Method for producing N-methylaniline

Abstract

The invention relates to the field of N-methylaniline production, and discloses a method for producing N-methylaniline. The method comprises the following step: in the presence of a catalyst, reacting reaction raw materials, namely a methylation reagent and aniline, the catalyst comprises a molecular sieve, an inorganic oxide and a modified component, and the modified component is selected from at least one of copper, alkali metal, alkaline earth metal and iron; wherein the sum of the amount of weak acids and the amount of medium and weak acids in the catalyst accounts for more than 80% of the total acid amount. When the method provided by the invention is used for producing the N-methylaniline, the selectivity of the target product N-methylaniline is relatively high.

Description

Technical Field

[0001] This invention relates to the field of N-methylaniline production, and more specifically to a method for producing N-methylaniline. Background Technology

[0002] The N-alkylation of aniline is a commercially important chemical reaction. N-methylaniline, the product of N-alkylation of aniline, is an important organic compound widely used in pharmaceuticals, pesticides, and dyes. It possesses excellent anti-knock properties and is a key intermediate. The synthesis of N-methylaniline is mainly divided into liquid-phase synthesis and gas-phase synthesis. Liquid-phase synthesis, due to the use of strong acids as catalysts, suffers from problems such as corrosiveness, environmental pollution, and difficulties in separating byproducts, and has been gradually replaced by gas-phase synthesis. Gas-phase synthesis uses environmentally friendly solid catalysts, with methanol as the alkylating agent, to catalytically synthesize N-methylaniline in a fixed-bed reactor.

[0003] In existing technologies, copper-zinc-cadmium (CCD) catalysts are commonly used in gas-phase synthesis methods. CCD catalysts are safer and more environmentally friendly than liquid acids, and they can be recycled. However, when used to prepare N-methylaniline, the target product selectivity is low and the catalytic performance is poor, while the byproduct selectivity is high. This makes the catalyst prone to deactivation, and the catalyst regeneration process is relatively complex, leaving room for further improvement in the economic efficiency of the catalyst. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a method for producing N-methylaniline. The method provided by this invention produces N-methylaniline with high selectivity for the target product, N-methylaniline.

[0005] To achieve the above objectives, the present invention provides a method for producing N-methylaniline, the method comprising reacting a methylating reagent and aniline in the presence of a catalyst;

[0006] The catalyst comprises a molecular sieve, an inorganic oxide, and a modifying component, wherein the modifying component is selected from copper, and at least one of alkali metals, alkaline earth metals, and iron.

[0007] The catalyst contains more than 80% of the total acid content, consisting of both weak and moderately weak acids.

[0008] Preferably, the method for preparing the catalyst includes the following steps:

[0009] (1) Mix the molecular sieve and the inorganic oxide precursor to obtain a mixture;

[0010] (2) The mixture obtained in step (1) is mixed with a solution containing the modified component precursor and then calcined.

[0011] The beneficial effects of the present invention through the above technical solution include:

[0012] The method provided by this invention uses a specific type of catalyst and controls the ratio of the weak acid and the sum of the weak acids in the catalyst within a specific range, which helps to reduce the occurrence of side reactions and improve the selectivity of N-methylaniline; it can effectively improve the catalyst's lifespan, realize the long-term continuous operation of the catalyst, facilitate continuous industrial production, and greatly save production costs.

[0013] Moreover, the method provided by this invention is green, environmentally friendly, and pollution-free, and the catalyst can be recycled, achieving zero pollution and zero emissions in the production process.

[0014] In a preferred embodiment, the method provided by the present invention controls the order of adding raw materials during the catalyst preparation process. The molecular sieve and inorganic oxide precursor are mixed first, and then directly mixed with the solution containing the modified component precursor without calcination to form the catalyst. Only one calcination is required during the catalyst preparation process, which avoids the multiple calcinations in the catalyst preparation process in the prior art, reduces the difficulty of the catalyst preparation process, and reduces energy consumption. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the 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.

[0016] The present invention provides a method for producing N-methylaniline, the method comprising reacting a methylating reagent and aniline in the presence of a catalyst;

[0017] The catalyst comprises a molecular sieve, an inorganic oxide, and a modifying component, wherein the modifying component is selected from copper, and at least one of alkali metals, alkaline earth metals, and iron.

[0018] The catalyst contains more than 80% of the total acid content, consisting of both weak and moderately weak acids.

[0019] The method provided by this invention has high selectivity for the target product, is green and environmentally friendly with no pollution, and the catalyst can be recycled, truly achieving zero pollution and zero emissions in the production process.

[0020] According to the present invention, the sum of the weak acid content and the moderately weak acid content of the catalyst accounts for more than 80% of the total acid content, specifically 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, and any two of these values ​​forming a range, preferably 85-95%. This preferred embodiment is advantageous for improving the selectivity of N-methylaniline and reducing the selectivity of byproducts such as dimethylaniline and trimethylaniline.

[0021] The acid content distribution of the catalyst described in this invention was characterized using the NH3-programmed temperature desorption method (NH3-TPD). The characterization method is as follows: Instrument: Quantachrome Chemstar TPx; Testing procedure: 0.15 g (20-40 mesh) of catalyst sample was weighed, heated to 550 °C to dry, and then cooled to 100 °C to saturate the catalyst with NH3 adsorption. The temperature was then raised to 250 °C, 350 °C, 450 °C, and 550 °C to desorb NH3, and the NH3 concentration was detected using a TCD detector. The adsorption curves obtained at different temperature ranges were integrated, and the instrument automatically calculated the acid density distribution at different temperatures. Specifically, the acid content obtained at 250 °C was weak acid, 250-350 °C was moderately weak acid, 350-450 °C was moderately strong acid, and 450-550 °C was strong acid.

[0022] According to the present invention, preferably, the ratio of the amount of Brønsted acid to the amount of Lewis acid in the catalyst is 0.5-10:1, specifically 0.5:1, 1:1, 1.2:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, and the range of any two of these values, preferably 1.2-8:1. This preferred embodiment is beneficial for improving the selectivity of N-methylaniline and reducing the selectivity of byproducts such as dimethylaniline and trimethylaniline.

[0023] The ratio of Brønsted acid (B) to Lewis acid (L) in the catalyst of this invention was determined by pyridine infrared spectroscopy. Specifically, this involved using a Bruker Tensor II Fourier transform infrared spectrometer. Approximately 25 mg of the catalyst sample was pressed into a tablet at 20 MPa for 5 min, placed in the in-situ cell of the infrared spectrometer, sealed, and heated to 450 °C at a rate of 10 °C / min. A vacuum was then applied to 10... -6The sample was treated at approximately 1000 Pa for 2 hours to desorb impurities such as water molecules physically adsorbed by the molecular sieve. After cooling to room temperature, background spectra were collected, followed by static adsorption of pyridine for 10 minutes. The temperature was then increased to 200℃ at a rate of 10℃ / min, and vacuumed for 30 minutes. After cooling to room temperature, the pyridine adsorption infrared spectrum was measured and integrated. Subsequently, the temperature was increased to 350℃, vacuumed for 30 minutes, and after cooling to room temperature, the pyridine adsorption infrared spectrum was measured and integrated. (1540 cm⁻¹) -1 The absorption peak at that location belongs to Acidic site (B acid), 1450 cm -1 The absorption peak is attributed to the Lewis acid site (L acid). The acidity of the Brønsted (B) acid and the Lewis (L) acid are calculated using the following formula:

[0024] C B =1.88A B R 2 / W

[0025] C L =1.42A L R 2 / W

[0026] C is the concentration of β-acid or L-acid (mmol / g);

[0027] A is the integral area of ​​the absorption peak of Brønsted acid or Lewis acid;

[0028] R is the radius (cm) of the sample piece;

[0029] W is the mass (mg) of the sample piece.

[0030] According to the present invention, preferably, the pore volume of the catalyst is 0.05-0.5 cm³. 3 / g, preferably 0.1-0.5cm 3 / g.

[0031] The pore volume of the catalyst described in this invention was measured using the BET method.

[0032] According to the present invention, preferably, the mass ratio of the molecular sieve to the inorganic oxide is 1-20:1, specifically 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, or 11:1. The ratios are 11.5:1, 12:1, 12.5:1, 13:1, 13.5:1, 14:1, 14.5:1, 15:1, 15.5:1, 16:1, 16.5:1, 17:1, 17.5:1, 18:1, 18.5:1, 19:1, 19.5:1, 20:1, and the range of any two points among these values, preferably 1-15:1.

[0033] According to the present invention, preferably, the mass ratio of the modified component (calculated as oxide) to the inorganic oxide is 0.01-1:1, specifically 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, and the range of any two of these values, preferably 0.02-0.8:1.

[0034] According to the present invention, preferably, the mass ratio of copper to at least one of alkali metals, alkaline earth metals and Fe, calculated as oxides, is 1:0.1-30, specifically 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, 30:1, and a range of any two of these values, preferably 1:1-20.

[0035] Controlling the content of each component in the catalyst within the above-mentioned preferred range is beneficial to improving the catalytic performance of the catalyst.

[0036] The present invention allows for a wide range of molecular sieve selection. Preferably, the molecular sieve is selected from at least one of Y-type molecular sieve, ZSM-5 molecular sieve, β-type molecular sieve, MCM-22 molecular sieve, and mordenite, and more preferably from at least one of Y-type molecular sieve, ZSM-5 molecular sieve, and β-type molecular sieve. Using the above-mentioned specific preferred types of molecular sieves results in better conversion and selectivity in the reaction.

[0037] According to the present invention, preferably, the silicon-aluminum molar ratio of the molecular sieve is 2-1000:1, more preferably 2-100:1.

[0038] The present invention has a wide range of choices for the types of inorganic oxides. Preferably, the inorganic oxides are aluminum oxide and / or silicon oxide, with aluminum oxide being the most preferred.

[0039] The present invention has a wide range of choices for the types of alkali metals, and preferably, the alkali metals are potassium and / or sodium.

[0040] The present invention has a wide range of choices for the alkaline earth metals, and preferably, the alkaline earth metals are calcium and / or magnesium.

[0041] This invention does not impose any particular limitation on the preparation method of the catalyst, as long as a catalyst with the above-described characteristics can be obtained. To further improve the performance of the catalyst and to better illustrate the preparation of the above-described catalyst, this invention also provides a method for preparing the catalyst.

[0042] According to the present invention, preferably, the method for preparing the catalyst includes the following steps:

[0043] (1) Mix the molecular sieve and the inorganic oxide precursor to obtain a mixture;

[0044] (2) The mixture obtained in step (1) is mixed with a solution containing the modified component precursor and then calcined.

[0045] According to the present invention, preferably, the inorganic oxide precursor exists in a solid and / or sol state, more preferably in a sol state. This preferred embodiment allows for better mixing and more uniform distribution of the molecular sieve and inorganic oxide, resulting in stronger interactions and better catalyst activity.

[0046] Preferably, when the inorganic oxide precursor exists in a solid state, the inorganic oxide precursor is selected from at least one of boehmite, aluminum chloride, aluminum hydroxide, water glass, and silica.

[0047] Preferably, when the inorganic oxide precursor exists in a sol state, the inorganic oxide precursor is a silica sol and / or an aluminum sol.

[0048] According to the present invention, preferably, when the inorganic oxide precursor exists in a sol state, the concentration of each inorganic oxide precursor is independently 10-30 wt%.

[0049] This invention does not particularly limit the precursor of the modified component, as long as it contains the modified component, it can be any compound containing the modified component commonly found in the art. Preferably, the precursor of the modified component is selected from at least one of the chloride, sulfate, and nitrate of the modified component, such as copper chloride, cuprous chloride, copper nitrate, copper sulfate, cuprous sulfate, magnesium sulfate, magnesium nitrate, magnesium chloride, ferric chloride, ferrous chloride, ferric sulfate, and ferrous sulfate, etc.

[0050] The present invention does not particularly limit the molding method in step (2), and those skilled in the art can choose according to actual needs.

[0051] According to the present invention, preferably, the calcination conditions in step (2) include: a temperature of 450-800℃ and a time of 1-15h.

[0052] According to the present invention, preferably, the method for preparing the catalyst further includes introducing a colloidal solvent during the mixing process in step (2). The colloidal solvent of the present invention can be a conventional choice in the art. Preferably, the colloidal solvent is selected from at least one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, and acetic acid.

[0053] In this invention, there is no particular limitation on the amount of adhesive solvent used, as long as it can meet the adhesive requirements. Those skilled in the art can select according to actual needs.

[0054] In this invention, there is no particular limitation on the amount of the methylating reagent and aniline used as reaction raw materials, as long as the reaction requirements are met. Preferably, the molar ratio of the methylating reagent to aniline is 0.1-3:1, more preferably 0.5-2:1.

[0055] The present invention allows for a wide range of choices of the methylating agent. Preferably, the methylating agent is methanol and / or formic acid.

[0056] The method provided by this invention selects a specific type of catalyst, which can improve catalyst stability and target product selectivity, reduce side reactions, enable the catalyst to operate stably for continuous production of N-methylaniline, and broaden the synthesis reaction temperature range, which is beneficial for industrial production.

[0057] According to the present invention, preferably, the reaction conditions include: a reaction temperature of 100-250°C and a mass hourly space velocity (HHSV) of 0.1-10 h⁻¹ for the methylating agent and aniline. -1 .

[0058] According to the present invention, preferably, the reaction conditions include: a reaction temperature of 120-230°C and a mass hourly space velocity (H₂S₀) of 0.2-8 h⁻¹ for the methylating agent and aniline. -1 .

[0059] According to the present invention, preferably, the reaction is a gas-phase reaction.

[0060] In this invention, it should be noted that the gas-phase reaction refers to the reaction raw materials, methylating reagent and aniline, being fed in gas phase or the reaction conditions during the reaction process causing the methylating reagent and aniline to be in a gas phase state. This invention does not have a particular limitation on the gasification method of the raw materials, and methods conventionally defined in the art can be applied to this invention.

[0061] The present invention will be described in detail below through embodiments.

[0062] In the following examples, the components in the catalyst were calculated based on the amount of feed.

[0063] The conversion rate of aniline and the selective distribution of the resulting product N-methylaniline were determined by gas chromatography using an Anglient-7890 gas chromatograph equipped with a high-pressure sampler (HP-PONA 50m × 0.2mm capillary column). The detection method for determining the catalyst's single-pass lifetime was as follows: the catalyst was considered deactivated when the aniline conversion rate decreased to 98%, and the reaction time experienced by the catalyst was the catalyst's single-pass lifetime.

[0064] Example 1

[0065] (1) 90g of HY molecular sieve (silicon-aluminum molar ratio of 5) and 10g of alumina were mixed evenly to obtain a mixture;

[0066] (2) Dissolve 3g of cuprous chloride and 8g of magnesium sulfate in 50g of water, adjust the pH to 3 with nitric acid solution, then add the mixture from step (1) and mix evenly. Then extrude the mixture using an extruder and calcine at 500℃ for 12h to obtain catalyst Y-1. The composition and characteristic parameters of the catalyst are shown in Table 1.

[0067] The catalyst was reacted in a fixed-bed reactor with a methanol:aniline molar ratio of 1:1 and a mass hourly space velocity (WHSV) of 1 h⁻¹ for both methanol and aniline. -1 The reaction temperature was 150℃. The raw materials were pumped into the reactor, where aniline and methanol were vaporized and reacted after contacting the catalyst bed. The reaction results after 4 hours and the catalyst lifetime are shown in Table 2.

[0068] Example 2

[0069] (1) 750g of β molecular sieve (silicon-aluminum molar ratio of 20) and 1250g of aluminum sol with a concentration of 20wt% were mixed evenly to obtain a mixture;

[0070] (2) Take 5g Cu2SO4 and 100g calcium chloride, add them to the above mixture, then adjust the pH to 2.5 with nitric acid, grind and extrude into small balls, and calcine at 600℃ for 1h to obtain catalyst β-1. The composition and characteristic parameters of the catalyst are shown in Table 1.

[0071] The catalyst was reacted in a fixed-bed reactor with a methanol:aniline molar ratio of 1:1 and a mass hourly space velocity (WHSV) of 1 h⁻¹ for both methanol and aniline. -1 The reaction temperature was 150℃. The raw materials were pumped into the reactor, where aniline and methanol were vaporized and reacted after contacting the catalyst bed. The reaction results after 4 hours and the catalyst lifetime are shown in Table 2.

[0072] Example 3

[0073] (1) 200g of ZSM-5 molecular sieve (silicon-aluminum molar ratio of 50) and 500g of silica sol with a concentration of 20wt% were mixed evenly to obtain a mixture;

[0074] (2) Take 10g Cu(NO3)2 and 20g ferrous chloride and add them to the above mixture. Mix them evenly, then extrude them using an extruder and calcine them at 800℃ for 2h to obtain catalyst ZSM-1. The composition and characteristic parameters of the catalyst are shown in Table 1.

[0075] The catalyst was reacted in a fixed-bed reactor with a methanol:aniline molar ratio of 1:1 and a mass hourly space velocity (WHSV) of 5 h⁻¹ for both methanol and aniline. -1 The reaction temperature was 225℃. The raw materials were pumped into the reactor, where aniline and methanol were vaporized and reacted after contacting the catalyst bed. The reaction results after 4 hours and the catalyst lifetime are shown in Table 2.

[0076] Comparative Example 1

[0077] The catalyst was prepared according to the method of Example 1, except that magnesium sulfate was not added, resulting in catalyst DY-1. The composition and characteristic parameters of the catalyst are shown in Table 1.

[0078] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results and catalyst lifetime results after 4 hours of reaction are shown in Table 2.

[0079] Comparative Example 2

[0080] The catalyst was prepared according to the method of Example 1, except that cuprous chloride was not added during the preparation of the catalyst, resulting in catalyst DY-2. The composition and characteristic parameters of the catalyst are shown in Table 1.

[0081] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results and catalyst lifetime results after 4 hours of reaction are shown in Table 2.

[0082] Comparative Example 3

[0083] The catalyst was prepared according to the method of Example 2, except that calcium chloride was not added during the preparation of the catalyst, resulting in catalyst Dβ-1. The composition and characteristic parameters of the catalyst are shown in Table 1.

[0084] The reaction was carried out according to the method and reaction conditions of Example 2. The reaction results and catalyst lifetime results after 4 hours of reaction are shown in Table 2.

[0085] Table 1

[0086]

[0087] Table 2

[0088]

[0089]

[0090] As shown in Table 2, the method provided by this invention can effectively improve the selectivity of the target product N-methylaniline and reduce the selectivity of the main byproducts N,N-dimethylaniline and N,N,C-trimethylaniline. Furthermore, the catalyst provided by this invention has a significantly improved lifespan, which is beneficial for long-term continuous operation and industrial continuous production.

[0091] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing N-methylaniline, characterized in that, The method includes reacting a methylating agent and aniline in the presence of a catalyst; The catalyst comprises a molecular sieve, an inorganic oxide, and a modifying component, wherein the modifying component is selected from copper, and at least one of alkali metals, alkaline earth metals, and iron. The catalyst contains more than 80% of the total acid content, consisting of both weak and moderately weak acids.

2. The method according to claim 1, wherein, The total acid content of the catalyst is 85-95% of the total acid content, consisting of weak acid and moderately weak acid. Preferably, the ratio of Brønsted acid to Lewis acid in the catalyst is 0.5-10:1, more preferably 1.2-8:1; Preferably, the catalyst has a pore volume of 0.05-0.5 cm³. 3 / g, preferably 0.1-0.5cm 3 / g.

3. The method according to claim 1 or 2, wherein, The mass ratio of molecular sieve to inorganic oxide is 1-20:1, preferably 1-15:1; Preferably, the mass ratio of the modified component (calculated as oxide) to the inorganic oxide is 0.01-1:1, more preferably 0.02-0.8:1; Preferably, the mass ratio of copper to at least one of alkali metals, alkaline earth metals and Fe, based on oxides, is 1:0.1-30, more preferably 1:1-20.

4. The method according to any one of claims 1-3, wherein, The molecular sieve is selected from at least one of Y molecular sieve, ZSM-5 molecular sieve, β molecular sieve, MCM-22 molecular sieve and mordenite, preferably selected from at least one of Y molecular sieve, ZSM-5 molecular sieve and β molecular sieve; Preferably, the silicon-aluminum molar ratio of the molecular sieve is 2-1000:1, more preferably 2-100:

1.

5. The method according to any one of claims 1-4, wherein, The inorganic oxide is aluminum oxide and / or silicon oxide; Preferably, the alkali metal is potassium and / or sodium; Preferably, the alkaline earth metal is calcium and / or magnesium.

6. The method according to any one of claims 1-5, wherein, The method for preparing the catalyst includes the following steps: (1) Mix the molecular sieve and the inorganic oxide precursor to obtain a mixture; (2) The mixture obtained in step (1) is mixed with a solution containing the modified component precursor and then calcined.

7. The method according to claim 6, wherein, The inorganic oxide precursor exists in a solid and / or sol state, preferably in a sol state; More preferably, the inorganic oxide precursor is silica sol and / or aluminum sol; Preferably, when the inorganic oxide precursor is silica sol and / or aluminum sol, the concentration of each inorganic oxide precursor is independently 10-30 wt%.

8. The method according to claim 6, wherein, The roasting conditions in step (2) include: a temperature of 450-800℃ and a time of 1-15h.

9. The method according to any one of claims 1-8, wherein, The molar ratio of the methylating agent to aniline is 0.1-3:1, preferably 0.5-2:1; Preferably, the methylating agent is methanol and / or formic acid.

10. The method according to any one of claims 1-9, wherein, The reaction conditions include: a reaction temperature of 100-250℃ and a mass hourly space velocity (HHSV) of 0.1-10 h⁻¹ for the methylating agent and aniline. -1 ; Preferably, the reaction conditions include: a reaction temperature of 120-230°C and a mass hourly space velocity (H₂S) of 0.2-8 h⁻¹ for the methylating agent and aniline. -1 ; Preferably, the reaction is a gas-phase reaction.

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