Process for the oxidation of cyclohexane and products thereof

Abstract

The application relates to the chemical industry field and discloses a method for preparing adipic acid from cyclohexane through one-step oxidation and an obtained product containing adipic acid. The method comprises the following steps: in the presence of a solvent and a catalyst, a gas containing free oxygen is contacted with cyclohexane to perform an oxidation reaction, and a product mixture containing adipic acid is obtained; the gas containing free oxygen contains oxygen and carbon monoxide, and the volume content of oxygen in the gas containing free oxygen is not higher than 21%. The method introduces carbon monoxide into a reaction system, and performs the cyclohexane oxidation reaction in an oxygen-poor atmosphere, so that the content of glutaric acid in the product is unexpectedly reduced, and in addition, the method has the advantages of high cyclohexane conversion rate and good adipic acid selectivity.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and more specifically, to a method for the oxidation of cyclohexane, and more particularly, to a method for the one-step oxidation of cyclohexane to produce adipic acid and the resulting adipic acid-containing product. Background Technology

[0002] Adipic acid is an important basic organic chemical raw material. Its main use is in the production of nylon 66 salt. It can also be used in the production of polyurethane, plasticizers, polyamides, synthetic leather, lubricants, etc.

[0003] Adipic acid is typically derived from the catalytic oxidation of cyclohexane. Cyclohexane is first catalytically oxidized to cyclohexanone and cyclohexanol, which are then purified and further oxidized to adipic acid. However, this reaction involves numerous side reactions, and the products contain adipic acid, glutaric acid, succinic acid, cyclohexanone, and cyclohexanol. In particular, the presence of a large amount of glutaric acid in the products negatively impacts the economic viability of this synthesis.

[0004] Existing technologies typically optimize the one-step oxidation of cyclohexane to adipic acid by developing new catalysts, but none of these methods can reduce the content of byproducts, especially glutaric acid, in the product. For example, CN101337879B and CN100445255C disclose methods for the direct production of adipic acid from cyclohexane using metalloporphyrin catalysis. Rhodia Polyamide Intermediates AG of France has subsequently published methods for the direct production of adipic acid from cyclohexane using cobalt acetylacetonate catalysis (CN1549805A, CN100338005C, FR2002 / 002508, WO2003 / 014055). South China University of Technology and Yantai University have successively published catalysts for the oxidation of cyclohexane to adipic acid using the noble metal Ru as the catalytically active component (CN101239899B, CN102329222A). South China University of Technology patents CN101239899B, CN101337878B, CN102329222A, CN102040504A, and CN102001931A disclose methods for catalytic oxidation of cyclohexane using carbon nanotubes, modified carbon nanotubes, and carbon nanotubes filled with magnetic iron oxide. CN104226317A discloses a method for catalytic oxidation of cyclohexane using catalysts containing transition metals and rare earth metals.

[0005] In summary, how to further improve the selectivity of adipic acid and reduce the content of byproducts, especially glutaric acid, in the product, and provide a simpler, more efficient, green and environmentally friendly method for the synthesis of adipic acid, so as to provide excellent raw materials for polyester production, has always been the research goal and direction of this field. Summary of the Invention

[0006] To address the problem of a large amount of glutaric acid byproduct in the one-step oxidation of cyclohexane to adipic acid synthesis solution in existing technologies, this invention provides a method for one-step oxidation of cyclohexane to adipic acid and the resulting adipic acid-containing product. This method introduces carbon monoxide into the reaction system and carries out the cyclohexane oxidation reaction in an oxygen-deficient atmosphere, unexpectedly reducing the glutaric acid content in the product. Moreover, the method of this invention also has the advantages of high cyclohexane conversion rate and good adipic acid selectivity.

[0007] The purpose of this invention is to provide a method for oxidizing cyclohexane, comprising: contacting a gas containing free oxygen with cyclohexane in the presence of a solvent and a catalyst to carry out an oxidation reaction, thereby obtaining a product mixture containing adipic acid; wherein the gas containing free oxygen contains oxygen and carbon monoxide, and the volume content of oxygen in the gas containing free oxygen is not higher than 21%.

[0008] According to the present invention, the cyclohexane oxidation reaction is carried out in a gas containing free oxygen (oxygen volume content not exceeding 21%) and carbon monoxide according to the above method, which has good technical effects, not only reducing the content of glutaric acid in the product, but also having high adipic acid selectivity.

[0009] The volume content of carbon monoxide in the free oxygen-containing gas can be selected within a wide range. In a preferred embodiment of the present invention, the volume content of carbon monoxide in the free oxygen-containing gas is 0.2% or more, preferably 0.5%-2%, for example, it can be 0.5%, 0.8%, 1.2%, 1.5%, 1.8%, 2%, or any two values ​​or any range of any two values.

[0010] According to the present invention, the gas containing free oxygen is an oxygen-deficient gas, and cannot be an oxygen-rich gas with an oxygen volume content higher than 21%. According to the present invention, the oxygen volume content in the gas containing free oxygen can be selected within a wide range. In a preferred embodiment of the present invention, the oxygen volume content in the gas containing free oxygen is 6%-21%, preferably 9%-16%, for example, it can be 9%, 11%, 13%, 15%, 16%, or any two values ​​or any range of any two values.

[0011] In a preferred embodiment of the present invention, the gas containing free oxygen contains oxygen, carbon monoxide, and a protective gas. Preferably, the gas containing free oxygen includes oxygen, carbon monoxide, and a protective gas. The protective gas can be any gas that does not participate in the reaction, preferably nitrogen and / or an inert gas.

[0012] According to the present invention, the solvent can be selected from a wide range, as long as it can dissolve the reactants. In a preferred embodiment of the present invention, the solvent is selected from at least one of polar protic solvents, preferably an organic polar protic solvent with 6 or fewer carbon atoms, more preferably an acidic compound with pKa ≥ 3, and even more preferably acetic acid and / or propionic acid.

[0013] According to the present invention, the mass ratio of cyclohexane to solvent can be selected within a wide range. In a preferred embodiment of the present invention, the mass ratio of cyclohexane to solvent is (0.4-1.5):1, preferably (0.6-1):1.

[0014] This invention does not have special requirements for the catalyst; any catalyst capable of achieving the above-described reactions can achieve the technical effects of this invention, such as the catalysts described in CN112521266A, CN113754531A, and CN112439452A. In a preferred embodiment of this invention, the catalyst contains at least one of the fourth-period transition metal elements; preferably, it contains at least one of copper, manganese, and cobalt.

[0015] According to the present invention, the mass ratio of cyclohexane to the catalyst can be selected in a wide range. Preferably, the mass ratio of cyclohexane to the catalyst is (600-20000):1, and more preferably (1500-10000):1.

[0016] In a preferred embodiment of the present invention, an auxiliary agent is also added to the oxidation reaction system. The present invention does not impose any particular limitations on the auxiliary agent; common auxiliary agents used in the art for the oxidation of cyclohexane to prepare adipic acid can be employed. Preferably, the auxiliary agent is selected from at least one of small-molecule aldehydes or ketones. In this preferred embodiment, the auxiliary agent has no corrosive side effects on the equipment, making it more economical, safe, and environmentally friendly.

[0017] According to the present invention, the mass ratio of cyclohexane to the auxiliary can be selected within a wide range. Preferably, the mass ratio of cyclohexane to the auxiliary is (50-1000):1, and more preferably (100-600):1.

[0018] In a more preferred embodiment of the present invention, the auxiliary agent is selected from at least one of small molecule aldehydes or ketones, and the mass ratio of cyclohexane to the auxiliary agent is (50-1000):1, preferably (100-600):1.

[0019] According to the present invention, the aldehyde can be selected from a wide range. In a preferred embodiment of the present invention, the aldehyde is an aldehyde with 7 or fewer carbon atoms in the molecule, such as, but not limited to, acetaldehyde.

[0020] According to the present invention, the ketone can be selected from a wide range of types, and the ketone is a ketone with 7 or fewer carbon atoms in the molecule, such as, but not limited to, acetone, cyclohexanone, etc.

[0021] According to the present invention, the temperature conditions of the contact can be selected within a wide range. In a preferred embodiment of the present invention, the contact conditions include a contact temperature of 85-125°C.

[0022] According to the present invention, the contact pressure conditions can be selected within a wide range. In a preferred embodiment of the present invention, the contact pressure is 1-4 MPa.

[0023] According to the present invention, the contact time condition can be selected within a wide range. In a preferred embodiment of the present invention, the contact time is 0.5-5h.

[0024] In a more preferred embodiment of the present invention, the contact conditions include: a contact temperature of 85-125°C; a contact pressure of 1-4 MPa; and a contact time of 0.5-5 h.

[0025] According to the present invention, the process can be carried out continuously or discontinuously. For example, the reaction liquid and the gas containing free oxygen can be continuously introduced, or all the liquid can be introduced first, and then the gas containing free oxygen can be introduced.

[0026] In a preferred embodiment of the present invention, the contact includes contacting cyclohexane in the reaction mixture with the oxygen-containing gas under continuous injection; in this preferred embodiment, the method of the present invention exhibits higher adipic acid selectivity and a lower glutaric acid content in the product.

[0027] Under continuous injection conditions, the ratio of the mass flow rate of the oxygen-containing gas to the flow rate of the reaction system mixture (based on the mass of the solvent) in this invention has a wide range of selection. Preferably, the ratio of the mass flow rate of the oxygen-containing gas to the flow rate of the reaction system mixture (based on the mass of the solvent) during the reaction process is (2-50):1, and more preferably (10-30):1.

[0028] In a more preferred embodiment of the present invention, such as Figure 1 As shown, the method includes the following steps:

[0029] 1) The catalyst (preferably Co-Mn-Cu catalyst) is mixed with acetic acid and heated to completely dissolve the catalyst. An aldehyde or ketone (preferably cyclohexanone) is added as an auxiliary agent, and cyclohexane is added as a reaction raw material. The above materials are mixed in the raw material storage tank 2 to prepare an acetic acid mixed solution.

[0030] 2) Gas containing free oxygen is continuously introduced into reactor 1 through gas inlet 3 containing free oxygen;

[0031] 3) Acetic acid mixed solution and gas containing free oxygen are continuously fed into reactor 1 for contact reaction, and the tail gas at the reaction outlet is discharged through tail gas outlet 5.

[0032] 4) After the reaction, stop feeding, end the reaction, and transfer the synthesis liquid from reactor 1 to synthesis liquid collection tank 4.

[0033] This invention does not impose any particular restrictions on the state of the reaction within the reactor; it can be carried out without mechanical disturbance or by mechanical mixing. Of course, there are no particular restrictions on the mixing method either; for example, conventional stirring can be used.

[0034] Of course, the one-step oxidation method for producing adipic acid from cyclohexane in this invention may further include a step of purifying the resulting synthetic solution to obtain purified adipic acid. This invention does not impose any particular limitations on the purification method; existing purification methods in the art can be used. Because the content of glutaric acid in the synthetic solution obtained by this invention is significantly reduced, overcoming the difficulty in separating adipic acid from glutaric acid, the crude adipic acid product contains fewer glutaric acid impurities and is easier to purify. Therefore, conventional purification methods can also more easily yield adipic acid with higher purity.

[0035] Another object of the present invention is to provide an adipic acid-containing product prepared by the cyclohexane oxidation method described in this invention. The obtained adipic acid-containing product has high purity and the glutaric acid content is controlled to a very low level; this reduces processing steps and process costs for subsequent purification.

[0036] According to the above technical solution, this invention produces adipic acid via a one-step oxidation of cyclohexane. By adding carbon monoxide gas to the oxygen-deficient gas containing free oxygen at the reactor inlet, and preferably by controlling the concentration of carbon monoxide in the gas, the formation of the byproduct glutaric acid is suppressed. This overcomes the problem of a large amount of glutaric acid byproduct in the synthesis solution and unexpectedly reduces the glutaric acid content in the product. This invention can significantly reduce the concentration of glutaric acid in the product, even as low as 1143 ppm. Furthermore, this invention exhibits high cyclohexane conversion rate and high adipic acid selectivity, making it highly valuable for widespread application.

[0037] The method of this invention features low glutaric acid content as a byproduct, low equipment investment, and simple operation, and can be used in the continuous industrial production of adipic acid via the one-step oxidation of cyclohexane. This adipic acid synthesis method is simple, efficient, green, and environmentally friendly, and can also provide an excellent raw material source for polyester production. Attached Figure Description

[0038] Figure 1This is a process flow diagram of a preferred embodiment of the present invention.

[0039] Explanation of reference numerals in the attached figures

[0040] 1. Reactor; 2. Raw material storage tank; 3. Gas inlet containing free oxygen; 4. Synthesis liquid collection tank; 5. Tail gas exhaust outlet. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0042] Unless otherwise specified, the Co-Mn-Cu catalysts in the following examples and comparative examples are obtained by dissolving commercially available cobalt acetate, manganese acetate, and copper acetate in acetic acid. Unless otherwise specified, the Co-Mn-Cu catalysts in the examples (e.g., Example 1) and comparative examples contain 6 wt% Co, 7 wt% Mn, and 21 wt% Cu, and the catalysts are in a fully dissolved state in the reaction system.

[0043] Unless otherwise specified, other raw materials and equipment are all commercially available products or equipment in this field.

[0044] In the following examples and comparative examples, high performance liquid chromatography was used to analyze the mass concentrations of adipic acid and glutaric acid in the reaction solution and to calculate the concentration ratio of adipic acid to glutaric acid.

[0045] The method for calculating the selectivity of adipic acid is as follows:

[0046] Adipic acid selectivity = (Moles of adipic acid produced / Moles of cyclohexane consumed) * 100%

[0047] The conversion rate of cyclohexane is calculated as follows:

[0048] Cyclohexane conversion rate = (Moles of cyclohexane consumed in the reaction) / (Moles of cyclohexane in the feed) * 100%

[0049]

Example 1

[0050] like Figure 1 As shown, the method for preparing adipic acid by cyclohexane oxidation includes the following steps:

[0051] 1) Mix 0.2 kg of Co-Mn-Cu catalyst with 100 kg of acetic acid, heat at 50°C until completely dissolved, add 0.2 kg of cyclohexanone as an auxiliary agent, and add 100 kg of cyclohexane as a reaction raw material. Mix the above materials in raw material storage tank 2 to prepare an acetic acid mixed solution.

[0052] 2) A gas containing free oxygen (oxygen volume content 12%, carbon monoxide content 1%, and the remainder nitrogen) is continuously introduced into the oxidation reactor through the free oxygen gas inlet 3 at a gas flow rate of 20 kg / h. The reactor is heated to a reaction temperature of 90°C and a reaction pressure of 3.0 MPa.

[0053] 3) Acetic acid mixed solution and free oxygen-containing gas are continuously fed into reactor 1. The feed flow rate of acetic acid mixed solution is 1 kg / h (calculated based on the amount of acetic acid in the solution). The equivalent liquid residence time is 3h. The flow rate of free oxygen-containing gas is 20 kg / h. All the tail gas at the reaction outlet is discharged through tail gas outlet 5.

[0054] 4) After 40 hours of reaction, stop feeding and end the reaction. Transfer the synthesis liquid from reactor 1 to synthesis liquid collection tank 4.

[0055] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0056]

Example 2

[0057] The reaction was carried out according to the method of Example 1 to obtain an adipic acid oxidation synthesis liquid. The difference is that the composition of the gas containing free oxygen is shown in Table 1, and the balance is nitrogen.

[0058] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0059]

Example 3

[0060] The reaction was carried out according to the method of Example 1 to obtain an adipic acid oxidation synthesis liquid. The difference is that the composition of the gas containing free oxygen is shown in Table 1, and the balance is nitrogen.

[0061] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0062]

Example 4

[0063] The reaction was carried out according to the method of Example 1 to obtain an adipic acid oxidation synthesis liquid. The difference is that the composition of the gas containing free oxygen is shown in Table 1, and the balance is nitrogen.

[0064] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0065]

Example 5

[0066] The reaction was carried out according to the method of Example 1 to obtain an adipic acid oxidation synthesis liquid. The difference is that the composition of the gas containing free oxygen is shown in Table 1, and the balance is nitrogen.

[0067] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0068]

Example 6

[0069] The reaction was carried out according to the method of Example 1 to obtain an adipic acid oxidation synthesis solution. The difference is that the composition of the gas containing free oxygen is shown in Table 1, and the balance is nitrogen. The specific oxidation process conditions are shown in Table 1, and other parameters not listed are the same as in Example 1.

[0070] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0071]

Example 7

[0072] The reaction was carried out according to the method of Example 1 to obtain an adipic acid oxidation synthesis solution. The difference is that the composition of the gas containing free oxygen is shown in Table 1, and the balance is nitrogen. The specific oxidation process conditions are shown in Table 1, and other parameters not listed are the same as in Example 1.

[0073] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0074]

Example 8

[0075] The reaction was carried out according to the method of Example 1 to obtain an adipic acid oxidation synthesis solution, except that the catalyst in Example 1 was replaced with an equal amount of the following catalyst:

[0076] Co-Mn-Cu catalyst: contains 11 wt% Co, 7 wt% Mn, 11 wt% Cu, with the remainder being carbon, hydrogen, and oxygen, all prepared using the corresponding acetates.

[0077] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0078]

Example 9

[0079] 1) Mix 0.2 kg of Co-Mn-Cu catalyst from Example 1 with 100 kg of acetic acid, heat at 50°C until completely dissolved, add 0.2 kg of cyclohexanone as an auxiliary agent, and add 100 kg of cyclohexane as a reaction raw material. Mix the above materials to prepare an acetic acid mixed solution and add it to the reaction vessel 1 through the raw material storage tank 2. The mass of the injected liquid is 3 kg (based on the mass of acetic acid in the solution).

[0080] 2) A gas containing free oxygen (oxygen volume content 12%, carbon monoxide volume content 1%, and the remainder is nitrogen) is continuously introduced into the oxidation reactor through the free oxygen gas inlet 3 at a gas flow rate of 20 kg / h. The reactor is heated to a reaction temperature of 90°C and a reaction pressure of 3.0 MPa.

[0081] 3) Gas containing free oxygen is continuously fed into reactor 1 at a flow rate of 20 kg / h, and all tail gas from the reaction outlet is discharged through tail gas outlet 5.

[0082] 4) After 3 hours of reaction, stop feeding and end the reaction. Transfer the synthesis solution from reactor 1 to synthesis solution collection tank 4. Take a sample of the adipic acid oxidation synthesis solution from synthesis solution collection tank 4 for composition analysis.

[0083] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0084] Comparative Example 1

[0085] 1) Mix 0.2 kg of Co-Mn-Cu catalyst from Example 1 with 100 kg of acetic acid, heat at 50°C until completely dissolved, add 0.2 kg of cyclohexanone as an auxiliary agent, and add 100 kg of cyclohexane as a reaction raw material. Mix the above materials in raw material storage tank 2 to prepare an acetic acid mixed solution.

[0086] 2) A gas containing free oxygen (oxygen volume content 12%, the remainder being nitrogen) is continuously introduced into the oxidation reactor through the free oxygen gas inlet 3 at a flow rate of 20 kg / h. The reactor is heated to a reaction temperature of 90°C and a reaction pressure of 3.0 MPa.

[0087] 3) Acetic acid mixed solution and free oxygen-containing gas are continuously fed into reactor 1. The feed flow rate of acetic acid mixed solution is 1 kg / h (calculated based on the amount of acetic acid in the solution). The equivalent liquid residence time is 3h. The flow rate of free oxygen-containing gas is 20 kg / h. All the tail gas at the reaction outlet is discharged through tail gas outlet 5.

[0088] 4) After 40 hours of reaction, stop feeding and end the reaction. Transfer the synthesis liquid from reactor 1 to synthesis liquid collection tank 4. Take a sample of the adipic acid oxidation synthesis liquid from synthesis liquid collection tank 4 to analyze its composition.

[0089] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0090] Comparative Example 2

[0091] Refer to the process conditions of Example 1 in CN112521266A:

[0092] 1) Mix 0.2 kg of Co-Mn-Cu catalyst from Example 1 with 100 kg of acetic acid, heat at 50°C until completely dissolved, add 0.2 kg of cyclohexanone as an auxiliary agent, and add 100 kg of cyclohexane as a reaction raw material. The above materials are mixed to prepare an acetic acid mixed solution and added to the reaction vessel 1 through the raw material storage tank 2. The mass of the injected liquid is 3 kg (based on the mass of acetic acid in the solution).

[0093] 2) A gas containing free oxygen (oxygen volume content 21%, the remainder being nitrogen) is continuously introduced into the oxidation reactor through the free oxygen gas inlet 3 at a flow rate of 20 kg / h. The reactor is heated to a reaction temperature of 110°C and a reaction pressure of 1.5 MPa.

[0094] 3) Gas containing free oxygen is continuously fed into reactor 1 at a flow rate of 20 kg / h, and all tail gas from the reaction outlet is discharged through tail gas outlet 5.

[0095] 4) After 3 hours of reaction, the feed was stopped, the reaction was terminated, and the synthesis liquid was transferred from reactor 1 to synthesis liquid collection tank 4. A sample of the adipic acid oxidation synthesis liquid was taken from synthesis liquid collection tank 4, and its composition was analyzed using high performance liquid chromatography. The mass concentration of adipic acid in the synthesis liquid, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0096] Comparative Example 3

[0097] The reaction was carried out according to the method of Example 1 to obtain the adipic acid oxidation synthesis solution. The difference is that the composition of the gas containing free oxygen is shown in Table 1, and the balance is nitrogen. The specific oxidation process conditions are shown in Table 1. Other unlisted parameters are the same as those in Example 1.

[0098] A sample of the adipic acid oxidation synthesis solution was taken from the synthesis solution collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis solution, the mass concentration of the byproduct glutaric acid, the mass concentration ratio of adipic acid to glutaric acid, the conversion rate of cyclohexane, and the selectivity of adipic acid were calculated. The results are shown in Table 2.

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103]

[0104] As shown in Table 2, this invention produces adipic acid via a one-step oxidation of cyclohexane. By adding carbon monoxide gas to the oxygen-deficient gas containing free oxygen at the reactor inlet, and preferably by controlling the carbon monoxide concentration in the gas, the formation of the byproduct glutaric acid is suppressed. This overcomes the problem of a large amount of glutaric acid byproduct in the synthesis solution and unexpectedly reduces the glutaric acid content in the product. This invention can significantly reduce the concentration of glutaric acid in the product, even as low as 1143 ppm. Furthermore, this invention exhibits high cyclohexane conversion rate and high adipic acid selectivity, making it highly valuable for widespread application.

[0105] The specific one-step oxidation method for producing adipic acid from cyclohexane proposed in this invention has been described through preferred embodiments. Those skilled in the art will readily be able to modify or appropriately alter and combine the structures and preparation methods described herein without departing from the content, spirit, and scope of this invention to achieve the technical requirements of this invention. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

[0106] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0107] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0108] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0109] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. 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. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0110] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0111] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art believe that the combination is obviously unreasonable.

Claims

1. A method for oxidizing cyclohexane, comprising: In the presence of a solvent and a catalyst, a gas containing free oxygen is contacted with cyclohexane to carry out an oxidation reaction, yielding a mixture of products containing adipic acid; The free oxygen-containing gas includes oxygen, carbon monoxide, and a protective gas; and the volume content of oxygen in the free oxygen-containing gas is 6%-21%, and the volume content of carbon monoxide is 0.2%-5%; the catalyst contains at least one of copper, manganese, and cobalt. The oxidation reaction system also contains additives; The auxiliary agent is selected from at least one of small molecule aldehydes or ketones; The aldehyde is an aldehyde with 7 or fewer carbon atoms in its molecule; the ketone is a ketone with 7 or fewer carbon atoms in its molecule.

2. The method according to claim 1, characterized in that: The volume content of carbon monoxide in the gas containing free oxygen is 0.5%-2%.

3. The method according to claim 1, characterized in that: The volume content of oxygen in the gas containing free oxygen is 9%-16%.

4. The method according to claim 1, characterized in that: The protective gas is nitrogen and / or an inert gas.

5. The method according to claim 1, characterized in that: The solvent is selected from at least one of polar protic solvents.

6. The method according to claim 1, characterized in that: The solvent is an organic polar protic solvent with 6 or fewer carbon atoms.

7. The method according to claim 6, characterized in that: The organic polar protic solvent is an acidic compound with pKa ≥ 3.

8. The method according to claim 6, characterized in that: The organic polar protic solvent is acetic acid and / or propionic acid.

9. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to solvent is (0.4-1.5):

1.

10. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to solvent is (0.6-1):

1.

11. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to the catalyst is (600-20000):

1.

12. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to the catalyst is (1500-10000):

1.

13. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to the auxiliary is (50-1000):

1.

14. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to the auxiliary is (100-600):

1.

15. The method according to claim 1, characterized in that: The contact involves contacting the cyclohexane in the reaction mixture with the oxygen-containing gas under continuous injection.

16. The method according to claim 1, characterized in that: During the reaction, the ratio of the mass flow rate of the gas containing free oxygen to the flow rate of the reaction mixture (based on the mass of the solvent) is (2-50):

1.

17. The method according to claim 1, characterized in that: During the reaction, the ratio of the mass flow rate of the gas containing free oxygen to the flow rate of the reaction mixture (based on the mass of the solvent) is (10-30):

1.

18. The method according to any one of claims 1-17, characterized in that: The conditions for contact include: The contact temperature is 85-125℃; and / or, the contact pressure is 1-4 MPa; and / or, the contact time is 0.5-5 h.

Images