Method for preparing aromatic carboxylic acid by adopting ionic liquid

Abstract

The invention provides a method for preparing aromatic carboxylic acid by adopting ionic liquid. The method comprises the following steps: (1) adding a catalyst, a solvent, ammonium salt and imidazolium ionic liquid into a reaction kettle; (2) adding substituted aromatic hydrocarbon (if the substituted aromatic hydrocarbon is a solid at normal temperature, the substituted aromatic hydrocarbon is heated to a molten state) into the reaction kettle at a certain flow rate, and simultaneously introducing air for reaction; and (3) continuously reacting for 0.5-3 hours after the substituted aromatic hydrocarbon is fed, so as to obtain an aromatic carboxylic acid product. The method disclosed by the invention is simple to operate, high in product purity, low in aldehyde intermediate content, suitable for various substituted aromatic hydrocarbons and capable of being used for large-scale production of various aromatic carboxylic acids.

Description

Technical Field

[0001] The invention belongs to the field of organic chemical synthesis and relates to a method for preparing aromatic carboxylic acid by liquid-phase air oxidation of substituted aromatic hydrocarbons. Background Art

[0002] Aromatic carboxylic acids are widely used in various industries, including medicine, chemicals, food and feed additives, etc., and are an indispensable chemical for human beings. Most of its main raw materials, alkyl aromatic hydrocarbons, are directly or indirectly derived from petroleum and are used to produce a variety of functional chemicals such as oil products, polyesters and various chemical intermediates.

[0003] In the early 20th century, large-scale industrial production of aromatic carboxylic acids appeared. The earliest process was nitric acid oxidation, which later developed into a liquid phase oxidation process using transition metal salts as catalysts. The liquid phase air oxidation processes implemented industrially in the 1940s include cyclohexane oxidation, butane oxidation, cumene oxidation, p-xylene oxidation and other liquid phase air oxidation processes. In addition, the reagent oxidation method is also a commonly used oxidation technology. It uses strong oxidants such as permanganate and dichromate to oxidize raw materials to produce corresponding carboxylic acids. However, due to the shortcomings of long process flow, low reaction efficiency, high cost and serious pollution, it does not meet the "green chemistry" requirements advocated by modern chemical industry and is gradually being eliminated. In 1958, Mid-Century developed a soluble divalent cobalt, divalent manganese and bromine salt catalyst system, and acetic acid as a solvent for the liquid phase catalytic oxidation of substituted aromatics. It was later bought out by Amoco and optimized into the existing Amoco-MC process, of which the most widely used is the oxidation of p-xylene to produce terephthalic acid. The catalyst system is highly active, so that the conversion rate of the raw materials and the selectivity of the target product are relatively high. In the process of catalytic liquid-phase catalytic oxidation of substituted aromatic hydrocarbons to produce aromatic carboxylic acids, if the substituted aromatic hydrocarbon has more than one substituted alkyl group (or a functional group with an oxidized methyl group), the first substituent is easily oxidized to a carboxylic acid. For example, p-xylene is oxidized to produce p-toluic acid, but due to the influence of the carboxyl group formed on the benzene ring, the subsequent oxidation of the methyl group is more difficult. At the same time, with the increase of the carboxyl group on the aromatic ring, the solubility of the aromatic carboxylic acid in acetic acid will continue to decrease, thus causing some incompletely oxidized aldehyde intermediates to precipitate during the oxidation process, so that the precipitated aldehyde intermediates no longer participate in the reaction.

[0004] Since the content of various impurities (such as incompletely oxidized aldehyde intermediates, bromoaromatic carboxylic acids introduced by catalysts, and some ring-opening byproducts in the oxidation process) in crude aromatic carboxylic acids is too high, it will affect the performance of the polymer and cannot be directly used in the production of polyester. Therefore, many domestic scientific research institutions have adopted a variety of different methods to reduce the content of incompletely oxidized aldehyde intermediates in crude aromatic carboxylic acids to reduce the difficulty of the purification step. CN 113620799 A (titled: Preparation method of 2,6-naphthalene dicarboxylic acid) adopts a method of adding alkali metal permanganate after 2,6-diisopropylnaphthalene for at least 0.5h to reduce the content of aldehyde intermediates. After analysis, the content of 2-acetyl-6-naphthoic acid in the product is 112ppm, and the content of 2-formyl-6-naphthoic acid is 4328ppm, which can effectively improve the purity of the product 2,6-naphthalene dicarboxylic acid. However, the catalyst concentration used in this method is relatively high, the cost is relatively high, and this method only reduces the content of 2-acetyl-6-naphthoic acid, and has no significant effect on the content of 2-formyl-6-naphthoic acid. CN 103772191 B (title: Preparation method of terephthalic acid) adopts adding Ce 3+ 、Nd 3 + Cr 3+ , Sb 3+ , Hf 4+ 、Zr 4+ At least one transition metal ion and a quaternary ammonium ion with a total number of carbon atoms of 4 to 8 and 21 to 30, respectively, are used as co-catalysts to significantly reduce the content of p-carboxybenzaldehyde. CN 114054085 B (titled: Catalyst composition and method for synthesizing isophthalic acid by oxidation of meta-xylene) adopts a new catalyst composition, introducing Br and amino groups on the aromatic ring of anthraquinone sulfonic acid to improve the activity of the catalyst. Compared with traditional hydrogen bromide and sodium bromide, the catalyst composition reduces the content of 3-carboxybenzaldehyde in the product by more than half. Summary of the invention

[0005] The technical problem to be solved by the present invention is the problem of high content of aldehyde intermediates in the preparation of aromatic carboxylic acids by oxidation of substituted aromatic hydrocarbons in the prior art. A method for preparing aromatic carboxylic acids using ionic liquids is provided. The method is applicable to a variety of substrates and can significantly reduce the content of aldehyde intermediates in crude aromatic carboxylic acids.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is as follows: The method for preparing aromatic carboxylic acid by oxidation of substituted aromatic hydrocarbons comprises the following steps: (1) placing a catalyst, a solvent, an ammonium salt and an imidazole ionic liquid in a reaction kettle; (2) using a high-pressure feed pump to add the substituted aromatic hydrocarbon (if the substituted aromatic hydrocarbon is solid at room temperature, it is heated to a molten state) into the above-mentioned reaction kettle, and at the same time, introducing air to react; (3) After the substituted aromatic hydrocarbon feed is completed, the reaction is continued for 0.5 to 3 hours to obtain a crude aromatic carboxylic acid mixture as a product.

[0007] The invention effectively reduces the content of aldehyde intermediates in crude aromatic carboxylic acid by adding ammonium salt and imidazole ionic liquid into the solution.

[0008] In the above technical solution, the solvent in step (1) is a mixture of one or more lower aliphatic carboxylic acids.

[0009] In the above technical solution, the catalyst in step (1) is a catalyst containing Co 2+ , Mn 2+ Br - of compounds.

[0010] In the above technical solution, in the catalyst of step (1), the mass concentration of the cobalt-based catalyst in the solution is 500-8000 ppm.

[0011] In the above technical solution, in the catalyst of step (1), the molar ratio of Mn / Co is 0.5-10.

[0012] In the above technical solution, in the catalyst of step (1), the molar ratio of Br / (Co+Mn) is 1-10.

[0013] In the above technical scheme, Co is preferably used in the form of cobalt acetate, Mn is preferably used in the form of manganese acetate, and Br is preferably used in the form of hydrobromic acid. For convenience, cobalt acetate is calculated as Co(OAc)2·4H2O, manganese acetate is calculated as Mn(OAc)2·4H2O, and hydrobromic acid is calculated as HBr (48wt% H2O).

[0014] In the above technical solution, the ammonium salt in step (1) is a mixture of one or more of ammonium acetate, ammonium sulfate and ammonium chloride.

[0015] In the above technical solution, the ionic liquid described in step (1) is an imidazole ionic liquid, mainly including but not limited to 1-butyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium tetrafluoroborate, etc.

[0016] In the above technical solution, the reaction temperature is 150~250℃.

[0017] In the above technical solution, the reaction pressure is 1~4MPa, and the pressure is gauge pressure.

[0018] In the above technical solution, the mass ratio of the substituted aromatic hydrocarbon added to the kettle to the solvent is 1:3-1:25.

[0019] In the above technical scheme, the substituted aromatic hydrocarbons described in step (2) refer to substances such as benzene, naphthalene or aromatic compounds having one or more substituted alkyl groups (or functional groups having oxidized methyl groups), mainly including but not limited to o-xylene, m-xylene, p-xylene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, 1,2,4,5-tetramethylbenzene, dimethyl substituted biphenyl, 2,6-dimethylnaphthalene, 2,6-diethylnaphthalene, 2,6-diisopropylnaphthalene, 2,7-dimethylnaphthalene, 2,3-dimethylnaphthalene, 2-methyl-6-acetylnaphthalene, 5-hydroxymethylfurfural, etc.

[0020] In the above technical scheme, the feed rate of the substituted aromatic hydrocarbon in step (2) has a significant effect on the oxidation effect. Although a high feed rate can increase the yield of aromatic carboxylic acid and reduce the possibility of deep oxidation, the purity of the obtained aromatic carboxylic acid is low, and the content of incompletely oxidized aldehyde intermediates in the product is high, which is not conducive to subsequent purification. The mass space velocity of the substituted aromatic hydrocarbon is 0.01~0.5min -1 .

[0021] The product of the invention is cooled, decompressed and separated. The crude product is centrifuged, washed with acetic acid and distilled water in sequence and then dried. The product is dissolved in dimethyl sulfoxide and analyzed by high performance liquid chromatography.

[0022] The technical key of the present invention is to convert the aldehyde intermediates generated in the reaction process into soluble ammonium salts by adding ammonium salts and imidazole ionic liquids, so that the aldehyde intermediate ammonium salts can fully react in the reaction process, thereby reducing the content of the aldehyde intermediates in the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a simplified process flow diagram for preparing aromatic carboxylic acids using ionic liquids. DETAILED DESCRIPTION

[0024] [Example 1] This example uses paraxylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O), 8.48 g NH4(OAc)2 and 3816 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of p-xylene was added into the reactor at a rate of 4.89 g / min to react. (4) After the feeding of paraxylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude terephthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of p-carboxybenzaldehyde was 434ppm after analysis and calculation. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0025] [Example 2] This example uses paraxylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O), 21.2 g 1-butyl-3-methylimidazolium bromide and 3816 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of p-xylene was added into the reactor at a rate of 4.89 g / min to react. (4) After the feeding of paraxylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude terephthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of p-carboxybenzaldehyde was 1684ppm after analysis and calculation. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0026] [Example 3] This example uses paraxylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O), 8.48 g NH4(OAc)2, 21.2 g 1-butyl-3-methylimidazolium bromide and 3816 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of p-xylene was added into the reactor at a rate of 4.89 g / min to react. (4) After the feeding of paraxylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude terephthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of p-carboxybenzaldehyde was 186ppm after analysis and calculation. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0027] [Example 4] This example uses paraxylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O), 21.2 g NH4(OAc)2, 21.2 g 1-butyl-3-methylimidazolium bromide and 3816 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of p-xylene was added into the reactor at a rate of 4.89 g / min to react. (4) After the feeding of paraxylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude terephthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of p-carboxybenzaldehyde was 156ppm after analysis and calculation. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0028] [Example 5] This example uses paraxylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O), 21.2 g NH4(OAc)2, 21.2 g 1-ethyl-3-methylimidazolium bromide and 3816 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of p-xylene was added into the reactor at a rate of 4.89 g / min to react. (4) After the feeding of paraxylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude terephthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of p-carboxybenzaldehyde was 165ppm after analysis and calculation. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0029] [Example 6] This example uses paraxylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O), 21.2 g NH4(OAc)2, 21.2 g 1-ethyl-3-methylimidazolium acetate and 3816 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of p-xylene was added into the reactor at a rate of 4.89 g / min to react. (4) After the feeding of paraxylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude terephthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of p-carboxybenzaldehyde was 165ppm after analysis and calculation. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0030] [Example 7] This example uses meta-xylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O), 21.2 g NH4(OAc)2, 21.2 g 1-butyl-3-methylimidazolium bromide and 3816 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of m-xylene was added into the reactor at a rate of 4.88 g / min to carry out the reaction. (4) After the feeding of meta-xylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude isophthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of m-carboxybenzaldehyde was calculated to be 108 ppm. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0031] [Example 8] This example uses 2,6-dimethylnaphthalene as raw material: (1) 3.68 g Co(OAc)2·4H2O, 10.86 g Mn(OAc)2·4H2O, 19.93 g HBr (48 wt% H2O), 31.25 g NH4(OAc)2, 31.25 g 1-ethyl-3-methylimidazolium acetate and 5623.92 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 625 g of 2,6-dimethylnaphthalene was added into the reactor at a rate of 6.19 g / min to react. (4) After the feeding of 2,6-dimethylnaphthalene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude 2,6-naphthalene dicarboxylic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of 6-formyl-2-naphthoic acid was 112 ppm after analysis and calculation. For ease of illustration and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0032] [Example 9] This example uses 2,6-diisopropylnaphthalene as raw material: (1) 4.25 g Co(OAc)2·4H2O, 12.54 g Mn(OAc)2·4H2O, 22.99 g HBr (48 wt% H2O), 42.47 g NH4(OAc)2, 42.47 g 1-ethyl-3-methylimidazolium acetate and 7643.88 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 849.32 g of 2,6-diisopropylnaphthalene was added into the reactor at a rate of 8.95 g / min to carry out reaction. (4) After the feeding of 2,6-diisopropylnaphthalene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude 2,6-naphthalene dicarboxylic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of 6-formyl-2-naphthoic acid was 105ppm after analysis and calculation, and the content of 6-acetyl-2-naphthoic acid was 89ppm. For ease of explanation and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0033] [Example 10] This example uses 2-methyl-6-acetylnaphthalene as raw material: (1) 3.68 g Co(OAc)2·4H2O, 10.86 g Mn(OAc)2·4H2O, 19.93 g HBr (48 wt% H2O), 36.8 g NH4(OAc)2, 36.8 g 1-ethyl-3-methylimidazolium acetate and 6624 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 736 g of 2-methyl-6-acetylnaphthalene was added into the reactor at a rate of 8.50 g / min to carry out reaction. (4) After the feeding of 2-methyl-6-acetylnaphthalene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude 2,6-naphthalene dicarboxylic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of 6-formyl-2-naphthoic acid was 98ppm after analysis and calculation, and the content of 6-acetyl-2-naphthoic acid was 101ppm. For ease of illustration and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0034] [Comparative Example 1] This comparative example uses paraxylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O) and 3816 g acetic acid were mixed and added into a 5 L titanium reactor. (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of p-xylene was added into the reactor at a rate of 4.89 g / min to react. (4) After the feeding of paraxylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude terephthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of p-carboxybenzaldehyde was 4385ppm after analysis and calculation. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0035] [Comparative Example 2] This comparative example uses meta-xylene as raw material: (1) 2.12 g Co(OAc)2·4H2O, 6.26 g Mn(OAc)2·4H2O, 11.48 g HBr (48 wt% H2O) and 3816 g acetic acid were mixed and added into a 5 L titanium reactor. (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 424 g of m-xylene was added into the reactor at a rate of 4.88 g / min to carry out the reaction. (4) After the feeding of meta-xylene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude isophthalic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of m-carboxybenzaldehyde was calculated to be 4077 ppm. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0036] [Comparative Example 3] This comparative example uses 2,6-dimethylnaphthalene as raw material: (1) 3.68 g Co(OAc)2·4H2O, 10.86 g Mn(OAc)2·4H2O, 19.93 g HBr (48 wt% H2O) and 5623.92 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 625 g of 2,6-dimethylnaphthalene was added into the reactor at a rate of 6.19 g / min to react. (4) After the feeding of 2,6-dimethylnaphthalene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude 2,6-naphthalene dicarboxylic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of 6-formyl-2-naphthoic acid was 8568ppm after analysis and calculation. For ease of illustration and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0037] [Comparative Example 4] This comparative example uses 2,6-diisopropylnaphthalene as the raw material: (1) 4.25 g Co(OAc)2·4H2O, 12.54 g Mn(OAc)2·4H2O, 22.99 g HBr (48 wt% H2O) and 7643.88 g acetic acid were mixed and added into a 5 L titanium reactor. (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 849.32 g of 2,6-diisopropylnaphthalene was added into the reactor at a rate of 8.95 g / min to carry out reaction. (4) After the feeding of 2,6-diisopropylnaphthalene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude 2,6-naphthalene dicarboxylic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of 6-formyl-2-naphthoic acid was 4089ppm after analysis and calculation, and the content of 6-acetyl-2-naphthoic acid was 2880ppm. For ease of illustration and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0038] [Comparative Example 5] This comparative example uses 2-methyl-6-acetylnaphthalene as raw material: (1) 3.68 g Co(OAc)2·4H2O, 10.86 g Mn(OAc)2·4H2O, 19.93 g HBr (48 wt% H2O) and 6624 g acetic acid were mixed and added into a 5 L titanium reactor; (2) First, use argon to exhaust the air in the reactor and then pressurize it to 1.5 MPa. Adjust the back pressure valve behind the condenser to keep the pressure in the reactor stable. (3) Stirring and heating were started. When the temperature reached 200°C, high-purity air was introduced at a rate of 20 L / min until the pressure reached 2.5 MPa. Then, 736 g of 2-methyl-6-acetylnaphthalene was added into the reactor at a rate of 8.50 g / min to carry out reaction. (4) After the feeding of 2-methyl-6-acetylnaphthalene is completed, the reaction temperature is maintained at 200°C and the reaction pressure is maintained at 2.5 MPa for a further 2 h; (5) After the reaction is completed, the mixed solution containing crude 2,6-naphthalene dicarboxylic acid is filtered and washed with 80°C acetic acid and 80°C distilled water in turn, with the amount of acetic acid and distilled water both being 500 g. After drying, the content of the aldehyde intermediate is measured by high performance liquid chromatography; The content of 6-formyl-2-naphthoic acid was 3865ppm after analysis and calculation, and the content of 6-acetyl-2-naphthoic acid was 101ppm. For ease of description and comparison, the catalyst composition, reaction conditions and analysis results are listed in the table.

[0039]

[0040] In the table, the aldehyde intermediates with 2-methyl-6-acetylnaphthalene as the raw material, and the / before and after respectively represent the contents of 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid.

Claims

1. A method for preparing aromatic carboxylic acid using ionic liquid, comprising the following steps: A catalyst, a solvent, an ammonium salt and an ionic liquid are placed in a reaction kettle, substituted aromatic hydrocarbons are introduced into the reaction kettle at a certain flow rate (if the substituted aromatic hydrocarbons are solid at room temperature, they are heated to a molten state), and air is introduced to react; after all the substituted aromatic hydrocarbons are added, the reaction is continued for 0.5 to 3 hours to obtain a product aromatic carboxylic acid; the catalyst is a mixture of cobalt, manganese and bromine compounds.

2. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The substituted aromatic hydrocarbons are benzene, naphthalene or aromatic-like compounds with one or more substituted alkyl groups (or functional groups with oxidized methyl groups). They mainly include but are not limited to o-xylene, m-xylene, p-xylene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, 1,2,4,5-tetramethylbenzene, dimethyl-substituted biphenyl, 2,6-dimethylnaphthalene, 2,6-diethylnaphthalene, 2,6-diisopropylnaphthalene, 2,7-dimethylnaphthalene, 2,3-dimethylnaphthalene, 2-methyl-6-acetylnaphthalene, 5-hydroxymethylfurfural, etc.

3. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The mass concentration of the cobalt-based catalyst in the solution is 500-8000 ppm.

4. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The Mn / Co molar ratio in the catalyst used is 0.5~10.

5. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The molar ratio of Br / (Co+Mn) in the catalyst used is 1-10.

6. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The reaction temperature is 150~250℃.

7. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The reaction pressure is 1~4MPa.

8. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The solvent used is one or more mixtures of lower aliphatic carboxylic acids.

9. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The ammonium salt used is a mixture of ammonium acetate, ammonium sulfate, ammonium chloride or one or more thereof.

10. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The ionic liquid used is an imidazolium ionic liquid, mainly including but not limited to 1-butyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium tetrafluoroborate, etc.

11. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The mass ratio of the substituted aromatic hydrocarbon added into the kettle to the solvent is 1:3-1:

25.

12. The method for preparing an aromatic carboxylic acid according to claim 1, characterized in that: The mass space velocity of the substituted aromatic hydrocarbon is 0.01~0.5min -1 .

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