Method for preparing adipic acid through cyclohexane oxidation and production system

Abstract

The invention discloses a method for preparing adipic acid through cyclohexane oxidation and a production system, and the method comprises the following steps: in the presence of an initiator, cyclohexane and oxygen-containing gas are subjected to a non-catalytic oxidation reaction to generate adipic acid; wherein the initiator comprises a free radical containing a cyclohexyl functional group or peroxide. The invention provides a novel method and a production process system for generating adipic acid through non-catalytic oxidation reaction of cyclohexane and oxygen-containing gas in the presence of an initiator, the method can realize that the selectivity of adipic acid is kept above 80% under the condition of higher conversion rate of cyclohexane, and the adipic acid solid product can be directly crystallized and separated out from the reaction liquid, so that the production process system is suitable for industrial production. The adipic acid production method is simple and pollution-free, and has important industrial application value.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and specifically relates to a method for preparing adipic acid by oxidation of cyclohexane and a production system. 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 produce cyclohexanol, and then nitric acid oxidation to obtain adipic acid, wherein cyclohexene is produced 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 relevant research has been reported, due to the stable CH bond in the cyclohexane molecule, a catalyst is required for the one-step oxidation of oxygen to adipic acid. 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 for adipic acid was only 57.5% (Catalysis Communications 2015, 58, 46); Bal et al. synthesized a Co3O4@ZrO2 nanostructured catalyst with a conversion rate of 40% for pure oxygen oxidation of cyclohexane and a selectivity of about 43% for adipic acid (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 for adipic acid was less than 52% (Chemical Engineering Journal 2019, 370, 1310); CN102816054B discloses an activated carbon-supported nanogold 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 also commonly 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 adipic acid, catalysts, solvents and initiators (such as cyclohexanone, tert-butyl hydroperoxide, etc.) are generally used, but this will bring about problems such as high production costs and difficult separation. At the same time, in the above cases, the reaction liquid must 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

[0006] 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.

[0007] The present invention aims to solve the problems of low efficiency, use of nitric acid and catalyst in the prior art of cyclohexane oxidation to produce adipic acid. One object of the present invention is to provide a new method for producing adipic acid by one-step oxidation of cyclohexane without catalyst and solvent. The method can achieve a high conversion rate of cyclohexane while maintaining adipic acid selectivity above 73%, and adipic acid solid product can be directly crystallized and precipitated from the reaction solution.

[0008] To solve the above technical solution, the technical solution of the present invention is as follows: a method for preparing adipic acid by one-step oxidation of cyclohexane, comprising reacting cyclohexane with an oxygen-containing gas in the presence of an initiator to produce adipic acid; The initiator includes peroxide or free radical containing cyclohexyl functional group, and the peroxide is peroxide containing cyclohexyl functional group; Cyclohexane, oxygen-containing gas and initiator enter the reactor, and cyclohexane and oxygen-containing gas generate adipic acid through non-catalytic oxidation reaction. Then the reaction liquid enters the cooling crystallization device. After the reaction liquid is cooled, the pressurized oxygen-containing gas is circulated to the reactor or emptied. The crystallized adipic acid solid is passed through the solid-liquid separator to obtain adipic acid. The reaction liquid is fully or partially circulated to the reactor for the next round of oxidation reaction with the added fresh cyclohexane.

[0009] 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 adipic acid. Compared with other types of peroxides (such as hydrogen peroxide, tert-butyl hydroperoxide, etc.), the use of peroxides or free radicals containing cyclohexyl functional groups has a faster oxidation rate for cyclohexane and is 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.

[0010] 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 oxidation 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.

[0011] In the above technical solution, it is preferred that the peroxide in the initiator is one or both of cyclohexanone peroxide and cyclohexyl hydroperoxide.

[0012] In the above technical solution, it is preferred that the peroxide in the initiator is a mixture of cyclohexyl hydroperoxide and cyclohexanone peroxide, and the molar ratio of the two is in the range of 0.01-100.

[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 cyclohexane is in the range of 0.0002-0.08, and preferably the molar ratio of the initiator to cyclohexane is in the range of 0.005-0.04, for example but not limited to 0.005, 0.01, 0.02, 0.03, 0.04.

[0015] In the above technical solution, the oxygen-containing gas is preferably selected from gases with an oxygen volume content of 5-100%, and the specific form may be but is not limited to air, oxygen-depleted, oxygen-enriched, and pure oxygen.

[0016] 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.

[0017] 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.

[0018] In the above technical solution, the oxygen partial pressure range in the cyclohexane oxidation reaction is 0.05-1.5 MPa, preferably the oxygen partial pressure range is 0.3-0.9 MPa.

[0019] In the above technical scheme, the cyclohexane oxidation reaction temperature ranges from 105 to 155°C, and the preferred reaction temperature range is 125 to 145°C.

[0020] In the above technical scheme, the cyclohexane oxidation reaction time ranges from 0.01 to 18 hours, and the preferred reaction time ranges from 4 to 12 hours.

[0021] Another object of the present invention is to overcome the deficiencies in the prior art and provide a process system for producing adipic acid by oxidizing cyclohexane, comprising: Gas-liquid mixer, oxidation reactor, crystallization device, heat exchanger, solid-liquid separator, reaction liquid circulation system; Among them, one end of the reaction liquid circulation system is connected to the gas-liquid mixer, and the other end is connected to the solid-liquid separator.

[0022] As a preferred solution of the process system of the present invention, the oxidation reactor, crystallization device and solid-liquid separator are independent devices with corresponding functions, or integrated devices with two or more functions.

[0023] As a preferred embodiment of the process system of the present invention, the oxidation reactor is one or more of a kettle reactor, a shell-and-tube reactor, a tower reactor, and a continuous flow reactor.

[0024] Beneficial effects of the present invention: (1) The present invention solves the problems of low efficiency, use of nitric acid and catalyst in the prior art of cyclohexane oxidation to produce adipic acid, and provides a new method for cyclohexane one-step oxidation to produce adipic acid without catalyst and solvent, and a production process system. The method can achieve a high conversion rate of cyclohexane while maintaining adipic acid selectivity above 73%, and adipic acid solid product can be directly crystallized from the reaction solution.

[0025] (2) The present invention proposes a catalyst-free, solvent-free one-step oxidation method for producing adipic acid by cyclohexane and a production process system. Compared with the existing adipic acid production process, the method is green, simple in process, and highly efficient, and the production cost is significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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 It is a diagram of the adipic acid production process system in an embodiment of the present invention.

[0027] Figure 2 It is a system diagram of the adipic acid production process of Example 1 of the present invention.

[0028] Figure 3 It is a gas chromatogram of the cyclohexane oxidation reaction liquid in Example 1 of the present invention.

[0029] Figure 4 It is a system diagram of the adipic acid production process of Example 2 of the present invention.

[0030] Figure 5 It is the infrared spectra of crude adipic acid and refined adipic acid solids obtained in Example 2 of the present invention.

[0031] Figure 6 It is the XRD spectra of crude adipic acid and refined adipic acid solids obtained in Example 2 of the present invention.

[0032] Figure 7 It is the gas chromatogram of the cyclohexane oxidation reaction liquid of Comparative Example 8 of the present invention. DETAILED DESCRIPTION

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The contents of cyclohexane, cyclohexanol, cyclohexanone, and cyclohexyl adipate in the reaction solution of the embodiment of the present invention were determined by gas chromatography, and the content of adipic acid was determined by acid-base titration. The calculation method of cyclohexane conversion, adipic acid selectivity, and cyclohexyl adipate selectivity is as follows: The raw materials in the embodiments of the present invention are all common commercially available products.

[0037] The adipic acid production process system diagram of the present invention is shown in Figure 1 , comprising a gas-liquid mixer (100), an oxidation reactor (200), a crystallization device (300), a heat exchanger (400), a solid-liquid separator (500), a reaction liquid circulation system (600), and an oxygen-containing gas circulation system (700); One end of the oxygen-containing gas circulation system (700) is connected to the gas-liquid mixer (100), and the other end is connected to the crystallization device (300); One end of the reaction liquid circulation system (600) is connected to the gas-liquid mixer (100), and the other end is connected to the solid-liquid separator (500); Further, specifically, cyclohexane, oxygen-containing gas, and initiator enter into an oxidation reactor (200) through a gas-liquid mixer (100), and cyclohexane and the oxygen-containing gas generate adipic acid through a non-catalytic oxidation reaction; The reaction liquid then enters a crystallization device (300) and is cooled by a heat exchanger (400). After the reaction liquid is cooled, adipic acid solid is crystallized and precipitated; The reaction liquid containing adipic acid solid enters the solid-liquid separator (500), and adipic acid solid is obtained through solid-liquid separation.

[0038] Example 1 See the adipic acid production process system diagram in this embodiment. Figure 2 , the process system includes a gas-liquid mixer (1), a high-pressure reactor (2), a heat exchanger (3) and a reaction liquid circulation system (4); Specifically, cyclohexanone peroxide and cyclohexane at a molar ratio of 0.01 are added to a high-pressure reactor (2) through a gas-liquid mixer (1), and heated to 130° C.; Then pure oxygen was charged to a pressure of 0.8 MPa. After 4 h of reaction, the reaction solution was cooled to 15 °C and the oxygen was exhausted; After solid-liquid separation, crude adipic acid solid is obtained, and the reaction liquid is completely circulated through the reaction liquid circulation system (4) to undergo the next round of oxidation reaction with supplemented fresh cyclohexane.

[0039] The cyclohexane single-pass conversion rate, adipic acid selectivity, and cyclohexyl adipate selectivity of the first reaction and the subsequent nine cycles are listed in Table 1. The gas chromatography analysis results of the first cycle reaction liquid are shown in Figure 3 .

[0040] Table 1 It can be seen that as the number of cycles increases, the single-pass conversion rate of cyclohexane stabilizes at 18%, the selectivity of adipic acid stabilizes at 84%, the selectivity of cyclohexyl adipate stabilizes at 10%, and the solid yield of crude adipic acid stabilizes at 15.1%.

[0041] When the single oxidation reaction time was extended to 12 hours, the cyclohexane conversion rate increased to 36%, the selectivity of adipic acid was 79%, and the solid yield of crude adipic acid was about 28.4%.

[0042] Example 2 See the adipic acid production process system diagram in this embodiment. Figure 4 The process system includes a gas-liquid mixer (10), a high-pressure reactor (20), a first crystallization device (30), a first heat exchanger (40), a first solid-liquid separator (50), a reaction liquid circulation system (60), a liquid-liquid mixer (70), a second crystallization device (80), a second heat exchanger (90), and a second solid-liquid separator (100).

[0043] Specifically, cyclohexanone peroxide and cyclohexane at a molar ratio of 0.01 are added to a high-pressure reactor (20) through a gas-liquid mixer (10), and heated to 130° C.; Then pure oxygen was charged to a pressure of 0.8 MPa. After reacting for 4 hours, the reaction solution was cooled to 15° C. in the first crystallization device ( 30 ) and the oxygen was exhausted. The solid-liquid mixed reaction liquid passes through the first solid-liquid separator (50) to obtain crude adipic acid solid, and 90% of the reaction liquid is circulated through the reaction liquid circulation system (60) through the gas-liquid mixer to the reactor to undergo the next round of oxidation reaction with the added fresh cyclohexane. The process system is as follows: Figure 4 shown.

[0044] 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.

[0045] Table 2 It can be seen that the single-pass conversion rate of cyclohexane is about 17%, the selectivity of adipic acid is stable at 85%, the selectivity of cyclohexyl adipate is about 11%, and the solid yield of crude adipic acid is about 14.5%; When the oxidation reaction time was extended to 12 hours, the cyclohexane conversion rate increased to 35%, the selectivity of adipic acid was 79%, and the solid yield of crude adipic acid was about 27.7%.

[0046] The obtained crude adipic acid solid was saturatedly dissolved in 80°C water, cooled to 10°C in the second crystallization device (80) for recrystallization, and then passed through the second solid-liquid separator (100) to obtain a refined adipic acid solid. The infrared spectra and XRD spectra of the crude adipic acid and the refined adipic acid solid are as follows: Figure 5 , 6 As shown; It can be found that the infrared spectra and XRD spectra of crude adipic acid and refined adipic acid solids are similar to those of adipic acid standard samples. Figure 1 The results show that the obtained adipic acid solid has high purity.

[0047] Example 3 Example 1 was repeated, except that the initiator was changed to cyclohexyl hydroperoxide.

[0048] The cyclohexane conversion, adipic acid selectivity, and cyclohexyl adipate selectivity of the first reaction and the subsequent nine cycles are listed in Table 3.

[0049] Table 3 It can be found that the single-pass conversion rate of cyclohexane is about 13%, the selectivity of adipic acid is stable at 85%, the selectivity of cyclohexyl adipate is about 11%, and the solid yield of crude adipic acid is about 11.1%.

[0050] When the oxidation reaction time was extended to 12 hours, the cyclohexane conversion rate increased to 32%, the selectivity of adipic acid was maintained at 78%, and the solid yield of crude adipic acid was about 25%.

[0051] Example 4 Example 1 was repeated, except that the initiator was changed to a mixture of cyclohexyl hydroperoxide and cyclohexanone peroxide in a molar ratio of 1:1.

[0052] The cyclohexane conversion, adipic acid selectivity, and cyclohexyl adipate selectivity of the first reaction and the subsequent nine cycles are listed in Table 4.

[0053] Table 4 It can be seen that the single-pass conversion rate of cyclohexane is about 15%, the selectivity of adipic acid is stable at 84%, the selectivity of cyclohexyl adipate is about 11%, and the solid yield of crude adipic acid is about 12.6%; When the oxidation reaction time was extended to 12 hours, the cyclohexane conversion rate increased to 33%, the selectivity of adipic acid was 76%, and the solid yield of crude adipic acid was about 25.1%.

[0054] Example 5 Example 1 was repeated, except that the molar ratio of cyclohexanone peroxide to cyclohexane was changed to 0.02, 0.03 and 0.04; In the first reaction, the cyclohexane conversion increased to 21%, 23%, and 26%, respectively; The single-pass conversion of cyclohexane in the subsequent nine cycles gradually decreased to 18%, and the selectivities of adipic acid and cyclohexyl adipate were approximately 84% and 10%, respectively.

[0055] Example 6 Example 1 was repeated, except that the reaction temperature was changed to 120°C; 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 5.

[0056] Table 5 It can be seen that the single-pass conversion rate of cyclohexane is about 10%, the selectivity of adipic acid is about 88%, the selectivity of cyclohexyl adipate is about 11%, and the solid yield of crude adipic acid is about 8.8%; When the oxidation reaction time was extended to 12 hours, the cyclohexane conversion rate increased to 23%, the selectivity of adipic acid was 80%, and the solid yield of crude adipic acid was about 18.4%.

[0057] Comparative Example 1 Example 1 was repeated except that no initiator was added; The single-pass conversion rate of cyclohexane oxidation was 1.3%, the selectivity of adipic acid was 6%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0058] Comparative Example 2 Example 1 was repeated, except that hydrogen peroxide was used as the initiator, and the molar ratio of hydrogen peroxide to cyclohexane was 0.01 (a strong oxidant, the amount added should be controlled, otherwise there is a risk of explosion); The single-pass conversion rate of cyclohexane was 2.5%, the selectivity of adipic acid was 8%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0059] Comparative Example 3 Example 1 was repeated, except that the initiator was dicumyl peroxide, and the molar ratio of dicumyl peroxide to cyclohexane was 0.01; The single-pass conversion rate of cyclohexane was 3.9%, the selectivity of adipic acid was 10%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0060] Comparative Example 4 Example 1 was repeated, except that peracetic acid was used as the initiator, and the molar ratio of peracetic acid to cyclohexane was 0.01 (a strong oxidant, the amount added should be controlled, otherwise there is a risk of explosion); The single-pass conversion rate of cyclohexane was 4.4%, the selectivity of adipic acid was 10%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0061] Comparative Example 5 Example 1 was repeated, except that tert-butyl hydroperoxide was used as the initiator, and the molar ratio of tert-butyl hydroperoxide to cyclohexane was 0.01 (a strong oxidant, the amount added should be controlled, otherwise there is a risk of explosion); The single-pass conversion rate of cyclohexane was 4.9%, the selectivity of adipic acid was 13%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0062] Comparative Example 6 Example 1 was repeated, except that cyclohexanone was used as the initiator, and the molar ratio of cyclohexanone to cyclohexane was 0.01; The single-pass conversion rate of cyclohexane was 3.9%, the selectivity of adipic acid was 9%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0063] Comparative Example 7 Example 1 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 of the first reaction and the subsequent five cycles are listed in Table 6.

[0064] Table 6 It can be found that the single-pass conversion rate of cyclohexane in the cycle is reduced to about 8%, the selectivity of adipic acid is about 53%, the selectivity of cyclohexyl adipate is about 12%, and the solid yield of crude adipic acid is about 4.2%.

[0065] Comparative Example 8 Example 1 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 3.8%, the adipic acid selectivity was 11%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled. The gas chromatography analysis results showed Figure 7 .

[0066] Comparative Example 9 Example 1 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 3.2%, the adipic acid selectivity was 8%, and no adipic acid solid crystals were precipitated after the reaction solution was cooled.

[0067] 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 3.3% 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.

[0068] 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 by oxidation of cyclohexane, characterized in that: include, In the presence of an initiator, cyclohexane reacts with an oxygen-containing gas through a non-catalytic oxidation reaction to produce 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 is 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: 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.

6. The method according to claim 1 or 5, characterized in that: In the oxidation reaction, the oxygen partial pressure is 0.05-1.5 MPa, the oxidation reaction temperature is 105-155° C., and the oxidation reaction time is 0.01-18 h.

7. The method according to claim 6, characterized in that: The method further comprises cooling the oxidized reaction liquid, performing solid-liquid separation on the crystallized adipic acid solid, and recycling all or part of the reaction liquid after the solid-liquid separation, mixing it with supplemented cyclohexane, and performing the next round of oxidation reaction; Among them, the reaction liquid cooling temperature is 0~42℃.

8. A process system for producing adipic acid using the method according to any one of claims 1 to 7, characterized in that: include, A gas-liquid mixer (100), an oxidation reactor (200), a crystallization device (300), a heat exchanger (400), a solid-liquid separator (500), and a reaction liquid circulation system (600); One end of the reaction liquid circulation system (600) is connected to the gas-liquid mixer (100), and the other end is connected to the solid-liquid separator (500).

9. The adipic acid production process system according to claim 8, characterized in that: The oxidation reactor (200), the crystallization device (300), and the solid-liquid separator (500) are independent devices each having a corresponding function, or are integrated devices having two or more functions.

10. The adipic acid production process system according to claim 9, characterized in that: The oxidation reactor (200) is one or more of a tank reactor, a shell-and-tube reactor, a tower reactor, and a continuous flow reactor.

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