A method for synthesizing p-methylanisole

Abstract

The present application provides a method for synthesizing p-methyl anisole, which comprises the following steps: adding Y-type molecular sieve into cesium salt aqueous solution for impregnation to obtain a mixture; filtering, drying and calcining the impregnated mixture to obtain a modified molecular sieve catalyst; and packing the modified molecular sieve catalyst into a fixed bed reactor, adding raw material p-cresol and dimethyl carbonate into the fixed bed reactor packed with the modified molecular sieve catalyst for gas phase reaction at a certain temperature to obtain p-methyl anisole. The present application uses modified Y-type molecular sieve as catalyst, maximally reduces the gas phase reaction temperature, has low energy consumption, high yield, low cost, strong economy, realizes the continuity of production by using fixed bed, has the advantages of no need to separate product and catalyst, high production efficiency and small safety risk.

Description

Technical Field

[0001] This invention belongs to the field of fine organic synthesis, and specifically relates to a method for synthesizing p-methyl anisole. Background Technology

[0002] p-Methyl anisole is an important chemical raw material widely used in organic synthesis, pharmaceuticals, and fragrances. It possesses an aroma similar to ylang-ylang oil and violet, and is a permitted edible flavoring in my country's GB2760-86 standard. It is primarily used to formulate nut-based flavorings such as walnut and hazelnut, and also for the formulation of artificial ylang-ylang, cananga, violet, and daffodil flavorings.

[0003] Patent CN110054549A discloses a method using p-cresol as a raw material, first reacting it with sodium hydroxide to form sodium phenolate, then reacting it with dimethyl sulfate in a nonpolar solvent to synthesize p-toluene. Finally, in a polar solvent, the byproduct sodium methyl sulfate can react with sodium p-cresol to obtain p-toluene and sodium sulfate. The yields of the two-step methylation reactions are 97% and 95.5%, respectively. Its disadvantages are: the use of highly toxic dimethyl sulfate in the reaction process poses significant safety and environmental risks.

[0004] Patent CN107721824A discloses a method for preparing p-methyl anisole from phenol as a starting material. First, p-cresol is synthesized under the action of a ZrO2 / mesoporous molecular sieve composite catalyst. Then, dimethyl carbonate is added to a mixed solution of phenolate, ammonia, and p-cresol, and the reaction is carried out at 80–120°C for 3 minutes. The pH of the reaction product is adjusted to 2–5, and the mixture is allowed to stand and separate into layers. The oil phase is washed with ammonia to obtain the p-methyl anisole product. The yield of p-cresol in the first step is over 91.65%, and the yield of p-methyl anisole in the second step is over 93.65%. Its disadvantages are: the synthesis process uses ammonia and phenolate, the system is relatively complex, and the post-processing is cumbersome, resulting in a significant amount of waste.

[0005] Patent CN106916055A discloses the synthesis of p-methyl anisole at 130–180°C using p-cresol as a raw material, water as a polar solvent, Y-type zeolite as a catalyst, and turquoise oil as an emulsifier. The yield is over 96%, and the product purity is over 99%. However, its disadvantages are: the use of water as a solvent leads to the dissolution and loss of the catalyst's active components due to well-known reasons, preventing catalyst reuse and increasing production costs. Furthermore, the alkaline wastewater generated also increases the discharge of waste gas, wastewater, and solid waste.

[0006] Patent CN1546448A discloses a gas-phase catalytic synthesis method for p-methyl anisole. The catalyst is activated carbon or molecular sieve treated with alkali metal fluorides or hydroxides. The apparatus is a fixed bed, the reaction temperature is 568 K, and the conversion rate reaches 81.19%, with a selectivity of 97.38%. Its disadvantages are: high reaction temperature, high energy consumption, and the catalyst is more prone to coking and deactivation at high temperatures.

[0007] Patent CN113509947A discloses the synthesis of p-methyl anisole using a combined catalytic system of a main catalyst and an antioxidant. The active component of the main catalyst is one or more of LiCl, NaCl, KCl, CaCl2, and MgCl2, and the auxiliary agent is one or more of CaCO3, CuCO3, MgCO3, ZnCO3, Al2(CO3)3, and MnCO3. The reaction temperature is 150–350℃, the reaction pressure is 2–7 MPa, and the reaction time is 2–8 h. Under optimal synthesis conditions, the yield of p-methyl anisole is greater than 98%, and the purity is greater than 99.9%. Its disadvantages are: high reaction pressure, high equipment requirements, and a relatively high safety risk. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention aims to provide a method for the gas-phase synthesis of p-methyl anisole. This method, through the use of a modified catalyst, enables the reaction to proceed continuously with high efficiency, high yield, and low energy consumption, making it safe, environmentally friendly, and economical.

[0009] To achieve the above objectives, the present invention provides a method for synthesizing p-methyl anisole, the method comprising the following steps: 1) impregnating a Y-type molecular sieve with a cesium salt aqueous solution to obtain a mixture; 2) filtering, drying, and calcining the impregnated mixture to obtain a modified molecular sieve catalyst; and 3) packing the modified molecular sieve catalyst into a fixed-bed reactor, and at a certain temperature, adding p-cresol and dimethyl carbonate to the fixed-bed reactor packed with the modified molecular sieve catalyst for a gas-phase reaction to obtain p-methyl anisole.

[0010] In a preferred embodiment of the method of the present invention, preferably, in step 1), the Y-type molecule is selected from one or more of the sodium form (NaY), potassium form (KY), ammonium form (NH4Y), and ultrastable form (USY). Preferably, the Y-type molecule is selected from one or more of the sodium form (NaY) and potassium form (KY).

[0011] In a preferred embodiment of the method of the present invention, preferably, in step 1), the Y-type molecular sieve is spherical.

[0012] In a preferred embodiment of the method of the present invention, preferably, in step 1), the cesium salt is selected from one or more of cesium carbonate and cesium nitrate. Preferably, the cesium salt is cesium nitrate.

[0013] In a preferred embodiment of the method of the present invention, preferably, in step 1), the concentration of the aqueous solution of the cesium salt is 0.01–0.2 wt%. Preferably, the concentration of the aqueous solution of the cesium salt is 0.03–0.1 wt%.

[0014] In a preferred embodiment of the method of the present invention, preferably, in step 1), the impregnation method is ultrasonic impregnation.

[0015] In a preferred embodiment of the method of the present invention, preferably, in step 1), the immersion temperature is 20-70°C and the immersion time is 5-15 hours.

[0016] In a preferred embodiment of the method of the present invention, preferably, in step 2), the drying temperature is 100-120°C, the drying time is 6-12 hours; the calcination temperature is 500-700°C; and the calcination time is 3-7 hours. Preferably, the calcination temperature is 500-650°C.

[0017] In a preferred embodiment of the method of the present invention, preferably, in step 3), the molar ratio of p-cresol to dimethyl carbonate is 1:1 to 2.5; and the liquid hourly space velocity (LHSV) of the mixture of p-cresol and dimethyl carbonate is 2 to 4 h⁻¹. -1 .

[0018] In a preferred embodiment of the method of the present invention, preferably, in step 3), the bed temperature of the gas phase reaction is 210-240°C, and the reaction pressure of the gas phase reaction is atmospheric pressure.

[0019] The inventors discovered through experiments that: 1) The methylation reaction of p-cresol mainly occurs at two positions: on or adjacent to the phenolic hydroxyl group. Studies have shown that methylation at the ortho position of the phenolic hydroxyl group requires a suitable acidic environment, while methylation on the phenolic hydroxyl group requires an alkaline environment to achieve high yields. 2) The stronger the alkalinity, the higher the activity and selectivity of the methylation reaction on the phenolic hydroxyl group. Therefore, cesium salt modification is very suitable, and even using a small amount of cesium salt modification can achieve high activity.

[0020] Furthermore, in the comparative example, this invention directly used NaY, KY, NH4Y, and USY for a gas-phase reaction, but did not yield satisfactory results. This invention employs a continuous gas-phase reaction without adding any solvent, resulting in a system virtually free of water. Therefore, the catalyst activity is stable and it can operate for extended periods.

[0021] The beneficial effects of this invention are as follows: 1) The modified Y-type molecular sieve used in this invention as a catalyst can minimize the reaction temperature, resulting in low energy consumption and high yield. Because the loading of the modified cesium metal salt is very small, the cost of the catalyst is also low, making it highly economical. 2) Using a fixed bed allows for continuous production, with advantages such as no need to separate the product from the catalyst, high production efficiency, and low safety risks. Detailed Implementation

[0022] The present invention will be further illustrated below with examples. These examples are merely illustrative and not intended to limit the scope of the invention. All raw and auxiliary materials used in this invention are commercially available.

[0023] Example 1

[0024] 100g of spherical NaY molecular sieve was added to 150g of 0.03wt% cesium nitrate aqueous solution, ultrasonically impregnated at 40℃ for 10 hours, then filtered, dried at 110℃ for 10 hours, and finally calcined in a muffle furnace at 600℃ for 5 hours to obtain the modified NaY molecular sieve catalyst, denoted as NaY-0.03CsN-600.

[0025] Example 2

[0026] 100g of spherical NaY molecular sieve was added to 150g of 0.06wt% cesium nitrate aqueous solution, ultrasonically impregnated at 40℃ for 10 hours, then filtered, dried at 110℃ for 10 hours, and finally calcined in a muffle furnace at 600℃ for 5 hours to obtain the modified NaY molecular sieve catalyst, denoted as NaY-0.06CsN-600.

[0027] Example 3

[0028] 100g of spherical KY molecular sieve was added to 150g of 0.03wt% cesium nitrate aqueous solution, ultrasonically impregnated at 40℃ for 10 hours, then filtered, dried at 110℃ for 10 hours, and finally calcined in a muffle furnace at 600℃ for 5 hours to obtain the modified KY molecular sieve catalyst, denoted as KY-0.03CsN-600.

[0029] Example 4

[0030] 100g of spherical KY molecular sieve was added to 150g of 0.06wt% cesium nitrate aqueous solution, ultrasonically impregnated at 40℃ for 10 hours, then filtered, dried at 110℃ for 10 hours, and finally calcined in a muffle furnace at 600℃ for 5 hours to obtain the modified KY molecular sieve catalyst, denoted as KY-0.06CsN-600.

[0031] Example 5

[0032] 100g of spherical KY molecular sieve was added to 150g of 0.1wt% cesium nitrate aqueous solution, ultrasonically impregnated at 40℃ for 10 hours, then filtered, dried at 110℃ for 10 hours, and finally calcined in a muffle furnace at 600℃ for 5 hours to obtain the modified KY molecular sieve catalyst, denoted as KY-0.1CsN-600.

[0033] Example 6

[0034] 100g of spherical NH4Y molecular sieve was added to 150g of 0.06wt% cesium nitrate aqueous solution, and ultrasonically impregnated at 40℃ for 10 hours. Then, it was filtered, dried at 100℃ for 12 hours, and finally calcined in a muffle furnace at 600℃ for 5 hours to obtain the modified NH4Y molecular sieve catalyst, denoted as NH4Y-0.06CsN-600.

[0035] Example 7

[0036] 100g of spherical USY molecular sieve was added to 150g of 0.06wt% cesium nitrate aqueous solution, ultrasonically impregnated at 40℃ for 10 hours, then filtered, dried at 120℃ for 6 hours, and finally calcined in a muffle furnace at 600℃ for 5 hours to obtain the modified USY molecular sieve catalyst, denoted as USY-0.06CsN-600.

[0037] Example 8

[0038] 100g of spherical KY molecular sieve was added to 150g of 0.06wt% cesium nitrate aqueous solution, ultrasonically impregnated at 70℃ for 5 hours, then filtered, dried at 110℃ for 10 hours, and finally calcined in a muffle furnace at 500℃ for 5 hours to obtain the modified KY molecular sieve catalyst, denoted as KY-0.06CsN-500.

[0039] Example 9

[0040] 100g of spherical KY molecular sieve was added to 150g of 0.06wt% cesium nitrate aqueous solution, ultrasonically impregnated at 40℃ for 10 hours, then filtered, dried at 110℃ for 10 hours, and finally calcined in a muffle furnace at 700℃ for 3 hours to obtain the modified KY molecular sieve catalyst, denoted as KY-0.06CsN-700.

[0041] Example 10

[0042] 100g of spherical KY molecular sieve was added to 150g of 0.06wt% cesium carbonate aqueous solution, ultrasonically impregnated at 20℃ for 15 hours, then filtered, dried at 110℃ for 10 hours, and finally calcined in a muffle furnace at 600℃ for 7 hours to obtain the modified KY molecular sieve catalyst, denoted as KY-0.06CsC-600.

[0043] Example 11

[0044] A fixed-bed reactor with an inner diameter of 20 mm and a length of 80 cm was packed with NaY-0.03CsN-600 molecular sieve catalyst. The bed temperature was 220 °C, the molar ratio of p-cresol to dimethyl carbonate was 1:1.2, and the liquid hourly space velocity (LHSV) of the p-cresol and dimethyl carbonate mixture was 3.0 h⁻¹. -1 The composition of the reaction products was analyzed by gas chromatography and the yield was calculated. The specific results are shown in Table 1.

[0045] Examples 12-26

[0046] Examples 12-26 compare the performance of modified catalysts under different conditions in catalyzing the reaction of p-cresol and dimethyl carbonate to synthesize p-methyl anisole. The feed volume hourly space velocity, feed ester-phenol ratio, and reaction temperature were adjusted, while other operations were the same as in Example 11. Specific results are shown in Table 1.

[0047] Table 1: Results of Catalytic Performance Evaluation of Different Catalysts in the Synthesis of p-Methyl Anisole

[0048]

[0049]

[0050] Note: Conversion rate is the conversion rate of p-cresol, selectivity is the selectivity of p-methyl anisole, and yield is the yield of p-methyl anisole.

[0051] Example 27 (Comparative Example)

[0052] A fixed-bed reactor with an inner diameter of 20 mm and a length of 80 cm was packed with NaY molecular sieve catalyst. The bed temperature was 220 °C, the molar ratio of p-cresol to dimethyl carbonate was 1:1.2, and the liquid hourly space velocity (LHSV) of the p-cresol and dimethyl carbonate mixture was 3.0 h⁻¹. -1 The reaction products were analyzed by gas chromatography. The conversion rate of p-cresol was 78.6%, the selectivity of p-methyl anisole was 88.9%, and the yield of p-methyl anisole was 69.9%.

[0053] Example 28 (Comparative Example)

[0054] A fixed-bed reactor with an inner diameter of 20 mm and a length of 80 cm was packed with KY molecular sieve catalyst. The bed temperature was 220 °C, the molar ratio of p-cresol to dimethyl carbonate was 1:1.2, and the liquid hourly space velocity (LHSV) of the p-cresol and dimethyl carbonate mixture was 3.0 h⁻¹. -1 The reaction products were analyzed by gas chromatography. The conversion rate of p-cresol was 88.6%, the selectivity of p-methyl anisole was 86.2%, and the yield of p-methyl anisole was 76.4%.

[0055] Example 29 (Comparative Example)

[0056] An NH4Y molecular sieve catalyst was packed into a fixed-bed reactor with an inner diameter of 20 mm and a length of 80 cm. The bed temperature was 220 °C, the molar ratio of p-cresol to dimethyl carbonate was 1:1.2, and the liquid hourly space velocity (LHSV) of the p-cresol and dimethyl carbonate mixture was 3.0 h⁻¹. -1 The reaction products were analyzed by gas chromatography. The conversion rate of p-cresol was 81.7%, the selectivity of p-methyl anisole was 82.5%, and the yield of p-methyl anisole was 67.4%.

[0057] Example 30 (Comparative Example)

[0058] A fixed-bed reactor with an inner diameter of 20 mm and a length of 80 cm was packed with USY molecular sieve catalyst. The bed temperature was 220 °C, the molar ratio of p-cresol to dimethyl carbonate was 1:1.2, and the liquid hourly space velocity (LHSV) of the p-cresol and dimethyl carbonate mixture was 3.0 h⁻¹. -1 The reaction products were analyzed by gas chromatography. The conversion rate of p-cresol was 85.3%, the selectivity of p-methyl anisole was 63.4%, and the yield of p-methyl anisole was 54.1%.

[0059] Example 31

[0060] Catalyst stability study: A fixed-bed reactor with an inner diameter of 20 mm and a length of 80 cm was loaded with KY-0.06CsN-600 molecular sieve catalyst. The bed temperature was 220℃, the molar ratio of p-cresol to dimethyl carbonate was 1:1.2, and the liquid hourly space velocity (LHSV) of the p-cresol and dimethyl carbonate mixture was 3.0 h⁻¹. -1 The results of the continuous feeding reaction at different times are shown in Table 2.

[0061] Table 2: Results of catalytic stability study under optimal process conditions

[0062]

[0063] As can be seen from the data in Table 2, the yield decreased by only 1.2% after the catalyst operated continuously for 7000 hours. Therefore, the catalyst of this invention has excellent stability, which is beneficial for large-scale industrial production. In addition, small-scale tests have verified that the deactivated catalyst can be regenerated by calcination at 600°C in air or by gas-phase washing with ethanol.

[0064] It should be stated that the above-described invention content and specific embodiments are intended to demonstrate the practical application of the technical solution provided by this invention and should not be construed as limiting the scope of protection of this invention. Those skilled in the art can make various modifications, equivalent substitutions, or improvements within the spirit and principles of this invention.

Claims

1. A method for synthesizing p-methyl anisole, the method comprising the following steps: 1) Y-type molecular sieves were added to a cesium salt aqueous solution for impregnation to obtain a mixture; wherein, The Y-type molecule is selected from one or more of sodium type NaY, potassium type KY, ammonium type NH4Y, and ultrastable type USY, and the cesium salt is selected from one or more of cesium carbonate and cesium nitrate. 2) The impregnated mixture is filtered, dried, and calcined to obtain the modified molecular sieve catalyst; as well as 3) The modified molecular sieve catalyst is packed into a fixed-bed reactor. At a certain temperature, p-cresol and dimethyl carbonate are added to the fixed-bed reactor packed with the modified molecular sieve catalyst for gas-phase reaction to obtain p-methyl anisole.

2. The method according to claim 1, characterized in that, In step 1), the Y-type molecular sieve is spherical.

3. The method according to claim 1, characterized in that, In step 1), the concentration of the aqueous solution of the cesium salt is 0.01–0.2 wt%.

4. The method according to claim 1, characterized in that, In step 1), the impregnation method is ultrasonic impregnation.

5. The method according to claim 1 or 4, characterized in that, In step 1), the immersion temperature is 20–70°C, and the immersion time is 5–15 hours.

6. The method according to claim 1, characterized in that, In step 2), the drying temperature is 100-120℃ and the drying time is 6-12 hours; the roasting temperature is 500-700℃ and the roasting time is 3-7 hours.

7. The method according to claim 1, characterized in that, In step 3), the molar ratio of p-cresol to dimethyl carbonate is 1:1 to 2.5; the liquid hourly space velocity (LHSV) of the mixture of p-cresol and dimethyl carbonate is 2 to 4 h⁻¹. -1 .

8. The method according to claim 1, characterized in that, In step 3), the bed temperature of the gas phase reaction is 210-240°C, and the reaction pressure of the gas phase reaction is atmospheric pressure.

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