Method for preparing amide by coupling low-carbon alcohol and nitrate through electrocatalytic cathode and anode

Abstract

The invention provides a method for preparing amide by coupling low-carbon alcohol and nitrate through electrocatalysis of a cathode and an anode, which comprises the following steps: coating two sides of an electrode substrate with a cathode electrocatalyst to obtain an electrode slice, and assembling a single electrolytic tank or a flowing electrolytic tank by taking the electrode slice as a cathode and an anode, the cathode electrocatalyst comprises a carrier and a transition metal oxide loaded on the carrier, and the anode is a titanium-containing anode catalyst; adding a low-carbon alcohol reactant into the electrolyte containing nitrate and alkali; and continuously electrolyzing in a constant potential manner to obtain amide. According to the method, under mild conditions, amide synthesis by using nitrate and low-carbon alcohol, coupled cathode and anode reaction and power generation by using renewable energy sources are realized, the energy consumption is reduced, the carbon emission is reduced, the propionamide yield reaches 1.8 mmol / cm < 2 > h, and the cathode Faraday efficiency reaches 82%.

Description

Technical Field

[0001] The invention belongs to the technical field of amide preparation, and in particular relates to a method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate. Background Art

[0002] Amides are widely used in medicine, agricultural chemicals, plastics, polymers, dyes and emulsifiers. Among them, propionamide is an important organic chemical that can be used as pharmaceutical raw materials, chemical raw materials, pesticide intermediates, etc. It is especially common in the synthesis of midecamycin drugs. In industry, it is obtained by the reaction of propionic acid and ammonia: ammonia is introduced into a reactor with propionic acid. When the temperature rises to about 140°C, all propionic acid generates ammonium propionate. Stop passing ammonia, increase the temperature for dehydration, and maintain it at 210-220°C for 1-2h to complete the dehydration. Cool down the crystals, filter the crude product, and then recrystallize it with ethanol to obtain the finished product. This process adopts a multi-step method. Although it has a good yield, it also has certain problems, such as high raw material costs and high reaction temperatures.

[0003] In recent years, electrocatalysis has been widely used in the synthesis of various nitrogen-containing organic compounds, including urea, oxime, ethylamine, etc. The electrocatalytic method has become a highly anticipated environmentally friendly and efficient synthesis method due to its mild reaction conditions, renewable energy generation as the only energy source, and the ability to easily regulate reaction selectivity and yield by adjusting the potential. The use of electrochemical synthesis methods to synthesize amides under mild conditions with cheap and readily available raw materials has become a very promising and challenging synthetic route. Summary of the invention

[0004] In order to solve the above technical problems, the present invention uses low-carbon alcohol and nitrate as reactants, and obtains amide with high yield and Faraday efficiency through electrocatalytic cathode and anode coupling.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate, comprising the following steps:

[0007] S1: coating a cathode electrocatalyst on both sides of an electrode substrate to obtain an electrode sheet, and assembling a single electrolytic cell or a flow electrolytic cell with the electrode sheet as a cathode and an anode; the cathode electrocatalyst includes a carrier and a transition metal oxide supported on the carrier; and the anode is a titanium-containing anode catalyst;

[0008] S2 prepares an electrolyte, wherein the electrolyte comprises a nitrate and an alkali;

[0009] S3 adding a low-carbon alcohol reactant to the electrolyte;

[0010] S4 is continuously electrolyzed in a constant potential manner to obtain amide.

[0011] The low-carbon alcohol includes methanol, ethanol or n-propanol; when the low-carbon alcohol is methanol, formamide is obtained; when the low-carbon alcohol is ethanol, acetamide is obtained; and when the low-carbon alcohol is n-propanol, propionamide is obtained.

[0012] The cathode catalyst supports include SiC, Ketjen black, silicon nitride and SiO 2 The transition metal oxide includes one or more of iron oxide, copper oxide, cobalt oxide and nickel oxide. Preferably, the transition metal oxide is cobalt oxide.

[0013] The mass percentage of the transition metal oxide in the catalyst is 0.2-30wt.%.

[0014] The cathode catalyst is obtained by dispersing a transition metal salt aqueous solution into a carrier for impregnation, followed by drying and calcining.

[0015] The transition metal salt is one or more of chloride, nitrate and acetate.

[0016] The calcination temperature is 250-800° C., and the calcination time is 0.5-4 hours.

[0017] The coating density of the cathode catalyst on the electrode substrate is 0.5-1.5 mg / cm 2 .

[0018] The preparation method of the electrode sheet specifically comprises uniformly dispersing the cathode catalyst in a mixed solvent of deionized water, ethanol and 5wt% Nafion solution by ultrasonic to obtain uniform catalyst slurry, then dripping the catalyst slurry on both sides of carbon paper and drying.

[0019] The titanium-containing anode catalyst comprises one of titanium mesh, platinum-coated titanium felt, platinum sheet, titanium felt and titanium oxide; it is ultrasonically cleaned with deionized water and ethanol respectively and then dried before use; preferably, the anode catalyst is titanium mesh.

[0020] The pH of the electrolyte is 8-11.

[0021] The concentration of nitrate in the electrolyte is 0.05-1.5 mol / L, and preferably, the nitrate is sodium nitrate.

[0022] The alkali includes one or both of potassium carbonate and potassium bicarbonate, and the concentration is 0.05-0.8 mol / L.

[0023] The volume ratio of low-carbon alcohol to electrolyte is 1:50-10:50.

[0024] The potential in step S4 includes 3-6V.

[0025] Compared with the prior art, the present invention has the following outstanding features:

[0026] The present invention realizes the synthesis of amides using nitrates and low-carbon alcohols under mild conditions, coupling cathode and anode reactions, and using renewable energy to generate electricity, thereby reducing energy consumption and carbon emissions. The yield of propionamide reaches 1.8 mmol / cm 2 h, cathode Faradaic efficiency reaches 82%. DETAILED DESCRIPTION

[0027] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the present invention is further described in detail below in conjunction with specific embodiments.

[0028] Example 1

[0029] At room temperature, a 0.278 mol / L cobalt nitrate solution was prepared, and 60 μL of the above solution was dispersed into 0.25 g of SiC solid powder by an equal volume impregnation method, and then quickly stirred and extruded, and then allowed to stand for 2 hours, transferred to a 50°C oven to dry overnight to dry the moisture, and then calcined in an air atmosphere at a heating rate of 5°C / min and calcined at 600°C for 2 hours to obtain a cathode catalyst, which was recorded as Co 3 O 4 / SiC.

[0030] 10 mg of the above Co 3 O 4 The SiC cathode catalyst was uniformly dispersed in 1 mL of a mixed solvent of deionized water, ethanol, and 5 wt% Nafion solution by ultrasound to obtain a uniform catalyst slurry. 200 μL of the slurry was applied to both sides of the carbon paper using a pipette, with a coating surface density of 0.9 mg / cm 2 , dried overnight in a vacuum oven at 100°C, and the obtained electrode sheet was used as the cathode. The titanium mesh (anode catalyst) was ultrasonically cleaned in deionized water and ethanol for 10 minutes respectively, and then dried to serve as the anode. A single electrolytic cell was assembled using the above cathode and anode, and the electrolyte was 0.1M KHCO 3 and 1M NaNO 3 50 mL of the mixed solution (pH 8.4) was added to the electrolyte, and 3 mL of n-propanol was added to the electrolyte. The cell voltage was set to 5 V, and the reaction was carried out at 600 rpm with argon as the protective gas for 2 hours. After the reaction, liquid nuclear magnetic resonance spectroscopy was used to detect the propionamide product, and the propionamide yield reached 142.37 μmol / cm 2 h, the cathode Faraday efficiency reaches 75%. Nitrate reduction reaction occurs at the cathode to generate NH 2 OH and NH 3 The product reacts with propionaldehyde produced by oxidation of n-propanol at the anode to further synthesize propionamide.

[0031] Example 2

[0032] At room temperature, a 0.278 mol / L cobalt nitrate solution was prepared, and 60 μL of the above solution was dispersed into 0.25 g of SiC solid powder by an equal volume impregnation method, and then quickly stirred and extruded, and then allowed to stand for 2 hours, transferred to a 50°C oven to dry overnight to dry the moisture, and then calcined in an air atmosphere at a heating rate of 5°C / min and calcined at 600°C for 2 hours to obtain a cathode catalyst, which was recorded as Co 3 O 4 / SiC.

[0033] 10 mg of the above Co 3 O 4 The SiC cathode catalyst was uniformly dispersed in 1 mL of a mixed solvent of deionized water, ethanol, and 5 wt% Nafion solution by ultrasound to obtain a uniform catalyst slurry. 200 μL of the slurry was applied to both sides of the carbon paper using a pipette, with a coating surface density of 0.9 mg / cm 2 , dried overnight in a vacuum oven at 100°C, and the obtained electrode sheet was used as the cathode. The titanium mesh (anode catalyst) was ultrasonically cleaned in deionized water and ethanol for 10 minutes respectively, and then dried to serve as the anode. A single electrolytic cell was assembled using the above cathode and anode, and the electrolyte was 0.5M KHCO 3 and 1M NaNO 3 50 mL of the mixed solution (pH 10.3) was added to the electrolyte, and 1 mL of n-propanol was added to the electrolyte. The cell voltage was set to 5 V, and the reaction was carried out at 600 rpm with argon as the protective gas for 2 hours. After the reaction, liquid nuclear magnetic resonance spectroscopy was used to detect the propionamide product, and the propionamide yield was 35.782 μmol / cm 2 h, the cathode Faradaic efficiency is 29.8%.

[0034] Example 3

[0035] The cathode and anode in Example 1 were used to assemble a flow electrolytic cell, and the electrolyte was 0.1 M KHCO 3 and 1M NaNO 3 250 mL of the mixed solution was added, and 15 mL of n-propanol was added to the electrolyte. The electrolyte flow rate was 75 mL / min, the electrolytic cell voltage was set to 5 V, and the reaction was carried out for 2 hours. After the reaction, liquid nuclear magnetic resonance spectroscopy was used to detect the propionamide product, and the propionamide yield reached 1800 μmol / cm 2 h, cathode Faradaic efficiency reaches 82%.

[0036] Comparative Example 1

[0037] The cathode catalyst and platinum sheet in Example 1 were used as anode catalysts to assemble a single electrolytic cell. The other test conditions were the same. After the reaction, liquid nuclear magnetic resonance spectroscopy was used to detect the products, which were mainly propionic acid generated by oxidation of propanol and ammonia generated by reduction of cathode nitrate, with basically no propionamide product.

Claims

1. A method for preparing amides by electrocatalytic cathode-cathode coupling of low-carbon alcohols and nitrates, characterized in that: The following steps are involved: S1: coating a cathode electrocatalyst on both sides of an electrode substrate to obtain an electrode sheet, and assembling a single electrolytic cell or a flow electrolytic cell with the electrode sheet as a cathode and an anode; the cathode electrocatalyst includes a carrier and a transition metal oxide supported on the carrier; and the anode is a titanium-containing anode catalyst; S2 prepares an electrolyte, wherein the electrolyte comprises a nitrate and an alkali; S3 adding a low-carbon alcohol reactant to the electrolyte; S4 is continuously electrolyzed in a constant potential manner to obtain amide.

2. The method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate as claimed in claim 1, characterized in that: The low-carbon alcohol includes methanol, ethanol or n-propanol.

3. The method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate as claimed in claim 1, characterized in that: The carrier of the cathode catalyst includes one or more of SiC, Ketjen black, silicon nitride and SiO2; the transition metal oxide includes one or more of iron oxide, copper oxide, cobalt oxide and nickel oxide.

4. The method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate as claimed in claim 1, characterized in that: The mass percentage of the transition metal oxide in the catalyst is 0.2-30wt.%.

5. The method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate as claimed in claim 1, characterized in that: The coating density of the cathode catalyst on the electrode substrate is 0.5-1.5 mg / cm 2 .

6. The method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate as claimed in claim 1, characterized in that: The titanium-containing anode catalyst includes titanium mesh, platinum-coated titanium felt, titanium felt and titanium oxide.

7. The method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate as claimed in claim 1, characterized in that: The pH of the electrolyte is 8-11.

8. A method for preparing amides by electrocatalytic cathode-cathode coupling of low-carbon alcohols and nitrates as claimed in claim 1 or 7, characterized in that: The concentration of nitrate in the electrolyte is 0.05-1.5 mol / L; and / or, The alkali includes one or both of potassium carbonate and potassium bicarbonate, and the concentration is 0.05-0.8 mol / L.

9. The method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate as claimed in claim 1, characterized in that: The volume ratio of low-carbon alcohol to electrolyte is 1:50-10:

50.

10. The method for preparing amide by electrocatalytic cathode-cathode coupling of low-carbon alcohol and nitrate as claimed in claim 1, characterized in that: The potential in step S4 includes 3-6V.