A method for preparing amide by coupling low carbon alcohol and nitrate through electro-catalytic anode and cathode

Abstract

The application provides a method for preparing amide by coupling low carbon alcohol and nitrate with electro-catalytic cathode and anode, which comprises the following steps: coating cathode electro-catalyst on both sides of an electrode substrate to obtain an electrode sheet, using the electrode sheet as a cathode and an anode to assemble a single electrolytic cell or a flow electrolytic cell, wherein the cathode electro-catalyst 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 an electrolyte containing nitrate and alkali; and continuously electrolyzing in a constant potential mode to obtain amide. The application realizes the synthesis of amide from nitrate and low carbon alcohol under mild conditions, couples the cathode and anode reactions, utilizes renewable energy for power generation, reduces energy consumption, and reduces carbon emissions, and the yield of propionamide 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 anode-cathode coupling of low-carbon alcohol and nitrate. Background Art

[0002] Amides are widely used in pharmaceuticals, agrochemicals, plastics, polymers, dyes, and emulsifiers. Propionamide, among others, is an important organic chemical used as a pharmaceutical raw material, chemical raw material, pesticide intermediate, and is particularly common in the synthesis of midecamycin. Industrially, it is produced by the reaction of propionic acid and ammonia: ammonia is introduced into a reactor containing n-propionic acid. When the temperature rises to around 140°C, all the propionic acid is converted to ammonium propionate. The ammonia flow is stopped, and the temperature is raised to dehydrate the product, maintaining it at 210-220°C for 1-2 hours to complete the dehydration. Cooling produces crystals, which are filtered to obtain the crude product, which is then recrystallized from ethanol to obtain the finished product. This multi-step process, while providing good yields, also presents certain challenges, such as high raw material costs and high reaction temperatures.

[0003] In recent years, electrocatalysis has been widely used to synthesize a variety of nitrogen-containing organic compounds, including urea, oximes, and ethylamines. Electrocatalysis has become a highly sought-after, environmentally friendly, and efficient synthetic method due to its mild reaction conditions, the sole energy source of renewable energy, and the ability to easily control reaction selectivity and yield by adjusting the potential. The use of electrochemical synthesis methods, using inexpensive and readily available raw materials under mild conditions, has become a very promising yet challenging synthetic route. Summary of the Invention

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

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

[0006] A method for preparing amides by electrocatalytic cathode-cathode coupling of low-carbon alcohols and nitrates comprises 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 the cathode and the 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 nitrate and alkali;

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

[0010] S4 is subjected to continuous electrolysis 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 carrier 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. Preferably, the transition metal oxide is cobalt oxide.

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

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

[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 includes uniformly dispersing the cathode catalyst in a mixed solvent of deionized water, ethanol and 5wt% Nafion solution by ultrasonication to obtain a uniform catalyst slurry, then drop-coating 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. Preferably, the nitrate is sodium nitrate.

[0022] The base includes one or both of potassium carbonate and potassium bicarbonate, with a concentration of 0.05-0.8 mol / L.

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

[0024] The potential in step S4 is within the range of 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 from nitrates and low-carbon alcohols under mild conditions, couples cathode and anode reactions, and utilizes renewable energy to generate electricity, thereby reducing energy consumption and carbon emissions. The propionamide yield 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 with reference to 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. The powder was rapidly stirred and extruded, and then allowed to stand for 2 hours. The powder was transferred to a 50°C oven and dried overnight to remove moisture. The powder was 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 Co3O4 / SiC.

[0030] 10 mg of the above-mentioned Co3O4 / SiC cathode catalyst was uniformly dispersed in 1 mL of a mixed solvent of deionized water, ethanol, and 5 wt% Nafion solution by ultrasonication to obtain a uniform catalyst slurry. 200 μL of the slurry was pipetted and dropped onto both sides of the carbon paper with a coating density of 0.9 mg / cm 2 , dried overnight at 100°C in a vacuum oven, 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. The electrolyte was 50mL of a mixed solution of 0.1M KHCO3 and 1M NaNO3 (pH 8.4), and 3mL of n-propanol was added to the electrolyte. The electrolytic cell voltage was set to 5V, and argon was passed as a protective gas at a speed of 600rpm for 2 hours. After the reaction, liquid nuclear magnetic resonance spectroscopy was used to detect the propionamide product, and the propionamide yield reached 142.37μmol / cm 2 h, the cathode Faradaic efficiency reaches 75%. Nitrate reduction reaction occurs at the cathode to produce NH2OH and NH3 products, which react 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. The powder was rapidly stirred and extruded, and then allowed to stand for 2 hours. The powder was transferred to a 50°C oven and dried overnight to remove moisture. The powder was 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 Co3O4 / SiC.

[0033] 10 mg of the above-mentioned Co3O4 / SiC cathode catalyst was uniformly dispersed in 1 mL of a mixed solvent of deionized water, ethanol, and 5 wt% Nafion solution by ultrasonication to obtain a uniform catalyst slurry. 200 μL of the slurry was pipetted and dropped onto both sides of the carbon paper with a coating density of 0.9 mg / cm 2 , dried overnight at 100°C in a vacuum oven, 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. The electrolyte was 50mL of a mixed solution of 0.5M KHCO3 and 1M NaNO3 (pH 10.3), and 1mL of n-propanol was added to the electrolyte. The electrolytic cell voltage was set to 5V, and argon was passed as a protective gas at a speed of 600rpm for 2 hours. After the reaction, liquid nuclear magnetic resonance spectroscopy was used to detect the propionamide product, and the propionamide yield was 35.782μmol / 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. The electrolyte was a 250 mL mixed solution of 0.1 M KHCO3 and 1 M NaNO3. 15 mL of n-propanol was added to the electrolyte. The electrolyte flow rate was 75 mL / min, the 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] A single electrolytic cell was assembled using the cathode catalyst and platinum sheet in Example 1 as the anode catalyst. The other test conditions were the same. After the reaction, the products were detected by liquid nuclear magnetic resonance spectroscopy, which showed that the products 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 the cathode and the 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 preparing an electrolyte, wherein the electrolyte comprises a nitrate and an alkali; S3 adding a low-carbon alcohol reactant to the electrolyte; S4 uses constant potential mode to continuously electrolyze to obtain amide; The cathode electrocatalyst carrier 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; The titanium-containing anode catalyst includes titanium mesh, platinum-coated titanium felt, titanium felt and titanium oxide.

2. The method for preparing amides by electrocatalytic cathode-cathode coupling of lower alcohols and nitrates according to claim 1, characterized in that: The low-carbon alcohol includes methanol, ethanol or n-propanol.

3. The method for preparing amides by electrocatalytic cathode-cathode coupling of lower alcohols and nitrates according to claim 1, characterized in that: The mass percentage of the transition metal oxide in the catalyst is 0.2-30 wt.%.

4. The method for preparing amides by electrocatalytic cathode-cathode coupling of lower alcohols and nitrates according to claim 1, characterized in that: The coating density of the cathode electrocatalyst on the electrode substrate is 0.5-1.5 mg / cm 2 .

5. The method for preparing amides by electrocatalytic cathode-cathode coupling of lower alcohols and nitrates according to claim 1, characterized in that: The pH of the electrolyte is 8-11.

6. The method for preparing amides by electrocatalytic cathode-cathode coupling of lower alcohols and nitrates according to claim 1 or 5, characterized in that: The concentration of nitrate in the electrolyte is 0.05-1.5 mol / L; and / or, The base includes one or both of potassium carbonate and potassium bicarbonate, with a concentration of 0.05-0.8 mol / L.

7. The method for preparing amides by electrocatalytic cathode-cathode coupling of lower alcohols and nitrates according to claim 1, characterized in that: The volume ratio of the low-carbon alcohol to the electrolyte is 1:50-10:

50.

8. The method for preparing amides by electrocatalytic cathode-cathode coupling of lower alcohols and nitrates according to claim 1, characterized in that: The potential in step S4 is 3-6 V.