Electrolytic synthesis method of p-aminophenol without adding surfactant

Abstract

A porous material is used as a working electrode, a hydrophobic layer of the working electrode faces a raw material solution containing nitrobenzene, and a reaction layer of the working electrode is electrolyzed by a sulfuric acid aqueous solution to synthesize p-aminophenol. According to the method, a surface active agent and nitrobenzene do not need to be added into the electrolyte, a p-aminophenol solution with the high concentration is synthesized, the separation and purification steps of the product are optimized, compared with a traditional method, the concentration of a sulfuric acid aqueous solution used in the traditional method is reduced to 10% from 20%, meanwhile, the reaction voltage is also reduced by 0.4 V, and the method is suitable for industrial production. The production cost and the energy consumption are reduced, the environmental pollution is reduced, and the current efficiency is improved by nearly 25% and the selectivity is improved by 10%.

Description

Technical Field

[0001] The present invention provides an electrolytic synthesis method for p-aminophenol, more specifically a method for synthesizing p-aminophenol by electrolytic reduction using a porous material containing a hydrophobic layer as a working electrode without adding cosolvents such as surfactants and nitrobenzene to the electrolyte. Background Art

[0002] p-Aminophenol (PAP) is an important organic fine chemical raw material and pharmaceutical synthesis intermediate. It is widely used in medicine (such as paracetamol, clofibrate, vitamin B1, compound nicotinamide, 6-hydroxyquinoline, etc.), dyes (such as the preparation of disperse fuels, acid dyes, direct dyes, hair dyes, etc.), rubber (such as the synthesis of 4010NA, 4020 / 4030 and other p-phenylenediamine antioxidants), photography (developer metol), and other fields.

[0003] The electrochemical reduction of nitrobenzene to prepare p-aminophenol offers advantages such as readily available and inexpensive raw materials, a reduced number of production steps, high product quality, minimal pollution, and easy disposal of the "three wastes," making it an environmentally friendly and competitive process. Nitrobenzene has low solubility in aqueous solutions, resulting in a low limiting diffusion current density and low intrinsic kinetic rate for the electrochemical process. Therefore, three main methods have been used to increase nitrobenzene's solubility: 1) increasing the reaction temperature; 2) adding cosolvents such as surfactants (dimethyldodecylamine oxide); and 3) adding water-miscible organic solvents (such as acetone, ethanol, and dimethyl sulfoxide). However, cosolvents suffer from poor temperature tolerance, low activity, and the associated difficulty in handling and contamination. Furthermore, their inclusion complicates product separation. Furthermore, the addition of organic solvents increases the reaction voltage and energy consumption. To reduce the reaction voltage, the use of large amounts of supporting electrolytes increases post-processing costs and recovery difficulties.

[0004] The present invention uses a porous material as a working electrode, wherein the hydrophobic layer faces a raw material liquid containing nitrobenzene, and the reaction layer faces a sulfuric acid aqueous solution, and electrolysis is performed to synthesize p-aminophenol without adding cosolvents such as surfactants. Summary of the Invention

[0005] The present invention provides a surfactant-free electrolytic synthesis method for p-aminophenol. The method utilizes a porous material as a working electrode, with the hydrophobic layer of the working electrode facing a raw material solution containing nitrobenzene and the reaction layer facing a sulfuric acid aqueous solution for electrolytic synthesis of p-aminophenol. This method eliminates the need for adding surfactants or other cosolvents to the electrolyte, as well as nitrobenzene, resulting in a highly concentrated p-aminophenol solution and optimizing the product separation and purification steps. Compared to conventional methods, this method reduces the concentration of the sulfuric acid aqueous solution used in conventional methods from 20% to 10%, while also lowering the reaction voltage by 0.4 V. This reduces production costs and energy consumption, minimizes environmental pollution, and improves current efficiency by nearly 25% and selectivity by 10%.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The porous material is used as the working electrode, which consists of a hydrophobic layer and a reaction layer. The electrolyte and the raw material liquid are placed on both sides of the working electrode, with the hydrophobic layer facing the raw material liquid and the reaction layer facing the electrolyte. The electrolyte is a sulfuric acid aqueous solution and the raw material liquid is a solution containing nitrobenzene.

[0008] Furthermore, the material of the hydrophobic layer includes hydrophobic carbon paper layer, carbon cloth, graphite felt, carbon foam, titanium, and stainless steel mesh.

[0009] Furthermore, the reaction layer is a carrier loaded with a catalyst, the carrier includes but is not limited to Nafion and PTFE mixed emulsion, carbon cloth, graphite felt, carbon foam, titanium, stainless steel mesh, and the catalyst includes but is not limited to carbon powder, multi-walled carbon nanotubes, carbon black, Pt / C, and copper.

[0010] The solvents of Nafion emulsion and PTFE emulsion are both mixed solvents of ethanol and isopropanol.

[0011] Furthermore, the solution pressure is greater than or equal to the raw material pressure, and the pressure difference is 0-1 atm.

[0012] Furthermore, the raw material solution containing nitrobenzene (B) diffuses into the reaction layer through the hydrophobic layer of the working electrode to electrolyze and synthesize p-aminophenol (A).

[0013]

[0014] The solvent of the nitrobenzene solution is a low water-soluble solvent such as toluene, dichloromethane, butyl acetate, etc.

[0015] Furthermore, no surfactant, organic solvent or other cosolvent is added to the electrolyte.

[0016] Furthermore, the concentration of nitrobenzene in the raw material liquid is 1-100 wt %.

[0017] Furthermore, the concentration of the sulfuric acid aqueous solution is 10 to 60 wt%.

[0018] Furthermore, the reaction temperature is 50-90°C and the reaction current is 30-70 mA / cm 2 , the reaction voltage is 3~5V.

[0019] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0020] The electrolyte solution does not require the addition of any cosolvents, such as surfactants or organic solvents, simplifying the product separation and purification steps, reducing reaction energy consumption (reaction voltage is reduced by approximately 0.5V), minimizing environmental pollution, and saving production costs. The working electrode is a porous material with a hydrophobic layer, and a 0-100wt% nitrobenzene solution can be used as the raw material, overcoming concentration limitations while improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 The schematic diagram of the reaction for synthesizing p-aminophenol using a porous material with a hydrophobic layer as the working electrode. DETAILED DESCRIPTION

[0023] Unless otherwise specified, all aqueous solutions in the experiments were prepared with deionized water; the pressure (gas pressure) in the raw material chamber and the electrolyte chamber was 1 atmosphere (1 atm).

[0024] In the following examples and comparative examples, the porous electrodes and platinum electrodes (platinum content 99.9%) were purchased from Hangzhou Saiao Electrochemical Instrument Co., Ltd.

[0025] like Figure 1 The porous material shown is a composite of a hydrophobic layer 1 and a reaction layer 2 , with an organic phase 3 on one side of the hydrophobic layer 1 and an aqueous phase 4 on one side of the catalytic layer 2 .

[0026] Example 1

[0027] p-Aminophenol was synthesized by electrolysis of nitrobenzene without adding cosolvent or emulsifier.

[0028] The cathode is a porous composite material consisting of a hydrophobic carbon paper layer as the hydrophobic layer and a carbon powder particle layer bonded by a Nafion and PTFE mixed emulsion as the reaction layer. The solvents for the Nafion and PTFE emulsions are both a mixed solvent of ethanol and isopropanol. The mass ratio of Nafion to PTFE can be 1:0.1-100, ensuring a contact angle of the catalyst layer between 90-150.

[0029] The area of the porous material is 3 cm 2 , carbon powder loading is 1mg / cm2 The pure water contact angle of the hydrophobic carbon paper layer is about 140 degrees, and the pure water contact angle of the reaction layer is about 100 degrees. The area is 3cm 2 The platinum sheet is used as the anode. A 10wt% sulfuric acid aqueous solution is used as the electrolyte, and a nitrobenzene solution is used as the raw material liquid (nitrobenzene content is 99.5wt%). The volume ratio of the raw material liquid to the electrolyte is preferably 1:1. The porous material is located between the raw material liquid and the electrolyte. The hydrophobic carbon paper layer of the porous material faces the raw material liquid, and the carbon powder layer of the porous material faces the electrolyte. The pressure difference between the electrolyte and the raw material liquid is 0.01atm, and the reaction temperature is 80°C. A current of 150mA is applied, the average voltage is 3.2V (the initial voltage is 3.1V, and the voltage is 3.3V at the end of electrolysis). The electrolysis is stopped after 9 hours. The selectivity of nitrobenzene electrolysis to para-aminophenol is 95.7%, and the current efficiency is 93.3%.

[0030] Examples 2-4

[0031] The difference from Example 1 is the pressure difference between the electrolysis and the raw material solution. The other conditions not specified are the same as those in Example 1. The synthesis results of p-aminophenol are shown in Table 2.

[0032] Table 2 Effects of different liquid level pressure differences on electrolytic synthesis results.

[0033] Example No. pressure difference Starting voltage End voltage Average voltage Current efficiency Selectivity 2 0atm 3.39V 4.8V 4.09V 93.2％ 96.3％ 3 0.2atm 3.21V 3.24V 3.23V 97.7％ 94.9％ 4 1atm 3.32V 3.28V 3.3V 83.7％ 89.3％

[0034] Example 5-17

[0035] The difference from Example 1 is that the hydrophobic layer material and the reaction layer material are different, and the contact angle between the reaction layer and pure water is different. Other conditions not specified are the same as those in Example 1. The synthesis results of p-aminophenol are shown in Table 3.

[0036] Table 3 Effect of materials and contact angles of the hydrophobic layer and reactive layer.

[0037]

[0038]

[0039] In Table 3, S indicates that the conditions are the same as those in Example 1.

[0040] Examples 18-29

[0041] The difference from Example 1 is the catalyst type and loading, electrolyte concentration, temperature, and current density. The other conditions not specified are the same as those in Example 1. The synthesis results of p-aminophenol are shown in Table 4.

[0042] Table 4 Effects of catalyst type, electrolyte concentration, temperature, and current density on electrolytic synthesis results.

[0043]

[0044] In Table 4, S indicates that the conditions are the same as those in Example 1.

[0045] Among them, MWCNT is multi-walled carbon nanotube, and XC-72R is carbon black.

[0046] Comparative Examples 1-4

[0047] The difference between Comparative Examples 1-4 and Example 1 is that the working electrodes are different, and the other conditions not specified are the same as those in Example 1. The synthesis results of p-aminophenol are shown in Table 5.

[0048] Table 5 Effects of different electrode structures on electrolytic synthesis results a

[0049]

[0050] In the reaction process of Comparative Example 1, the voltage was unstable and a circuit was broken. In the electrolysis process of Comparative Example 4, the electrolyte permeated into the raw material solution.

[0051] Comparative Example 5

[0052] Conventional electrolytic synthesis of p-aminophenol.

[0053] An H-type diaphragm electrolytic cell was used, with a 10% sulfuric acid aqueous solution as the anolyte, 1 mol / L sulfuric acid + 0.25 mol / L nitrobenzene + 2 mmol / L DDAO as the catholyte, and a platinum electrode as the anode (area: 2 cm 2 , thickness: 2 mm), monel as cathode (area: 2×3 cm 2 ), with Nafion-324 membrane as the diaphragm. The reaction system temperature was controlled at 80°C, and a current of 150 mA was applied for electrolysis (cathode current density: 4.78 A / dm 2 The electrolysis was stopped after 9 hours. The current efficiency of the electrolysis of nitrobenzene to synthesize p-aminophenol was 74.22%, the selectivity was 86.42%, the conversion rate was 82.19%, the yield was 54.06%, and the average voltage was 3.84 V (the initial voltage was 3.79 V and the voltage at the end of the electrolysis was 3.88 V).

[0054] Comparative Example 6

[0055] Electrolytic synthesis of p-aminophenol using carbon paper as the working electrode and surfactant.

[0056] An H-type diaphragm electrolytic cell was used, with a 10% sulfuric acid aqueous solution as the anolyte, 1 mol / L sulfuric acid + 0.25 mol / L nitrobenzene + 2 mmol / L DDAO as the catholyte; a platinum electrode was used as the anode (area: 2 cm 2, thickness: 2 mm), a hydrophobic carbon paper electrode as cathode (area: 3 cm 2 ), with a Nafion-324 membrane as the separator. The reaction system temperature was controlled at 80°C, and electrolysis was performed with an applied current of 150 mA (cathode current density: 4.78 A / dm²). Electrolysis was terminated after 9 hours. The electrolysis of nitrobenzene to p-aminophenol achieved a current efficiency of 93.10%, a selectivity of 94.36%, a conversion of 82.35%, a yield of 62.19%, and an average voltage of 3.74 V (initial voltage: 3.82 V, end voltage: 3.78 V).

[0057] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications based on the present invention to solve substantially the same technical problems and achieve substantially the same technical effects are included within the scope of protection of the present invention.

Claims

1. A surfactant-free electrolytic synthesis method for p-aminophenol, characterized in that: The porous material is used as the working electrode, which consists of a hydrophobic layer and a reaction layer. The electrolyte and the raw material liquid are placed on both sides of the working electrode respectively, with the hydrophobic layer facing the raw material liquid and the reaction layer facing the electrolyte. The electrolyte is a sulfuric acid aqueous solution and the raw material liquid is a solution containing nitrobenzene.

2. The method for electrolytic synthesis of p-aminophenol without adding a surfactant according to claim 1, wherein: Materials of the hydrophobic layer include hydrophobic carbon paper layer, carbon cloth, graphite felt, carbon foam, titanium, and stainless steel mesh.

3. The method for electrolytic synthesis of p-aminophenol without adding a surfactant according to claim 1, wherein: The reaction layer is a carrier loaded with a catalyst, the carrier includes but is not limited to Nafion and PTFE mixed emulsion, carbon cloth, graphite felt, carbon foam, titanium, stainless steel mesh, and the catalyst includes but is not limited to Pd / C, carbon powder, multi-walled carbon nanotubes, carbon black, Pt / C, and copper.

4. The method for electrolytic synthesis of p-aminophenol without adding a surfactant according to claim 1, wherein: The electrolytic hydraulic pressure is greater than or equal to the raw material hydraulic pressure, and the pressure difference is 0-1atm.

5. The method for electrolytic synthesis of p-aminophenol without adding a surfactant according to claim 1, wherein: The raw material solution containing nitrobenzene diffuses into the reaction layer through the hydrophobic layer of the working electrode to electrolyze and synthesize p-aminophenol.

6. The method for electrolytic synthesis of p-aminophenol without adding a surfactant according to claim 1, wherein: No surfactant or organic solvent is added to the electrolyte.

7. The method for electrolytic synthesis of p-aminophenol without adding a surfactant according to claim 1, wherein: The concentration of nitrobenzene in the raw material liquid is 1-100wt%.

8. The method for electrolytic synthesis of p-aminophenol without adding a surfactant according to claim 1, wherein: The concentration of the sulfuric acid aqueous solution is 10 to 60 wt%.

9. The method for electrolytic synthesis of p-aminophenol without adding a surfactant according to claim 1, wherein: The reaction temperature is 50-90°C and the reaction current is 30-70 mA / cm 2 , the reaction voltage is 3~5V.

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