Method for removing alkyl side chain in polycyclic aromatic hydrocarbon containing alkyl side chain and application

Abstract

The invention discloses a method for removing alkyl side chains in polycyclic aromatic hydrocarbon containing the alkyl side chains and application, and relates to the technical field of organic chemistry. The method for removing the alkyl side chain in the polycyclic aromatic hydrocarbon containing the alkyl side chain comprises the following steps: S1, in the presence of a first catalyst, carrying out oxidation reaction on the polycyclic aromatic hydrocarbon containing the alkyl side chain to obtain polycyclic aromatic hydrocarbon containing a carboxylic acid group; s2, in the presence of a second catalyst, carrying out a decarboxylation reaction on the polycyclic aromatic hydrocarbon containing the carboxylic acid group to obtain the polycyclic aromatic hydrocarbon, wherein the first catalyst comprises an alumina carrier and a metal oxide loaded on the alumina carrier, and the metal oxide comprises a cobalt oxide and a manganese oxide; and the second catalyst comprises cuprous oxide, so that the alkyl side chain in the polycyclic aromatic hydrocarbon containing the alkyl side chain can be efficiently removed, the reaction selectivity and the product yield can be remarkably improved, and the generation of byproducts can be reduced, thereby reducing the production cost.

Description

Technical Field

[0001] This invention relates to the field of organic chemistry, and more specifically, to a method and application for removing alkyl side chains from fused-ring aromatic hydrocarbons containing alkyl side chains. Background Technology

[0002] In petroleum refining and chemical production, product purity directly impacts product quality and final application value. Coal direct liquefaction oil is an important product of the clean and efficient conversion of coal resources. Its composition is extremely complex, rich in polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, phenanthrene, and pyrene, with a small amount of alkyl side chains. PAHs containing alkyl side chains (such as methylnaphthalene) have similar boiling points and polarities to PAHs containing naphthalene. In the post-processing of coal direct liquefaction oil, the application of traditional distillation and extraction technologies is limited by the similar boiling points and polarities of the components to be separated. This makes it difficult to effectively separate PAHs containing alkyl side chains, such as methylnaphthalene. This not only fails to meet the requirements of specific applications for high-purity naphthalene but also leads to low separation efficiency, forcing the product to be downgraded to a diesel blending component. Furthermore, PAHs containing alkyl side chains, such as methylnaphthalene, are more prone to decomposition or participation in side reactions at high temperatures, generating corrosive substances that corrode refining or chemical equipment, increasing maintenance costs and safety hazards.

[0003] Currently, most methods for removing alkyl side chains from polycyclic aromatic hydrocarbons (PAHs) containing alkyl side chains employ a combination of oxidation and decarboxylation. Specifically, strong oxidants (such as potassium permanganate or nitric acid) are used to oxidize PAHs containing alkyl side chains into PAHs containing carboxyl groups. Then, noble metals such as Pd, Ag, Rh, and Au are used as catalysts for carboxyl removal, yielding PAHs. However, during oxidation, strong oxidants often over-oxidize the target molecule, leading to unnecessary carbon chain breakage or excessive oxidation, producing low-value-added byproducts and reducing the yield of the target product. During decarboxylation, noble metal catalysts are expensive. While copper-based catalysts are currently used to reduce costs, their conversion rate is low, making effective decarboxylation difficult and resulting in low PAH yields. Therefore, how to effectively remove alkyl side chains from PAHs containing alkyl side chains, improve PAH yields, and effectively enrich and separate PAHs from coal direct liquefaction oil is a pressing technical problem in this field. Summary of the Invention

[0004] The main objective of this invention is to provide a method and application for removing alkyl side chains from polycyclic aromatic hydrocarbons containing alkyl side chains, in order to solve the problems of high cost and low yield of polycyclic aromatic hydrocarbons in the prior art.

[0005] To achieve the above objective, according to one aspect of the present invention, a method for removing alkyl side chains from fused-ring aromatic hydrocarbons containing alkyl side chains is provided, comprising the following steps:

[0006] S1, in the presence of a first catalyst, a fused-ring aromatic hydrocarbon containing an alkyl side chain is oxidized to obtain a fused-ring aromatic hydrocarbon containing a carboxylic acid group;

[0007] S2, in the presence of a second catalyst, causes a decarboxylation reaction of a polycyclic aromatic hydrocarbon containing a carboxylic acid group to yield a polycyclic aromatic hydrocarbon;

[0008] The first catalyst includes an alumina support and a metal oxide supported on the alumina support, the metal oxide including cobalt oxide and manganese oxide; the second catalyst includes cuprous oxide.

[0009] Furthermore, based on the mass of the first catalyst (100%), the content of manganese oxide is 15%–50%, and the content of cobalt oxide is 10%–30%; and / or,

[0010] The second catalyst has a layered nanocluster structure and a specific surface area of ​​5 m² / g to 20 m² / g; and / or,

[0011] The second catalyst has a layered nanocluster structure with a nanocluster size of 10 nm to 500 nm.

[0012] Preferably, the size of the nanoclusters is 20 nm to 150 nm.

[0013] Furthermore, the preparation method of the first catalyst includes: providing an alumina support; mixing the alumina support with a solution containing a metal oxide precursor, and then impregnating the mixture to obtain an impregnated product; and subjecting the impregnated product to a first drying and calcination process to obtain the first catalyst.

[0014] Preferably, the temperature for the first drying is 50℃~120℃, and the drying time is 1h~10h;

[0015] Preferably, the calcination temperature is 200℃~600℃, and the calcination time is 1h~10h;

[0016] Preferably, the solution containing the metal oxide precursor includes cobalt salt and manganese salt, wherein the cobalt salt includes cobalt nitrate and the manganese salt includes manganese nitrate.

[0017] Furthermore, the preparation method of the second catalyst includes:

[0018] A copper source, reducing agent, stabilizer, and organic solvent are mixed to obtain a mixture; the mixture is then heat-treated to obtain a mixed reaction product; the mixed reaction product is then subjected to a second drying process to obtain a second catalyst.

[0019] Preferably, the heat treatment temperature is 100℃~150℃, and the heat treatment time is 10min~20min;

[0020] Preferably, the second drying is carried out under vacuum conditions, the temperature of the second drying is 40℃~150℃, and the time of the second drying is 1h~10h;

[0021] Preferably, the copper source includes copper acetate;

[0022] Preferably, the reducing agent includes sodium borohydride;

[0023] Preferably, the stabilizer includes polyvinylpyrrolidone;

[0024] Preferably, the organic solvent includes dimethylformamide;

[0025] Preferably, the molar ratio of copper source to reducing agent is (1~15):1;

[0026] Preferably, the molar ratio of reducing agent to stabilizer is 1:(5~30).

[0027] Further, step S1 includes: in the presence of a first catalyst and a first auxiliary agent, oxidizing a fused-ring aromatic hydrocarbon containing an alkyl side chain to obtain a fused-ring aromatic hydrocarbon containing a carboxylic acid group; wherein the first auxiliary agent includes N-hydroxyphthalimide; and / or,

[0028] Step S2 includes: in the presence of a second catalyst and a second auxiliary agent, a fused-ring aromatic hydrocarbon containing a carboxylic acid group undergoes a decarboxylation reaction to obtain a fused-ring aromatic hydrocarbon; wherein the second auxiliary agent includes tetramethylethylenediamine.

[0029] Further, the mass ratio of the alkyl-side chain-containing polycyclic aromatic hydrocarbon to the first catalyst is 100:(0.1~0.6); and / or,

[0030] The molar ratio of the fused-ring aromatic hydrocarbon containing a carboxylic acid group to the second catalyst is 100:(1~7); and / or,

[0031] The molar ratio of the alkyl-side chain-containing polycyclic aromatic hydrocarbon to the first auxiliary agent is 100:(1~10); and / or,

[0032] The molar ratio of the polycyclic aromatic hydrocarbon containing a carboxylic acid group to the second auxiliary agent is 100:(1~15).

[0033] Furthermore, the oxidation reaction is carried out in an oxygen-containing atmosphere at a temperature of 50℃ to 200℃ for a duration of 10 min to 300 min; and / or,

[0034] The decarboxylation reaction is carried out under an inert atmosphere at a temperature of 60℃ to 240℃ for 1 to 10 hours.

[0035] Further, step S1 includes: mixing a first catalyst, a first auxiliary agent, a fused-ring aromatic hydrocarbon containing an alkyl side chain, and a first solvent to obtain a first reaction system; subjecting the first reaction system to an oxidation reaction to obtain a fused-ring aromatic hydrocarbon containing a carboxylic acid group; wherein the first solvent includes acetic acid; and / or,

[0036] Step S2 includes: mixing a second catalyst, a second auxiliary agent, a polycyclic aromatic hydrocarbon containing a carboxylic acid group, and a second solvent to obtain a second reaction system; subjecting the second reaction system to a decarboxylation reaction to obtain a polycyclic aromatic hydrocarbon; wherein the second solvent includes N-methylpyrrolidone.

[0037] Furthermore, fused-ring aromatic hydrocarbons containing alkyl side chains include 1-methylnaphthalene and / or 2-methylnaphthalene.

[0038] A second aspect of the present invention provides a method for enriching polycyclic aromatic hydrocarbons from coal direct liquefaction oil, wherein the enrichment is performed using the method for removing alkyl side chains from polycyclic aromatic hydrocarbons containing alkyl side chains as described in the first aspect.

[0039] By employing the technical solution of this invention and using a specific catalyst, not only can the efficient removal of alkyl side chains from polycyclic aromatic hydrocarbons containing alkyl side chains be achieved, but the selectivity of the reaction and the product yield can also be significantly improved, and the generation of by-products can be reduced, thereby reducing production costs. In addition, the method of this invention is particularly suitable for the upgrading and separation process of coal direct liquefaction oil, and can effectively enrich and separate high-value-added polycyclic aromatic hydrocarbons. Attached Figure Description

[0040] Figure 1 This is a SEM image of the first catalyst in Example 1 of the present invention;

[0041] Figure 2 This is a second SEM image of the first catalyst in Example 1 of the present invention;

[0042] Figure 3 This is a SEM image of the second catalyst in Example 1 of the present invention;

[0043] Figure 4 This is a SEM image of the second catalyst in Comparative Example 4 of the present invention;

[0044] Figure 5 Here is a SEM image of the second catalyst in Comparative Example 5 of this invention;

[0045] Figure 6 The graphs show the yields of 1-naphthoic acid in Examples 1, 2, and 3 at different reaction temperatures.

[0046] Figure 7 The graphs show the conversion rates of 1-methylnaphthalene in Examples 1, 2, and 3 at different reaction temperatures.

[0047] Figure 8 The graphs show the selectivity of 1-naphthoic acid for Examples 1, 2, and 3 at different reaction temperatures.

[0048] Figure 9 The graphs show the yields of 1-naphthoic acid in Examples 1, 2, and 3 at different reaction times.

[0049] Figure 10 The graphs show the conversion rates of 1-methylnaphthalene for Examples 1, 2, and 3 at different reaction times.

[0050] Figure 11 The graphs show the selectivity of 1-naphthoic acid for Examples 1, 2, and 3 at different reaction times.

[0051] Figure 12 The liquid chromatogram of the first product formed using 1-methylnaphthalene as a reactant is shown.

[0052] Figure 13 The liquid chromatogram of the first product formed from 2-methylnaphthalene as a reactant is shown.

[0053] Figure 14 The yield of 1-naphthoic acid in the first catalyst of Examples 1, 2, and 3 at different cycles. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0055] As described in the background section of this invention, the prior art suffers from high cost and low yield of alkyl side chains in polycyclic aromatic hydrocarbons containing alkyl side chains. To address these issues, in a typical embodiment of this invention, a method for removing alkyl side chains from polycyclic aromatic hydrocarbons containing alkyl side chains is provided, comprising the following steps:

[0056] S1, in the presence of a first catalyst, a fused-ring aromatic hydrocarbon containing an alkyl side chain is oxidized to obtain a fused-ring aromatic hydrocarbon containing a carboxylic acid group;

[0057] S2, in the presence of a second catalyst, the polycyclic aromatic hydrocarbon containing a carboxylic acid group undergoes a decarboxylation reaction to obtain a polycyclic aromatic hydrocarbon;

[0058] The first catalyst includes an alumina support and a metal oxide supported on the alumina support, wherein the metal oxide includes cobalt oxide and manganese oxide; the second catalyst includes layered cuprous oxide.

[0059] Specifically, in step S1, the polycyclic aromatic hydrocarbon containing alkyl side chains undergoes an oxidation reaction under the action of a first catalyst, converting the alkyl side chains into carboxylic acid groups. The first catalyst is a metal oxide supported on an alumina support, wherein the metal oxide mainly includes cobalt oxide (CoO2). x ) and manganese oxide (MnO) x The combination of these two metal oxides forms a synergistic effect, which can efficiently convert fused-ring aromatics containing alkyl side chains into fused-ring aromatics containing carboxylic acid groups under mild conditions. Compared with traditional strong oxidants such as potassium permanganate and nitric acid, this invention utilizes a specific catalyst, which results in higher atom utilization, helps to improve the conversion rate, generates less pollution, and the catalyst is easy to separate and recycle.

[0060] In step S2, after the oxidation reaction, the resulting polycyclic aromatic hydrocarbon containing carboxylic acid groups undergoes a decarboxylation reaction under the action of a second catalyst to further remove the carboxylic acid groups, yielding a pure polycyclic aromatic hydrocarbon. The second catalyst comprises layered cuprous oxide (Cu₂O). This transition metal catalyst is inexpensive, and the layered structure of cuprous oxide provides a large specific surface area, offering more surface active sites, which is beneficial for improving catalytic efficiency. This results in the second catalyst exhibiting excellent catalytic activity during the decarboxylation process, enabling highly selective decarboxylation under mild conditions.

[0061] The method provided by this invention combines the advantages of two highly efficient catalysts. Through a two-step reaction of oxidation and decarboxylation, it not only achieves efficient removal of alkyl side chains from polycyclic aromatic hydrocarbons containing alkyl side chains, but also significantly improves reaction selectivity and product yield, reduces by-product formation, and thus lowers production costs. This method is particularly suitable for enriching and separating high-value-added polycyclic aromatic hydrocarbons from direct coal liquefaction oil, and can also simplify subsequent separation processes, increase yield, and reduce production costs.

[0062] In some embodiments, based on the mass of the first catalyst, the loading of manganese oxide is 15% to 50%, and the content of cobalt oxide is 10% to 30%. By controlling the content of metal oxides in the first catalyst to meet the above requirements, it is helpful to further improve the catalytic activity and stability of the first catalyst.

[0063] Specifically, based on the mass of the first catalyst being 100%, the content of manganese oxide can be in the range of 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any two of these, and the content of cobalt oxide can be in the range of 10%, 15%, 20%, 25%, 30%, or any two of these.

[0064] In some embodiments, the specific surface area of ​​layered cuprous oxide is 5 m². 2 / g~20m 2 / g. By controlling the specific surface area of ​​layered cuprous oxide to meet the above requirements, it is helpful to further increase the active sites of the second catalyst, which is beneficial to the contact between reactants and catalyst, and improves the reaction rate and selectivity.

[0065] Specifically, the specific surface area of ​​layered cuprous oxide can be 5 m². 2 / g、8m 2 / g, 10m 2 / g、12m 2 / g, 15m 2 / g、18m 2 / g、20m 2 / g or a range consisting of any two of them.

[0066] In some embodiments, the second catalyst is a layered nanocluster structure, i.e., the second catalyst is composed of irregular cuprous oxide particles aggregated together. Compared with cubic Cu₂O and octahedral Cu₂O without corners, the layered nanocluster structure of Cu₂O exhibits higher catalytic activity. In some preferred embodiments, the size of the nanoclusters is 10 nm to 500 nm, preferably 20 nm to 150 nm, for example, a range of 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, or any combination thereof.

[0067] In some embodiments, the method for preparing the first catalyst includes: providing an alumina support; mixing the alumina support with a solution containing a metal oxide precursor, and then impregnating the mixture to obtain an impregnated product; and subjecting the impregnated product to a first drying and calcination process to obtain the first catalyst. The metal oxide precursor includes cobalt salts and manganese salts.

[0068] Specifically, alumina supports can be obtained commercially or in-house. For example, a method for preparing an alumina support includes: grinding spherical activated alumina in a ball mill for 2 to 10 hours, then mixing it with ammonia water and treating it at 100°C to 300°C for 1 to 15 hours to obtain a reaction product; the reaction product is then dried, ground, and calcined to obtain the alumina support.

[0069] In some preferred embodiments, the temperature of the first drying is 50°C to 120°C, and the time of the first drying is 1 hour to 10 hours. The product after impregnation is dried. By controlling the temperature and time of the first drying, the damage to the alumina carrier structure can be prevented, and the metal salt can be solidified.

[0070] In some preferred embodiments, the calcination temperature is 200°C to 600°C, for example, a range of 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, or any combination thereof. The calcination time is 1 hour to 10 hours, for example, 1 hour, 3 hours, 5 hours, 8 hours, 10 hours, or any combination thereof. The dried product needs to be further calcined to promote the transformation of the metal salt to the metal oxide, while simultaneously fixing the position of the metal oxide on the support to form a stable catalyst.

[0071] In some preferred embodiments, the solution containing the metal oxide precursor includes cobalt salt and manganese salt. The present invention does not limit the specific types of cobalt salt and manganese salt. For example, cobalt salt may include cobalt nitrate, and manganese salt may include manganese nitrate.

[0072] In some preferred embodiments, an alumina support is mixed with water to obtain a first mixture; a solution containing cobalt salt is added to the first mixture to obtain a second mixture; the second mixture is ultrasonically treated, allowed to stand, then centrifuged and dried to obtain a first solid product; the first solid product is ground into powder and then pre-calcined to obtain an alumina support loaded with cobalt oxide; then the alumina support loaded with cobalt oxide is mixed with water to obtain a third mixture; a solution containing manganese salt is added to the third mixture to obtain a fourth mixture; the fourth mixture is ultrasonically treated, allowed to stand, then centrifuged and dried to obtain a second solid product; the second solid product is ground into powder and then pre-calcined to obtain an alumina support loaded with cobalt oxide and manganese oxide, i.e., the first catalyst.

[0073] The mixing process can be performed using ultrasonic-assisted stirring, which helps to ensure uniform mixing of the raw materials. The cobalt salt concentration in the cobalt salt solution can be from 10 mg / mL to 30 mg / mL, for example, 10 mg / mL, 12 mg / mL, 15 mg / mL, 18 mg / mL, 20 mg / mL, 22 mg / mL, 25 mg / mL, 28 mg / mL, 30 mg / mL, or any combination thereof. The manganese salt concentration in the manganese salt solution can be from 1 mg / mL to 15 mg / mL, for example, 1 mg / mL, 2 mg / mL, 5 mg / mL, 8 mg / mL, 10 mg / mL, 12 mg / mL, 15 mg / mL, or any combination thereof. The settling time after ultrasonication can be from 3 h to 15 h, for example, 3 h, 5 h, 8 h, 10 h, 12 h, 14 h, 15 h, or any combination thereof. This settling time after ultrasonication allows the metal salts to be uniformly deposited on the alumina support surface.

[0074] In some embodiments, the preparation method of the second catalyst includes: mixing a copper source, a reducing agent, a stabilizer and an organic solvent to obtain a mixture; heat-treating the mixture to obtain a mixed reaction product; and subjecting the mixed reaction product to a second drying process to obtain the second catalyst.

[0075] Specifically, a copper source, reducing agent, stabilizer, and organic solvent are mixed in a specific ratio, and these components together constitute the basis of the mixture. In some preferred embodiments, the copper source is preferably copper acetate (Cu(C)). The reducing agent is preferably sodium borohydride (NaBH4), the stabilizer is preferably polyvinylpyrrolidone, and the organic solvent is preferably dimethylformamide (DMF). The mixture can be heat-treated in an oil bath, preferably at a temperature of 100℃~150℃ for 10min~20min. These temperature and time conditions promote Cu2O formation while maintaining its good morphology and stability. The heat-treated mixture needs to be dried under vacuum to remove excess solvent and moisture. Vacuum drying effectively reduces the oxidation of Cu2O by oxygen in the air, maintaining its catalytic activity. Preferably, the second drying temperature is 40℃~150℃ for 1h~10h.

[0076] To ensure catalytic performance and avoid raw material waste, in some preferred embodiments, the molar ratio of copper source to reducing agent is (1~15):1, preferably (1~5):1, for example, 1:1, 2:1, 3:1, 4:1, 5:1 or any two of these ranges; the molar ratio of reducing agent to stabilizer is 1:(5~30), preferably 1:(10~20), for example, 1:10, 1:12, 1:15, 1:18, 1:20 or any two of these ranges.

[0077] In some embodiments, step S1 includes: oxidizing a fused-ring aromatic hydrocarbon containing an alkyl side chain in the presence of a first catalyst and a first auxiliary agent to obtain a fused-ring aromatic hydrocarbon containing a carboxylic acid group; wherein the first auxiliary agent includes N-hydroxyphthalimide (NHPI). The first auxiliary agent promotes the oxidation of the alkyl side chain through a free radical mechanism in the oxidation reaction, which helps to further promote the conversion of the fused-ring aromatic hydrocarbon containing an alkyl side chain to the fused-ring aromatic hydrocarbon containing a carboxylic acid group. The selective oxidation performance of the first auxiliary agent, synergistically with the first catalyst, can further ensure high reaction efficiency and high product selectivity.

[0078] In some embodiments, step S2 includes: in the presence of a second catalyst and a second promoter, subjecting the polycyclic aromatic hydrocarbon containing a carboxylic acid group to a decarboxylation reaction to obtain a polycyclic aromatic hydrocarbon; wherein the second promoter includes tetramethylethylenediamine (TMEDA). The aforementioned second promoter can form effective coordination with Cu2O, accelerating the removal of the carboxyl group in the decarboxylation reaction by forming a complex with Cu2O. Furthermore, by providing σ-donor properties, the aforementioned second promoter promotes the breaking of C-C bonds, improves the electron transfer efficiency of Cu2O, and helps to further increase the reaction rate, thereby further improving product selectivity and promoting efficient utilization of the catalyst.

[0079] In some embodiments, the mass ratio of the alkyl-side-chain fused-ring aromatic hydrocarbon to the first catalyst is 100:(0.1~0.6). By controlling the amount of the first catalyst added, sufficient contact and reaction between the alkyl-side-chain fused-ring aromatic hydrocarbon and the first catalyst can be promoted, thus avoiding affecting the efficiency of the oxidation reaction.

[0080] In some embodiments, the molar ratio of the alkyl-side chain-containing polycyclic aromatic hydrocarbon to the first auxiliary agent is 100:(1~10). By controlling the amount of the first auxiliary agent added, the oxidation reaction can be promoted, further improving the reaction rate and selectivity.

[0081] In some embodiments, the molar ratio of the polycyclic aromatic hydrocarbon containing a carboxylic acid group to the second catalyst is 100:(1~7). By controlling the amount of the second catalyst added, the effective utilization of the catalyst can be promoted, while avoiding increased costs due to excessive catalyst and avoiding side reactions.

[0082] In some embodiments, the molar ratio of the polycyclic aromatic hydrocarbon containing a carboxylic acid group to the second auxiliary agent is 100:(1~15). By controlling the amount of the second auxiliary agent added, the catalytic activity of Cu2O is further enhanced, and the decarboxylation reaction is promoted.

[0083] Specifically, the mass ratio of the alkyl-side-chain fused-ring aromatic hydrocarbon to the first catalyst can be within the range of 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.6, or any two of these ratios. The molar ratio of the alkyl-side-chain fused-ring aromatic hydrocarbon to the first auxiliary agent can be within the range of 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, or any two of these ratios. The molar ratio of the carboxylic acid group fused-ring aromatic hydrocarbon to the second catalyst can be within the range of 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, or any two of these ratios. The molar ratio of the polycyclic aromatic hydrocarbon containing a carboxylic acid group to the second auxiliary can be 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:12, 100:14, 100:15, or any combination thereof.

[0084] In some embodiments, the oxidation reaction is carried out in an oxygen-containing atmosphere at a temperature of 50°C to 200°C for a time of 10 min to 300 min. The catalytic oxidation reaction is carried out in an oxygen-containing atmosphere, the presence of which is crucial for the conversion of alkyl side chains to carboxylic acid groups during the reaction. In some preferred embodiments, the partial pressure of oxygen can be controlled within the range of 0.1 to 1 MPa to provide sufficient oxidizing power. By controlling the temperature and time of the oxidation reaction to meet the above requirements, the oxidation reaction can be fully carried out while avoiding the increase of side reactions or the decrease of catalyst activity.

[0085] In some embodiments, the decarboxylation reaction is carried out under an inert atmosphere at a temperature of 60°C to 240°C for a duration of 1 to 10 hours. The decarboxylation reaction is conducted under an inert atmosphere, such as using nitrogen or argon to remove oxygen from the air and prevent oxidation side reactions. The use of an inert atmosphere can further improve the purity of the product. By controlling the temperature and time of the decarboxylation reaction to meet the above requirements, it is helpful to further promote the removal of the carboxylic acid group, generating a pure parent polycyclic aromatic hydrocarbon.

[0086] In some embodiments, step S1 includes: mixing a first catalyst, a first auxiliary agent, a fused-ring aromatic hydrocarbon containing an alkyl side chain, and a first solvent to obtain a first reaction system; subjecting the first reaction system to an oxidation reaction to obtain a fused-ring aromatic hydrocarbon containing a carboxylic acid group; wherein the first solvent includes acetic acid. By using acetic acid as a solvent in the oxidation reaction, not only can the reactants be dissolved, but the necessary acidic environment can also be provided to promote the oxidation reaction.

[0087] In some embodiments, step S2 includes: mixing a second catalyst, a second auxiliary agent, a fused-ring aromatic hydrocarbon containing a carboxylic acid group, and a second solvent to obtain a second reaction system; subjecting the second reaction system to a decarboxylation reaction to obtain a fused-ring aromatic hydrocarbon; wherein the second solvent includes N-methylpyrrolidone. By using N-methylpyrrolidone as a solvent in the decarboxylation reaction, naphthoic acid can be effectively dissolved, and a milder reaction environment can be provided for the decarboxylation reaction, which helps to further improve the selectivity and efficiency of the decarboxylation reaction.

[0088] This invention does not limit the specific type of fused-ring aromatic hydrocarbon containing alkyl side chains; for example, it can be methylnaphthalene, specifically 1-methylnaphthalene or 2-methylnaphthalene. When the fused-ring aromatic hydrocarbon containing alkyl side chains is methylnaphthalene, the methyl group is directionally removed and eliminated through a two-step reaction of catalytic oxidation and decarboxylation, ultimately yielding pure naphthalene.

[0089] In a second aspect, the present invention provides a method for enriching polycyclic aromatic hydrocarbons from coal direct liquefaction oil, wherein the enrichment is performed by a method for removing alkyl side chains from polycyclic aromatic hydrocarbons containing alkyl side chains.

[0090] Coal direct liquefaction oil typically contains a complex mixture of polycyclic aromatic hydrocarbons (PAHs), including a large number of alkyl side-chain compounds (such as various methylnaphthalenes). The presence of these alkyl side chains not only reduces the quality of the oil but also makes subsequent separation and utilization difficult. The method for removing alkyl side chains from PAHs containing alkyl side chains provided by this invention is particularly suitable for improving the quality and efficiency of coal direct liquefaction oil. Specifically, by efficiently converting these alkyl side chains into carboxyl groups (-COOH) and removing them through a decarboxylation reaction under mild conditions, the alkyl side chains in PAHs containing alkyl side chains (such as methylnaphthalene) are selectively trimmed and removed, thereby achieving the enrichment and separation of high-value-added PAHs in coal direct liquefaction oil.

[0091] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0092] Example 1

[0093] I. The preparation method of the first catalyst in this embodiment includes the following steps:

[0094] S11, spherical activated alumina is ground in a ball mill for 6 hours to obtain powder; the powder is mixed with ammonia water at a ratio of 0.3 g / mL and added to a reaction vessel and allowed to stand at 180℃ for 6 hours; the solid produced by the reaction is dried, ground and placed in a muffle furnace and calcined at 500℃ for 5 hours to obtain alumina carrier.

[0095] S12, mix 5g of alumina support with 20mL of deionized water, stir for 60min, sonicate for 30min, and then continue stirring at room temperature for 3h until uniformly dispersed to obtain solution A; dissolve 0.38g of cobalt nitrate hexahydrate in 20mL of deionized water to obtain a cobalt salt solution; add the cobalt salt solution dropwise to solution A to obtain suspension B;

[0096] S13, after sonicating suspension B for 30 min, let it stand for 6 h, then centrifuge and dry it; grind the dried solid into powder and place it in a muffle furnace to heat to 500℃ at a heating rate of 5℃ / min and hold for 50 h to obtain an alumina support loaded with cobalt oxide.

[0097] S14, dissolve 2g of alumina support loaded with cobalt oxide in deionized water to obtain suspension C; dissolve 0.1609g of manganese nitrate in 20mL of deionized water to obtain manganese salt solution; add manganese salt solution dropwise to suspension C to obtain suspension D;

[0098] S15, the suspension D was sonicated for 30 min and then allowed to stand for 6 h, followed by centrifugation and drying; the dried solid was ground into powder and placed in a muffle furnace and heated to 500℃ at a heating rate of 5℃ / min and held for 50 h to obtain the first catalyst.

[0099] II. The preparation method of the second catalyst in this embodiment includes the following steps:

[0100] 2 mmol of Cu(CH3COO)2·H2O was added to 30 mL of dimethylformamide and stirred for 5 min. Then, 1.06 mmol of NaBH4 and 0.4 g of polyvinylpyrrolidone were added to obtain a mixed raw material. The mixed raw material was heated and stirred in an oil bath at 110 °C for 18 min. After centrifugation, Cu2O particles were obtained. The particles were washed with deionized water and anhydrous ethanol, and then dried under vacuum at 60 °C for 4 h to obtain a layered nanocluster Cu2O catalyst, i.e., the second catalyst.

[0101] III. Methods for removing alkyl side chains from fused-ring aromatic hydrocarbons containing alkyl side chains

[0102] S31, 1-methylnaphthalene, the first catalyst, N-hydroxyphthalimide, and 10 mL of acetic acid were added to a reaction vessel, sealed, and purged with 0.2 MPa of oxygen. The reaction was carried out at 115 °C for 240 min. After the reaction was completed, the mixture was cooled to room temperature to obtain a product containing 1-naphthoic acid. The content of 1-naphthoic acid in the first product was qualitatively and quantitatively analyzed by HPLC after being diluted to volume with chromatographically pure acetonitrile. The mass ratio of 1-methylnaphthalene to the first catalyst was 100:0.5, and the molar ratio of 1-methylnaphthalene to N-hydroxyphthalimide was 100:6.

[0103] S32, the product containing 1-naphthoic acid, the second catalyst, tetramethylethylenediamine, and 30 mL of N-methylpyrrolidone (NMP) were added to a reaction vessel, sealed, and purged with nitrogen. The reaction was carried out at 170 °C for 6 h. After the reaction was completed, the mixture was cooled to room temperature to obtain a product containing naphthalene. The naphthalene content in the product was qualitatively and quantitatively analyzed by HPLC after being diluted to volume with chromatographically pure acetonitrile. The molar ratio of 1-naphthoic acid to the second catalyst was 100:0.5, and the molar ratio of 1-naphthoic acid to tetramethylethylenediamine was 100:1.

[0104] Example 2

[0105] The difference from Example 1 is that in step S32, tetramethylethylenediamine is replaced with 1,10-phenanthroline.

[0106] Example 3

[0107] The difference from Example 1 is that tetramethylethylenediamine is not added in step S32.

[0108] Example 4

[0109] The difference from Example 1 is that in step S32, tetramethylethylenediamine is replaced with N,N-diisopropylethylamine.

[0110] Example 5

[0111] The difference from Example 1 is that in step S32, tetramethylethylenediamine is replaced with N,N-dimethylaniline.

[0112] Example 6

[0113] The difference from Example 1 is that in step S32, tetramethylethylenediamine is replaced with 1,4-dimethylpiperazine.

[0114] Example 7

[0115] The difference from Example 1 is that in step S32, tetramethylethylenediamine is replaced with quinoline.

[0116] Example 8

[0117] The difference from Example 1 is that in step S32, tetramethylethylenediamine is replaced with triethylamine.

[0118] Comparative Example 1

[0119] The difference from Example 1 is that the first catalyst is replaced with an Al2O3 support.

[0120] Comparative Example 2

[0121] The difference from Example 1 is that the preparation method of the first catalyst includes the following steps:

[0122] S11, spherical activated alumina is ground in a ball mill for 6 hours to obtain powder; the powder is mixed with ammonia water at a ratio of 0.3 g / mL and added to a reaction vessel and allowed to stand at 180℃ for 6 hours; the solid produced by the reaction is dried, ground and placed in a muffle furnace and calcined at 500℃ for 5 hours to obtain alumina carrier.

[0123] S12, mix 5g of alumina support with 20mL of deionized water, stir for 60min, sonicate for 30min, and then continue stirring at room temperature for 3h until uniformly dispersed to obtain solution A; dissolve 0.38g of cobalt nitrate hexahydrate in 20mL of deionized water to obtain a cobalt salt solution; add the cobalt salt solution dropwise to solution A to obtain suspension B;

[0124] S13, the suspension B was sonicated for 30 min and then allowed to stand for 6 h, followed by centrifugation and drying; the dried solid was ground into powder and placed in a muffle furnace and heated to 500 °C at a heating rate of 5 °C / min and held for 50 h to obtain an alumina support loaded with cobalt oxide, which is the first catalyst of this comparative example.

[0125] Replace the first catalyst with the first catalyst of this comparative example.

[0126] Comparative Example 3

[0127] The difference from Example 1 is that the preparation method of the first catalyst includes the following steps:

[0128] S11, spherical active alumina was ground in a ball mill for 6 hours to obtain powder; the powder was mixed with ammonia water at a ratio of 0.3 g / mL and added to a reaction vessel and allowed to stand at 180℃ for 6 hours; the solid produced by the reaction was dried, ground and then placed in a muffle furnace and calcined at 500℃ for 5 hours to obtain alumina support;

[0129] S12, mix 5g of alumina carrier with 20mL of deionized water, stir for 60min, sonicate for 30min, and then continue stirring at room temperature for 3h until uniformly dispersed to obtain solution A; dissolve 0.1609g of manganese nitrate in 20mL of deionized water to obtain manganese salt solution; add manganese salt solution dropwise to suspension A to obtain suspension D;

[0130] S13, the suspension D is sonicated for 30 min and then allowed to stand for 6 h, followed by centrifugation and drying; the dried solid is ground into powder and placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min and held for 50 h to obtain an alumina support loaded with manganese oxide, which is the first catalyst of this embodiment.

[0131] Replace the first catalyst with the first catalyst of this comparative example.

[0132] Comparative Example 4

[0133] The difference from Example 1 is that the preparation method of the second catalyst includes the following steps:

[0134] 2 mmol of Cu(NO3)2·3H2O was added to 30 mL of dimethylformamide and stirred for 5 min. Then, 1.06 mmol of NaBH4 and 0.37 g of polyvinylpyrrolidone were added to obtain a mixed raw material. The mixed raw material was heated and stirred in an oil bath at 120 °C for 25 min. After centrifugation, Cu2O particles were obtained. The particles were washed with deionized water and anhydrous ethanol, and then dried under vacuum at 60 °C for 4 h to obtain a cube-shaped Cu2O catalyst, which is the second catalyst of this comparative example.

[0135] Replace the second catalyst with the second catalyst of this comparative example.

[0136] Comparative Example 5

[0137] The difference from Example 1 is that the preparation method of the second catalyst includes the following steps:

[0138] 2 mmol of CuSO4 was added to 30 mL of dimethylformamide and stirred for 5 min. Then, 1.06 mmol of NaBH4 and 0.18 g of polyvinylpyrrolidone were added to obtain a mixed raw material. The mixed raw material was heated and stirred in an oil bath at 20 °C for 5 min. Then, NaOH aqueous solution was added, followed by 2 mL of hydrazine hydrate aqueous solution and reacted for 30 min. Finally, the mixture was centrifuged to obtain Cu2O particles. The particles were washed alternately with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 4 h to obtain a non-angular octahedral Cu2O catalyst, which is the second catalyst of this comparative example.

[0139] Replace the second catalyst with the second catalyst of this comparative example.

[0140] Test case

[0141] 1. Test on the effect of reaction temperature:

[0142] Following step S31 of Example 1, 1-methylnaphthalene, the first catalyst, the first auxiliary agent, and 10 mL of acetic acid were added to a reaction vessel. After sealing, 0.2 MPa of oxygen was introduced, and the reaction was carried out at 105°C, 110°C, 115°C, 120°C, and 125°C for 240 min, respectively. After the reaction was completed, the mixture was cooled to room temperature to obtain a product containing 1-naphthoic acid. The content of naphthoic acid in the first product was qualitatively and quantitatively analyzed by HPLC after being diluted to volume with chromatographically pure acetonitrile. The mass ratio of 1-methylnaphthalene to the first catalyst was 100:0.5, and the molar ratio of 1-methylnaphthalene to the first auxiliary agent was 100:6.

[0143] Test results are available Figures 6 to 8 ,according to Figures 6 to 8 It can be seen that the sensitivity of the first catalyst to the reaction temperature is consistent. After increasing the reaction temperature, the yield of 1-naphthoic acid gradually increases, and the yield of 1-naphthoic acid is the highest at 115℃. After further increasing the reaction temperature, although the conversion rate of 1-naphthoic acid is further improved, the selectivity of the product 1-naphthoic acid gradually decreases, the color of the reaction solution darkens, the by-products gradually increase, and the yield of the main product 1-naphthoic acid decreases.

[0144] 2. Test on the effect of reaction time:

[0145] Following step S31 of Example 1, 1-methylnaphthalene, the first catalyst, the first auxiliary agent, and 10 mL of acetic acid were added to a reaction vessel. After sealing, 0.2 MPa of oxygen was introduced, and the reaction was carried out at 115 °C. The reaction product was taken out at 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h, respectively. After being diluted to volume with chromatographically pure acetonitrile, the content of 1-naphthoic acid in the product was qualitatively and quantitatively analyzed by HPLC. The mass ratio of 1-methylnaphthalene to the first catalyst was 100:0.5, and the molar ratio of 1-methylnaphthalene to the first auxiliary agent was 100:6.

[0146] Test results are available Figures 9 to 11 ,according to Figures 9 to 11 It can be seen that the yield of 1-naphthoic acid increases with the increase of reaction time. The reaction rate is relatively fast in the first 4 hours, and the reaction rate gradually slows down after 4 hours. This indicates that the oxidation process of 1-methylnaphthalene is basically completed after 4 hours. Further extending the reaction time shows a decreasing trend in the selectivity of 1-naphthoic acid. Therefore, an appropriate reaction time is beneficial to improving the yield and selectivity of 1-naphthoic acid.

[0147] 3. Catalyst suitability and stability testing:

[0148] Using the first and second catalysts of Example 1, 1-methylnaphthalene, the first catalyst, the first auxiliary agent, and 10 mL of acetic acid were added to a reaction vessel, sealed, and purged with 0.2 MPa of oxygen. The reaction was carried out at 115 °C for 240 min. After the reaction was completed, the mixture was cooled to room temperature to obtain a product containing 1-naphthoic acid. The content of 1-naphthoic acid in the first product was qualitatively and quantitatively analyzed by HPLC after being diluted to volume with chromatographically pure acetonitrile. The mass ratio of 1-methylnaphthalene to the first catalyst was 100:0.5, and the molar ratio of 1-methylnaphthalene to the first auxiliary agent was 100:6.

[0149] Similarly, using the first and second catalysts of Example 1, 2-methylnaphthalene, the first catalyst, the first auxiliary agent, and 10 mL of acetic acid were added to a reaction vessel. After sealing, oxygen was introduced at 0.2 MPa, and the reaction was carried out at 115 °C for 240 min. After the reaction was completed, the mixture was cooled to room temperature to obtain a product containing 2-naphthoic acid. The content of 2-naphthoic acid in the first product was qualitatively and quantitatively analyzed by HPLC after being diluted to volume with chromatographically pure acetonitrile. The mass ratio of 2-methylnaphthalene to the first catalyst was 100:0.5, and the molar ratio of 2-methylnaphthalene to the first auxiliary agent was 100:6.

[0150] Using the above method, the first catalyst can be recycled.

[0151] The test results of the products after the reaction are as follows: Figure 12 and Figure 13 As shown, the results after removing solvent and additive peaks from the spectrum indicate that the yield of 1-methylnaphthalene to 1-naphthoic acid is 94.57%, demonstrating the good applicability of the catalyst. Furthermore, as... Figure 14 As shown, with the increase of the number of cycles, the catalytic activity of the first catalyst in Example 1 did not decrease significantly. After the tenth cycle, the yield of the product 1-naphthoic acid only decreased slightly, indicating that the catalyst has good stability.

[0152] Calculate using the following formula:

[0153] Conversion rate of 1-methylnaphthalene (%) = (Initial amount of 1-methylnaphthalene - Residual amount of 1-methylnaphthalene) / Initial amount of 1-methylnaphthalene × 100%;

[0154] Selectivity of 1-naphthoic acid (%) = Amount of 1-naphthoic acid produced / (Initial amount of 1-methylnaphthalene - Residual amount of 1-methylnaphthalene) × 100%;

[0155] Yield of 1-naphthoic acid (%) = Amount of 1-naphthoic acid produced / Amount of 1-methylnaphthalene starting material × 100%;

[0156] 1-Naphthoic acid conversion rate (%) = (Initial amount of 1-naphthoic acid - Residual amount of 1-naphthoic acid) / Initial amount of 1-naphthoic acid × 100%;

[0157] Naphthalene selectivity (%) = Amount of naphthalene produced / (Initial amount of 1-naphthoic acid - Residual amount of 1-naphthoic acid) × 100%;

[0158] The yield of naphthalene (%) = amount of naphthalene produced / initial amount of 1-naphthoic acid × 100%.

[0159] The test results are shown in Tables 1, 2 and 3.

[0160] Table 1

[0161]

[0162] Table 2

[0163]

[0164] Table 3

[0165]

[0166] Figure 1 and Figure 2 Scanning electron microscopy (SEM) analysis of the first catalyst in Example 1 is shown in the figure. As can be seen from the figure, a large number of irregular flocs formed on the surface of the first catalyst in Example 1, with some areas showing the growth of 3D nanosheets. These flocs and 3D nanosheets not only improved the dispersibility of the metal active component but also increased the catalyst's structural stability, specific surface area, and surface active sites.

[0167] Figure 3 The image shows an SEM image of the second catalyst in Example 1 of this invention. It can be seen that the catalyst as a whole is composed of irregular Cu₂O particles, forming many irregular agglomerated units resembling spherical particles. Table 3 shows that the second catalyst in Example 1 has good dispersibility and a large specific surface area, thus exhibiting better catalytic performance.

[0168] Figure 4 The image shows an SEM image of the second catalyst in Comparative Example 4, which is a cube-shaped Cu2O crystal with no corners, composed of cube-shaped Cu2O with no corners. This cube-shaped Cu2O crystal is composed of 12 small facets. Figure 5 The image shows the SEM image of the second catalyst in Comparative Example 5. The second catalyst in Comparative Example 5 is a cornerless octahedral Cu2O crystal composed of 14 small planes, including 8 triangular (111) crystal planes and 6 square (110) crystal planes. The entire structure contains 24 Cu(110) / Cu(111) interfaces.

[0169] Table 1 shows that in Comparative Example 1, when Al₂O₃ was used as the first catalyst, only 1.34% of 1-methylnaphthalene was converted to 1-naphthoic acid. In Comparative Example 2, when alumina supported with cobalt oxide was used as the first catalyst, the conversion rate of 1-methylnaphthalene increased to 80.33%, however, the selectivity for 1-naphthoic acid was only 72.41%. Comparative Example 3 used MnO₂... x While Al₂O₃ as the first catalyst can improve the selectivity of 1-naphthoic acid, only 71.08% of 1-methylnaphthoic acid is converted. In Example 1, when an alumina support loaded with cobalt oxide and manganese oxide is used as the first catalyst, the conversion rate of 1-methylnaphthoic acid is 96.72%, the selectivity of 1-naphthoic acid is 98.47%, and the yield is 95.24%, indicating that the first catalyst prepared in Example 1 can catalyze the conversion of 1-methylnaphthoic acid with high selectivity.

[0170] As shown in Table 2, the naphthalene yield in Example 3 was only 10.73% without the addition of the second auxiliary agent. However, the yield of naphthalene in Examples 1-2 and 4-8 was further improved by introducing the second auxiliary agent. In particular, the yield of naphthalene in Example 1 reached more than 90% by introducing tetramethylethylenediamine. This may be because during the reaction, copper atoms complex with C-COO bonds, then form Cu(III) intermediates through addition, and finally rapidly reduce and eliminate to obtain aryl copper and carbon dioxide.

[0171] As shown in Table 3, Comparative Example 4, using cube-shaped Cu₂O without corners as the second catalyst, achieved a naphthalene yield of 80.61% in the decarboxylation reaction. Comparative Example 5, using octahedral Cu₂O without corners as the second catalyst, achieved a naphthalene yield of 86.22% in the decarboxylation reaction. Example 1, using layered nanoclusters of Cu₂O as the second catalyst, increased the conversion rate of 1-naphthoic acid to 90.80% and achieved 100% selectivity for naphthalene, indicating that the layered nanoclusters of Cu₂O provided by this invention possess the best catalytic activity. The smaller size of the layered nanoclusters of Cu₂O and the quantum size effect enhance the reduction-oxidation ability of holes.

[0172] Therefore, by employing a specific catalyst, this invention not only achieves efficient removal of alkyl side chains from polycyclic aromatic hydrocarbons containing alkyl side chains, but also significantly improves reaction selectivity and product yield, reduces the generation of by-products, and thus lowers production costs. Furthermore, the method of this invention is particularly suitable for the upgrading and separation process of coal direct liquefaction oil, and can effectively enrich and separate high-value-added polycyclic aromatic hydrocarbons.

[0173] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for removing alkyl side chains from polycyclic aromatic hydrocarbons containing alkyl side chains, characterized in that, Includes the following steps: S1, in the presence of a first catalyst, a fused-ring aromatic hydrocarbon containing an alkyl side chain is oxidized to obtain a fused-ring aromatic hydrocarbon containing a carboxylic acid group; S2, in the presence of a second catalyst, the polycyclic aromatic hydrocarbon containing a carboxylic acid group undergoes a decarboxylation reaction to obtain a polycyclic aromatic hydrocarbon; The first catalyst comprises an alumina support and a metal oxide supported on the alumina support, wherein the metal oxide comprises cobalt oxide and manganese oxide; the second catalyst comprises cuprous oxide.

2. The removal method according to claim 1, characterized in that, Based on the mass of the first catalyst (100%), the content of the manganese oxide is 15%~50%, and the content of the cobalt oxide is 10%~30%; and / or, The second catalyst has a layered nanocluster structure and a specific surface area of ​​5 m². 2 / g~20m 2 / g; and / or, The second catalyst has a layered nanocluster structure, and the size of the nanocluster is 10 nm to 500 nm; Preferably, the size of the nanoclusters is 20nm~150nm.

3. The removal method according to claim 1 or 2, characterized in that, The preparation method of the first catalyst includes: providing an alumina support; mixing the alumina support with a solution containing a metal oxide precursor, and then impregnating the mixture to obtain an impregnated product; and subjecting the impregnated product to a first drying and calcination process to obtain the first catalyst. Preferably, the temperature of the first drying is 50℃~120℃, and the drying time is 1h~10h; Preferably, the calcination temperature is 200℃~600℃, and the calcination time is 1h~10h; Preferably, the solution containing the metal oxide precursor includes a cobalt salt and a manganese salt, wherein the cobalt salt includes cobalt nitrate and the manganese salt includes manganese nitrate.

4. The removal method according to claim 1 or 2, characterized in that, The preparation method of the second catalyst includes: A copper source, a reducing agent, a stabilizer, and an organic solvent are mixed to obtain a mixture; the mixture is then heat-treated to obtain a mixed reaction product; the mixed reaction product is then subjected to a second drying process to obtain the second catalyst. Preferably, the heat treatment temperature is 100℃~150℃, and the heat treatment time is 10min~20min; Preferably, the second drying is carried out under vacuum conditions, the temperature of the second drying is 40℃~150℃, and the drying time is 1h~10h; Preferably, the copper source includes copper acetate; Preferably, the reducing agent includes sodium borohydride; Preferably, the stabilizer comprises polyvinylpyrrolidone; Preferably, the organic solvent includes dimethylformamide; Preferably, the molar ratio of the copper source to the reducing agent is (1~15):1; Preferably, the molar ratio of the reducing agent to the stabilizer is 1:(5~30).

5. The removal method according to any one of claims 1 to 4, characterized in that, Step S1 includes: oxidizing the fused-ring aromatic hydrocarbon containing alkyl side chains in the presence of the first catalyst and the first auxiliary agent to obtain the fused-ring aromatic hydrocarbon containing carboxylic acid groups; wherein the first auxiliary agent includes N-hydroxyphthalimide; and / or, Step S2 includes: in the presence of the second catalyst and the second auxiliary agent, the fused-ring aromatic hydrocarbon containing a carboxylic acid group undergoes a decarboxylation reaction to obtain a fused-ring aromatic hydrocarbon; wherein the second auxiliary agent includes tetramethylethylenediamine.

6. The removal method according to claim 5, characterized in that, The mass ratio of the alkyl-side-chain polycyclic aromatic hydrocarbon to the first catalyst is 100:(0.1~0.6); and / or, The molar ratio of the polycyclic aromatic hydrocarbon containing a carboxylic acid group to the second catalyst is 100:(1~7); and / or, The molar ratio of the alkyl-side chain-containing polycyclic aromatic hydrocarbon to the first auxiliary agent is 100:(1~10); and / or, The molar ratio of the polycyclic aromatic hydrocarbon containing a carboxylic acid group to the second auxiliary agent is 100:(1~15).

7. The removal method according to any one of claims 1 to 6, characterized in that, The oxidation reaction is carried out in an oxygen-containing atmosphere, at a temperature of 50°C to 200°C, and for a duration of 10 min to 300 min; and / or, The decarboxylation reaction is carried out under an inert atmosphere, the temperature of the decarboxylation reaction is 60℃~240℃, and the time of the decarboxylation reaction is 1h~10h.

8. The removal method according to any one of claims 1 to 7, characterized in that, Step S1 includes: mixing the first catalyst, the first auxiliary agent, the fused-ring aromatic hydrocarbon containing alkyl side chains, and a first solvent to obtain a first reaction system; subjecting the first reaction system to the oxidation reaction to obtain the fused-ring aromatic hydrocarbon containing carboxylic acid groups; wherein the first solvent includes acetic acid; and / or, Step S2 includes: mixing the second catalyst, the second auxiliary agent, the polycyclic aromatic hydrocarbon containing a carboxylic acid group, and the second solvent to obtain a second reaction system; subjecting the second reaction system to the decarboxylation reaction to obtain the polycyclic aromatic hydrocarbon; wherein the second solvent includes N-methylpyrrolidone.

9. The removal method according to any one of claims 1 to 8, characterized in that, The fused-ring aromatic hydrocarbons containing alkyl side chains include 1-methylnaphthalene and / or 2-methylnaphthalene.

10. A method for enriching polycyclic aromatic hydrocarbons from direct coal liquefaction oil, characterized in that, Enrichment is performed using the method for removing alkyl side chains from fused-ring aromatic hydrocarbons containing alkyl side chains as described in any one of claims 1 to 9.

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