Method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene

Abstract

The invention discloses a method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene, which comprises the following steps: by taking a cheap and easily available Cu-based material as a catalytic electrode, applying constant potential at room temperature in an alkaline electrolyte containing high-concentration nitrobenzene to electrolyze and synthesize aniline; the solubility of nitrobenzene is improved by adding an organic cosolvent, so that high yield of aniline is realized; the catalyst used in the method is low in cost, the preparation process is simple, the reaction condition is mild, inert gas protection is not needed, the method can be carried out under the conditions of room temperature and normal pressure, the aniline selectivity and yield are high, and the method has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of organic electrosynthesis technology, specifically relating to a method for the electrocatalytic hydrogenation synthesis of aniline from high-concentration nitrobenzene. Background Technology

[0002] Nitrobenzene (C6H5NO2) is an important basic chemical raw material, widely used in the synthesis of dyes, pharmaceuticals, explosives, and polymer materials. Its downstream high-value-added product, aniline (C6H5NH2), is a key raw material for synthetic rubber additives, pharmaceutical intermediates, and dyes, with a global annual production exceeding 7.85 million tons. Currently, the industrial production of aniline mainly relies on the chemical reduction of nitrobenzene (such as the iron / zinc reduction method) or catalytic hydrogenation (using precious metal catalysts and hydrogen), which suffers from high energy consumption, low selectivity, and severe pollution. In contrast, electrocatalytic reduction technology can be carried out at ambient temperature and pressure, offering advantages such as being green, sustainable, and less polluting, and has therefore attracted considerable attention.

[0003] Most reported electrocatalytic systems employ noble metal electrodes, exhibiting high catalytic activity but still facing the problem of high catalyst costs. Meanwhile, nitrobenzene is highly volatile and has extremely low solubility in water (approximately 1.9 g / L). For example, CN202311659686.0 discloses an electrocatalytic method for preparing aniline, which couples the electrocatalytic hydrogenation of nitrobenzene to aniline with the electrooxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, demonstrating good economic benefits and energy utilization efficiency. However, the concentration of nitrobenzene used is still below 10 mM. To increase the reactant concentration, Carvajal et al. (Advanced Sustainable Systems, 2022, 6, 2100367) used a 0.25 M NaH2PO4 solution containing 30 mM nitrobenzene and a water / acetonitrile mixed solvent (70 / 30) as the electrolyte solution, and a Pd-doped CuPd electrode as the working electrode, achieving a 70.4% aniline yield, which remained stable for 70 hours. However, this electrode material is highly dependent on precious metals, and the yield of aniline needs to be further improved.

[0004] Therefore, developing non-precious metal electrocatalysts that are low-cost, highly selective, highly active, and suitable for high-concentration nitrobenzene reduction systems has significant research value and application prospects. Summary of the Invention

[0005] This invention discloses a method for the electrocatalytic hydrogenation synthesis of aniline from high-concentration nitrobenzene.

[0006] The technical solution of the present invention is as follows: A method for the electrocatalytic hydrogenation synthesis of aniline from high-concentration nitrobenzene includes: In an H-shaped tank equipped with a proton exchange membrane, a mixed aqueous solution containing KOH, an organic co-solvent, and nitrobenzene was used as the catholy solution, and an aqueous KOH solution was used as the anoly solution. A three-electrode system was constructed with a self-supporting Cu-based catalytic electrode as the cathode, a platinum sheet as the anode, and an Hg / HgO electrode as the reference electrode. The catholy solution was stirred at room temperature and atmospheric pressure, and constant potential electrolysis was applied to obtain the product aniline. in, The organic co-solvent is selected from methanol, ethanol, and N,N-dimethylformamide (DMF), with methanol being preferred; In the preferred cathode solution, the concentration of KOH is 1~3 M, the concentration of nitrobenzene is 5~500 mM (which can successfully achieve the conversion of high concentrations of nitrobenzene >100 mM), and the volume percentage of the organic co-solvent is 20~75% (more preferably 25~50%). The preferred anolyte is a 1-3M KOH aqueous solution; The preferred electrolysis potential is 0.1 to -0.3 V vs. RHE, and the electrolysis time is 1 to 6 h. The aniline selectivity of the method of the present invention is >70%, and the nitrobenzene conversion rate is >90%.

[0007] In this invention, the self-supporting Cu-based catalytic electrode is selected from one of copper foam, Cu(OH)2 nanowire self-supporting electrode, and CuO nanowire array self-supporting electrode, with CuO nanowire array self-supporting electrode being preferred.

[0008] Copper foam is readily available through regular commercial purchases.

[0009] The preparation method of Cu(OH)2 nanowire self-supporting electrode is as follows: using copper foam as a substrate, it is immersed in a mixed aqueous solution of NaOH and (NH4)2S2O8 at room temperature for 15~45 min (preferably 25 min), and then taken out, washed and dried to obtain blue Cu(OH)2 nanowire self-supporting electrode. Before use, the foamed copper should be cleaned in sequence with acetone, ethanol, hydrochloric acid (0.5~3M) and deionized water to remove the surface oxide layer. The preferred aqueous solution is a mixture of NaOH and (NH4)2S2O8, with NaOH concentration of 0.5-3 M and (NH4)2S2O8 concentration of 0.5-3 M.

[0010] The preparation method of CuO nanowire array self-supporting electrode is as follows: Place the Cu(OH)2 nanowire self-supporting electrode prepared above into a muffle furnace, heat it to 150~300 ℃ (preferably 250 ℃) and keep it for 2 h to obtain the electrode.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: Traditional high-performance electrodes used for nitrobenzene electrocatalysis often rely on precious metal materials, resulting in high manufacturing costs. Furthermore, the low solubility of nitrobenzene in water limits conventional electrolysis systems to low concentrations of nitrobenzene reactants, severely restricting the feasibility of industrial-scale production.

[0012] This invention significantly improves the solubility of nitrobenzene in the electrolyte by introducing an organic co-solvent, and successfully develops a self-supporting copper-based catalytic electrode suitable for this system, achieving efficient electrocatalytic reduction of high-concentration nitrobenzene to aniline. The entire process is mild, the electrode materials are inexpensive, the synthesis process is environmentally friendly, and the selectivity and yield of aniline are ideal, demonstrating good potential for industrial application. Attached Figure Description

[0013] Figure 1 Scanning electron microscope (SEM) image of Cu(OH)2 catalyst material in Example 1 of this invention.

[0014] Figure 2 Scanning electron microscope (SEM) image of the CuO catalyst material in Example 1 of this invention.

[0015] Figure 3 Linear sweep voltammetry (LSV) curves of copper foam, Cu(OH)2, and CuO catalytic electrodes in Example 1 of this invention.

[0016] Figure 4 The results of constant potential electrolysis of CuO in a solution containing 100 mM nitrobenzene in Example 1 of this invention.

[0017] Figure 5 The constant potential electrolysis performance of copper foam, Cu(OH)2, and CuO in Example 2 of this invention.

[0018] Figure 6 Example 3 of this invention: LSV of CuO in different organic co-solvents.

[0019] Figure 7 In Example 4 of this invention, CuO is in an LSV containing a 500 mM nitrobenzene solution. Detailed Implementation

[0020] To facilitate understanding of the present invention, specific embodiments will be further described below. These embodiments are for illustrative purposes only and do not limit the scope of the invention. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention.

[0021] Example 1: Weigh out 2.5 g NaOH and 0.575 g ammonium persulfate and dissolve them in a beaker containing 25 mL of deionized water. After stirring thoroughly to dissolve, add a clean 1 cm piece of [unclear - possibly a type of granulated glass]. A 2 cm piece of copper foam was soaked for 25 minutes, then rinsed with deionized water and dried at room temperature for 24 hours to obtain a Cu(OH)₂ nanowire self-supported electrode with the following morphology. Figure 1 As shown, it is characterized by a smooth surface and an average diameter of approximately ~100 nm in nanowire structures. It was transferred to a muffle furnace and heated to 250 °C for 2 hours. After the reaction, the material was removed to obtain a CuO nanowire self-supported electrode, with the morphology shown... Figure 2 As shown, a few cracks appear on the nanowires, and the tips of the nanowires become thinner.

[0022] In an H-type electrolytic cell containing a proton exchange membrane diaphragm, a three-electrode system was constructed using copper foam, self-supported Cu(OH)₂, and self-supported CuO as working electrodes, a platinum sheet as the counter electrode, and an Hg / HgO electrode as the reference electrode. A mixed solution of ethanol and water containing 100 mM nitrobenzene and 1 M KOH (ethanol to water volume ratio 1:1) was added to the cathode chamber as the cathode electrolyte, and a 1 M KOH solution was added to the anode chamber as the anode electrolyte. The cathode electrolytes were stirred at room temperature and atmospheric pressure. The linear sweep voltammetry (LSV) curves are shown below. Figure 3 As shown, the dashed line represents the area without nitrobenzene. By comparison, it can be seen that when nitrobenzene substrate is added, the cathode current density increases significantly (solid line), indicating that copper foam, Cu(OH)2, and CuO all have obvious electrocatalytic reduction performance of nitrobenzene. Moreover, from the current density, it can be seen that CuO>Cu(OH)2>copper foam.

[0023] Using CuO as the catalytic electrode, electrolysis was performed under a constant potential of -0.2 V vs. RHE, and the results were detected by liquid chromatography. Figure 4 As shown, the conversion rate of nitrobenzene was 97%, and the selectivity of aniline was 91%.

[0024] Example 2: Based on Example 1, the catholyte was a mixed solution of ethanol and water containing 20 mM nitrobenzene and 1 M KOH (ethanol to water volume ratio 1:3). Electrolysis was performed under a constant potential of -0.1 V vs. RHE for 60 minutes. Samples were then taken for liquid chromatography analysis, and the results were as follows: Figure 5 As shown, the conversion rate of nitrobenzene on CuO was 98%, and the aniline selectivity was 96%; the conversion rate of nitrobenzene on Cu(OH)2 was 96%, and the aniline selectivity was 86%; the conversion rate of nitrobenzene on copper foam was 94%, and the aniline selectivity was 73%.

[0025] Example 3: Based on Example 1, using a CuO catalytic electrode as the working electrode, the ethanol additive in the catholyte was replaced with methanol and DMF, respectively, and the LSV curve was tested. Figure 6 As shown in the figure, the comparison shows that when nitrobenzene substrate is added, the cathode current density increases significantly (solid line), indicating that methanol, ethanol and DMF can all be used as effective additives to dissolve nitrobenzene. CuO also shows obvious electrocatalytic reduction performance of nitrobenzene, and the current density shows that methanol > ethanol > DMF.

[0026] Example 4: In an H-type electrolyzer containing a proton exchange membrane diaphragm, a three-electrode system was constructed using a CuO catalytic electrode as the working electrode, a platinum sheet as the counter electrode, and an Hg / HgO electrode as the reference electrode. A mixed solution of ethanol and water (ethanol to water volume ratio 3:1) containing 500 mM nitrobenzene and 1 M KOH was added to the cathode chamber as the cathode electrolyte, and a 1 M KOH solution was added to the anode reaction chamber as the anode electrolyte. The cathode electrolyte was stirred at room temperature and atmospheric pressure, and its LSV was as follows: Figure 7 As shown, when the ethanol content is increased to 75%, the conductivity of the electrolyte decreases and the current density is much lower than that in Examples 1-3; however, CuO still has the electrocatalytic activity of nitrobenzene.

Claims

1. A method for the electrocatalytic hydrogenation synthesis of aniline from high-concentration nitrobenzene, characterized in that, The method includes: In an H-shaped tank equipped with a proton exchange membrane, a mixed aqueous solution containing KOH, an organic co-solvent, and nitrobenzene was used as the catholy solution, and an aqueous KOH solution was used as the anoly solution. A three-electrode system was constructed with a self-supporting Cu-based catalytic electrode as the cathode, a platinum sheet as the anode, and an Hg / HgO electrode as the reference electrode. The catholy solution was stirred at room temperature and atmospheric pressure, and constant potential electrolysis was applied to obtain the product aniline. in, The organic co-solvent is selected from methanol, ethanol, and N,N-dimethylformamide.

2. The method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene as described in claim 1, characterized in that, In the catholy solution, the concentration of KOH is 1~3 M, the concentration of nitrobenzene is 5~500 mM, and the volume percentage of organic co-solvent is 20~75%.

3. The method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene as described in claim 2, characterized in that, In the catholy solution, the concentration of KOH is 1~3 M, the concentration of nitrobenzene is 100~500 mM, and the volume percentage of organic co-solvent is 25~50%.

4. The method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene as described in claim 1, characterized in that, The anolyte is a 1-3 M KOH aqueous solution.

5. The method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene as described in claim 1, characterized in that, Electrolysis potential 0.1~-0.3 V vs. RHE, electrolysis time 1~6 h.

6. The method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene as described in claim 1, characterized in that, The self-supporting Cu-based catalytic electrode is selected from one of the following: copper foam, Cu(OH)2 nanowire self-supporting electrode, and CuO nanowire array self-supporting electrode.

7. The method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene as described in claim 6, characterized in that, The preparation method of Cu(OH)2 nanowire self-supporting electrode is as follows: using copper foam as a substrate, it is immersed in a mixed aqueous solution of NaOH and (NH4)2S2O8 at room temperature for 15~45 min, and then taken out, washed and dried to obtain Cu(OH)2 nanowire self-supporting electrode.

8. The method for synthesizing aniline by electrocatalytic hydrogenation of high-concentration nitrobenzene as described in claim 6, characterized in that, The preparation method of CuO nanowire array self-supporting electrode is as follows: Place the Cu(OH)2 nanowire self-supporting electrode prepared according to claim 7 into a muffle furnace, heat it to 150~300 ℃ and hold it for 2 h to obtain CuO nanowire array self-supporting electrode.

Images