A supported composite catalyst for producing N-methyl-o-fluoroaniline and a preparation method thereof

Abstract

This application provides a supported composite catalyst for the production of N-methyl-o-fluoroaniline, with Al2O3 as the support and K2CO3, MgO, and Cu as the active components. A method for preparing the supported composite catalyst includes the following steps: Step 1: Dissolving a predetermined mass of potassium carbonate and magnesium nitrate in anhydrous ethanol to obtain a primary impregnation solution; dissolving copper acetate in anhydrous ethanol to obtain a secondary impregnation solution; Step 2: Adding Al2O3 to the primary impregnation solution for thorough impregnation, and drying to obtain a first precursor; Step 3: Adding the first precursor to the secondary impregnation solution for thorough impregnation, and drying to obtain a second precursor; Step 4: Calcining the second precursor at high temperature, and then cooling to room temperature to obtain a K2CO3-MgO-CuO / Al2O3 intermediate; Step 5: Reducing the K2CO3-MgO-CuO / Al2O3 intermediate with hydrogen at high temperature to obtain K2CO3-MgO-Cu / Al2O3, which is the supported composite catalyst of this application. The catalyst of this application can significantly improve the reaction rate, reduce side reactions, and has high stability.

Description

Technical Field

[0001] This application relates to the field of pesticide intermediate preparation, and in particular to a supported composite catalyst for the production of N-methyl-o-fluoroaniline and its preparation method. Background Technology

[0002] N-Methyl-o-fluoroaniline, as a fine chemical intermediate and raw material, is widely used in fuels, plastics, pharmaceuticals, and pesticides. There are several methods for preparing N-methyl-o-fluoroaniline. One method involves using o-fluoroaniline as a raw material, mixing it with toluene and formic acid, heating the mixture, and dehydrating it during the reaction by reflux to obtain N-(2-fluorophenyl)formamide. Dimethyl carbonate (DMC) and a catalyst are then added, and the mixture is placed in a high-pressure reactor and heated for methylation to obtain N-methyl-N-(2-fluorophenyl)formamide. This N-methyl-N-(2-fluorophenyl)formamide is then hydrolyzed by mixing it with water and sulfuric acid, and post-processed to obtain N-methyl-o-fluoroaniline.

[0003] Currently, potassium carbonate is generally used as a catalyst for the methylation of N-(2-fluorophenyl)formamide. Besides the main reaction that produces N-methyl-N-(2-fluorophenyl)formamide, other side reactions occur, such as O-methylation (methylation of the oxygen atom of formamide to form an ester) and polymethylation (secondary methylation of the atom to form an N,N-dimethyl product). These side reactions significantly affect the yield of N-methyl-N-(2-fluorophenyl)formamide, and consequently, the formation of the final product, N-methylo-fluoroaniline. Summary of the Invention

[0004] In view of this, this application proposes a supported composite catalyst for the production of N-methyl-o-fluoroaniline, which can suppress side reactions and improve the yield of N-methyl-N-(2-fluorophenyl)formamide in the main reaction.

[0005] This application also proposes a method for preparing a supported composite catalyst.

[0006] A supported composite catalyst for the production of N-methyl-o-fluoroaniline, wherein the support is Al2O3 and the active components are K2CO3, MgO, and Cu.

[0007] A method for preparing a supported composite catalyst includes the following steps:

[0008] Step 1: Dissolve a predetermined amount of potassium carbonate and magnesium nitrate in anhydrous ethanol to obtain a primary impregnation solution; dissolve copper acetate in anhydrous ethanol to obtain a secondary impregnation solution;

[0009] Step 2: Add Al2O3 to the first impregnation solution and fully impregnate it. After drying, the first precursor is obtained.

[0010] Step 3: Add the first precursor to the secondary impregnation solution and soak it thoroughly. After drying, the second precursor is obtained.

[0011] Step 4: The second precursor is calcined at high temperature and then cooled to room temperature to obtain the K2CO3-MgO-CuO / Al2O3 intermediate;

[0012] Step 5: Reduce the K2CO3-MgO-CuO / Al2O3 intermediate with hydrogen at high temperature to obtain K2CO3-MgO-Cu / Al2O3, which is the supported composite catalyst of this application.

[0013] The technical advantages of this application are as follows: Compared with a single K2CO3 catalyst, the supported composite catalyst of this application has the following advantages:

[0014] First, the reaction rate is relatively fast. Under the synergistic effect of Cu sites and basic sites, the reaction energy barrier of the main reaction is significantly reduced, the main reaction rate is accelerated, and the occurrence of side reactions can be suppressed.

[0015] Second, fewer byproducts. The synergistic effect of K2CO3 and MgO in this application can promote the formation of N-methyl-N-(2-fluorophenyl)formamide in the main reaction and inhibit the formation of polymethylation in the side reaction. At the same time, the pores of Al2O3 can limit the contact mode between o-fluoroaniline and DMC, avoid the excessive activation of the benzene ring of o-fluoroaniline, and reduce the formation of byproducts such as fluorotoluene.

[0016] Third, it has good stability. The hydroxyl groups on the surface of Al2O3 can anchor the active components through Al-OM bonds (M=K, Mg, Cu), reducing the loss of K2CO3 and MgO and inhibiting Cu aggregation, thereby improving the catalytic effect and extending the catalytic life. Detailed Implementation

[0017] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0018] A supported composite catalyst for the production of N-methyl-o-fluoroaniline, wherein the support is Al2O3 and the active components are K2CO3, MgO, and Cu.

[0019] K₂CO₃ acts as the main catalyst, methylating N-(2-fluorophenyl)formamide to N-methyl-N-(2-fluorophenyl)formamide. MgO stabilizes the o-fluoroaniline anion in N-methyl-N-(2-fluorophenyl)formamide, preventing excessive reaction and thus polymethylation. The synergistic effect of these two catalysts ensures the reaction rate while controlling side reactions, significantly increasing the yield of the main product.

[0020] Cu can promote the main reaction and suppress side reactions in catalysts. First, Cu activates the carbonyl carbon of DMC, lowering the nucleophilic barrier of N-(2-fluorophenyl)formamide and accelerating the methyl transfer process, thereby promoting the main reaction. Second, Cu selectively adsorbs reactants and limits the contact of active sites in side reaction pathways, reducing polymethylation of products, benzene ring methylation, and DMC decomposition.

[0021] The combined effect of K2CO3, MgO, and Cu can significantly improve the yield of the intermediate product N-methyl-N-(2-fluorophenyl)formamide, thereby increasing the yield of N-methyl-o-fluoroaniline.

[0022] The Al2O3 support provides anchoring sites for K2CO3, MgO, and Cu, while also ensuring their uniform distribution. Without these anchoring sites, K2CO3 and MgO would gradually be lost along with the product separation as the reaction proceeds; simultaneously, copper powder would easily agglomerate, significantly reducing its contact area with the reactants and thus its effectiveness. Furthermore, the significant density differences among K2CO3, MgO, and Cu prevent their uniform distribution during the reaction. Without the Al2O3 support, localized reactions could be too fast or too slow, leading to over- or under-reaction, which would increase the formation of byproducts and reduce the yield of the main product.

[0023] In a preferred embodiment, the support is γ-Al₂O₃ with a specific surface area >200 m². 2 / g, pore size 5-10 nm, particle size 20-40 mesh. Compared with α-Al2O3, γ-Al2O3 has a larger specific surface area, which is conducive to loading active components.

[0024] In a preferred embodiment, the mass ratio of Al2O3 to K2CO3, MgO, and Cu is 1:0.08-0.12:0.05-0.08:0.02-0.04.

[0025] If the K2CO3 ratio is too low, the density of basic sites will be insufficient, the -NH2 activation of o-fluoroaniline will be inadequate, the reaction rate will be slow, and the yield of N-methyl-o-fluoroaniline will be low. If the K2CO3 ratio is too high, it will lead to an increase in side reactions. At the same time, K2CO3 is prone to agglomeration and blockage of the carrier pores, thereby reducing the utilization rate of active sites.

[0026] If the MgO ratio is too low, the o-fluoroaniline anion cannot be effectively stabilized, resulting in more polymethylation byproducts. If the MgO ratio is too high, the moderately strong basicity of MgO will competitively adsorb o-fluoroaniline, inhibiting its contact with Cu sites and causing a decrease in the main reaction rate.

[0027] If the Cu ratio is too low, there will be insufficient metal active sites, the carbonyl activation of DMC will be inadequate, and the yield of the main reaction will be low. If the Cu ratio is too high, Cu nanoparticles will easily agglomerate, the utilization rate of active sites will decrease, and Cu will compete with basic sites for adsorption of reactants, thereby inhibiting the main reaction.

[0028] A method for preparing a supported composite catalyst includes the following steps:

[0029] Step 1: Dissolve a predetermined amount of potassium carbonate and magnesium nitrate in anhydrous ethanol to obtain a primary impregnation solution; dissolve copper acetate in anhydrous ethanol to obtain a secondary impregnation solution;

[0030] Step 2: Add Al2O3 to the first impregnation solution and fully impregnate it. After drying, the first precursor is obtained.

[0031] Step 3: Add the first precursor to the secondary impregnation solution and soak it thoroughly. After drying, the second precursor is obtained.

[0032] Step 4: The second precursor is calcined at high temperature and then cooled to room temperature to obtain the K2CO3-MgO-CuO / Al2O3 intermediate;

[0033] Step 5: Reduce the K2CO3-MgO-CuO / Al2O3 intermediate with hydrogen at high temperature to obtain K2CO3-MgO-Cu / Al2O3, which is the supported composite catalyst of this application.

[0034] In a preferred embodiment, the reduction temperature of the intermediate is 250–300°C: if the temperature is too low, the reduction of CuO will be incomplete; if the temperature is too high, the Cu nanoparticles will easily agglomerate, reducing their activity.

[0035] The pretreatment of the support in this application directly affects the uniformity and stability of the loading of active components, and the drying and calcination conditions must be strictly controlled. Therefore, in a preferred embodiment, the pretreatment of the Al2O3 support includes the following steps:

[0036] Step 11: Select γ-Al2O3 as a carrier and perform drying treatment to remove surface adsorbed water;

[0037] Step 12: Transfer γ-Al2O3 to a furnace for calcination to remove residual hydroxyl groups on the support surface and enhance the mechanical strength of the support;

[0038] Step 13: Allow to cool naturally to room temperature and store in a dry place.

[0039] This application employs a stepwise impregnation method to load the active component or its precursor onto γ-Al₂O₃, specifically by first loading potassium carbonate and magnesium nitrate, followed by copper acetate. This method avoids interference between different components and improves the uniformity of loading. Simultaneously, stepwise impregnation allows for the stratified loading of different active components: K₂CO₃-MgO is distributed within the pores of the support, providing basic sites; while Cu is distributed on the surface of the support, providing metallic active sites.

[0040] After distribution and impregnation, the mixture is then roasted at high temperature, causing magnesium nitrate to decompose into magnesium oxide, copper acetate to decompose into copper oxide, and potassium carbonate to remain stable.

[0041] Then, copper oxide is reduced by hydrogen to become metallic copper, ultimately resulting in a synergistic catalytic system that combines alkalinity and metallic activity.

[0042] The following is a preferred embodiment of this application.

[0043] Carrier pretreatment: γ-Al₂O₃ with a specific surface area >200 m² was selected. 2 / g, pore size 5~10 nm, particle size 20~40 mesh; place γ-Al2O3 in a vacuum drying oven and dry at 120℃ for 12 h to remove surface physically adsorbed water; after drying, transfer to a muffle furnace and calcine at 500℃ in air atmosphere for 4 h; after calcination, cool naturally to room temperature and immediately transfer to a desiccator for storage to avoid moisture absorption.

[0044] Preparation of impregnation solution: Calculate the raw material usage according to the target loading, i.e., Al2O3:K2CO3:MgO:Cu = 1:0.08:0.05:0.02; Dissolve potassium carbonate and magnesium nitrate in anhydrous ethanol at a liquid-to-solid ratio of 3:1, i.e., 1g Al2O3 corresponds to 3 mL ethanol, stir for 30 min until completely dissolved to obtain the first impregnation solution; Dissolve copper acetate in anhydrous ethanol at a liquid-to-solid ratio of 3:1, stir for 20 min until completely dissolved to obtain the second impregnation solution;

[0045] Preparation of the first precursor: The pretreated Al2O3 support was slowly added to the first impregnation solution and stirred for 10 min to fully impregnate the support; it was then allowed to stand at room temperature for 12 h to allow the active components to penetrate into the pores of the support through capillary action; the impregnated Al2O3 support was transferred to a vacuum drying oven and dried at 60 °C for 6 h to remove the ethanol solvent. The vacuum condition can accelerate the evaporation of the solvent and prevent the components from agglomerating, thus obtaining the first precursor.

[0046] Preparation of the second precursor: The first precursor was added to the second impregnation solution and stirred for 10 min; it was allowed to stand at room temperature for 8 h to allow copper acetate to be uniformly loaded onto the surface of the carrier; it was dried in a vacuum drying oven at 60 °C for 6 h to remove the ethanol solvent and obtain the dried second precursor.

[0047] Calcination and reduction: The second precursor was transferred to a muffle furnace and calcined at 350°C in air atmosphere for 4 h with a heating rate of 5°C / min to avoid cracking of the support due to rapid heating; after calcination, it was naturally cooled to room temperature to obtain the K2CO3-MgO-CuO / Al2O3 intermediate; the intermediate was transferred to a fixed-bed reactor, pure hydrogen was introduced at a flow rate of 50 mL / min, and it was reduced at 250°C for 3 h with a heating rate of 2°C / min; after reduction, it was cooled to room temperature under N2 protection to avoid re-oxidation of Cu to obtain K2CO3-MgO-Cu / Al2O3.

[0048] The obtained K2CO3-MgO-Cu / Al2O3 supported composite catalyst was compared with the existing K2CO3 catalyst under the same conditions to verify the catalytic effect, as follows:

[0049] Reactants: o-fluoroaniline (PFA, 99%), dimethyl carbonate (DMC, 99.5%), molar ratio 1:3;

[0050] Catalyst dosage: 0.1 g;

[0051] Reaction conditions: 180℃, 1.0 MPa N2 atmosphere, stirring speed 500 rpm, reaction time 4 h;

[0052] Analytical methods: Gas chromatography-FID was used to quantitatively analyze the product composition and calculate the PFA conversion rate, N-methyl-o-fluoroaniline (MFA) selectivity, and byproduct content.

[0053] The results are shown in Table 1:

[0054] Table 1:

[0055]

[0056] In the table, PFA conversion (4 h) represents the molar percentage of converted o-fluoroaniline (PFA) relative to the initial PFA after 4 hours of reaction. A higher value indicates a more complete reaction and stronger overall catalyst activity. The conversion rate of K2CO3-MgO-Cu / Al2O3 is 92.3%, meaning that 92.3% of the PFA participated in the reaction. The conversion rate of K2CO3 is only 56.7%.

[0057] The initial reaction rate represents the amount of PFA converted per unit mass of catalyst per hour at the beginning of the reaction. It directly reflects the intrinsic activity of the catalyst; the higher the value, the faster the main reaction starts. The initial rate of K2CO3-MgO-Cu / Al2O3 is 2.5 times that of the K2CO3 support, indicating that it can rapidly drive the reaction.

[0058] As can be seen from the PFA conversion rate (4h) and the initial reaction rate, the K2CO3-MgO-Cu / Al2O3 of this application can significantly improve the methylation reaction rate.

[0059] MFA selectivity represents the molar percentage of the main product N-methyl-o-fluoroaniline (MFA) generated out of all reaction products. A higher value indicates stronger catalyst specificity for the main reaction and fewer side reactions. The selectivity of K₂CO₃-MgO-Cu / Al₂O₃ reaches 96.1%, indicating that the vast majority of converted PFAs yielded the target product. In contrast, the selectivity of K₂CO₃ is only 78.5%.

[0060] N,N-Dimethyl-o-fluoroaniline (DMFA) is the result of further methylation of the main product MFA. Its high content indicates that the catalyst cannot effectively inhibit over-methylation. The DMFA content of K2CO3-MgO-Cu / Al2O3 is only 2.3%, far lower than the 12.1% of the K2CO3 support. The moderately strong basic sites of MgO can preferentially adsorb PFA, reducing the contact between MFA and basic sites. At the same time, Cu promotes the rapid completion of the main reaction, shortening the residence time of MFA, thus reducing the DMFA content from 12.1% to 2.3%.

[0061] The formation of o-fluorotoluene (OFT) originates from the reaction of activated PFA benzene rings with DMC. Its high content indicates a weak ability of the catalyst to regulate the reaction sites. The mesoporous channels of Al2O3 can restrict the adsorption orientation of PFA, causing its amino groups to face towards the channel surface, close to Cu and basic sites. The benzene rings are shielded by the channel walls, preventing activation by strongly basic sites, thus reducing the OFT content from 6.8% to 1.2%.

[0062] The DMC decomposition rate represents the molar percentage of initial DMC that decomposes directly into methanol and CO2 without participating in the main reaction. A high decomposition rate not only wastes raw materials but may also lead to catalyst deactivation. The selective adsorption of Cu on DMC reduced the DMC decomposition rate of K2CO3-MgO-Cu / Al2O3 from 15.3% to 3.5%.

[0063] The PFA conversion rate in the 5th cycle represents the PFA conversion rate in the 5th reaction after the catalyst has been reused 5 times. It directly reflects the catalyst's durability; the higher the value, the better the stability. The conversion rate of K2CO3-MgO-Cu / Al2O3 still reaches 87.6%, far exceeding the 38.2% of the K2CO3 support.

[0064] The activity retention rate after the 5th cycle represents the ratio (percentage) of the conversion rate after the 5th cycle to the conversion rate after the 1st cycle. It quantitatively reflects the degree of decline in catalyst activity; the higher the retention rate, the stronger the stability. The activity retention rate of K2CO3-MgO-Cu / Al2O3 is 94.9%, indicating that it can still maintain high catalytic efficiency after multiple cycles.

[0065] The K2CO3 loss rate after 5 cycles represents the percentage of K2CO3 mass lost from the catalyst after recycling. The lower the loss rate, the stronger the stability of the active component. The formation of Al-OK bonds reduced the K2CO3 loss rate of K2CO3-MgO-Cu / Al2O3 from 12.5% ​​to 2.1%, avoiding a significant loss of basic sites.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A supported composite catalyst for the production of N-methyl-o-fluoroaniline, characterized in that: The support is Al2O3, and the active components are K2CO3, MgO, and Cu. The mass ratio of Al2O3 to K2CO3, MgO, and Cu is 1:0.08–0.12:0.05–0.08:0.02–0.

04. The supported composite catalyst for the production of N-methyl-o-fluoroaniline is prepared by the following method: Step 1: Dissolve a predetermined amount of potassium carbonate and magnesium nitrate in anhydrous ethanol to obtain a primary impregnation solution; dissolve copper acetate in anhydrous ethanol to obtain a secondary impregnation solution; Step 2: Add Al2O3 to the first impregnation solution and fully impregnate it. After drying, the first precursor is obtained. Step 3: Add the first precursor to the secondary impregnation solution and soak it thoroughly. After drying, the second precursor is obtained. Step 4: The second precursor is calcined at high temperature and then cooled to room temperature to obtain the K2CO3-MgO-CuO / Al2O3 intermediate; Step 5: Reduce the K2CO3-MgO-CuO / Al2O3 intermediate with hydrogen at a high temperature of 250-300℃ to obtain K2CO3-MgO-Cu / Al2O3.

2. The supported composite catalyst for the production of N-methyl-o-fluoroaniline as described in claim 1, characterized in that: The support is γ-Al₂O₃ with a specific surface area >200 m². 2 / g, pore size 5-10 nm, particle size 20-40 mesh.

3. The method for preparing the supported composite catalyst for the production of N-methyl-o-fluoroaniline as described in claim 1, characterized in that: Includes the following steps: Step 1: Dissolve a predetermined amount of potassium carbonate and magnesium nitrate in anhydrous ethanol to obtain a primary impregnation solution; dissolve copper acetate in anhydrous ethanol to obtain a secondary impregnation solution; Step 2: Add Al2O3 to the first impregnation solution and fully impregnate it. After drying, the first precursor is obtained. Step 3: Add the first precursor to the secondary impregnation solution and soak it thoroughly. After drying, the second precursor is obtained. Step 4: The second precursor is calcined at high temperature and then cooled to room temperature to obtain the K2CO3-MgO-CuO / Al2O3 intermediate; Step 5: Reduce the K2CO3-MgO-CuO / Al2O3 intermediate with hydrogen at a high temperature of 250-300℃ to obtain K2CO3-MgO-Cu / Al2O3.

4. The preparation method according to claim 3, characterized in that: The Al2O3 is γ-Al2O3.

5. The preparation method according to claim 4, characterized in that: The pretreatment of the γ-Al2O3 support includes the following steps: Step 11: Select γ-Al2O3 as a carrier and perform drying treatment to remove surface adsorbed water; Step 12: Transfer γ-Al2O3 to a furnace for calcination to remove residual hydroxyl groups on the support surface and enhance the mechanical strength of the support; Step 13: Allow to cool naturally to room temperature and store in a dry place.

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