Process for the production of pyromellitic acid

Abstract

The present application relates to a method for producing pyromellitic acid, which comprises: (1) contacting durene, an oxidation source, an acetic acid solvent and a catalyst to obtain a first oxidized material by liquid phase oxidation, wherein the catalyst contains a Co salt, a Mn salt, a Zr salt and a bromide compound; (2) using the first oxidized material as a raw material, adding a bromide solution, and continuing to contact the oxidation source to produce pyromellitic acid by oxidation; and steps (1) and / or (2) are carried out in the presence of carbon dioxide. The method for producing pyromellitic acid of the present application is carried out in the presence of carbon dioxide in steps (1) and / or (2), which can improve the yield of pyromellitic acid and reduce the impurity content in the product.

Description

Technical Field

[0001] This invention relates to a method for producing pyromellitic acid. Background Technology

[0002] Benzene polycarboxylic acids and their derivatives are important organic chemical raw materials, as well as basic raw materials for the development of new chemical materials and high-value-added fine chemical products. They are widely used in the production of resins, plastics, plasticizers and high-end materials.

[0003] 1,2,4,5-Benzenetetracarboxylicacid, a white crystalline powder with the molecular formula C2. 10 H6O8, with a molecular weight of 254.16, is slightly soluble in water, readily soluble in ethanol, and sparingly soluble in ether; it can sublimate. Its density is 1.79 (g / mL, 25 / 4℃), and its boiling point is 397–400℃ (dihydrate). It is used in the preparation of polyesters, polyamides, and polyimides, etc. It loses water at high temperatures to form an anhydride. The acid slowly absorbs moisture from the air, making it a key raw material for the production of matting curing agents.

[0004] The traditional method for producing pyromellitic acid involves heating benzenehexacarboxylic acid with potassium hydrogen sulfate and sulfuric acid. This process requires high temperatures and prolonged heating, resulting in poor product quality and low yield. Furthermore, it generates various side reactions and makes separation difficult.

[0005] Existing technologies also disclose that the alkaline-oxygen controlled oxidation method of coal can produce coal acid with a yield as high as 60%-70%, which contains up to 80% benzene polycarboxylic acid homologues. For a long time, many scholars have done a lot of work on the controlled oxidation of coal and the utilization of its products, but the difficulty of separating and purifying benzene polycarboxylic acid homologues has not been overcome. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low yield and high impurity content in the existing technology, and to provide a method for producing pyromellitic acid with high yield and low impurity content.

[0007] To achieve the above objectives, the present invention provides a method for producing pyromellitic tetracarboxylic acid, the method comprising:

[0008] (1) The first oxide material is obtained by contacting mesitylene, an oxidant source, acetic acid solvent and a catalyst in a liquid phase oxidation process. The catalyst contains Co salt, Mn salt, Zr salt and bromine-containing compounds.

[0009] (2) Using the first oxide material as raw material, add bromide solution and continue to contact with the oxidation source to produce pyromellitic acid;

[0010] Steps (1) and / or steps (2) are carried out in the presence of carbon dioxide, preferably steps (1) and (2) are carried out in the presence of carbon dioxide.

[0011] Preferably, in step (1), the oxidation source is a gas containing elemental oxygen, and more preferably, the content of elemental oxygen in the oxidation source is 5-40 wt%, and even more preferably 5-15 wt%.

[0012] Preferably, in step (1), the amount of carbon dioxide introduced is 5 to 10% of the total amount of the oxidation source and the total amount of carbon dioxide introduced, by mass.

[0013] Preferably, in step (1), the contact conditions include: a temperature of 100–190°C, a pressure of 1.0–10.0 MPa, and a time of 30–80 min.

[0014] Preferably, in step (2), the oxidation source is a gas containing elemental oxygen, and more preferably, the content of elemental oxygen in the oxidation source is 5-40 wt%, and more preferably 20-40 wt%.

[0015] Preferably, in step (2), the bromide solution is an aqueous bromide solution with a bromide concentration of 0.1 to 3 wt%, and the amount of bromide solution added is 0.1 to 3.0 times the mass of mesitylene.

[0016] Preferably, in step (2), the contact conditions include: a temperature of 200-250°C, a pressure of 1.0-10.0 MPa, and a time of 30-80 min.

[0017] Preferably, the mass ratio of acetic acid to mesitylene is 1 to 10, more preferably 1 to 3.

[0018] Preferably, the concentration of the oxidant in the oxidation source in step (1) is lower than the concentration of the oxidant in the oxidation source in step (2), preferably 15-25% lower.

[0019] Preferably, the temperature in step (1) is lower than the temperature in step (2), preferably 20-50°C lower.

[0020] In the present invention, steps (1) and / or (2) of the method for producing pyromellitic acid are carried out in the presence of carbon dioxide, which can improve the yield of pyromellitic acid and reduce the impurity content in the product. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] This invention provides a method for producing pyromellitic acid, the method comprising:

[0023] (1) The first oxide material is obtained by contacting mesitylene, an oxidant source, acetic acid solvent and a catalyst in a liquid phase oxidation process, wherein the catalyst contains Co salt, Mn salt, Zr salt and bromine compound;

[0024] (2) Using the first oxide material as raw material, add bromide solution and continue to contact with the oxidation source to produce pyromellitic acid;

[0025] Steps (1) and / or steps (2) are carried out in the presence of carbon dioxide, preferably steps (1) and (2) are carried out in the presence of carbon dioxide.

[0026] In the method for producing pyromellitic acid of the present invention, steps (1) and / or (2) are carried out in the presence of carbon dioxide, which can improve the yield of pyromellitic acid and reduce the impurity content in the product.

[0027] According to a preferred embodiment of the present invention, based on 100g of mesitylene, the Co salt, calculated as Co, has a content of 100-2000 ppmw, preferably 300-1000 ppmw; the Mn salt, calculated as Mn, has a content of 100-1000 ppmw, preferably 200-800 ppmw; the Zr salt, calculated as Zr, has a content of 1-100 ppmw, preferably 2-50 ppmw; and the bromine-containing compound, calculated as Br, has a content of 50-2000 ppmw, preferably 100-1000 ppmw. By adopting the aforementioned preferred embodiment, the yield of mesitylene tetracarboxylic acid can be further improved and the impurity content in the product can be reduced.

[0028] In this invention, the Co salt in the catalyst can be any conventional choice in the art, as long as it achieves the objective of the invention. According to a preferred embodiment of the invention, the Co salt in the catalyst is cobalt acetate. By adopting the aforementioned preferred solution, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0029] In this invention, the Mn salt in the catalyst can be any conventional choice in the art, as long as the objective of the invention can be achieved. According to a preferred embodiment of the invention, the Mn salt in the catalyst is manganese acetate. By adopting the aforementioned preferred solution, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0030] In this invention, the Zr salt in the catalyst can be any conventional choice in the art, as long as it achieves the purpose of the invention. According to a preferred embodiment of the invention, the Zr salt in the catalyst is zirconium acetate. By adopting the aforementioned preferred solution, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0031] In this invention, the bromine compound in the catalyst can be any conventional choice in the art, as long as it achieves the purpose of the invention. According to a preferred embodiment of the invention, the bromine compound in the catalyst is a bromine compound soluble in pure water or acetic acid, preferably selected from one or both of hydrogen bromide and tetrabromoethane. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0032] According to a preferred embodiment of the present invention, in step (1), the oxidation source is a gas containing elemental oxygen, preferably a gas containing elemental oxygen diluted with an inert gas, and more preferably the inert gas is selected from at least one of nitrogen, helium and argon.

[0033] According to a preferred embodiment of the present invention, in step (1), the content of elemental oxygen in the oxidation source is 5-40 wt%, preferably 5-15 wt%, and more preferably 8-15 wt%. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0034] In this invention, as long as the objective of this invention can be achieved, there is no particular limitation on the amount of carbon dioxide introduced in step (1). According to a preferred embodiment of this invention, the amount of carbon dioxide introduced in step (1) is 5-10% by mass of the total amount of the oxidation source and the total amount of carbon dioxide introduced. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0035] In this invention, as long as the objective of this invention can be achieved, the contact conditions in step (1) can be conventionally chosen in the art. According to a preferred embodiment of this invention, the contact conditions in step (1) include: a temperature of 100–190°C, and pressure and time determined according to specific needs, preferably a pressure of 1.0–10.0 MPa and a time of 30–80 min. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0036] In this invention, the contact conditions in step (1) include: a programmed temperature rise reaction is carried out in the temperature range of 100 to 190°C, the temperature difference between the initial temperature and the final reaction temperature is 50-80°C, and the heating rate is 1-5°C / min.

[0037] In this invention, as long as the objective of this invention can be achieved, there is no particular limitation on the volumetric flow rate of the mixed gas composed of the oxidant and carbon dioxide in step (1) to the volume ratio of the liquid raw material mixture. According to a preferred embodiment of this invention, in step (1), the volumetric flow rate of the mixed gas composed of the oxidant and carbon dioxide to the volume ratio of the liquid raw material mixture is 1-10 h. -1 Preferably 2-6h -1 For example, it could be 2.5h -1 3.0h -1 3.5h -1 4.0h -1 4.5h -1 6.0h -1 By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0038] According to a preferred embodiment of the present invention, in step (2), the oxidation source is a gas containing elemental oxygen, preferably a gas containing elemental oxygen diluted with an inert gas, and more preferably the inert gas is selected from at least one of nitrogen, helium and argon.

[0039] According to a preferred embodiment of the present invention, in step (2), the content of elemental oxygen in the oxidation source is 5-40 wt%, preferably 20-40 wt%, and more preferably 26-35 wt%. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0040] In this invention, as long as the objective of the invention can be achieved, there are no particular restrictions on the concentration of bromide in the bromide solution and the amount of bromide solution added in step (2). According to a preferred embodiment of the invention, the concentration of bromide in the bromide solution in step (2) is 0.1-3 wt%, preferably 0.5-2.5 wt%, and the amount of bromide solution added is 0.1-3.0 times the mass of mesitylene, preferably 0.3-2.0 times. The mass flow rate of the bromide solution is 1-20 g / min, and preferably the bromide solution is an aqueous bromide solution. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0041] In this invention, as long as the objective of this invention can be achieved, the contact conditions in step (2) can be conventionally chosen in the art. According to a preferred embodiment of this invention, the contact conditions in step (2) include: a temperature of 200–250°C, a pressure of 1.0–10.0 MPa, and a time of 30–80 min. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0042] In this invention, as long as the objective of this invention can be achieved, there is no particular limitation on the volume flow rate of the mixed gas composed of the oxidant source and carbon dioxide to the volume ratio of the first oxide material in step (2). According to a preferred embodiment of this invention, in step (2), the volume flow rate of the mixed gas composed of the oxidant source and carbon dioxide to the volume ratio of the first oxide material is 1-10 h. -1 Preferably 2-6h -1 For example, it could be 2.5h -1 3.0h -1 3.5h -1 4.0h -1 4.5h -1 6.0h -1 By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0043] In this invention, as long as the objective of this invention can be achieved, there is no particular limitation on the amount of carbon dioxide introduced in step (2). According to a preferred embodiment of this invention, the amount of carbon dioxide introduced in step (2) is 5-10% by mass of the total amount of the oxidation source and the total amount of carbon dioxide introduced. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0044] In this invention, the mass ratio of acetic acid to mesitylene is not particularly limited as long as the objective of the invention can be achieved. According to a preferred embodiment of the invention, the mass ratio of acetic acid to mesitylene is 1 to 10, preferably 1 to 3. By adopting the aforementioned preferred embodiment, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0045] According to a preferred embodiment of the present invention, the concentration of the oxidant in the oxidation source in step (1) is lower than the concentration of the oxidant in the oxidation source in step (2), preferably 15-25% lower. By adopting the aforementioned preferred solution, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0046] According to a preferred embodiment of the present invention, the temperature in step (1) is lower than the temperature in step (2), preferably 20-50°C lower, and preferably the temperature difference between step (1) and step (2) is the final temperature difference, that is, the temperature difference between the final temperature of step (1) and the final temperature of step (2). By adopting the aforementioned preferred scheme, the yield of pyromellitic acid can be further improved and the impurity content in the product can be reduced.

[0047] The method of the present invention further includes: checking the airtightness of the reaction system before adding the oxidant source, and purging the reaction system with an inert gas such as nitrogen. Specifically, before adding the oxidant source, the present invention adds nitrogen at a certain pressure, for example 3.0 MPa(a), and performs an airtightness test for a certain time, for example 30 minutes. A pressure drop of no more than 0.1 MPa is considered acceptable; then an inert gas, such as nitrogen, is added at a certain space velocity, for example 6 h⁻¹. -1 (The space velocity is the ratio of the volume of nitrogen gas to the volume of the liquid raw material mixture) purge, and stir at a certain stirring rate, such as 400 rpm, and heat to a certain temperature, such as 120°C, while maintaining a certain pressure, such as 2.0 MPa (a).

[0048] In this invention, the reactor in which the oxidation reaction occurs can be a conventional choice in the art. According to a preferred embodiment of the invention, the oxidation reaction is carried out in a high-pressure reactor equipped with a stirrer, a gas delivery pipe, a cooling bypass pipe, a reflux condenser, a thermocouple, and a rupture disc.

[0049] According to a preferred embodiment of the present invention, the conditions for the oxidation reaction include: a stirring speed of 100-1000 rpm and heating by circulating hot oil.

[0050] The present invention will be described in detail below through embodiments. The following embodiments include:

[0051] Product composition analysis: First, the sample to be analyzed was completely dissolved in dimethyl sulfoxide and analyzed by high performance liquid chromatography (HPLC).

[0052] Co, Mn, and Zr in the product were analyzed by ICP.

[0053]

[0054]

[0055] Example 1

[0056] The reaction was carried out in a 1000ml titanium autoclave equipped with a magnetic stirrer, gas delivery pipe, internal cooling bypass pipe, reflux condenser, thermocouple, and rupture disc. The stirring speed was 400 rpm, and heating was achieved via circulating hot oil. The reaction steps are as follows:

[0057] 1) Mix mesitylene, acetic acid, cobalt acetate tetrahydrate, manganese acetate tetrahydrate, zirconium acetate and hydrogen bromide evenly to obtain a liquid raw material mixture. The liquid raw material mixture contains 100 g of mesitylene, 300 g of acetic acid, 500 ppmw of cobalt, 250 ppmw of manganese, 10 ppmw of Zr, and 600 ppmw of bromine. Add the liquid raw material mixture to an autoclave and seal it.

[0058] 2) Add nitrogen at 3.0 MPa for a hermetic test for 30 min. If the pressure drop is no more than 0.1 MPa within 30 min, it is qualified.

[0059] 3) Add nitrogen with an airspeed (the ratio of the nitrogen volume flow rate to the volume of the liquid raw material mixture) of 6 h -1 and start the stirrer with a stirring rate of 400 rpm. Heat up to 120 °C while maintaining the pressure at 2.0 MPa.

[0060] 4) At 120 °C, use a N2 / O2 / CO2 mixed gas, in which the mass fraction of O2 is 10 wt%, the mass fraction of CO2 is 8 wt%, the pressure is 2.0 MPa, and the airspeed of the N2 / O2 / CO2 mixed gas (the ratio of the N2 / O2 / CO2 mixed gas volume flow rate to the volume of the liquid raw material mixture) is 6 h -1 , and raise the temperature to 180 °C at a heating rate of 1 °C / min to complete the first-stage reaction.

[0061] 5) After completing the first stage, continue heating to 210 °C for 10 min. At the same time, add 100 g of 1.0 wt% hydrogen bromide aqueous solution to the reaction kettle at a flow rate of 10 g / min. The pressure is 2.0 MPa. Use a N2 / O2 / CO2 mixed gas, in which the mass fraction of O2 is 30 wt%, the mass fraction of CO2 is 8 wt%, and the airspeed of the N2 / O2 / CO2 mixed gas (the ratio of the N2 / O2 / CO2 mixed gas volume flow rate to the volume of the liquid raw material mixture) is 6 h -1 , continue the reaction at 210 °C for 50 min. After completing the second-stage reaction, switch to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure, add dimethyl sulfoxide to completely dissolve the oxidation product, and analyze the product by high-performance liquid chromatography. The analysis data is shown in Table 1.

[0062] Example 2

[0063] Same as Example 1, except that in step 4), a N2 / O2 mixed gas (without CO2) is used.

[0064] Analyze the product by high-performance liquid chromatography. The analysis data is shown in Table 1.

[0065] Example 3

[0066] Same as Example 1, except that step 5) uses a N2 / O2 mixture (without CO2).

[0067] The product was analyzed using high performance liquid chromatography, and the analytical data are shown in Table 1.

[0068] Example 4

[0069] Same as Example 1, except that in step 4), the mass fraction of O2 in the N2 / O2 / CO2 mixture is 16 wt%.

[0070] The product was analyzed using high performance liquid chromatography, and the analytical data are shown in Table 1.

[0071] Example 5

[0072] Same as Example 1, except that in step 4), the CO2 mass fraction in the N2 / O2 / CO2 mixture is 5 wt%.

[0073] The product was analyzed using high performance liquid chromatography, and the analytical data are shown in Table 1.

[0074] Example 6

[0075] Same as Example 1, except that in step 4), the CO2 mass fraction in the N2 / O2 / CO2 mixture is 4 wt%.

[0076] The product was analyzed using high performance liquid chromatography, and the analytical data are shown in Table 1.

[0077] Example 7

[0078] Same as Example 1, except that in step 4), the CO2 mass fraction in the N2 / O2 / CO2 mixture is 11 wt%.

[0079] The product was analyzed using high performance liquid chromatography, and the analytical data are shown in Table 1.

[0080] Example 8

[0081] Same as Example 1, except that in step 5), the mass fraction of O2 in the N2 / O2 / CO2 mixture is 36 wt%.

[0082] The product was analyzed using high performance liquid chromatography, and the analytical data are shown in Table 1.

[0083] Example 9

[0084] Same as Example 1, except that in step 5), the CO2 mass fraction in the N2 / O2 / CO2 mixture is 4 wt%.

[0085] The product was analyzed using high performance liquid chromatography, and the analytical data are shown in Table 1.

[0086] Example 10

[0087] Same as Example 1, except that in step (5), the mass fraction of CO2 in the N2 / O2 / CO2 mixed gas is 11 wt%.

[0088] The product was analyzed by high performance liquid chromatography, and the analysis data are shown in Table 1.

[0089] Example 11

[0090] Same as Example 1, except that the final temperature in step (4) is 170 °C and the final temperature in step (5) is 210 °C.

[0091] Example 12

[0092] Same as Example 1, except that the final temperature in step (4) is 170 °C and the final temperature in step (5) is 230 °C.

[0093] Example 13

[0094] Same as Example 1, except that the final temperature in step (4) is 175 °C and the final temperature in step (5) is 220 °C.

[0095] Comparative Example 1

[0096] The reaction was carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery pipe, an internal cooling side pipe, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed was 400 rpm, and it was heated by circulating hot oil. The reaction steps were as follows:

[0097] 1) Mesitylene, acetic acid, cobalt acetate tetrahydrate, manganese acetate tetrahydrate, zirconium acetate, and hydrogen bromide were mixed evenly to obtain a liquid raw material mixture. The liquid raw material mixture contained 100 g of mesitylene, 300 g of acetic acid, 500 ppmw of cobalt, 250 ppmw of manganese, 10 ppmw of Zr, and 600 ppmw of bromine. The liquid raw material mixture was added to the autoclave and sealed.

[0098] 2) Nitrogen at 3.0 MPa was added for a 30-minute airtightness test. A pressure drop of no more than 0.1 MPa within 30 minutes was considered qualified.

[0099] 3) Nitrogen was added, and the space velocity (the volume flow rate of nitrogen gas to the volume of the liquid raw material mixture) was 6 h -1 and the stirrer was started with a stirring rate of 400 rpm, and the temperature was raised to 120 °C while maintaining the pressure at 2.0 MPa.

[0100] 4) At 120℃, a N2 / O2 mixture with an O2 mass fraction of 24 wt% was used for switching, at a pressure of 2.0 MPa, and the N2 / O2 mixture space velocity (the ratio of the N2 / O2 mixture volumetric flow rate to the volume of the liquid feedstock mixture) was 6 h⁻¹. -1 The temperature was increased to 180℃ at a rate of 1℃ / min to complete the first stage of the reaction.

[0101] 5) After completing the first stage, continue heating to 210℃ for 10 minutes. Simultaneously, add 100g of 1.0wt% hydrogen bromide aqueous solution to the reactor at a flow rate of 10g / min, with a pressure of 2.0MPa. Use an N2 / O2 mixture, where the mass fraction of O2 is 24wt%, and the N2 / O2 gas hourly space velocity (the ratio of the N2 / O2 gas volumetric flow rate to the volume of the liquid raw material mixture) is 6h. -1 The reaction was continued at 210℃ for 50 min. After the second stage of reaction was completed, nitrogen gas was switched back to the atmosphere and the mixture was cooled to room temperature. The pressure in the reactor was released to atmospheric pressure, and dimethyl sulfoxide was added to completely dissolve the oxidized product. The product was analyzed by high performance liquid chromatography, and the analysis data are shown in Table 1.

[0102] Table 1

[0103]

[0104] If the data in the table differs from that in the examples, the examples shall prevail.

[0105] In summary, the production of pyromellitic acetic acid using this invention has the advantages of high yield and low impurity content.

[0106] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing pyromellitic tetracarboxylic acid, characterized in that, The method includes: (1) The first oxide material is obtained by contacting mesitylene, an oxidant source, acetic acid solvent and a catalyst in the liquid phase to obtain the first oxide material, wherein the catalyst contains Co salt, Mn salt, Zr salt and bromine compound; (2) Using the first oxide material as raw material, add bromide solution and continue to contact with the oxidation source to produce pyromellitic acid; Steps (1) and (2) are carried out in the presence of carbon dioxide; Of which, based on 100g of mesitylene, Co salts, calculated as Co, range from 100 to 2000 ppmw; Mn salts, calculated as Mn, range from 100 to 1000 ppmw; Zr salts, calculated as Zr, range from 1 to 100 ppmw; Bromine-containing compounds, expressed as Br, range from 50 to 2000 ppmw; In steps (1) and (2), the oxidation source is a gas containing elemental oxygen; In steps (1) and (2), the amount of carbon dioxide introduced is 5-10% by mass of the total amount of the oxidation source and the total amount of carbon dioxide introduced; The concentration of the oxidant in the oxidation source in step (1) is lower than the concentration of the oxidant in the oxidation source in step (2).

2. The method according to claim 1, wherein, In the catalyst, The Co salt is cobalt acetate; and / or The Mn salt is manganese acetate; and / or The Zr salt is zirconium acetate; and / or The bromine compound is a bromine compound that can dissolve in pure water or acetic acid.

3. The method according to claim 2, wherein, In the catalyst, The bromine compound is selected from one or more of hydrogen bromide and tetrabromoethane.

4. The method according to any one of claims 1-3, wherein, In step (1), The content of elemental oxygen in the oxidation source is 5-40 wt%; The contact conditions include: a temperature of 100~190℃, a pressure of 1.0~10.0MPa, and a time of 30~80min.

5. The method according to claim 4, wherein, In step (1), The content of elemental oxygen in the oxidation source is 5-15 wt%; The contact conditions include: a programmed temperature rise reaction within a temperature range of 100~190℃, with a temperature difference of 50-80℃ between the initial temperature and the final reaction temperature, and a heating rate of 1-5℃ / min.

6. The method according to any one of claims 1-3, wherein, In step (1), The volumetric flow rate of the mixture of the oxidant and carbon dioxide is 1-10 h / min to the volume of the liquid feedstock mixture. -1 .

7. The method according to any one of claims 1-3, wherein, In step (2), The content of elemental oxygen in the oxidation source is 5-40 wt%; The contact conditions include: a temperature of 200~250℃, a pressure of 1.0~10.0MPa, and a time of 30~80min.

8. The method according to claim 7, wherein, In step (2), The content of elemental oxygen in the oxidation source is 20~40wt%.

9. The method according to any one of claims 1-3, wherein, In step (2), the volumetric flow rate of the mixed gas of the oxidation source and carbon dioxide to the volume of the first oxide material is 1-10 h. -1 .

10. The method according to any one of claims 1-3, wherein, In step (2), the concentration of bromide in the bromide solution is 0.1~3wt%, and the amount of bromide solution added is 0.1~3.0 times the mass of mesitylene.

11. The method according to claim 10, wherein, In step (2), The bromide solution is an aqueous bromide solution.

12. The method according to any one of claims 1-3, wherein, The mass ratio of acetic acid to mesitylene is 1 to 10; and / or The concentration of the oxidant in the oxidation source in step (1) is 15-25% lower than the concentration of the oxidant in the oxidation source in step (2); The temperature in step (1) is lower than the temperature in step (2).

13. The method according to claim 12, wherein, The mass ratio of acetic acid to mesitylene is 1-3; and / or The temperature in step (1) is 20-50°C lower than the temperature in step (2).

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