A method for preparing adipic acid from cyclohexene by electrocatalysis

Abstract

The application discloses a method for preparing adipic acid from cyclohexene by electrocatalysis, which comprises the following steps: (I) generating hydrogen peroxide by electrocatalytic reduction of oxygen at a cathode; (II) reacting the hydrogen peroxide with cyclohexene to obtain cyclohexanediol; (III) generating adipate by electrocatalytic oxidation reaction of the cyclohexanediol at an anode; and (IV) obtaining solid adipic acid by acidification, washing and drying of the adipate. The method utilizes renewable energy to drive the electrochemical reaction and realizes the cascade reaction from cyclohexene to adipic acid. The preparation method is mild, green and environmentally friendly, and has high product selectivity. The cathode oxygen reduction and the anode cyclohexanediol oxidation are performed by using renewable energy, the hydrogen peroxide generated at the cathode reacts with the cyclohexene in a flow system to generate the cyclohexanediol, the reaction solution can be directly injected into the anode for reaction, and only oxygen, dilute alkali solution and dilute acid solution are input in the reaction process in addition to the cyclohexene, thereby avoiding the use of strong acid and strong oxidant.

Description

Technical Field

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

[0002] Adipic acid is an important chemical raw material with a wide range of uses and high market demand. Its primary use is in the production of nylon 66, a key engineering plastic used in a wide variety of applications. The global adipic acid market is substantial and showing a positive growth trend, making it a major commodity 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 aims to provide a method for preparing adipic acid from cyclohexene via electrocatalysis.

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

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

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

[0009] An electrolytic cell is assembled using a gas diffusion substrate loaded with a cathode catalyst as the cathode, a conductive substrate loaded with an anode catalyst as the anode, a cation exchange membrane to separate the cathode and the anode, an acid solution as the cathode electrolyte, and an alkaline solution as the anode electrolyte. Oxygen is continuously introduced into the acid solution, and hydrogen is continuously introduced into the alkaline solution. The 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 produce 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 produce adipate

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

[0014] (IV) Adipic acid solid is obtained by acidification, washing and drying of the adipate

[0015] Acid is added to the electrolyte containing adipic acid 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 solution, 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 using anhydrous ethanol to prepare the mixture into a dispersion, spraying the dispersion on the surface of the gas diffusion substrate, and drying to obtain the cathode.

[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 titanium sheet, nickel sheet, copper sheet, nickel foam, copper foam, carbon fiber cloth, 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 technical scheme, the flow rate of oxygen in the acid solution in step (I) is at least 200sccm, and one-way gas feeding is adopted.

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

[0025] In the technical scheme, the concentration of the base solution in step (I) is 1M-3M.

[0026] In the technical scheme, the flow rate of hydrogen in the base solution in step (I) is at least 100sccm, and one-way gas feeding is adopted.

[0027] In the technical scheme, the constant potential in step (I) is 1V-3V.

[0028] In the technical scheme, the heating condition in step (II) is 40℃-70℃.

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

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

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

[0032] In the technical scheme, the concentration of the base solution in step (II) is 1M-3M.

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

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

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

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

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

[0038] In the technical scheme, the base 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 present invention provides a method for preparing adipic acid from cyclohexene through electrocatalysis, wherein electricity generated by renewable energy is used to drive an electrochemical reaction, thereby realizing a cascade reaction from cyclohexene to adipic acid. The preparation method has mild conditions, is environmentally friendly, and has high product selectivity. Electricity generated by renewable energy is used for cathode oxygen reduction and anode cyclohexanediol oxidation. Hydrogen peroxide generated at the cathode reacts with cyclohexene in a flow system to generate cyclohexanediol. The reaction solution can be directly injected into the anode for reaction. During the reaction, in addition to cyclohexene, only oxygen, a dilute alkaline solution, and a dilute acid solution are input, thereby avoiding the use of strong acids and strong oxidants. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0046] Figure 2 This 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 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 will be 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 (Nfion) were prepared in anhydrous ethanol at a mass ratio of 9:1:1 to form an ink. The ink was evenly sprayed onto the surface of the gas diffusion layer and then transferred to a drying apparatus and dried at 60°C for 6 hours to obtain a cathode electrode. After drying, nickel foam was placed as the working electrode in a mixed solution of 0.15M Ni(NO3)2 and 0.15M Fe(NO3)2. A nickel foam was used as the counter electrode for electrodeposition at -1V. After deposition, the working electrode was thoroughly washed and dried at 60°C for 6 hours to obtain an anode electrode. The cathode and anode electrodes were placed in a reaction apparatus. A 1M H2SO4 solution with an oxygen flow rate of 300sccm was introduced to the cathode, and a 1M KOH solution with a hydrogen flow rate of 150sccm was introduced to the anode. The reaction was carried out at a constant potential of 2V. The mass fraction of hydrogen peroxide in the effluent acid solution was 10.65%, and the Faradaic efficiency of oxygen to hydrogen peroxide conversion was 85.72%.

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

[0053] Nickel foam was placed as the working electrode in a 0.3M Ni(NO₃)₂ solution, and another nickel foam was used as the counter electrode. Electrodeposition was performed at -1V. After deposition, the working electrode was thoroughly washed and dried at 60°C for 6 hours to obtain the anode. Nitrogen-doped carbon nanotubes, conductive carbon black, and Nafion were prepared in anhydrous ethanol at a mass ratio of 9:1:1 to form an ink. This ink was evenly sprayed onto the surface of the gas diffusion layer and then transferred to a drying apparatus and dried at 60°C for 6 hours to obtain the cathode. The cathode and anode electrodes were placed in a reaction apparatus. An alkaline cyclohexanediol solution was introduced into the anode, and a 1M KOH solution was introduced into the cathode. The reaction was carried out at a constant voltage of 2V. The concentration of adipic acid in the effluent alkaline solution was 1.0M. The Faradaic efficiency of cyclohexanediol to adipic acid conversion was 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 resulting precipitate was separated by filtration and washed three times with deionized water. The washed adipic acid solid was vacuum-dried at 60°C for 24 hours to obtain adipic acid solid product.

[0055] Liquid phase product diagram Figure 1 As shown, the visible product is adipic acid.

[0056] Example 2

[0057] An ink consisting of single-atom platinum catalyst, conductive carbon black, and Nafion (a ionic liquid) in an 8:1:2 mass ratio was prepared in anhydrous ethanol and evenly sprayed onto the surface of a gas diffusion layer. The ink was then transferred to a drying apparatus and dried at 60°C for 6 hours to obtain a cathode electrode. A nickel-iron hydride (NiFe-LDH), conductive carbon black, and Nafion (a ionic liquid) in an 9:1:1 mass ratio was prepared in anhydrous ethanol and evenly sprayed onto the surface of conductive carbon paper. The ink was then transferred to a drying apparatus and dried at 60°C for 6 hours to obtain an anode electrode. The cathode and anode electrodes were placed in a reaction apparatus. A 1.5M H2SO4 solution with an oxygen flow rate of 350 sccm was introduced into the cathode, and a 2M KOH solution with a hydrogen flow rate of 200 sccm was introduced into the anode. The reaction was carried out at a constant potential of 2.5 V. The mass fraction of hydrogen peroxide in the effluent acid solution was 13.54%, and the Faradaic efficiency of oxygen to hydrogen peroxide conversion was 85.69%.

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

[0059] An ink consisting of NiCo-LDH, conductive carbon black, and Nafion at a mass ratio of 9:1:1 was prepared in anhydrous ethanol and evenly sprayed onto the surface of conductive carbon paper. The ink was then transferred to a drying machine and dried at 60°C for 6 hours to obtain an anode electrode. An ink consisting of a single-atom platinum catalyst, conductive carbon black, and Nafion at a mass ratio of 8:1:2 was prepared in anhydrous ethanol and evenly sprayed onto the surface of a gas diffusion layer. The ink was then transferred to a drying machine and dried at 60°C for 6 hours to obtain a cathode electrode. An ink consisting of NiFe-LDH, conductive carbon black, and Nafion at a mass ratio of 9:1:1 was prepared in anhydrous ethanol and evenly sprayed onto the surface of conductive carbon paper. The ink was then transferred to a drying machine and dried at 60°C for 6 hours to obtain an anode electrode. A cathode electrode and an 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 Faradaic efficiency of converting cyclohexanediol to 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 resulting precipitate was separated by filtration and washed three times with deionized water. The washed adipic acid solid was vacuum-dried at 60°C for 24 hours to obtain adipic acid solid product.

[0061] Liquid phase product diagram Figure 2 As shown, the visible product is adipic acid.

[0062] Example 3

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

[0064] The 12.84% hydrogen peroxide acid solution flowing out of the cathode was mixed via an infusion line with cyclohexene delivered via a separate infusion line at a molar ratio of 3.5:1. The mixture was reacted in the line at 50°C for 1 hour. After the reaction, the mixed solution was mixed via another separate infusion line with a 2M KOH solution at a molar ratio of 3.5:0.05 for 10 minutes. The cyclohexanediol concentration in the alkali solution after the reaction was 1.24M, and the yield of cyclohexene to cyclohexanediol was 82.74%.

[0065] A nickel sheet was placed in a hydrothermal autoclave containing a 0.05M Co(NO₃)₂ solution and reacted at 120°C for 12 hours. The sheet was then removed, rinsed with deionized water, and transferred to a drying apparatus for drying at 60°C for 6 hours to obtain the anode electrode. An ink consisting of Pt-MOFs, conductive carbon black, and Nafion (9:1:1 by mass) was prepared using an 8:2 volume ratio of anhydrous ethanol:isopropanol. This ink was evenly sprayed onto the surface of the gas diffusion layer and then transferred to a drying apparatus for drying at 60°C for 6 hours to obtain the cathode electrode. The cathode and anode electrodes were then placed in a reaction apparatus. An alkaline cyclohexanediol solution was introduced into the anode, and a 2M KOH solution into the cathode. The reaction was carried out at a constant voltage of 2.8V. The concentration of adipic acid in the effluent alkaline solution was 1.1M, and the Faradaic efficiency of cyclohexanediol to adipic acid conversion was 89.4%.

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

[0067] Liquid phase product diagram Figure 3 As shown, the visible 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. Cyclohexanediol is electrocatalytically oxidized at the anode to obtain adipic acid salt, which is then 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 embodiment of the present invention, but the scope of protection 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 fall within the scope of protection and disclosure 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 An electrolytic cell is assembled using a gas diffusion substrate loaded with a cathode catalyst as the cathode, a conductive substrate loaded with an anode catalyst as the anode, a cation exchange membrane to separate the cathode and the anode, an acid solution as the cathode electrolyte, and an alkaline solution as the anode electrolyte. Oxygen is continuously introduced into the acid solution, and hydrogen is continuously introduced into the alkaline solution. The reaction is carried out at a constant potential, and oxygen is electrocatalytically reduced to hydrogen peroxide by the cathode. The acid solution in step (I) is H2SO4 solution or HClO4 solution; The concentration of the acid solution in step (I) is 0.1 M to 2 M; The alkaline solution in step (I) is KOH solution or NaOH solution; The concentration of the alkaline solution in step (I) is 1 M to 3 M; (II) Hydrogen peroxide reacts with cyclohexene to produce 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; The alkaline solution in step (II) is KOH solution or NaOH solution; The concentration of the alkaline solution in step (II) is 1 M to 3 M; (III) Cyclohexanediol undergoes electrocatalytic oxidation at the anode to produce adipate A conductive substrate carrying an anode catalyst is used as an anode, a gas diffusion substrate carrying a cathode catalyst is used as a cathode, a cation exchange membrane is used to separate the anode and the cathode, an electrolytic cell is assembled using the alkaline solution containing cyclohexanediol obtained in step (II) as an anolyte, and an alkaline solution as a cathode electrolyte, and electrooxidation is carried out at a constant potential, whereby the cyclohexanediol is oxidized to adipic acid salt by the anode catalyst; (IV) Adipic acid solid is obtained by acidification, washing and drying of the adipate Acid is added to the electrolyte containing adipic acid 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 flow rate of oxygen in step (I) is at least 200 sccm; The flow rate of hydrogen in step (I) is at least 100 sccm; The constant potential in step (I) is 1 V to 3 V.

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 molar ratio of the base to the cyclohexene in 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 1 M to 3 M; The constant potential in step (III) is 1.2 V to 3 V.

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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