Method and system for preparing adipic acid through cyclohexane oxidation

Abstract

The invention provides a method and a system for preparing adipic acid by cyclohexane oxidation. The method comprises the following steps: (1) contacting cyclohexane with ozone-containing gas to obtain a material I; and (2) carrying out oxidation reaction on the material I and O2-containing gas to obtain a product material II containing adipic acid. The method is simple, efficient, green and environment-friendly, and the obtained adipic acid provides an excellent raw material for polyester production.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a method and system for preparing adipic acid by oxidizing cyclohexane. Background Technology

[0002] Adipic acid, also known as fatty acid, is an important organic dicarboxylic acid. It can undergo salt formation, esterification, and amidation reactions, and can condense with diamines or diols to form high molecular weight polymers. Adipic acid plays a vital role in chemical production, organic synthesis, pharmaceuticals, and lubricant manufacturing. Specifically, it can be used to synthesize nylon 66 and produce polyurethane; it can also be used as a food acidifier to maintain the freshness and stability of food; furthermore, it can be used in the production of fragrances and dyes.

[0003] In 1937, DuPont in the United States first achieved the industrial production of adipic acid by oxidizing cyclohexanol (obtained by hydrogenating phenol) with nitric acid. In the 1960s, the industry gradually switched to the cyclohexane oxidation method, which first produces an intermediate product of cyclohexane ketone and cyclohexanol (i.e., ketol oil, also known as KA oil) from cyclohexane, and then oxidizes the KA oil with nitric acid or air.

[0004] Cyclohexane, being a rigid ring, presents significant challenges in oxidative ring-opening, especially when using air as an oxidant due to its poor oxidizing properties. Not only is reaction initiation difficult, but once initiated, the free radical reaction chain is hard to control, easily generating various byproducts and impurities, making it difficult to improve the selectivity of the target product, adipic acid. While using hydrogen peroxide directly as an oxidant can improve reaction efficiency, it decomposes easily at high temperatures, resulting in low utilization. Furthermore, cyclohexane is prone to explosion, increasing production costs and significantly reducing system safety.

[0005] Therefore, the conversion efficiency of direct cyclohexane feeding in existing technologies is not high. It usually requires high reaction temperature and long reaction time, and a large amount of cyclohexane recycling is used to increase the yield of adipic acid. The separation of impurity byproducts generated in the reaction is difficult, the separation energy consumption is high, and the atom economy is poor. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method and system for preparing adipic acid by cyclohexane oxidation. This method is simple, efficient, and environmentally friendly, and the resulting adipic acid provides an excellent raw material for polyester production.

[0007] In a first aspect, the present invention provides a method for preparing adipic acid by cyclohexane oxidation, comprising:

[0008] (1) Cyclohexane is contacted with ozone-containing gas to obtain material I;

[0009] (2) The material I is oxidized with O2 gas to obtain product material II containing adipic acid.

[0010] The inventors of this application unexpectedly discovered that by first pre-activating cyclohexane with ozone gas, and then oxidizing the pre-activated cyclohexane with O2 gas, the reaction rate is greatly accelerated, while the impurity content in the product is greatly reduced, thereby improving the yield and selectivity of adipic acid.

[0011] In some embodiments, the volume concentration of ozone in the ozone-containing gas is 0.1-8.0%, for example, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0% or any value between them.

[0012] In some embodiments, the ozone volume concentration in the ozone-containing gas is 0.5-5.0%.

[0013] In some embodiments, the ozone-containing gas also includes nitrogen.

[0014] In some embodiments, the mass ratio of ozone to cyclohexane in the ozone-containing gas is (0.005-0.1):1, for example, 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1 or any value between them.

[0015] In some embodiments, the temperature of the contact is 10-80°C, for example 15°C, 25°C, 35°C, 45°C, 55°C, 65°C, 75°C or any value between them.

[0016] In some embodiments, the temperature of the contact is 40-60°C.

[0017] In some implementations, the contact time is 10-120 min, for example 20 min, 40 min, 60 min, 80 min, 100 min, 120 min or any value between them.

[0018] In some implementations, the contact time is 10-60 minutes.

[0019] In some embodiments, the oxidation reaction is carried out in the presence of a catalyst and a solvent.

[0020] In some embodiments, the solvent is selected from acetic acid.

[0021] In some embodiments, the catalyst is selected from metal salt catalysts.

[0022] In some embodiments, the metal element in the metal salt catalyst is selected from one or more of copper, manganese, or chromium.

[0023] In some embodiments, the metal salt is an acetate of a metal element.

[0024] In some embodiments, the catalyst is a mixture of copper acetate, manganese acetate, and cobalt acetate.

[0025] In some embodiments, the mass ratio of copper, manganese, and cobalt in the catalyst is (5-10):(1-5):1, for example, 5:(1-5):1, 6:(1-5):1, 7:(1-5):1, 8:(1-5):1, 9:(1-5):1, 10:(1-5):1, (5-10):1:1, (5-10):2:1, (5-10):3:1, (5-10):4:1, (5-10):5:1, or any value thereof.

[0026] In some embodiments, the mass ratio of copper, manganese and cobalt in the catalyst is 8:3:1.

[0027] In some embodiments, the oxidation reaction includes the following steps:

[0028] S1, the catalyst and solvent are mixed to obtain a catalyst solution;

[0029] S2, the catalyst solution, material I and O2-containing gas are subjected to an oxidation reaction.

[0030] In some embodiments, the mass ratio of the catalyst solution to the material I is (1.5-8):1, for example, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or any value between them.

[0031] In some embodiments, the mass concentration of the catalyst in the catalyst solution is 0.05-5%, for example, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any value between them.

[0032] In some embodiments, the mass ratio of the O2-containing gas to the material I is (5-15):1, for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1 or any value between them.

[0033] In some embodiments, the volume content of O2 in the O2-containing gas is 10-25%, for example, 10%, 13%, 16%, 19%, 21%, 24% or any value between them.

[0034] In some embodiments, the volume content of O2 in the O2-containing gas is 15-25%.

[0035] In some embodiments, the oxidation reaction is carried out at a temperature of 85-110°C; for example, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C or any value between them.

[0036] In some embodiments, the pressure of the oxidation reaction is 1.5-5 MPa; for example, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa or any value between them.

[0037] In some embodiments, the oxidation reaction time is 0.5-2 h, for example 0.5 h, 0.7 h, 0.9 h, 1.1 h, 1.3 h, 1.5 h, 1.7 h, 1.9 h or any value between them.

[0038] In a second aspect, the present invention provides a system for the oxidation of cyclohexane to prepare adipic acid, which is used in the method for the oxidation of cyclohexane to prepare adipic acid described in the first aspect of the present invention, the system comprising:

[0039] Cyclohexane feedstock tank;

[0040] A gas-liquid contact device connected to the cyclohexane feedstock tank is used to contact cyclohexane with ozone-containing gas to obtain material I;

[0041] A reactor connected to the gas-liquid contact device is used to oxidize material I with O2-containing gas to obtain product material II containing adipic acid.

[0042] In some embodiments, the system further includes a catalyst tank connected to the reactor so that the oxidation reaction is carried out in the presence of a catalyst solution.

[0043] In some embodiments, the system further includes a discharge tank connected to the reactor to receive material II.

[0044] In some implementations, the flow rate of cyclohexane can be controlled using a pump.

[0045] In some implementations, the flow rate of ozone-containing gas can be controlled using a flow meter.

[0046] In some implementations, the volume concentration of ozone in the ozone-containing gas is adjusted by controlling the power of the ozone generator.

[0047] In some implementations, pure oxygen is introduced into an ozone generator, and different concentrations of ozone-containing gas can be obtained by adjusting the power of the ozone generator.

[0048] In some embodiments, the gas-liquid contactor is a gas bubbling tower.

[0049] In some embodiments, the gas-liquid bubbling tower includes a gas distributor and a heater located in the tower body.

[0050] In some implementations, according to Figure 1 The process shown, the method for preparing adipic acid by cyclohexane oxidation, includes:

[0051] 1) Cyclohexane in the cyclohexane raw material tank is introduced into the gas-liquid contact device through the cyclohexane feed pipe, and ozone-containing gas is introduced into the gas-liquid contact device through the ozone-containing gas feed pipe and comes into contact with the cyclohexane to obtain material I. The ozone-containing gas after contact is discharged through the ozone-containing gas discharge pipe.

[0052] 2) Material I flows into the reactor through the material I outlet pipe, and O2-containing gas flows into the reactor through the O2-containing gas inlet pipe; the catalyst solution in the catalyst tank flows into the reactor through the catalyst solution inlet pipe; Material I and O2-containing gas undergo an oxidation reaction in the reactor to obtain product material II containing adipic acid and tail gas;

[0053] 3) The product material II containing adipic acid flows into the discharge tank.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] (1) The present invention uses ozone gas to treat cyclohexane, which significantly improves the reaction activity, accelerates the reaction rate of cyclohexane with O2 gas, greatly reduces the impurity content, and improves the yield and selectivity of adipic acid.

[0056] (2) The system equipment of the present invention has low investment and simple operation process, and can be used in the continuous industrial production of cyclohexane oxidation to prepare adipic acid. Attached Figure Description

[0057] Figure 1 This is a flowchart illustrating Embodiment 1 of the present invention;

[0058] Explanation of reference numerals in the attached figures:

[0059] 1. Cyclohexane feed tank; 2. Cyclohexane feed pipe; 3. Gas-liquid contact device; 4. Ozone gas feed pipe; 5. Material I discharge pipe; 6. Ozone gas discharge pipe; 7. Catalyst tank; 8. Catalyst solution feed pipe; 9. Reactor; 10. O2 gas feed pipe; 11. Discharge tank; 12. Tail gas. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way.

[0061] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0062] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or by existing methods; unless otherwise specified, the reagent dosages are those used in routine experimental operations; unless otherwise specified, the experimental methods are conventional methods.

[0063] In the following examples and comparative examples, the Co-Mn-Cu catalyst solution contains 0.01 wt% Co, 0.03 wt% Mn, and 0.08 wt% Cu, all of which are acetates, and the remaining solvent is acetic acid.

[0064] The feedstock cyclohexane was calculated based on a flow rate of 100 g / h.

[0065] The gas chromatograph used in this invention is an Agilent 7890 with an HP5 column.

[0066] The liquid chromatography used in this invention employs an Agilent 1260 column with a C18 column.

[0067] In this embodiment of the invention, the O2-containing gas is air with an O2 content of 21% (by volume).

[0068] The method for calculating the selectivity of adipic acid is as follows:

[0069] Adipic acid selectivity = (Moles of adipic acid produced in the reaction / Moles of cyclohexane consumed in the reaction) * 100%. The yield of adipic acid is calculated as follows:

[0070] Adipic acid yield = (Molar amount of adipic acid produced in the reaction) / (Molar amount of cyclohexane in the feed) * 100%

[0071] Example 1 (Activation by contact of 1 vol% ozone gas with cyclohexane)

[0072] Example 1: Preparation of adipic acid by oxidizing cyclohexane with O2 gas (air containing 21% O2 by volume).

[0073] I) Such as Figure 1 As shown, cyclohexane from cyclohexane feed tank 1 enters gas-liquid contact device 3 from the top via cyclohexane feed pipe 2. Ozone-containing gas generated by the ozone generator enters gas-liquid contact device 3 from the bottom via ozone-containing gas feed pipe 4. The ozone-containing gas contacts the cyclohexane in gas-liquid contact device 3, and the resulting ozone-containing gas is discharged via ozone-containing gas discharge pipe 6. The resulting material I enters reactor 9 from the top via material I discharge pipe 5. The flow rate of the feed cyclohexane is 100 g / h, the flow rate of the ozone-containing gas is 100 g / h, the ozone volume concentration in the ozone-containing gas is 1%, and the remainder is nitrogen. The contact time is 30 min, and the contact temperature is 50℃. The flow rate of material I is 100 g / h.

[0074] II) The catalyst and solvent are combined in the catalyst tank 7 to form a catalyst solution, which is then added to the reactor 9 from the top through the catalyst solution feed pipe 8. The catalyst solution flow rate is 400 g / h.

[0075] III) Gas containing 21% by volume of O2 is introduced into reactor 9 through O2 gas feed pipe 10, and the reactor is heated to the reaction temperature of 95°C, the reaction pressure is 2MPa, and the flow rate of O2 gas is 500g / h.

[0076] IV) O2-containing gas under working pressure is continuously fed into reactor 9 through O2-containing gas feed pipe 10 for contact for 1.5 hours;

[0077] V) Stop feeding to end the reaction. The product material II containing adipic acid flows into the discharge tank 11, and the tail gas 12 after the oxidation reaction is discharged.

[0078] The concentration of cyclohexane in material II of discharge tank 11 was analyzed by gas chromatography to calculate the cyclohexane consumption, and the concentration of adipic acid was analyzed by liquid chromatography to calculate the adipic acid production. Combined with the cyclohexane feed rate, the adipic acid yield and selectivity were calculated to be 86.4% and 98.2%, respectively.

[0079] Examples 2-9

[0080] The steps are the same as in Example 1, and the operating conditions are shown in Table 1.

[0081] Comparative Example 1 (activated by contact between nitrogen and cyclohexane)

[0082] Comparative Example 1 uses O2 gas (air containing 21% O2 by volume) to oxidize cyclohexane to prepare adipic acid.

[0083] I) Cyclohexane enters the gas-liquid contact device, and nitrogen enters the liquid contact device to contact the cyclohexane. After contact, the nitrogen is discharged. The mixed liquid after contact enters the reactor, wherein the flow rate of the raw material cyclohexane is 100 g / h, the flow rate of nitrogen is 100 g / h, the contact time is 30 min, and the contact temperature is 50℃.

[0084] II) The above-mentioned mixed liquid enters the reactor at a flow rate of 100 g / h and a temperature of 20°C;

[0085] III) Add the catalyst and solvent solution to the oxidation reactor at a catalyst solution flow rate of 400 g / h;

[0086] IV) Introduce O2 gas into the reactor, wherein the O2 volume concentration is 21% and the remainder is nitrogen gas, and heat the reactor to the reaction temperature of 95°C, the reaction pressure is 2MPa, and the air flow rate is 500g / h.

[0087] V) O2-containing gas at the working pressure is continuously fed into the reactor for contact for 1.5 hours;

[0088] VI) Stop feeding to end the reaction.

[0089] The cyclohexane consumption was calculated by analyzing the concentration of cyclohexane in the synthesis solution effluent using gas chromatography, and the adipic acid production was calculated by analyzing the concentration of adipic acid in the solution using liquid chromatography. Combined with the cyclohexane feed rate, the adipic acid yield and selectivity were calculated to be 19.6% and 81.3%, respectively.

[0090] Comparative Example 2 (using ozone-containing gas as the oxidant instead of O2-containing gas)

[0091] Comparative Example 2 uses ozone-containing gasified cyclohexane to prepare adipic acid.

[0092] I) The catalyst and solvent are added to the reactor in a solution, with a catalyst solution flow rate of 400 g / h;

[0093] II) Introduce ozone-containing gas (from an ozone generator) into the reactor. The ozone volume concentration is 1%, the O2 volume concentration is 21%, and the remainder is nitrogen. Heat the reactor to the reaction temperature of 95°C, the reaction pressure is 2MPa, and the gas flow rate is 500g / h.

[0094] III) The raw material under working pressure is continuously fed into the reactor for contact for 1.5 hours;

[0095] IV) Stop feeding to end the reaction.

[0096] The cyclohexane consumption was calculated by analyzing the concentration of cyclohexane in the synthesis solution effluent using gas chromatography, and the adipic acid production was calculated by analyzing the concentration of adipic acid in the solution using liquid chromatography. Combined with the cyclohexane feed rate, the adipic acid yield and selectivity were calculated to be 43.8% and 44.2%, respectively.

[0097] Comparative Example 3 (using air instead of ozone for activation with cyclohexane)

[0098] Comparative Example 3 uses O2 gas (air containing 21% O2 by volume) to oxidize cyclohexane to prepare adipic acid.

[0099] I) Cyclohexane enters the gas-liquid contact device. Air with an O2 concentration of 21% by volume enters the gas-liquid contact device and comes into contact with the cyclohexane. After contact, the air is discharged. The resulting mixed liquid enters the reactor, where the cyclohexane flow rate is 100 g / h, the contact time is 30 min, and the contact temperature is 50 °C.

[0100] II) The above-mentioned mixed liquid enters the reactor at a flow rate of 100 g / h and a temperature of 20°C;

[0101] III) Add the catalyst and solvent solution to the reactor at a flow rate of 400 g / h.

[0102] IV) Introduce O2 gas into the reactor, wherein the O2 volume concentration is 21% and the remainder is nitrogen gas, and heat the reactor to the reaction temperature of 95°C, the reaction pressure is 2MPa, and the air flow rate is 500g / h.

[0103] V) Oxygen-containing gas at the working pressure is continuously fed into the reactor for contact for 1.5 hours;

[0104] VI) Stop feeding to end the reaction.

[0105] The cyclohexane consumption was calculated by analyzing the concentration of cyclohexane in the synthesis solution effluent using gas chromatography, and the adipic acid production was calculated by analyzing the concentration of adipic acid in the solution using liquid chromatography. Combined with the cyclohexane feed rate, the adipic acid yield and selectivity were calculated to be 19.7% and 81.4%, respectively.

[0106] The yield and selectivity of adipic acid in Comparative Example 3 were almost the same as those in Comparative Example 1, proving that ordinary air has no activating effect.

[0107] Comparative Example 4

[0108] I) Cyclohexane enters the reactor;

[0109] II) Cyclohexane flow rate is 100 g / h, temperature is 20℃;

[0110] III) Add the catalyst and solvent to form a catalyst solution and add it to the reactor at a flow rate of 400 g / h;

[0111] IV) Introduce O2-containing gas with a volume of 21% into the reactor and heat the reactor to a reaction temperature of 95°C, a reaction pressure of 2 MPa, and an O2-containing gas flow rate of 500 g / h.

[0112] V) O2-containing gas at the working pressure is continuously fed into the reactor through an O2-containing gas feed pipe for contact for 1.5 hours;

[0113] VI) Stop feeding to end the reaction.

[0114] The amount of cyclohexane consumed was calculated by analyzing the concentration of cyclohexane in the synthesis liquid output using gas chromatography, and the amount of adipic acid generated was calculated by analyzing the concentration of adipic acid in the liquid chromatography output.

[0115] Table 1

[0116]

[0117] In Table 1, the ozone concentration in ozone-containing gas and the O2 concentration in O2-containing gas during pretreatment are both volume concentrations.

[0118] As can be seen from Table 1, the yield and selectivity of adipic acid prepared from cyclohexane after pretreatment with ozone gas are higher.

[0119] Comparative Examples 1 and 3-4 show that the reaction effect is almost unchanged by using nitrogen or air pretreatment or no pretreatment, and only ozone activation has an effect.

[0120] In addition, the addition of ozone in the second step of Comparative Example 2 resulted in a violent oxidation reaction, leading to over-oxidation, increased byproducts, and decreased selectivity.

[0121] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing adipic acid by oxidizing cyclohexane, comprising: (1) Cyclohexane is contacted with ozone-containing gas to obtain material I; (2) The material I is oxidized with O2 gas to obtain product material II containing adipic acid.

2. The method according to claim 1, characterized in that, The ozone volume concentration in the ozone-containing gas is 0.1-8.0%, preferably 0.5-5.0%; and / or The mass ratio of ozone to cyclohexane in the ozone-containing gas is (0.005-0.1):

1.

3. The method according to claim 1 or 2, characterized in that, The contact temperature is 10-80℃; preferably 40-60℃; and / or The contact time is 10-120 min, preferably 10-60 min.

4. The method according to any one of claims 1-3, characterized in that, The oxidation reaction is carried out in the presence of a catalyst and a solvent; Preferably, the solvent is selected from acetic acid.

5. The method according to claim 4, characterized in that, The catalyst is selected from metal salt catalysts; Preferably, the metal element in the metal salt catalyst is selected from one or more of copper, manganese, or cobalt; Preferably, the metal salt is an acetate of a metal element; Preferably, the catalyst is a mixture of copper acetate, manganese acetate and cobalt acetate; Preferably, the mass ratio of copper, manganese and cobalt in the catalyst is (5-10):(1-5):

1.

6. The method according to any one of claims 1-5, characterized in that, The oxidation reaction includes the following steps: S1, the catalyst and solvent are mixed to obtain a catalyst solution; S2, the catalyst solution, material I and O2-containing gas are subjected to an oxidation reaction; Preferably, the mass ratio of the catalyst solution to the material I is (1.5-8):1; and / or The mass concentration of the catalyst in the catalyst solution is 0.05-5%.

7. The method according to any one of claims 1-6, characterized in that, The mass ratio of the O2-containing gas to the material I is (5-15):1; and / or The volume content of O2 in the O2-containing gas is 10-25%, preferably 15-25%.

8. The method according to any one of claims 1-7, characterized in that, The oxidation reaction is carried out at a temperature of 85-110°C; and / or The oxidation reaction is carried out at a pressure of 1.5-5 MPa; and / or The oxidation reaction time is 0.5-2 hours.

9. A system for the oxidation of cyclohexane to prepare adipic acid, used in the method of any one of claims 1-8, said system comprising: Cyclohexane feedstock tank; A gas-liquid contact device connected to the cyclohexane feedstock tank is used to contact cyclohexane with ozone-containing gas to obtain material I; A reactor connected to the gas-liquid contact device is used to oxidize material I with O2-containing gas to obtain product material II containing adipic acid.

10. The system according to claim 9, characterized in that, The system also includes a catalyst tank connected to the reactor, so that the oxidation reaction is carried out in the presence of a catalyst solution; Preferably, the system further includes a discharge tank connected to the reactor to receive material II.

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