetrapropylammonium bromide, 21.4 g of methylimidazole, and 180 g of water were thoroughly mixed. Then, 528 g of tetraethyl orthosilicate and 8.3 g of sodium aluminate were added and thoroughly mixed to obtain synthesis solution A. Next, 107 g of ZSM-5 seed crystals were added and stirred thoroughly to obtain synthesis solution B. Synthesis solution B was crystallized at 120°C for 20 hours, then at 170°C for 40 hours, with a stirring rate of 60 rpm. After drying at 120°C for 8 hours, ZSM-5 molecular sieve was obtained. The composition of the mixture B, with silicon source calculated as SiO2 and alkali source as OH... - The molar ratio of aluminum nitrate (calculated as Al2O3) to water (calculated as H2O) is 40:8:2:1:200. The obtained ZSM-5 molecular sieve needs to undergo ammonium exchange treatment. The mass concentration of the ammonium nitrate solution in the ammonium exchange is 10%, the solid-liquid ratio is 5:1, the temperature is 80℃, the exchange time is 6 hours, and the exchange is performed 4 times. After ammonium exchange, the molecular sieve needs to be dried at 120℃ for 8 hours to obtain ZSM-5 molecular sieve for toluene disproportionation reaction.

[0084] SEM images of ZSM-5 molecular sieve D and Figure 1 resemblance.

[0085] The synthesized ZSM-5 molecular sieve D has a SiO2 / Al2O3 molar ratio of 38. The acid content on the outer surface of ZSM-5 molecular sieve D is 102 μmol tert-butylamine / g, the total acid content is 675 μmol n-butylamine / g, and the acid content within the pores is 573 μmol tert-butylamine / g. The BET specific surface area of ​​ZSM-5 molecular sieve D is 398 m² / g. 2 / g, with an external specific surface area of ​​24m² 2 / g.

[0086] Take 70g of ZSM-5 molecular sieve D, mix it evenly with 30g of pseudoboehmite A, add 3ml of pure nitric acid and 60g of 1.5% ammonium heptamolybdate tetrahydrate solution, knead evenly, extrude into strips, dry at 120℃ for 4 hours and calcine at 540℃ for 3 hours to obtain catalyst D.

[0087] Example 5

[0088] First, ZSM-5 molecular sieve E was synthesized.

[0089] 16 g of sodium hydroxide, 26.6 g of tetrapropylammonium bromide, 21.4 g of methylimidazole, and 180 g of water were thoroughly mixed. Then, 528 g of tetraethyl orthosilicate and 8.3 g of sodium aluminate were added and thoroughly mixed to obtain synthesis solution A. Next, 53.5 g of ZSM-5 seed crystals were added and stirred thoroughly to obtain synthesis solution B. Synthesis solution B was crystallized at 120°C for 20 hours, then at 170°C for 40 hours, with a stirring rate of 60 rpm. After drying at 120°C for 8 hours, ZSM-5 molecular sieve was obtained. The composition of the mixture B, with silicon source calculated as SiO2 and alkali source as OH... - The molar ratio of aluminum nitrate (calculated as Al2O3) to water (calculated as H2O) is 40:8:2:1:200. The obtained ZSM-5 molecular sieve needs to undergo ammonium exchange treatment. The mass concentration of the ammonium nitrate solution in the ammonium exchange is 10%, the solid-liquid ratio is 5:1, the temperature is 80℃, the exchange time is 6 hours, and the exchange is performed 4 times. After ammonium exchange, the molecular sieve needs to be dried at 120℃ for 8 hours to obtain ZSM-5 molecular sieve for toluene disproportionation reaction.

[0090] SEM images of ZSM-5 molecular sieve E and Figure 1 resemblance.

[0091] The synthesized ZSM-5 molecular sieve E has a SiO2 / Al2O3 molar ratio of 38. The outer surface acidity of ZSM-5 molecular sieve D is 96 μmol tert-butylamine / g, the total acidity is 680 μmol n-butylamine / g, and the acidity within the pores is 584 μmol tert-butylamine / g. The BET specific surface area of ​​ZSM-5 molecular sieve E is 395 m² / g. 2 / g, with an external specific surface area of ​​116m² 2 / g.

[0092] Take 70g of ZSM-5 molecular sieve E, mix it evenly with 30g of pseudoboehmite A, add 3ml of pure nitric acid and 60g of 1.5% ammonium heptamolybdate tetrahydrate solution, knead evenly, extrude into strips, dry at 120℃ for 4 hours and calcine at 540℃ for 3 hours to obtain catalyst E.

[0093] Example 6

[0094] Take 70g of ZSM-5 molecular sieve A, mix it evenly with 30g of pseudoboehmite A, add 3ml of pure nitric acid and 60g of 0.3% ammonium molybdate solution, knead evenly, extrude into strips, dry at 120℃ for 4 hours and calcine at 540℃ for 3 hours to obtain catalyst F.

[0095] Comparative Example 1

[0096] First, ZSM-5 molecular sieve F was synthesized.

[0097] 16 g of sodium hydroxide, 26.6 g of tetrapropylammonium bromide, and 180 g of water were thoroughly mixed, followed by the addition of 528 g of tetraethyl orthosilicate and 8.3 g of sodium aluminate, and the mixture was thoroughly mixed to obtain synthesis solution A. Then, 75 g of ZSM-5 seed crystals were added, and the mixture was stirred thoroughly to obtain synthesis solution B. Synthesis solution B was crystallized at 120°C for 20 hours, followed by crystallization at 170°C for 40 hours, with a stirring rate of 60 rpm. The mixture was then dried at 120°C for 8 hours to obtain ZSM-5 molecular sieve. The composition of the mixture B, with silicon source calculated as SiO2 and alkali source as OH... - The molar ratio of aluminum nitrate (calculated as Al2O3) to water (calculated as H2O) is 40:8:2:1:200. The obtained ZSM-5 molecular sieve needs to undergo ammonium exchange. The mass concentration of the ammonium nitrate solution in the ammonium exchange is 10%, the solid-liquid ratio is 5:1, the temperature is 80℃, the exchange time is 6 hours, and the exchange is performed 4 times. After ammonium exchange, the molecular sieve needs to be dried at 120℃ for 8 hours to obtain ZSM-5 molecular sieve for toluene disproportionation reaction.

[0098] The synthesized ZSM-5 molecular sieve F had a SiO2 / Al2O3 molar ratio of 36. The acid content on the outer surface of ZSM-5 molecular sieve F was 306 μmol tert-butylamine / g, the total acid content was 689 μmol n-butylamine / g, and the acid content within the pores was 383 μmol tert-butylamine / g. The BET specific surface area of ​​ZSM-5 molecular sieve F was 346 m² / g. 2 / g, with an external specific surface area of ​​78m² 2 / g. SEM image of ZSM-5 molecular sieve F is shown below. Figure 2 As shown, this is a nano-molecular sieve.

[0099] Take 70g of ZSM-5 molecular sieve F, mix it evenly with 30g of pseudoboehmite A, add 3ml of pure nitric acid and 60g of 1.5% ammonium heptamolybdate tetrahydrate solution, knead evenly, extrude into strips, dry at 120℃ for 4 hours and calcine at 540℃ for 3 hours to obtain catalyst G.

[0100] Comparative Example 2

[0101] First, ZSM-5 molecular sieve G was synthesized.

[0102] 16 g of sodium hydroxide, 26.6 g of tetrapropylammonium bromide, 21.4 g of methylimidazole, and 180 g of water were thoroughly mixed. Then, 528 g of tetraethyl orthosilicate and 8.3 g of sodium aluminate were added and thoroughly mixed to obtain synthesis solution A. Synthesis solution A was crystallized at 120 °C for 20 hours, and then at 170 °C for 40 hours, with a stirring rate of 60 rpm. After drying at 120 °C for 8 hours, ZSM-5 molecular sieve was obtained. The composition of the mixture B, wherein the silicon source is calculated as SiO2 and the alkali source is calculated as OH... - The molar ratio of aluminum nitrate (calculated as Al2O3) to water (calculated as H2O) is 40:8:2:1:200. The obtained ZSM-5 molecular sieve needs to undergo ammonium exchange treatment. The mass concentration of the ammonium nitrate solution in the ammonium exchange is 10%, the solid-liquid ratio is 5:1, the temperature is 80℃, the exchange time is 6 hours, and the exchange is performed 4 times. After ammonium exchange, the molecular sieve needs to be dried at 120℃ for 8 hours to obtain ZSM-5 molecular sieve for toluene disproportionation reaction.

[0103] The synthesized ZSM-5 molecular sieve G had a SiO2 / Al2O3 molar ratio of 37. The acid content on the outer surface of ZSM-5 molecular sieve G was 113 μmol tert-butylamine / g, the total acid content was 682 μmol n-butylamine / g, and the acid content within the pores was 569 μmol tert-butylamine / g. The BET specific surface area of ​​ZSM-5 molecular sieve G was 334 m². 2 / g, with an external specific surface area of ​​10⁸ m² 2 / g. SEM image of ZSM-5 molecular sieve G is shown below. Figure 3 As shown, it has a typical nanoparticle stacked structure with a relatively large outer surface.

[0104] Take 70 g of ZSM-5 molecular sieve G, mix it evenly with 30 g of pseudoboehmite A, add 3 ml of pure nitric acid and 60 g of 1.5% ammonium heptamolybdate tetrahydrate solution, knead evenly, extrude into strips, dry at 120℃ for 4 hours and calcine at 540℃ for 3 hours to obtain catalyst H.

[0105] Comparative Example 3

[0106] The preparation method of ZSM-5 molecular sieve is the same as in Example 1.

[0107] 70 g of ZSM-5 molecular sieve A with a SiO2 / Al2O3 molar ratio of 38 was mixed thoroughly with 30 g of pseudoboehmite B. Then, 3 mL of pure nitric acid and 60 g of a 1.5% ammonium heptamolybdate tetrahydrate solution were added. After kneading until homogeneous, the mixture was extruded and shaped into strips. Catalyst I was obtained by drying at 120°C for 4 hours and calcining at 540°C for 3 hours. The pore size distribution diagram of pseudoboehmite B is shown below. Figure 5 The distribution is unipore; SEM image is shown below. Figure 7 As can be seen from the SEM image, the structure of pseudoboehmite B is relatively compact, and the pore distribution is mostly concentrated in the micropore distribution.

[0108] Example 7

[0109] The preparation method of ZSM-5 molecular sieve is the same as in Example 1.

[0110] Take 70g of ZSM-5 molecular sieve A with a SiO2 / Al2O3 molar ratio of 38, mix it evenly with 30g of pseudoboehmite A, add 3ml of pure nitric acid and 60g of deionized water, knead evenly, extrude into strips, dry at 120℃ for 4 hours and calcine at 540℃ for 3 hours to obtain catalyst J.

[0111] The performance of toluene disproportionation reaction was evaluated using catalysts A through J in a fixed-bed reactor under the following conditions: pure toluene as feedstock, catalyst loading of 5 g, and toluene feed weight hourly space velocity of 5 h⁻¹. -1 The reaction hydrogen-to-hydrocarbon molar ratio was 1.2, and the reaction pressure was 3.0 MPa. The reaction temperature was adjusted to control the toluene conversion rate to approximately 50%, and the evaluation results are shown in Table 1.

[0112] Table 1

[0113]

[0114]

[0115] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A toluene disproportionation method for producing xylene, wherein under hydrogen-containing conditions, toluene feedstock comes into contact with a catalyst to undergo a toluene disproportionation reaction to produce benzene and xylene; The catalyst comprises ZSM-5 molecular sieve with a SiO2 / Al2O3 molar ratio of 10 to 100, a binder, and modified metal elements; in, In the ZSM-5 molecular sieve, the acid content on the outer surface accounts for 5-40% of the total acid content, and the specific surface area on the outer surface accounts for 5-30% of the total specific surface area of ​​the ZSM-5 molecular sieve. The binder in the catalyst is derived from boehmite; the binder has a biporous distribution, wherein the small pore size is distributed in the range of 1~7 nm and the large pore size is distributed in the range of 8~20 nm. The modified metal is selected from at least one element in Group VIB of the periodic table.

2. The method according to claim 1, characterized in that, By weight, ZSM-5 molecular sieve is 10-90 parts and binder is 10-90 parts.

3. The method according to claim 1, characterized in that, The modified metal element is 0.01 to 1 part by weight.

4. The method according to claim 1, characterized in that, The binder in the catalyst is derived from boehmite; the binder has a biporous distribution, wherein the small pore size is distributed in the range of 3~6 nm and the large pore size is distributed in the range of 9~16 nm.

5. The method according to claim 1, characterized in that, The preparation method of the ZSM-5 molecular sieve includes the following steps: (1) After mixing the alkali source, template agent, and modifier with water, add the silicon source and aluminum source and mix to obtain synthesis solution A; (2) ZSM-5 seed crystals were added to synthesis solution A to obtain synthesis solution B, which underwent two-stage crystallization treatment; (3) The solid after crystallization in step (2) is subjected to ammonium exchange to obtain ZSM-5 molecular sieve for toluene disproportionation reaction.

6. The method according to claim 5, characterized in that, Based on the total weight of silicon source, aluminum source, alkali source, template agent and water, the mass of the modifier mentioned in step (1) is 1~5% of the total weight; the mass of the ZSM-5 seed crystal mentioned in step (2) is 5~10% of the total weight.

7. The method according to claim 5, characterized in that, In step (2), the composition of the synthesis solution B is as follows: silicon source is SiO2, and alkali source is OH. - The molar ratio of the template agent, aluminum source (calculated as Al2O3), and water (calculated as H2O) is 15~150:5~10:0.1~2:1:50~200.

8. The method according to claim 5, characterized in that, In step (2), the two-stage crystallization is as follows: the first stage crystallization is carried out at 80~120℃ for 10~24 hours, and the second stage crystallization is carried out at 160~180℃ for 24~48 hours; the two-stage crystallization is dynamic crystallization with a stirring rate of 20~140 rpm.

9. The method according to claim 5, characterized in that, In the ammonium exchange described in step (3), the ammonium salt is selected from at least one of ammonium nitrate, ammonium chloride, and ammonium sulfate, and the mass concentration of the ammonium salt solution is 5% to 20%; the ammonium exchange temperature is 65 to 95°C, the ammonium exchange time is 1 to 10 hours, and the number of ammonium exchanges is 1 to 5 times; the ammonium salt solution and the solid obtained after crystallization in step (2) are mixed at a mass ratio of 1 to 10:

1.

10. The method according to claim 1, characterized in that, The method for preparing the catalyst includes: The catalyst is obtained by mixing ZSM-5 molecular sieve, binder, inorganic acid, and optionally modified metal salt solution, molding, drying, and calcining.

11. The method according to claim 1, characterized in that, The reaction conditions are as follows: reaction temperature 300~500℃, reaction pressure 0.1~5MPa, hydrogen / toluene molar ratio 0.2~4, and feed weight hourly space velocity 1~8h. -1 .

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