Method for preparing adipic acid through electro-catalysis of cyclohexene

Abstract

The invention discloses a method for preparing adipic acid through electro-catalysis of cyclohexene. The method comprises the following steps: (I) carrying out electro-catalysis reduction on oxygen at a cathode to generate hydrogen peroxide; (2) reacting hydrogen peroxide with cyclohexene to obtain cyclohexanediol; (3) carrying out electrocatalytic oxidation reaction on cyclohexanediol at an anode to obtain adipate; and (IV) acidifying, washing and drying the adipate to obtain an adipic acid solid, and the like. According to the invention, the electrochemical reaction is driven by the electric power generated by renewable energy sources, so that the cascade reaction from cyclohexene to adipic acid is realized; the preparation method is mild in condition, green and environment-friendly and high in product selectivity, cathode oxygen reduction and anode cyclohexanediol oxidation are carried out by utilizing electric power generated by renewable energy sources, hydrogen peroxide generated by a cathode reacts with cyclohexene in a flowing system to generate cyclohexanediol, reaction liquid can be directly injected into an anode for reaction, and the yield is high. In the reaction process, only oxygen, dilute alkali solution and dilute acid solution are input except for cyclohexene, so that the use of strong acid and strong oxidant is avoided.

Description

Technical Field

[0001] The invention belongs to the field of electrochemistry, and in particular relates to a method for preparing adipic acid by electrocatalyzing cyclohexene. Background Art

[0002] Adipic acid is an important chemical raw material with a wide range of uses and a large market demand. Its main use is in the production of nylon 66, an important engineering plastic that is widely used in various fields. The global adipic acid market is huge and shows a certain growth trend. It is a bulk chemical.

[0003] At present, the preparation of adipic acid from cyclohexene by thermal catalysis in industry usually requires high temperature, high pressure and strong oxidants, which not only increases energy consumption and equipment costs, but also increases safety risks in the production process. In addition, due to the harsh reaction conditions, there are many side reactions in the oxidation of cyclohexene to adipic acid, such as ring-opening reaction, over-oxidation, etc., which result in low selectivity of adipic acid and require complex subsequent separation and purification steps. In addition to the impact on product selectivity, the thermal catalytic oxidation process also produces a large amount of waste gas and waste liquid, such as nitrogen oxides (NO x ), causing serious pollution to the environment. The treatment of these wastes requires additional costs and also increases the environmental burden.

[0004] Therefore, providing a green, environmentally friendly, safe and efficient method for catalyzing cyclohexene to prepare adipic acid is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0005] The present invention is proposed to overcome the shortcomings of the prior art, and its purpose is to provide a method for preparing adipic acid from cyclohexene by electrocatalysis.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing adipic acid by electrocatalytic cyclohexene comprises the following steps:

[0008] (I) Oxygen is electrocatalytically reduced at the cathode to produce hydrogen peroxide

[0009] A gas diffusion substrate loaded with a cathode catalyst is used as a cathode, a conductive substrate loaded with an anode catalyst is used as an anode, a cation exchange membrane is used to separate the cathode and the anode, an acid solution is used as a cathode electrolyte, and an alkaline solution is used as an anode electrolyte to assemble an electrolytic cell, oxygen is continuously introduced into the acid solution, hydrogen is continuously introduced into the alkaline solution, and a reaction is carried out at a constant potential, and oxygen is electrocatalytically reduced to hydrogen peroxide by the cathode;

[0010] (II) Hydrogen peroxide reacts with cyclohexene to obtain cyclohexanediol

[0011] The electrolyte containing hydrogen peroxide obtained after the electrocatalysis in step (I) is reacted with cyclohexene under heating conditions, and the reaction solution after the reaction is mixed with an alkaline solution to obtain an alkaline solution containing cyclohexanediol;

[0012] (III) Cyclohexanediol undergoes electrocatalytic oxidation at the anode to obtain adipate

[0013] The conductive substrate carrying the anode catalyst is used as the anode, the gas diffusion substrate carrying the cathode catalyst is used as the cathode, the anode and the cathode are separated by a cation exchange membrane, the alkaline solution containing cyclohexanediol obtained in step (II) is used as the anode electrolyte, and the alkaline solution is used as the cathode electrolyte to assemble an electrolytic cell, and electro-oxidation is carried out at a constant potential, wherein the cyclohexanediol is oxidized to adipic acid salt by the anode catalyst;

[0014] (IV) The adipic acid salt is acidified, washed and dried to obtain adipic acid solid

[0015] Acid is added to the electrolyte containing adipic acid salt obtained after the electrocatalysis in step (I) for acidification, and after acidification, the electrolyte is evaporated and crystallized, filtered, and washed to obtain adipic acid solid.

[0016] In the above technical solution, the cathode catalyst in step (I) is a noble metal-based catalyst, a nitrogen-doped carbon material or a carbon nanotube.

[0017] In the above technical scheme, the preparation method of the cathode in step (Ⅰ) is: mixing the cathode catalyst, conductive carbon black and Nafion in a mass ratio of 9:1:1, then configuring the mixture of the three into a dispersion with anhydrous ethanol, spraying the dispersion on the surface of the gas diffusion substrate, and obtaining the cathode after drying.

[0018] In the above technical solution, the gas diffusion substrate in step (I) is a carbon paper or carbon cloth gas diffusion electrode.

[0019] In the above technical solution, the anode catalyst in step (I) is a transition metal oxide / hydroxide or spinel.

[0020] In the above technical solution, the conductive substrate in step (I) is any one of a titanium sheet, a nickel sheet, a copper sheet, a nickel foam, a copper foam, a carbon fiber cloth, a carbon fiber paper, or FTO conductive glass.

[0021] In the above technical solution, the acid solution in step (I) is H2SO4 solution or HClO4 solution.

[0022] In the above technical solution, the concentration of the acid solution in step (I) is 0.1M to 2M.

[0023] In the above technical solution, the flow rate of oxygen in the acid solution in step (I) is at least 200 sccm, and a unidirectional air intake is adopted.

[0024] In the above technical solution, the alkaline solution in step (I) is KOH solution or NaOH solution.

[0025] In the above technical solution, the concentration of the alkaline solution in step (I) is 1M to 3M.

[0026] In the above technical solution, the flow rate of hydrogen in the alkaline solution in step (I) is at least 100 sccm, and a unidirectional gas inlet is adopted.

[0027] In the above technical solution, the constant potential in step (I) is 1V to 3V.

[0028] In the above technical solution, the heating condition in step (II) is 40°C to 70°C.

[0029] In the above technical solution, the reaction time of the hydrogen peroxide electrolyte and cyclohexene in step (II) is 1 h to 3 h.

[0030] In the above technical solution, the molar ratio of hydrogen peroxide to cyclohexene in the electrolyte in step (II) is at most 2:1.

[0031] In the above technical solution, the alkaline solution in step (II) is KOH solution or NaOH solution.

[0032] In the above technical solution, the concentration of the alkaline solution in step (II) is 1M to 3M.

[0033] In the above technical solution, the molar ratio of the base to the cyclohexene in the step (II) is at least 2:0.05.

[0034] In the above technical solution, the anode catalyst in step (III) is a transition metal oxide / hydroxide or spinel.

[0035] In the above technical solution, the conductive substrate in step (III) is any one of a titanium sheet, a nickel sheet, a copper sheet, a nickel foam, a copper foam, a carbon fiber cloth, a carbon fiber paper or a FTO conductive glass.

[0036] In the above technical solution, the cathode catalyst in step (III) is a noble metal-based catalyst, a nitrogen-doped carbon material or a carbon nanotube.

[0037] In the above technical solution, the gas diffusion substrate in step (III) is a carbon paper or carbon cloth gas diffusion electrode.

[0038] In the above technical solution, the alkaline solution in step (III) is KOH solution or NaOH solution.

[0039] In the above technical solution, the concentration of the alkaline solution in step (III) is 1M to 3M.

[0040] In the above technical solution, the constant potential in step (III) is 1.2V to 3V.

[0041] In the above technical solution, the acid in step (IV) is any one of HCl, H2SO4, formic acid or acetic acid.

[0042] In the above technical solution, in step (IV), acid is added to the electrolyte containing adipate until the pH of the solution is at least 5.

[0043] The beneficial effects of the present invention are:

[0044] The invention provides a method for preparing adipic acid from cyclohexene by electrocatalysis, which utilizes electricity generated by renewable energy to drive an electrochemical reaction, thereby realizing a cascade reaction from cyclohexene to adipic acid. The preparation method has mild conditions, is green and environmentally friendly, and has high product selectivity. Electricity generated by renewable energy is utilized to carry out cathode oxygen reduction and anode cyclohexanediol oxidation, hydrogen peroxide generated at the cathode reacts with cyclohexene in a flow system to generate cyclohexanediol, and the reaction solution can be directly injected into the anode for reaction. In the reaction process, only oxygen, a dilute alkali solution and a dilute acid solution are input in addition to cyclohexene, thereby avoiding the use of strong acids and strong oxidants. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a diagram of the liquid phase product obtained in Example 1 of the present invention, and the product is adipic acid;

[0046] Figure 2 is a diagram of the liquid phase product obtained in Example 2 of the present invention, and the product is adipic acid;

[0047] Figure 3 This is a diagram of the liquid phase product obtained in Example 3 of the present invention, and the product is adipic acid.

[0048] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0050] Example 1

[0051] Nitrogen-doped carbon nanotubes, conductive carbon black and Nafion were prepared into ink with anhydrous ethanol in a mass ratio of 9:1:1, and evenly sprayed on the surface of the gas diffusion layer, and then transferred to a drying device and dried at 60°C for 6 hours to obtain a cathode electrode. After drying, a cathode electrode was obtained. Nickel foam was placed as a working electrode in a mixed solution of 0.15M Ni(NO3) and 0.15M Fe(NO3)2, and nickel foam was taken as a counter electrode. Electrodeposition was performed at -1V. After the deposition was completed, the working electrode was fully washed and dried at 60°C for 6 hours to obtain an anode electrode. The cathode electrode and the anode electrode were installed in a reaction device, and a 1M H2SO4 solution with an oxygen flow rate of 300sccm was introduced into the cathode, and a 1M KOH solution with a hydrogen flow rate of 150sccm was introduced into the anode. The reaction was carried out at a constant potential of 2V. The mass fraction of hydrogen peroxide in the outflowing acid solution was 10.65%, and the Faraday efficiency of oxygen conversion to hydrogen peroxide was 85.72%.

[0052] The 10% hydrogen peroxide acid solution flowing out of the cathode is mixed with cyclohexene delivered by another independent infusion pipeline through an infusion pipeline, the molar ratio of hydrogen peroxide to cyclohexene is 2:1, and reacted in the pipeline at 50°C for 2.5 hours. After the reaction, the mixed solution is mixed with a 2M KOH solution delivered by another independent infusion pipeline through an infusion pipeline for 10 minutes, and the molar ratio of the base to cyclohexene is 2:0.05. After the reaction, the concentration of cyclohexanediol in the alkaline solution flowing out is 1.2M, and the yield of cyclohexene converted to cyclohexanediol is 80.19%.

[0053] Place nickel foam as a working electrode in a 0.3M Ni(NO3)2 solution, and take another nickel foam as a counter electrode, and perform electroplating at -1V. After the deposition is completed, the working electrode is fully washed and dried at 60℃ for 6h to obtain an anode electrode. Nitrogen-doped carbon nanotubes, conductive carbon black and Nafion are prepared into ink with anhydrous ethanol in a mass ratio of 9:1:1, and evenly sprayed on the surface of the gas diffusion layer, and then transferred to a drying device, dried at 60℃ for 6h, and the cathode electrode is obtained after drying. The cathode electrode and the anode electrode are installed in a reaction device, and an alkaline cyclohexanediol solution is passed into the anode, and a 1M KOH solution is passed into the cathode. The reaction is carried out at a constant voltage of 2V. The concentration of adipic acid in the outflowing alkaline solution is 1.0M, and the Faraday efficiency of cyclohexanediol conversion to adipic acid is 81.2%.

[0054] The solution flowing out of the anode was acidified by adding 5M HCl to a pH of 4, and then evaporated and crystallized, the obtained precipitate was separated by filtration and washed three times with deionized water, and the washed adipic acid solid was vacuum dried at 60°C for 24 hours to finally obtain adipic acid solid product.

[0055] Liquid phase product diagram Figure 1 As shown, it can be seen that the product is adipic acid.

[0056] Example 2

[0057] The single-atom platinum catalyst, conductive carbon black and Nafion were prepared into ink with anhydrous ethanol in a mass ratio of 8:1:2, and evenly sprayed on the surface of the gas diffusion layer, then transferred to a drying device, dried at 60°C for 6h, and the cathode electrode was obtained after drying. After drying, the cathode electrode was obtained. NiFe-LDH, conductive carbon black and Nafion were prepared into ink with anhydrous ethanol in a mass ratio of 9:1:1, and evenly sprayed on the surface of the conductive carbon paper, then transferred to a drying device, dried at 60°C for 6h, and the anode electrode was obtained after drying. The cathode electrode and the anode electrode were loaded into a reaction device, and a 1.5M H2SO4 solution with an oxygen flow rate of 350sccm was introduced into the cathode, and a 2M KOH solution with a hydrogen flow rate of 200sccm was introduced into the anode. The reaction was carried out at a constant potential of 2.5V, and the mass fraction of hydrogen peroxide in the outflowing acid solution was 13.54%, and the Faraday efficiency of oxygen conversion into hydrogen peroxide was 85.69%.

[0058] The 13% hydrogen peroxide acid solution flowing out of the cathode is mixed with cyclohexene delivered by another independent infusion pipeline through an infusion pipeline, the molar ratio of hydrogen peroxide to cyclohexene is 3:1, and reacted in the pipeline at 50°C for 1.5 hours. After the reaction, the mixed solution is mixed with a 2M KOH solution delivered by another independent infusion pipeline through an infusion pipeline for 10 minutes, and the molar ratio of the base to cyclohexene is 3:0.05. After the reaction, the concentration of cyclohexanediol in the alkaline solution flowing out is 1.3M, and the yield of cyclohexene converted to cyclohexanediol is 85.8%.

[0059] NiCo-LDH, conductive carbon black and Nafion were prepared into ink with anhydrous ethanol at a mass ratio of 9:1:1, and evenly sprayed on the surface of conductive carbon paper, then transferred to a drying device, dried at 60°C for 6h, and the anode electrode was obtained after drying. Single-atom platinum catalyst, conductive carbon black and Nafion were prepared into ink with anhydrous ethanol at a mass ratio of 8:1:2, and evenly sprayed on the surface of the gas diffusion layer, then transferred to a drying device, dried at 60°C for 6h, and the cathode electrode was obtained after drying. After drying, the cathode electrode was obtained. NiFe-LDH, conductive carbon black and Nafion were prepared into ink with anhydrous ethanol at a mass ratio of 9:1:1, and evenly sprayed on the surface of conductive carbon paper, then transferred to a drying device, dried at 60°C for 6h, and the anode electrode was obtained after drying. The cathode electrode and the anode electrode were installed in a reaction device, an alkaline cyclohexanediol solution was introduced into the anode, and a 1.5M KOH solution was introduced into the cathode. The reaction was carried out at a constant voltage of 2.5V. The concentration of adipic acid in the outflowing alkaline solution was 0.98M, and the Faraday efficiency of converting cyclohexanediol into adipic acid was 79.38%.

[0060] The solution flowing out of the anode was acidified by adding 3M H2SO4 to a pH of 3.5, and then evaporated and crystallized, the obtained precipitate was separated by filtration and washed three times with deionized water, and the washed adipic acid solid was vacuum dried at 60°C for 24 hours to finally obtain adipic acid solid product.

[0061] Liquid phase product Figure 2 As shown, it can be seen that the product is adipic acid.

[0062] Example 3

[0063] Cu-MOFs, conductive carbon black and Nafion were prepared into ink in a mass ratio of 9:1:1 with anhydrous ethanol: isopropanol in a volume ratio of 8:2, and evenly sprayed on the surface of the gas diffusion layer, and then transferred to a drying device and dried at 60°C for 6 hours to obtain a cathode electrode. After drying, the cathode electrode was obtained. The nickel sheet was placed in a hydrothermal kettle containing a mixed solution of 0.025M Co(NO3)2 and 0.025M Fe(NO3)3, reacted at 120°C for 12 hours, then taken out, rinsed with deionized water, transferred to a drying device, dried at 60°C for 6 hours, and obtained an anode electrode. A cathode electrode and an anode electrode were installed in a reaction device, a 2.5M HClO4 solution with an oxygen flow rate of 400sccm was introduced into the cathode, and a 2.5M KOH solution with a hydrogen flow rate of 300sccm was introduced into the anode. The reaction was carried out at a constant potential of 2.5V. The mass fraction of hydrogen peroxide in the outflowing acid solution was 12.84%, and the Faraday efficiency of converting oxygen into hydrogen peroxide was 84.02%.

[0064] The 12.84% hydrogen peroxide acid solution flowing out of the cathode is mixed with cyclohexene delivered by another independent infusion pipeline through an infusion pipeline, the molar ratio of hydrogen peroxide to cyclohexene is 3.5:1, and reacted in the pipeline at 50°C for 1 hour. After the reaction, the mixed solution is mixed with a 2M KOH solution delivered by another independent infusion pipeline through an infusion pipeline for 10 minutes, and the molar ratio of the base to cyclohexene is 3.5:0.05. After the reaction, the concentration of cyclohexanediol in the alkaline solution flowing out is 1.24M, and the yield of cyclohexene converted to cyclohexanediol is 82.74%.

[0065] The nickel sheet was placed in a hydrothermal autoclave containing 0.05M Co(NO3)2 solution, reacted at 120℃ for 12h, then taken out, rinsed with deionized water, transferred to a drying device, dried at 60℃ for 6h, and dried to obtain an anode electrode. Pt-MOFs, conductive carbon black and Nafion were prepared into ink in a mass ratio of 9:1:1 with anhydrous ethanol:isopropanol in a volume ratio of 8:2, and evenly sprayed on the surface of the gas diffusion layer, then transferred to a drying device, dried at 60℃ for 6h, and dried to obtain a cathode electrode. After drying, the cathode electrode was obtained. The cathode electrode and the anode electrode were loaded into a reaction device, an alkaline cyclohexanediol solution was introduced into the anode, and a 2M KOH solution was introduced into the cathode. The reaction was carried out at a constant voltage of 2.8V. The concentration of adipic acid in the outflowing alkaline solution was 1.1M, and the Faraday efficiency of cyclohexanediol conversion to adipic acid was 89.4%.

[0066] The solution flowing out of the anode was acidified by adding 3M H2SO4 to a pH of 3, and then evaporated and crystallized, the obtained precipitate was separated by filtration and washed three times with deionized water, and the washed adipic acid solid was vacuum dried at 60°C for 24 hours to finally obtain adipic acid solid product.

[0067] Liquid phase product diagram Figure 3 As shown, it can be seen that the product is adipic acid.

[0068] Principle of the present invention:

[0069] Oxygen is electrocatalytically reduced at the cathode to generate hydrogen peroxide, which reacts with cyclohexene to obtain cyclohexanediol, which is electrocatalytically oxidized at the anode to obtain adipic acid salt, which is acidified, washed, and dried to obtain adipic acid solid.

[0070] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0071] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing adipic acid from cyclohexene by electrocatalysis, characterized in that: The following steps are involved: (I) Oxygen is electrocatalytically reduced at the cathode to produce hydrogen peroxide A gas diffusion substrate loaded with a cathode catalyst is used as a cathode, a conductive substrate loaded with an anode catalyst is used as an anode, a cation exchange membrane is used to separate the cathode and the anode, an acid solution is used as a cathode electrolyte, and an alkaline solution is used as an anode electrolyte to assemble an electrolytic cell, oxygen is continuously introduced into the acid solution, hydrogen is continuously introduced into the alkaline solution, and a reaction is carried out at a constant potential, and oxygen is electrocatalytically reduced to hydrogen peroxide by the cathode; (II) Hydrogen peroxide reacts with cyclohexene to obtain cyclohexanediol The electrolyte containing hydrogen peroxide obtained after the electrocatalysis in step (I) is reacted with cyclohexene under heating conditions, and the reaction solution after the reaction is mixed with an alkaline solution to obtain an alkaline solution containing cyclohexanediol; (III) Cyclohexanediol undergoes electrocatalytic oxidation at the anode to obtain adipate The conductive substrate carrying the anode catalyst is used as the anode, the gas diffusion substrate carrying the cathode catalyst is used as the cathode, the anode and the cathode are separated by a cation exchange membrane, the alkaline solution containing cyclohexanediol obtained in step (II) is used as the anode electrolyte, and the alkaline solution is used as the cathode electrolyte to assemble an electrolytic cell, and electro-oxidation is carried out at a constant potential, wherein the cyclohexanediol is oxidized to adipic acid salt by the anode catalyst; (IV) The adipic acid salt is acidified, washed and dried to obtain adipic acid solid Acid is added to the electrolyte containing adipic acid salt obtained after the electrocatalysis in step (I) for acidification, and after acidification, the electrolyte is evaporated and crystallized, filtered, and washed to obtain adipic acid solid.

2. The method for preparing adipic acid from cyclohexene by electrocatalysis according to claim 1, characterized in that: The cathode catalyst in step (I) is a noble metal-based catalyst, a nitrogen-doped carbon material or a carbon nanotube; The gas diffusion substrate in step (I) is carbon paper or carbon cloth; The anode catalyst in step (I) is a transition metal oxide / hydroxide or spinel; The conductive substrate in step (I) is any one of a titanium sheet, a nickel sheet, a copper sheet, a nickel foam, a copper foam, a carbon fiber cloth, a carbon fiber paper, or FTO conductive glass; The acid solution in step (I) is H2SO4 solution or HClO4 solution; The concentration of the acid solution in step (I) is 0.1M to 2M; The flow rate of oxygen in step (I) is at least 200 sccm; The alkaline solution in step (I) is a KOH solution or a NaOH solution; The concentration of the alkaline solution in step (I) is 1M to 3M; The flow rate of hydrogen in step (I) is at least 100 sccm; The constant potential in the step (I) is 1V to 3V.

3. The method for preparing adipic acid from cyclohexene by electrocatalysis according to claim 1, characterized in that: The heating condition in step (II) is 40°C to 70°C; The reaction time of the hydrogen peroxide electrolyte and cyclohexene in step (II) is 1 h to 3 h; In step (II), the molar ratio of hydrogen peroxide to cyclohexene in the electrolyte is at most 2:1; The alkaline solution in step (II) is a KOH solution or a NaOH solution; The concentration of the alkaline solution in step (II) is 1M to 3M; The molar ratio of the base to the cyclohexene in the step (II) is at least 2:0.

05.

4. The method for preparing adipic acid from cyclohexene by electrocatalysis according to claim 1, characterized in that: The anode catalyst in step (III) is a transition metal oxide, hydroxide or spinel; The conductive substrate in step (III) is any one of a titanium sheet, a nickel sheet, a copper sheet, a nickel foam, a copper foam, a carbon fiber cloth, a carbon fiber paper, or FTO conductive glass; The cathode catalyst in step (III) is a noble metal-based catalyst, a nitrogen-doped carbon material or a carbon nanotube; The gas diffusion substrate in step (III) is carbon paper or carbon cloth; The alkaline solution in step (III) is a KOH solution or a NaOH solution; The concentration of the alkaline solution in step (III) is 1M to 3M; The constant potential in the step (III) is 1.2V to 3V.

5. The method for preparing adipic acid from cyclohexene by electrocatalysis according to claim 1, characterized in that: The acid in step (IV) is any one of HCl, H2SO4, formic acid or acetic acid; In step (IV), an acid is added to the electrolyte containing adipate until the pH of the solution is at least 5.

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