Catalyst for methyl benzene aromatic hydrocarbon demethylation reaction and methyl benzene aromatic hydrocarbon demethylation method

Abstract

The invention provides a catalyst for methyl benzene aromatic hydrocarbon demethylation reaction, the catalyst is used for methyl benzene aromatic hydrocarbon demethylation reaction to prepare a compound shown in a formula (I), the catalyst is composed of metal and a carrier, the metal is one or two or more of nickel, rhodium, yttrium, iron, cobalt, zinc, gallium, copper, manganese, molybdenum and cerium, and the carrier is one or more of metal and carrier. The carrier is one or two or more of MgO, Al2O3, CrO3, SiO2 and a molecular sieve. The catalyst provided by the invention catalyzes demethylation of methyl benzene aromatic hydrocarbons in a high-temperature water vapor environment to generate light aromatic hydrocarbons. According to the methyl benzene aromatic hydrocarbon demethylation reaction method constructed by using the catalyst, the continuous reaction regeneration process of the catalyst can be realized, and high-selectivity, low-cost and continuous production is realized. The catalyst can be recycled and has high efficiency and economical efficiency, and a green and low-carbon industrial solution is provided for light aromatic hydrocarbon production.

Description

Technical Field

[0001] The present application relates to the fields of petrochemical and coal chemical processing, and in particular to a catalyst and a method for demethylating methylbenzene aromatic hydrocarbons. Background Art

[0002] As the core building block of the "triolefins and triphenyls" chemical industry, innovations in benzene production technology are closely intertwined with the development of high-end industrial chains such as polymer materials, pharmaceuticals, and pesticides. Through reactions such as alkylation, chlorination, and nitration, benzene can be derived into key intermediates such as styrene, phenol, and cyclohexane (ultimately used in high-value-added products such as nylon, polyurethane, and polyester). While naphtha catalytic reforming, a traditional mainstream process, can convert linear alkanes into aromatics using platinum-based catalysts, benzene accounts for less than 10% of the product. The yield of coking benzene, a byproduct of coal coking, is even lower, typically below 1%. In recent years, methanol aromatization technology has achieved efficient conversion of methanol to aromatics using molecular sieve catalysis, significantly increasing the total amount of liquid aromatics recovered, but the benzene yield remains around 10%. The fundamental reason for this is that after the aromatic ring is formed, the methylation reaction becomes thermodynamically advantageous, resulting in a surge in the proportion of methyl-substituted aromatics such as toluene, xylenes, and trimethylbenzenes. Similarly, while one-step production of aromatics from syngas or CO2 has achieved breakthroughs in feedstock diversification, the product distribution is more skewed toward heavier aromatics (such as trimethylbenzene and tetramethylbenzene), and benzene selectivity remains limited. Methane aromatization, the only technology capable of directly producing high-purity benzene (with a liquid product benzene content of up to 90%), has been hampered by stringent reaction temperatures (>700°C) and rapid catalyst deactivation due to carbon deposition, hindering industrialization.

[0003] To address the high proportion of heavy aromatics, the industry has developed dealkylation processes for toluene and polymethylbenzenes. For example, hydrothermal cracking or hydrocatalytic cracking can significantly increase benzene yields through dealkylation. However, these processes consume large amounts of hydrogen to convert the removed methyl groups into methane, resulting in inefficient use of hydrogen resources and weakening the economic viability of the entire industry chain due to the low economic value of methane.

[0004] Application Contents To address the aforementioned issues in the prior art, the present application provides a catalyst for demethylating methylbenzene aromatics to produce light aromatics under steam conditions, and a method for demethylating methylbenzene aromatics using the catalyst. This catalyst can effectively utilize the large amounts of high-temperature steam and polymethylbenzenes generated by various chemical processes. The specific technical solutions of the present application are as follows: A catalyst for the demethylation reaction of methylbenzene aromatic hydrocarbons, wherein: The catalyst is used for the demethylation reaction of methylbenzene aromatic hydrocarbons to prepare the compound shown in the following formula (I):

[0005] Formula (I) R1, R2, R3, R4 and R5 are hydrogen or methyl; The catalyst is composed of a metal and a carrier, wherein the metal is one or two or more of nickel, rhodium, yttrium, iron, cobalt, zinc, gallium, copper, manganese, molybdenum and cerium, and the carrier is one or two or more of MgO, Al2O3, CrO3, SiO2 and molecular sieve.

[0006] Specifically, the mass fraction of the metal is 0.03% to 5%.

[0007] Specifically, the molecular sieve is one, two or three of Y-type molecular sieve, β-type molecular sieve and ZSM-5 type molecular sieve.

[0008] The present application also provides the use of the above catalyst in the demethylation reaction of methylbenzene aromatic hydrocarbons.

[0009] A method for demethylating methylbenzene aromatic hydrocarbons, comprising: The methylbenzene aromatic hydrocarbons, water vapor and catalyst are contacted to react to form the compound shown in the following formula (I):

[0010] Formula (I) R1, R2, R3, R4 and R5 are hydrogen or methyl; The reaction temperature is 520-600° C.; the methylbenzene aromatic hydrocarbons are one or two or more of toluene, xylene, trimethylbenzene, tetramethylbenzene, pentamethylbenzene and hexamethylbenzene.

[0011] Specifically, before the methylbenzene aromatic hydrocarbons and water vapor are brought into contact with the catalyst for reaction, the process further includes: vaporizing the methylbenzene aromatic hydrocarbons.

[0012] Specifically, the catalyst is the catalyst mentioned above.

[0013] Specifically, the method further includes a step of preheating the catalyst before the catalyst contacts and reacts with the methylbenzene aromatic hydrocarbon.

[0014] Specifically, the preheating temperature is 550-650°C.

[0015] Specifically, the preheating step includes: A preheating gas is introduced into the catalyst, wherein the preheating gas temperature is 850-1000° C. and the gas is one or two or more of air, nitrogen, carbon dioxide and flue gas.

[0016] The catalyst provided in this application catalyzes the demethylation of methylbenzene aromatics to produce light aromatics in a high-temperature steam environment. The catalyst achieves high selectivity, low cost, and continuous production. Furthermore, the catalyst is recyclable, combining high efficiency and economical efficiency, providing a green, low-carbon industrial solution for the production of light aromatics. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings: Figure 1 The flow chart of the preparation process is shown, in which vaporized methylbenzene aromatic hydrocarbons are used as starting materials and are contacted with water vapor and a catalyst to react to produce the compound of formula (I).

[0018] Reference numerals: 1: reactor; 2: catalyst regenerator; 3: first pipeline; 4: second pipeline; 5: third pipeline; 6: fourth pipeline; 7: fifth pipeline; 8: sixth pipeline; 9: seventh pipeline; 10: eighth pipeline; 11: ninth pipeline. DETAILED DESCRIPTION

[0019] The present application is described in detail below in conjunction with the described embodiments. Although specific embodiments of the present application are shown, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0020] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" are open-ended terms and should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present application, but the description is based on the general principles of the specification and is not intended to limit the scope of the present application. The scope of protection of this application shall be as defined by the attached claims.

[0021] The present application provides a catalyst for the demethylation reaction of methylbenzene aromatic hydrocarbons, wherein: The catalyst is used for the demethylation reaction of methylbenzene aromatic hydrocarbons to prepare the compound shown in the following formula (I):

[0022] Formula (I) R1, R2, R3, R4 and R5 are hydrogen or methyl; The catalyst is composed of a metal and a carrier, wherein the metal is one or two or more of nickel, rhodium, yttrium, iron, cobalt, zinc, gallium, copper, manganese, molybdenum and cerium, and the carrier is one or two or more of MgO, Al2O3, CrO3, SiO2 and molecular sieve.

[0023] Specifically, the catalyst achieves the demethylation of methylbenzene-type aromatic hydrocarbons through the synergistic effect of the metal and the carrier: the active site of the metal promotes the breakage of the CC bond and water vapor activation, generating hydroxyl radicals and active hydrogen, driving the demethylation reaction and inhibiting the formation of methane; the molecular sieve carrier attacks the methyl group through the Brønsted acid site, and its microporous-mesoporous structure optimizes mass transfer and limits side reactions; the oxide carrier enhances the thermal stability of the catalyst and disperses the metal particles.

[0024] In one embodiment, the mass fraction of the metal is 0.03% to 5%, for example, 0.03%, 0.05%, 0.08%, 0.1%, 0.5%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, or 5%, or any two of these. At low loadings, the precious metals provide efficient and cost-effective catalysis, with benzene selectivity reaching 80%. At medium loadings, the transition metals work in conjunction with the molecular sieve support, maintaining selectivity for light aromatics while reducing carbon deposition. At high loadings, the stable conversion of complex feedstocks such as polymethylbenzenes is ensured.

[0025] In one embodiment, the molecular sieve is one, two, or three of a Y-type molecular sieve, a β-type molecular sieve, and a ZSM-5 molecular sieve. Through the flexible combination of single or composite components, the advantages of each molecular sieve are fully utilized: the Y-type molecular sieve provides a large pore structure to promote the diffusion of large molecules such as methylbenzene, the β-type molecular sieve increases the density of acidic sites to improve demethylation activity, and the ZSM-5 molecular sieve utilizes its shape selectivity to selectively suppress side reactions.

[0026] In one embodiment, the molecular sieve is a Y-type molecular sieve.

[0027] In one embodiment, the molecular sieve is a β-type molecular sieve.

[0028] In one embodiment, the molecular sieve is a ZSM-5 molecular sieve.

[0029] In a specific embodiment, the molecular sieve is a Y-type molecular sieve or a β-type molecular sieve.

[0030] In a specific embodiment, the molecular sieve is Y-type molecular sieve and ZSM-5 type molecular sieve.

[0031] In a specific embodiment, the molecular sieve is a β-type molecular sieve or a ZSM-5 type molecular sieve.

[0032] In a specific embodiment, the molecular sieve is Y-type molecular sieve, β-type molecular sieve and ZSM-5 type molecular sieve.

[0033] The present application also provides the use of the above catalyst in the preparation of C6-C8 aromatic hydrocarbons.

[0034] The present application provides a method for preparing C6-C8 aromatic hydrocarbons, which comprises: Methylbenzene aromatics, water vapor, and a catalyst are brought into contact to react and produce the compound of formula (I). The reaction temperature is 520-600°C. The methylbenzene aromatics are one, two, or more of toluene, xylene, trimethylbenzene, tetramethylbenzene, pentamethylbenzene, and hexamethylbenzene. A catalytic demethylation reaction converts polymethylated aromatics into high-value-added products such as benzene, toluene, and xylene. The selective demethylation of polymethylbenzenes is achieved through the synergistic action of the catalyst and water vapor. The water vapor acts as a reaction medium, promoting the cleavage of methyl groups to produce synthesis gas (CO + H2) and effectively suppressing catalyst deactivation by carbon accumulation.

[0035] In one embodiment, the reaction temperature is 520-600° C., for example, 520° C., 523° C., 525° C., 528° C., 530° C., 533° C., 535° C., 538° C., 540° C., 543° C., 545° C., 548° C., 550° C., 553° C., 555° C., 558° C., 560° C., 563° C., 565° C., 568° C., 570° C., 573° C., 575° C., 578° C., 580° C., 583° C., 585° C., 588° C., 590° C., 593° C., 595° C., 598° C., and 600° C. This temperature range matches the acid potential of the catalyst, significantly reducing energy consumption compared to conventional cracking processes.

[0036] In one embodiment, the catalyst is the catalyst described above.

[0037] In a specific embodiment, the step of preheating the catalyst is further included before the catalyst is contacted with the methylbenzene aromatic hydrocarbon to react.

[0038] Specifically, the preheating step eliminates the cold start phase in conventional processes, ensuring that an efficient demethylation reaction can be initiated the moment the raw materials contact the catalyst. Uniform preheating reduces the axial temperature difference of the catalyst bed, effectively preventing excessive cracking caused by local overheating, and reducing the amount of by-products such as methane. It is particularly suitable for raw materials with a high coking tendency such as polymethylbenzenes of tetra-hexamethylbenzene, reducing the initial carbon deposition rate of the catalyst after preheating, and significantly extending the single-cycle operation time.

[0039] In a specific embodiment, the preheating temperature is 550-650°C, for example, it can be 550°C, 553°C, 555°C, 558°C, 560°C, 563°C, 565°C, 568°C, 570°C, 573°C, 575°C, 578°C, 580°C, 583°C, 585°C, 588°C, 590°C, 593°C, 595°C, 598°C, 600°C, 603°C, 605°C, 608°C, 610°C, 613°C, 615°C, 618°C, 620°C, 623°C, 625°C, 628°C, 630°C, 633°C, 635°C, 638°C, 640°C, 643°C, 645°C, 648°C, and 650°C, or any two of the range values.

[0040] In one embodiment, the preheating step is performed by introducing a preheating gas into the catalyst, wherein the gas is one or two or more of air, nitrogen, carbon dioxide and flue gas.

[0041] Specifically, the combination of flue gas and air not only recovers the waste heat of industrial waste gas, but also uses oxygen to partially burn off the pre-deposited carbon on the catalyst surface, reducing the energy consumption required for preheating; nitrogen and CO2 act as inert gases to prevent the oxidation and deactivation of metal active components at high temperatures. At the same time, CO2 can react with carbon deposits to gasify, reducing the regeneration and carbon burning load and improving the initial activity of the catalyst. In addition, using flue gas instead of electric heating can reduce dependence on external energy and reduce carbon emissions. Gas components such as CO2 can participate in the subsequent synthesis gas to generate CO and H2, improving raw material utilization. By optimizing gas selection and ratio, preheating efficiency, catalyst life and process economy are taken into account, providing reliable guarantees for continuous production.

[0042] In one embodiment, the temperature of the preheating gas is 850-1000°C, for example, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, or 1000°C, or any two thereof. When the preheating gas at this temperature contacts the catalyst, it can be heated to the preheating temperature within a few minutes, thereby shortening the reaction startup time. Furthermore, when the preheating gas is an oxygen-containing gas such as flue gas or air, this temperature can partially oxidize pre-deposited carbon on the catalyst surface when the catalyst contacts the preheating gas, thereby reducing the initial carbon deposit on the catalyst and extending the single-cycle operation time. Furthermore, the preheating gas at this temperature can promote the conversion of CO2 to synthesis gas for recycling as a by-product, thereby improving carbon utilization.

[0043] Use Figure 1 The reaction equipment for demethylating methylbenzene aromatic hydrocarbons to generate compounds of formula (I) is used for the reaction, which includes a reactor 1, a catalyst regenerator 2, a first pipeline 3, a second pipeline 4, a third pipeline 5, a fourth pipeline 6, a fifth pipeline 7, a sixth pipeline 8, a seventh pipeline 9, an eighth pipeline 10, and a ninth pipeline 11. Figure 1 Fresh methylbenzene aromatic raw materials enter the reactor 1 through the first pipeline 3. The methylbenzene aromatic raw materials and the water vapor entering the reactor from the second pipeline 4 are contacted with the catalyst heated by the catalyst regenerator 2 to react. The C6-C8 aromatics generated by the reaction and the unreacted raw materials enter the subsequent separation device through the third pipeline 5. The unconverted raw materials are recycled back to the reactor 1 to continue the reaction. At the same time, the carbon-deactivated catalyst is transported to the catalyst regenerator 2 through the fourth pipeline 6 and the sixth pipeline 8. After being burned and regenerated by air through the eighth pipeline 10, the high-temperature regenerated catalyst is returned to the reactor 1 through the seventh pipeline 9 and the fifth pipeline 7. In addition, the flue gas generated in the catalyst regenerator is discharged from the pipeline 11. Water vapor and methylbenzene raw materials are introduced into the reactor 1 at the same time. The water vapor not only participates in the demethylation reaction but also inhibits the carbon deposition of the catalyst, thereby realizing continuous production.

[0044] This application utilizes catalytic demethylation of methylbenzenes to produce light aromatics in a high-temperature steam environment. Combined with continuous catalyst charring and heat recycling, this technology achieves toluene conversions of 40-70% and benzene selectivities of 66-80% at reaction temperatures of 520-600°C. For example, at conversions of 60-70% for polymethylbenzenes (PMBs) such as trimethylbenzenes, the combined selectivity for benzene, toluene, and xylenes remains stable at 80-90%. Replacing hydrogen with steam reduces raw material costs by 20-25%, while combined with preheating with high-temperature gas at 850-1000°C and utilizing waste heat from the regenerated catalyst, system energy consumption is reduced by 30-40%. This technology achieves high selectivity, low cost, and continuous production. This technology utilizes PMBs and high-temperature steam for the reaction, eliminating hydrogen consumption and reducing methane byproduct production. Preheating the raw materials and catalyst with high-temperature gas from the regenerator significantly reduces energy consumption. The recyclable catalyst offers both high efficiency and economical efficiency, providing a green and low-carbon industrial solution for the production of light aromatics.

[0045] Example Example 1 The catalyst, composed of 1% by mass iron, 2.5% by mass manganese, and 96.5% by mass beta molecular sieve, was preheated to 630°C in a regenerator under 900°C N2, and the catalyst in the reactor was heated to 630°C through a circulation process. Water vapor preheated to 500°C and vaporized toluene were introduced into the reactor to react with the preheated catalyst. The weight space velocity of toluene was 0.3 h -1 The reaction is carried out under a pressure of 0.5 MPa. The high-temperature gases generated by the reaction are separated, and the unconverted toluene and water vapor are returned to the reactor for further reaction. After the carbon deposits in the reactor are deactivated, the catalyst is transferred to a catalyst regenerator. Air is introduced into the regenerator to react with the carbon deposits on the catalyst. When the temperature in the regenerator reaches 690°C, the regenerated high-temperature catalyst is transferred back to the reactor for a cyclic reaction. The high-temperature gases from the reaction are used to preheat the water vapor and toluene.

[0046] The reaction products were analyzed by gas chromatography, and the conversion and selectivity were calculated. The toluene conversion was 60%. The products were benzene and xylene, with a benzene selectivity of 70%.

[0047] Example 2 The catalyst, composed of 5% by mass iron and 95% by mass aluminum oxide, was preheated to 580°C in the regenerator by flue gas at 870°C, and the catalyst in the reactor was heated to 540°C through a circulation process. Water vapor preheated to 540°C and vaporized toluene were introduced into the reactor to contact the preheated catalyst for reaction. The weight space velocity of toluene was 0.5 h -1The reaction is carried out under a pressure of 0.8 MPa. The high-temperature gases generated by the reaction are separated, and the unconverted toluene and water vapor are returned to the reactor for further reaction. After the carbon deposits in the reactor are deactivated, the catalyst is transferred to a catalyst regenerator. Air is introduced into the regenerator to react with the carbon deposits on the catalyst. When the temperature in the regenerator reaches 650°C, the regenerated high-temperature catalyst is transferred back to the reactor for a cyclic reaction. The high-temperature gases from the reaction are used to preheat the water vapor and toluene.

[0048] The reaction products were analyzed by gas chromatography, and the conversion rate and selectivity were calculated. Among them, the conversion rate of toluene was 50%, and the selectivity of benzene in the product was 70%.

[0049] Example 3 The catalyst, composed of 3% by mass of zinc, 1.7% by mass of nickel, 0.3% by mass of cerium, 75% by mass of Y-type molecular sieve, and 20% by mass of beta-type molecular sieve, was preheated to 650°C in the regenerator by 770°C flue gas, and the catalyst in the reactor was heated to 570°C through a circulation process. The water vapor preheated to 570°C and the vaporized trimethylbenzene were introduced into the reactor to contact the preheated catalyst for reaction. The weight space velocity of trimethylbenzene was 3 h -1 The reaction is carried out under a pressure of 0.9 MPa. The high-temperature gases generated by the reaction are separated, and the unconverted trimethylbenzene and water vapor are returned to the reactor for further reaction. After the carbon deposits in the reactor are deactivated, the catalyst is transferred to a catalyst regenerator. Air is introduced into the catalyst regenerator to react with the carbon deposits on the catalyst. When the temperature in the catalyst regenerator reaches 680°C, the regenerated high-temperature catalyst is transferred back to the reactor for a cyclic reaction. The high-temperature gases after the reaction are used to preheat the water vapor and trimethylbenzene.

[0050] The reaction products were analyzed by gas chromatography, and the conversion rate and selectivity were calculated. Among them, the conversion rate of trimethylbenzene was 60%, and the total selectivity of benzene, toluene, and xylene in the product was 80%.

[0051] Example 4 A catalyst composed of 3% by mass zinc, 0.3% by mass copper, 0.7% by mass molybdenum, 50% by mass Y molecular sieve, and 46% by mass beta molecular sieve was preheated to 650°C in a regenerator with 1000°C flue gas, and the catalyst in the reactor was heated to 550°C through a circulation process. Water vapor preheated to 550°C and a 1:1 mixture of vaporized toluene and xylene were introduced into the reactor to contact the preheated catalyst for reaction. The weight space velocity of the 1:1 mixture of toluene and xylene was 0.5 h -1The reaction is carried out at a pressure of 0.8 MPa. The high-temperature gases generated by the reaction are separated, and the unconverted mixed aromatic feedstock and water vapor are returned to the reactor for further reaction. After the carbon deposits in the reactor are deactivated, the catalyst is transferred to a catalyst regenerator. Air is introduced into the regenerator to react with the carbon deposits on the catalyst. When the temperature in the regenerator reaches 680°C, the regenerated high-temperature catalyst is transferred back to the reactor for a cyclic reaction. The high-temperature gases from the reaction are used to preheat water vapor and a 1:1 mixture of toluene and xylene.

[0052] The reaction products were analyzed by gas chromatography, and the conversion and selectivity were calculated. The conversion of a 1:1 mixture of toluene and xylene as the starting material was 60%, and the overall selectivity of benzene and toluene in the product was 80%.

[0053] Example 5 The catalyst, composed of 0.3% rhodium, 2.7% cobalt, 47% CrO3, and 50% MgO, was preheated to 550°C in a regenerator using a 1:1 mixture of CO· and N2 at 900°C. The catalyst in the reactor was then heated to 520°C through a circulation process. Water vapor and vaporized toluene preheated to 520°C were introduced into the reactor to react with the preheated catalyst. The weight space velocity of toluene was 10 h / min. -1 The reaction is carried out under a pressure of 0.1 MPa. The high-temperature gases generated by the reaction are separated, and the unconverted toluene and water vapor are returned to the reactor for further reaction. After the carbon deposits in the reactor are deactivated, the catalyst is transferred to a catalyst regenerator. Air is introduced into the regenerator to react with the carbon deposits on the catalyst. When the temperature in the regenerator reaches 650°C, the regenerated high-temperature catalyst is transferred back to the reactor for a cyclic reaction. The high-temperature gases from the reaction are used to preheat the water vapor and toluene.

[0054] The reaction products were analyzed by gas chromatography, and the conversion rate and selectivity were calculated. The conversion rate of toluene was 40%, and the selectivity of benzene in the product was 80%.

[0055] Example 6 A catalyst composed of 1% nickel by mass, 1.7% gallium by mass, 0.3% iridium by mass, 40% Y-type molecular sieve by mass, 10% beta-type molecular sieve by mass, 20% ZSM-5 molecular sieve by mass, and 27% silica by mass was preheated to 650°C in a regenerator with air at 850°C. The catalyst in the reactor was then heated to 560°C through a circulation process. Water vapor preheated to 560°C and vaporized raw materials (10% toluene by mass, 60% trimethylbenzene by mass, 20% pentamethylbenzene by mass, and 10% hexamethylbenzene by mass) were introduced into the reactor to react with the preheated catalyst at a weight space velocity of 0.2 h-1. -1 The reaction is carried out under a pressure of 1 MPa. The high-temperature gases generated by the reaction are separated, and the unconverted mixed aromatic feedstock and water vapor are returned to the reactor for further reaction. After the carbon deposits in the reactor are deactivated, the catalyst is transferred to a catalyst regenerator. Air is introduced into the regenerator to react with the carbon deposits on the catalyst. When the temperature in the regenerator reaches 700°C, the regenerated high-temperature catalyst is transferred back to the reactor for a cyclic reaction. The high-temperature gases from the reaction are used to preheat the water vapor and feedstock.

[0056] The reaction products were analyzed by gas chromatography, and the conversion and selectivity were calculated. The conversion of the raw materials was 70%, and the total selectivity of light aromatics with one methyl group removed in the products was 85%.

[0057] Example 1 uses a catalyst in which iron and manganese are loaded on a β-type molecular sieve to achieve a toluene conversion rate of 60% and a benzene selectivity of 70% at 500°C; Example 2 uses a high-loaded iron-based alumina catalyst to obtain a 50% conversion rate and a 70% benzene selectivity at 540°C; Example 3 combines zinc, nickel, and cerium composite metals with Y-type-β-type molecular sieves to efficiently convert trimethylbenzene at 570°C, with a conversion rate of 60% and a total selectivity of benzene, toluene, and xylene of 80%; Example 4 uses zinc, copper, and molybdenum multi-metal and composite molecular sieves to treat a toluene-xylene mixture, with a conversion rate of 60% and a benzene-toluene selectivity of 80%; Example 5 uses trace rhodium-cobalt and CrO3-MgO carriers to achieve a benzene selectivity of 80% at 520°C; Example 6 uses a multi-metal and composite molecular sieve system to treat complex raw materials containing hexamethylbenzene, with a conversion rate of 70% and a light aromatics selectivity of 85%. This application achieves a conversion rate of 40-70% and a selectivity of 66-90% in the range of 520-600°C through catalyst design optimization, steam-assisted reaction and regeneration system integration, combining high efficiency, economy and industrialization potential.

[0058] The above description is merely a preferred embodiment of the present application and does not constitute any other form of limitation to the present application. Any technician familiar with the present profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification of the above embodiment based on the technical essence of the present application without departing from the content of the technical solution of the present application shall still fall within the scope of protection of the technical solution of the present application.

Claims

1. A catalyst for the demethylation reaction of methylbenzene aromatic hydrocarbons, characterized in that: The catalyst is used for the demethylation reaction of methylbenzene aromatic hydrocarbons to prepare the compound shown in the following formula (I): Formula (I) R1, R2, R3, R4 and R5 are hydrogen or methyl; The catalyst is composed of a metal and a carrier, wherein the metal is one or two or more of nickel, rhodium, yttrium, iron, cobalt, zinc, gallium, copper, manganese, molybdenum and cerium, and the carrier is one or two or more of MgO, Al2O3, CrO3, SiO2 and molecular sieve.

2. The catalyst according to claim 1, characterized in that The mass fraction of the metal is 0.03% to 5%.

3. The catalyst according to claim 1, characterized in that The molecular sieve is one, two or three of Y-type molecular sieve, β-type molecular sieve and ZSM-5 type molecular sieve.

4. Use of the catalyst according to any one of claims 1 to 3 in the demethylation reaction of methylbenzene aromatic hydrocarbons.

5. A method for demethylating methylbenzene aromatic hydrocarbons, characterized in that: include: The methylbenzene aromatic hydrocarbons, water vapor and catalyst are contacted to react to form the compound shown in the following formula (I): Formula (I) R1, R2, R3, R4 and R5 are hydrogen or methyl; The reaction temperature is 520-600° C.; the methylbenzene aromatic hydrocarbons are one or two or more of toluene, xylene, trimethylbenzene, tetramethylbenzene, pentamethylbenzene and hexamethylbenzene.

6. The method according to claim 5, characterized in that Before the methylbenzene aromatic hydrocarbons and water vapor are contacted with the catalyst for reaction, the following steps are further included: The process of vaporizing the methylbenzene aromatic hydrocarbons.

7. The method according to claim 8, characterized in that The catalyst is the catalyst according to any one of claims 1 to 3.

8. The method according to claim 5, characterized in that Before the catalyst is contacted with the methylbenzene aromatic hydrocarbon, the method further comprises: The catalyst is preheated.

9. The method according to claim 7, characterized in that The preheating temperature is 550-650°C.

10. The method according to claim 7, characterized in that The preheating step comprises: A preheating gas is introduced into the catalyst, wherein the preheating gas temperature is 850-1000° C. and the gas is one or two or more of air, nitrogen, carbon dioxide and flue gas.

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