Aromatic hydrocarbon selective hydrodealkylation catalyst and preparation method and application thereof

Abstract

The invention discloses an aromatic hydrocarbon selective hydrodealkylation catalyst as well as a preparation method and application thereof. The aromatic hydrocarbon selective hydrodealkylation catalyst comprises a composite modified alumina carrier, a VIII group transition metal oxide and a rare earth metal oxide. By adopting the catalyst disclosed by the invention, the C2 + side chain substituent of alkyl aromatic hydrocarbon can be subjected to selective terminal removal, the C2 + side chain substituent is effectively utilized to increase the yield of methyl, and the yield of polymethyl aromatic hydrocarbon in a product is increased.

Description

Technical Field

[0001] The present invention relates to the field of catalytic conversion of aromatic hydrocarbons, and more specifically to an aromatic hydrocarbon selective hydrogenation dealkylation catalyst and a preparation method and application thereof. Background Art

[0002] Aromatics is an important pillar of the national economy, with a long industrial chain and a wide product coverage, and it also undertakes the two major markets of oil and chemical products consumption. In recent years, China's aromatics industry has shown a leapfrog development and has become the world's aromatics investment and production center.

[0003] In the petrochemical production process, the main sources of aromatics include catalytic reforming, steam cracking, catalytic cracking, light hydrocarbon aromatization, etc. In addition to producing common light aromatics such as benzene (B), toluene (T) and xylene (X), the above processes also produce some carbon nine / carbon ten aromatics (C9 / C 10 Aromatics). This part of C9 / C 10 Aromatic hydrocarbons are monocyclic aromatic hydrocarbons containing side chain substituents. According to the number of carbon atoms in the substituents, the side chain substituents can be divided into methyl and C2 + Substituents, such as trimethylbenzene, methylethylbenzene, propylbenzene, tetramethylbenzene, etc. C9 / C 10 In addition to polymethyl substituents, aromatic hydrocarbons also contain a large amount of C2 + Side chain substituents, for example, in C9 aromatics produced by catalytic reforming, the content of trimethylbenzene is 53-54%, the content of methyl and ethylbenzene is 27-28%, and the content of propylbenzene is 8-10%.

[0004] At this stage, this part of C9 / C 10 The main purpose of aromatics is to increase the production of light aromatics such as BTX. Commonly used technologies include but are not limited to: (1) Toluene disproportionation and transalkylation technology: This technology uses toluene and C9 / C 10 Aromatic hydrocarbons are used as raw materials to increase the production of benzene and xylene through methyl transfer reaction and aromatic side chain hydrogenation dealkylation reaction. In this technology, methyl groups mainly undergo transfer reactions between aromatic hydrocarbons, while C2 + The side chain substituents are removed by hydrogenation dealkylation reaction (Aromatics Technology [M]. Beijing: China Petrochemical Press, 2014: 156-191.), and the common catalyst is metal-modified molecular sieve; (2) Aromatics catalytic hydrogenation dealkylation technology: This technology uses toluene and above alkyl aromatics as raw materials, and removes all side chain substituents including methyl through side chain catalytic hydrogenation dealkylation reaction, and C2 + The removal rate of side chain substituents is higher than that of methyl groups. Common catalysts include Cr2O3 / Al2O3, MoO3 / Al2O3, etc. (Research Progress of Catalysts for Catalytic Hydrodealkylation of Alkyl Aromatics, Industrial Catalysis, 2004, 12(11): 1-6.)

[0005] It can be seen that in the above catalytic conversion process of alkyl aromatics, C2 + The side chain substituents are all removed by hydrogenation to generate the corresponding C2 + Alkanes, if this part of C2 + The side chain substituents can be selectively removed at the terminal position, such as the selective removal of the methyl group of the ethyl group to generate methyl and methane, and the selective dealkylation of the propyl group to generate methyl and ethane, so that the C2 + The side chain substituents increase the number of methyl groups in the aromatic hydrocarbon stream, and the resulting polymethyl aromatics can be introduced into the aromatic hydrocarbon complex to increase the production of xylene and improve the PX output of the unit. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention aims to develop a catalyst for selective hydrogenation and dealkylation of aromatic hydrocarbons and its preparation method and application. The catalyst of the present invention can be used to dealkylate alkyl aromatic hydrocarbons C2 + Selective terminal removal of side chain substituents allows efficient utilization of C2 + The side chain substituents increase the production of methyl groups and improve the yield of polymethyl aromatics in the product.

[0007] A first aspect of the present invention provides a catalyst for selective hydrodealkylation of aromatic hydrocarbons, the catalyst comprising a composite modified alumina carrier, a Group VIII transition metal oxide and a rare earth metal oxide.

[0008] Furthermore, in the catalyst, based on the mass of the catalyst, the mass content of the Group VIII transition metal oxide is 0.01% to 1%, the mass content of the rare earth metal oxide is 1% to 5%, and the mass content of the composite modified alumina carrier is 94% to 98%.

[0009] Furthermore, the metal in the Group VIII transition metal oxide is preferably at least one of Ru, Ir and Rh; the metal in the rare earth metal oxide is preferably La and / or Ce.

[0010] Furthermore, the composite modified alumina carrier comprises modified alumina and metal oxide.

[0011] Furthermore, the mesopore maximum probable pore size of the modified alumina in the composite modified alumina carrier is 8 to 12 nm, and the macropore maximum probable pore size is 1000 to 2000 nm. The mesopore maximum probable pore size of the modified alumina is 30% to 200% higher than that of conventional unmodified alumina, and the macropore maximum probable pore size of the modified alumina is only 20% to 70% of that of conventional unmodified alumina.

[0012] Furthermore, the metal oxide in the composite modified alumina carrier is an oxide of an alkali metal and / or an alkaline earth metal, preferably magnesium oxide and / or potassium oxide.

[0013] Furthermore, the mass content of the metal oxide in the composite modified alumina carrier is 1% to 5%, and the mass content of the modified alumina is 95% to 99%.

[0014] The second aspect of the present invention provides a method for preparing the above-mentioned selective hydrodealkylation catalyst for aromatic hydrocarbons, comprising the following steps:

[0015] (1) preparing a composite modified alumina carrier;

[0016] (2) Take the composite modified alumina carrier described in step (1), introduce a Group VIII transition metal salt and a rare earth metal salt, dry and calcine to obtain an aromatics selective hydrodealkylation catalyst.

[0017] Furthermore, the preparation method of the composite modified alumina carrier in step (1) comprises: treating alumina with water vapor, then mixing with a metal salt, and then forming, drying, and calcining to obtain a composite modified alumina carrier.

[0018] Furthermore, the molding described in step (1) can adopt a conventional molding method, preferably extrusion molding. During extrusion molding, a molding aid can be added as needed, such as at least one of sesbania powder and cellulose. The amount of the molding aid added accounts for 0.1% to 10% of the mass of alumina. After molding, the composite modified alumina carrier can be obtained by conventional drying and calcining conditions in the art. Preferably, the drying temperature is 90 to 150°C, the drying time is 2 to 10 hours; the calcining temperature is 400 to 600°C, and the calcining time is 2 to 10 hours.

[0019] Furthermore, the aluminum oxide used in step (1) is preferably γ-Al2O3, wherein the most probable mesopore diameter of γ-Al2O3 is 4-6 nm, and the most probable macropore diameter is 3000-5000 nm.

[0020] Furthermore, the temperature of the steam treatment in step (1) is 300-500° C., and the treatment time is 2-5 hours.

[0021] Furthermore, the metal salt in step (1) is an alkali metal and / or alkaline earth metal salt, preferably at least one of magnesium nitrate and potassium nitrate. The amount of the metal salt added, calculated as oxide, is 1% to 5% of the mass of the composite modified alumina support.

[0022] Furthermore, the method of introducing the Group VIII transition metal salt and the rare earth metal salt in step (2) can adopt conventional methods in the art, preferably an equal volume impregnation method.

[0023] Furthermore, the Group VIII transition metal in step (2) is selected from at least one of Ru, Ir and Rh.

[0024] Furthermore, the rare earth metal in step (2) is preferably La and / or Ce.

[0025] Furthermore, in step (2), the drying temperature is 90-150° C., and the drying time is 2-10 hours; the roasting temperature is 400-600° C., and the roasting time is 2-10 hours.

[0026] Furthermore, in the aromatics selective hydrodealkylation catalyst obtained in step (2), the Group VIII transition metal salt, calculated as metal oxide, accounts for 0.01% to 1% of the catalyst mass, and the rare earth metal salt, calculated as metal oxide, accounts for 1% to 5% of the catalyst mass.

[0027] The third aspect of the present invention provides the use of the above-mentioned selective hydrodealkylation catalyst for aromatic hydrocarbons in the selective hydrodealkylation reaction of alkyl aromatic hydrocarbons.

[0028] Furthermore, the reaction conditions of the selective hydrodealkylation of aromatics are as follows: temperature of 350-550°C, pressure of 2-5 MPa, mass space velocity of alkyl aromatics of 1-10 h -1 , the molar ratio of hydrogen to alkyl aromatics is 2 to 6.

[0029] Furthermore, the alkyl aromatic hydrocarbon is C2 + The aromatic hydrocarbon having a side chain substituent (a side chain substituent having two or more carbon atoms) is preferably methyl ethyl benzene.

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] The selective hydrogenation dealkylation catalyst for aromatic hydrocarbons provided by the present invention can fully utilize C2 + The side chain substituent increases the production of methyl groups, and the methyl / benzene ring ratio in the product is greatly improved. The polymethyl aromatics produced can be introduced into the aromatics combined unit to achieve the purpose of increasing the production of xylene and improving the PX output of the unit. In particular, the modified alumina of the present invention has more mesoporous structures and less macroporous structures, which is beneficial to the diffusion performance of the raw materials and products and reduces the side chain deep demethylation side reaction.

[0032] In the preparation method of the present invention, the alumina carrier is treated with water vapor to dredge the pores and improve the diffusion performance of the catalyst. The introduction of metal into the alumina modified by water vapor can modify the acidity of the catalyst and inhibit the C2 + The side chain is completely released as a side reaction. DETAILED DESCRIPTION

[0033] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0034] The raw materials used in the examples and comparative examples of the present invention are commercially available and have an analytical purity (AR).

[0035] The most probable pore size of the mesopores of the catalyst is measured by a physical adsorption instrument (such as the TriStar 3000 physical adsorption instrument of Micromeritics Instruments, USA) to obtain the nitrogen physical adsorption and desorption isotherms, and then calculated by the BJH method of the desorption curve. The experimental conditions for the catalyst are: the measurement temperature is -196°C, and the molecular sieve is vacuum pretreated at 300°C for 10 hours before the measurement. The most probable pore size of the macropores is tested using a mercury intrusion instrument (such as the PoreMaster mercury intrusion instrument of Anton Paconta, USA). According to the size of the pores that mercury can enter and the pressure, it conforms to the Washburn equation. By controlling different pressures, the volume of mercury pressed into the pores can be measured, thereby obtaining a cumulative distribution curve or differential curve of the pore size corresponding to different pressures.

[0036] Example 1

[0037] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 4.3nm, macropore maximum probable pore size 4368nm), treat it with steam at 450℃ for 5 hours, and obtain steam-treated modified alumina (mesopore maximum probable pore size 8.5nm, macropore maximum probable pore size 1530nm). Take 100g of the steam-treated modified alumina, add 2g of sesbania powder, 7.36g of magnesium nitrate and an appropriate amount of deionized water, knead and extrude, dry at 120℃ for 3 hours, and calcine at 550℃ for 5 hours to obtain a composite modified alumina carrier, in which the mass content of magnesium oxide in the composite modified alumina carrier is 2.5%.

[0038] Take 100g of the above-mentioned composite modified alumina carrier, introduce rhodium chloride and lanthanum nitrate by equal volume impregnation method, dry at 90°C for 5 hours, and calcine at 550°C for 5 hours to obtain aromatics selective hydrogenation dealkylation catalyst A1, in which the mass content of rhodium oxide is 0.5% and the mass content of lanthanum oxide is 1.5%.

[0039] The catalyst A1 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 500°C, the reaction pressure was 3 MPa, and the mass space velocity of the methyl ethyl benzene feed was 2 h -1 The molar ratio of hydrogen to aromatics was 6 / 1. The reaction performance results evaluated are shown in Table 1.

[0040] Example 2

[0041] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 5.8nm, macropore maximum probable pore size 3870nm), treat it with steam at 500℃ for 2 hours, and obtain steam-treated modified alumina (mesopore maximum probable pore size 11.4nm, macropore maximum probable pore size 1590nm). Take 100g of the steam-treated modified alumina, add 2g of sesbania powder, 14.72g of magnesium nitrate and an appropriate amount of deionized water, knead and extrude, dry at 120℃ for 3 hours, and calcine at 550℃ for 5 hours to obtain a composite modified alumina carrier, in which the mass content of magnesium oxide in the composite modified alumina carrier is 4.5%.

[0042] Take 100g of the above-mentioned composite modified alumina carrier, introduce iridium chloride and cerium nitrate by equal volume impregnation method, dry at 120°C for 3 hours, and calcine at 550°C for 3 hours to obtain aromatics selective hydrogenation dealkylation catalyst A2, in which the mass content of iridium oxide is 1.0% and the mass content of cerium oxide is 5.0%.

[0043] The catalyst A2 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 400°C, the reaction pressure was 5 MPa, and the mass space velocity of the methyl ethyl benzene feed was 1 h -1 The molar ratio of hydrogen to aromatics was 3 / 1. The reaction performance results evaluated are shown in Table 1.

[0044] Example 3

[0045] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 5.8nm, macropore maximum probable pore size 4680nm), treat it with steam at 400℃ for 5 hours, and obtain steam-treated modified alumina (mesopore maximum probable pore size 8.2nm, macropore maximum probable pore size 1850nm). Take 100g of the steam-treated modified alumina, add 2g of sesbania powder, 2.58g of potassium nitrate and an appropriate amount of deionized water, knead and extrude, dry at 120℃ for 3 hours, and calcine at 550℃ for 5 hours to obtain a composite modified alumina carrier, wherein the mass content of potassium oxide in the composite modified alumina carrier is 1.2%.

[0046] Take 100g of the above-mentioned composite modified alumina carrier, introduce iridium chloride and lanthanum nitrate by equal volume impregnation method, dry at 90°C for 5 hours, and calcine at 550°C for 5 hours to obtain aromatics selective hydrogenation dealkylation catalyst A3, in which the mass content of iridium oxide is 1.0% and the mass content of lanthanum oxide is 2.5%.

[0047] The catalyst A3 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 500°C, the reaction pressure was 3 MPa, and the feed mass space velocity of methyl ethyl benzene was 1 h-1 The molar ratio of hydrogen to aromatics was 3 / 1. The reaction performance results evaluated are shown in Table 1.

[0048] Example 4

[0049] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 6.0nm, macropore maximum probable pore size 3180nm), treat it with steam at 300℃ for 5 hours, and obtain steam-treated modified alumina (mesopore maximum probable pore size 8.5nm, macropore maximum probable pore size 1990nm). Take 100g of the steam-treated modified alumina, add 2g of sesbania powder, 8.16g of potassium nitrate and an appropriate amount of deionized water, knead and extrude, dry at 120℃ for 3 hours, and calcine at 550℃ for 5 hours to obtain a composite modified alumina carrier, in which the mass content of potassium oxide in the composite modified alumina carrier is 3.5%.

[0050] Take 100g of the above-mentioned composite modified alumina carrier, introduce ruthenium chloride and lanthanum nitrate by equal volume impregnation method, dry at 90°C for 5 hours, and calcine at 550°C for 5 hours to obtain aromatics selective hydrogenation dealkylation catalyst A4, in which the mass content of ruthenium oxide is 0.65% and the mass content of lanthanum oxide is 4.0%.

[0051] The catalyst A4 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 500°C, the reaction pressure was 3 MPa, and the feed mass space velocity of methyl ethyl benzene was 1 h -1 The molar ratio of hydrogen to aromatics was 4 / 1. The reaction performance results evaluated are shown in Table 1.

[0052] Comparative Example 1

[0053] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 4.3nm, macropore maximum probable pore size 4368nm), treat it with steam at 450℃ for 5 hours, and obtain steam-treated modified alumina (mesopore maximum probable pore size 8.5nm, macropore maximum probable pore size 1530nm). Take 100g of steam-treated modified alumina, add 2g of sesbania powder and an appropriate amount of deionized water, knead and extrude, dry at 120℃ for 3 hours, and calcine at 550℃ for 5 hours to obtain alumina carrier T1.

[0054] Take 100g of the above-mentioned alumina carrier T1, introduce rhodium chloride and lanthanum nitrate by equal volume impregnation method, dry at 90°C for 5 hours, and calcine at 550°C for 5 hours to obtain aromatics selective hydrogenation dealkylation catalyst D1, in which the mass content of rhodium oxide is 0.5% and the mass content of lanthanum oxide is 1.5%.

[0055] The catalyst D1 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 500°C, the reaction pressure was 3 MPa, and the feed mass space velocity of methyl ethyl benzene was 2 h -1 The molar ratio of hydrogen to aromatics was 6 / 1. The reaction performance results evaluated are shown in Table 1.

[0056] Comparative Example 2

[0057] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 4.3nm, macropore maximum probable pore size 4368nm), add 2g of sesbania powder, 7.36g of magnesium nitrate and an appropriate amount of deionized water, knead and extrude, dry at 120°C for 3 hours, and calcine at 550°C for 5 hours to obtain an alumina carrier T2, in which the mass content of magnesium oxide is 2.5%.

[0058] Take 100g of alumina carrier T2, introduce rhodium chloride and lanthanum nitrate by equal volume impregnation method, dry at 90°C for 5 hours, and calcine at 550°C for 5 hours to obtain aromatics selective hydrogenation dealkylation catalyst D2, in which the mass content of rhodium oxide is 0.5% and the mass content of lanthanum oxide is 1.5%.

[0059] The catalyst D2 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 500°C, the reaction pressure was 3 MPa, and the feed mass space velocity of methyl ethyl benzene was 2 h -1 The molar ratio of hydrogen to aromatics was 6 / 1. The reaction performance results evaluated are shown in Table 1.

[0060] Comparative Example 3

[0061] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 4.3nm, macropore maximum probable pore size 4368nm), add 2g of sesbania powder and an appropriate amount of deionized water, knead and extrude, dry at 120℃ for 3 hours, and calcine at 550℃ for 5 hours to obtain alumina carrier T3.

[0062] Take 100g of the above-mentioned alumina carrier T3, introduce rhodium chloride and lanthanum nitrate by equal volume impregnation method, dry at 90°C for 5 hours, and calcine at 550°C for 5 hours to obtain aromatics selective hydrogenation dealkylation catalyst D3, in which the mass content of rhodium oxide is 0.5% and the mass content of lanthanum oxide is 1.5%.

[0063] The catalyst D3 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 500°C, the reaction pressure was 3 MPa, and the mass space velocity of the methyl ethyl benzene feed was 2 h -1 The molar ratio of hydrogen to aromatics was 6 / 1. The reaction performance results evaluated are shown in Table 1.

[0064] Comparative Example 4

[0065] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 4.3nm, macropore maximum probable pore size 4368nm), treat it with steam at 450℃ for 5 hours, and obtain steam-treated modified alumina (mesopore maximum probable pore size 8.5nm, macropore maximum probable pore size 1530nm). Take 100g of the steam-treated modified alumina, add 2g of sesbania powder, 7.36g of magnesium nitrate and an appropriate amount of deionized water, knead and extrude, dry at 120℃ for 3 hours, and calcine at 550℃ for 5 hours to obtain a composite modified alumina carrier, in which the mass content of magnesium oxide in the composite modified alumina carrier is 2.5%.

[0066] Take 100g of the above-mentioned composite modified alumina carrier, introduce rhodium chloride by equal volume impregnation method, dry at 90°C for 5 hours, and calcine at 550°C for 5 hours to obtain aromatics selective hydrogenation dealkylation catalyst D4, in which the mass content of rhodium oxide is 0.5%.

[0067] The catalyst D4 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 500°C, the reaction pressure was 3 MPa, and the mass space velocity of the methyl ethyl benzene feed was 2 h -1 The molar ratio of hydrogen to aromatics was 6 / 1. The reaction performance results evaluated are shown in Table 1.

[0068] Comparative Example 5

[0069] Take 100g of γ-Al2O3 (mesopore maximum probable pore size 5.8nm, macropore maximum probable pore size 3870nm), treat it with steam at 500℃ for 2 hours, and obtain steam-treated modified alumina (mesopore maximum probable pore size 11.4nm, macropore maximum probable pore size 1590nm). Take 100g of the steam-treated modified alumina, add 2g of sesbania powder, 14.72g of magnesium nitrate and an appropriate amount of deionized water, knead and extrude, dry at 120℃ for 3 hours, and calcine at 550℃ for 5 hours to obtain a composite modified alumina carrier, in which the mass content of magnesium oxide in the composite modified alumina carrier is 4.5%.

[0070] Take 100g of the above-mentioned composite modified alumina carrier, introduce cerium nitrate by equal volume impregnation method, dry at 120°C for 3 hours, and calcine at 550°C for 3 hours to obtain aromatics selective hydrodealkylation catalyst D5, with a cerium oxide mass content of 5%.

[0071] The catalyst D5 in the example was used for the selective hydrodealkylation of aromatics, wherein the reaction raw material was methyl ethyl benzene, the reaction temperature was 400°C, the reaction pressure was 5 MPa, and the feed mass space velocity of methyl ethyl benzene was 1 h -1 The molar ratio of hydrogen to aromatics was 3 / 1. The reaction performance results evaluated are shown in Table 1.

[0072] Table 1 Aromatic Selective Hydrodealkylation Performance in Examples and Comparative Examples

[0073]

[0074] The above detailed description of the specific implementation of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the various technical features are combined in any other suitable manner, these simple modifications and combinations should also be regarded as the contents disclosed by the present invention, all belong to the protection scope of the present invention.

Claims

1. A catalyst for selective hydrodealkylation of aromatic hydrocarbons, comprising a composite modified alumina carrier, a Group VIII transition metal oxide and a rare earth metal oxide.

2. The catalyst according to claim 1, characterized in that In the catalyst, based on the mass of the catalyst, the mass content of the Group VIII transition metal oxide is 0.01% to 1%, the mass content of the rare earth metal oxide is 1% to 5%, and the mass content of the composite modified alumina carrier is 94% to 98%.

3. The catalyst according to claim 1, characterized in that The metal in the Group VIII transition metal oxide is selected from at least one of Ru, Ir and Rh; the metal in the rare earth metal oxide is La and / or Ce.

4. The catalyst according to claim 1 or 3, characterized in that The composite modified alumina carrier comprises modified alumina and metal oxide.

5. The catalyst according to claim 1 or 3, characterized in that The mesopore maximum probable pore size of the modified alumina in the composite modified alumina carrier is 8 to 12 nm, and the macropore maximum probable pore size is 1000 to 2000 nm; and / or the metal oxide in the composite modified alumina carrier is an oxide of an alkali metal and / or an alkaline earth metal, preferably magnesium oxide and / or potassium oxide.

6. The method for preparing the selective hydrodealkylation catalyst for aromatic hydrocarbons according to any one of claims 1 to 5, comprising the following steps: (1) preparing a composite modified alumina carrier; (2) Take the composite modified alumina carrier described in step (1), introduce a Group VIII transition metal salt and a rare earth metal salt, dry and calcine to obtain an aromatics selective hydrodealkylation catalyst.

7. The preparation method according to claim 6, characterized in that: The preparation method of the composite modified alumina carrier in step (1) comprises: treating alumina with water vapor, then mixing with a metal salt, and then forming, drying and calcining to obtain a composite modified alumina carrier.

8. The preparation method according to claim 7, characterized in that: The temperature of the steam treatment in step (1) is 300-500° C., and the treatment time is 2-5 hours.

9. The preparation method according to claim 7, characterized in that: The metal salt in step (1) is an alkali metal and / or alkaline earth metal salt, preferably at least one of magnesium nitrate and potassium nitrate.

10. The preparation method according to claim 6, characterized in that: The Group VIII transition metal in step (2) is at least one selected from Ru, Ir and Rh; and / or, the rare earth metal in step (2) is preferably La and / or Ce.

11. Use of the selective hydrodealkylation catalyst for aromatic hydrocarbons according to any one of claims 1 to 5 in the selective hydrodealkylation reaction for alkyl aromatic hydrocarbons.

12. The method according to claim 11, characterized in that The reaction conditions of the selective hydrogenation dealkylation reaction of aromatics are as follows: temperature of 350-550° C., pressure of 2-5 MPa, mass space velocity of alkyl aromatics of 1-10 h -1 , the molar ratio of hydrogen to alkyl aromatics is 2 to 6.

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