A method for oxidizing a polysubstituted benzene

Abstract

The present invention relates to a method for oxidizing a polysubstituted benzene, which method comprises: in an oxygen-containing atmosphere, bringing the polysubstituted benzene into contact with a catalyst for an oxidation reaction, wherein the catalyst contains a nitrogen-carbon material treated with ammonium chloride. The method of the present invention has a relatively high conversion rate of the reactants and a high selectivity to the target product, effectively avoiding over-oxidation.

Description

Technical Field

[0001] The present invention relates to a method for oxidizing polysubstituted benzene. Background Art

[0002] Pyromellitic dianhydride, the oxidation product of durene, is an important chemical intermediate.

[0003] Pyromellitic dianhydride is mainly used in the production of high-tech materials such as polyimide films or as a curing agent for high-grade powder coatings. It is one of the important monomers for synthesizing the novel heat-resistant resin polyimide. In recent years, the consumption in the fields of high-speed railways and wind power generation has increased rapidly, driving the development of the pyromellitic dianhydride industry. The vast majority of global pyromellitic dianhydride producers are concentrated in China, and the same is true for the production of high-purity electronic-grade pyromellitic dianhydride. The current mature process is to first oxidize the raw material into an acid and then dehydrate it into pyromellitic dianhydride. For example, in the oxidation section of durene, the existing process is mainly the high-temperature gas-phase catalytic oxidation method of durene. After melting, durene is vaporized by a vaporizer and then enters the oxidation reactor, where an oxidation reaction occurs under the action of a catalyst. Since the gas-phase catalytic oxidation process of durene to produce pyromellitic dianhydride is a complex multiphase catalytic process consisting of a series of reactions. The demethylation reaction of durene generates pseudocumene, o-xylene, mesitylene, benzene, etc., which are respectively oxidized to phthalic anhydride, trimellitic anhydride, and trimellitic anhydride on the catalyst, resulting in low selectivity and yield of pyromellitic dianhydride. The gas-phase oxidation process uses a catalyst with vanadium-titanium oxide as the main active component to catalytically oxidize durene with air. However, the existing durene oxidation methods have problems such as low conversion rate and poor selectivity, and urgent improvement is needed. Summary of the Invention

[0004] The object of the present invention is to provide a method for oxidizing polysubstituted benzene, which has a high conversion rate for polysubstituted benzene, excellent selectivity for the target product, and low selectivity for the completely oxidized product COx.

[0005] To achieve the above object, the present invention provides a method for oxidizing polysubstituted benzene, which includes: in an oxygen-containing atmosphere, bringing polysubstituted benzene into contact with a catalyst for an oxidation reaction, and the catalyst contains a nitrogen-carbon material treated with ammonium chloride.

[0006] Optionally, the conditions of the oxidation reaction include: temperature is 250 - 500 °C, time is 0.1 - 24 hours, and pressure is 0.2 - 5 MPa.

[0007] Optionally, relative to 100 mL of the polysubstituted benzene, the amount of the catalyst used is 0.1 - 10 g.

[0008] Optionally, the oxygen-containing atmosphere is oxygen or air; the concentration of oxygen in the oxygen-containing atmosphere is 10 - 100% by volume, preferably 20 - 100% by volume, and more preferably 99 - 100% by volume.

[0009] Optionally, the molar ratio of oxygen in the oxygen-containing atmosphere to the amount of the polysubstituted benzene is (2-20):1.

[0010] Optionally, the nitrogen-carbon material after being treated with ammonium chloride is prepared by a method including the following steps: calcining melamine at 500-1000 °C for 1-12 hours to obtain a nitrogen-carbon material; and subjecting the nitrogen-carbon material and an aqueous solution of ammonium chloride to hydrothermal treatment.

[0011] Optionally, the conditions of the hydrothermal treatment include: temperature being 120-300 °C and time being 0.1-24 hours.

[0012] Optionally, the weight ratio of the nitrogen-carbon material to the amount of the aqueous solution of ammonium chloride is 1:(1-100); and the concentration of ammonium chloride in the aqueous solution of ammonium chloride is 1-30% by weight.

[0013] Optionally, the average particle size of the nitrogen-carbon material after being treated with ammonium chloride is 10-500 nm, preferably 50-200 nm;

[0014] The weight of the nitrogen-carbon material after being treated with ammonium chloride and having an average particle size of 20-100 nm accounts for 5-45% of the total weight of the nitrogen-carbon material after being treated with ammonium chloride, preferably 10-40%.

[0015] Optionally, the polysubstituted benzene is selected from durene, alkyl-substituted durene or halogenated durene.

[0016] Through the above technical solution, the method of the present invention is simple, efficient and easy to realize industrialization, has a high conversion rate of raw materials, a high selectivity for the target product, and can also effectively avoid over-oxidation.

[0017] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation part. Specific Embodiments

[0018] The following details the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention and are not used to limit the present invention.

[0019] The present invention provides a method for oxidizing a polysubstituted benzene, the method comprising: in an oxygen-containing atmosphere, bringing the polysubstituted benzene into contact with a catalyst for an oxidation reaction, wherein the catalyst contains a nitrogen-carbon material after being treated with ammonium chloride.

[0020] The method of the present invention uses a nitrogen-carbon material after being treated with ammonium chloride as a catalyst to oxidize a polysubstituted benzene. The method is simple, efficient and easy to operate, can be carried out on existing industrial equipment, has a high conversion rate of raw materials, a high yield of the target product, and can also effectively avoid over-oxidation.

[0021] In a specific embodiment of the present invention, the conditions for the oxidation reaction include: a temperature of 250 - 500 °C, a time of 0.1 - 24 hours, and a pressure of 0.2 - 5 MPa; preferably, the temperature is 300 - 450 °C, the time is 0.5 - 12 hours, and the pressure is 0.5 - 3 MPa. Under the above reaction conditions, the conversion rate of the raw material and the selectivity to the target product can be further improved.

[0022] According to the present invention, the polysubstituted benzene may be selected from durene, alkyl-substituted durene, or halogenated durene, and preferably the polysubstituted benzene is durene. Among them, the alkyl in the alkyl-substituted durene may be an alkyl group having 1 - 10 carbon atoms, including but not limited to methyl, ethyl, propyl, n-butyl, isobutyl, etc.; the halogenated durene may include chlorinated durene, brominated durene, etc. In a specific embodiment of the present invention, relative to 100 mL of the polysubstituted benzene, the amount of the catalyst used is 0.1 - 10 g, preferably 1 - 5 g.

[0023] The present invention does not make specific limitations on the oxygen-containing atmosphere, as long as it is an atmosphere containing oxygen, such as oxygen or air; the oxygen content in the oxygen-containing atmosphere can vary within a large range. In one embodiment, the oxygen concentration in the oxygen-containing atmosphere is 10 - 100 vol%, preferably 20 - 100 vol%, and more preferably 99 - 100 vol%.

[0024] According to the present invention, the molar ratio of oxygen in the oxygen-containing atmosphere to the amount of the polysubstituted benzene used can vary within a large range, for example, it can be (2 - 20):1. In a specific embodiment, the molar ratio of oxygen in the oxygen-containing atmosphere to the amount of the polysubstituted benzene used is (5 - 10):1.

[0025] In a specific implementation method of the present invention, the nitrogen-carbon material treated with ammonium chloride is prepared by a method including the following steps: first, melamine is calcined at 500 - 1000 °C for 1 - 12 hours to obtain a nitrogen-carbon material; then the nitrogen-carbon material is contacted with an aqueous solution of ammonium chloride for hydrothermal treatment. The calcination can be carried out in a device commonly used by those skilled in the art, such as a muffle furnace or a tube furnace. No specific limitations are made on the calcination atmosphere, which can be an inert atmosphere or an air atmosphere. The nitrogen-carbon material treated with ammonium chloride prepared by the above method has relatively excellent activity for catalytic oxidation of polysubstituted benzene.

[0026] In a specific embodiment of the present invention, the calcination temperature is 600 - 800 °C, and the time is 2 - 10 hours.

[0027] In a specific embodiment of the present invention, the conditions for hydrothermal treatment may include: the temperature is 120 - 300 °C, and the time is 0.1 - 24 hours; preferably, the temperature is 150 - 250 °C, and the time is 5 - 18 hours. Among them, no specific limitation is imposed on the pressure of hydrothermal treatment, which can be autogenous pressure or external pressure, and preferably it is carried out under autogenous pressure.

[0028] In a specific embodiment of the present invention, the weight ratio of the nitrogen-carbon material to the amount of the aqueous solution of ammonium chloride can vary within a relatively large range, preferably 1:(1 - 100), more preferably 1:(5 - 75); the concentration of ammonium chloride in the aqueous solution of ammonium chloride can also vary within a relatively large range, for example, it can be 1 - 30% by weight, preferably 5 - 20% by weight. When the weight ratio of the nitrogen-carbon material and the amount of the aqueous solution of ammonium chloride is within the above range, a nitrogen-carbon material treated with ammonium chloride having better catalytic performance can be prepared.

[0029] According to the present invention, the average particle size of the nitrogen-carbon material treated with ammonium chloride can be 10 - 500 nm, preferably 50 - 200 nm. In a specific embodiment, the weight of the nitrogen-carbon material treated with ammonium chloride having an average particle size of 20 - 100 nm can account for 5 - 45% of the total weight of the nitrogen-carbon material treated with ammonium chloride, preferably 10 - 40%. In the present invention, "particle size" refers to the maximum three-dimensional length of the particle, that is, the distance corresponding to the two points with the largest distance on the particle. The inventors of the present application surprisingly found that when the weight of the nitrogen-carbon material treated with ammonium chloride having an average particle size of 20 - 100 nm accounts for the total weight of the nitrogen-carbon material treated with ammonium chloride within the above preferred range, the nitrogen-carbon material treated with ammonium chloride has better performance in catalyzing the oxidation of polysubstituted benzene.

[0030] In a specific embodiment of the present invention, the content of the nitrogen-carbon material treated with ammonium chloride in the catalyst can vary within a relatively large range, for example, it can be 50 - 100% by weight, preferably 90 - 100% by weight. The catalyst may also contain transition metal oxides and the like conventionally used by those skilled in the art.

[0031] In a specific embodiment of the present invention, the oxidation reaction of 1,2,4,5-tetramethylbenzene is carried out intermittently in a slurry bed reactor, including the following steps: adding a catalyst, 1,2,4,5-tetramethylbenzene, and oxygen into the slurry bed reactor, and carrying out the reaction under the conditions of the oxidation reaction. The slurry bed reactor is well-known to those skilled in the art, for example, it can be a high-pressure closed reaction kettle.

[0032] In another specific embodiment of the present invention, the oxidation reaction of durene is carried out in a fixed-bed reactor, including the following steps: adding a catalyst in the isothermal section of the fixed-bed reactor, and after preheating and vaporizing durene, it is introduced into the reactor simultaneously with oxygen and contacts with the catalyst under oxidation reaction conditions for reaction. The total space velocity of the oxidation reaction can be 1-2000 h -1 , preferably 1-500 h -1 , more preferably 5-80 h -1 , and the molar ratio of the amount of durene to oxygen is 1:(2-20), preferably 1:(5-10).

[0033] The present invention will be further illustrated by the following examples, but the present invention is not limited thereby.

[0034] For those not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained by purchasing commercially.

[0035] In the following examples and comparative examples, gas chromatography (GC: Agilent, 7890A) and gas chromatography-mass spectrometry (GC-MS: Thermo Fisher Trace ISQ) were used to analyze the oxidation products.

[0036] In the following examples and comparative examples, taking the oxidation of durene as an example, the following formulas were used to calculate the raw material conversion rate, the selectivity of the target product, and the CO x Selectivity %:

[0037] Durene conversion % = (the molar amount of durene added before the reaction - the molar amount of durene remaining after the reaction) / the molar amount of durene added before the reaction × 100%;

[0038] Target product selectivity % = the molar amount of the target product formed after the reaction / (the molar amount of durene added before the reaction - the molar amount of durene remaining after the reaction) × 100%;

[0039] CO x Selectivity % = the molar amount of CO x formed after the reaction / [10 × (the molar amount of durene added before the reaction - the molar amount of durene remaining after the reaction)] × 100%.

[0040] The nitrogen-carbon material A treated with ammonium chloride used in Examples 1-5 was prepared by the following method:

[0041] In a nitrogen atmosphere, 50 g of melamine was placed in a 100 mL crucible, covered with a lid and sealed with a vacuum sealing ester. Then, the crucible was placed in a muffle furnace at 650 °C and calcined for 8 hours. After natural cooling to room temperature (20 °C, the same below), a nitrogen-carbon material was obtained. Then, the nitrogen-carbon material was added to an aqueous solution of ammonium chloride (concentration: 5 wt%) and mixed. The weight ratio of the nitrogen-carbon material to the aqueous solution of ammonium chloride was 1:8. Hydrothermal treatment was carried out at 220 °C for 12 hours, and then drying was carried out at 120 °C for 6 hours to obtain nitrogen-carbon material A treated with ammonium chloride. The average particle size of nitrogen-carbon material A treated with ammonium chloride was 180 nm, and the weight of the nitrogen-carbon material A treated with ammonium chloride with an average particle size of 20 - 100 nm accounted for 16% of the total weight of the nitrogen-carbon material A treated with ammonium chloride.

[0042] The nitrogen-carbon material B treated with ammonium chloride used in Example 6 was prepared by a method similar to that for preparing the nitrogen-carbon material A treated with ammonium chloride, except that: the calcination temperature in the muffle furnace was 850 °C and the time was 10 hours, and the weight ratio of the nitrogen-carbon material to the aqueous solution of ammonium chloride was 1:1. The average particle size of the nitrogen-carbon material B treated with ammonium chloride was 550 nm, and the weight of the nitrogen-carbon material B treated with ammonium chloride with an average particle size in the range of 20 - 100 nm accounted for 0.5% of the total weight of the nitrogen-carbon material B treated with ammonium chloride.

[0043] Example 1

[0044] The method for oxidizing 1,2,4,5-tetramethylbenzene provided in this example includes the following steps: 0.25 g of catalyst A and 10 mL of 1,2,4,5-tetramethylbenzene were respectively added into a 250 mL high-pressure sealed reaction kettle. After sealing, the air in the reaction kettle was displaced with oxygen (volume concentration > 99%). Then, the reaction kettle was heated to make the reaction temperature in the kettle 360 °C. Then, the pressure in the reaction kettle was increased to 2.0 MPa with oxygen and kept under pressure, and the reaction was timed. After 6 h of reaction, the product was detected, and the results are shown in Table 1, the same below.

[0045] Example 2

[0046] The method for oxidizing 1,2,4,5-tetramethylbenzene provided in this example includes the following steps: 0.5 g of catalyst A and 20 mL of 1,2,4,5-tetramethylbenzene were respectively added into a 250 mL high-pressure sealed reaction kettle. After sealing, the air in the reaction kettle was displaced with oxygen (volume concentration > 99%). Then, the reaction kettle was heated to make the reaction temperature in the kettle 380 °C. Then, the pressure in the reaction kettle was increased to 3.0 MPa with oxygen and kept under pressure. The results after 6 h of reaction are shown in Table 1.

[0047] Example 3

[0048] The method for oxidizing durene provided in this embodiment includes the following steps: Add 0.25 g of catalyst A and 60 mL of durene into a 250 mL high-pressure sealed reactor. After sealing, displace the air in the reactor with oxygen (volume concentration greater than 99%), then heat the reactor to make the reaction temperature in the reactor 400 °C, and then use oxygen to increase the pressure in the reactor to 1.0 MPa for pressure holding. The results after 6 h of reaction are shown in Table 1.

[0049] Example 4

[0050] Use a small fixed-bed micro-reactor to oxidize durene. Add 2 g of catalyst A in the isothermal section of the fixed bed. After preheating and vaporizing durene, it is introduced into the reactor together with oxygen and contacts with the catalyst at 350 °C and 2 MPa for reaction. The molar ratio of durene to oxygen is 1:8, and the total space velocity is 20 h -1 。

[0051] Example 5

[0052] Use the same method as in Example 4 to oxidize durene, except that the oxidation reaction temperature is 380 °C, the molar ratio of durene to oxygen is 1:4, and the total space velocity is 100 h -1 。

[0053] Example 6

[0054] Use the same method as in Example 1 to oxidize durene, except that catalyst B is used instead of catalyst A to oxidize durene.

[0055] Comparative Example 1

[0056] Oxidize durene according to the method of Example 1, except that no catalyst is added.

[0057] Comparative Example 2

[0058] Oxidize durene according to the method of Example 1, except that the catalyst is a nitrogen-carbon material not modified with ammonium chloride.

[0059] The nitrogen-carbon material not modified with ammonium chloride is prepared by a method including the following steps: In a nitrogen atmosphere, place 50 g of melamine in a 100 mL crucible, cover it with a vacuum sealant, and place the crucible in a muffle furnace at 650 °C for roasting for 8 hours. After natural cooling at room temperature (20 °C, the same below), nitrogen-carbon material a is obtained. The average particle size of nitrogen-carbon material a is 400 nm, and the weight of the nitrogen-carbon material with an average particle size of 20 - 100 nm accounts for 1% of the total weight of the nitrogen-carbon material.

[0060] Table 1

[0061]

[0062]

[0063] As can be seen from the above, the method of the present invention can effectively improve the conversion rate of mesitylene and the selectivity of the target product pyromellitic dianhydride relative to the comparative example method, and effectively reduce over-oxidation, especially the selectivity of complete oxidation to generate CO x .

[0064] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0065] In addition, it should be noted that, in the case of no conflict, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0066] In addition, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for oxidizing a polysubstituted benzene, the method comprising: Under an oxygen-containing atmosphere, a polysubstituted benzene is contacted with a catalyst to carry out an oxidation reaction, and the catalyst contains a nitrogen-carbon material treated with ammonium chloride; The nitrogen-carbon material treated with ammonium chloride is prepared by a method including the following steps: Melamine is calcined at 500-1000 °C for 1-12 hours to obtain a nitrogen-carbon material; The nitrogen-carbon material is contacted with an aqueous solution of ammonium chloride for hydrothermal treatment; The weight ratio of the nitrogen-carbon material to the amount of the aqueous solution of ammonium chloride is 1:(5-75); The concentration of ammonium chloride in the aqueous solution of ammonium chloride is 1-30 wt%; The average particle size of the nitrogen-carbon material treated with ammonium chloride is 10-500 nm; The weight of the nitrogen-carbon material treated with ammonium chloride having an average particle size of 20-100 nm accounts for 5-45% of the total weight of the nitrogen-carbon material treated with ammonium chloride; The polysubstituted benzene is 1,2,4,5-tetramethylbenzene.

2. The method according to claim 1, wherein The conditions of the oxidation reaction include: The temperature is 250-500 °C, the time is 0.1-24 hours, and the pressure is 0.2-5 MPa.

3. The method according to claim 1, wherein Relative to 100 mL of the polysubstituted benzene, the amount of the catalyst used is 0.1-10 g.

4. The method according to claim 1, wherein, The oxygen-containing atmosphere is oxygen or air; The concentration of oxygen in the oxygen-containing atmosphere is 10-100 vol%.

5. The method according to claim 4, wherein, The concentration of oxygen in the oxygen-containing atmosphere is 20-100 vol%.

6. The method according to claim 4, wherein The concentration of oxygen in the oxygen-containing atmosphere is 99-100 vol%.

7. The method according to claim 1, wherein The molar ratio of oxygen in the oxygen-containing atmosphere to the amount of the polysubstituted benzene used is (2-20):

1.

8. The method according to claim 1, wherein, The conditions of the hydrothermal treatment include: The temperature is 120-300 °C, and the time is 0.1-24 hours.

9. The method according to claim 1, wherein The average particle size of the nitrogen-carbon material treated with ammonium chloride is 50-200 nm; The weight of the nitrogen-carbon material treated with ammonium chloride having an average particle size of 20-100 nm accounts for 10-40% of the total weight of the nitrogen-carbon material treated with ammonium chloride.

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