Process for the liquid phase oxidation of durene

Abstract

The present application relates to a method for liquid phase oxidation of durene, which comprises: a first stage, in the presence of a catalyst, with acetic acid as a solvent, a liquid phase oxidation reaction of an oxidant source and durene to produce an intermediate mixture, the catalyst containing Co salt, Mn salt, Zr salt and bromide compound; a second stage, adding a mixture of bromide and pure water to the intermediate mixture, and continuing the oxidation reaction with the oxidant source to produce pyromellitic acid; wherein the concentration of oxidant in the oxidant source of the first stage is lower than the concentration of oxidant in the oxidant source of the second stage. By controlling the concentration of oxidant in the oxidant source of the first stage to be lower than the concentration of oxidant in the oxidant source of the second stage in the liquid phase oxidation process of durene, the yield of pyromellitic acid and the purity of crude pyromellitic acid are significantly improved.

Description

Technical Field

[0001] This invention relates to a method for liquid-phase oxidation of mesitylene. Background Technology

[0002] Pyromellitic acid (PMA) is obtained by oxidizing pyromellitic toluene and its derivatives. It is mainly used to synthesize pyromellitic dianhydride (PMDA). PMDA is an important raw material for organic synthesis industry and a basic raw material for the development of new chemical materials and high-value-added fine chemical products. It is a monomer for polymerizing with diamines to form polyimide (PI). Polyimide (PI) is widely used in aerospace, microelectronics, nanotechnology, liquid crystal, separation membrane, laser and other fields.

[0003] Polyimide is a novel synthetic material that is resistant to high and low temperatures, radiation, and impact, and possesses excellent electrical and mechanical properties. It plays a crucial role in the aerospace, nuclear energy, and electromechanical industries, where it has applications that other engineering plastics cannot replace. As the market demand for polyimide continues to expand, the demand for pyromellitic dianhydride (PMA), the main raw material for its synthesis, is also increasing daily. Simultaneously, PMA can undergo dehydration condensation with various alcohols and phenols, making it suitable as a shrinkage agent with different properties.

[0004] There are currently two main production methods for PMA. One method uses gas-phase oxidation, which can directly generate PMDA, using vanadium dioxide as the main catalyst and oxidizing at 450–500℃. The characteristic of this oxidation is that it can produce PMDA in one step, but the purity is not high, and the yield of PMDA is low. Currently, the industrial yield is below 45 wt%, with a large portion being further oxidized into CO2. The other method uses liquid-phase oxidation, which is the same as the MC process, using Co / Mn / Br / Zr as the catalyst system and oxidizing at 150–250℃ and 1.0–3.0 MPa. Then, purification processes such as crystallization, separation, and activated carbon adsorption are used to obtain PMA.

[0005] JP2014152143A discloses a method for preparing pyromellitic acid (PMA) using a two-step oxidation process: First, using Co / Mn / Br as a catalyst, the reaction is carried out at 150°C and 3.6 MPa with oxygen introduced for 30 minutes. Then, Co / Mn / Br catalyst is added, along with pure water, and the reaction continues for another 60 minutes until the temperature reaches 230°C. The reaction is then continued at 230°C for another 30 minutes. The entire reaction consumes 1.1% Br and 3000 ppm Co / Mn. The PMA yield is approximately 75%.

[0006] US5041633A discloses a two-step method for preparing aromatic polycarboxylic acids, using a Co / Mn / Br / Zr catalyst system. The materials and catalyst are added in a semi-continuous manner, with Br added at 1.5 wt%. The highest PMA yield is 84%, and the main impurities are trimellitic acid, 2,4,5-tricarboxytoluene, and 1,2-dicarboxyphenyl peptide.

[0007] The above methods for producing pyromellitic acid result in high impurity content, and the yield of pyromellitic acid still needs to be improved. Summary of the Invention

[0008] To address the aforementioned problems in the existing technology, this invention provides a method for the liquid-phase oxidation of pyromellitic acid, which has the characteristics of high product yield and high purity.

[0009] To achieve the above objectives, the present invention provides a method for the liquid-phase oxidation of mesitylene, the method comprising:

[0010] In the first stage, in the presence of a catalyst, acetic acid is used as a solvent and a source of oxidant is reacted with mesitylene in a liquid phase oxidation reaction to obtain an intermediate mixture. The catalyst contains Co salt, Mn salt, Zr salt and bromine compound.

[0011] In the second stage, a mixture of bromide and pure water is added to the intermediate material mixture to continue the oxidation reaction with the oxidant source to produce pyromellitic acid.

[0012] In this case, the concentration of oxidant in the first-stage oxidant source is lower than the concentration of oxidant in the second-stage oxidant source.

[0013] By adopting the above solution, the present invention has the following advantages:

[0014] This invention significantly improves the yield and purity of pyromellitic acid by controlling the concentration of the oxidant in the first-stage oxidant source during the liquid-phase oxidation of pyromellitic acid to be lower than that in the second-stage oxidant source. Detailed Implementation

[0015] 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.

[0016] This invention provides a method for the liquid-phase oxidation of mesitylene, the method comprising:

[0017] In the first stage, in the presence of a catalyst, acetic acid is used as a solvent and a source of oxidant is reacted with mesitylene in a liquid phase oxidation reaction to obtain an intermediate mixture. The catalyst contains Co salt, Mn salt, Zr salt and bromine compound.

[0018] In the second stage, a mixture of bromide and pure water is added to the intermediate material mixture to continue the oxidation reaction with the oxidant source to produce pyromellitic acid.

[0019] In this case, the concentration of oxidant in the first-stage oxidant source is lower than the concentration of oxidant in the second-stage oxidant source.

[0020] In the first and second stages of this invention, the oxidant source is a mixed gas. By controlling the concentration of the oxidant in the first stage oxidant source to be lower than that in the second stage oxidant source during the liquid-phase oxidation of pyromellitic acid, the yield and purity of crude pyromellitic acid are significantly improved.

[0021] According to a preferred embodiment of the present invention, the concentration of the oxidant in the first-stage oxidant source is 11-27% lower than the concentration of the oxidant in the second-stage oxidant source, preferably 15-25%. This further improves the yield of pyromellitic acid and the purity of crude pyromellitic acid.

[0022] The present invention can switch to the oxidant source with the concentration required for the second stage reaction during the second stage reaction.

[0023] In this invention, apart from the oxidant, the remaining components of the oxidant source are inert gases. Preferably, the first-stage oxidant source and the second-stage oxidant source each contain an inert gas and an oxidant.

[0024] The present invention does not have any special requirements for the type of inert gas. Preferably, the inert gas is selected from one or more of helium, nitrogen, and argon, with nitrogen being the most preferred.

[0025] In this invention, the oxidant is preferably an oxygen-containing gas, and more preferably elemental oxygen.

[0026] According to a preferred embodiment of the present invention, the temperature of the first stage is 10-130°C lower than the temperature of the second stage, preferably 20-50°C. This allows for further improvement in the yield and purity of the crude pyromellitic acid.

[0027] According to a preferred embodiment of the present invention, the temperature difference between the first stage and the second stage is the final temperature difference, that is, the temperature difference between the final temperature of the first stage and the final temperature of the second stage. For example, when the first stage or the second stage is a temperature-programmed reaction, it is the final temperature difference.

[0028] The present invention allows the temperature to be preheated to the temperature required for the second stage reaction after the first stage reaction is completed, and then the second stage reaction can be carried out.

[0029] In this invention, the second stage takes place in the presence of a catalyst to achieve a continued oxidation reaction. The catalysts for the first and second stages can be the same or different; preferably, the catalyst for the second stage is the catalyst remaining after the first stage reaction is complete, meaning that the oxidation reaction continues in the presence of the catalyst in both stages. After the catalyst completes the first stage reaction, the second stage reaction is continued by changing conditions such as the oxidant source.

[0030] In this invention, the other gas components in the gas mixture are gas components that are inert to this reaction, such as inert gases.

[0031] 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).

[0032] In this invention, there is no particular limitation on the concentration of the oxidant in the oxidant source in the first stage. According to a preferred embodiment of the invention, the mass content of the oxidant in the oxidant source in the first stage is 8-15%. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0033] According to a preferred embodiment of the present invention, the oxidant in the oxidant source in the first stage is elemental oxygen. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0034] In this invention, as long as the objective of this invention can be achieved, there are no particular restrictions on the conditions of the oxidation reaction in the first stage. According to a preferred embodiment of this invention, the conditions of the oxidation reaction in the first stage include: a temperature of 100–180°C, a pressure of 1.0–5.0 MPa, a time of 30–80 min, and a volumetric flow rate of the oxidant source to the volume of the liquid raw material of 2–6 h. -1 For example, the ratio of the volumetric flow rate of the oxidant to the volume of mesitylene can be 2.5 h. -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 and the purity of crude pyromellitic acid can be further improved.

[0035] According to a preferred embodiment of the present invention, the conditions for the oxidation reaction in the first stage include: a programmed temperature rise reaction is carried out in a temperature range of 100 to 180°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.

[0036] In this invention, there is no particular limitation on the concentration of the oxidant in the oxidant source in the second stage. According to a preferred embodiment of the invention, the mass content of the oxidant in the oxidant source in the second stage is 26-35%. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0037] According to a preferred embodiment of the present invention, the oxidant in the oxidant source in the second stage is elemental oxygen. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0038] In this invention, as long as the objective of this invention can be achieved, there are no particular restrictions on the conditions of the oxidation reaction in the second stage. According to a preferred embodiment of this invention, the conditions of the oxidation reaction in the second stage include: a temperature of 180–230°C, a pressure of 1.0–5.0 MPa, a time of 30–80 min, and a volumetric flow rate of the oxidant source to the volume of the liquid raw material of 2–6 h. -1 For example, the ratio of the volumetric flow rate of the oxidant source to the volume of mesitylene can be 2.5 h. -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 and the purity of crude pyromellitic acid can be further improved.

[0039] According to a preferred embodiment of the present invention, the oxidant source in the first stage is a N2 / O2 mixture, wherein the mass fraction of O2 is 8-15 wt%; the oxidation temperature is 100-180°C; the oxidation pressure is 1.0-5.0 MPa; and the oxidation time is 30-80 min. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0040] According to a preferred embodiment of the present invention, the oxidant source in the second stage is a N2 / O2 mixture, wherein the mass fraction of O2 is 26-35 wt%; the oxidation temperature is 180-230°C; and / or the oxidation pressure is 1.0-5.0 MPa; and the oxidation time is 30-80 min. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0041] In this invention, the Co salt 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 Co salt is cobalt acetate. By adopting the aforementioned preferred solution, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0042] In this invention, the Mn salt 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 Mn salt is manganese acetate. By adopting the aforementioned preferred solution, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0043] In this invention, the Zr salt 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 is zirconium acetate. By adopting the aforementioned preferred solution, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0044] In this invention, the bromine compound 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 bromine compound is one that is soluble in pure water or acetic acid. By adopting the aforementioned preferred embodiment, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0045] According to a preferred embodiment of the present invention, the bromine compound is selected from one or both of hydrogen bromide and tetrabromoethane. By adopting the aforementioned preferred embodiment, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0046] In this invention, as long as the objective of the invention can be achieved, there is no particular limitation on the concentration of bromide in the mixture of bromide and pure water in the second stage. According to a preferred embodiment of the invention, the concentration of bromide in the mixture of bromide and pure water in the second stage is 0.5–2.5 wt%, the amount of bromide and pure water added is 0.3–2.0 times the mass of mesitylene, and the mass flow rate of the mixture of bromide and pure water is 1–20 g / min. By adopting the aforementioned preferred scheme, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0047] 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. By adopting the aforementioned preferred embodiment, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0048] According to a preferred embodiment of the present invention, the mass ratio of acetic acid to mesitylene is 1 to 3. By adopting the aforementioned preferred embodiment, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0049] According to a preferred embodiment of the present invention, in 100g of pyromellitic acid, the catalyst comprises: Co salt (calculated as Co) of 300-1000 ppmw; Mn salt (calculated as Mn) of 200-800 ppmw; Zr salt (calculated as Zr) of 2-50 ppmw; and bromine compound (calculated as Br) of 100-1000 ppmw. By adopting the aforementioned preferred embodiment, the yield of pyromellitic acid and the purity of crude pyromellitic acid can be further improved.

[0050] 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.

[0051] 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.

[0052] The present invention does not have special requirements for the reactors used to realize the first-stage reaction and the second-stage reaction. For example, it can be a commonly used reactor such as an autoclave. The autoclave reactor includes, for example, a magnetic stirrer, a gas delivery pipe, an internal cooling bypass pipe, a reflux condenser, a thermocouple, a rupture disc, etc. Those skilled in the art will know this, and the present invention will not describe it in detail here.

[0053] The present invention will be described in detail below through embodiments. The following embodiments include:

[0054] Determination of each component: The sample to be analyzed was completely dissolved in dimethyl sulfoxide and analyzed by high performance liquid chromatography (HPLC);

[0055] Co, Mn, and Zr in the product were analyzed by ICP.

[0056]

[0057]

[0058] Example 1

[0059] The reaction was carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery tube, an internal cooling side tube, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed was 400 rpm, and heating was carried out by circulating hot oil. The reaction steps were as follows:

[0060] 1) Mesitylene, acetic acid, cobalt acetate tetrahydrate, manganese acetate tetrahydrate, zirconium acetate, and hydrogen bromide were mixed uniformly 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.

[0061] 2) Nitrogen at 3.0 MPa was added for a 30 - minute airtight test. A pressure drop of no more than 0.1 MPa within 30 minutes was considered qualified.

[0062] 3) Nitrogen was added, and the space velocity (the ratio of the nitrogen gas volume flow rate to the volume of the liquid raw material) was 6 h -1 The stirrer was started at a stirring rate of 400 rpm, and the temperature was raised to 120 °C while maintaining the pressure at 2.0 MPa.

[0063] 4) At 120 °C, an oxidant source (N2 / O2 mixture) with an O2 mass fraction of 10 wt% was switched, the pressure was 2.0 MPa, and the space velocity of the oxidant source (the ratio of the oxidant source volume flow rate to the volume of the liquid raw material) was 6 h -1 , and the temperature was raised to 180 °C at a heating rate of 1 °C / min to complete the first - stage reaction.

[0064] 5) After completing the first stage, the temperature was continued to be raised to 210 °C for 10 min. At the same time, 100 g of a 1.0 wt% hydrogen bromide aqueous solution was added to the reaction kettle at a flow rate of 10 g / min. The oxidant source was switched, the pressure was 2.0 MPa, the oxidant source was a N2 / O2 mixture with an O2 mass fraction of 30 wt%, and the space velocity of the oxidant source (the ratio of the oxidant source volume flow rate to the volume of the liquid raw material) was 6 h -1 , and the reaction was continued at 210 °C for 50 min. After completing the second - stage reaction, it was switched back to nitrogen again, cooled to room temperature, the pressure in the reaction kettle was released to atmospheric pressure, dimethyl sulfoxide was added to completely dissolve the oxidation product, and the product was analyzed by high - performance liquid chromatography. The analysis data are shown in Table 1.

[0065] Example 2

[0066] Same as Example 1, except that in the N2 / O2 mixture in step (4), the mass fraction of O2 was 8 wt%.

[0067] Example 3

[0068] Same as Example 1, except that in step (4), the mass fraction of O2 in the N2 / O2 mixture is 15 wt%.

[0069] Example 4

[0070] Same as Example 1, except that in step (4), the mass fraction of O2 in the N2 / O2 mixture is 7 wt%.

[0071] Example 5

[0072] Same as Example 1, except that in step (4), the mass fraction of O2 in the N2 / O2 mixture is 16 wt%.

[0073] Example 6

[0074] Same as Example 1, except that in step (5), the mass fraction of O2 in the N2 / O2 mixture is 26 wt%.

[0075] Example 7

[0076] Same as Example 1, except that in step (5), the mass fraction of O2 in the N2 / O2 mixture is 25 wt%.

[0077] Example 8

[0078] Same as Example 1, except that in step (5), the mass fraction of O2 in the N2 / O2 mixture is 35 wt%.

[0079] Example 9

[0080] Same as Example 1, except that in step (5), the mass fraction of O2 in the N2 / O2 mixture is 36 wt%.

[0081] Example 10

[0082] Similar to Example 1, except that the final temperature in step (4) is 170°C and the final temperature in step (5) is 210°C.

[0083] Example 11

[0084] Similar to Example 1, except that the final temperature in step (4) is 180°C and the final temperature in step (5) is 190°C.

[0085] Example 12

[0086] Similar to Example 1, except that the final temperature in step (4) is 175°C and the final temperature in step (5) is 220°C.

[0087] Comparative Example 1

[0088] The reaction was carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery tube, an internal cooling side tube, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed was 400 rpm, and heating was carried out by circulating hot oil. The reaction steps were as follows:

[0089] 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.

[0090] 2) Nitrogen at 3.0 MPa was added for a 30 - minute airtight test. A pressure drop of no more than 0.1 MPa within 30 minutes was considered qualified.

[0091] 3) Nitrogen was added with an airspeed (the ratio of the nitrogen gas volume flow rate to the volume of the liquid raw material) of 6 h -1 and the stirrer was started at a stirring rate of 400 rpm. The temperature was raised to 120 °C while maintaining the pressure at 2.0 MPa.

[0092] 4) At 120 °C, an oxidant source (N2 / O2 mixed gas) with an O2 mass fraction of 24 wt% was switched, the pressure was 2.0 MPa, and the oxidant source airspeed (the ratio of the oxidant source volume flow rate to the volume of the liquid raw material) was 6 h -1 , and the temperature was raised to 180 °C at a heating rate of 1 °C / min to complete the first - stage reaction.

[0093] 5) After completing the first stage, the temperature was continued to be raised to 210 °C for 10 min. At the same time, a 100 g 1.0 wt% aqueous hydrogen bromide solution was added to the reaction kettle at a flow rate of 10 g / min, the pressure was 2.0 MPa, the oxidant source was N2 / O2 mixed gas with an O2 mass fraction of 24 wt%, and the oxidant source airspeed (the ratio of the oxidant source volume flow rate to the volume of the liquid raw material) was 6 h -1 , and the reaction was continued at 210 °C for 50 min. After the temperature reaction was completed, it was switched back to nitrogen again, cooled to room temperature, the pressure in the reaction kettle was released to atmospheric pressure, dimethyl sulfoxide was added to completely dissolve the oxidation product, and the product was analyzed by high - performance liquid chromatography. The analysis data are shown in Table 1.

[0094] Table 1

[0095]

[0096] If the data in the table do not match the records in the examples, the examples shall prevail.

[0097] In summary, the method of this invention for producing pyromellitic acid has the advantages of high product yield and high purity.

[0098] 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 liquid-phase oxidation of mesitylene, characterized in that, The method includes: In the first stage, in the presence of a catalyst, acetic acid is used as a solvent and a source of oxidant is reacted with mesitylene in a liquid phase oxidation reaction to obtain an intermediate mixture. The catalyst contains Co salt, Mn salt, Zr salt and bromine compound. In the second stage, a mixture of bromide and pure water is added to the intermediate material mixture to continue the oxidation reaction with the oxidant source to produce pyromellitic acid. in, The concentration of oxidant in the first-stage oxidant source is 11-27% lower than the concentration of oxidant in the second-stage oxidant source; The first-stage oxidant source and the second-stage oxidant source each contain an inert gas and an oxidant, wherein the oxidant is an oxygen-containing gas.

2. The method according to claim 1, wherein, The concentration of the oxidant in the first-stage oxidant source is 15-25% lower than the concentration of the oxidant in the second-stage oxidant source; and / or The inert gas is selected from one or more of helium, nitrogen, and argon; and / or The temperature in the first stage is 10-130℃ lower than that in the second stage.

3. The method according to claim 2, wherein, The temperature in the first stage is 20-50℃ lower than that in the second stage.

4. The method according to any one of claims 1-3, wherein, Phase 1: The oxidant source contains 8-15% by mass of the oxidant; and / or The conditions for the oxidation reaction include: temperature of 100~180℃, pressure of 1.0~5.0MPa, time of 30~80min, and a volumetric flow rate ratio of the oxidant source to the liquid feedstock of 2~6h. -1 ; and / or Phase Two: The oxidant source contains 26-35% by mass; and / or The conditions for the oxidation reaction include: temperature of 180~230℃, pressure of 1.0~5.0MPa, time of 30~80min, and a volumetric flow rate ratio of the oxidant source to the liquid feedstock of 2~6h. -1 .

5. The method according to claim 4, wherein, First stage: The oxidant is elemental oxygen; and / or Second stage: The oxidant is elemental oxygen.

6. The method according to claim 1, wherein, Phase 1 The oxidant source is a N2 / O2 mixture, wherein the mass fraction of O2 is 8~15wt%; the oxidation temperature is 100~180℃; and / or the oxidation pressure is 1.0~5.0MPa, and the oxidation time is 30~80min.

7. The method according to claim 1, wherein, The second phase, The oxidant source is a N2 / O2 mixture, wherein the mass fraction of O2 is 26~35wt%; the oxidation temperature is 180~230℃; and / or the oxidation pressure is 1.0~5.0MPa; the oxidation time is 30~80min.

8. The method according to claim 1, wherein, 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.

9. The method according to claim 8, wherein, The bromine compound is selected from one or both of hydrogen bromide and tetrabromoethane.

10. The method according to claim 1, wherein, In the second stage, the concentration of bromide in the mixture of bromide and pure water is 0.5~2.5wt%, and the amount of bromide and pure water added is 0.3~2.0 times the mass of mesitylene.

11. The method according to claim 1, wherein, The mass ratio of acetic acid to mesitylene is 1 to 10.

12. The method according to claim 11, wherein, The mass ratio of acetic acid to mesitylene is 1 to 3.

13. The method according to claim 1, wherein, Based on 100g of mesitylene, the Co salt in the catalyst, calculated as Co, is 300~1000ppmw; Mn salts, calculated as Mn, range from 200 to 800 ppmw; Zr salts, calculated as Zr, range from 2 to 50 ppmw; Bromine compounds, expressed as Br, range from 100 to 1000 ppmw.

Images