A process for the preparation of N,N-dimethylformamide

Abstract

The application provides a preparation method of N,N-dimethylformamide (DMF). The method uses carbon dioxide, hydrogen and dimethylamine as reaction raw materials, and N,N-dimethylformamide is prepared through N-formylation of carbon dioxide under the action of a catalyst. The method uses an oxide supported transition metal as the catalyst, the catalyst composition and the preparation method are simple and low in cost, the reaction is carried out in a fixed bed reactor, the reaction continuity is good, the catalyst and the reaction system are easy to separate, the catalyst is convenient to recycle, the reaction condition is relatively mild, the conversion rate of dimethylamine and the selectivity of DMF are high, and the method provides an economic, environment-friendly and effective way for the synthesis of DMF.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide utilization, and specifically relates to a method for preparing N,N-dimethylformamide. Background Technology

[0002] CO2 is the most abundant greenhouse gas in the atmosphere, and its excessive emissions have had a serious impact on the global climate and environment. At the same time, CO2 is also considered a cheap, abundant, non-toxic, and renewable C1 resource. Catalytically converting CO2 into high-value-added chemicals can not only alleviate the predicament of humankind's long-term dependence on fossil resources, but also effectively reduce CO2 emissions.

[0003] N,N-Dimethylformamide (DMF) is a chemical that serves as an important intermediate in pharmaceuticals, pesticides, and organic synthesis. It can also be used directly as a solvent, earning it the nickname "universal solvent." It has a wide range of applications in leather, fiber, pharmaceuticals, petrochemicals, electronics, dyes, coatings, and metal processing.

[0004] Currently, the industrial synthesis of DMF mainly utilizes the direct reaction of dimethylamine and carbon monoxide catalyzed by sodium methoxide, a method widely adopted by large-scale enterprises both domestically and internationally. However, this method generates side reactions during actual production, producing odorous byproducts such as methylformamide and dimethylacetamide, as well as solid crystalline salts such as sodium formate, sodium bicarbonate, sodium carbonate, and sodium hydroxide. During continuous production, these crystalline salts accumulate, causing pipeline blockages. Therefore, periodic shutdowns are necessary for solid deposit removal and equipment maintenance, increasing production costs and being environmentally unfriendly. Furthermore, the carbon monoxide used in this production method primarily comes from non-renewable fossil resources, resulting in large consumption volumes in large-scale DMF production, which is detrimental to long-term sustainable development.

[0005] Therefore, if DMF can be prepared using cheap, abundant and safe CO2, it is undoubtedly a green and sustainable development approach. It can reduce CO2 emissions and produce no odorous byproducts, which is an effective way to solve the energy and environmental problems in DMF production.

[0006] Currently, some progress has been made in the preparation of N,N-dimethylformamide by carbon dioxide hydrogenation coupled with dimethylamine. For example, Ding et al. (CN 105985254A, CN 109553641A) used the relatively expensive dimethylamine carbon dioxide salt (DIMCARB) as the amine source and Ru complex as the catalyst to synthesize DMF in organic solvents or under solvent-free conditions. Yoon et al. (ChemSusChem, 2020, 13(7):1735.) coordinated RuCl3 with phosphine-based porous organic polymers to form Ru@PP-POP catalyst for CO2 to synthesize DMF. Tu et al. (Chem.Asian J., 2018, 13(20):3018.) used azacarbene (NHC) to coordinate Ir to generate NHC-Ir solid molecular catalyst to efficiently catalyze various aminoformylation reactions, among which the isolated yield of DMF synthesized from DIMCARB was 53%. Most reported catalysts are homogeneous systems, often using precious metals as active components. The ligands used are also expensive, and the catalyst preparation methods are complex, resulting in high costs. Furthermore, the reaction methods are mostly batch reactors, with harsh reaction conditions, difficult catalyst recovery, low recycling efficiency, and poor production continuity. Therefore, there is an urgent need to develop an economical, environmentally friendly, and efficient method for preparing N,N-dimethylformamide to meet the needs of continuous industrial production of DMF from carbon dioxide. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing N,N-dimethylformamide. The provided method can use carbon dioxide as a raw material to achieve economical, environmentally friendly, and efficient continuous preparation of N,N-dimethylformamide, and the process route is simple.

[0008] This invention provides a method for preparing N,N-dimethylformamide, the method comprising the following steps: CO2, H2 and dimethylamine react in contact under the presence of a catalyst to obtain N,N-dimethylformamide.

[0009] Furthermore, according to some specific embodiments of the present invention, the catalyst comprises a support and an active metal component, wherein the support is at least one of inorganic refractory oxides, preferably one or more of CeO2, Al2O3, TiO2, ZrO2, and MgO; and the active metal component is a transition metal, preferably at least one of Co, Ni, Cu, and Zn.

[0010] Furthermore, according to some specific embodiments of the present invention, the catalyst is a supported catalyst, and the transition metal exists in elemental form on the oxide support.

[0011] Furthermore, according to some specific embodiments of the present invention, the transition metal component, based on the weight of the catalyst, has a mass content of 1% to 30%, preferably 5% to 15%, in terms of elemental mass.

[0012] Furthermore, according to some specific embodiments of the present invention, the reaction is preferably carried out in a fixed-bed reactor, wherein the catalyst is packed inside the fixed-bed reactor.

[0013] Furthermore, according to some specific embodiments of the present invention, the reaction temperature for the reaction of CO2, H2 and dimethylamine is 150-350°C, preferably 200-300°C; the reaction pressure is 0.5-6 MPa, preferably 2-5 MPa.

[0014] Furthermore, according to some specific embodiments of the present invention, the total gas volume hourly space velocity (VHSV) after mixing carbon dioxide and hydrogen is 300–12000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 0.1–10 h⁻¹. -1 .

[0015] Furthermore, according to some specific embodiments of the present invention, the molar ratio of carbon dioxide to hydrogen is 0.2 to 2.

[0016] Furthermore, according to some specific embodiments of the present invention, before CO2, H2 and dimethylamine react in contact, it is preferable to first purge the reactor with an inert gas. After the treatment is completed, the pressure is adjusted to the required reaction pressure (e.g., by introducing CO2 and H2). Then, liquid dimethylamine is introduced and vaporized online through a vaporizer. The vaporized dimethylamine is then mixed with CO2 and H2 through a preheater and introduced into a fixed-bed reactor for reaction to obtain N,N-dimethylformamide.

[0017] Furthermore, according to some specific embodiments of the present invention, the catalyst can be prepared by one or more of the following methods: complexation, co-precipitation, and impregnation.

[0018] In a further preferred embodiment, the catalyst preparation using the complexation method includes the following steps: dissolving a transition metal-containing precursor and a support precursor together in water to prepare a corresponding mixed salt solution; then adding a complexing agent to the mixed salt solution; heating the solution to allow the reaction to proceed until a viscous gel-like substance is obtained; and further drying, calcining, and reduction treatments are performed to obtain the catalyst.

[0019] Furthermore, the transition metal-containing precursor is at least one of a transition metal-containing salt and a transition metal-containing hydroxide; wherein the transition metal-containing salt is a soluble salt, specifically including but not limited to one or more of nitrates, acetates, sulfates, halides, etc., preferably one or more of nitrates and sulfates. The concentration of the soluble salt solution is 0.1–1 mol / L.

[0020] Furthermore, the carrier precursor is a soluble salt containing the corresponding metal element in the carrier, specifically including but not limited to one or more of nitrates, acetates, sulfates, halides, etc., preferably one or more of nitrates and sulfates. The concentration of the soluble salt solution containing the corresponding metal element in the carrier is 0.1–1 mol / L.

[0021] Furthermore, the complexing agent can be at least one of citric acid, ethylenediamine, glucose, and disodium ethylenediaminetetraacetate, preferably citric acid; the concentration of the aqueous solution of the complexing agent is generally 0.5 to 3 mol / L, and the molar ratio of the complexing agent to all metal ions is 0.5 to 3.

[0022] Furthermore, the reaction temperature is 70–90°C, and the reaction is preferably carried out under stirring conditions.

[0023] Furthermore, the drying temperature is 60–150℃, and the drying time is 1–24 hours.

[0024] Furthermore, the calcination temperature is 250–800℃, and the calcination time is 2–24 hours.

[0025] Furthermore, the reduction treatment is carried out in the presence of hydrogen, the reduction treatment temperature is 200-500℃, the reduction treatment time is 0.5-2h, and more preferably the heating rate is controlled at 5-10℃ / min.

[0026] In a further preferred embodiment, when the catalyst is prepared by co-precipitation, the following steps are included: dissolving the precursor containing the transition metal and the support precursor together in water to prepare a corresponding mixed salt solution; then adding the precipitant to the mixed salt solution to carry out a co-precipitation reaction (preferably, after the reaction, a static or stirring aging treatment can also be performed); and then obtaining the catalyst after further separation, washing, drying, calcination, and reduction treatment.

[0027] Furthermore, the transition metal-containing precursor is at least one of a transition metal-containing salt and a transition metal-containing hydroxide; wherein the transition metal-containing salt is a soluble salt, specifically including but not limited to one or more of nitrates, acetates, sulfates, halides, etc., specifically one or more of nitrates and sulfates. The concentration of the soluble salt solution is 0.1–1 mol / L.

[0028] Furthermore, the carrier precursor is a soluble salt containing the corresponding metal element in the carrier, specifically including but not limited to one or more of nitrates, acetates, sulfates, halides, etc., specifically one or more of nitrates and sulfates. The concentration of the soluble salt solution is 0.1–1 mol / L.

[0029] Furthermore, the precipitant includes, but is not limited to, at least one of sodium carbonate, potassium carbonate, ammonium carbonate, ammonia, sodium hydroxide, and potassium hydroxide. The concentration of the precipitant solution is 0.1–2 mol / L.

[0030] Furthermore, the separation is a solid-liquid separation, which can be achieved by one or more of the existing technologies that can achieve solid-liquid two-phase separation, such as filtration, centrifugation, and vacuum filtration.

[0031] Furthermore, the washing is a water wash, specifically washing the precipitate with deionized water until the filtrate is neutral.

[0032] Furthermore, the co-precipitation temperature is 25–70°C, and the precipitant is added dropwise to co-precipitate until the pH of the resulting suspension is 6–12.

[0033] Furthermore, the aging temperature is 25–70℃, and the aging time is 0.5–6 hours.

[0034] Furthermore, the drying temperature is 60–150℃, and the drying time is 1–24 hours.

[0035] Furthermore, the calcination temperature is 250–800℃, and the calcination time is 2–24 hours.

[0036] Furthermore, the reduction treatment is carried out in the presence of hydrogen, the reduction treatment temperature is 200-500℃, the reduction treatment time is 0.5-2h, and more preferably the heating rate is controlled at 5-10℃ / min.

[0037] In a further preferred embodiment, when the catalyst is prepared by impregnation, the following steps are included: impregnating the support in a solution containing a transition metal precursor, and after impregnation, obtaining the catalyst by separation, drying, calcination, and reduction treatment.

[0038] Furthermore, the transition metal-containing precursor is at least one of a transition metal-containing salt and a transition metal-containing hydroxide; wherein the transition metal-containing salt is a soluble salt, specifically including but not limited to one or more of nitrates, acetates, sulfates, halides, etc., preferably one or more of nitrates and sulfates. The concentration of the soluble salt solution is 0.1–3 mol / L.

[0039] Furthermore, the carrier is at least one of inorganic refractory oxides, preferably one or more of CeO2, Al2O3, TiO2, ZrO2, and MgO; the oxide carrier includes, but is not limited to, commercially available oxide carriers, or oxides prepared using corresponding nitrates, acetates, sulfates, chlorides, etc.

[0040] Furthermore, the impregnation process is carried out under stirring conditions, preferably after ultrasound; the impregnation stirring temperature is 25-70℃, and the impregnation time is 1-24h.

[0041] Furthermore, the separation is a solid-liquid separation, which can be achieved by one or more of the existing technologies that can achieve solid-liquid two-phase separation, such as heating and evaporation, filtration, centrifugation, and vacuum filtration.

[0042] Furthermore, the drying temperature is 60–150℃, and the drying time is 1–24 hours.

[0043] Furthermore, the calcination temperature is 250–800℃, and the calcination time is 2–24 hours.

[0044] Furthermore, the reduction treatment is carried out in the presence of hydrogen, the reduction treatment temperature is 200-500℃, the reduction treatment time is 0.5-2h, and more preferably the heating rate is controlled at 5-10℃ / min.

[0045] Compared with the prior art, the method for preparing N,N-dimethylformamide provided by the present invention has the following beneficial effects:

[0046] The method for preparing N,N-dimethylformamide provided by this invention utilizes inexpensive, abundant, and safe carbon dioxide as a raw material in a continuous fixed-bed reactor. This heterogeneous catalytic reaction system allows for easy catalyst recovery, and the catalyst used is a supported, non-precious metal-based catalyst. The preparation method is simple, the catalyst cost is low, and it is beneficial for industrial applications. Furthermore, it represents a green and sustainable development approach, achieving CO2 emission reduction without generating odorous byproducts, thus effectively addressing the energy and environmental problems associated with DMF production.

[0047] The method for preparing N,N-dimethylformamide provided by this invention has good reaction continuity, mild reaction conditions, high dimethylamine conversion and DMF selectivity, and the catalyst is easy to separate from the reactants and products, providing an economical, environmentally friendly and effective route for the synthesis of DMF. Detailed Implementation

[0048] The embodiments of the present invention will be described in further detail below with reference to examples. These examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0049] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0050] In this document, the terms "first," "second," etc., are used to distinguish two different elements or parts, and are not used to define specific positions or relative relationships. In other words, in some embodiments, the terms "first," "second," etc., can also be used interchangeably.

[0051] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0052] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0053] In the context of this invention, all numerical values ​​of parameters (e.g., quantities or conditions) should be understood to be modified by the term "about" in all cases, regardless of whether "about" actually appears before the numerical value. The endpoints of the disclosed ranges and any values ​​are not limited to the precise ranges or values, but should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of the various ranges, endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0054] In the context of this invention, "substantially" means that deviations that are acceptable or considered reasonable to those skilled in the art are permitted, such as deviations within ±5%, ±2%, ±1%, ±0.5%, or ±0.1%.

[0055] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this instruction manual are based on weight, and the pressure is gauge pressure.

[0056] In the context of this invention, any two or more embodiments or aspects of this invention can be arbitrarily combined, and the resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of this invention.

[0057] In the context of this invention, the dimethylamine conversion rate is calculated using the following formula:

[0058]

[0059] In the context of this invention, DMF selectivity is calculated using the following formula:

[0060]

[0061] Example 1

[0062] Catalyst preparation: 8.43 g Cu(NO3)2·3H2O and 50.46 g Ce(NO3)3·6H2O were weighed and dissolved in 200 mL of deionized water to prepare a mixed aqueous solution of copper nitrate and cerium nitrate. Then, 200 mL of 1.5 mol / L citric acid aqueous solution was added while stirring at 40 °C. The temperature was then raised to 80 °C and the solution was continuously stirred to evaporate the water until it became a viscous gel. The resulting gel was dried in an oven at 110 °C for 12 h, ground into a fine powder, and calcined at 400 °C in air for 3 h. Then, hydrogen gas was introduced and the catalyst was reduced at 300 °C for 1 h to obtain the final catalyst sample, denoted as 10Cu / CeO2(CA).

[0063] Preparation of N,N-dimethylformamide: The obtained catalyst was compressed into tablets and sieved to a mesh size of 20-40. 10 mL of the sieved catalyst was then loaded into a stainless steel reaction tube, with magnetic balls inserted at both ends for fixation. Nitrogen gas was then introduced for purging. After purging, CO2 and H2 were introduced, and the total reaction pressure was adjusted to 3 MPa using a back pressure valve. Liquid dimethylamine was then introduced using a dual-plunger pump and vaporized online via a vaporizer. The vaporized dimethylamine was mixed with CO2 and H2 in a preheater and then introduced into a fixed-bed reactor. The reactor was prepared at 250 °C, 3 MPa, CO2:H2 = 1:1, and a total gas hourly space velocity (GHSV) of 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The reaction was carried out under the specified conditions. The results after 48 hours of reaction are shown in Table 1.

[0064] Example 2

[0065] Example 1 was repeated, but in the catalyst preparation process, Ce(NO3)3·6H2O was replaced with 40.05g TiOSO4·xH2O, and the final catalyst was designated as 10Cu / TiO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 280℃, 3MPa, CO2:H2 = 1:1.5, and the total gas hourly space velocity (GHSV) of CO2 and H2 was 8000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0066] Example 3

[0067] Example 1 was repeated, but in the catalyst preparation process, Ce(NO3)3·6H2O was replaced with 69.68g Zr(NO3)4·5H2O, and the final catalyst was designated as 10Cu / ZrO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 250℃, 3MPa, CO2:H2 = 1:1.5, and the total gas hourly space velocity (GHSV) of CO2 and H2 was 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 4 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0068] Example 4

[0069] Example 1 was repeated, but in the catalyst preparation process, Ce(NO3)3·6H2O was replaced with 147.17g Al(NO3)3·9H2O, and the final catalyst was designated as 10Cu / Al2O3(CA). The reaction conditions for preparing N,N-dimethylformamide were 280℃, 3MPa, CO2:H2 = 1:2, and the total gas hourly space velocity (GHSV) of CO2 and H2 was 8000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 4 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0070] Example 5

[0071] Example 1 was repeated, but in the catalyst preparation process, Ce(NO3)3·6H2O was replaced with 127.21 g Mg(NO3)2·6H2O, and the final catalyst was denoted as 10Cu / MgO(CA). The reaction conditions for preparing N,N-dimethylformamide were 300 °C, 3 MPa, CO2:H2 = 1:2, and the total gas hourly space velocity (VHSV) of CO2 and H2 was 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0072] Example 6

[0073] Example 1 was repeated, but in the catalyst preparation process, Cu(NO3)2·3H2O was replaced with 10.99g Ni(NO3)2·6H2O, and the final catalyst was denoted as 10Ni / CeO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 250℃, 3MPa, CO2:H2 = 1:1, and the total gas hourly space velocity of CO2 and H2 was 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0074] Example 7

[0075] Example 1 was repeated, but in the catalyst preparation process, Cu(NO3)2·3H2O was replaced with 10.10g Zn(NO3)2·6H2O, and the final catalyst was denoted as 10Zn / CeO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 250℃, 3MPa, CO2:H2 = 1:1, and the total gas hourly space velocity of CO2 and H2 was 6000h. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0076] Example 8

[0077] Example 1 was repeated, but in the catalyst preparation process, Cu(NO3)2·3H2O was replaced with 10.96g Co(NO3)2·6H2O, and the final catalyst was denoted as 10Co / CeO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 250℃, 3MPa, CO2:H2 = 1:1, and the total gas hourly space velocity of CO2 and H2 was 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0078] Example 9

[0079] Example 1 was repeated, but in the catalyst preparation process, 8.43 g Cu(NO3)2·3H2O was replaced with 4.22 g Cu(NO3)2·3H2O and 5.49 g Ni(NO3)2·6H2O, and the catalyst was designated as 5Ni-5Cu / CeO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 250 °C, 3 MPa, CO2:H2 = 1:3, and the total gas hourly space velocity (GHSV) of CO2 and H2 was 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0080] Example 10

[0081] Example 1 was repeated, but in the catalyst preparation process, 8.43 g Cu(NO3)2·3H2O was replaced with 4.22 g Cu(NO3)2·3H2O and 5.48 g Co(NO3)2·6H2O, and the catalyst was designated as 5Co-5Cu / CeO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 250 °C, 3 MPa, CO2:H2 = 1:3, and the total gas hourly space velocity (GHSV) of CO2 and H2 was 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0082] Example 11

[0083] Example 1 was repeated, but in the catalyst preparation process, 8.43 g Cu(NO3)2·3H2O was replaced with 4.22 g Cu(NO3)2·3H2O and 5.05 g Zn(NO3)2·6H2O, and the catalyst was designated as 5Zn-5Cu / CeO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 250 °C, 3 MPa, CO2:H2 = 1:3, and a total gas hourly space velocity (GHSV) of 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0084] Example 12

[0085] Example 1 was repeated, but in the catalyst preparation process, 8.43 g Cu(NO3)2·3H2O was replaced with 5.48 g Co(NO3)2·6H2O and 5.05 g Zn(NO3)2·6H2O, and the catalyst was designated as 5Zn-5Co / CeO2(CA). The reaction conditions for preparing N,N-dimethylformamide were 250 °C, 3 MPa, CO2:H2 = 1:3, and the total gas hourly space velocity (GHSV) of CO2 and H2 was 6000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0086] Example 13

[0087] Catalyst preparation: 4.22 g Cu(NO3)2·3H2O, 5.05 g Zn(NO3)2·6H2O, and 50.46 g Ce(NO3)3·6H2O were weighed and dissolved in 200 mL of deionized water to prepare a mixed aqueous solution of copper nitrate, zinc nitrate, and cerium nitrate. Then, under stirring at 40 °C, a 2 mol / L Na2CO3 solution was slowly added dropwise until the pH of the suspension reached approximately 10. After stirring at 40 °C for 6 h, the precipitate was filtered and washed with a large amount of deionized water until the filtrate became neutral (pH = 7) to remove residual sodium ions from the precipitate. The resulting solid was dried in an oven at 110 °C for 6 h, then calcined at 400 °C for 3 h in air. Finally, hydrogen gas was introduced to reduce the catalyst at 300 °C for 1 h to obtain the final catalyst sample, denoted as 5Zn-5Cu / CeO2(CP).

[0088] The steps for preparing N,N-dimethylformamide in Example 1 were repeated, with the reaction conditions being 280°C, 3 MPa, CO2:H2 = 1:2, and a total gas hourly space velocity (GBHV) of 8000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0089] Example 14

[0090] Catalyst preparation: 4.22 g Cu(NO3)2·3H2O and 5.05 g Zn(NO3)2·6H2O were weighed and dissolved in 30 mL of deionized water to prepare a copper nitrate aqueous solution. 20 g CeO2 support was added, and the mixture was dispersed by sonication at room temperature for 30 min, followed by continuous stirring at room temperature for 24 h. After impregnation, the resulting mixture was heated and stirred at 80 °C until the water was almost completely evaporated. The sample was then dried in an oven at 110 °C for 6 h. Finally, the sample was calcined at 400 °C for 3 h in air, followed by reduction treatment with hydrogen gas at 300 °C for 1 h to obtain the final catalyst sample, denoted as 5Zn-5Cu / CeO2(IM).

[0091] The steps for preparing N,N-dimethylformamide in Example 1 were repeated, with the reaction conditions being 280°C, 3 MPa, CO2:H2 = 1:2, and a total gas hourly space velocity (GBHV) of 8000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The results after 48 hours of reaction are shown in Table 1.

[0092] Comparative Example 1

[0093] The catalyst used in Example 1 was the same, except for the preparation of N,N-dimethylformamide: the obtained catalyst was compressed into tablets and sieved to a mesh size of 20-40. Then, 10 mL of the sieved catalyst was measured and loaded into a stainless steel reaction tube, with magnetic balls inserted at both ends for fixation. Nitrogen gas was then introduced for purging. After purging, CO was introduced, and the total reaction pressure was adjusted to 3 MPa using a back pressure valve. Subsequently, a dual-plunger pump was used to introduce liquid dimethylamine, which was then vaporized online using a vaporizer. The vaporized dimethylamine and CO were mixed in a preheater and then introduced into a fixed-bed reactor. The reactor was operated at 250°C, 3 MPa, and a CO gas hourly space velocity of 3000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The reaction was carried out under the specified conditions. The results after 48 hours of reaction are shown in Table 1.

[0094] Comparative Example 2

[0095] The catalyst used in Example 11 is the same, except for the preparation of N,N-dimethylformamide: the obtained catalyst is compressed into tablets and sieved to a mesh size of 20-40. Then, 10 mL of the sieved catalyst is measured and loaded into a stainless steel reaction tube, with magnetic balls inserted at both ends for fixation. Nitrogen gas is then introduced for purging. After purging, CO is introduced, and the total reaction pressure is adjusted to 3 MPa using a back pressure valve. Subsequently, a dual-plunger pump is used to introduce liquid dimethylamine, which is then vaporized online via a vaporizer. The vaporized dimethylamine and CO are mixed in a preheater and then introduced into a fixed-bed reactor at 250°C, 3 MPa, and a CO gas hourly space velocity of 3000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The reaction was carried out under the specified conditions. The results after 48 hours of reaction are shown in Table 1.

[0096] Comparative Example 3

[0097] The catalyst used in Example 13 was the same, except for the preparation of N,N-dimethylformamide: the obtained catalyst was compressed into tablets and sieved to a mesh size of 20-40. Then, 10 mL of the sieved catalyst was measured and loaded into a stainless steel reaction tube, with magnetic balls inserted at both ends for fixation. Nitrogen gas was then introduced for purging. After purging, CO was introduced, and the total reaction pressure was adjusted to 3 MPa using a back pressure valve. Subsequently, a dual-plunger pump was used to introduce liquid dimethylamine, which was then vaporized online using a vaporizer. The vaporized dimethylamine and CO were mixed in a preheater and then introduced into a fixed-bed reactor. The reactor was operated at 280°C, 3 MPa, and a CO gas hourly space velocity of 4000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 3 h⁻¹. -1 The reaction was carried out under the specified conditions. The results after 48 hours of reaction are shown in Table 1.

[0098] Table 1 Reaction performance results

[0099] catalyst Dimethylamine conversion rate (%) DMF selectivity (%) Example 1 <![CDATA[10Cu / CeO2(CA)]]> 80.2 97.6 Example 2 <![CDATA[10Cu / TiO2(CA)]]> 66.3 93.2 Example 3 <![CDATA[10Cu / ZrO2(CA)]]> 77.4 95.5 Example 4 <![CDATA[10Cu / Al2O3(CA)]]> 73.6 93.7 Example 5 10Cu / MgO(CA) 70.2 92.8 Example 6 <![CDATA[10Ni / CeO2(CA)]]> 60.5 91.2 Example 7 <![CDATA[10Zn / CeO2(CA)]]> 72.9 95.4 Example 8 <![CDATA[10Co / CeO2(CA)]]> 65.3 92.7 Example 9 <![CDATA[5Ni-5Cu / CeO2(CA)]]> 83.5 94.2 Example 10 <![CDATA[5Co-5Cu / CeO2(CA)]]> 81.1 93.8 Example 11 <![CDATA[5Zn-5Cu / CeO2(CA)]]> 94.4 98.7 Example 12 <![CDATA[5Zn-5Co / CeO2(CA)]]> 74.2 93.5 Example 13 <![CDATA[5Zn-5Cu / CeO2(CP)]]> 87.7 98.4 Example 14 <![CDATA[5Zn-5Cu / CeO2(IM)]]> 82.6 98.0 Comparative Example 1 <![CDATA[10Cu / CeO2(CA)]]> 32.5 92.6 Comparative Example 2 <![CDATA[5Zn-5Cu / CeO2(CA)]]> 38.4 93.0 Comparative Example 3 <![CDATA[5Zn-5Cu / CeO2(CP)]]> 33.9 92.1

Claims

1. A method for preparing N,N-dimethylformamide, the method comprising: reacting CO2, H2 and dimethylamine in the presence of a catalyst to obtain N,N-dimethylformamide; wherein the catalyst comprises a support and an active metal component, wherein the support is at least one of inorganic refractory oxides; and the active metal component is a transition metal.

2. The method for preparing N,N-dimethylformamide according to claim 1, wherein, The support is one or more of CeO2, Al2O3, TiO2, ZrO2, and MgO; the active metal component is at least one of Co, Ni, Cu, and Zn.

3. The method for preparing N,N-dimethylformamide according to claim 1 or 2, wherein, The catalyst is a supported catalyst, in which the transition metal exists in elemental form on the oxide support.

4. The method for preparing N,N-dimethylformamide according to claim 1, wherein, Based on the weight of the catalyst, the transition metal component has a mass content of 1% to 30%, preferably 5% to 15%, by element.

5. The method for preparing N,N-dimethylformamide according to claim 1, wherein, The reaction takes place in a fixed-bed reactor, with the catalyst packed inside.

6. The method for preparing N,N-dimethylformamide according to claim 1, wherein, The reaction temperature for CO2, H2 and dimethylamine to react is 150–350°C, preferably 200–300°C; the reaction pressure is 0.5–6 MPa, preferably 2–5 MPa.

7. The method for preparing N,N-dimethylformamide according to claim 1, wherein, The total gas hourly space velocity (VHSV) of a mixture of carbon dioxide and hydrogen is 300–12000 h⁻¹. -1 The liquid hourly space velocity (LHSV) of dimethylamine is 0.1–10 h⁻¹. -1 .

8. The method for preparing N,N-dimethylformamide according to claim 1, wherein, The molar ratio of carbon dioxide to hydrogen is 0.2 to 2.

9. The method for preparing N,N-dimethylformamide according to claim 1, wherein, Before reacting with CO2, H2 and dimethylamine, an inert gas is first introduced into the reactor for purging. After purging, the pressure is adjusted to the required reaction pressure. Then, the vaporized dimethylamine is mixed with CO2 and H2 through a preheater and introduced into a fixed-bed reactor for reaction to produce N,N-dimethylformamide.

10. The method for preparing N,N-dimethylformamide according to claim 1, wherein, The catalyst is prepared by one or more of the following methods: complexation, co-precipitation, and impregnation.

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