A process for the synthesis of 2-methylpyridine from aniline
By using a metal-supported β-zeolite catalyst for the isomerization rearrangement reaction of aniline under mild reaction conditions, the problems of low yield and easy deactivation of 2-methylpyridine in the prior art have been solved, and high yield and high selectivity of 2-methylpyridine production have been achieved, which is suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2021-10-31
- Publication Date
- 2026-06-02
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of fine chemicals, specifically relating to a process for synthesizing 2-methylpyridine from aniline. Background Technology
[0002] 2-Methylpyridine, with the molecular formula C6H7N, also known as α-methylpyridine or α-picolin, is a colorless, oily liquid at room temperature with a strong, unpleasant odor. It has a freezing point of -38.9°C and a boiling point of 129.5°C. It is highly toxic and miscible with solvents such as acetone, ethanol, ether, and water.
[0003] 2-Methylpyridine is an important chemical intermediate and a key raw material for fine chemicals. It can be used to produce long-acting sulfonamides, pesticide intermediates, and feed intermediates. It can also be used to synthesize specialty resins such as vinylpyridine and 2-vinylpyridine intermediates. The domestic consumption of 2-methylpyridine is increasing at a rate of approximately 25% annually, indicating a significant potential market for 2-methylpyridine in China.
[0004] The industrial production of pyridine bases mainly includes coal tar separation and chemical synthesis. Coal tar separation not only suffers from severe pollution, limited product variety, high costs, poor quality, and high energy consumption, but also has low yields that are difficult to increase. Chemical synthesis typically employs ammonium-aldehyde condensation, reacting aldehydes, ketones, and ammonia as raw materials to synthesize pyridine bases. However, the products of ammonium-aldehyde condensation include 3-methylpyridine, 2-methylpyridine, and 4-methylpyridine, which present challenges in the separation of subsequent products.
[0005] The article, "Synthesis of picolines and other aza-aromatics from arylamines by isomerization-rearrangement and from dinitriles by hydrogenation-cyclization reactions [J]. Catalysis Today, 1997, 37(2): 103-120," describes a process under high temperature and pressure using arylamines such as aniline, methylaniline, and naphthylamine as raw materials. A large amount of ammonia is introduced under the catalysis of an acid catalyst, and through a series of reactions including rearrangement and isomerization, methylpyridine compounds are generated. Taking the synthesis of 2-methylpyridine from aniline as an example, 2-methylpyridine can be generated under the catalysis of an acid zeolite molecular sieve catalyst, but the yield is very low. Furthermore, the catalyst easily loses its activity due to sintering at high temperatures, and a large amount of byproducts such as quinoline, acetonitrile, and indole are also produced. Because of the low yield of pyridine bases, this method cannot achieve large-scale production.
[0006] CN105384683A discloses a method for separating 2-methylpyridine and 4-methylpyridine, byproducts of aniline synthesis of diphenylamine. The steps are as follows: aniline is used as a raw material and flows through a fixed-bed reactor packed with a molecular sieve catalyst. The temperature and pressure of the reactor are controlled, and the mixture undergoes a condensation reaction to convert into diphenylamine, ammonia, and byproducts such as 2-methylpyridine, 4-methylpyridine, water, acridine, and 4-aminobiphenyl. The mixture is then subjected to multi-stage distillation to obtain a low-boiling-point mixed fraction. This low-boiling-point mixed fraction is dehydrated, and the dehydrated mixture is dried. The dried mixture is then distilled, and 2-methylpyridine and 4-methylpyridine are obtained based on their different boiling points. Essentially, this method is a traditional method for separating 2-methylpyridine and 4-methylpyridine, byproducts of aniline synthesis of diphenylamine. Therefore, 2-methylpyridine in this patent is a byproduct of the reaction process, and its yield is low, making large-scale production impossible. Summary of the Invention
[0007] The technical problem to be solved by this invention is to provide a process for synthesizing 2-methylpyridine from aniline. The method of this invention features mild reaction conditions, high yield of 2-methylpyridine, and good reaction selectivity, and has excellent prospects for industrial application.
[0008] The method for synthesizing 2-methylpyridine from aniline of the present invention includes the following steps: in the presence of a catalyst, at a reaction temperature of 100°C to 260°C and a reaction pressure of 1.5 MPa to 4 MPa, the raw material aniline undergoes an isomerization rearrangement reaction, and the reaction product is separated to obtain 2-methylpyridine.
[0009] Further, the catalyst is a metal-supported β-zeolite catalyst. Preferably, the catalyst comprises, by weight: 50%~85% Hβ-zeolite, more preferably 65%~80%; active metal 0.5%~5.0%; auxiliary metal, based on oxides, 0%~6.5%, more preferably 0.5%~5.2%; and alumina 10%~45%, more preferably 15%~34.5%. The silicon-aluminum (i.e., SiO2 / Al2O3) molar ratio of the Hβ-zeolite is 25~300, more preferably 60~220.
[0010] Furthermore, the active metal is selected from at least one of W, Mo, Ni, and Co; the auxiliary metal is selected from at least one of Li, Na, K, Mg, and Ca.
[0011] Furthermore, the β-zeolite-containing catalyst is generally in the form of strip-shaped or spherical particles. When it is strip-shaped, its cross-section can be cylindrical, clover-shaped, or four-leaf clover-shaped. The diameter of the strip-shaped particles is 0.5~3.0 mm, preferably 1.0~2.0 mm. When it is spherical, its particle diameter is 0.5~5.0 mm, preferably 1.0~3.0 mm.
[0012] Furthermore, the specific surface area of the β-zeolite-containing catalyst is 400~700 m². 2 / g, preferably 450~650m 2 / g; pore volume is 0.25~0.60mL / g, preferably 0.40~0.55mL / g; average pore diameter is 1.5~5.0nm, preferably 2.0~4.0nm.
[0013] The preparation method of the Hβ zeolite catalyst is conventional knowledge for those skilled in the art.
[0014] Furthermore, the reaction temperature is 100–260°C, specifically 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 199°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, and any value within any range formed by any two of these values. The preferred reaction temperature is 130–180°C, specifically 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, and any value within any range formed by any two of these values.
[0015] Furthermore, the method for synthesizing 2-methylpyridine from aniline according to the present invention can be a batch operation or a continuous operation, preferably a continuous operation. Batch operation typically refers to a batch operation, in which aniline and a catalyst are added to a reaction vessel and reacted under suitable conditions to obtain 2-methylpyridine. The amount of catalyst used is 1% to 4% of the amount of aniline used. The reaction time is generally 4 to 8 hours. The preferred reaction temperature is 130°C to 180°C, and the preferred reaction pressure is 2 MPa to 4 MPa.
[0016] Furthermore, the method for synthesizing 2-methylpyridine from aniline in this invention is a continuous operation. The raw material aniline passes through a fixed-bed reactor containing a catalyst at a certain rate, and the reaction product is separated to obtain 2-methylpyridine. The preferred reaction temperature is 160℃~220℃, and the preferred reaction pressure is 1.5MPa~3MPa; the liquid hourly space velocity (LHSV) of aniline is 0.5 h⁻¹. -1 ~3h -1 Preferably 1.0h -1 ~1.5h -1 .
[0017] Furthermore, in the continuous operation process, the raw material aniline is preferably fed into the catalyst bed of the fixed-bed reactor via a bottom-feed method.
[0018] Furthermore, the isomer rearrangement reaction of the present invention is preferably carried out in a hydrogen-containing atmosphere, especially a hydrogen atmosphere.
[0019] In this invention, the inventors discovered through research that the mechanism by which aniline isomerization rearrangement directly generates 2-methylpyridine is as shown in formula (1):
[0020] (1);
[0021] The mechanism for the synthesis of diphenylamine from aniline is shown in equation (2).
[0022] (2).
[0023] The inventors of this application have also discovered that the isomerization rearrangement of aniline to 2-methylpyridine and the condensation of aniline to prepare diphenylamine are both influenced by the catalyst and the reaction temperature. Using the metal-supported β-zeolite catalyst of this invention, the reaction route of aniline can be switched between 2-methylpyridine and diphenylamine due to the change in the catalytic active center. Furthermore, a lower reaction temperature is more favorable for the synthesis of 2-methylpyridine. Based on this discovery, the present invention proposes the above-mentioned technical solution.
[0024] Compared with the prior art, the process of the present invention has the following beneficial effects:
[0025] 1. The method of this invention has a high conversion rate and high selectivity for the target product, 2-methylpyridine (for example, in Example 4, when the Ni loading is 1.5 wt%, the selectivity for 2-methylpyridine is as high as 67.6%). The possible reason for this is that the selection of a β-zeolite catalyst containing an active metal significantly alters the reaction mechanism: the main reaction, which involves the condensation of two aniline molecules to form one diphenylamine molecule, is transformed into a main reaction primarily involving the isomerization rearrangement of aniline molecules to generate 2-methylpyridine. Therefore, the method of this invention can achieve the goal of producing 2-methylpyridine from aniline.
[0026] 2. Through extensive research, the inventors of this application unexpectedly discovered that when synthesizing diphenylamine from aniline at reaction temperatures far below conventional conditions, the target product shifts from predominantly diphenylamine to predominantly 2-methylpyridine. Analyzing the reasons, the inventors believe that thermodynamic factors are one of the influences on the selectivity of 2-methylpyridine. Thermodynamic analysis of the reaction system revealed that when the reaction is carried out under liquid-phase conditions, the isomerization of aniline to 2-methylpyridine is exothermic, and low-temperature conditions favor the reaction. However, for the synthesis of diphenylamine from aniline, high-temperature conditions are more favorable. Therefore, the process of this invention provides a feasible technical route for the synthesis of 2-methylpyridine.
[0027] 3. Existing techniques for synthesizing pyridine base compounds typically require the introduction of large amounts of ammonia gas. The presence of ammonia gas occupies acidic sites on the catalyst, leading to a decrease in catalyst activity. Furthermore, the high temperature and pressure required limit the industrial application of this method. The method described in this invention, however, does not require the introduction of ammonia gas, has mild reaction conditions, and uses only aniline as a reactant. High-purity 2-methylpyridine can be obtained through subsequent distillation. Detailed Implementation
[0028] The process of the present invention will be described in more detail below through specific embodiments.
[0029] In the examples and comparative examples: the calculation methods for aniline conversion and 2-methylpyridine selectivity:
[0030] Aniline molar conversion rate = (moles of aniline in the feedstock - moles of aniline in the product) / moles of aniline in the feedstock before the reaction;
[0031] 2-Methylpyridine molar selectivity = (moles of 2-methylpyridine in the product) / (moles of aniline in the starting material before reaction - moles of aniline in the product).
[0032] The properties of the catalysts used in the examples and comparative examples are listed in Table 1.
[0033] Table 1 Catalysts
[0034]
[0035] Example 1
[0036] A batch reactor (200 mL) was selected for the reaction, which was carried out under a hydrogen atmosphere. Catalyst A (1 g) was used, aniline (50 g) was added, and the reaction temperature was 130°C, the reaction time was 6 h, and the reaction pressure was 4 MPa.
[0037] Example 2
[0038] A batch reactor (200 mL) was selected, and the reaction was carried out under a hydrogen atmosphere. Catalyst B was used, with a catalyst dosage of 1 g and aniline dosage of 50 g. The reaction temperature was 180 °C, the reaction time was 6 h, and the reaction pressure was 4 MPa.
[0039] Example 3
[0040] A batch reactor was still selected, and the reaction was carried out under a hydrogen atmosphere. The catalyst used was the aforementioned catalyst E, with a catalyst dosage of 1g and aniline dosage of 50g. The reaction temperature was 130℃, the reaction time was 6h, and the reaction pressure was 4MPa.
[0041] Example 4
[0042] A fixed-bed reactor is loaded with 100 mL of catalyst B. The feedstock, aniline, is fed through the catalyst bed. The reaction temperature is 160 °C, the reaction pressure is 1.5 MPa, and the hydrogen flow rate is 15 L·h. -1 The liquid hourly space velocity (LHSV) is 1.5 h⁻¹. -1 .
[0043] Example 5
[0044] A fixed-bed reactor is loaded with 100 mL of catalyst B. Aniline is fed directly through the catalyst bed. The reaction temperature is 220 °C and the reaction pressure is 3 MPa. The hydrogen flow rate is 10 L / h. -1 The liquid hourly space velocity (LHSV) is 1.5 h⁻¹. -1 .
[0045] Example 6
[0046] A fixed-bed reactor is loaded with 100 mL of catalyst C. Aniline is fed directly through the catalyst bed. The reaction temperature is 200 °C and the reaction pressure is 2 MPa. The hydrogen flow rate is 5 L / h. -1 The liquid hourly space velocity is 1 h⁻¹ -1 .
[0047] Example 7
[0048] A fixed-bed reactor is loaded with 100 mL of catalyst D. Aniline is fed directly through the catalyst bed. The reaction temperature is 200 °C and the reaction pressure is 3 MPa. The hydrogen flow rate is 15 L / h. -1 The liquid volume hourly space velocity is 1.5 h⁻¹. -1 .
[0049] Example 8
[0050] A fixed-bed reactor was loaded with 100 mL of catalyst C. Aniline was fed directly through the catalyst bed. The reaction temperature was 240 °C, the reaction pressure was 2.0 MPa, and the hydrogen flow rate was 5 L / h. -1 The liquid hourly space velocity (LHSV) is 1.0 h⁻¹. -1 .
[0051] Example 9
[0052] A fixed-bed reactor was loaded with 100 mL of catalyst C. The feedstock, aniline, was fed through the catalyst bed. The reaction temperature was 260 °C, the reaction pressure was 2.0 MPa, and the hydrogen flow rate was 5 L·h. -1 The liquid hourly space velocity (LHSV) is 1.0 h⁻¹. -1 .
[0053] Table 2
[0054]
[0055] Table 3
[0056]
[0057] Comparative Example 1
[0058] In existing technologies, alkylpyridine is synthesized in a fixed-bed reactor using Co / ZSM-5 molecular sieve catalysis. The Si / Al ratio is 30, the Co content is 0.75 wt%, the operation is at atmospheric pressure, the reaction temperature is 450 ℃, and the reactants are formaldehyde and acetaldehyde in a 1:1 molar ratio with a mass hourly space velocity (HHSV) of 1 h⁻¹. -1 2-methylpyridine can be obtained.
[0059] Comparative Example 2
[0060] In the existing technology, the reaction is carried out in a fixed-bed reactor using a Pb / ZSM-5 catalyst with a Pd content of 1.0 wt% and a Si / Al ratio of 150. Ethanol, formaldehyde, and ammonia are used as raw materials in a molar ratio of 1:0.8:1.5, and the mass hourly space velocity (HHSV) is 0.5 h⁻¹. -1 The operation was carried out under normal pressure at a reaction temperature of 420 °C.
[0061] Comparative Example 3
[0062] In existing technologies, when carried out in a fixed-bed reactor using an HZSM-5 molecular sieve catalyst, with a Si / Al ratio of 30 and a molar ratio of aniline to ammonia of 1:8, the mass hourly space velocity (HHSV) is 1.0 h⁻¹. -1 2-methylpyridine is generated at a temperature of 510℃ and a pressure of 2.9MPa.
[0063] Comparative Example 4
[0064] A fixed-bed reactor is loaded with 100 mL of catalyst F. Aniline is fed directly through the catalyst bed. The reaction temperature is 200 °C and the reaction pressure is 3 MPa. The hydrogen flow rate is 15 L / h. -1 The liquid volume hourly space velocity is 1.5 h⁻¹. -1 .
[0065] Table 4
[0066]
Claims
1. A method for synthesizing 2-methylpyridine from aniline, comprising the following steps: in the presence of a catalyst, at a reaction temperature of 100℃~260℃ and a reaction pressure of 1.5MPa~4MPa, the raw material aniline undergoes an isomerization rearrangement reaction, and the reaction product is separated to obtain 2-methylpyridine; in, The catalyst comprises, by weight: 50%~85% Hβ zeolite, 0.5%~5.0% active metal, 0.5%~6.5% auxiliary metal (based on oxides), and 10%~45% alumina; The silicon-aluminum molar ratio of the Hβ zeolite is 25-300; the active metal is selected from at least one of W, Mo, Ni and Co.
2. The method according to claim 1, characterized in that, The auxiliary metal is selected from at least one of Li, Na, K, Mg, and Ca.
3. The method according to claim 1, characterized in that, The catalyst comprises, by weight: 65% to 80% Hβ zeolite, 0.5% to 5.2% auxiliary metal (based on oxides), and 15% to 34.5% alumina; the silicon-to-alumina molar ratio of the Hβ zeolite is 25 to 200.
4. The method according to claim 1, characterized in that, The isomer rearrangement reaction is carried out in a hydrogen-containing atmosphere.
5. The method according to claim 4, characterized in that, The isomer rearrangement reaction was carried out in a hydrogen atmosphere.
6. The method according to claim 1, characterized in that, The catalyst has a specific surface area of 400~700 m². 2 / g, with a specific pore volume of 0.25~0.60mL / g and an average pore diameter of 1.5~5.0nm.
7. The method according to claim 6, characterized in that, The catalyst has a specific surface area of 450~650m². 2 / g, with a specific pore volume of 0.40~0.55mL / g and an average pore diameter of 2.0~4.0nm.
8. The method according to claim 1, characterized in that, The catalyst is in the form of strip-shaped or spherical particles, with the diameter of the strip-shaped particles being 0.5~3.0 mm and the diameter of the spherical particles being 0.5~5.0 mm.
9. The method according to claim 1, characterized in that, The reaction temperature is 130℃~180℃.
10. The method according to any one of claims 1-8, characterized in that, The method is an intermittent operation, in which the raw material aniline and the catalyst are reacted in a reactor at a temperature of 130℃~180℃, the amount of catalyst is 1wt%~4wt% of the amount of raw material aniline, the reaction pressure is 2MPa~4MPa, and the reaction time is 4h~8h.
11. The method according to any one of claims 1-8, characterized in that, The method is a continuous operation, in which the raw material aniline is reacted in a fixed-bed reactor containing a catalyst; the reaction temperature is 160℃~260℃, the reaction pressure is 1.5MPa~3MPa, and the liquid hourly space velocity (LHSV) of aniline is 0.5h⁻¹. -1 ~3h -1 .
12. The method according to claim 11, characterized in that, The raw material aniline is fed into the fixed bed reactor via a bottom feed method and passes through the catalyst bed.