An apparatus for extracting and rectifying methylpyridine and water by NMP

Abstract

The present application relates to the technical field of chemical separation, in particular to an extractive distillation equipment for separating methylpyridine and water, and an equipment for extractive distillation of methylpyridine and water by NMP, which comprises a raw material pretreatment unit, a crude distillation unit, an extractive distillation unit, a product refining unit and an extractant circulating unit in sequence in fluid communication; the raw material pretreatment unit comprises a raw material buffer tank and a feed pump, which are used for storing and conveying a raw material mixture of methylpyridine and water to the crude distillation unit; the crude distillation unit comprises a crude distillation column, a crude distillation reboiler and a crude distillation condenser, which are used for preliminarily separating the raw material to remove most of the water, and conveying the crude methylpyridine material after preliminary dehydration to the extractive distillation unit; the extractive distillation unit comprises an extractive distillation column and an extractive column bottom pump; an extractant inlet is arranged at the upper part of the extractive distillation column, which is used for receiving N-methylpyrrolidone (NMP) extractant from the extractant circulating unit.

Description

Technical Field

[0001] This invention relates to the field of chemical separation technology, specifically to an extractive distillation apparatus for separating methylpyridine and water, and particularly to a highly efficient separation system that uses N-methylpyrrolidone (NMP) as the extractant and integrates an extractant circulation and vacuum system. Background Technology

[0002] Methylpyridine is an important chemical intermediate widely used in the pharmaceutical, pesticide, and dye industries. During the production and purification of methylpyridine, it often forms an azeotropic mixture with water, making effective separation difficult using conventional distillation methods. Current technologies mostly employ ordinary distillation, azeotropic distillation, or simple extraction processes for separation, but these methods have the following problems and drawbacks:

[0003] 1. Low separation efficiency and insufficient product purity: Methylpyridine forms an azeotrope with water, which traditional distillation methods cannot break through, resulting in incomplete dehydration and a high water content in the product, making it difficult to obtain high-purity methylpyridine. Furthermore, the lack of an efficient extractant (such as NMP) prevents a significant change in the relative volatility of the components, leading to low separation efficiency.

[0004] 2. High energy consumption and high operating costs: Existing technologies typically operate at atmospheric or higher pressures, requiring higher operating temperatures and resulting in significant energy consumption. Furthermore, the lack of a vacuum system design prevents the reduction of component boiling points, leading to high heat loads, low energy efficiency, and potential thermal decomposition of materials.

[0005] Therefore, there is an urgent need in this field to develop a separation device and process that can efficiently overcome azeotropic distillation and significantly reduce energy consumption in order to solve the above problems. Summary of the Invention

[0006] To overcome the problems of low separation efficiency, high energy consumption, and ineffective recycling of extractant in existing technologies for methylpyridine and water azeotropes, this invention provides an NMP extraction and distillation apparatus for methylpyridine and water. By employing NMP extractant and an integrated distillation unit, combined with a vacuum system and closed-loop circulation of extractant, it achieves efficient breakthrough of azeotropy, significantly reduces energy consumption, and enables the recycling of extractant.

[0007] The technical solution adopted by this invention to solve its technical problem is: an NMP extractive distillation apparatus for methylpyridine and water, comprising a raw material pretreatment unit, a crude distillation unit, an extractive distillation unit, a product purification unit, and an extractant circulation unit connected in sequence; the raw material pretreatment unit includes a raw material buffer tank and a feed pump, used to store and transport the raw material mixture of methylpyridine and water to the crude distillation unit; the crude distillation unit includes a crude distillation column, a crude distillation reboiler, and a crude distillation condenser, used to perform preliminary separation of the raw material to remove most of the water, and to transport the preliminarily dehydrated crude methylpyridine material to the extractive distillation unit; the extractive distillation unit includes an extractive distillation column and... The extraction column includes a bottom pump; the upper part of the extractive distillation column is equipped with an extractant inlet for receiving N-methylpyrrolidone (NMP) extractant from the extractant circulation unit to break the azeotropic reaction between methylpyridine and water and achieve deep dehydration; the bottom outlet of the extractive distillation column is connected to the product purification unit via the bottom pump; the product purification unit includes a 3-methylpyridine column and a 3-methylpyridine bottom pump; the 3-methylpyridine column is used to separate methylpyridine product from NMP, producing high-purity methylpyridine product at the top and NMP at the bottom; the bottom outlet of the 3-methylpyridine column is connected to the extractant circulation unit via the bottom pump.

[0008] The aforementioned NMP extraction and distillation apparatus for methylpyridine and water further includes a crude distillation unit comprising two crude distillation reflux pumps arranged side-by-side. One of the crude distillation reflux pumps is connected to the reflux port at the top of the crude distillation column, and the other crude distillation reflux pump is connected to the feed port of the extraction and distillation unit.

[0009] The aforementioned NMP extraction and distillation apparatus for methylpyridine and water further includes an extraction distillation unit comprising two extraction tower reflux pumps arranged side-by-side. One extraction tower reflux pump is connected to the reflux port at the top of the extraction distillation column, and the other extraction tower reflux pump is connected to a wastewater discharge system.

[0010] The aforementioned NMP extraction and distillation apparatus for methylpyridine and water further includes an extraction and distillation unit that includes an extraction tower vacuum buffer tank and a product purification unit that includes a 3-methylpyridine vacuum buffer tank. The tops of the extraction tower vacuum buffer tank and the 3-methylpyridine vacuum buffer tank are respectively provided with a nitrogen inlet and a vacuum system interface.

[0011] The aforementioned apparatus for NMP extraction and distillation of methylpyridine and water further includes a bottom cooler in the product refining unit. The bottom cooler is located between the bottom outlet of the 3-methylpyridine column and the bottom pump of the 3-methylpyridine column, and is used to cool the NMP collected from the bottom of the column.

[0012] The aforementioned NMP extraction and distillation apparatus for methylpyridine and water further includes a product purification unit comprising a 3-methylpyridine reflux pump, a 3-methylpyridine cooler, and a product tank. The apparatus comprises two 3-methylpyridine reflux pumps arranged side-by-side, one of which is connected to the reflux port at the top of the 3-methylpyridine column, and the other 3-methylpyridine reflux pump is connected to the product tank via the 3-methylpyridine cooler.

[0013] The aforementioned NMP extractive distillation apparatus for methylpyridine and water further includes an extraction distillation unit comprising an extraction column condenser, an extraction column reflux tank, an extraction column tail condenser, and an extraction column vacuum buffer tank. The inlet of the extraction column tail condenser is connected to the non-condensable gas outlet of the extraction column condenser, and its condensate outlet is connected to the extraction column reflux tank. The inlet of the extraction column vacuum buffer tank is connected to the tail gas outlet of the extraction column tail condenser.

[0014] The aforementioned NMP extraction and distillation apparatus for methylpyridine and water further includes a product refining unit comprising a 3-methylpyridine condenser, a 3-methylpyridine reflux tank, a 3-methylpyridine tail condenser, and a 3-methylpyridine vacuum buffer tank. The inlet of the 3-methylpyridine tail condenser is connected to the non-condensable gas outlet of the 3-methylpyridine condenser, and its condensate outlet is connected to the 3-methylpyridine reflux tank. The inlet of the 3-methylpyridine vacuum buffer tank is connected to the tail gas outlet of the 3-methylpyridine tail condenser.

[0015] The above-mentioned NMP extraction distillation apparatus for methylpyridine and water includes an extractant circulation unit comprising an extractant tank and an extractant pump, for receiving and storing NMP recovered from the product refining unit, and for conveying NMP to the extractant inlet of the extraction distillation column via the extractant pump, thereby realizing a closed-loop circulation of the extractant.

[0016] The aforementioned NMP extraction and distillation apparatus for methylpyridine and water has a fresh extractant replenishment port at the top of the extractant tank.

[0017] The beneficial effects of this invention are:

[0018] 1. By using NMP as the extractant and setting up an integrated extractive distillation unit, the azeotropic reaction between methylpyridine and water is effectively broken, achieving deep dehydration and significantly improving separation efficiency and product purity.

[0019] 2. By setting up vacuum systems in the extraction distillation unit and the product refining unit, the operating boiling points of each component are significantly reduced, thereby greatly reducing energy consumption and avoiding thermal decomposition of materials.

[0020] 3. By setting up an extractant circulation unit, the NMP extractant is able to be circulated and reused in a closed loop, effectively reducing production costs and material consumption. Attached Figure Description

[0021] The present invention will be further described below with reference to the embodiments and examples.

[0022] Figure 1 This is a schematic diagram of the process flow for the raw material pretreatment unit.

[0023] Figure 2 This is a schematic diagram of the process flow for the crude distillation unit.

[0024] Figure 3 This is a schematic diagram of the process flow for the extractive distillation unit.

[0025] Figure 4 A schematic diagram of the process flow for the product refining unit.

[0026] Figure 5 This is a schematic diagram of the process flow for the extractant circulation unit.

[0027] In the diagram: 1. Raw material buffer tank; 2. Feed pump; 3. Crude distillation column; 4. Crude distillation reboiler; 5. Crude distillation column bottom pump; 6. Crude distillation condenser; 7. Crude distillation reflux tank; 8. Crude distillation reflux pump; 9. Extractive distillation column; 10. Extractive column reboiler; 11. Extractive column condenser; 12. Extractive column reflux tank; 13. Extractive column reflux pump; 14. Extractive column tail condenser; 15. Extractive column vacuum buffer tank; 16. Extractive column bottom pump. 17. 3-Methylpyridine column; 18. 3-Methylpyridine reboiler; 19. Column bottom cooler; 20. 3-Methylpyridine condenser; 21. 3-Methylpyridine reflux tank; 22. 3-Methylpyridine reflux pump; 23. 3-Methylpyridine tail condenser; 24. 3-Methylpyridine vacuum buffer tank; 25. 3-Methylpyridine cooler; 26. Product tank; 27. 3-Methylpyridine column bottom pump; 28. Extractant tank; 29. ​​Extractant pump. Detailed Implementation

[0028] This invention relates to an apparatus for NMP extraction and distillation of methylpyridine and water, such as... Figure 1-5 As shown, the equipment includes a raw material pretreatment unit, a crude distillation unit, an extractive distillation unit, a product refining unit, and an extractant circulation unit that are connected in sequence by fluid.

[0029] The raw material pretreatment unit includes a raw material buffer tank 1 and a feed pump 2. Its function is to provide a stable and continuous raw material flow to the system. The raw material buffer tank 1 is used to store and homogenize the raw material mixture of methylpyridine and water from the previous process. Its bottom outlet is connected to the feed port of the crude distillation unit through the feed pump 2. The function of the feed pump 2 is to overcome the system resistance and deliver the raw material quantitatively and stably to the subsequent process.

[0030] The function of the crude distillation unit is to perform preliminary separation and remove most of the water from the feedstock. It includes a crude distillation column 3, a crude distillation reboiler 4, a crude distillation column bottom pump 5, a crude distillation condenser 6, a crude distillation reflux tank 7, and a crude distillation reflux pump 8. The crude distillation column 3 is the core equipment for preliminary gas-liquid separation. The crude distillation reboiler 4 is connected to the crude distillation column 3 in a loop, and its function is to provide the necessary heat for the distillation process using external steam (the steam inlet is located at the top of the crude distillation reboiler 4). The inlet of the crude distillation column bottom pump 5 is connected to the condensate outlet at the bottom of the crude distillation column 3 to extract the condensate accumulated at the bottom of the column. The inlet of the crude distillation condenser 6 is connected to the outlet of the crude distillation column 3. The top steam outlet is connected, and its function is to condense the top steam of the column into liquid using circulating water. The inlet of the crude distillation reflux tank 7 is connected to the liquid phase outlet of the crude distillation condenser 6 for receiving and temporarily storing condensate. The bottom outlet of the crude distillation reflux tank 7 is connected to the crude distillation reflux pump 8. There are two crude distillation reflux pumps 8 arranged side by side. One crude distillation reflux pump 8 is connected to the reflux port at the top of the crude distillation column 3. Its function is to pump part of the condensate back into the column to control the reflux ratio of the distillation process and ensure separation efficiency. The other crude distillation reflux pump 8 is connected to the feed port of the extractive distillation unit. Its function is to transport the crude methylpyridine material after preliminary dehydration to the next unit.

[0031] The extractive distillation unit is the core of this invention. Its function is to add the extractant NMP to break the azeotropic reaction between methylpyridine and water, achieving deep dehydration. It includes an extractive distillation column 9, an extractive column reboiler 10, an extractive column condenser 11, an extractive column reflux tank 12, an extractive column reflux pump 13, an extractive column tail condenser 14, an extractive column vacuum buffer tank 15, and an extractive column bottom pump 16. The upper part of the extractive distillation column 9 is equipped with an extractant inlet for receiving NMP from the extractant circulation unit. The addition of NMP alters the reaction between methylpyridine and water. The relative volatility of water makes it a volatile component. The reboiler 10 of the extraction column is connected to the reboiler in a circulating manner to provide heat for extractive distillation. The inlet of the condenser 11 of the extraction column is connected to the top vapor outlet of the extractive distillation column 9 to condense the water-rich vapor discharged from the top of the column. The inlet of the reflux tank 12 of the extraction column is connected to the liquid phase outlet of the condenser 11. The bottom outlet of the reflux tank 12 is connected to two reflux pumps 13 arranged side-by-side, one of which is... 13 is connected to the reflux port at the top of the extractive distillation column 9; another extractive column reflux pump 13 is connected to the wastewater discharge system to discharge the separated aqueous phase and light component impurities. The inlet of the extractive column tail condenser 14 is connected to the non-condensable gas outlet of the extractive column condenser 11, and its function is to further condense the vapor entrained in the non-condensable gas to improve the yield. The condensate outlet of the extractive column tail condenser 14 is connected to the extractive column reflux tank 12. The inlet of the extractive column vacuum buffer tank 15 is connected to the tail gas outlet of the extractive column tail condenser 14. It is equipped with a nitrogen inlet (for charging nitrogen as a protective gas and for regulating pressure) and a vacuum system interface (for connecting a vacuum pump). Its bottom is equipped with a condensate outlet connected to the extraction tower reflux tank 12. The function of this vacuum system is to maintain negative pressure operation in the tower, reduce the boiling point of each component, save energy, and prevent thermal decomposition of materials. The bottom outlet of the extractive distillation tower 9 is connected to the feed port of the product purification unit through an extraction tower bottom pump 16. Its function is to transport the mixture, which has been dehydrated and is rich in methylpyridine and NMP, to the product purification unit.

[0032] The product refining unit separates methylpyridine from the extractant NMP to obtain a high-purity final product, while also preparing for the recycling of NMP. It includes a 3-methylpyridine column 17, a 3-methylpyridine reboiler 18, a bottom cooler 19, a 3-methylpyridine condenser 20, a 3-methylpyridine reflux tank 21, a 3-methylpyridine reflux pump 22, a 3-methylpyridine tail condenser 23, a 3-methylpyridine vacuum buffer tank 24, and a 3-methylpyridine cooler 25. [Product details omitted] Tank 26 and 3-methylpyridine column bottom pump 27, 3-methylpyridine column 17 are the core equipment for the final purification of the product. 3-methylpyridine reboiler 18 is connected to the column bottom in a circulation connection to provide the heat required for separation. The inlet of 3-methylpyridine condenser 20 is connected to the top vapor outlet of 3-methylpyridine column 17 to condense high-purity methylpyridine product vapor. The inlet of 3-methylpyridine reflux tank 21 is connected to the liquid phase outlet of 3-methylpyridine condenser 20. 3-methylpyridine reflux tank 21... The bottom outlet is connected to two 3-methylpyridine reflux pumps 22, arranged side by side. One 3-methylpyridine reflux pump 22 is connected to the reflux port at the top of the 3-methylpyridine column 17; the other 3-methylpyridine reflux pump 22 is connected to the inlet of the 3-methylpyridine cooler 25, the outlet of which is connected to the product tank 26. Its function is to further cool the product to a safe storage temperature before sending it into the product tank 26. Similar to the extractive distillation unit, this column also... Equipped with a vacuum system consisting of a 3-methylpyridine tail condenser 23 and a 3-methylpyridine vacuum buffer tank 24 (which also has a nitrogen inlet and a vacuum system interface on the top), it ensures gentle separation under high vacuum, guaranteeing product quality and energy saving. The bottom outlet of the 3-methylpyridine tower 17 is connected to the extractant circulation unit in sequence through the bottom cooler 19 and the 3-methylpyridine bottom pump 27. Its function is to cool the high-temperature NMP extractant and then send it back to the extractant tank 28 for recycling.

[0033] The function of the extractant circulation unit is to receive, store, replenish, and circulate the extractant NMP. It includes an extractant tank 28 and an extractant pump 29. The top inlet of the extractant tank 28 is connected to the outlet of the bottom pump 27 of the 3-methylpyridine column in the product purification unit to receive pure NMP recovered from the product purification unit. It also has a fresh extractant replenishment port at the top for periodically replenishing system losses. The bottom outlet of the extractant tank 28 is connected to the extractant inlet of the extractive distillation column 9 through the extractant pump 29, thereby completing the closed-loop circulation of NMP in the entire system.

[0034] The working process of the device of this invention:

[0035] 1. Equipment start-up and feeding: First, the raw material mixture containing methylpyridine and water is transported to the raw material buffer tank 1 for buffering and homogenization. Then, the raw material is stably pumped into the middle of the crude distillation column 3 by the feed pump 2.

[0036] 2. Crude Dehydration and Pre-Separation: Preliminary separation is carried out in the crude distillation column 3. The bottom of the column is heated by the crude distillation reboiler 4 (usually using steam) to remove most of the water and high-boiling-point impurities from the bottom of the column. The steam generated at the top of the column (rich in methylpyridine and a small amount of water) enters the crude distillation condenser 6, is condensed into liquid by circulating water, and then flows into the crude distillation reflux tank 7. The liquid in the tank is divided into two paths by the crude distillation reflux pump 8: one path is returned to the top of the crude distillation column 3 as reflux liquid to control the distillation effect of the column; the other path is sent to the middle of the extractive distillation column 9 as the crude product after most of the water has been removed, to enter the next separation stage.

[0037] 3. NMP extractive distillation for deep dehydration: This is a key step in the separation process. NMP from the extractant circulation unit is drawn from the extractant tank 28 by the extractant pump 29 and transported to the upper part of the extractive distillation column 9. The addition of NMP significantly changes the relative volatility of methylpyridine and water, making water a more volatile component.

[0038] Top operation: Water vapor and non-condensable gases are discharged from the top of the tower and enter the condenser 11 of the extraction tower. Most of the water vapor is condensed, and the condensate enters the reflux tank 12 of the extraction tower. Part of it is pumped back to the top of the tower as reflux through the reflux pump 13 of the extraction tower, and the other part is discharged as wastewater containing trace organic matter. The uncondensed gas enters the tail condenser 14 of the extraction tower for deep condensation to further recover the entrained organic matter. The vacuum buffer tank 15 of the extraction tower is connected to the vacuum system and nitrogen is introduced at the top as a protective gas to maintain the negative pressure operating environment at the top of the tower, effectively reducing the operating temperature, avoiding material decomposition and saving energy.

[0039] Bottom column operation: The bottom column yields a mixture of methylpyridine and NMP, which is then pumped entirely to the 3-methylpyridine column 17 of the product purification unit via bottom pump 16 of the extraction column.

[0040] 4. Product purification and NMP recovery: Methylpyridine and NMP are separated in 3-methylpyridine column 17.

[0041] Top operation: High-purity methylpyridine product vapor is collected from the top of the column, condensed by 3-methylpyridine condenser 20, and then enters 3-methylpyridine reflux tank 21. The liquid in the tank is divided into two parts by 3-methylpyridine reflux pump 22: one part is refluxed to the top of the column, and the other part is collected as product. After being further cooled by 3-methylpyridine cooler 25, it enters product tank 26 for storage. Similar to extractive distillation column 9, this column is also equipped with a vacuum system consisting of 3-methylpyridine tail condenser 23 and 3-methylpyridine vacuum buffer tank 24 to ensure that the separation is carried out under mild conditions.

[0042] Tower bottom operation: High-boiling-point NMP is collected from the tower bottom at a high temperature. It is first cooled by the tower bottom cooler 19, and then transported back to the extractant tank 28 by the 3-methylpyridine tower bottom pump 27 to realize the recycling of NMP extractant. The top of the extractant tank 28 is equipped with a replenishment port for periodically replenishing fresh NMP to make up for system losses.

[0043] This equipment achieves a balance between separation efficiency, energy efficiency, and environmental benefits through unit integration, extractant circulation, and a two-stage vacuum system. It is particularly suitable for the industrial continuous separation of methylpyridine and water azeotropes.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An apparatus for the extractive distillation of methylpyridine and water with NMP, characterized by: The process comprises a raw material pretreatment unit, a crude rectification unit, an extractive rectification unit, a product refining unit and an extractant circulation unit connected in sequence; The raw material pretreatment unit comprises a raw material buffer tank (1) and a feed pump (2) for storing and delivering the raw material mixture of methylpyridine and water to the crude rectification unit; The crude rectification unit comprises a crude rectification column (3), a crude rectification reboiler (4) and a crude rectification condenser (6) for preliminarily separating the raw material to remove most of the water and delivering the preliminarily dehydrated crude methylpyridine material to the extractive rectification unit; The extractive rectification unit comprises an extractive rectification column (9) and an extractive column bottom pump (16); the upper part of the extractive rectification column (9) is provided with an extractant inlet for receiving N-methylpyrrolidone (NMP) extractant from the extractant circulation unit to break the azeotrope of methylpyridine and water and achieve deep dehydration; the column bottom outlet of the extractive rectification column (9) is connected to the product refining unit through the extractive column bottom pump (16); The product refining unit comprises a 3-methylpyridine column (17) and a 3-methylpyridine column bottom pump (27); the 3-methylpyridine column (17) is used for separating methylpyridine product and NMP, with high-purity methylpyridine product being output at the top and NMP being output at the bottom; the column bottom outlet of the 3-methylpyridine column (17) is connected to the extractant circulation unit through the 3-methylpyridine column bottom pump (27).

2. The apparatus for extractive rectification of methylpyridine and water by NMP according to claim 1, characterized in that: The crude rectification unit further comprises two crude rectification reflux pumps (8) arranged side by side, one of which is connected to the reflux port of the upper part of the crude rectification column (3) and the other of which is connected to the feed inlet of the extractive rectification unit.

3. The apparatus for extractive distillation of methylpyridine and water according to claim 1, characterized in that: The extractive rectification unit further comprises two extractive column reflux pumps (13) arranged side by side, one of which is connected to the reflux port of the upper part of the extractive rectification column (9) and the other of which is connected to the wastewater discharge system.

4. The apparatus for extractive distillation of methylpyridine and water according to claim 1, characterized in that: The extractive rectification unit further comprises an extractive column vacuum buffer tank (15) and the product refining unit further comprises a 3-methylpyridine vacuum buffer tank (24), the top parts of the extractive column vacuum buffer tank (15) and the 3-methylpyridine vacuum buffer tank (24) are respectively provided with a nitrogen inlet and a vacuum system interface.

5. The apparatus for extractive distillation of methylpyridine and water according to claim 1, characterized in that: The product refining unit further comprises a column bottom cooler (19) arranged between the column bottom outlet of the 3-methylpyridine column (17) and the 3-methylpyridine column bottom pump (27) for cooling the NMP collected from the column bottom.

6. The apparatus for extractive rectification of methylpyridine and water according to claim 1, characterized in that: The product refining unit further comprises two 3-methylpyridine reflux pumps (22) arranged side by side, one of which is connected with the reflux port of the upper part of the 3-methylpyridine column (17), and the other is connected with the product tank (26) through the 3-methylpyridine cooler (25).

7. The apparatus for extractive rectification of methylpyridine and water according to claim 1, characterized in that: The extractive distillation unit further comprises an extractive column condenser (11), an extractive column reflux tank (12), an extractive column tail condenser (14) and an extractive column vacuum buffer tank (15), the gas inlet of the extractive column tail condenser (14) is connected with the non-condensable gas outlet of the extractive column condenser (11), and the condensate outlet is connected with the extractive column reflux tank (12); the gas inlet of the extractive column vacuum buffer tank (15) is connected with the tail gas outlet of the extractive column tail condenser (14).

8. The apparatus for extractive rectification of methylpyridine and water according to claim 1, characterized in that: The product refining unit further comprises a 3-methylpyridine condenser (20), a 3-methylpyridine reflux tank (21), a 3-methylpyridine tail condenser (23) and a 3-methylpyridine vacuum buffer tank (24), the gas inlet of the 3-methylpyridine tail condenser (23) is connected with the non-condensable gas outlet of the 3-methylpyridine condenser (20), and the condensate outlet is connected with the 3-methylpyridine reflux tank (21); the gas inlet of the 3-methylpyridine vacuum buffer tank (24) is connected with the tail gas outlet of the 3-methylpyridine tail condenser (23).

9. The apparatus for extractive rectification of methylpyridine and water according to claim 1, characterized in that: The extractant circulating unit comprises an extractant tank (28) and an extractant pump (29) for receiving and storing NMP recovered from the product refining unit and delivering NMP to the extractant inlet of the extractive distillation column (9) through the extractant pump (29) to realize closed-loop circulation of the extractant.

10. The apparatus for extractive rectification of methylpyridine and water according to claim 9, characterized in that: The top of the extractant tank (28) is provided with a fresh extractant supplement port.

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