Rectification column and method of use thereof

Abstract

Embodiments of the present application provide a rectification tower and an application method thereof. The rectification tower comprises a lower section, a middle section and an upper section arranged in sequence along the tower height direction. The height of the lower section is 20-35% of the height of the rectification tower, and the lower section is provided with a lower section packing. The specific surface area of the lower section packing is BET 下 . The height of the middle section is 30-45% of the height of the rectification tower, and the middle section is provided with a middle section packing. The specific surface area of the middle section packing is BET 中 . The height of the upper section is 15-25% of the height of the rectification tower, and the upper section is provided with an upper section packing. The specific surface area of the upper section packing is BET 上 . Wherein, BET 上 ≤ BET 下 ≤ BET 中 . The rectification tower can effectively pre-separate 2-methyl glutaronitrile and ethyl succinonitrile with close boiling points without significantly increasing energy consumption and equipment complexity, and provide stable and controllable feed conditions for subsequent processes.

Description

Technical Field

[0001] This invention relates to the chemical industry, and more particularly to a distillation column and its application method. Background Technology

[0002] Polynitrile compounds are an important class of organic intermediates, widely used in polymer materials, fine chemicals, and pharmaceuticals. For example, 2-methylglutaronitrile and ethylbutadionitrile are often used as precursors for special polyamides, modified resins, or fine chemicals (such as 2-methylpentanediamine), and can also be used to prepare pharmaceutical and pesticide intermediates. Industrially, polynitrile compounds are usually prepared through addition, dehydration, or cyanation reactions of nitrogen-containing compounds, for example, by reacting the corresponding diols, dihalogenated compounds, or unsaturated compounds with nitrogen-containing raw materials such as ammonia and hydrogen cyanide. In the industrial production of polynitrile compounds, structurally similar nitrile byproducts such as 2-methylglutaronitrile and ethylbutadionitrile are often generated simultaneously. Among them, 2-methylglutaronitrile and ethylbutadionitrile have a small difference in boiling point at normal pressure and relatively low volatility, making effective separation difficult under conventional distillation conditions.

[0003] Existing technologies typically employ single-tower high reflux or multi-tower series purification methods for separation. Single-tower high reflux enhances gas-liquid mass transfer efficiency by increasing the reflux ratio and reboiler temperature, thereby achieving the separation of near-boiling-point components. However, high reflux ratios lead to a dramatic increase in energy consumption, the high reboiler temperature easily triggers thermal decomposition of the material, and the operating window is narrow, making it sensitive to feed fluctuations and difficult to operate stably. Multi-tower series purification is a method of gradually separating different components through multiple distillation steps. While this method can improve separation accuracy, it significantly increases equipment investment and operational complexity, and the material transfer efficiency between towers is low, making overall energy consumption difficult to control.

[0004] Therefore, how to effectively pre-separate mixed crude materials containing polynitrile compounds, especially 2-methylglutaronitrile and ethylbutadionitrile with similar boiling points, without significantly increasing energy consumption and equipment complexity, so as to provide stable and controllable feeding conditions for subsequent processes, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a distillation column that can effectively pre-separate mixed crude feed containing polynitrile compounds, especially 2-methylglutaronitrile and ethylbutadionitrile with similar boiling points, without significantly increasing energy consumption and equipment complexity, thus providing stable and controllable feed conditions for subsequent processes.

[0006] This invention also provides a method for preparing 2-methylpentanediamine. The 2-methylglutaronitrile raw material used in this method often contains the near-boiling-point byproduct ethylbutadionitrile. By using the aforementioned distillation column, the separation effect between the target component 2-methylglutaronitrile and the near-boiling-point impurity ethylbutadionitrile can be effectively improved, thereby increasing the purity of 2-methylpentanediamine.

[0007] In a first aspect, the present invention provides a distillation column, the distillation column comprising a lower section, a middle section and an upper section arranged sequentially along the column height;

[0008] The height of the lower section of the column is 20-35% of the height of the distillation column, and the lower section is equipped with lower packing material, the specific surface area of ​​which is BET. 下 ;

[0009] The height of the middle section of the column is 30-45% of the total height of the distillation column. The middle section is equipped with packing material, and the specific surface area of ​​the packing material is BET. 中 ;

[0010] The height of the upper section of the column is 15-25% of the total height of the distillation column. The upper section is equipped with upper packing material, and the specific surface area of ​​the upper packing material is BET. 上 ;

[0011] Wherein, the BET 上 ≤The BET 下 ≤The BET 中 .

[0012] In one possible embodiment, the distillation column as described above further includes: the BET 下 The range is 200-250 m 2 / m 3 The BET 中 The range is 350-500 m 2 / m 3 The BET 上 The range is 100-170 m 2 / m 3 ;

[0013] And / or, the porosity of the lower section packing is ≥95%, the porosity of the middle section packing is 97-98%, and the porosity of the upper section packing is 98-99%.

[0014] In one possible embodiment, the distillation column as described above further includes: a liquid redistributor disposed within the middle section of the column, wherein the liquid redistributor has a distribution point density of 40 points / m³. 2 The above; the liquid redistributor is located above the intermediate packing; and / or,

[0015] An anti-entrapment device is installed in the upper section of the tower, and the anti-entrapment device is located above the packing in the upper section.

[0016] In one possible embodiment, the distillation column as described above further includes: a side-stream reflux heater disposed outside the middle section of the column, the side-stream reflux heater being connected to the middle section of the column via a pipe, and the outlet reflux temperature of the side-stream reflux heater being higher than the natural reflux temperature of the middle section of the column.

[0017] In one possible embodiment, the distillation column as described above further includes: the outlet reflux temperature of the side-stream reflux heater is 3-15 °C higher than the natural reflux temperature at the same height, and the phase flow rate of the side-stream liquid is 3-15% of the liquid phase load in the middle section of the column.

[0018] In one possible embodiment, the distillation column as described above further includes: a pressure gradient control module, the pressure gradient control module comprising a first pressure control zone and a second pressure control zone; wherein the first pressure control zone is located in the upper section of the column, the second pressure control zone is located in the lower section of the column, and the operating pressure of the first pressure control zone is lower than the operating pressure of the second pressure control zone.

[0019] In one possible embodiment, the distillation column as described above further includes: an inert gas inlet located in the middle of the middle section of the column, the inert gas inlet being connected to an inert gas source via a pipe.

[0020] In a second aspect, the present invention provides a method for preparing 2-methylpentanediamine, comprising the step of distilling crude 2-methylglutaronitrile; wherein the distillation is performed using the distillation column described in any one of the first aspects of the present invention.

[0021] In one possible embodiment, the preparation method described above further includes: controlling the pressure in the upper section of the tower at 2-6 kPa and the temperature at 90-115 ℃; and controlling the pressure in the lower section of the tower at 5-10 kPa and the temperature at 150-175 ℃.

[0022] In one possible embodiment, the preparation method described above further includes: during the start-up phase of the distillation column, the reflux ratio is controlled at 8-15; during the steady-state operation phase, the reflux ratio is 4-8.

[0023] The distillation column provided by this invention is configured with lower, middle, and upper sections of varying heights along its length, each equipped with packing structures of different specific surface areas. This creates a gradient match between the mass transfer capacity and the gas-liquid load along the column's height. Specifically, the middle section uses packing with a higher specific surface area to enhance the gas-liquid contact efficiency in the main separation zone; the lower section balances mass transfer and throughput capacity; and the upper section uses packing with a lower specific surface area to reduce pressure drop and suppress liquid entrainment. This distillation column can effectively separate mixed feeds containing multiple nitrile compounds without significantly increasing system energy consumption or equipment complexity. It is particularly suitable for the pre-separation process of 2-methylglutaronitrile and ethylbutadienenitrile, which have similar boiling points, thus providing stable and controllable feed conditions for subsequent processes and helping to reduce subsequent separation loads and improve overall process stability. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0025] Figure 1 This is a schematic diagram of the distillation column structure according to the first embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the distillation column structure according to the second embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the distillation column structure according to the third embodiment of the present invention.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1-Upper section of the tower; 2-Middle section of the tower; 3-Lower section of the tower; 4-Upper section packing; 5-Middle section packing; 6-Lower section packing; 7-Reboiler; 8-Liquid pump; 9-Condenser; 10-Gas pump; 11-Liquid redistributor; 12-Anti-entrainment device; 13-Side-stream reflux heater; 14-Reflux pump.

[0030] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0031] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0032] Polynitrile compounds are an important class of organic intermediates, widely used in polymer materials, fine chemicals, and pharmaceuticals. For example, 2-methylglutaronitrile and ethylbutadionitrile are often used as important precursors for specialty polyamides, modified resins, and fine chemicals (such as 2-methylpentanediamine). Industrially, polynitrile compounds are typically prepared through addition, dehydration, or cyanation reactions involving nitrogen-containing feedstocks, often simultaneously generating structurally similar byproducts such as 2-methylglutaronitrile and ethylbutadionitrile. Due to their small difference in boiling points at atmospheric pressure and low relative volatility, efficient separation using conventional distillation conditions is difficult. Existing technologies typically employ single-tower high reflux or multi-tower series purification methods, but these methods generally suffer from high energy consumption, narrow operating windows, high reboiler temperatures, and susceptibility to thermal decomposition of the materials.

[0033] To address this, the inventors analyzed the mass transfer mechanism of near-boiling point component separation and discovered that the key lies in improving local mass transfer efficiency. For example, the separation interface between 2-methylglutaronitrile and ethylbutadiene is extremely sensitive to differences in gas-liquid contact efficiency and phase equilibrium, but traditional packing materials have insufficient mass transfer capacity in this region. Subsequently, the inventors proposed optimizing the mass transfer efficiency within the column through a combination of functionalized packing materials, and ultimately constructed the distillation column of this invention.

[0034] In a first aspect, the present invention provides a distillation column, comprising a lower section, a middle section, and an upper section arranged sequentially along the column height; the height of the lower section is 20-35% of the height of the distillation column, and the lower section is provided with lower packing material, the specific surface area of ​​which is BET. 下 The height of the middle section of the column is 30-45% of the total height of the distillation column. This middle section contains packing material with a specific surface area of ​​BET. 中 The height of the upper section of the column is 15-25% of the total height of the distillation column. The upper section contains upper packing material with a specific surface area of ​​BET. 上 Among them, BET 上 ≤BET 下 ≤BET 中 .

[0035] Figure 1The diagram shows a schematic of the distillation column structure according to the first embodiment. The distillation column is arranged sequentially along its height as an upper section 1, a middle section 2, and a lower section 3. These sections are continuously connected within the column shell and together form a complete gas-liquid mass transfer space. The upper section 1, middle section 2, and lower section 3 are sequentially filled with upper packing 4, middle packing 5, and lower packing 6, respectively.

[0036] It is understood that the distillation column of the present invention also includes a condenser 9 and a reboiler 7, which are common in the art. The inlet of the condenser 9 is connected to the outlet of the upper section 1 of the column via a gas pump 10, and the liquid phase outlet of the condenser 9 is connected to the condensate inlet of the upper section 1 of the column. The inlet of the reboiler 7 is connected to the outlet of the lower section 3 of the column via a liquid pump 8, and the outlet of the reboiler 7 is connected to the reboiler inlet of the lower section 3 of the column. The outlet of the gas pump 10 is also connected to the top of the column's outflow pipeline. The outlet of the liquid pump 8 is also connected to the bottom of the column's outflow pipeline.

[0037] The lower section 3 is located in the lower part of the distillation column, accounting for 20-35% of the total height of the column. The lower section 3 includes the reboiler and the lower packing 6, which has a specific surface area of ​​BET. 下 Taking the separation of 2-methylglutaronitrile and ethylbutadionitrile as an example, during the distillation process, part of the liquid in the column bottom is collected by the liquid pump 8 through the column bottom outlet pipeline, and the other part is transferred to the reboiler 7 for heating and local vaporization to form rising steam. The steam first enters the lower section 3 of the column, and part of it forms a thin film liquid layer on the surface of the packing 6 in the lower section. The remaining steam comes into full contact with this liquid film when passing through the packing voids. Driven by the concentration and temperature differences, mass exchange occurs, making it easier for the more volatile ethylbutadionitrile component to transfer from the liquid phase to the gas phase, while the less volatile 2-methylglutaronitrile component is more easily absorbed by the liquid phase, thus achieving preliminary component distribution in the lower section 3 of the column.

[0038] Controlling the height of the lower section 3 within the range of 20-35% allows the rising steam to obtain sufficient gas-liquid contact time before entering the main separation zone, the middle section 2, enabling the gas and liquid phases to gradually approach equilibrium. Simultaneously, it avoids excessive height in the lower section 3, which could lead to a significant increase in system pressure drop or a decrease in steam velocity. On the other hand, the specific surface area of ​​the lower packing 6 (BET) 下 The design is at a moderate level, providing sufficient mass transfer area while reducing gas flow resistance and ensuring stable steam flux. This structural design allows the steam generated at the bottom of the column to undergo initial gas-liquid phase redistribution before entering the high-efficiency separation zone in the middle section, creating stable operating conditions for further enhanced separation and thus improving overall distillation efficiency.

[0039] Meanwhile, the middle section 2 is located in the central region of the distillation column, accounting for 30-45% of the total height, and is equipped with middle section packing 5 within this region. Taking the separation of 2-methylglutaronitrile and ethylbutadionitrile as an example, during the distillation process, the vapor from the lower section 3 enters the middle section 2 from bottom to top, forming a thin liquid film on the surface of the middle section packing 5 with the liquid flowing from the upper section 1 from top to bottom. When the vapor passes through, component transfer occurs between the gas phase and the liquid film driven by the concentration and temperature gradients, causing the more volatile ethylbutadionitrile component to continuously accumulate in the gas phase, while the less volatile 2-methylglutaronitrile component gradually accumulates in the liquid phase, thus forming a continuous gas-liquid countercurrent mass transfer process.

[0040] Setting the height of the middle section of the tower to 30-45% creates a larger effective mass transfer zone in the middle of the tower, allowing for longer contact paths and residence times for the gas and liquid phases. This increases the number of theoretical mass transfer units and improves separation efficiency. The specific surface area of ​​the packing material 5 in the middle section of the tower is [BET value missing]. 中 The packing is designed to be the largest of the three sections to enhance the mass transfer efficiency of the main separation zone within the column by increasing the gas-liquid contact area per unit volume of packing. This is because section 2 of the column is located where the temperature and composition gradients change most significantly within the column, and the compositional difference between the rising vapor and the descending reflux liquid is greatest in this region. It is the main mass transfer zone for distillation separation, and therefore requires higher mass transfer efficiency to achieve effective separation between the near-boiling components 2-methylglutaronitrile and ethylbutadiene.

[0041] Finally, the upper section 1 is located in the upper region of the distillation column, accounting for 15-25% of the total height of the column, and is filled with upper packing 4. Taking the separation of 2-methylglutaronitrile and ethylbutadionitrile as an example, during the distillation process, the vapor, after further separation in the middle section 2, continues to enter the upper section 1. It then undergoes final gas-liquid contact with the liquid formed by the reflux from the top of the column on the surface of the upper packing 4, further enriching the ethylbutadionitrile component in the vapor. A small amount of residual 2-methylglutaronitrile is absorbed by the reflux liquid and flows downwards with the liquid phase. After passing through the upper section 1, part of the vapor is discharged by the gas pump 10 through the top outlet pipeline, and the other part is pumped by the gas pump 10 to the condenser 9 to exchange heat with the cooling medium and condense into liquid, which returns to the top of the column as reflux liquid and flows downwards from the surface of the upper packing 4.

[0042] Controlling the height of the upper section of the tower within the range of 15-25% ensures sufficient gas-liquid contact time while preventing excessive packing in the top region, which could lead to pressure drop accumulation or limited gas load. Within this range, the rising vapor and the liquid formed by condensation and reflux can still achieve final gas-liquid equilibrium contact on the packing surface, allowing residual heavy components to be further absorbed by the reflux liquid, while lighter components continue to accumulate in the vapor and enter the top system. The specific surface area of ​​the upper packing 4 is BET. 上The packing was designed to be the smallest of the three sections because the light component ethyl succinate in the vapor of the reflux condenser at the top of the upper section 1 is significantly enriched, resulting in a relatively large gas volumetric flow rate. Continuing to use packing with a high specific surface area would easily lead to increased pressure drop and a higher risk of droplet entrainment. Therefore, by setting the upper section packing 4 with a lower specific surface area and reasonably controlling the height of the upper section 1, the pressure drop can be effectively reduced, liquid entrainment suppressed, and the stability of the top operation improved while maintaining necessary mass transfer, thereby increasing the operating efficiency of the distillation column.

[0043] Overall, BET 上 ≤BET 下 ≤BET 中 This design employs a gradient matching of mass transfer interface density and fluid resistance based on the gas-liquid load, component gradient, and mass transfer requirements at different heights within the column. By using a packing specific surface area structure that gradually varies along the column height, the mass transfer capacity can be matched to the actual separation requirements within the column. This ensures efficient mass transfer in the main separation zone while reducing flow resistance in the top and bottom regions, thereby improving overall separation efficiency and operational stability without significantly increasing energy consumption. Taking the separation of 2-methylglutaronitrile and ethylbutadionitrile as an example, the relatively more volatile ethylbutadionitrile gradually accumulates in the upper section of the column and is output through the top outlet pipeline. In contrast, the slightly less volatile 2-methylglutaronitrile tends to remain in the liquid phase during gas-liquid equilibrium, gradually accumulating in the lower section and bottom region of the column, and finally being output from the bottom through the bottom outlet pipeline, thus achieving effective separation of two compounds with similar boiling points.

[0044] It should be noted that the distillation column provided by this invention is not only suitable for the separation of the 2-methylglutaronitrile and ethylbutadienenitrile system, but also for the distillation separation of other component systems with similar boiling points or relatively low volatility. For near-boiling point substances with similar separation difficulties, good mass transfer and separation performance can also be obtained by adopting the structural design and operation method of this invention. This invention is not limited herein.

[0045] In one possible embodiment, such as the distillation column described above, wherein BET 下 The range is 200-250 m 2 / m 3 BET 中 The range is 350-500 m 2 / m 3 BET 上 The range is 100-170 m 2 / m 3 .

[0046] In this embodiment, the specific surface area of ​​the intermediate packing is set to 350-500 m². 2 / m 3This can significantly increase the theoretical mass transfer unit number and enhance the separation of near-boiling point components. The lower section of the column mainly serves as the initial enrichment of steam and the redistribution of gas and liquid. If the specific surface area is too large, it can easily lead to an increase in pressure drop. Therefore, BET... 下 Controlled at 200-250 m 2 / m 3 This allows the system to maintain a high throughput while ensuring a certain mass transfer efficiency. The upper section of the column is close to the top condensation zone, where the vapor flow rate is high and the lighter components are largely concentrated. To reduce pressure drop and suppress droplet entrainment, BET... 上 Controlled between 100-170 m 2 / m 3 This improves the stability of the tower top operation while ensuring necessary gas-liquid contact.

[0047] In one specific implementation, the packing material in the lower section of the tower is preferably a high-throughput, low-pressure-drop structured packing or a large-channel random packing, such as: a metal structured packing equivalent to a high-throughput structured packing (specific surface area of ​​approximately 200-250 m²). 2 / m 3 The packing material in the middle section of the tower is preferably a structured packing material with high specific surface area and high mass transfer efficiency, such as Mellapak 350Y or 500Y; or equivalent high-efficiency structured packing material (specific surface area 350-500 m²). 2 / m 3 When the raw material composition fluctuates significantly, the middle section of the column can be further divided into two or more sub-sections, with independent redistribution devices installed between each sub-section to enhance the stability of the separation interface. The packing material in the upper section of the column is preferably low-stagnant-volume, fast-phase-renewal type, such as Mellapak 125Y or Mellapak 170Y; or equivalent low-specific-surface-area structured packing (specific surface area 100-170 m²). 2 / m 3 It can also be designed as a standardized packing module for easy loading, unloading and optimization.

[0048] In one possible embodiment, such as the distillation column described above, the void fraction of the lower packing is ≥95%, the void fraction of the middle packing is 97-98%, and the void fraction of the upper packing is 98-99%.

[0049] In this embodiment, the porosity of the packing is designed in a gradient manner according to the gas-liquid load characteristics of different regions within the tower. The middle section of the tower is the main separation zone, which needs to maintain good throughput while ensuring a large mass transfer interface. Therefore, a porosity of 97-98% is selected to enable the gas and liquid phases to form a stable liquid film and maintain efficient mass transfer. The lower section of the tower mainly undertakes the initial contact and redistribution of steam, so a porosity of ≥95% is set to balance a certain mass transfer capacity and a low pressure drop. The upper section of the tower has a large steam flow rate and the light components are highly enriched. To reduce resistance and droplet entrainment, a high porosity structure of 98-99% is adopted to ensure smooth discharge of the gas phase at the top of the tower and maintain stable operation.

[0050] In one specific implementation, the middle section of the tower can preferably use Sulzer Mellapak 350Y or Mellapak 500Y, with a typical porosity of approximately 97-98%, which can provide a high specific surface area (350-500 m²). 2 / m 3 This allows for both low pressure drop and good liquid distribution performance. For the lower section of the column, Sulzer Mellapak 250Y or Koch-Glitsch Flexipac 250Y are preferred, with porosities typically around 95-97% and specific surface areas around 250 m². 2 / m 3 This design ensures initial gas-liquid mass transfer while providing a large vapor channel, which is beneficial for the stable rise of vapor from the bottom of the column. For the upper section of the column, low-density structured packings such as Sulzer Mellapak 125Y or Koch-Glitsch Flexipac 1Y are preferred, with porosities typically between 98-99% and specific surface areas of approximately 100-170 m². 2 / m 3 This can significantly reduce pressure drop and liquid entrainment, thereby improving the stability of gas phase transport at the top of the tower and optimizing overall operating conditions.

[0051] In one possible embodiment, as in the distillation column described above, a liquid redistributor is provided in the middle section of the column, and the liquid distribution point density of the liquid redistributor is 40 points / m³. 2 The liquid redistributor is located above the intermediate packing.

[0052] In this embodiment, as Figure 2The diagram shows a schematic of the distillation column structure according to the second embodiment. A liquid redistributor 11 is installed in the middle section 2 of the column, located above the middle packing 5. During packed distillation, as the liquid flows downwards along the packing surface, it is easily affected by factors such as the packing structure, column wall effect, and local flow fluctuations, gradually leading to flow deviation or local enrichment, resulting in uneven distribution at the gas-liquid interface and reduced mass transfer efficiency. By installing a liquid redistributor 11 above the middle packing 5 in the middle section 2 (with a liquid distribution point density of 40 points / m³), this problem is mitigated. 2 The collected liquid can be redistributed into multiple uniform distribution points and sprayed evenly onto the top of the intermediate packing 5, so that the liquid forms a relatively uniform liquid film distribution when entering the packing layer. This can effectively reduce the tower wall effect and liquid channeling phenomenon, thereby further enhancing the mass transfer efficiency of the intermediate packing region.

[0053] In one specific implementation, a Koch-Glitsch 985 type trough liquid redistributor or a Sulzer V-type trough liquid redistributor can be used. These devices use multiple parallel liquid troughs evenly arranged across the column cross-section, with regularly distributed distribution holes or drip points at the bottom of the troughs, achieving 40-80 points / m. 2 The above liquid distribution density. For distillation columns with smaller diameters (usually less than 1.2 m), a tubular porous redistributor can also be used to uniformly spray the liquid onto the packing layer below through porous pipes.

[0054] In one possible embodiment, such as the distillation column described above, an anti-entrainment device is provided in the upper section of the column, the anti-entrainment device being located above the upper packing.

[0055] In this embodiment, as Figure 2 The diagram shows a schematic of the distillation column structure according to the second embodiment. An anti-entrainment device 12 is installed in the upper section 1 of the column, located above the upper packing 4. During distillation, when vapor passes through the upper packing 4, it may carry fine droplets upwards due to high gas velocity or liquid film disturbance. If these droplets directly enter the condenser 9, not only will heavy components be carried out of the top of the column, affecting product purity, but it may also cause fluctuations in the reflux composition. The anti-entrainment device 12, by changing the gas flow path and providing a trapping surface, causes droplets in the vapor to collide, coalesce, and fall back to the packing layer, thereby stabilizing the vapor composition at the top of the column and reducing material loss.

[0056] In one specific implementation, the anti-entrainment device 12 can be selected according to the column diameter, gas phase load, and separation accuracy requirements. A wire mesh demister or a corrugated plate demister is preferred. For example, a Sulzer KnitMesh wire mesh demister or a Koch-Glitsch Style 431 wire mesh demister can be selected. These devices have high collection efficiency and low pressure drop for droplets larger than 3-5 μm, and are suitable for gas-liquid separation at the top of conventional distillation columns. When the column diameter is large or the gas velocity is high, a Koch-Glitsch 421 corrugated plate demister or a Sulzer Mellachevron demister is preferred, as it has higher gas handling capacity and better anti-clogging performance. Through appropriate selection, liquid entrainment can be effectively reduced while maintaining a low pressure drop.

[0057] In one possible embodiment, such as the distillation column described above, a side-stream reflux heater is further included. The side-stream reflux heater is located outside the middle section of the column and is connected to the middle section of the column via a pipe. The outlet reflux temperature of the side-stream reflux heater is higher than the natural reflux temperature of the middle section of the column.

[0058] In this embodiment, as Figure 3 The diagram shows a schematic of the distillation column structure according to the third embodiment. The inlet of the side-stream reflux heater 13 is connected to the outside of the middle section 2 of the column, and the outlet of the side-stream reflux heater 13 is connected to the middle section 2 of the column via the reflux pump 14. The outlet reflux liquid temperature of the side-stream reflux heater 13 is higher than the natural reflux liquid temperature of the middle section 2 of the column. During the distillation operation, the middle section 2 of the column is both the region with the most active gas-liquid two-phase mass transfer and the most critical section for component separation. By drawing a portion of the liquid phase from the middle section 2 and heating it in the side-stream reflux heater 13 to a temperature higher than the natural reflux liquid temperature of the middle section 2 before returning it to the column, local heat replenishment can be formed at this height, thereby promoting the revaporation and upward enrichment of some light components, while causing heavy components to reflux downward, which is beneficial to improving the separation efficiency of near-boiling point components and stabilizing the temperature gradient within the column.

[0059] In one specific implementation, the inlet of the side-stream reflux heater 13 is connected to the side-stream extraction outlet on the outside of the middle section 2 of the tower via a pipeline. Part of the liquid inside the tower is drawn out from this location and enters the side-stream reflux heater 13. The side-stream reflux heater 13 can be a shell-and-tube heat exchanger or a plate heat exchanger, using steam or thermal oil as the heating medium to heat the extracted liquid. The heated liquid flows out from the outlet of the side-stream reflux heater 13 and is transported to the middle section 2 of the tower by the reflux pump 14. The reinjection position is generally 3-8 theoretical stages higher than the original extraction position, allowing the reflux liquid to re-enter the middle section packing 5 at a temperature higher than the natural reflux liquid temperature at that height. By controlling the pump flow rate and heating load, the side-stream reflux flow rate and reflux temperature can be adjusted, enabling precise control of mass transfer and temperature distribution.

[0060] In one possible embodiment, such as the distillation column described above, the outlet reflux temperature of the side-stream reflux heater is 3-15 °C higher than the natural reflux temperature at the same height, and the phase flow rate of the side-stream liquid is 3-15% of the liquid load in the middle section of the column.

[0061] In this embodiment, when the reflux liquid temperature is increased by 3-15°C, a certain amount of heat can be supplemented to the middle section of the tower, causing some of the more volatile components to re-vaporize and migrate upwards, thereby enhancing the gas-liquid mass transfer process in this region and reducing the risk of disordered temperature gradients or fluctuations in gas-liquid load. Similarly, when the side stream extraction rate is between 3-15%, the possibility of affecting the packing wetting state can be reduced, while also allowing for more precise regulation of heat and material distribution within the tower. Through the synergistic control of the above temperature and flow ranges, the separation capacity of the middle section of the tower can be effectively enhanced without significantly increasing energy consumption.

[0062] In one possible embodiment, such as the distillation column described above, the column further includes a pressure gradient control module, which includes a first pressure control zone and a second pressure control zone. The first pressure control zone is located in the upper section of the column, and the second pressure control zone is located in the lower section of the column. The operating pressure of the first pressure control zone is lower than that of the second pressure control zone.

[0063] In this embodiment, by creating a stable pressure gradient distribution along the height of the column, the gas phase density and phase equilibrium conditions within the column can be further adjusted. This allows the rising steam to gradually decrease in pressure as it flows upward, thereby lowering the boiling point of the corresponding components and enhancing the tendency of lighter components to accumulate in the gas phase. On one hand, maintaining a relatively high pressure in the lower section of the column helps maintain stable reboiling vaporization conditions, making the steam generation process more stable. On the other hand, maintaining a relatively low pressure in the upper section of the column helps mitigate the problems of overheating at the top or excessive evaporation at the bottom, thus improving operational stability and reducing energy consumption fluctuations while ensuring separation efficiency.

[0064] In one specific implementation, a vacuum regulating device or pressure control valve, such as a vacuum regulating valve, a variable frequency vacuum pump, or a steam jet vacuum system, can be installed in the upper section of the column to stabilize and control the operating pressure in the upper section. Simultaneously, a back pressure valve or pressure control valve assembly can be installed in the reboiler and reboiler circulation system to maintain a relatively high operating pressure in the lower section, thus forming zoned pressure control. Furthermore, buffer packing (such as 125Y / 250Y) or large-size corrugated plate packing can be used in the middle section of the column, or pressure regulating valves, orifice plates, overflow weirs, or local resistance components can be installed between the two pressure zones to limit the impact of instantaneous gas volume fluctuations on the pressure distribution within the column.

[0065] In one possible embodiment, such as the distillation column described above, an inert gas inlet is further included. The inert gas inlet is located in the middle of the middle section of the column and is connected to an inert gas source via a pipeline.

[0066] In this embodiment, introducing an appropriate amount of inert gas (such as nitrogen) can reduce the partial pressure and relative volatility of condensable components in the gas phase within the tower, thereby altering the local vapor-liquid equilibrium conditions and making it easier for some lighter components to transfer from the liquid phase to the gas phase and accumulate. It can also increase the overall gas flow rate within the tower, enhance the contact and disturbance between the gas and liquid phases, and help reduce the thickness of the liquid film and improve the interfacial mass transfer rate.

[0067] In one specific implementation, nitrogen is preferred as the inert gas, but argon or other chemical inert gases can also be used depending on process requirements. The inert gas inlet can be located between the packing layers in the middle section of the tower or near the packing support structure. The amount of inert gas introduced is typically controlled at 0.2-2% of the gas phase flow rate inside the tower to reduce the risk of excessive dilution of the vapor composition while enhancing gas-liquid mass transfer. The gas can enter the tower using an annular distribution pipe or a multi-hole injection pipe structure, allowing the inert gas to be evenly distributed across the tower cross-section and rapidly mixed with the rising vapor. Simultaneously, flow control valves and flow meters can be installed on the gas supply line to adjust the inert gas flow rate according to the temperature, pressure, and separation effect inside the tower, thereby maintaining stable operating conditions.

[0068] In a second aspect, the present invention provides a method for preparing 2-methylpentanediamine, comprising the step of distilling crude 2-methylpentanedione; the distillation process employs any one of the distillation columns of the first aspect of the present invention.

[0069] In the industrial production of 2-methylpentanediamine, 2-methylglutaronitrile is typically used as a raw material, and the nitrile group is converted to an amino group by catalytic hydrogenation to obtain the target product, 2-methylpentanediamine. However, the synthesis of 2-methylglutaronitrile often involves various impurities. Therefore, the crude 2-methylglutaronitrile of this application includes not only 2-methylglutaronitrile but also light components such as ethylbutadionitrile, unsaturated nitrile compounds (e.g., pentenenitrile compounds), and mononitrile compounds (e.g., pentadionitrile, hexadionitrile), as well as heavy components consisting of other C6 dianitrile isomers and high-boiling-point substances such as oligomeric nitriles or polymerization byproducts. Furthermore, the content of ethylbutadionitrile is generally 10-25 wt%, the content of light components is generally about 1-8 wt%, the content of heavy components is 1-5 wt%, and the remainder is 2-methylglutaronitrile. Since the physicochemical properties of ethylbutadionitrile are most similar to those of 2-methylglutaronitrile, efficient separation of ethylbutadionitrile is the key to the distillation process.

[0070] In one possible embodiment, as described above, the preparation method includes distillation of the crude material, hydrogenation reduction, and subsequent purification steps. First, the crude 2-methylglutaronitrile is distilled. The crude material typically contains 2-methylglutaronitrile, ethylbutadionitrile, and small amounts of light and high-boiling components. Distillation separates the components with different boiling points, yielding an intermediate fraction primarily composed of 2-methylglutaronitrile, while simultaneously removing some light and heavy component impurities, thus obtaining a 2-methylglutaronitrile raw material with high purity.

[0071] Subsequently, the 2-methylglutaronitrile raw material obtained above is fed into a hydrogenation reaction system, where it undergoes a hydrogenation reduction reaction with hydrogen in the presence of a catalyst, converting the nitrile group in the molecule into an amino group, thereby generating the reaction product 2-methylpentanediamine.

[0072] Furthermore, in order to improve the purity of the final product, the crude 2-methylpentanediamine obtained from the hydrogenation reaction can be further purified by distillation to remove byproducts such as low-carbon amines (e.g., methylamine, ethylamine, etc.) and condensed amines, ultimately obtaining a 2-methylpentanediamine product with higher purity.

[0073] In this invention, the distillation column described in the first aspect is used to perform the above-mentioned distillation process. For example... Figure 1As shown, during the distillation of crude 2-methylglutaronitrile, the crude 2-methylglutaronitrile is introduced into the distillation column from the lower section 3 or the middle section 2. In the lower section 3, the liquid in the bottom of the column is heated by the reboiler 7, causing part of the liquid to vaporize and form rising steam. This steam first passes through the lower packing 6 and has preliminary gas-liquid contact with the liquid refluxed from the middle section 2. This causes the relatively volatile components (including ethylbutadienenitrile, etc.) to gradually accumulate in the gas phase and be transported upward, while the less volatile heavy components (including 2-methylglutaronitrile, etc.) gradually accumulate in the liquid phase. Part of the liquid is discharged through the bottom outlet pipeline via the liquid pump 8, and the other part is heated and refluxed by the reboiler 7. A mixed vapor containing 2-methylglutaronitrile and ethylbutadionitrile enters the middle section 2 of the column. In the middle packing 5, it undergoes more thorough gas-liquid mass transfer with the descending liquid. 2-methylglutaronitrile and ethylbutadionitrile repeatedly undergo evaporation and condensation processes, with lighter components such as ethylbutadionitrile gradually enriching in the gas phase and continuing to rise, while the relatively heavier components, such as 2-methylglutaronitrile, remain more in the liquid phase and flow downwards. The rising vapor, mainly composed of ethylbutadionitrile, enters the upper section 1 of the column and undergoes final gas-liquid contact with the reflux liquid returned from the condenser 9 in the upper packing 4. This allows a small amount of entrained heavy components to be absorbed by the reflux liquid and returned to the column. Subsequently, the vapor rich in light components is drawn from the top of the column and fed into the gas pump 10. Part of it is sent to the condenser 9 to condense into liquid and returned to the top of the column as reflux liquid to continue participating in distillation separation. The other part is collected as the product mainly containing light components of ethylbutadionitrile. As the distillation process proceeds, the main heavy component enriched in the bottom of the column is 2-methylglutaronitrile, which is discharged through the bottom of the column by the liquid pump 8 and participates in the hydrogenation reduction as an intermediate to prepare the target product 2-methylpentanediamine.

[0074] In this embodiment, packing materials with different specific surface areas are respectively set in the upper section 1, middle section 2, and lower section 3 of the tower, and are made to meet the BET requirements. 上 ≤BET 下 ≤BET 中 The relationship between the packing structure and the mass transfer requirements of different zones within the column allows for matching the packing structure with these requirements. The middle section 2, serving as the primary separation zone, utilizes a packing 5 with a large specific surface area. This significantly increases the gas-liquid interface, improves mass transfer efficiency, and ensures thorough separation of 2-methylglutaronitrile and ethylbutadiene, which have similar boiling points. The lower section 3 employs a packing 6 with a medium specific surface area. This provides a larger gas passage while maintaining a certain mass transfer efficiency, allowing the reboiling vapor to rise steadily and complete the initial component distribution. The upper section uses a packing 4 with a lower specific surface area to reduce pressure drop and droplet entrainment, resulting in more stable vapor flow at the top of the column.

[0075] In one possible embodiment, as described in the preparation method above, the pressure in the upper section of the column is controlled at 2-6 kPa and the temperature at 90-115 ℃; the pressure in the lower section of the column is controlled at 5-10 kPa and the temperature at 150-175 ℃.

[0076] In this embodiment, during the distillation separation of crude 2-methylglutaronitrile, a stable temperature and pressure gradient can be formed within the column by controlling the pressure and temperature in the upper and lower sections of the column. This optimizes the gas-liquid phase equilibrium conditions and enhances the separation effect between 2-methylglutaronitrile and ethylbutadionitrile. The pressure in the lower section is controlled at 5-10 kPa and the temperature at 150-175 °C. Sufficient heat is provided by the reboiler to stably vaporize the liquid in the column bottom and form continuously rising steam, providing the driving force for the distillation process within the column. Simultaneously, components with higher volatility (such as ethylbutadionitrile) preferentially enter the gas phase. As the steam flows upward and enters the upper section, the pressure decreases to 2-6 kPa, and the boiling point of the corresponding system decreases with the pressure reduction, making it easier for the lighter components in the steam to remain in the gas phase and further enrich. Meanwhile, the temperature in the upper section is controlled at 90-115 °C, which is beneficial for the condensation of heavier components (such as 2-methylglutaronitrile) in the reflux liquid and their downward reflux.

[0077] In one possible embodiment, as described above, the reflux ratio is controlled at 8-15 during the start-up phase of the distillation column and at 4-8 during steady-state operation.

[0078] In this embodiment, during the start-up phase of the distillation column, before the temperature and concentration distributions in each section of the column have fully formed, increasing the reflux ratio to 8-15 significantly increases the reflux volume, allowing the liquid in the upper part of the column to quickly wet the packing surface and form a stable liquid film. This also enhances the gas-liquid contact frequency, thereby accelerating the mass transfer process within the column. This promotes the enrichment of relatively volatile components such as ethyl succinate at the top of the column, while relatively less volatile components such as 2-methylglutaronitrile migrate to the lower part, enabling the distillation column to quickly enter an effective separation state. Once the temperature and component distributions within the column stabilize, the reflux ratio can be reduced to a steady-state operating range of 4-8. A lower reflux ratio, while maintaining the necessary separation efficiency, reduces the reflux circulation volume and condensation load, thereby reducing the energy consumption of the reboiler and condenser. The reflux ratio can also be dynamically adjusted according to the demand for the produced product to further improve operational economy.

[0079] The present invention will now be described through specific embodiments.

[0080] Example

[0081] This embodiment uses, as follows: Figure 3The distillation column shown is used to distill crude 2-methylglutaronitrile from the preparation method of 2-methylpentanediamine. The operating parameters of the distillation column are shown in Table 1, and the distillation operating parameters are shown in Table 2.

[0082]

[0083] The 2-methylglutaronitrile crude feedstock used in this embodiment contains 93.5% 2-methylglutaronitrile, 5.8% ethylbutadionitrile, and 0.7% other impurities. The reflux ratio during the stable operation phase is 6.5:1.

[0084] During the stable operation of the distillation column, the light component collected from the top of the column contained 99.2% ethylbutadionitrile, while the heavy component collected from the bottom of the column contained 99.8% 2-methylglutaronitrile. This demonstrates a good separation effect.

[0085] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A distillation column, characterized in that, The distillation column includes a lower section, a middle section, and an upper section arranged sequentially along the column height. The height of the lower section of the column is 20-35% of the height of the distillation column, and the lower section is equipped with lower packing material, the specific surface area of ​​which is BET. 下 ; The height of the middle section of the column is 30-45% of the total height of the distillation column. The middle section is equipped with packing material, and the specific surface area of ​​the packing material is BET. 中 ; The height of the upper section of the column is 15-25% of the total height of the distillation column. The upper section is equipped with upper packing material, and the specific surface area of ​​the upper packing material is BET. 上 ; Wherein, the BET 上 ≤The BET 下 ≤The BET 中 .

2. The distillation column according to claim 1, characterized in that, The BET 下 The range is 200-250 m 2 / m 3 The BET 中 The range is 350-500 m 2 / m 3 The BET 上 The range is 100-170 m 2 / m 3 ; And / or, the porosity of the lower section packing is ≥95%, the porosity of the middle section packing is 97-98%, and the porosity of the upper section packing is 98-99%.

3. The distillation column according to claim 2, characterized in that, A liquid redistributor is installed in the middle section of the tower, and the liquid redistributor has a distribution point density of 40 points / m³. 2 The above; the liquid redistributor is located above the intermediate packing; and / or, An anti-entrapment device is installed in the upper section of the tower, and the anti-entrapment device is located above the packing in the upper section.

4. The distillation column according to claim 3, characterized in that, It also includes a side-stream reflux heater, which is located on the outside of the middle section of the tower. The side-stream reflux heater is connected to the middle section of the tower through a pipe, and the outlet reflux liquid temperature of the side-stream reflux heater is higher than the natural reflux liquid temperature of the middle section of the tower.

5. The distillation column according to claim 4, characterized in that, The outlet reflux liquid temperature of the side-stream reflux heater is 3-15 ℃ higher than the natural reflux liquid temperature at the same height, and the phase flow rate of the side-stream liquid is 3-15% of the liquid phase load in the middle section of the tower.

6. The distillation column according to claim 5, characterized in that, It also includes a pressure gradient control module, which includes a first pressure control zone and a second pressure control zone; wherein the first pressure control zone is located in the upper section of the tower and the second pressure control zone is located in the lower section of the tower, and the operating pressure of the first pressure control zone is lower than the operating pressure of the second pressure control zone.

7. The distillation column according to any one of claims 1-6, characterized in that, It also includes an inert gas inlet, which is located in the middle of the middle section of the tower and is connected to an inert gas source through a pipeline.

8. A method for preparing 2-methylpentanediamine, characterized in that, The method includes a step of distilling crude 2-methylglutaronitrile; the distillation process is carried out using the distillation column described in any one of claims 1-8.

9. The preparation method according to claim 8, characterized in that, The pressure in the upper section of the tower is controlled at 2-6 kPa and the temperature at 90-115 ℃; the pressure in the lower section of the tower is controlled at 5-10 kPa and the temperature at 150-175 ℃.

10. The preparation method according to claim 8 or 9, characterized in that, During the start-up phase of the distillation column, the reflux ratio is controlled at 8-15; during steady-state operation, the reflux ratio is 4-8.

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