Electrochemical synthesis method for synthesizing adiponitrile by taking cyclohexene as raw material

Abstract

The invention relates to an electrochemical synthesis method for synthesizing adiponitrile by taking cyclohexene as a raw material. According to the method, cyclohexene is used as a raw material, a self-made titanium-based copper-lead composite electrode is used as a cathode, commercial isostatic pressing graphite is used as an anode, and electrolysis is performed in an aqueous solution containing halide salt and nitric acid or nitrite to obtain an adiponitrile product. The method is simple in process, raw materials are easy to obtain, high-toxicity and highly-toxic substances are not needed, high temperature and high pressure are not needed, tail gas does not contain oxygen, the reaction risk is greatly reduced, and a new synthesis process is provided for the adiponitrile product.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical synthesis, and in particular relates to an electrochemical synthesis method for synthesizing adiponitrile using cyclohexene as a raw material. Background Art

[0002] The mainstream synthesis methods of adiponitrile are butadiene cyanation, acrylonitrile electrolytic dimerization, and adipic acid cyanation. INVISTA and Ascend have been working on the butadiene method and acrylonitrile electrolysis method for many years, respectively, and it is difficult for domestic manufacturers to catch up with the technology in a short period of time. The adipic acid method has a significant cost gap compared to the previous two methods, so we urgently need to find a new adiponitrile process, that is, a method with easy-to-obtain raw materials, simple synthesis method, and lower investment cost.

[0003] Patent CN113956180B discloses a process of using cyclohexene as a raw material to oxidize adipaldehyde and then aminating to obtain adiponitrile. If a simpler method can be used to directly synthesize adiponitrile from cheap and readily available cyclohexene in a one-step reaction, it is more likely to occupy a place in the various synthetic routes of adiponitrile in the future. Summary of the invention

[0004] The invention provides an electrochemical synthesis method for synthesizing adiponitrile using cyclohexene as a raw material. The method for preparing adiponitrile has a simple process, very little three wastes, no high-grade materials, no tail gas safety risks, and has high practical value.

[0005] In order to practice the above invention purpose, the technical solution adopted by the present invention is as follows:

[0006] An electrochemical synthesis method for synthesizing adiponitrile using cyclohexene as a raw material, the method comprising the following steps:

[0007] (1) mixing cyclohexene, halide, nitrate / nitrite, organic alcohol and pure water to prepare an electrolyte;

[0008] (2) A titanium-based copper-lead composite electrode is used as the cathode, isostatically pressed graphite is used as the anode, and a diaphragm-free electrolytic cell is used to electrolyze adiponitrile.

[0009] In the present invention, in step (1), the halide salt is one or more of sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide, and potassium iodide;

[0010] The content of the halogen salt in the electrolyte is 0.1wt%-3wt%, preferably 0.5-2.5wt%.

[0011] In the present invention, in step (1), the nitrate / nitrite is one or more of sodium nitrate, potassium nitrate, zirconium nitrate, cerium nitrate, sodium nitrite, and potassium nitrite;

[0012] In the present invention, the content of nitrate / nitrite in the electrolyte prepared in step (1) is 0.1wt%-10wt%, preferably 1-5wt%.

[0013] In the present invention, the organic alcohol in step (1) is one or more of methanol, ethanol, ethylene glycol, and isopropanol;

[0014] Preferably, the content of organic alcohol in the electrolyte is 1%-30wt%, preferably 5wt%-15wt%.

[0015] In the present invention, in step (1), the content of cyclohexene in the electrolyte is 1%-7wt%, preferably 2-5wt%.

[0016] The electrolytic cell used in the present invention is a single-chamber non-diaphragm electrolytic cell, which uses a direct current power supply and adopts a constant current method to carry out electrolytic reaction on the electrolyte, and the voltage is strictly controlled below 10V.

[0017] In the present invention, in the step (2), the electrolysis reaction temperature is 20-50°C.

[0018] In the present invention, in step (2), the current density is 500A / m 2 -3000A / m 2 .

[0019] In the present invention, in step (2), the cathode is a titanium-based copper-lead composite electrode, and the anode is a commercial isostatically pressed graphite electrode.

[0020] In the present invention, the preparation method of the cathode in step (2) is: using a pure titanium plate as a substrate, etching it with a hydrofluoric acid solution to activate it; using a copper-lead alloy as a target material, using a vacuum evaporation method to evaporate copper and lead onto the substrate to obtain a titanium-based copper-lead composite electrode;

[0021] The concentration of hydrofluoric acid is 0.01wt%-10wt%, preferably 1wt%-10wt%, and the etching time is 15s-30s;

[0022] In the present invention, the mass ratio of copper to lead in the target copper-lead alloy is 1:1-49:1, preferably 3:1-24:1, and more preferably 3:1-15:1;

[0023] In the present invention, the vacuum degree during vacuum evaporation is less than 10 -3 Pa; the evaporation temperature is 1150°C-1500°C; the coating thickness is 0.1-20 μm, preferably 1-15 μm.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The electrochemical synthesis method of the present invention has cheap and readily available raw materials, a short synthesis route, a simplified process, no need for highly resistant substances, and compared with the acrylonitrile electrolysis method, has no tail gas safety risk, has a high molecular utilization rate, and is green and environmentally friendly. DETAILED DESCRIPTION

[0026] The following is a detailed description of the embodiments of the present invention. The embodiments are implemented based on the technical solution of the present invention. Although it is impossible to list them all, representative detailed implementation methods and specific operation processes are given based on experimental results. The protection scope of the present invention is not limited to the following embodiments.

[0027] Analysis method: The product was analyzed by gas chromatography, conditions: Agilent gas chromatography, chromatographic column HP-5 for online determination, two-step program temperature increase, initial temperature 20°C, maintained for 1 minute, then increased to 50°C at a rate of 5°C / min; then increased to 280°C at a rate of 10°C / min. Carrier gas high-purity N 2 , split ratio 100: 1. Injection temperature 180℃, detector is FID, detector temperature 280℃.

[0028] Source of raw materials:

[0029] Isostatic graphite: Kebowei.

[0030] Example 1

[0031] Electrode preparation:

[0032] The pure titanium substrate was polished with 600, 1500, and 5000 mesh sandpaper, ultrasonically cleaned in anhydrous ethanol for 10 min, and dried in an oven for later use;

[0033] Prepare an aqueous solution containing 5 wt% hydrofluoric acid, immerse the treated pure titanium substrate in the hydrofluoric acid solution for 30 seconds, take it out and place it in a nitrogen environment for drying for later use;

[0034] Weigh 5g of powdered alloy target with a copper-lead ratio of 6:1 and place it in a heated crucible. Reduce the vacuum to <10 -3 Pa. The dried titanium substrate was placed 25 cm above the crucible, the evaporation temperature was 1500°C, and the coating was evaporated to 10 μm.

[0035] Electrolysis reaction:

[0036] Weigh 6g of cyclohexene, 2g of sodium bromide, 5g of sodium nitrate, 5g of potassium nitrite, and 15g of ethylene glycol and add them into deionized water to make 200g of electrolyte. Pour it into the above 4cm 2 Titanium-based copper-lead composite cathode, 4cm 2 In a single-chamber electrolytic cell composed of an isostatically pressed graphite electrode as the anode, electrolysis begins when the electrolyte temperature reaches 30°C. The current density is controlled to be 800A / m2 , constant current electrolysis, control the maximum voltage not to exceed 10 V. Cut off the power supply after 8 hours of electrolysis.

[0037] Sampling analysis showed that the cyclohexene conversion rate was 80%, the product adiponitrile selectivity was 61%, the main by-products were adipic acid 20%, and adipic aldehyde 15%.

[0038] Example 2

[0039] Electrode preparation:

[0040] The pure titanium substrate was polished with 600, 1500, and 5000 mesh sandpaper, ultrasonically cleaned in anhydrous ethanol for 10 min, and dried in an oven for later use;

[0041] Prepare a 10wt% hydrofluoric acid aqueous solution, immerse the treated pure titanium substrate in the hydrofluoric acid solution for 15 seconds, take it out and place it in a nitrogen environment for drying for later use;

[0042] Weigh 5g of powdered alloy target with a copper-lead ratio of 3:1 and place it in a heated crucible. Reduce the vacuum to <10 -3 Pa. The dried titanium substrate was placed 25 cm above the crucible, the evaporation temperature was 1200°C, and the coating was evaporated to 5 μm.

[0043] Electrolysis reaction:

[0044] Weigh 10g cyclohexene, 1g sodium bromide, 20g potassium nitrate, 5g methanol, and 5g ethylene glycol and add them into deionized water to make 200g electrolyte. Pour it into the above 4cm 2 Titanium-based copper-lead composite cathode, 4cm 2 In a single-chamber electrolytic cell composed of an isostatically pressed graphite electrode as the anode, electrolysis begins when the electrolyte temperature reaches 20°C. The current density is controlled to be 1200A / m 2 , constant current electrolysis, control the maximum voltage not to exceed 10 V. Cut off the power supply after 11 hours of electrolysis.

[0045] Sampling analysis showed that the cyclohexene conversion rate was 79%, the product adiponitrile selectivity was 65%, the main by-products were adipic acid 20%, and adipaldehyde 11%.

[0046] Example 3

[0047] Electrode preparation:

[0048] The pure titanium substrate was polished with 600, 1500, and 5000 mesh sandpaper, ultrasonically cleaned in anhydrous ethanol for 10 min, and dried in an oven for later use;

[0049] Prepare an aqueous solution containing 1 wt% hydrofluoric acid, immerse the treated pure titanium substrate in the hydrofluoric acid solution for 20 seconds, take it out and place it in a nitrogen environment for drying for later use;

[0050] Weigh 5g of powdered alloy target with a copper-lead ratio of 12:1 and place it in a heated crucible. Reduce the vacuum to <10 -3 Pa. The dried titanium substrate was placed 25 cm above the crucible, the evaporation temperature was 1400°C, and the coating was evaporated to 1 μm.

[0051] Electrolysis reaction:

[0052] Weigh 4g cyclohexene, 5g potassium bromide, 3g sodium nitrate, and 50g methanol, add them into deionized water to make 200g electrolyte, and pour into the above 4cm 2 Titanium-based copper-lead composite cathode, 4cm 2 In a single-chamber electrolytic cell composed of an isostatically pressed graphite electrode as the anode, electrolysis begins when the electrolyte temperature reaches 50°C. The current density is controlled to be 1500A / m 2 , constant current electrolysis, control the maximum voltage not to exceed 10 V. Cut off the power supply after 6 hours of electrolysis.

[0053] Sampling analysis showed that the cyclohexene conversion rate was 82%, the product adiponitrile selectivity was 75%, the main by-products adipic acid was 13%, and adipic aldehyde was 7%.

[0054] Comparative Example 1

[0055] Electrode preparation:

[0056] The pure titanium substrate was polished with 600, 1500, and 5000 mesh sandpaper, ultrasonically cleaned in anhydrous ethanol for 10 min, and dried in an oven for later use;

[0057] A 1 wt % hydrofluoric acid aqueous solution was prepared, and the treated pure titanium substrate was immersed in the hydrofluoric acid solution for 20 seconds, and then taken out and dried in a nitrogen environment for later use.

[0058] Electrolysis reaction:

[0059] Weigh 4g cyclohexene, 5g potassium bromide, 3g sodium nitrate, and 50g methanol, add them into deionized water to make 200g electrolyte, and pour into the above 4cm 2 Titanium cathode, 4cm 2 In a single-chamber electrolytic cell composed of an isostatically pressed graphite electrode as the anode, electrolysis begins when the electrolyte temperature reaches 50°C. The current density is controlled to be 1500A / m 2 , constant current electrolysis, control the maximum voltage not to exceed 10 V. Cut off the power supply after 6 hours of electrolysis.

[0060] Sampling analysis showed that the cyclohexene conversion rate was 15%, the product adiponitrile selectivity was 20%, the main by-products adipic acid was 45%, and adipic aldehyde was 15%.

Claims

1. An electrochemical synthesis method for synthesizing adiponitrile using cyclohexene as a raw material, characterized in that: The method comprises the following steps: (1) mixing cyclohexene, halide, nitrate / nitrite, organic alcohol and pure water to prepare an electrolyte; (2) A titanium-based copper-lead composite electrode is used as the cathode, isostatically pressed graphite is used as the anode, and a diaphragm-free electrolytic cell is used to electrolyze adiponitrile.

2. The method according to claim 1, characterized in that The halide salt in step (1) is at least one of sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide and potassium iodide; Preferably, the content of the halogen salt in the electrolyte is 0.1wt%-3wt%, preferably 0.5-2.5wt%.

3. The method according to claim 1, characterized in that The nitrate / nitrite in step (1) is one or more of sodium nitrite, sodium nitrate, potassium nitrite and potassium nitrate; Preferably, the content of nitrate / nitrite in the electrolyte is 0.1 wt%-10 wt%, preferably 1-5 wt%.

4. The method according to claim 1, characterized in that: The cyclohexene content in the electrolyte is 1%-7wt%; Preferably it is 2-5 wt%.

5. The method according to claim 1, characterized in that: The organic alcohol in step (1) is one or more of methanol, ethanol, ethylene glycol, and isopropanol; Preferably, the content of organic alcohol in the electrolyte is 1%-30wt%, preferably 5wt%-15wt%.

6. The method according to claim 1, characterized in that: The titanium-based copper-lead composite electrode in step (2) is prepared by using a pure titanium plate as a substrate and a copper-lead alloy as a target material using a vacuum evaporation method.

7. The method according to claim 6, characterized in that: The preparation method of the titanium-based copper-lead composite electrode comprises: using a pure titanium plate as a substrate, etching it with a hydrofluoric acid solution to activate it; using a copper-lead alloy as a target material, and using a vacuum evaporation method to evaporate copper and lead onto the substrate to obtain a titanium-based copper-lead composite electrode; Preferably, the concentration of hydrofluoric acid is 0.01wt%-10wt%, preferably 1wt%-10wt%, and the etching time is 15s-30s; Preferably, the mass ratio of copper to lead in the target copper-lead alloy is 1:1-49:1, preferably 3:1-24:1, more preferably 3:1-15:1; Preferably, the vacuum degree during vacuum evaporation is less than 10 -3 Pa; the evaporation temperature is 1150°C-1500°C; the coating thickness is 0.1-20 μm, preferably 1-15 μm.

8. The method according to any one of claims 1 to 7, characterized in that: The electrolyte is electrolyzed by constant current method, and the voltage is controlled below 10V; Preferably, the electrolysis reaction temperature is 20-50°C; Current density is 500A / m 2 -3000A / m 2 .