A method for synthesizing methyl acetophenone

Abstract

This invention discloses a method for synthesizing methyl acetophenone, belonging to the field of organic synthesis technology. The method uses methyl benzoic acid and acetic acid as raw materials, and Nd₂O₃-Pr₆O₂ as the catalyst. 11 Using MgO-Al2O3 composite oxide as a catalyst, methyl acetophenone is synthesized via a fixed-bed gas-solid phase catalytic reaction. After the raw materials are mixed to form a homogeneous solution, they are pumped into the fixed-bed reactor by a metering pump. Under conditions of 350–450°C and 0.1–1 MPa, the raw materials are vaporized and flow through the catalyst bed. Methylbenzoic acid undergoes decarboxylation to produce methylphenyl, and acetic acid undergoes dehydroxylation to produce acetyl. These two react in a coupling reaction to generate the target product. Byproducts are CO2 and H2O. This invention utilizes inexpensive raw materials, a highly active catalyst that is easily separated and recyclable, and enables continuous production. It effectively improves reaction selectivity and raw material conversion rate, simplifies post-processing, reduces environmental protection and equipment maintenance costs, and overcomes many shortcomings of existing processes, making it suitable for large-scale industrial applications.

Description

Technical Field

[0001] This invention relates to the field of organic chemistry, and more particularly to a method for synthesizing methyl acetophenone. Background Technology

[0002] Methyl acetophenone is an important aromatic ketone compound widely used in pharmaceuticals, fragrances, dyes, pesticides and other fields. It is a key raw material for the synthesis of ibuprofen, fragrance intermediates and new materials. The market demand is large, and the optimization of its synthesis process is of great significance to the development of related industries.

[0003] Currently, the main methods for synthesizing methyl acetophenone in industry include Friedel-Crafts acylation, oxidation, keto-acid condensation, and rearrangement. All of these methods have significant technical defects and cannot meet the demands for high efficiency, green production, and low cost in industrial production.

[0004] Among them, the Friedel-Crafts acylation method is currently a widely used synthetic method. This method uses toluene and acetyl chloride or acetic anhydride as raw materials, and the acylation reaction occurs under the action of Lewis acid catalysts such as aluminum trichloride and ferric chloride to produce methyl acetophenone. However, this method has many drawbacks: First, the raw materials acetyl chloride and acetic anhydride are expensive and highly corrosive and irritating, making storage and transportation difficult, increasing production safety risks and raw material costs; Second, the homogeneous Lewis acid catalysts used are difficult to separate from the product, requiring complex post-processing such as water washing and neutralization after the reaction, generating a large amount of acidic waste liquid and waste salt, resulting in high environmental treatment costs and easy corrosion of production equipment, increasing equipment operation and maintenance costs; Third, side reactions such as polyacylation and isomerization are prone to occur during the reaction, leading to low product selectivity, low raw material conversion rate, and difficulty in subsequent purification, affecting product quality.

[0005] The oxidation method typically uses ethylbenzene or methyl ethylbenzene as raw materials, which undergo an oxidation reaction under the action of heavy metal oxidants to produce methyl acetophenone. This method has problems such as high cost and high toxicity of oxidants, harsh reaction conditions, complex by-products, and easy generation of large amounts of organic waste liquid, which pollutes the environment and does not conform to the trend of green chemical development.

[0006] Other synthetic methods, such as keto acid condensation and rearrangement, either suffer from the drawbacks of scarce raw materials, complicated reaction steps, and low production efficiency, or require extreme reaction conditions such as high temperature and high pressure, making industrial scale-up difficult, energy consumption high, and large-scale continuous production difficult to achieve.

[0007] Furthermore, the catalysts used in existing synthesis processes are mostly single metal oxides or traditional homogeneous catalysts, which suffer from low catalytic activity, poor selectivity, insufficient stability, or difficulty in recycling, further limiting the optimization and upgrading of the methyl acetophenone synthesis process. At the same time, solid feedstocks in existing processes are prone to clogging and imbalance, resulting in low reaction mass transfer efficiency and poor batch-to-batch product stability, making it difficult to meet the needs of continuous industrial production.

[0008] Therefore, developing a method for synthesizing methyl acetophenone that uses inexpensive and readily available raw materials, is environmentally friendly and low in toxicity, has high catalyst activity and is easy to separate, has a simple and continuous process, and is environmentally safe and produces stable product quality has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] This invention addresses the problems of poor reaction selectivity, numerous byproducts, low raw material conversion rate, high energy consumption, insufficient activity, poor stability, and complex post-processing in existing methyl acetophenone synthesis processes. It provides a method for synthesizing methyl acetophenone to achieve green, efficient, and continuous industrial production.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for synthesizing methyl acetophenone, using methylbenzoic acid and acetic acid as raw materials, and Nd2O3-Pr6O 11 Using MgO-Al2O3 composite oxide as a catalyst, methyl acetophenone was synthesized via a fixed-bed gas-solid phase catalytic reaction. The specific steps of the synthesis are as follows: Catalyst loading: The catalyst Nd2O3-Pr6O is loaded. 11 The MgO-Al2O3 catalyst is uniformly packed in a fixed-bed reactor to ensure a uniform catalyst bed distribution and provide a stable reaction environment for the gas-solid phase catalytic reaction. In this catalyst, Nd2O3 and Pr6O... 11 The two rare earth components work synergistically. MgO-Al2O3, as a composite support, provides excellent porous structure, thermal stability, and dual acid-base active sites. Its core role is to reduce the reaction activation energy, promote the smooth progress of the reaction of methylbenzoic acid and acetic acid to synthesize methyl acetophenone, and significantly improve the selectivity of the reaction and the conversion rate of raw materials.

[0011] Raw material pretreatment and feeding: Solid methylbenzoic acid is added to acetic acid and heated and stirred until the methylbenzoic acid is completely dissolved to form a uniform and stable raw material solution; the above raw material solution is continuously and stably pumped into the fixed bed reactor using a metering pump; this avoids problems such as clogging and imbalance that are easy to occur when feeding solid raw materials alone.

[0012] Catalytic reaction conditions control: The reaction temperature in the fixed-bed reactor is controlled at 350-450℃ and the reaction pressure is controlled at 0.1-1MPa. Under these conditions, the pumped feed solution is converted into a gaseous state. The gaseous feed flows uniformly through the catalyst bed in the reactor, and a gas-solid phase catalytic reaction occurs, ultimately synthesizing methyl acetophenone.

[0013] Preferably, the above-mentioned Nd2O3-Pr6O 11 The MgO-Al2O3 composite oxide is composed of rare earth oxides Nd2O3 and Pr6O. 11 It is constructed by supporting MgO-modified Al2O3, wherein the mass fraction of MgO-Al2O3 support is 70%–80%, the mass fraction of Nd2O3 is 3.3%–20%, and the mass fraction of Pr6O is... 11 The mass fraction of MgO in the MgO-Al2O3 support is 4% to 25%, and the mass fraction of MgO in the MgO-Al2O3 support is 1% to 5%.

[0014] Preferably, Nd₂O₃ is 4%–20%, and Pr₆O₃ is 4%–20%. 11 The content is 4%–20%, and the content of MgO-Al2O3 support is 76%–80%.

[0015] The chemical equation for the above catalytic reaction is: CH3C6H4COOH + CH3COOH = CH3C6H4COCH3 + H2O +CO2.

[0016] The specific reaction mechanism is as follows: The methylbenzoic acid (MephCOOH) molecule first loses its carboxyl group (-COOH) to generate methylphenyl (Meph-). The removed carboxyl group is converted into CO2 and discharged from the reactor. The H atom generated during the decarboxylation of methylbenzoic acid combines with the hydroxyl group (-OH) in the acetic acid (CH3COOH) molecule to generate water (H2O) which is then discharged. The acetic acid molecule, having lost its hydroxyl group, is converted into an acetyl group (CH3CO-). The acetyl group (CH3CO-) then undergoes a coupling (condensation) reaction with the previously generated methylphenyl (Meph-) to finally generate the target product, methyl acetophenone (MephCOCH3). In addition, an auxiliary reaction pathway may also exist during the reaction, where acetic acid first undergoes a decarboxylation reaction and then undergoes a coupling reaction with methylbenzoic acid to generate methyl acetophenone.

[0017] The beneficial effects of this invention are: it uses methylbenzoic acid and acetic acid, two inexpensive, readily available, green, and low-toxic chemical raw materials, to replace the highly corrosive and costly acylation reagents in traditional processes; and it employs Nd₂O₃-Pr₆O₂. 11The MgO-Al2O3 composite oxide catalyst overcomes the shortcomings of traditional catalysts, such as low activity, poor selectivity, and difficulty in separation. Combined with a fixed-bed gas-solid continuous reaction process, it achieves continuous feedstock and continuous reaction, improving production efficiency. Furthermore, the reaction byproducts are only CO2 and H2O, resulting in a simple system composition and simplified subsequent purification and separation processes, significantly reducing environmental treatment and equipment maintenance costs. The synthesis method of this invention is simple, easy to operate, allows for catalyst recycling, exhibits high reaction selectivity and feedstock conversion rate, and provides stable product quality. It is suitable for large-scale industrial production and possesses significant economic value and environmental benefits. Attached Figure Description

[0018] Figure 1 This is a gas chromatogram of methyl acetophenone prepared in Example 1 of the present invention.

[0019] Figure 2 This is a gas chromatogram of methyl acetophenone prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0020] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0021] Example 1 This embodiment provides a method for synthesizing methyl acetophenone, which is carried out according to the following steps: S1. Preparation of catalyst support γ-Al₂O₃ modified with basic oxide MgO was prepared by precipitation method. 2.6 g of magnesium nitrate hydrate (Mg(NO₃)₂·6H₂O) and 149 g of aluminum nitrate hydrate (AL(NO₃)₃·9H₂O) were dissolved in 100 ml of deionized water. While stirring, 10% NaOH solution was added dropwise until the pH reached 8. The resulting precipitate was filtered and washed with deionized water to remove Na₂O. + Ions. After drying at 110℃ and calcining at 500℃ for 4 hours, approximately 41 g of a composite support containing 1 wt% MgO and 99 wt% Al2O3 was obtained, denoted as 1%MgO-Al2O3, with a measured specific surface area of ​​200 m². 2 / g, water absorption rate 100%.

[0022] S2, Preparation of catalyst 5g of Nd(NO3)3·6H2O was dissolved in 10ml of deionized water to obtain solution one, and 25g of Pr(NO3)3·6H2O was dissolved in 50ml of deionized water to obtain solution two. Solutions one and two were mixed, and 40g of the above-mentioned substance with a specific surface area of ​​approximately 200m² was impregnated. 2 / g of 1% MgO-Al2O3 support was impregnated for 12 hours. Then it was dried in an oven at 110℃. After drying, it was calcined in a muffle furnace at 590℃ for 5 hours to obtain 51g of a methyl acetophenone synthesis method using Nd2O3-Pr6O. 11 / MgO-Al2O3, wherein Nd2O3 is 4wt% and Pr6O 11 The content is 20 wt%, and 1 wt% MgO-Al2O3 is 76 wt%.

[0023] Characterization by X-ray diffraction (XRD) and Beta-Earth Expansion Test (BET) confirmed that the catalyst possesses a high specific surface area, ranging from 185 to 210 m². 2 The catalyst contains uniformly dispersed rare earth active centers, which can effectively enhance the activity and selectivity of the catalytic reaction.

[0024] S3, Catalyst Loading 50g of the above catalyst was loaded into a single-tube reactor, and inert coarse quartz sand was filled at both ends of the reactor to fix the catalyst bed; the reactor temperature was precisely controlled by a temperature controller.

[0025] S4. Raw material pretreatment and feeding The raw materials are mixed according to a molar ratio of acetic acid to methyl benzoic acid of 1.5, heated to 70°C to completely dissolve the methyl benzoic acid and form a homogeneous mixed raw material liquid. The mixed raw material liquid is quantitatively delivered by a metering pump, and then preheated to about 350°C by a preheater before being introduced into the reactor for catalytic reaction.

[0026] The reaction process conditions are: feed liquid mass hourly space velocity 0.5 h⁻¹, reaction temperature 350 °C, and reaction pressure 0.12 MPa.

[0027] After the reaction was completed, the reaction liquid was collected and purified by two-step distillation. The first step was atmospheric distillation. The first distillation column was operated at atmospheric pressure, and the top temperature of the column was controlled at about 56°C and the bottom temperature at about 100°C. The byproduct acetone was separated at the top of the column. The bottom material after the acetone was removed was sent to the second distillation column for vacuum distillation. The vacuum degree was controlled at about 90 kPa, the top temperature at about 140°C, and the bottom temperature at about 150°C. The target product methyl acetophenone was obtained by distillation.

[0028] The product was quantitatively detected using a GC9890-ES gas chromatograph paired with a BP-1 column. The gas chromatogram is shown below. Figure 1 As shown in Table 1, the test results indicate that this process can stably prepare methyl acetophenone with a purity of up to 99.94%. Detailed product properties and reaction data are shown in Table 1.

[0029] Example 2 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, except that the liquid hourly space velocity of the raw material is 0.2 h⁻¹. -1 The results are shown in Table 1.

[0030] Example 3 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, except that the liquid hourly space velocity of the raw material is 3.0 h⁻¹. -1 The results are shown in Table 1.

[0031] Example 4 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, and the reaction conditions are the same as in Example 1. The catalyst was continuously used in the reactor for 3600 hours, and the cycle life of the catalyst was observed. The results are shown in Table 1.

[0032] Example 5 The method for synthesizing methyl acetophenone in this embodiment is carried out according to the following steps: S1. Preparation of catalyst support γ-Al₂O₃ modified with basic oxide MgO was prepared by precipitation method. 13g of magnesium nitrate hydrate (Mg(NO₃)₂·6H₂O) and 150g of aluminum nitrate hydrate (Al(NO₃)₃·9H₂O) were dissolved in 100ml of deionized water. While stirring, 10% NaOH solution was added dropwise until the pH reached 8. The resulting precipitate was filtered and washed with deionized water to remove Na₂O. + Ions. After drying at 110℃ and calcining at 500℃ for 4 hours, approximately 43.5 g of a support containing 5% MgO and 95% Al2O3 was obtained, denoted as 5%MgO-Al2O3, with a measured specific surface area of ​​180 m². 2 / g, water absorption rate 95%.

[0033] S2, Preparation of catalyst Dissolve 25g of Nd(NO3)3·6H2O in 50ml of deionized water, and dissolve 5g of Pr(NO3)3·6H2O in 50ml of deionized water. After mixing, impregnate 40g of the above-mentioned material with a specific surface area of ​​approximately 180m². 2 The catalyst was impregnated with a 5% MgO-Al2O3 support for 12 hours. It was then dried in an oven at 110℃ and finally calcined in a muffle furnace at 590℃ for 5 hours. Approximately 51 g of catalyst was obtained, with an oxide weight composition of 20% Nd2O3 and 10% Pr6O3. 11 4%, 5% MgO-Al2O3 76%.

[0034] S3. The application of the catalyst is the same as in Example 1. The results are shown in Table 1.

[0035] Example 6 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1. The difference is that in the step of catalytic synthesis of methyl acetophenone, water is added to the mixture of raw materials acetic acid and methyl benzoic acid, wherein the weight of the added water is 20% of the weight of methyl benzoic acid. The results are shown in Table 1.

[0036] Example 7 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, and the reaction conditions are the same as those in Example 6. The catalyst was continuously used in the reactor for 3600 hours, and the cycle life of the catalyst was observed. The results are shown in Table 1.

[0037] Example 8 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, except that the weight composition of the prepared oxide is 35% Nd2O and 35% Pr6O. 11 25%, 1% MgO-Al2O3 70%. The results are shown in Table 1.

[0038] Example 9 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1. The difference is that the weight composition of the prepared oxide is 3.3% Nd₂O₃ and 3.3% Pr₆O₃. 11 16.7%, 1%MgO-Al2O3 80%. The results are shown in Table 1.

[0039] Example 10 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, except that the reaction conditions in step S4 are: liquid hourly space velocity of the raw material is 0.5 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 0.1MPa. The results are shown in Table 1.

[0040] Example 11 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, except that the reaction conditions in step S4 are: liquid hourly space velocity of the raw material is 0.2 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 0.1MPa. The results are shown in Table 1.

[0041] Example 12 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, except that the reaction conditions in step S4 are: liquid hourly space velocity of the raw material 3.0 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 0.1MPa. The results are shown in Table 1.

[0042] Example 13 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, except that the reaction conditions in step S4 are: liquid hourly space velocity of the raw material is 0.5 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 1.0MPa. The results are shown in Table 1.

[0043] Example 14 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1, except that the reaction conditions in step S4 are: liquid hourly space velocity of the raw material is 0.2 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 1.0MPa. The results are shown in Table 1.

[0044] Example 15 The steps of the methyl acetophenone synthesis method in this embodiment are basically the same as those in Example 1. The difference is that the reaction conditions in step S4 are: liquid hourly space velocity of the raw material is 3 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 1.0MPa. The results are shown in Table 1.

[0045] Comparative Example 1 In this comparative example, the catalyst support for the synthesis of methyl acetophenone was γ-Al₂O₃ without MgO modification, and the other steps were the same as in Example 1. The results are shown in Table 1. Chromatographic analysis was performed on the methyl acetophenone product obtained in this comparative example; the chromatogram is shown below. Figure 2 It can be seen that the purity of the obtained methyl acetophenone is 99.73%.

[0046] Comparative Example 2 The steps of the comparative example of methyl acetophenone synthesis are the same as steps S1 and S2 of Example 1, except that the catalyst support 1% MgO-Al2O3 is replaced with MgO. The application method of the catalyst is also the same as step S3 of Example 1. The results are shown in Table 1.

[0047] Comparative Example 3 The catalyst preparation method in this comparative example is basically the same as steps S1 and S2 of Example 1. The difference is that Pr(NO3)3·6H2O was not used in the catalyst preparation process; that is, the catalyst is a neodymium-doped magnesium-aluminum composite oxide. The application method of the catalyst is also the same as step S3 of Example 1. The results are shown in Table 1.

[0048] Comparative Example 4 The preparation method of the catalyst in this comparative example is basically the same as steps S1 and S2 of Example 1. The difference is that Nd(NO3)3·6H2O was not used in the catalyst preparation process; that is, the catalyst is a praseodymium-doped magnesium-aluminum composite oxide. The application method of the catalyst is also the same as step S3 of Example 1. The results are shown in Table 1.

[0049] Comparative Example 5 The catalyst used in this comparative example was a commercially available copper-zinc-aluminum TH309 catalyst, and the application method was the same as step S3 in Example 1. The results are shown in Table 1.

[0050] Comparative Example 6 The catalyst used in this comparative example was the commercially available existing molecular sieve catalyst H-ZSM-5, and the application method of the catalyst was the same as step S3 in Example 1. The results are shown in Table 1.

[0051] The gas chromatogram patterns of the methyl acetophenone products obtained in Examples 2-9 above are basically the same. Figure 1 The purity of the obtained methyl acetophenone was all above 99.9%, which will not be elaborated here. The purity of the methyl acetophenone obtained in Comparative Examples 2-4 was all below 99.9%, which will not be elaborated here.

[0052] The yield data of the product methyl acetophenone in the above examples and comparative examples are shown in Table 1, wherein the yield of methyl acetophenone = conversion of methyl benzoic acid * selectivity of methyl acetophenone.

[0053] Table 1

[0054] As shown in Table 1, the method for synthesizing methyl acetophenone using the process of this invention yields Nd2O3-Pr6O 11 / MgO-Al2O3 exhibits excellent specific catalytic performance in the synthesis of methyl acetophenone from acetic acid and methylbenzoic acid. The product after the catalytic reaction, after conventional distillation, yields methyl acetophenone with a purity of over 99.9%, and the yield is consistently above 70%. This opens a new route for the synthesis of methyl acetophenone, and the catalyst preparation method is simple and suitable for industrial production. A comparison of Examples 1, 4, 6, and 7 shows that the catalyst prepared in this invention can be used to synthesize methyl acetophenone without the addition of water during the reaction, but its recyclability is poor. Adding water during the reaction significantly improves the catalyst's lifespan and ensures the quality of the synthesized product. Comparative Examples 1-4 characterize the synergistic effect between the components in the catalyst prepared in this invention, i.e., the absence of Nd2O3 and Pr6O3. 11 When composite oxides formed from any of the elements selected from MgO and Al2O3 are used for the catalytic synthesis of methyl acetophenone, the results are not ideal. The extremely low yield of methyl acetophenone obtained in Comparative Examples 5-6 indicates that the catalytic synthesis has extremely low reactivity, characterizing the reaction specificity of the catalyst prepared in this invention. The specificity of its effect is unmatched by conventional catalysts in the prior art.

[0055] The reaction mechanism is as follows: methylbenzoic acid ( The molecule first removes the carboxyl group. ), to generate methylphenyl ( -), the removed carboxyl group is converted into Excretion; H atoms produced during decarboxylation react with acetic acid ( ) hydroxyl group in the molecule The acetic acid molecules combine to form water and are expelled; the acetic acid molecule that loses its hydroxyl group is converted into an acetyl group. ), acetyl ( ) and methylphenyl ( A coupling (condensation) reaction occurs, ultimately producing methyl acetophenone. Furthermore, there may also be a pathway where acetic acid undergoes decarboxylation first, followed by a coupling reaction with methylbenzoic acid. The core function of the methyl acetophenone synthesis method provided by this invention is to lower the activation energy of the above reactions, thereby facilitating the successful synthesis of methyl acetophenone from methylbenzoic acid and acetic acid, and improving the selectivity and conversion rate of the reaction.

Claims

1. A method for synthesizing methyl acetophenone, characterized in that: Using methylbenzoic acid and acetic acid as reactants, and Nd₂O₃-Pr₆O₂ as the reactants... 11 Methyl acetophenone was prepared by a fixed-bed gas-solid phase catalytic reaction using MgO-Al2O3 composite oxide as a catalyst.

2. The method for synthesizing methyl acetophenone according to claim 1, characterized in that, Includes the following steps: Catalyst loading: Nd2O3-Pr6O 11 The MgO-Al2O3 composite oxide catalyst was uniformly packed into the fixed-bed reactor. Raw material pretreatment: Add methylbenzoic acid to acetic acid, heat and stir until completely dissolved, and prepare a homogeneous raw material mixture; Continuous catalytic reaction: The raw material mixture is continuously pumped into a fixed-bed reactor via a metering pump, where a gas-solid phase catalytic reaction occurs under set temperature and pressure conditions; Product separation: The reaction effluent was purified by distillation to obtain high-purity methyl acetophenone.

3. The method for synthesizing methyl acetophenone according to claim 1, characterized in that: The Nd2O3-Pr6O 11 In the MgO-Al2O3 composite oxide catalyst, the mass fraction of the MgO-Al2O3 composite support is 70%–80%, the mass fraction of Nd2O3 is 3.3%–20%, and the mass fraction of Pr6O is [missing information]. 11 The mass fraction is 4% to 25%; in the MgO-Al2O3 composite carrier, the mass fraction of MgO is 1% to 5%.

4. The method for synthesizing methyl acetophenone according to claim 3, characterized in that: The Nd2O3 mass fraction is 4%–20%, and Pr6O 11 The mass fraction is 4% to 20%, and the mass fraction of the MgO-Al2O3 composite carrier is 76% to 80%.

5. The method for synthesizing methyl acetophenone according to claim 1, characterized in that: The catalytic reaction temperature is 350–450℃, and the reaction pressure is 0.1–1.0 MPa.

6. The method for synthesizing methyl acetophenone according to claim 2, characterized in that: The mass hourly space velocity (MSV) of the feed liquid is 0.2–3.0 h⁻¹.

7. The method for synthesizing methyl acetophenone according to claim 2, characterized in that: The molar ratio of acetic acid to methylbenzoic acid is 1.5:1, and the raw material preheating temperature is 350℃.

8. The method for synthesizing methyl acetophenone according to claim 2, characterized in that: Water can be added to the reaction system, with the mass of water being 20% ​​of the mass of methylbenzoic acid, to improve the catalyst's lifespan.

9. The method for synthesizing methyl acetophenone according to claim 2, characterized in that: The product separation is achieved through a two-step distillation process: first, acetone is removed by atmospheric distillation, and then methyl acetophenone is obtained by vacuum distillation.

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