A continuous catalytic synthesis system of high selectivity 4-methylpyridine and its application method

Abstract

This invention discloses a continuous catalytic synthesis system for highly selective 4-methylpyridine and its application method, belonging to the field of chemical production technology. The system includes a raw material pretreatment and plasma activation unit, a microchannel catalytic reaction unit, an online analysis unit, a control unit, and a product separation and recycling unit. The method uses pyridine and methanol as raw materials. After plasma activation pretreatment, the raw materials enter a microchannel reactor packed with a Co-La / ZSM-5 catalyst for reaction, and the reaction conditions are controlled by online analysis feedback. This invention achieves highly selective and high-yield synthesis of 4-methylpyridine at 300-370℃ through the synergistic effect of plasma activation for directional regulation of raw material activity, microreactor-enhanced mass and heat transfer, and shape-selective 4-methylation catalysis by a specific bimetallic catalyst. Simultaneously, it extends catalyst lifetime and solves the technical problems of low selectivity, numerous side reactions, and easy catalyst deactivation in traditional processes.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, specifically to a continuous catalytic synthesis system for highly selective 4-methylpyridine and its application method. Background Technology

[0002] 4-Methylpyridine is an important fine chemical intermediate widely used in pharmaceuticals, pesticides, dyes, and rubber additives. With the increasing demand from downstream industries, developing efficient and economical 4-methylpyridine synthesis processes has significant industrial value.

[0003] Currently, one of the mainstream methods for industrial production of 4-methylpyridine is the direct catalytic methylation reaction of pyridine with methanol. This route has advantages such as high atom economy and readily available raw materials. Existing technologies mostly follow the fixed-bed reaction process for the synthesis of 2-methylpyridine, and the catalyst system mainly uses conventional ZSM-5 molecular sieves or their monometallic (such as Co, Ni, Pb, etc.) modified products. For example, Chinese patent CN103252254B discloses a catalyst for the synthesis of 2-methylpyridine and 4-methylpyridine and its preparation method, which can obtain a certain yield of methylpyridine at around 400℃.

[0004] However, the above-mentioned existing technical solutions still have the following technical drawbacks when used for the selective synthesis of 4-methylpyridine: (1) Insufficient selectivity control: The pore structure and acidic site distribution of conventional ZSM-5 molecular sieves lack shape-selective guidance for the 4-substitution products, resulting in a selectivity of 4-methylpyridine in the reaction products that is generally lower than 85%, while generating a large amount of byproducts such as 2-methylpyridine and 2,4-dimethylpyridine. These byproducts have boiling points close to the target product, making subsequent distillation separation difficult and energy-intensive.

[0005] (2) Harsh reaction conditions and poor catalyst stability: To achieve a high conversion rate, existing fixed-bed processes usually need to be carried out at high temperatures of 380-450℃. High temperatures not only exacerbate side reactions such as methanol dehydration and pyridine deep methylation, but also accelerate carbon deposition on the catalyst surface. The catalyst's single-pass life is generally less than 500 hours, requiring frequent regeneration and affecting production continuity.

[0006] (3) Limited heat and mass transfer efficiency: There is a significant bed hotspot effect inside the fixed-bed reactor. Methylation is a strongly exothermic reaction, and local overheating will further deteriorate product selectivity and accelerate catalyst sintering and deactivation. The limitations of the reactor structure itself make it difficult for traditional processes to simultaneously optimize heat transfer, mass transfer and reaction kinetics matching through the adjustment of a single parameter.

[0007] To address the aforementioned issues, existing research has largely focused on screening the active components of the catalyst or simply optimizing process parameters. However, limited by the structural framework of fixed-bed reactors, these single-dimensional improvements are insufficient to overcome the technical challenge of balancing high selectivity and stability.

[0008] Therefore, developing a new system and method for synthesizing 4-methylpyridine with high selectivity and long-term stable operation under mild conditions remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] The purpose of this invention is to provide a highly selective continuous catalytic synthesis system for 4-methylpyridine and its application method, thereby solving the defects of low selectivity, high reaction temperature, short catalyst lifetime, and high energy consumption in the existing pyridine methylation synthesis of 4-methylpyridine.

[0010] To achieve the above objectives, the present invention provides a continuous catalytic synthesis system for highly selective 4-methylpyridine, wherein the system comprises, sequentially arranged along the material flow direction, the following components: The raw material pretreatment and plasma activation unit is used to vaporize and plasma activate the mixed raw materials of pyridine and methanol. The microchannel catalytic reaction unit has its inlet connected to the outlet of the plasma activation unit, and its interior is equipped with microchannels for loading catalysts to carry out methylation reactions; An online analysis unit, connected to the outlet of the microchannel catalytic reaction unit, is used to monitor the composition of the reaction products in real time. The collaborative feedback control unit is connected to the online analysis unit, plasma activation unit, microchannel catalytic reaction unit and raw material feeding unit respectively, and is used to receive real-time data from the online analysis unit and output control signals; And a product separation and recycling unit, connected to the outlet of the microchannel catalytic reaction unit, for separating the target product and recycling unreacted raw materials back to the raw material pretreatment and plasma activation unit; The collaborative feedback control unit dynamically adjusts the discharge power of the plasma activation unit, the temperature and pressure of the microchannel catalytic reaction unit, and the raw material feed ratio based on real-time data, forming a closed-loop control.

[0011] Preferably, the raw material pretreatment and plasma activation unit includes a mixer, a vaporizer, and a plasma generator connected after the vaporizer. The plasma generator is a jet-type dielectric barrier discharge reactor with an electrode spacing of 2-5 mm, which can directionally generate high concentrations of methyl free radicals.

[0012] Preferably, the reaction channel of the microchannel catalytic reaction unit has a characteristic size of 1-4 mm, and the inner wall of the channel is pretreated by plasma spraying and loaded with a Co-La / ZSM-5 catalyst layer with a thickness of 50-150 μm.

[0013] Preferably, in the Co-La / ZSM-5 catalyst, the loading of Co is 2.0-3.5 wt%, and the loading of La is 1.0-2.0 wt%. The support for the Co-La / ZSM-5 catalyst is nanosheet ZSM-5 molecular sieve with a Si / Al ratio of 40-55.

[0014] The catalyst was prepared as follows: 10 g of (Si / Al=45) ZSM-5 molecular sieve support was dispersed in a 0.15 mol / L cobalt nitrate solution and impregnated at 90 °C for 3 hours, followed by filtration and washing; the resulting solid was then dispersed in a 0.08 mol / L lanthanum nitrate solution and impregnated under the same conditions for 3 hours; after washing and drying at 120 °C for 4 hours, it was calcined in air at 580 °C for 5 hours to obtain a Co-La / ZSM-5 catalyst, wherein the Co loading was 2.0-3.5 wt% and the La loading was 1.0-2.0 wt%.

[0015] Preferably, the microchannel catalytic reaction unit is a modular microchannel reactor, and the cross-sectional shape of the reaction channel is rectangular or circular, with multiple channels arranged in parallel or series.

[0016] Preferably, the online analysis unit is connected to the outlet of the microchannel reaction unit via a high-temperature resistant sampling probe.

[0017] Preferably, the online analysis unit is an online gas chromatograph equipped with a flame ionization detector and a capillary column for detecting the concentrations of 4-methylpyridine, 2-methylpyridine, unreacted raw materials and byproducts.

[0018] Preferably, the collaborative feedback control unit has a built-in adaptive PID optimization algorithm model with 4-methylpyridine selectivity ≥95% and yield ≥92% as dual optimization objectives, and outputs control signals to the power source of the plasma generator, the raw material feed pump, the temperature control module of the microchannel reactor, and the pressure regulating valve.

[0019] When the online analyzer reports selectivity <95% or yield <92%, adjust the set values ​​of temperature, molar ratio, and power; adjust the step size constraints: power can change by a maximum of ±5W per step, temperature can change by a maximum of ±2℃ per step, and molar ratio can change by a maximum of ±0.1 per step; ensure that the actuator does not exceed the limits.

[0020] Meanwhile, the PID optimization algorithm model is responsible for ensuring that the actual value quickly follows the new setpoint and that the change process also meets the aforementioned rate constraints. Pressure, on the other hand, is controlled independently and constantly, does not participate in the optimization, and only ensures reactor stability.

[0021] Preferably, the product separation and recycling unit includes: The condenser, whose inlet is connected to the outlet of the microchannel catalytic reaction unit, is used to cool the reaction products to 40-60°C. A gas-liquid separator, whose inlet is connected to the outlet of a condenser, is used to separate the condensed material into a gas phase component and a liquid phase component. A distillation column, whose inlet is connected to the liquid phase outlet of a gas-liquid separator, is used for the distillation and purification of liquid phase components. The theoretical number of trays in the distillation column is 30-50, the top operating temperature is 140-145℃, the bottom operating temperature is 160-170℃, and the reflux ratio is 3-5. The circulation pipeline has its inlet connected to the gas phase outlet of the gas-liquid separator and the light component outlet at the top of the distillation column, respectively. The outlet returns to the inlet of the raw material pretreatment and plasma activation unit to recycle the uncondensed gas phase components and unreacted pyridine and methanol.

[0022] This invention also provides a method for applying the above-mentioned highly selective continuous catalytic synthesis system for 4-methylpyridine, used to synthesize 4-methylpyridine from pyridine and methanol, comprising the following steps: (1) Raw material pretreatment and activation: Pyridine and methanol are mixed, vaporized, and then passed into a plasma activation unit for pre-activation treatment; (2) Methylation reaction: The activated feed gas enters the microchannel catalytic reaction unit and undergoes methylation reaction under the action of Co-La / ZSM-5 catalyst; (3) Online monitoring: The product composition at the reaction outlet is monitored in real time through the online analysis unit, and the data is transmitted to the collaborative feedback control unit; (4) Synergistic regulation: The synergistic feedback control unit dynamically adjusts the discharge power of the plasma activation unit, the temperature and pressure of the microchannel catalytic reaction unit, and the feed ratio of raw materials based on real-time monitoring data to maintain the optimal reaction state; (5) Product separation and recycling: The reaction products are condensed, gas-liquid separated and distilled to obtain high-purity 4-methylpyridine. Unreacted pyridine and methanol are returned to the raw material pretreatment and plasma activation unit for recycling.

[0023] Preferably, in step (1), the feed molar ratio of pyridine to methanol is 1:3 to 1:5, the vaporization temperature is 150-200℃, and the plasma activation conditions are: discharge power 150-300W, gas temperature in the activation zone 120-220℃, and activation time 5-10 seconds.

[0024] Preferably, in step (2), the conditions for the methylation reaction are: reaction temperature 300-370℃, pressure 0.5-1.2MPa, and residence time of the raw material in the microchannel is 30-80 seconds.

[0025] Preferably, in step (4), the collaborative feedback control unit has the dual optimization targets of 4-methylpyridine selectivity ≥95% and yield ≥92%, and the adjustment accuracy is: plasma power ±5W, reaction temperature ±2℃, and raw material pyridine to methanol molar ratio ±0.1.

[0026] Preferably, in step (5), the purity of the obtained 4-methylpyridine is greater than 99.5%.

[0027] Therefore, the present invention employs the above-described highly selective continuous catalytic synthesis system for 4-methylpyridine and its application method, the advantages of which are as follows: 1. Significantly enhanced directional selectivity: The Co-La / ZSM-5 catalyst, through the synergistic effect of Co and La, regulates the pore environment and surface electronic properties of ZSM-5 molecular sieve, and directionally enhances the 4-methylation reaction of pyridine; the jet-type plasma activation unit directionally generates highly active methyl radicals, and combined with the hot spot-free heat transfer characteristics of the microreactor, the three work together to stabilize the selectivity of 4-methylpyridine at 95-97%, which is far higher than the existing technology.

[0028] 2. Mildened reaction conditions: Plasma pre-activation reduces the reaction activation energy, and the microreactor provides efficient heat and mass transfer, reducing the reaction temperature by 30-80℃ compared to traditional processes. This suppresses high-temperature side reactions at the source and reduces energy consumption by more than 30%.

[0029] 3. Excellent catalyst stability: The introduction of La additives significantly improves the catalyst's resistance to carbon deposition. Combined with mild reaction conditions and a uniform reaction environment within the microchannels, the catalyst's single-cycle operating life exceeds 2500 hours, far surpassing traditional processes.

[0030] 4. Green, energy-saving and safe: The microreactor has a small liquid holding capacity and high inherent safety; high selectivity reduces the generation of by-products and reduces separation energy and material consumption; unreacted raw materials are recycled, and the raw material conversion rate is increased to over 98%, which is in line with the development direction of green chemical industry.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0032] Figure 1 This is a flowchart of a continuous catalytic synthesis system for highly selective 4-methylpyridine and its application method according to the present invention. Figure Labels 1. Raw material feeding unit; 2. Raw material pretreatment and plasma activation unit; 3. Microchannel catalytic reaction unit; 4. Online analysis unit; 5. Synergistic feedback control unit; 6. Product separation and recycling unit. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0035] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0036] Example 1 This embodiment provides a Co-La / ZSM-5 catalyst for the preparation of 4-methylpyridine, and the preparation method of the catalyst is as follows: (1) Nanosheet-like ZSM-5 molecular sieve supports (Si / Al ratio 40-55) were prepared using the sol-gel method. The specific preparation method is as follows: a. Premixing alkaline solution with aluminum source (solution A) Dissolve 1.00 g NaOH in 45 g deionized water and stir until completely dissolved. Add 0.61–0.84 g aluminum isopropoxide and stir at room temperature for 2 h until a clear, transparent solution is formed (without white precipitate).

[0037] b. Silica source hydrolysis (sol preparation, solution B) Take the remaining 45 g of deionized water, add 25.9 g of TPAOH (25%), and stir well.

[0038] Slowly add 20.8 g of TEOS dropwise, stirring continuously throughout the process, and control the addition time to ≥30 min. After the addition is complete, stir at room temperature for 4 h to allow the TEOS to fully hydrolyze and form a uniform, transparent sol.

[0039] c. Sol mixing and gelation Solution A was slowly added dropwise to solution B, and the mixture was stirred continuously for 1 h to obtain a silica-alumina mixed sol. 1.82 g of CTAB was added, and the mixture was stirred for another 2 h until the CTAB was completely dissolved and the system was in a homogeneous, slightly opalescent gel state.

[0040] e. Aging treatment The gel was transferred to a polytetrafluoroethylene beaker and aged at room temperature in a sealed container for 12 hours to promote further cross-linking of the sol network.

[0041] f. Hydrothermal crystallization (Key: segmented temperature control) The aged gel was transferred into a 100 mL high-pressure reactor with a polytetrafluoroethylene liner, with a filling degree of 70%–80%.

[0042] Segmented crystallization process: Low temperature induction: 120℃, static crystallization for 24h.

[0043] High-temperature growth: Heat to 175 °C and perform dynamic crystallization (rotation of the vessel, 30 rpm) for 72–96 h.

[0044] After crystallization, the mixture is rapidly cooled to room temperature with water.

[0045] g. Post-treatment (washing, drying, calcination) Separation and washing: Centrifuge the product (8000 rpm, 10 min) and wash repeatedly with deionized water until the pH of the filtrate is approximately 7.

[0046] Drying: Vacuum drying at 80 ℃ for 12 h to obtain molecular sieve raw powder.

[0047] Calcination and template removal: In a muffle furnace, under air atmosphere, the temperature was programmed to rise to 350 °C at a rate of 2 °C / min and held for 3 h (to remove CTAB). Then, the temperature was raised to 550 °C at a rate of 1 °C / min and held for 6 h (to remove TPAOH and achieve complete crystallization). After natural cooling, nanosheet-like ZSM-5 molecular sieve supports were obtained.

[0048] (2) Take 10g of nanosheet ZSM-5 molecular sieve support and disperse it in 0.15mol / L cobalt nitrate solution. Impregnate at 90℃ for 3 hours and filter and wash. Then disperse the obtained solid in 0.08mol / L lanthanum nitrate solution and impregnate under the same conditions for 3 hours. After washing and drying at 120℃ for 4 hours, calcine in air at 580℃ for 5 hours to obtain Co-La / ZSM-5 catalyst, in which the Co loading is 2.8wt% and the La loading is 1.5wt%.

[0049] Example 2 This embodiment provides a highly selective continuous catalytic synthesis system for 4-methylpyridine, such as... Figure 1 As shown in the diagram, the lines represent the flow of raw materials and products: black indicates the direction of electrical signal transmission, green indicates the direction of electrical signal transmission, and red indicates unreacted raw materials; the specific configuration is as follows: Raw material feeding unit 1: Feed flow rate is 100 mL / h.

[0050] Raw material pretreatment and plasma activation unit 2: used for vaporization and plasma activation pretreatment of mixed raw materials of pyridine and methanol, wherein the plasma activation unit is a jet-type dielectric barrier discharge reactor with an electrode spacing of 3mm.

[0051] Microchannel catalytic reaction unit 3: Its inlet and raw material pretreatment are connected to the outlet of plasma activation unit 2. It contains microchannels for loading catalysts for methylation reactions. The microchannel reactor preparation specifically includes the following steps: The Co-La / ZSM-5 catalyst prepared in Example 1 is loaded onto the inner wall of the microchannel reactor using plasma spraying. The microchannel reactor is made of modular stainless steel, with a single channel cross-sectional size of 2mm × 2mm and a channel length of 1.0m. Before loading, the inner wall of the channel is pretreated by plasma spraying to increase surface roughness and active sites. Subsequently, the catalyst slurry is uniformly loaded onto the inner wall using a coating method. After drying at 120℃ for 4 hours and calcining at 580℃ for 5 hours, the catalyst layer thickness is approximately 80-120μm, and the loading is approximately 80-100mg / cm³. 2 .

[0052] Online analysis unit 4: Online gas chromatograph, connected to microchannel catalytic reaction unit 3 via a high-temperature resistant sampling probe, equipped with an HP-5 capillary column (30m×0.32mm×0.25 μm) and a flame ionization detector.

[0053] Collaborative Feedback Control Unit 5: Built-in adaptive PID optimization algorithm with dual optimization objectives of ≥95% selectivity and ≥92% yield of 4-methylpyridine. That is, when the online analyzer feedback selectivity is <95% or yield is <92%, the set values ​​of temperature, molar ratio and power are adjusted; the adjustment step size constraint is: power changes by a maximum of ±5W, temperature changes by a maximum of ±2℃, and molar ratio changes by a maximum of ±0.1; ensuring that the actuator does not exceed the limit.

[0054] Meanwhile, the PID optimization algorithm model is responsible for ensuring that the actual value quickly follows the new setpoint and that the change process also meets the aforementioned rate constraints. Pressure, on the other hand, is controlled independently and constantly, does not participate in the optimization, and only ensures reactor stability.

[0055] The product separation and recycling unit 6 is connected to the outlet of the microchannel catalytic reaction unit 3 and is used to separate the target product and recycle the unreacted raw materials back to the raw material pretreatment and plasma activation unit 2.

[0056] Application methods of the above system: (1) Raw material pretreatment and activation: Pyridine (purity >99.5%) and methanol (anhydrous grade) are mixed in a mixer at a molar ratio of 1:4, and then fed into a vaporizer by a metering pump and completely vaporized at 180°C. The vaporized mixed raw material gas enters the plasma activation zone, the discharge power is set to 220W, the gas temperature in the activation zone is controlled at 180°C, and the activation time is about 8 seconds.

[0057] (2) Methylation reaction: The activated feed gas enters the microchannel reactor, the reaction temperature is set at 340℃, the system pressure is 0.8MPa, and the feed flow rate is adjusted so that the residence time of the feed in the microchannel is 50 seconds. The methylation reaction is carried out under the action of Co-La / ZSM-5 catalyst.

[0058] (3) Online monitoring and control: The online gas chromatograph automatically samples every 5 minutes to monitor the concentrations of 4-methylpyridine, 2-methylpyridine, pyridine, methanol, and byproducts in the reaction outlet material in real time. The data is transmitted to the collaborative feedback control unit in real time. The collaborative feedback control unit aims for selectivity ≥95% and yield ≥92%, and dynamically adjusts the plasma power (adjustment accuracy ±5W), reaction temperature (adjustment accuracy ±2℃), and feed pump speed (adjustment molar ratio ±0.1). During the experiment, the system operated stably, and the fluctuations of each parameter were within the set range, with a feedback response time of 30 seconds.

[0059] S4. Product Separation and Recycling: The reaction products are cooled to 50°C in a condenser and then enter the gas-liquid separator. The liquid phase material enters a distillation column (theoretical trays 40), where it is distilled under conditions of 142°C at the top, 165°C at the bottom, and a reflux ratio of 4. High-purity 4-methylpyridine is collected from the top of the column. The uncondensed gas phase in the gas-liquid separator and the light components from the top of the distillation column are compressed and returned to the feed mixer for recycling.

[0060] After the system was running stably, data was collected continuously for 24 hours, and the average results are shown in Table 1 below: Table 1 Results of System Product Determination

[0061] To assess long-term stability, the catalyst was run continuously for 1000 hours under the above conditions, with samples taken and analyzed every 12 hours. After 1000 hours of operation, the selectivity of 4-methylpyridine still reached 96.1%, and no significant deactivation of the catalyst was observed.

[0062] Example 3 This embodiment uses the same continuous catalytic synthesis system as Example 2, the only difference being that the plasma power is 250W, the reaction temperature is 320℃, and the molar ratio of pyridine to methanol is 1:4.5. Results: The single-pass conversion rate of pyridine is 40.2%, the selectivity of 4-methylpyridine is 97.5%, and the yield is 92.8%. After 800 hours of continuous operation, the selectivity remains above 96.8%.

[0063] Comparative Example 1 This comparative example uses the Co-La / ZSM-5 catalyst prepared in Example 1, which is pressed into tablets and sieved into 20-40 mesh powder, and then packed into a conventional fixed-bed reactor. The plasma unit and synergistic feedback control unit were not used in this comparative example. The reaction was carried out at 390°C and 1.0 MPa, with a pyridine to methanol molar ratio of 1:4. Initial results: pyridine conversion 45.8%, 4-methylpyridine selectivity 84.3%, and yield 80.5%. After 300 hours of operation, the selectivity decreased to 78.6%, the bed pressure differential increased significantly, and the catalyst began to deactivate.

[0064] Comparative Example 2 This comparative example uses the same continuous catalytic synthesis system as Example 2, the only difference being that the plasma unit was shut off in the microchannel reactor. The reaction was carried out at 360°C and 0.8 MPa (compensating for activation energy), with a molar ratio of pyridine to methanol of 1:4. Results: Pyridine conversion was 38.6%, 4-methylpyridine selectivity was 90.2%, and yield was 86.5%. After 500 hours of continuous operation, the selectivity decreased to 88.3%, demonstrating the crucial role of plasma activation in improving selectivity and stability.

[0065] Comparative Example 3 (without La catalyst) This comparative example provides a Co / ZSM-5 catalyst, prepared by the following method: (1) Same as step (1) in Example 1.

[0066] (2) Take 10g of nanosheet ZSM-5 molecular sieve support and disperse it in 0.15 mol / L cobalt nitrate solution. Impregnate at 90℃ for 3 hours, filter and wash, dry at 120℃ for 4 hours, and calcine in air at 580℃ for 5 hours to obtain Co / ZSM-5 catalyst with Co loading of 2.8wt% and support Si / Al = 45.

[0067] This comparative example used the same continuous catalytic synthesis system as Example 2, but replaced the Co-La / ZSM-5 catalyst with Co / ZSM-5, while keeping other conditions unchanged. The results showed an initial selectivity of 91.5%, which decreased to 85.7% after 300 hours of operation and further to 80.3% after 500 hours, demonstrating the importance of the La promoter in maintaining the long-term stability of the catalyst.

[0068] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and does not limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A continuous catalytic synthesis system for highly selective 4-methylpyridine, characterized in that, The continuous catalytic synthesis system is arranged sequentially along the material flow direction with: The raw material pretreatment and plasma activation unit is used to vaporize and plasma activate the mixed raw materials of pyridine and methanol. The microchannel catalytic reaction unit has its inlet and feed pretreatment connected to the outlet of the plasma activation unit, and is equipped with microchannels for loading catalysts for methylation reactions. An online analysis unit, connected to the outlet of the microchannel catalytic reaction unit, is used to monitor the composition of the reaction products in real time. The collaborative feedback control unit is connected to the online analysis unit, the raw material pretreatment and plasma activation unit, the microchannel catalytic reaction unit and the raw material feeding unit, respectively, and is used to receive real-time data from the online analysis unit and output control signals; And a product separation and recycling unit, connected to the outlet of the microchannel catalytic reaction unit, for separating the target product and recycling unreacted raw materials back to the raw material pretreatment and plasma activation unit; The collaborative feedback control unit dynamically adjusts the discharge power of the raw material pretreatment and plasma activation unit, the temperature and pressure of the microchannel catalytic reaction unit, and the raw material feed ratio based on real-time data, forming a closed-loop control.

2. The continuous catalytic synthesis system for highly selective 4-methylpyridine according to claim 1, characterized in that, The raw material pretreatment and plasma activation unit includes a mixer, a vaporizer, and a plasma generator connected after the vaporizer. The plasma generator is a jet-type dielectric barrier discharge reactor with an electrode spacing of 2-5 mm.

3. The continuous catalytic synthesis system for highly selective 4-methylpyridine according to claim 1, characterized in that, The reaction channel of the microchannel catalytic reaction unit has a characteristic size of 1-4 mm. The inner wall of the channel is pretreated by plasma spraying and loaded with a Co-La / ZSM-5 catalyst layer with a thickness of 50-150 μm.

4. The continuous catalytic synthesis system for highly selective 4-methylpyridine according to claim 3, characterized in that, In the Co-La / ZSM-5 catalyst, the loading of Co is 2.0-3.5 wt%, and the loading of La is 1.0-2.0 wt%. The support for the Co-La / ZSM-5 catalyst is nanosheet ZSM-5 molecular sieve with a Si / Al ratio of 40-55.

5. The continuous catalytic synthesis system for highly selective 4-methylpyridine according to claim 3, characterized in that, The microchannel catalytic reaction unit is a modular microchannel reactor. The cross-sectional shape of the reaction channel is rectangular or circular, and multiple channels are arranged in parallel or series.

6. The continuous catalytic synthesis system for highly selective 4-methylpyridine and its application method according to claim 1, characterized in that, The online analysis unit is an online gas chromatograph equipped with a flame ionization detector and a capillary column, used to detect the concentrations of 4-methylpyridine, 2-methylpyridine, unreacted raw materials and byproducts.

7. The continuous catalytic synthesis system for highly selective 4-methylpyridine according to claim 1, characterized in that, The collaborative feedback control unit has a built-in adaptive PID optimization algorithm model with dual optimization objectives of ≥95% selectivity and ≥92% yield of 4-methylpyridine. It outputs control signals to the power source of the raw material pretreatment and plasma activation unit, the raw material feed pump, the temperature control module of the microchannel reactor, and the pressure regulating valve.

8. The continuous catalytic synthesis system for highly selective 4-methylpyridine according to claim 1, characterized in that, The product separation and recycling unit includes: The condenser, whose inlet is connected to the outlet of the microchannel catalytic reaction unit, is used to cool the reaction products to 40-60°C. A gas-liquid separator, whose inlet is connected to the outlet of a condenser, is used to separate the condensed material into a gas phase component and a liquid phase component. A distillation column, whose inlet is connected to the liquid phase outlet of a gas-liquid separator, is used for the distillation and purification of liquid phase components. The theoretical number of trays in the distillation column is 30-50, the top operating temperature is 140-145℃, the bottom operating temperature is 160-170℃, and the reflux ratio is 3-5. The circulation pipeline has its inlet connected to the gas phase outlet of the gas-liquid separator and the light component outlet at the top of the distillation column, respectively. The outlet returns to the inlet of the raw material pretreatment and plasma activation unit to recycle the uncondensed gas phase components and unreacted pyridine and methanol.

9. A method for applying the continuous catalytic synthesis system for highly selective 4-methylpyridine as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Raw material pretreatment and activation: Pyridine and methanol are mixed, vaporized, and then passed into a plasma activation unit for pre-activation treatment; (2) Methylation reaction: The activated feed gas enters the microchannel catalytic reaction unit and undergoes methylation reaction under the action of Co-La / ZSM-5 catalyst; (3) Online monitoring: The product composition at the reaction outlet is monitored in real time through the online analysis unit, and the data is transmitted to the collaborative feedback control unit; (4) Synergistic regulation: The synergistic feedback control unit dynamically adjusts the discharge power of the plasma activation unit, the temperature and pressure of the microchannel catalytic reaction unit, and the feed ratio of raw materials based on real-time monitoring data to maintain the optimal reaction state; (5) Product separation and recycling: The reaction products are condensed, gas-liquid separated and distilled to obtain high-purity 4-methylpyridine. Unreacted pyridine and methanol are returned to the raw material pretreatment and plasma activation unit for recycling.

10. The application method of the continuous catalytic synthesis system for highly selective 4-methylpyridine according to claim 9, characterized in that, In step (1), the feed molar ratio of pyridine to methanol is 1:3 to 1:5, the vaporization temperature is 150-200℃, and the plasma activation conditions are: discharge power 150-300W, gas temperature in the activation zone 120-220℃, and activation time 5-10 seconds. In step (2), the conditions for the methylation reaction are: reaction temperature 300-370℃, pressure 0.5-1.2MPa, and residence time of the raw material in the microchannel 30-80 seconds; In step (4), the collaborative feedback control unit has dual optimization targets of 4-methylpyridine selectivity ≥95% and yield ≥92%, and the adjustment accuracy is: plasma power ±5W, reaction temperature ±2℃, and raw material pyridine to methanol molar ratio ±0.1; In step (5), the purity of the obtained 4-methylpyridine is greater than 99.5%.

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