Safe synthesis method for preparing adipic acid through one-step oxidation of cyclohexane

Abstract

The invention provides a safe synthesis method for preparing adipic acid through one-step oxidation of cyclohexane, and the method comprises the following steps: in the presence of a catalyst and a solvent, cyclohexane and an oxygen molecule-containing oxidant are subjected to a contact reaction to obtain adipic acid, the catalyst is a transition metal salt, and the solvent comprises an anhydride solvent. The method has the advantages that adipic acid can be efficiently prepared through one-step oxidation of cyclohexane, the reaction conversion rate and selectivity are high, the tail oxygen content is low, and the reaction safety is good. By adopting the technical scheme provided by the invention, the conversion per pass of cyclohexane in continuous reaction is more than or equal to 10%, the selectivity of adipic acid is more than or equal to 80%, the oxygen content of reaction tail gas is less than or equal to 5%, and compared with the prior art, the conversion rate is only 4-7%, and the selectivity is less than 65%, so that a better technical effect is achieved, and the method is particularly suitable for industrial production of preparing adipic acid by one-step oxidation of cyclohexane.

Description

Technical Field

[0001] The invention relates to a safe synthesis method for preparing adipic acid by one-step oxidation of cyclohexane. Background Art

[0002] Adipic acid, also known as fatty acid, is an important organic dibasic acid and an important raw material for the preparation of polyurethane and nylon 66. Internationally, adipic acid is used in more than 70% of nylon 66 fields, and in my country, adipic acid is used in 78% of polyurethane fields. At present, the production processes of adipic acid worldwide are mainly cyclohexane two-step method and cyclohexene method. The cyclohexane two-step method uses cobalt and manganese catalysts to first oxidize cyclohexane into a mixture of cyclohexanone and cyclohexanol, and then oxidize it with nitric acid to obtain adipic acid, accounting for more than 60% of the total production capacity of adipic acid. The cyclohexene method uses Ru and other catalysts to partially hydrogenate benzene to produce cyclohexene, which is then hydrated to obtain cyclohexanol, and then oxidized with nitric acid or hydrogen peroxide to obtain adipic acid. In recent years, with the construction and expansion of domestic equipment, its production capacity has grown rapidly, and currently accounts for about 40% of the total production capacity.

[0003] However, both the cyclohexane two-step process and the cyclohexene process require nitric acid to oxidize KA oil, which causes serious equipment corrosion and produces a large amount of nitrogen oxide emissions, polluting the air. In order to solve this problem, researchers have explored a greener, more environmentally friendly and simpler process for synthesizing adipic acid using cyclohexane as raw material and air or oxygen as oxidant.

[0004] Cyclohexane one-step direct oxidation process for adipic acid (CN 104109083 B) adopts a catalytic mode of synergistic promotion of free radical initiators and metal catalysts, which not only ensures the conversion rate of the reaction, but also effectively improves the selectivity of the reaction, and the reaction temperature is low, the amount of catalyst is small, and it is one of the most promising routes for industrial transformation. However, the tail oxygen content is high during the process reaction, which has a large safety hazard, and the space velocity is reduced. Although the tail oxygen content can be controlled within a safe range, there are more side reactions and by-products, and the reaction conversion rate and selectivity decrease significantly. There is still a certain distance from the industrial production of adipic acid. Summary of the invention

[0005] The present invention mainly solves the technical defects in the prior art of preparing adipic acid by one-step oxidation of cyclohexane, such as high tail oxygen content, great potential safety hazards, difficulty in achieving safe production of adipic acid, low cyclohexane conversion rate and low target selectivity, and provides a safe synthesis method for preparing adipic acid by one-step oxidation of cyclohexane.

[0006] In order to solve the above technical problems, the present invention provides a safe synthesis method for preparing adipic acid by one-step oxidation of cyclohexane, which comprises: in the presence of a catalyst and a solvent, cyclohexane is contacted with an oxidant containing oxygen molecules to react to obtain adipic acid, wherein the catalyst is a transition metal salt, the solvent comprises an acid anhydride solvent, and the acid anhydride solvent is selected from one or more of the following structures A and B:

[0007]

[0008] R1 to R10 are independently selected from H or a C1-C4 alkyl group.

[0009] The invention has the advantages that cyclohexane can be efficiently oxidized to produce adipic acid in one step, the reaction conversion rate and selectivity are high, the tail oxygen content is low, and the reaction safety is good.

[0010] By adopting the technical scheme of the present invention, the single-pass conversion rate of cyclohexane in the continuous reaction is ≥10%, the selectivity of adipic acid is ≥80%, and the reaction tail oxygen content is ≤5%. Compared with the prior art, the conversion rate is only 4-7%, and the selectivity is below 65%, thereby achieving a good technical effect. The present invention is particularly suitable for the industrial production of adipic acid by one-step oxidation of cyclohexane. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a reaction flow chart according to one embodiment of the present invention. DETAILED DESCRIPTION

[0012] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0013] In the present invention, unless otherwise specified, directional words such as "upper, lower, left, right" generally refer to the upper, lower, left, and right shown in the accompanying drawings; "inner and outer" refer to the inner and outer relative to the outline of each component itself.

[0014] In the present invention, unless otherwise specified, directional words such as "up, down, top, bottom" are usually used with reference to the directions shown in the drawings or are used to describe the relative positional relationships of components in the vertical, perpendicular or gravity direction.

[0015] “Vertical direction” refers to the up-down direction of the paper as shown in the diagram, and “lateral direction” refers to the left-right direction of the roughly horizontal paper as shown in the diagram; “inside and outside” usually refer to the inside and outside of the chamber relative to the chamber or the radial inside and outside relative to the center of a circle.

[0016] The present invention provides a safe synthesis method for preparing adipic acid by one-step oxidation of cyclohexane, the method comprising: in the presence of a catalyst and a solvent, cyclohexane is contacted with an oxidant containing oxygen molecules to react to obtain adipic acid, wherein the catalyst is a transition metal salt, the solvent comprises an acid anhydride solvent, and the acid anhydride solvent is selected from one or more of the following structures A and B:

[0017]

[0018] R1 to R10 are independently selected from H or a C1-C4 alkyl group.

[0019] In order to achieve the solvent function, the anhydride solvent of the present invention is liquid at the reaction temperature, for example, liquid after melting or dissolved with other solvents to form a liquid.

[0020] According to a preferred embodiment of the present invention, R1 to R10 are independently H or methyl, preferably R1 to R10 are independently H; more preferably, the anhydride solvent is glutaric anhydride and / or succinic anhydride. The use of the above-mentioned preferred anhydride solvent can achieve high reaction conversion rate and selectivity, low tail oxygen content, and good reaction safety.

[0021] According to a preferred embodiment of the present invention, the solvent includes a protic solvent with a pKa of 3.0≤pKa≤5.0, and the protic solvent is preferably selected from one or more of acetic acid, propionic acid, butyric acid, isobutyric acid and valeric acid, preferably acetic acid and / or propionic acid, thereby further reducing the severity of the reaction conditions and ensuring the reaction results.

[0022] According to a preferred embodiment of the present invention, the mass ratio of anhydride solvent: protic solvent = 1: (0.2-5), preferably, the mass ratio of anhydride solvent: protic solvent = 1: (1-3). This can further reduce the severity of the reaction conditions and ensure the best reaction results.

[0023] According to a preferred embodiment of the present invention, the contact reaction is carried out in the presence of an initiator; there is no special requirement for the type of the initiator. For the present invention, preferably, the initiator is selected from at least one of the substance group consisting of nitroxide free radical organic compounds, aldehydes or ketones. According to a preferred embodiment of the present invention, more preferably, the initiator is selected from one or more of N-hydroxyphthalimide and cyclohexanone. Using the preferred technical solution of the present invention, the continuous reaction cyclohexane single-pass conversion rate is ≥10%, the selectivity of adipic acid is ≥80%, and the reaction tail oxygen content is ≤5%.

[0024] According to a preferred embodiment of the present invention, the mass ratio of initiator: cyclohexane is (0.1-10): 100, preferably the mass ratio of initiator: cyclohexane is (0.2-5): 100. By adopting the preferred technical scheme of the present invention, the continuous reaction cyclohexane single-pass conversion rate is ≥10%, the selectivity of adipic acid is ≥80%, and the reaction tail oxygen content is ≤5%.

[0025] In the present invention, transition metal salts can be used as catalysts to achieve the purpose of the present invention. The present invention has no special requirements for them. For the present invention, the catalyst is preferably selected from at least two of carboxylates, organic complexes and halogen salts of one or more metals selected from iron, cobalt, nickel, copper, ruthenium, palladium, platinum and manganese; more preferably at least two of cobalt, copper and manganese; more preferably a mixture of cobalt acetylacetonate and manganese acetylacetonate, the ratio of the two being 0.1-10:1. In the embodiments of the present invention, the mass ratio of the two is 1:1 as an example to illustrate the advantages of the present invention, but the scope of the present invention is not limited thereby.

[0026] In the present invention, the amount of catalyst can be selected in a wide range, and commonly used catalyst amounts can be used in the present invention. For the present invention, the preferred mass ratio of catalyst: cyclohexane is (0.01-1):100; preferably, the mass ratio of catalyst: cyclohexane is (0.02-0.5):100.

[0027] In the present invention, the optional range of the amount of solvent is relatively wide, which is exemplified below, but does not limit the scope of the present invention. For the present invention, the volume ratio of cyclohexane: solvent is preferably 1: (0.1-10); more preferably, the volume ratio of cyclohexane: solvent is 1: (0.5-5).

[0028] In the present invention, there is no special requirement for the conditions of the contact reaction, and commonly used contact conditions can be applied to the present invention, but the scope of the present invention is not limited thereto. For the present invention, preferred contact reaction conditions include: a temperature of 80-130°C, for example, 80°C, 90°C, 100°C, 110°C, 120°C, preferably 90-100°C; a time of 2-8h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h. In the embodiments, 6h is used as an example to illustrate the advantages of the present invention, but the scope of the present invention is not limited thereto.

[0029] In the present invention, the contact reaction is preferably carried out in the presence of an oxygen-containing gas, more preferably in the presence of air, and the residence time of the gas is 1-3 min, for example, 1 min, 2 min, 3 min. In the embodiment, 2 min is used as an example to illustrate the advantages of the present invention, but the scope of the present invention is not limited thereto. In the present invention, the residence time of the gas refers to the ratio of the reactor volume / air flow rate.

[0030] The present invention has no special requirements for the equipment used in the synthesis reaction. For example, Figure 1 The system shown in the figure includes a reactor 1 and a collecting tank. The reactor adopts a continuous feeding and discharging method. The reactor 1 is provided with a liquid phase inlet, preferably in the middle and lower part, a gas phase inlet (preferably arranged at the lower part of the liquid phase inlet) and a gas phase outlet (preferably arranged at the top) and a liquid phase outlet (preferably arranged at the side line to achieve side line extraction). The catalyst, optionally an initiator, cyclohexane and a solvent enter the reactor 1 for reaction, the reaction liquid is extracted from the side line and enters the collecting tank, the condensed and non-condensable gas is discharged from the top gas phase outlet, and an oxygen-containing gas is introduced from the bottom gas phase inlet of the reactor 1, preferably air is introduced for oxidation reaction; the reaction liquid in the collecting tank can enter a subsequent separation unit for solvent recovery, product concentration and crystallization, and impurity removal, and finally realizes the circulation of solvent and catalyst, and the continuous production of the product adipic acid.

[0031] In the specific implementation process, in order to achieve continuous feeding, a solvent can be used to dissolve the catalyst and the initiator and then introduced into the reactor, which can be selected according to the actual working conditions. The present invention will not be described in detail here.

[0032] In the present invention, the reactor is provided with a stirring paddle as required, and the stirring speed is more preferably 400-1000 r / min. 500 r / min is used as an example in the embodiment, but the scope of the present invention is not limited thereto. There is no special requirement for the overflow liquid level under stirring, for example, it is generally 1 / 3 to 2 / 3 of the volume of the reactor, and the embodiment takes 1 / 2 volume as the overflow liquid level.

[0033] The present invention has no special requirements for the equipment used in the subsequent separation unit, etc. For example, the separation unit includes equipment such as a flash tank, an evaporation crystallizer and a centrifuge, wherein the flash tank is mainly used to recover unreacted cyclohexane; the evaporation crystallizer is mainly used to concentrate the mother liquor and complete the crystallization of the adipic acid product at the same time; the centrifuge is mainly used for centrifugal drying of the adipic acid product.

[0034] According to a particularly preferred embodiment of the present invention, the catalyst and the initiator are respectively dissolved in a molten anhydride solvent, the reaction solvent is an anhydride solvent: protic solvent mass ratio = 1: (1-3) or a pure anhydride solvent, the mass ratio of the initiator: cyclohexane is regulated to be (0.2-5): 100, the volume ratio of cyclohexane: solvent is regulated to be 1: (0.5-5), the reaction temperature is 90-120° C., the reaction time is 3-6 hours, and the air residence time is 1-3 minutes, so that the safe synthesis of adipic acid by one-step oxidation of cyclohexane can be efficiently achieved.

[0035] The present invention will be described in detail below through examples. In the following examples, the cyclohexane content is measured by gas chromatography; the adipic acid content is measured by liquid chromatography, and the raw material cyclohexane is purchased from a commercial product of Sinopharm Reagent.

[0036] The pressures described in the present invention are all gauge pressures.

[0037] The product adipic acid of the present invention is selectively obtained by liquid phase HPLC detection. The solid-liquid mixed product obtained by the cyclohexane oxidation reaction to produce adipic acid is dissolved by electromagnetic stirring with water: methanol = 90:10 (V / V), filtered and diluted into high performance liquid phase for detection. Chromatographic analysis conditions: the chromatographic column model is ZORBAX SAX 4.6mm×250mm 5μm, the mobile phase is methanol: 50mmol / LKH2PO4: aqueous solution = 5:95 (V / V), the column temperature is 25°C, the flow rate is 1.0mL / min, the injection volume is 20μL, and the detection wavelength is 210nm.

[0038] The tail oxygen content in the reactor refers to the oxygen content in the tail gas in the reactor, which is measured by an online tail oxygen analyzer.

[0039] The calculation method of the reaction single-pass conversion rate is: the molar amount of cyclohexane consumed per unit time / the total molar amount of cyclohexane added per unit time.

[0040] The selectivity is calculated as follows: molar amount of adipic acid generated per unit time / molar amount of cyclohexane consumed per unit time.

[0041] The following examples adopt Figure 1 The process shown is carried out.

[0042] [Example 1]

[0043] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in molten glutaric anhydride in a mass ratio of 1:1 to prepare a catalyst solution, a certain amount of molten glutaric anhydride solution of N-hydroxyphthalimide (NHPI) was placed in the initiator tank, and a certain amount of molten glutaric anhydride was placed in the solvent tank. The flow rates of catalyst (net content), initiator (net content), cyclohexane and solvent (including the amount of solvent for dissolving catalyst and initiator) were adjusted and added to reactor 1 continuously according to the proportion shown in Table 1, wherein the volume of the reactor was 2.0L, the overflow level under stirring was 1.0L (liquid phase outlet position), and the total residence time of the liquid material in the reactor was ensured to be 6h. The reaction pressure was 3.0MPa, the reaction temperature was 100℃, the stirring speed was 500r / min, and air was continuously introduced into the reactor to ensure that the residence time of the air in the reactor was 2min. After stabilization, the tail oxygen content in the reactor was 3.53%, the reaction single-pass conversion rate was 11.72%, and the selectivity was 81.63%.

[0044] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0045] [Example 2]

[0046] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in a mixed solvent (mass ratio of glutaric anhydride: acetic acid = 1:1) at a mass ratio of 1:1 to prepare a catalyst solution, a certain amount of N-hydroxyphthalimide (NHPI) mixed solvent (mass ratio of glutaric anhydride: acetic acid = 1:1) solution was placed in the initiator tank, and a certain amount of mixed solvent (mass ratio of glutaric anhydride: acetic acid = 1:1) was placed in the solvent tank, and the flow rates of catalyst (net content), initiator (net content), cyclohexane and solvent (including the amount of solvent for dissolving catalyst and initiator) were adjusted and continuously added to the reactor according to the ratio shown in Table 1, wherein the reactor volume was 2.0L, the overflow level under stirring was 1.0L, and the total residence time of the liquid material in the reactor was ensured to be 6h. The reaction pressure was 3.0MPa, the reaction temperature was 100℃, the stirring speed was 500r / min, and air was continuously introduced into the reactor to ensure that its residence time in the reactor was 2min. After stabilization, the tail oxygen content in the reactor was 3.91%, the single-pass conversion rate was 10.56%, and the selectivity was 82.38%.

[0047] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0048] [Example 3]

[0049] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in a mixed solvent (mass ratio of glutaric anhydride: propionic acid = 1:3) at a mass ratio of 1:1 to prepare a catalyst solution of a certain concentration, a certain amount of cyclohexanone was placed in the initiator tank, and a certain amount of mixed solvent (mass ratio of glutaric anhydride: propionic acid = 1:3) was placed in the solvent tank, the flow rate of catalyst (net content), initiator, cyclohexane and solvent (including the amount of solvent for dissolving the catalyst) was regulated, and the reactor was continuously added according to the ratio shown in Table 1, wherein the reactor volume was 2.0L, the overflow level under stirring was 1.0L, and the total residence time of the liquid material in the reactor was ensured to be 6h. The reaction pressure was 3.0MPa, the reaction temperature was 100℃, the stirring speed was 500r / min, and air was continuously introduced into the reactor to ensure that its residence time in the reactor was 2min. After stabilization, the tail oxygen content in the reactor was 4.01%, the reaction single-pass conversion rate was 10.29%, and the selectivity was 81.41%.

[0050] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0051] [Example 4]

[0052] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in molten glutaric anhydride in a mass ratio of 1:1 to prepare a catalyst solution of a certain concentration, a molten glutaric anhydride solution of a certain amount of N-hydroxyphthalimide (NHPI) was placed in the initiator tank, and a certain amount of molten glutaric anhydride was placed in the solvent tank. The flow rates of catalyst (net content), initiator (net content), cyclohexane and solvent (including the amount of solvent for dissolving catalyst and initiator) were adjusted and added to the reactor continuously according to the proportion shown in Table 1, wherein the volume of the reactor was 2.0L, the overflow level under stirring was 1.0L, and the total residence time of the liquid material in the reactor was ensured to be 6h. The reaction pressure was 3.0MPa, the reaction temperature was 100℃, the stirring speed was 500r / min, and air was continuously introduced into the reactor to ensure that its residence time in the reactor was 2min. After stabilization, the tail oxygen content in the reactor was 3.88%, the reaction single-pass conversion rate was 11.20%, and the selectivity was 80.69%.

[0053] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0054] [Example 5]

[0055] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in molten glutaric anhydride in a mass ratio of 1:1 to prepare a catalyst solution of a certain concentration, a molten glutaric anhydride solution of a certain amount of N-hydroxyphthalimide (NHPI) was placed in the initiator tank, and a certain amount of molten glutaric anhydride was placed in the solvent tank. The flow rates of catalyst (net content), initiator (net content), cyclohexane and solvent (including the amount of solvent for dissolving catalyst and initiator) were adjusted and added to the reactor continuously according to the proportion shown in Table 1, wherein the volume of the reactor was 2.0L, the overflow level under stirring was 1.0L, and the total residence time of the liquid material in the reactor was ensured to be 6h. The reaction pressure was 3.0MPa, the reaction temperature was 100℃, the stirring speed was 500r / min, and air was continuously introduced into the reactor to ensure that its residence time in the reactor was 2min. After stabilization, the tail oxygen content in the reactor was 3.74%, the reaction single-pass conversion rate was 10.95%, and the selectivity was 80.73%.

[0056] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0057] [Example 6]

[0058] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in molten glutaric anhydride in a mass ratio of 1:1 to prepare a catalyst solution of a certain concentration, a molten glutaric anhydride solution of a certain amount of N-hydroxyphthalimide (NHPI) was placed in the initiator tank, and a certain amount of molten glutaric anhydride was placed in the solvent tank. The flow rates of catalyst (net content), initiator (net content), cyclohexane and solvent (including the amount of solvent for dissolving catalyst and initiator) were adjusted and added to the reactor continuously according to the proportion shown in Table 1, wherein the volume of the reactor was 2.0L, the overflow level under stirring was 1.0L, and the total residence time of the liquid material in the reactor was ensured to be 6h. The reaction pressure was 3.0MPa, the reaction temperature was 90℃, the stirring speed was 500r / min, and air was continuously introduced into the reactor to ensure that its residence time in the reactor was 2min. After stabilization, the tail oxygen content in the reactor was 3.82%, the reaction single-pass conversion rate was 11.04%, and the selectivity was 81.19%.

[0059] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0060] [Example 7]

[0061] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in molten glutaric anhydride in a mass ratio of 1:1 to prepare a catalyst solution of a certain concentration. A certain amount of molten glutaric anhydride solution of N-hydroxyphthalimide (NHPI) was placed in the initiator tank, and a certain amount of molten glutaric anhydride was placed in the solvent tank. The flow rates of catalyst (net content), initiator (net content), cyclohexane and solvent (including the amount of solvent for dissolving the catalyst and initiator) were adjusted and continuously added into the reactor in the proportions shown in Table 1 (see the reaction unit flow chart below). Figure 1 ), wherein the reactor volume is 2.0L, the overflow level under stirring is 1.0L, and the total residence time of the liquid material in the reactor is ensured to be 6h. The reaction pressure is 2.0MPa, the reaction temperature is 100℃, the stirring speed is 500r / min, and air is continuously introduced into the reactor to ensure that its residence time in the reactor is 2min. After stabilization, the tail oxygen content in the reactor is 3.96%, the reaction single-pass conversion rate is 10.87%, and the selectivity is 81.22%.

[0062] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0063] [Example 8]

[0064] The method of Example 1 is followed, except that the solvent is molten 3-methylglutaric anhydride, the tail oxygen content in the reactor after stabilization is 4.13%, the single-pass conversion rate of the reaction is 10.17%, and the selectivity is 80.32%.

[0065] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0066] [Example 9]

[0067] The method of Example 1 is followed, except that the solvent is molten succinic anhydride, the tail oxygen content in the reactor after stabilization is 3.78%, the single-pass conversion rate of the reaction is 10.68%, and the selectivity is 81.04%.

[0068] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0069] [Example 10]

[0070] The method of Example 1 is followed, except that the solvent is molten methylsuccinic anhydride, the tail oxygen content in the reactor after stabilization is 4.45%, the single-pass conversion rate of the reaction is 10.09%, and the selectivity is 80.11%.

[0071] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0072] [Comparative Example 1]

[0073] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in acetic acid at a mass ratio of 1:1 to prepare a catalyst solution of a certain concentration, a certain amount of acetic acid solution of N-hydroxyphthalimide (NHPI) was placed in the initiator tank, and a certain amount of acetic acid was placed in the solvent tank. The flow rates of catalyst (net content), initiator (net content), cyclohexane and solvent (including the amount of solvent for dissolving catalyst and initiator) were adjusted and added to the reactor continuously according to the proportion shown in Table 1, wherein the volume of the reactor was 2.0L, the overflow level under stirring was 1.0L, and the total residence time of the liquid material in the reactor was ensured to be 6h. The reaction pressure was 3.0MPa, the reaction temperature was 100℃, the stirring speed was 500r / min, and air was continuously introduced into the reactor to ensure that its residence time in the reactor was 2min. After stabilization, the tail oxygen content in the reactor was 6.95%, the reaction single-pass conversion rate was 6.52%, and the selectivity was 63.79%.

[0074] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0075] [Comparative Example 2]

[0076] Cobalt acetylacetonate and manganese acetylacetonate were dissolved in acetic anhydride in a mass ratio of 1:1 to prepare a catalyst solution of a certain concentration, a certain amount of acetic anhydride solution of N-hydroxyphthalimide (NHPI) was placed in the initiator tank, and a certain amount of acetic anhydride was placed in the solvent tank. The flow rates of catalyst (net content), initiator (net content), cyclohexane and solvent (including the amount of solvent for dissolving catalyst and initiator) were adjusted and added to the reactor continuously according to the proportion shown in Table 1, wherein the volume of the reactor was 2.0L, the overflow level under stirring was 1.0L, and the total residence time of the liquid material in the reactor was ensured to be 6h. The reaction pressure was 3.0MPa, the reaction temperature was 100℃, the stirring speed was 500r / min, and air was continuously introduced into the reactor to ensure that its residence time in the reactor was 2min. After stabilization, the tail oxygen content in the reactor was 7.38%, the reaction single-pass conversion rate was 6.10%, and the selectivity was 57.64%.

[0077] For easy comparison, the main reaction conditions and reaction results are listed in Table 1.

[0078] Table 1

[0079]

[0080]

[0081] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A safe synthesis method for preparing adipic acid by one-step oxidation of cyclohexane, characterized in that: The method comprises: in the presence of a catalyst and a solvent, cyclohexane is contacted with an oxidant containing oxygen molecules to react to obtain adipic acid, wherein the catalyst is a transition metal salt, the solvent comprises an anhydride solvent, and the anhydride solvent is selected from one or more of the following structures A and B: R1 to R10 are independently selected from H or a C1-C4 alkyl group.

2. The synthesis method according to claim 1, wherein R1-R10 are independently H or methyl, preferably R1-R10 are independently H; preferably, the anhydride solvent is glutaric anhydride and / or succinic anhydride.

3. The synthesis method according to claim 1 or 2, wherein The solvent comprises a protic solvent with a pKa of 3.0≤PKa≤5.0, and the protic solvent is preferably selected from one or more of acetic acid, propionic acid, butyric acid, isobutyric acid and valeric acid, preferably acetic acid and / or propionic acid.

4. The synthesis method according to claim 3, wherein The mass ratio of anhydride solvent:protic solvent=1:(0.2-5), preferably, the mass ratio of anhydride solvent:protic solvent=1:(1-3).

5. The synthesis method according to any one of claims 1 to 4, wherein The contact reaction is carried out in the presence of an initiator; Preferably, the initiator is at least one selected from the group consisting of nitroxide free radical organic compounds, aldehydes or ketones; More preferably, the initiator is selected from one or more of N-hydroxyphthalimide and cyclohexanone.

6. The synthesis method according to claim 5, wherein The mass ratio of initiator:cyclohexane=(0.1-10):100, preferably the mass ratio of initiator:cyclohexane=(0.2-5):

100.

7. The synthesis method according to any one of claims 1 to 6, wherein The catalyst is selected from at least two of carboxylates, organic complexes and halogen salts of one or more metals selected from iron, cobalt, nickel, copper, ruthenium, palladium, platinum and manganese; Preferably, it is at least two of cobalt, copper and manganese; more preferably, it is a mixture of cobalt acetylacetonate and manganese acetylacetonate, with the ratio of the two being 0.1-10:

1.

8. The synthesis method according to any one of claims 1 to 7, wherein The mass ratio of catalyst: cyclohexane is (0.01-1):100; preferably, the mass ratio of catalyst: cyclohexane is (0.02-0.5):

100.

9. The synthesis method according to any one of claims 1 to 8, wherein The volume ratio of cyclohexane:solvent=1:(0.1-10); more preferably, the volume ratio of cyclohexane:solvent=1:(0.5-5).

10. The synthesis method according to any one of claims 1 to 9, wherein The conditions of the contact reaction include: temperature of 80-130°C; time of 2-8h; Preferably, the contact reaction is carried out in the presence of an oxygen-containing gas, more preferably in the presence of air, and the residence time of the gas is 1-3 minutes.

Images