A method for the electroreduction synthesis of dmf from carbon dioxide and dimethylamine

Abstract

The application relates to a method for synthesizing DMF by electro-reducing carbon dioxide and dimethylamine, and belongs to the technical field of green organic synthesis. x The application relates to a method for synthesizing DMF by electro-reducing carbon dioxide and dimethylamine, and belongs to the technical field of green organic synthesis. The catalyst is used for the electro-catalytic C-N coupling reaction of dimethylamine and carbon dioxide, and DMF is efficiently synthesized under mild conditions. The catalyst has the advantages of rich active sites, high mass transfer efficiency and good stability, does not need to use a noble metal catalyst, and has the characteristics of low cost, environmental friendliness and easy scale production.

Description

Technical Field

[0001] This invention relates to a method for the electroreduction synthesis of DMF from carbon dioxide and dimethylamine, belonging to the field of green organic synthesis technology. Background Technology

[0002] N,N-Dimethylformamide (DMF) is an extremely important industrial solvent and chemical raw material, widely used in pharmaceuticals, polymer synthesis, and electronic chemical manufacturing. Currently, its industrial production heavily relies on traditional catalytic processes using carbon monoxide or carbon dioxide and dimethylamine as raw materials under high temperature and pressure. This process is energy-intensive and poses safety and environmental risks.

[0003] Patent application CN119425660A relates to a non-precious metal heterogeneous catalyst, its preparation method, and its application. The non-precious metal heterogeneous catalyst comprises an indium-zinc bimetallic oxide and aluminum doped in the indium-zinc bimetallic oxide. The molar amount of indium in the non-precious metal heterogeneous catalyst is 30%–60% of the total molar amount of indium and zinc, and the molar amount of aluminum is 2.5%–10% of the total molar amount of indium, zinc, and aluminum. The application of this non-precious metal heterogeneous catalyst includes its use in the reaction of carbon dioxide, hydrogen, and dimethylamine as raw materials to produce N,N-dimethylformamide. The reaction pressure is ≥3 MPa, the temperature is 230℃, and the volume ratio of hydrogen to carbon dioxide is 1 / 1.

[0004] Patent application CN118702590A relates to a method for preparing N,N-dimethylformamide from flue gas using a carbon-supported silica-bonded metal catalyst. The method uses dimethylamine, CO2, and H2 from the flue gas as raw materials. Under the action of a carbon-supported silica-bonded metal catalyst, the CO2 in the flue gas undergoes a hydrogenation carbonylation reaction to obtain N,N-dimethylformamide. The carbon-supported silica-bonded metal catalyst uses carbon-supported silica as a support, with highly dispersed metal particles bonded to its surface. The catalyst is prepared by hydrolyzing a silicon source on a surfactant-modified graphene oxide surface to prepare the carbon-supported silica support. Then, the surfactant is removed, and amino groups are grafted onto the surface of the fabricated porous structure. Finally, the highly dispersed amino groups are used to bond metal sites to obtain the carbon-supported silica-bonded metal catalyst M-NH2-mSiO2 / GO. Metal M is one or more of Ru, Cu, Zn, Al, Ni, and Fe. In this technology, the reaction pressure is 1.0–8.0 MPa, and the reaction temperature is 120–250 °C.

[0005] This invention uses Cu xUsing O nanowire arrays as electrocatalytic electrodes, DMF is synthesized efficiently via carbon dioxide and dimethylamine at ambient temperature and pressure. The unique array structure of this electrode provides a large electrochemically active surface area and excellent mass transfer channels. Its surface oxide layer further enhances reactant adsorption and CN coupling activity, thereby achieving high Faradaic efficiency and long-term stability. This provides a promising new method for the green, safe, and sustainable production of DMF. Summary of the Invention

[0006] The purpose of this invention is to provide a method for synthesizing N,N-dimethylformamide (DMF) by electrocatalytic CN coupling, which solves the defects of high energy consumption, high emissions and low efficiency of traditional N,N-dimethylformamide synthesis methods, and achieves the goals of low carbon, environmental protection, energy saving and emission reduction.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention discloses a method for the electroreduction synthesis of DMF from carbon dioxide and dimethylamine, using carbon dioxide and dimethylamine as raw materials and Cu... x N,N-dimethylformamide was prepared by electrochemical reaction using an O nanowire array as a catalyst.

[0009] This invention discloses a method for the electroreduction synthesis of DMF from carbon dioxide and dimethylamine, wherein the Cu used... x The O nanowire array is a self-supporting structure, obtained by hot pressing copper foil with a porous anodic aluminum oxide template (AAO template), removing the porous anodic aluminum oxide template, and then chemically oxidizing it.

[0010] During the electrochemical reaction, the concentration of dimethylamine was 0.5–10 mol / L, the concentration of potassium bicarbonate was 0.4–0.6 mol / L, and the current density was 10–60 mA / cm². 2 The reaction time is greater than or equal to 30 minutes.

[0011] Preferably, the electrochemical reaction is carried out at a constant current density.

[0012] The copper foil includes commercial copper foil.

[0013] Preferably, the preparation of the catalyst includes the following steps:

[0014] S1. Clean and dry the copper foil;

[0015] S2. The porous anodized aluminum template is brought into contact with copper foil and then laminated and hot-pressed.

[0016] S3. After hot pressing, the porous anodic aluminum oxide template and copper foil composite are placed in sodium hydroxide solution and stirred to remove the porous anodic aluminum oxide template, thus obtaining a copper nanowire array electrode.

[0017] S4. The copper nanowire array electrode is chemically oxidized in a sodium persulfate / sodium hydroxide mixed solution and then calcined in a tube furnace using argon gas. The morphology and electronic state of the copper nanowire array are further controlled to obtain the Cu... x O nanowire array catalyst.

[0018] In a preferred embodiment, the thickness of the copper foil in step S1 is 0.02~0.1mm.

[0019] In industrial applications, the length and width of the copper foil used in step S1 can be adjusted accordingly; however, the preferred length of the copper foil is 2-5 cm and the width is 2-5 cm.

[0020] In a preferred embodiment, the porous anodic aluminum oxide template in step S2 can be a thin sheet with a diameter of 1.3 to 2.5 cm. As a further preferred embodiment, its thickness is 50 to 100 micrometers.

[0021] In industrial applications, copper foil can be ultrasonically cleaned in anhydrous ethanol and then dried.

[0022] In the preferred embodiment, in S2, the porous anodized aluminum template is placed on the upper and lower surfaces of the copper foil and then laminated and hot-pressed.

[0023] In the preferred embodiment, S2, the hot pressing temperature is 200~500℃, the pressure is 2~5 tons, and the holding time is 5~120min.

[0024] In a preferred embodiment, the concentration of sodium hydroxide solution in step S3 is 0.1 mol / L to 3 mol / L, and the stirring time is 5 to 30 minutes.

[0025] In a preferred embodiment, in step S4, the concentration of sodium persulfate is 0.01 mol / L to 1 mol / L, the concentration of sodium hydroxide is 0.1 mol / L to 3 mol / L, and the chemical oxidation time is 40 s to 9 min, preferably 1 to 5 min. In this invention, excessive oxidation will cause a rapid decrease in the Faraday efficiency of DMF production.

[0026] As a further preferred embodiment, in step S4, the concentration of sodium persulfate is 0.08 mol / L to 0.12 mol / L, and the chemical oxidation time is 4 to 6 min.

[0027] In a preferred embodiment, the calcination temperature in step S4 is 100~400℃ and the calcination time is 30~240 minutes.

[0028] As a further preferred embodiment, the calcination temperature in step S4 is 180~220℃, and the calcination time is 100~140min.

[0029] In industrial applications, the calcination in step S4 can be carried out in a tube furnace, or other sintering furnaces with controllable atmosphere.

[0030] Research has found that by controlling the concentrations of sodium sulfate and sodium hydroxide within the aforementioned ranges, a Cu layer with controllable morphology can be formed on the surface of the copper nanowires described in step S3. x O, the final electrosynthesis Faraday efficiency of DMF is affected by morphology.

[0031] Preferably, the present invention provides a method for synthesizing N,N-dimethylformamide by electrocatalytic CN coupling, comprising the following steps:

[0032] A1. Use an H-type electrolytic cell, with an Ag / AgCl electrode as the reference electrode, a Pt sheet as the counter electrode, and a copper oxide nanowire array electrode as the working electrode.

[0033] A2. Add the supporting electrolyte potassium bicarbonate and the reactant dimethylamine to an H-type electrolytic cell, introduce carbon dioxide gas, and carry out an electrochemical reaction under the condition of electricity.

[0034] During or after the electrochemical reaction, use 1 H-NMR spectroscopy analysis of liquid phase products; using 1 When performing H-NMR spectroscopy analysis on liquid products, the NMR sample is prepared as 500 µL of post-reaction electrolyte + 100 µL of heavy aqueous solution with a concentration of 250 ppm.

[0035] Preferably, the concentration of dimethylamine in step A2 is 0.5~10 mol / L, more preferably 1~8 mol / L, even more preferably 2~6 mol / L, and even more preferably 2~4 mol / L. The concentration of potassium bicarbonate is 0.4~0.6 mol / L, more preferably 0.5 mol / L.

[0036] In step A2, an electrochemical reaction is carried out at a constant current density.

[0037] Preferably, the current density in step A2 is 10~60 mA / cm². 2 The reaction time is greater than or equal to 30 minutes, including 90 to 150 minutes. As a further preferred option, the current density in step A2 is 20 to 40 mA / cm². 2 This includes 30mA / cm 2 .

[0038] The reaction mechanism is as follows: First, carbon dioxide molecules are adsorbed onto Cu x On the surface of the O catalyst, it spontaneously combines with nucleophilic dimethylamine to form carbon-nitrogen bonds. In the generated -OCN... + H(CH3)2O- In the intermediate, a proton from the positively charged nitrogen atom migrates to the negatively charged oxygen atom, forming the -OCN(CH3)2OH intermediate. This compound undergoes electrochemical reduction on the catalyst surface to gain a proton and break the C=O bond to form the -OCHN(CH3)2OH intermediate. This intermediate is ultimately reduced electrochemically, causing the carbon atom in the carbon-nitrogen bond to reach a charge saturation state. Therefore, the oxygen atom accepts an electron to form a C=O bond, thus forming -HCON(CH3)2, which is simultaneously desorbed from the catalyst surface.

[0039] Beneficial effects: 1. Compared with the traditional method of thermocatalytic synthesis of DMF, the catalyst material of this invention uses clean electrical energy, at 30mA / cm 2 At the relevant current density, the Faraday efficiency of synthesized DMF can be 28.32%, and it can maintain a Faraday efficiency of over 20% within an 80-hour production cycle.

[0040] 2. The prepared Cu x The O nanoarray catalyst exhibits good reproducibility and high stability. It enables a low-cost, controllable reaction of carbon dioxide and dimethylamine, facilitating the rational application of renewable energy and the sustainable synthesis of high-value chemicals. Attached Figure Description

[0041] Figure 1 Scanning electron microscope image of the Cu nanowire array prepared in Example 1;

[0042] Figure 2 5 min-P-Cu prepared in Example 1 x O NWs scanning electron microscope image;

[0043] Figure 3 5min-N-Cu prepared in Example 2 x O NWs scanning electron microscope image;

[0044] Figure 4 5min-S-Cu prepared in Example 3 x O NWs scanning electron microscope image;

[0045] Figure 5 To explore the 1min-N-Cu prepared in Case 1 x O NWs scanning electron microscope image;

[0046] Figure 6 To explore the 10 min-N-Cu prepared in Case 2 x O NWs scanning electron microscope image;

[0047] Figure 7 To explore the 1min-P-Cu prepared in Case 3 xO NWs scanning electron microscope image;

[0048] Figure 8 To explore the 10 min-P-Cu prepared in Case 4 x O NWs scanning electron microscope image;

[0049] Figure 9 The Cu foil, Cu nanowire array, and Cu in Example 2 x XRD pattern of O nanowire array;

[0050] Figure 10 Cu in Embodiment 2 of the present invention x The product of CO2 and dimethylamine electroreduction by O array catalyst 1 H NMR spectrum. Detailed Implementation

[0051] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments, but the scope of protection of the present invention is not limited to the following.

[0052] Example 1

[0053] An electrosynthetic DMF Cu x The specific steps for fabricating the O-nanometer array electrode are as follows:

[0054] S1. A porous anodic aluminum oxide template circular sheet (60 μm thick) with a diameter of 1.3 cm was hot-pressed with a Cu foil stack (50 μm thick) at a temperature of 350℃ and a pressure of 3 tons for 60 minutes. The porous anodic aluminum oxide template was removed using a sodium hydroxide concentration of 0.5 mol / L, and the mixture was stirred for 20 minutes. The resulting Cu nanowire array is shown below. Figure 1 As shown.

[0055] S2. The Cu nanowire array from step S1 was placed in a 3 mol / L sodium hydroxide + 0.01 mol / L sodium persulfate solution and allowed to stand for 5 minutes. After that, it was placed in a tube furnace and calcined at 200°C in an argon atmosphere for 2 hours to obtain Cu nanoparticles. x O nanowire arrays such as Figure 2 As shown, a granular structure is formed in situ oxidized on the copper wire, named 5min-P-Cu. x O NWs.

[0056] S3. Using an H-type electrolytic cell, with an Ag / AgCl electrode as the reference electrode and a Pt sheet as the counter electrode, the 5min-P-Cu obtained in S2 was used. x O NWs is the working electrode;

[0057] An electrolyte consisting of 0.5 mol / L potassium bicarbonate and 2 mol / L dimethylamine was added to an H-type electrolytic cell, and high-purity carbon dioxide gas (purity of carbon dioxide greater than or equal to 99.999%, and a carbon dioxide introduction rate of 20 sccm) was continuously introduced to perform constant current polarization (30 mA / cm). 2 The polarization time is 2h, and its Faraday efficiency (FE) is shown in Table 1.

[0058] Table 1. Faradaic efficiency of catalysts prepared with different oxidant concentrations

[0059] The results in Table 1 show that the Faraday efficiency is optimal when the oxidant concentration is 3 mol / L sodium hydroxide + 0.1 mol / L sodium persulfate.

[0060] Example 2

[0061] S1 is the same as S1 in Example 1.

[0062] S2. The Cu nanowire array from step S1 was placed in a 3 mol / L sodium hydroxide + 0.1 mol / L sodium persulfate solution and allowed to stand for 5 minutes. After that, it was placed in a tube furnace and calcined at 200°C in an argon atmosphere for 2 hours to obtain Cu with a higher degree of oxidation. x O nanowire arrays, such as Figure 3 As shown, the needle-like structure formed in situ on the copper wire is named 5min-N-Cu. x O NWs.

[0063] S3. Using an H-type electrolytic cell, with an Ag / AgCl electrode as the reference electrode and a Pt sheet as the counter electrode, the 5min-N-Cu obtained in S2 was used. x O NWs is the working electrode;

[0064] An electrolyte consisting of 0.5 mol / L potassium bicarbonate and 2 mol / L dimethylamine was added to an H-type electrolytic cell, and high-purity carbon dioxide gas (purity of carbon dioxide greater than or equal to 99.999%, and a carbon dioxide introduction rate of 20 sccm) was continuously introduced to perform constant current polarization (30 mA / cm). 2 The polarization time is 2h, and its Faraday efficiency (FE) is shown in Table 1.

[0065] Example 3

[0066] S1 is the same as S1 in Example 1.

[0067] S2. Place the Cu nanowire array from step S1 in a 3 mol / L sodium hydroxide + 0.5 mol / L sodium persulfate solution and let it stand for 5 minutes. After that, place it in a tube furnace and calcine it at 200°C in an argon atmosphere for 2 hours. Figure 4The copper wire shown exhibits in-situ oxidation of a lamellar structure, named 5min-S-Cu. x O NWs.

[0068] S3. Using an H-type electrolytic cell, with an Ag / AgCl electrode as the reference electrode and a Pt sheet as the counter electrode, the 5min-S-Cu obtained in S2 was used. x O NWs is the working electrode;

[0069] An electrolyte consisting of 0.5 mol / L potassium bicarbonate and 2 mol / L dimethylamine was added to an H-type electrolytic cell, and high-purity carbon dioxide gas (purity of carbon dioxide greater than or equal to 99.999%, and a carbon dioxide introduction rate of 20 sccm) was continuously introduced to perform constant current polarization (30 mA / cm). 2 The polarization time is 2h, and its Faraday efficiency (FE) is shown in Table 1.

[0070] Exploring Case 1

[0071] The remaining operations are the same as in Example 2, except that the settling time in step S2 is changed from 5 minutes to 1 minute, resulting in Cu. x O nanowire arrays such as Figure 5 As shown, only a small number of needle-like structures appear at the nanowire head, and the main body of the wire is not fully oxidized, named 1min-N-Cu. x O NWs.

[0072] An H-type electrolytic cell was used, with an Ag / AgCl electrode as the reference electrode and a Pt sheet as the counter electrode. The obtained 1 min-N-Cu... x O NWs is the working electrode;

[0073] An electrolyte consisting of 0.5 mol / L potassium bicarbonate and 2 mol / L dimethylamine was added to an H-type electrolytic cell, and high-purity carbon dioxide gas (purity of carbon dioxide greater than or equal to 99.999%, and a carbon dioxide introduction rate of 20 sccm) was continuously introduced to perform constant current polarization (30 mA / cm). 2 The polarization time is 2h, and its Faraday efficiency (FE) is shown in Table 2.

[0074] Table 2. Faradaic efficiency of catalysts prepared at different oxidation times.

[0075] Explore Case 2

[0076] The remaining operations are the same as in Example 2, except that the settling time in step S2 is changed from 5 minutes to 10 minutes, resulting in Cu. x O nanowire arrays such as Figure 6As shown, when the oxide layer is too thick, adjacent nanowires agglomerate together, greatly reducing the number of active sites. This is named 10min-N-Cu. x O NWs.

[0077] An H-type electrolytic cell was used, with an Ag / AgCl electrode as the reference electrode and a Pt sheet as the counter electrode. The obtained 10 min-N-Cu... x O NWs is the working electrode;

[0078] An electrolyte consisting of 0.5 mol / L potassium bicarbonate and 2 mol / L dimethylamine was added to an H-type electrolytic cell, and high-purity carbon dioxide gas (purity of carbon dioxide greater than or equal to 99.999%, and a carbon dioxide introduction rate of 20 sccm) was continuously introduced to perform constant current polarization (30 mA / cm). 2 The polarization time is 2h, and its Faraday efficiency (FE) is shown in Table 2.

[0079] Explore Case 3

[0080] The remaining operations are the same as in Example 1, except that the settling time in step S2 is changed from 5 minutes to 1 minute, resulting in Cu. x O nanowire arrays such as Figure 7 As shown, only a slight oxide layer was obtained on the surface, named 1min-P-Cu. x O NWs.

[0081] An H-type electrolytic cell was used, with an Ag / AgCl electrode as the reference electrode and a Pt sheet as the counter electrode. The obtained 1 min-P-Cu... x O NWs is the working electrode;

[0082] An electrolyte consisting of 0.5 mol / L potassium bicarbonate and 2 mol / L dimethylamine was added to an H-type electrolytic cell, and high-purity carbon dioxide gas (purity of carbon dioxide greater than or equal to 99.999%, and a carbon dioxide introduction rate of 20 sccm) was continuously introduced to perform constant current polarization (30 mA / cm). 2 The polarization time is 2h, and its Faraday efficiency (FE) is shown in Table 3.

[0083] Table 3. Faradaic efficiency of catalysts prepared by oxidation with low concentration oxidant for different times.

[0084] Explore Case 4

[0085] The remaining operations are the same as in Example 1, except that the settling time in step S2 is changed from 5 minutes to 10 minutes, resulting in Cu. x O nanowire arrays such as Figure 8 As shown, granular Cu particles are still formed on the surface. xO, but the overall oxide layer is thicker, with some strands agglomerated; the catalyst is named 10min-P-Cu. x O NWs.

[0086] An H-type electrolytic cell was used, with an Ag / AgCl electrode as the reference electrode and a Pt sheet as the counter electrode. The obtained 10 min-P-Cu... x O NWs is the working electrode;

[0087] An electrolyte consisting of 0.5 mol / L potassium bicarbonate and 2 mol / L dimethylamine was added to an H-type electrolytic cell, and high-purity carbon dioxide gas (purity of carbon dioxide greater than or equal to 99.999%, and a carbon dioxide introduction rate of 20 sccm) was continuously introduced to perform constant current polarization (30 mA / cm). 2 The polarization time is 2h, and its Faraday efficiency (FE) is shown in Table 3.

[0088] Explore Case 5

[0089] The remaining operations were the same as in Example 2, except that the concentration of dimethylamine in step S3 was changed to 0.5 mol / L, 1 mol / L, 2 mol / L, 6 mol / L, and 8 mol / L, respectively, to investigate the effect of different concentrations of dimethylamine in electrolyte preparation on DMF synthesis. The Faraday efficiency (FE) is shown in Table 4.

[0090] Table 4. Faradaic efficiency of DMF synthesis with different concentrations of dimethylamine

[0091] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims, and modifications may be made to the present invention in any form without departing from its basic structure.

Claims

1. A method for the electroreduction synthesis of DMF from carbon dioxide and dimethylamine, characterized in that: Using carbon dioxide and dimethylamine as raw materials, and Cu x N,N-dimethylformamide was prepared by electrochemical reaction using an O nanowire array as a catalyst. The Cu used x The O nanowire array is a self-supporting structure, obtained by hot pressing copper foil with a porous anodic aluminum oxide template, removing the porous anodic aluminum oxide template and then chemically oxidizing it. The Cu used x O nanowire arrays were prepared through the following steps; S1. Clean and dry the copper foil; S2. The porous anodized aluminum template is brought into contact with copper foil and then laminated and hot-pressed. S3. After hot pressing, the porous anodic aluminum oxide template and copper foil composite are placed in sodium hydroxide solution and stirred to remove the porous anodic aluminum oxide template, thus obtaining a copper nanowire array electrode. S4. The copper nanowire array electrode is chemically oxidized in a sodium persulfate / sodium hydroxide mixed solution and calcined under an argon atmosphere; in step S4, the concentration of sodium persulfate is 0.08 mol / L~0.12 mol / L, the concentration of sodium hydroxide is 0.1 mol / L~3 mol / L, and the chemical oxidation time is 4~6 min; in step S4, the calcination temperature is 180~220℃, and the calcination time is 100~140 min.

2. The method for electroreduction synthesis of DMF from carbon dioxide and dimethylamine according to claim 1, characterized in that: In step S1, the thickness of the copper foil is 0.02~0.1mm; the thickness of the porous anodized aluminum template is 50~100 micrometers.

3. The method for electroreduction synthesis of DMF from carbon dioxide and dimethylamine according to claim 1, characterized in that: In S2, porous anodized aluminum templates are placed on the upper and lower surfaces of copper foil and then hot-pressed in layers.

4. The method for electroreduction synthesis of DMF from carbon dioxide and dimethylamine according to claim 1, characterized in that: In S2, the hot pressing temperature is 200~500℃, the pressure is 2~5 tons, and the holding time is 5~120min.

5. The method for electroreduction synthesis of DMF from carbon dioxide and dimethylamine according to claim 1, characterized in that: In step S3, the concentration of the sodium hydroxide solution is 0.1 mol / L to 3 mol / L, and the stirring time is 5 to 30 minutes.

6. A method for the electroreduction synthesis of DMF from carbon dioxide and dimethylamine according to any one of claims 1-5, characterized in that: Includes the following steps: A1. Using an H-type electrolytic cell, with an Ag / AgCl electrode as the reference electrode, a Pt sheet as the counter electrode, and Cu... x O nanowire arrays serve as working electrodes; A2. Add the supporting electrolyte potassium bicarbonate and the reactant dimethylamine to an H-type electrolytic cell, introduce carbon dioxide gas, and carry out an electrochemical reaction under the condition of electricity.

7. The method for electroreduction synthesis of DMF from carbon dioxide and dimethylamine according to claim 6, characterized in that: In step A2, the electrochemical reaction is carried out at a constant current density; the current density in step A2 is 10~60 mA / cm². 2 The reaction time is greater than or equal to 30 minutes. In step A2, the concentration of dimethylamine is 0.5~10 mol / L, and the concentration of potassium bicarbonate is 0.4~0.6 mol / L.

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