A method for preparing adipic acid by coupling hydrogen production through electro-catalytic oxidation of cyclohexanol / cyclohexanone

Abstract

The application discloses a method for preparing adipic acid by coupling hydrogen production through electro-catalytic oxidation of cyclohexanol / cyclohexanone. The H-shaped electrolytic tank is used for catalytic oxidation; the working electrode of the anode chamber and the cathode chamber and the reference electrode jointly form an electro-catalytic reactor; the reaction raw material liquid is a water solution of cyclohexanol / cyclohexanone and electrolyte, and the anode is oxidized into adipic acid and hydrogen is generated in the cathode under a certain working voltage and current density after reaction for a period of time. Compared with the traditional process, the application has the advantages of high efficiency, high selectivity, green, low cost, simple operation and the like, is suitable for industrial implementation, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic organic synthesis and hydrogen production technology, specifically to a method for the electrocatalytic oxidation of cyclohexanol / cyclohexanone to prepare adipic acid coupled with hydrogen production. Background Technology

[0002] Adipic acid is a white monoclinic crystal at room temperature and is an important organic chemical raw material. It is also the most valuable aliphatic diacid. Adipic acid can undergo condensation reactions with multifunctional compounds to form high molecular weight polymers, thus its applications are very wide, mainly in the nylon and polyurethane industries. In the nylon field, adipic acid products undergo condensation reactions with hexamethylenediamine to produce nylon 66 salt, which is then further polycondensed to produce nylon 66 fibers and nylon 66 resin. In the polyurethane field, adipic acid undergoes esterification reactions with polyols to produce polyester polyols, which in turn produce various polyurethane products, such as polyurethane shoe sole resins and polyurethane adhesives. It can also be used in plasticizers, lubricants, and food additives. DuPont in the United States began industrial production in 1973, while my country began large-scale production in the 1970s. Adipic acid production processes are already mature. Commonly used adipic acid production processes include the phenol method, the cyclohexane method, and the cyclohexene method. Detailed descriptions are as follows:

[0003] 1. Phenol method

[0004] The phenol process is a relatively "old" method for producing adipic acid. Its main principle is that phenol undergoes a catalytic hydrogenation reaction to first produce cyclohexanol. Then, the cyclohexanol is oxidized to ultimately produce adipic acid. For a considerable period, due to the underdeveloped state of chemical production systems, the phenol process was almost the only method for producing adipic acid. However, the low production capacity of phenol kept the price of adipic acid consistently high. In recent years, new processes for producing adipic acid, including the cyclohexane process, have gradually matured, rendering the phenol process obsolete.

[0005] 2. Cyclohexane process

[0006] Currently, the most mainstream and widely used adipic acid production process is the cyclohexane process. Data shows that adipic acid produced using this method accounts for over 90% of the global market. The main production process is as follows: using cyclohexane as the main raw material (the preparation of cyclohexane involves continuously feeding benzene and hydrogen into a cyclohexane production unit, where a directional chemical reaction can produce cyclohexane), the cyclohexane enters the alcohol-ketone production unit, where light components and EI oil are separated. The purified alcohol-ketone is then transported to the adipic acid unit, where it reacts with added nitric acid to ultimately obtain an adipic acid mixture. The core step is the reaction between the alcohol-ketone and nitric acid, which is also a core step in the phenol process mentioned above. To ensure the production efficiency of adipic acid, a large amount of nitric acid must be used in the core oxidation reaction—the preparation of adipic acid—resulting in a large amount of nitrous oxide (N₂O) and various other types of nitrogen oxides (NO, NO₂, N₂O₃, N₂O₄, etc.). x Among these substances, only NO2 is relatively stable. Other substances, once directly released into the natural environment, will undergo a variety of uncertain reactions, with unpredictable final results and potential risks.

[0007] 3. Cyclohexene method

[0008] The cyclohexene method is an improvement on the cyclohexane method, primarily focusing on the production process of cyclohexanol. It also uses benzene as a raw material, adding hydrogen to guide the reaction of water and directly generate cyclohexanol. Compared to the cyclohexane method, the cyclohexene method offers greater stability in the formation of the intermediate cyclohexanol, resulting in higher purity cyclohexanol. This improvement significantly reduces energy consumption and the number of reaction steps in the early and mid-stages of the process (separation and purification of key components), thus improving the economic efficiency of this stage. After the formation of cyclohexanol, the subsequent adipic acid production process is identical to the cyclohexane method, with no difference in the principle of generating gaseous nitrogen oxides. The drawback of this method is the high cost of the catalysts required for the preparation and purification of cyclohexanol, coupled with the lack of improvement in nitrogen oxide treatment, limiting its current widespread application.

[0009] Since the core step of "catalytic oxidation of cyclohexanol and cyclohexanone by adding nitric acid" is indispensable in many processes for producing adipic acid, gaseous nitrous oxide (N2O) and various forms of NO will inevitably be generated in the relevant chemical reactions. x Nitrous oxide is a greenhouse gas whose harmfulness far exceeds that of carbon dioxide and methane. With the deepening of green development in my country and the increasing emphasis on resource conservation and environmental protection, the development of new, green, environmentally friendly, and efficient adipic acid production processes has become increasingly urgent.

[0010] Renewable electricity-driven chemical synthesis can effectively reduce carbon emissions, providing a new pathway for the sustainable production of chemicals and energy carriers. Utilizing the electrocatalytic oxidation of KA oil to produce adipic acid, with water as the oxygen source, avoids the use of oxidants such as O2, H2O2, and HNO3, while simultaneously coupling with cathode hydrogen production, holds promise for a new method of green adipic acid synthesis. Specifically, the electrocatalytic process can leverage the concept of electro-reforming, simultaneously producing hydrogen as a green fuel at the cathode and electrochemically generating oxidants or high-valence substances for the oxidation process in situ. This not only eliminates the capital costs of oxidant production but also benefits from the co-production of the required oxidation products and hydrogen powered by renewable electricity. Compared to traditional water splitting technology, this electro-reforming process can also replace the slow oxygen evolution reaction (OER), reducing energy costs and obtaining high-value products instead of low-value oxygen. Therefore, the electro-reforming of cyclohexanol or cyclohexanone into adipic acid and hydrogen is a promising strategy. Summary of the Invention

[0011] In view of the shortcomings and deficiencies of the existing technology, the purpose of this invention is to overcome the problems of high cost of raw materials and catalysts, complex production process and serious environmental pollution in the current adipic acid synthesis process, and to provide a method for the electrocatalytic oxidation of cyclohexanol / cyclohexanone to prepare adipic acid and couple hydrogen production. The process is green and environmentally friendly, the production process is simple and the reaction efficiency is high.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] 1. The present invention provides a method for electrocatalytic oxidation of cyclohexanol / cyclohexanone to prepare adipic acid coupled with hydrogen production, comprising: catalytic oxidation using an H-type electrolytic cell; a working electrode and a reference electrode in an anode chamber and a cathode chamber, which together constitute an electrocatalytic reactor; the reaction feed solution is an aqueous solution of cyclohexanol / cyclohexanone and an electrolyte; under a certain working voltage and current density, the anode is oxidized to adipic acid, and hydrogen is generated at the cathode.

[0014] 2. In the method for electrocatalytic oxidation of cyclohexanol / cyclohexanone to prepare adipic acid coupled with hydrogen production, the working electrode is a metal oxide / hydroxide supported on a foamed metal, and the reference electrode is Hg / HgO;

[0015] 3. In the method for preparing adipic acid by electrocatalytic oxidation of cyclohexanol / cyclohexanone to produce hydrogen, the molar concentration of the reaction substrate cyclohexanol / cyclohexanone is 10-500 mmol / L, and the alkaline solution is a 0.1-2.0 mol / L KOH or NaOH solution;

[0016] 4. The method for preparing adipic acid by electrocatalytic oxidation of cyclohexanol / cyclohexanone and coupled hydrogen production has an operating voltage of 1.2V to 1.6V and a reaction time of 1 to 60 min;

[0017] 5. In the method for preparing adipic acid by electrocatalytic oxidation of cyclohexanol / cyclohexanone and coupled hydrogen production, the size of the foam metal support is (1-3) cm × (1-3) cm;

[0018] 6. In the method for electrocatalytic oxidation of cyclohexanol / cyclohexanone to prepare adipic acid coupled with hydrogen production, the carrier foam metal is selected from one of the following: nickel foam, copper foam, nickel-iron foam, nickel-copper foam, cobalt-nickel foam, nickel-molybdenum foam, nickel-chromium-aluminum foam, nickel-iron-chromium-aluminum foam, copper-tin foam, and nickel-aluminum foam;

[0019] 7. The method for preparing adipic acid coupled with hydrogen production by electrocatalytic oxidation of cyclohexanol / cyclohexanone, wherein the preparation method of the metal oxide / hydroxide supported on foam metal includes: (1) preparing a metal oxide / hydroxide containing 5 mmol / L Fe 2+ (2) Wash the foam metal with a thickness of 0.3 mm to 1.5 mm with anhydrous ethanol, analytical grade acetone and deionized water for 15 min each, and then soak it in the above solution for 2 to 15 min; (3) After the reaction is completed, take it out, rinse the surface with deionized water and dry it at 60°C to obtain the metal oxide / hydroxide loaded with foam metal.

[0020] In step 1), the mass fraction of the hydrogen peroxide reaction solution is 1% to 35%, preferably 5% to 15%.

[0021] In step 2), the thickness of the foamed metal is 0.3 mm to 1.5 mm, preferably 0.5 mm to 1 mm.

[0022] Compared with existing technologies, the advantages of this invention include:

[0023] (1) This invention uses metal oxides / hydroxides supported on foam metal as catalysts to electrocatalyze the conversion of cyclohexanol / cyclohexanone into adipic acid without the need to add nitric acid, which is green and environmentally friendly.

[0024] (2) This invention can be carried out at room temperature and pressure, without the equipment requirements of reaction temperature and pressure in traditional processes, does not produce toxic or harmful gases, and achieves coupled hydrogen production. The product has high selectivity and conversion rate, is suitable for industrial implementation, and has broad application prospects. Attached Figure Description

[0025] Figure 1 This is the linear sweep voltammetric curve of the electrocatalytic process in Example 3 of the present invention.

[0026] Figure 2 The results are obtained by liquid chromatography after the catalyst was reacted at a constant voltage for 20 minutes in Example 3 of this invention.

[0027] Figure 3 This is the current density, charge, and time curve during the oxidation process in Embodiment 3 of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0029] Example 1

[0030] Prepare 50 mL of a reaction solution containing 5 mmol / L ferrous carbonate and 5% hydrogen peroxide. Then, a 0.5 mm thick nickel foam with a size of 1 cm × 1 cm is ultrasonically washed for 15 min each with anhydrous ethanol, analytical grade acetone, and deionized water. After that, it is immersed in the above solution for 2 min. After the reaction is completed, it is taken out, the surface is rinsed with deionized water, and dried at 60 °C to obtain nickel and iron oxide / hydroxide loaded on nickel foam.

[0031] An H-type electrolytic cell is used for catalytic oxidation; nickel and iron oxides / hydroxides supported on nickel foam serve as the working electrodes for the cathode and anode, and Hg / HgO serves as the reference electrode, forming a three-electrode electrocatalytic reactor.

[0032] In the cathodic electrolysis chamber, a 0.1 mol / L NaOH solution was used as the cathodic electrolyte, and in the anodic electrolysis chamber, 10 mM cyclohexanol dissolved in a 0.1 mol / L NaOH solution was used as the anodic electrolyte. The mixture was magnetically stirred. The two electrodes were separated by an ion-exchange membrane.

[0033] The reaction was carried out under constant voltage (1.4V vs. RHE) for 5 min at room temperature and pressure with continuous stirring. After the reaction was completed, the reaction product was analyzed by high performance liquid chromatography, and the yield of adipic acid was 70%.

[0034] Example 2

[0035] Prepare 50 mL of a reaction solution containing 5 mmol / L ferrous phosphate and 5% hydrogen peroxide. Wash a 0.5 mm thick, 1 cm × 1 cm nickel foam with an anhydrous ethanol, analytical grade acetone and deionized water by sonication for 15 min each. Then soak it in the above solution for 2 min. After the reaction, remove it, rinse the surface with deionized water and dry it at 60 °C to obtain nickel foam loaded with iron and nickel oxide / hydroxide.

[0036] An H-type electrolytic cell was used for catalytic oxidation; a three-electrode electrocatalytic reactor was constructed, consisting of iron and nickel oxides / hydroxides supported on nickel foam as the working electrodes of the cathode and anode, and Hg / HgO as the reference electrode.

[0037] In the cathode electrolysis chamber, a 0.5 mol / L NaOH solution was used as the cathode electrolyte, and in the anolyte chamber, 50 mM cyclohexanol dissolved in a 0.5 mol / L NaOH solution was used as the anolyte. The mixture was magnetically stirred. The two electrodes were separated by an ion-exchange membrane.

[0038] The reaction was carried out under constant temperature and pressure with continuous stirring for 10 min at a constant voltage of 1.4 V. After the reaction was completed, the reaction product was analyzed by high performance liquid chromatography, and the yield of adipic acid was 73%.

[0039] Example 3

[0040] Prepare 50 mL of a reaction solution containing 5 mmol / L ferrous sulfate and 10% hydrogen peroxide. Then, a foamed nickel-copper alloy with a thickness of 0.5 mm and a size of 1 cm × 1 cm is ultrasonically washed for 15 min each with anhydrous ethanol, analytical grade acetone, and deionized water. After that, it is immersed in the above solution for 5 min. After the reaction is completed, it is taken out, the surface is rinsed with deionized water, and dried at 60 °C to obtain iron, nickel, and copper oxide / hydroxide loaded on the foamed nickel-copper alloy.

[0041] An H-type electrolytic cell is used for catalytic oxidation; the working electrodes of iron, nickel, and copper oxides / hydroxides supported on nickel-copper foam are the cathode and anode, and Hg / HgO is the reference electrode, forming a three-electrode electrocatalytic reactor.

[0042] In the cathodic electrolysis chamber, a 1 mol / L KOH solution was used as the cathodic electrolyte, and in the anodic electrolysis chamber, 100 mM cyclohexanol dissolved in a 1 mol / L KOH solution was used as the anodic electrolyte. The mixture was magnetically stirred. The two electrodes were separated by an ion-exchange membrane.

[0043] The reaction was carried out under constant voltage (1.4V vs. RHE) at room temperature and pressure for 20 min with continuous stirring. After the reaction was completed, the reaction product was analyzed by high performance liquid chromatography, and the yield of adipic acid was 77%.

[0044] Example 4

[0045] Prepare 50 mL of a reaction solution containing 5 mmol / L ferrous chloride and 10% hydrogen peroxide. Then, a foamed nickel-copper alloy with a thickness of 1 mm and a size of 1.5 cm × 1.5 cm is ultrasonically washed for 15 min each with anhydrous ethanol, analytical grade acetone, and deionized water. After that, it is immersed in the above solution for 5 min. After the reaction is completed, it is taken out, the surface is rinsed with deionized water, and dried at 60 °C to obtain iron, nickel, and copper oxide / hydroxide loaded on the foamed nickel-copper alloy.

[0046] An H-type electrolytic cell is used for catalytic oxidation; the working electrodes of iron, nickel, and copper oxides / hydroxides supported on nickel-copper foam are the cathode and anode, and Hg / HgO is the reference electrode, forming a three-electrode electrocatalytic reactor.

[0047] In the cathodic electrolysis chamber, a 1.5 mol / L KOH solution was used as the cathodic electrolyte, and in the anodic electrolysis chamber, 200 mM cyclohexanone dissolved in a 1.5 mol / L KOH solution was used as the anodic electrolyte. The electrodes were magnetically stirred. The two electrodes were separated by an ion-exchange membrane.

[0048] The reaction was carried out under constant voltage (1.5V vs. RHE) at room temperature and pressure for 30 min with continuous stirring. After the reaction was completed, the reaction product was analyzed by high performance liquid chromatography, and the yield of adipic acid was 85%.

[0049] Example 5

[0050] Prepare 50 mL of a reaction solution containing 5 mmol / L ferrous nitrate and 15% hydrogen peroxide. Then, a 1 mm thick, 2 cm × 2 cm foam nickel-cobalt was ultrasonically washed for 15 min each with anhydrous ethanol, analytical grade acetone, and deionized water. After that, it was immersed in the above solution for 10 min. After the reaction, it was taken out, the surface was rinsed with deionized water, and dried at 60 °C to obtain iron, nickel, and cobalt oxides / hydroxides supported on the foam nickel-cobalt.

[0051] The catalytic oxidation was carried out using an H-type electrolytic cell; the working electrodes of the three-electrode system were formed by using iron, nickel, and cobalt oxides / hydroxides supported on nickel-cobalt foam as the cathode and anode, and Hg / HgO as the reference electrode.

[0052] In the cathodic electrolysis chamber, a 1.5 mol / L NaOH solution was used as the cathodic electrolyte, and in the anodic electrolysis chamber, 300 mM cyclohexanone dissolved in a 1.5 mol / L NaOH solution was used as the anodic electrolyte. The mixture was magnetically stirred. The two electrodes were separated by an ion-exchange membrane.

[0053] The reaction was carried out under constant voltage (1.5V vs. RHE) at room temperature and pressure for 40 min with continuous stirring. After the reaction was completed, the reaction product was analyzed by high performance liquid chromatography, and the yield of adipic acid was 87%.

[0054] Example 6

[0055] Prepare 50 mL of a reaction solution containing 5 mmol / L ferric chloride and 15% hydrogen peroxide. Then, a 1 mm thick, 3 cm × 3 cm foam nickel-cobalt was ultrasonically washed for 15 min each with anhydrous ethanol, analytical grade acetone, and deionized water. After that, it was immersed in the above solution for 10 min. After the reaction, it was taken out, the surface was rinsed with deionized water, and dried at 60 °C to obtain iron, nickel, and cobalt oxides / hydroxides supported on the foam nickel-cobalt.

[0056] The catalytic oxidation was carried out using an H-type electrolytic cell; the working electrodes of the three-electrode system were formed by using iron, nickel, and cobalt oxides / hydroxides supported on nickel-cobalt foam as the cathode and anode, and Hg / HgO as the reference electrode.

[0057] In the cathodic electrolysis chamber, a 2 mol / L KOH solution was used as the cathodic electrolyte, and in the anodic electrolysis chamber, 500 mM cyclohexanone dissolved in a 2 mol / L KOH solution was used as the anodic electrolyte. The electrodes were magnetically stirred. The two electrodes were separated by an ion-exchange membrane.

[0058] The reaction was carried out under constant voltage (1.5V vs. RHE) at room temperature and pressure for 60 min with continuous stirring. After the reaction was completed, the product was analyzed by high-performance liquid chromatography (HPLC), and the yield of adipic acid was 95%.

[0059] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for the electrocatalytic oxidation of cyclohexanone to prepare adipic acid coupled with hydrogen production, characterized in that: Catalytic oxidation was carried out using an H-type electrolytic cell; the working electrode and reference electrode of the anode chamber and cathode chamber together constitute the electrocatalytic reactor; the working electrode is a metal oxide / hydroxide supported on porous foam metal, which is prepared by the following method: (1) preparing a metal oxide / hydroxide containing 5 mmol / L Fe 2+ (1) Salt and hydrogen peroxide reaction solution with a mass fraction of 5% to 15%; (2) Wash the foam metal with a thickness of 0.3 to 1.5 mm in sequence with anhydrous ethanol, acetone and deionized water for 15 min each, and then soak it in the solution obtained in step (1) for 2 to 15 min; (3) Take it out and rinse it with deionized water and dry it at 60℃ to obtain the solution; The reference electrode is Hg / HgO; The reaction raw material solution is a mixed aqueous solution of 500 mmol / L cyclohexanone and 0.1 to 2.0 mol / L KOH; The reaction is carried out at a working voltage of 1.5 V (vs. RHE) for 5 to 60 min, adipic acid is generated at the anode and hydrogen gas is generated at the cathode; The foam metal is foamed nickel-cobalt.

2. The method for preparing adipic acid by electrocatalytic oxidation of cyclohexanone coupled with hydrogen production according to claim 1, characterized in that, The dimensions of the foamed metal are (1-3) cm × (1-3) cm.

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