Method for preparing adipic acid by adopting microchannel reactor

Abstract

The invention discloses a method for preparing adipic acid by adopting a micro-channel reactor, which comprises the following steps: taking cyclohexane containing an initiator and oxygen-containing gas as raw materials, adding the raw materials into the micro-channel reactor, and carrying out oxidation reaction to generate the adipic acid, wherein the initiator comprises a free radical containing a cyclohexyl functional group and peroxide. The invention provides a novel method for generating adipic acid through oxidation in a short time of more than ten seconds to several minutes by taking cyclohexane containing an initiator and oxygen-containing gas as raw materials in a micro-channel reactor through preheating, mixing, reacting, post-processing and circulating. The whole process of feeding, preheating, mixing and oxidizing reaction is continuous, compared with intermittent reaction, the cyclohexane conversion rate, the adipic acid selectivity and the production efficiency are greatly improved, meanwhile, the safety of the oxidizing reaction process is effectively improved, and the method can be used for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and in particular relates to a method for preparing adipic acid by adopting a microchannel reactor. Background Art

[0002] Adipic acid is an important organic dibasic acid, widely used in chemical industry, food industry, fragrance and dye industry, etc.

[0003] At present, the cyclohexane method and the cyclohexene method are the two main ways to produce adipic acid in industry. Using oxygen as an oxidant, cyclohexane is catalytically oxidized to cyclohexanol and cyclohexanone intermediates, and then oxidized by nitric acid under copper and vanadium catalysts to produce adipic acid. This process requires controlling the cyclohexane single-pass conversion rate to less than 5% to ensure that the total selectivity of cyclohexanol and cyclohexanone is maintained at a high level (70-90%), resulting in low product yield and complex process. The cyclohexene process mainly includes cyclohexene hydration to cyclohexanol, and then nitric acid oxidation to obtain adipic acid, wherein cyclohexene is prepared from benzene by selective catalytic hydrogenation, which has the disadvantages of low selectivity and high catalyst cost. It can be seen that the above two adipic acid production processes have the disadvantages of complex process, low product yield and the use of nitric acid and catalysts, especially the use of nitric acid leads to the emission of a large amount of nitrogen oxides, which brings very serious environmental pollution problems.

[0004] The method of producing adipic acid by one-step oxidation of cyclohexane with oxygen overcomes the shortcomings of the traditional process and avoids the emission of nitrogen oxides, which is more environmentally friendly and is the development trend of adipic acid production technology.

[0005] Although related research has been reported, due to the stable CH bond in the cyclohexane molecule, the one-step oxidation of oxygen to adipic acid requires the use of a catalyst to shorten the induction period and increase the reaction rate. Yin et al. developed a hollow manganese-doped titanium silicon catalyst for pure oxygen oxidation of cyclohexane, with a conversion rate of 13.4%, but the selectivity of adipic acid was only 57.5% (Catalysis Communications 2015, 58, 46); Bal et al. synthesized a Co3O4@ZrO2 nanostructured catalyst, with a pure oxygen oxidation of cyclohexane conversion rate of up to 40%, and adipic acid selectivity of about 43% (Molecular Catalysis 2022,528, 112473); Ghiaci et al. prepared an amorphous carbon nitride-supported Cu catalyst that showed excellent activity for oxygen oxidation of cyclohexane, but the selectivity of adipic acid was less than 52% (Chemical Engineering Journal 2019, 370, 1310); CN102816054B discloses an activated carbon-supported nano-gold catalyst. Under the conditions of butanone as solvent and cyclohexanone as initiator, the cyclohexane conversion rate reaches up to 45%, and the adipic acid selectivity is 55%; CN113754531B ​​discloses a nitrogen-containing aromatic organic catalyst for solvent-free oxidation of cyclohexane, with a conversion rate of about 10% and adipic acid selectivity between 80-90%. In addition, in order to improve the efficiency of cyclohexane oxidation to prepare adipic acid, polar molecules such as acetic acid and acetonitrile are generally used as solvents, and aldehydes or ketone organics are used as initiators (Journal of Catalysis 2019, 378, 256; Nano Research 2022, 15, 7662; CN112209816B; CN112521266B). It can be seen that in order to improve the efficiency of cyclohexane oxidation to prepare adipic acid, catalysts, solvents or initiators are generally used, but this will bring about problems such as high production costs and separation difficulties. At the same time, the kettle reactor used in the current cyclohexane oxidation process has a huge liquid holding capacity and intense local heat release, and is prone to major safety accidents such as explosions if operated improperly.

[0006] Microchannel reactor is a continuous flow pipeline reactor, including mixing, heat exchange, reaction, control and other modules. Compared with traditional conventional reactors, microchannel reactor has a very small mass transfer and heat transfer distance, which can significantly improve the heat and mass transfer efficiency and space utilization, realize accurate control of reaction temperature, reaction time and material ratio, and has intrinsic safety. CN102746111A and CN112209816A respectively disclose the method for preparing adipic acid by cyclohexane oxidation using microchannel reactor, but both need to use organic solvents and catalysts, which will undoubtedly bring high production costs, separation difficulties and other problems. At the same time, in the above cases, the reaction solution also needs to be evaporated and concentrated to obtain adipic acid crystals, and adipic acid solid products cannot be directly obtained, which will undoubtedly greatly increase production energy consumption. Summary of the invention

[0007] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0008] The present invention aims to solve the problems of low efficiency, great safety hazards, and use of nitric acid and catalysts in the prior art of cyclohexane oxidation to prepare adipic acid, and provides a method for preparing adipic acid in one step based on non-catalytic oxidation of cyclohexane using a microchannel reactor. The method can achieve efficient conversion of cyclohexane in a short reaction time while achieving adipic acid selectivity of more than 90%, and adipic acid solid product is directly crystallized from the reaction solution.

[0009] To solve the above technical solution, the technical solution of the present invention is as follows: Cyclohexane containing an initiator and an oxygen-containing gas are used as raw materials, and after the ratio is adjusted by a metering pump, they enter a microchannel reactor for oxidation reaction. After the reaction liquid is cooled, crystallized, and solid-liquid separated, a crude adipic acid solid is obtained. At the same time, the initiator generated in situ circulates with the reaction liquid and undergoes the next round of oxidation reaction together with the supplemented fresh cyclohexane. The initiator includes peroxide or a free radical containing a cyclohexyl functional group, and the peroxide is a peroxide containing a cyclohexyl functional group.

[0010] The study found that the introduced peroxide containing cyclohexyl functional groups can decompose into free radicals at the reaction temperature, thereby greatly promoting the oxidation of cyclohexane to produce adipic acid. Compared with other types of peroxides (such as hydrogen peroxide, tert-butyl hydroperoxide, etc.), the cyclohexane oxidation rate using peroxides or free radicals containing cyclohexyl functional groups is faster and more conducive to the production of adipic acid. By selecting "peroxides or free radicals containing cyclohexyl functional groups", it is possible to directly initiate and promote the oxidation of cyclohexane to adipic acid in one step, avoiding the use of catalysts and solvents, and greatly reducing production costs.

[0011] In addition, it is found that during the cooling and crystallization process of the reaction liquid at a suitable temperature, peroxides and free radicals containing cyclohexyl functional groups can be generated in situ. By setting a reaction liquid circulation pipeline connecting the cooling crystallization device and the microchannel reactor, the reaction liquid containing peroxides and free radicals containing cyclohexyl functional groups is circulated into the reactor. During the circulation process of the cyclohexane oxidation method for preparing adipic acid, the consumption and generation of peroxides and free radicals containing cyclohexyl functional groups gradually reach a balance, and no additional initiator needs to be added in subsequent cycles, thereby further optimizing the process and reducing production costs.

[0012] In the above technical solution, the peroxide is a peroxide containing a cyclohexyl functional group, and preferably the peroxide is one or both of cyclohexyl hydroperoxide and cyclohexanone peroxide.

[0013] In the above technical solution, the initiator is introduced by adding it outside the reaction system and / or generating it in situ during the reaction.

[0014] In the above technical solution, the molar ratio of the initiator to the cyclohexane is 0.0002-0.08, and more preferably the molar ratio of the initiator to the cyclohexane is 0.005-0.04.

[0015] In the above technical solution, the residence time of the reactants in the microchannel reactor during the reaction is 0.15-13 min, preferably 2-7 min.

[0016] In the above technical solution, the oxygen-containing gas is a gas with an oxygen volume content of 5-100%, and preferably the oxygen-containing gas is one of air, oxygen-depleted, oxygen-enriched, and pure oxygen.

[0017] In the above technical solution, the molar ratio of oxygen to cyclohexane is 0.05-0.8, preferably 0.25-0.55.

[0018] In the above technical solution, the oxygen-containing gas can be introduced together with cyclohexane at the inlet of the micro-reaction channel, or can be introduced in sections at different locations of the micro-reaction channel.

[0019] In the above technical solution, the oxygen partial pressure range in the oxidation reaction is 0.1-1.5 MPa, and preferably the oxygen partial pressure range is 0.5-0.9 MPa.

[0020] In the above technical solution, the cyclohexane oxidation reaction temperature is 105-150°C, preferably the reaction temperature is 125-145°C.

[0021] In the above technical solution, the oxidized reaction liquid is cooled, and the crystallized adipic acid solid is subjected to solid-liquid separation. The cooling crystallization temperature range is 0-42°C, and the preferred crystallization temperature range is 8-30°C.

[0022] In the above technical solution, the reaction liquid after solid-liquid separation is fully or partially recycled and mixed with supplementary cyclohexane to carry out the next round of oxidation reaction. The amount of the recycled reaction liquid accounts for 70-100% of the total reaction liquid by mass.

[0023] Beneficial effects of the present invention: (1) The present invention adopts a continuous flow microchannel reactor, and the reaction time is shortened from several hours in a traditional kettle reactor to tens of seconds to a few minutes, while improving the selectivity of adipic acid and significantly improving the production efficiency; (2) The present invention adopts a method for preparing adipic acid by non-catalytic oxidation of cyclohexane, which eliminates the need for solvents and catalysts, saves costs, and adipic acid is directly precipitated from the reaction solution as a solid. The initiator can be generated in situ and circulated together with the reaction solution, and no additional initiator needs to be added during the reaction. (3) The process of the present invention is a continuous process from feeding, preheating, gas-liquid mixing to reaction. Compared with the conventional intermittent oxidation process, it reduces the number of auxiliary devices, greatly reduces the liquid holding capacity of the reactor during industrial implementation, and improves the process safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them: Figure 1 The present invention is a process flow chart of using the microchannel reactor of the present invention to produce adipic acid by one-step oxidation of cyclohexane.

[0025] Figure 2 It is the infrared spectra of the adipic acid solid and the adipic acid standard sample prepared in Example 1 of the present invention.

[0026] Figure 3 It is the XRD spectra of the adipic acid solid and the adipic acid standard sample prepared in Example 1 of the present invention.

[0027] Figure 4 It is the infrared spectra of the adipic acid solid and the adipic acid standard sample prepared in Example 2 of the present invention.

[0028] Figure 5 It is the XRD spectra of the adipic acid solid and the adipic acid standard sample prepared in Example 2 of the present invention.

[0029] Figure 6 It is the gas chromatogram of the cyclohexane oxidation reaction liquid of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0031] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0033] Reference Figure 1 The microchannel reactor of the present invention is used for the process of preparing adipic acid by one-step oxidation of cyclohexane. The microchannel reactor is mainly composed of a preheater, a mixer, and a microreaction channel. The steps are as follows: (1) First, inject cyclohexane containing initiator and oxygen-containing gas into the preheating module in a certain ratio for preheating; (2) The preheated reaction raw materials pass through a gas-liquid mixing module to achieve high dispersion of oxygen in cyclohexane; (3) The mixed gas-liquid two phases enter the micro-reaction channel module for oxidation reaction; (4) The oxidation reaction liquid is finally cooled and crystallized to obtain adipic acid solid product. The remaining reaction liquid is circulated and injected into the preheating module together with the added fresh cyclohexane for the next round of reaction.

[0034] The contents of cyclohexane, cyclohexanol, cyclohexanone and cyclohexyl adipate in the reaction solution were determined by gas chromatography, and the content of adipic acid was determined by acid-base titration. The determination methods of relevant parameters are as follows: Example 1 The device used is a high-throughput microchannel reactor (including preheating, gas-liquid mixing, and reaction modules), refer to Figure 1 The connection mode of the microchannel reactor is determined, the number of reaction modules is determined according to the flow rate and the reaction residence time, and the heat exchange medium is heat transfer oil.

[0035] Cyclohexane containing 1% cyclohexanone peroxide by mass and oxygen are pumped into each preheating module via a metering pump, and the molar ratio of oxygen to cyclohexane is 0.35; The gas-liquid two-phase enters the micro-reaction channel module through the gas-liquid mixing module. The reaction temperature is 130°C, the residence time is 5 min, and the pressure of the reaction system is controlled to 1.2 MPa by adjusting the back pressure valve at the outlet. The collected reaction liquid was cooled to 15° C., and crude adipic acid solid was obtained after solid-liquid separation. The remaining cyclohexane reaction liquid was circulated and supplemented with fresh cyclohexane for the next round of oxidation reaction.

[0036] The cyclohexane single-pass conversion, adipic acid selectivity, and cyclohexyl adipate selectivity of the first reaction and the subsequent nine cycles are listed in Table 1.

[0037] Table 1 As the number of cycles increases, the single-pass conversion rate of cyclohexane stabilizes at 14%, the selectivity of adipic acid stabilizes at 92%, the selectivity of cyclohexyl adipate stabilizes at 4%, and the solid yield of crude adipic acid stabilizes at 12.9%.

[0038] The infrared spectrum and XRD spectrum of the crude adipic acid solid obtained after the ninth cycle are as follows: Figure 2 , 3 As shown in the figure, it can be found that the infrared spectrum and XRD spectrum of crude adipic acid are similar to those of adipic acid standard sample. Figure 1 The results show that the obtained adipic acid solid has high purity.

[0039] Example 2 The microchannel reactor used is the same as that in Example 1.

[0040] Cyclohexane containing 1% by mass of cyclohexanone peroxide and oxygen are pumped into each preheater via a metering pump, and the molar ratio of oxygen to cyclohexane is 0.45; The gas-liquid two-phase enters the micro-reaction channel through the gas-liquid mixer. The reaction temperature is 130°C, the residence time is 5 min, and the pressure of the reaction system is controlled to 1.2 MPa by adjusting the back pressure valve at the outlet. The collected reaction liquid was cooled to 15° C., and crude adipic acid solid was obtained after solid-liquid separation. The remaining cyclohexane was circulated and combined with the supplemented fresh cyclohexane for the next round of oxidation reaction.

[0041] The cyclohexane single-pass conversion, adipic acid selectivity, and cyclohexyl adipate selectivity of the first reaction and the subsequent nine cycles are listed in Table 2.

[0042] Table 2 As the number of cycles increases, the single-pass conversion rate of cyclohexane stabilizes at 17%, the selectivity of adipic acid stabilizes at 91%, the selectivity of cyclohexyl adipate stabilizes at 4%, and the solid yield of crude adipic acid stabilizes at 15.5%.

[0043] The infrared spectrum and XRD spectrum of the crude adipic acid solid obtained after the ninth cycle are as follows: Figure 4 , 5 As shown in the figure, it can be found that the infrared spectrum and XRD spectrum of crude adipic acid are similar to those of adipic acid standard sample. Figure 1 The results show that the obtained adipic acid solid has high purity.

[0044] Example 3 The microchannel reactor used is the same as that in Example 1.

[0045] Cyclohexane containing 1% by mass of cyclohexyl hydroperoxide and oxygen are pumped into each preheater via a metering pump, and the molar ratio of oxygen to cyclohexane is 0.35; The gas-liquid two-phase enters the micro-reaction channel module through the gas-liquid mixer. The reaction temperature is 130°C, the residence time is 5 min, and the pressure of the reaction system is controlled to 1.2 MPa by adjusting the back pressure valve at the outlet. The collected reaction liquid was cooled to 15° C., and crude adipic acid solid was obtained after solid-liquid separation. The remaining cyclohexane was circulated and combined with the supplemented fresh cyclohexane for the next round of oxidation reaction.

[0046] The cyclohexane single-pass conversion, adipic acid selectivity, and cyclohexyl adipate selectivity of the first reaction and the subsequent nine cycles are listed in Table 3.

[0047] Table 3 As the number of cycles increases, the single-pass conversion rate of cyclohexane stabilizes at 12%, the selectivity of adipic acid stabilizes at 93%, the selectivity of cyclohexyl adipate stabilizes at 3%, and the solid yield of crude adipic acid stabilizes at 11.2%.

[0048] Example 4 Example 2 was repeated, except that the molar ratio of oxygen:cyclohexane was changed to 0.25; In the first reaction, the cyclohexane conversion rate decreased to 8.1%; The single-pass conversion rate of cyclohexane in the subsequent nine cycles gradually stabilized at 10.1%, and the selectivities of adipic acid and cyclohexyl adipate were approximately 93% and 4%, respectively.

[0049] Example 5 Example 2 was repeated, except that the reaction temperature was changed to 120°C; In the first reaction, the cyclohexane conversion rate was 6.0%; The single-pass conversion rate of cyclohexane in the subsequent nine cycles gradually stabilized at 8.4%, and the selectivity of adipic acid was 93%.

[0050] Example 6 Example 2 was repeated, except that the reaction temperature was changed to 140°C; In the first reaction, the cyclohexane conversion rate was 15.1%; The single-pass conversion rate of cyclohexane in the subsequent nine cycles gradually stabilized at 18.4%, and the selectivity of adipic acid was 86%.

[0051] Example 7 Example 2 was repeated, except that the residence time was changed to 2 min; In the first reaction, the cyclohexane conversion rate was 6.3%; The single-pass conversion rate of cyclohexane in the subsequent nine cycles gradually stabilized at 8.1%, and the selectivity of adipic acid was 94%.

[0052] Example 8 Example 2 was repeated, except that the residence time was changed to 7 min; In the first reaction, the cyclohexane conversion rate was 14.3%. The single-pass conversion rate of cyclohexane in the subsequent nine cycles gradually stabilized at 17.3%, and the selectivity of adipic acid was 91%.

[0053] Comparative Example 1 Example 2 was repeated except that a batch reactor was used.

[0054] Cyclohexane containing 1% by mass of cyclohexanone peroxide was added into a high-pressure reactor and heated to 130°C; Then pure oxygen was charged to a pressure of 1.2 MPa. After reacting for 1 h, the reaction solution was cooled to 15 °C and the oxygen was exhausted; The single-pass conversion rate of cyclohexane oxidation was 3.2%, the selectivity of adipic acid was 12%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0055] Comparative Example 2 Example 2 was repeated except that no initiator was added; The single-pass conversion rate of cyclohexane oxidation was 1.0%, the selectivity of adipic acid was 6%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled. The results of gas chromatography analysis were shown in Figure 6 .

[0056] Comparative Example 3 Example 2 was repeated, except that hydrogen peroxide was used as the initiator, and the content was 1% by mass of cyclohexane (a strong oxidant, and the amount added was controlled, otherwise there would be a risk of explosion); The single-pass conversion rate of cyclohexane oxidation was 2.1%, the selectivity of adipic acid was 22%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0057] Comparative Example 4 Example 2 was repeated, except that peracetic acid was used as the initiator, and the content was 1% by mass of cyclohexane (a strong oxidant, and the amount added was controlled, otherwise there would be a risk of explosion); The single-pass conversion rate of cyclohexane oxidation was 3.2%, the selectivity of adipic acid was 26%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0058] Comparative Example 5 Example 2 was repeated, except that cyclohexanone was used as the initiator, and the content was 1% of the mass of cyclohexane; The single-pass conversion rate of cyclohexane oxidation was 2.4%, the selectivity of adipic acid was 17%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0059] Comparative Example 6 Example 2 was repeated, except that the reaction solution cooling crystallization temperature was changed to 50°C. The cyclohexane single-pass conversion, adipic acid selectivity, and cyclohexyl adipate selectivity for the first reaction and the subsequent five cycles are listed in Table 4.

[0060] Table 4 It can be found that the single-pass conversion rate of cyclohexane in the cycle is reduced to about 9%, the selectivity of adipic acid is about 93%, the selectivity of cyclohexyl adipate is about 4%, and the solid yield of crude adipic acid is about 8.4%.

[0061] Comparative Example 7 Example 2 was repeated, except that acetic acid was introduced as the solvent, and the volume ratio of the solvent to cyclohexane was 5:1; The reaction results showed that the cyclohexane conversion rate was only 4.3%, the adipic acid selectivity was 20%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0062] Comparative Example 8 Example 2 was repeated, except that cyclohexyl acetate was introduced as a solvent, and the volume ratio of the solvent to cyclohexane was 5:1; The reaction results showed that the cyclohexane conversion rate was only 3.9%, the adipic acid selectivity was 21%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0063] This may be because the introduction of solvents caused cyclohexanone peroxide to become unstable and decompose prematurely, thus weakening its ability to initiate cyclohexane oxidation; On the other hand, the cyclohexane conversion rate was only 4.1% in the subsequent cycles, which may be due to the effect of the solvent, which hindered the generation and stable existence of cyclohexanone peroxide and free radicals during the cooling process.

[0064] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the present invention.

Claims

1. A method for preparing adipic acid using a microchannel reactor, characterized in that: include, Cyclohexane containing an initiator and an oxygen-containing gas are used as raw materials and added into a microchannel reactor for oxidation reaction to generate adipic acid; Wherein, the initiator comprises a free radical or a peroxide containing a cyclohexyl functional group.

2. The method according to claim 1, characterized in that: The peroxide is a peroxide containing a cyclohexyl functional group, including one or both of cyclohexanone peroxide and cyclohexyl hydroperoxide.

3. The method according to claim 2, characterized in that: The peroxide comprises a mixture of cyclohexyl hydroperoxide and cyclohexanone peroxide, and the molar ratio of the two is 0.01-100:

1.

4. The method according to any one of claims 1 to 3, characterized in that: The molar ratio of the initiator to cyclohexane is 0.0002-0.08:

1.

5. The method according to claim 4, characterized in that: During the reaction, the residence time of the reactants in the microchannel reactor is 0.15-13 min.

6. The method according to claim 5, characterized in that: The oxygen-containing gas is a gas with an oxygen volume content of 5 to 100%, including one of air, oxygen-depleted, oxygen-enriched, and pure oxygen.

7. The method according to claim 1, 5 or 6, characterized in that: The molar ratio of oxygen to cyclohexane is 0.05-0.8:

1.

8. The method according to claim 7, characterized in that: The oxygen partial pressure range in the oxidation reaction is 0.1-1.5 MPa, and the cyclohexane oxidation reaction temperature is 105-150°C.

9. The method according to claim 1 or 8, characterized in that: The method also includes cooling the oxidized reaction liquid and performing solid-liquid separation on the crystallized adipic acid solid, wherein the cooling temperature of the oxidized reaction liquid is 0-42°C.

10. The method according to claim 9, characterized in that: The reaction liquid after solid-liquid separation is fully or partially recycled and mixed with supplementary cyclohexane to carry out the next round of oxidation reaction.

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