A method for purifying m-xylylenediamine by rectification

Abstract

This invention discloses a method for the distillation purification of m-phenylenediamine, relating to the field of fine chemical purification technology, comprising the following steps: S1, feeding crude m-phenylenediamine into a deammoniation and light-light ... m-Phenylenediamine products fully meet the usage requirements of high-end applications such as nylon MXD6 and high-end epoxy curing agents, and can be applied directly without additional treatment.

Description

Technical Field

[0001] This invention relates to the field of fine chemical purification technology, and more specifically to a method for the distillation purification of m-phenylenediamine. Background Technology

[0002] m-Phenylenediamine (m-PPE), as a key fine chemical intermediate, has irreplaceable application value in fields such as the synthesis of nylon MXD6, the preparation of high-end wind turbine epoxy curing agents, and high-performance coatings and adhesives. In particular, high-end applications such as nylon MXD6 and epoxy curing agents for wind turbine blades place extremely high demands on the purity of m-PPE, requiring it to reach 99.8% or higher. Simultaneously, stringent standards are set for the content of characteristic impurities such as 3-cyanobenzylamine, secondary amines, and tertiary amines, as well as moisture content, product color, and long-term storage stability. Exceeding any of these standards will directly affect the performance and lifespan of the final product.

[0003] Currently, the industrial purification process for m-phenylenediamine mainly uses a single-tower batch distillation method. This traditional process is limited by equipment structure and operation methods, and has many insurmountable technical defects, which seriously restrict product quality upgrades and large-scale production, as follows: Firstly, the purification precision is insufficient and cannot meet high-end requirements. The mass transfer efficiency of the single-tower distillation system is limited, making it difficult to achieve precise fractionation and separation of ammonia, light component impurities, and heavy component impurities. As a result, the product purity can only be maintained at 99.0%~99.5%, and the residual amount of harmful impurities such as 3-cyanobenzylamine and secondary amine exceeds the limit value for high-end scenarios. Therefore, the product cannot be directly applied to nylon MXD6 and high-end epoxy curing agents.

[0004] Secondly, the product has inherent quality defects and its overall cost is relatively high. The color of the finished m-phenylenediamine prepared by traditional processes is generally ≥20, with a dull color. It requires an additional decolorization process for post-treatment, which not only prolongs the overall production process and reduces production continuity, but also significantly increases production costs due to material loss and reagent consumption in the decolorization process. At the same time, the traditional process is not effective in removing trace amounts of ammonia. Residual ammonia can cause discoloration and degradation reactions in the product during storage, greatly reducing the product's storage stability and affecting its shelf life and reliability.

[0005] Third, production efficiency is low and batch stability is poor. The intermittent operation mode has limited capacity, making it difficult to meet the needs of large-scale industrial production; and due to fluctuations in operating conditions, key indicators such as purity, color, and impurity content of different batches of products vary greatly, making it difficult to guarantee batch consistency, which further limits its application in high-end large-scale production scenarios.

[0006] Fourth, resource utilization is low and economic efficiency is poor. The purification yield of traditional single-tower batch distillation process is only 94% to 96%. Material loss mainly comes from component entrainment and decolorization post-processing during distillation, which not only wastes raw material resources, but also results in high overall production costs due to high material loss and energy consumption.

[0007] In summary, the existing single-tower batch distillation process suffers from multiple problems, including low purification accuracy, poor product quality, limited production efficiency, and insufficient resource utilization, and cannot meet the stringent requirements for m-phenylenediamine in high-end applications.

[0008] Therefore, it is necessary to propose a distillation purification method for m-phenylenediamine to solve the above problems. Summary of the Invention

[0009] The purpose of this invention is to address the problems mentioned in the background section by providing a distillation purification method for m-phenylenediamine. By optimizing the process route and key process parameters, this invention enables the continuous and large-scale production of m-phenylenediamine with high purity, low impurities, excellent color, and high stability, thus fully meeting the stringent quality requirements of downstream high-end applications such as nylon MXD6 and high-end wind power epoxy curing agents.

[0010] To achieve the above objectives, the present invention specifically adopts the following technical solution: A method for purifying m-phenylenediamine by distillation includes the following steps: S1. Crude m-phenylenediamine is fed into a deammoniation and light-light ... The temperature at the top of the ammonia removal and light nitrate removal tower is 100~110℃, and the temperature at the bottom of the tower is 120~130℃. S2. The crude m-phenylenediamine after ammonia and light impurity removal is sent to the impurity removal tower to remove heavy impurities by vacuum distillation, and then sent to the product tower for purification by vacuum distillation to obtain refined m-phenylenediamine. The top temperature of the impurity removal tower is 120~130℃ and the bottom temperature is 250~260℃; the top temperature of the product tower is 128~132℃ and the bottom temperature is 255~265℃. S3. Add modified activated carbon to the refined m-phenylenediamine, stir and decolorize at 70~80℃, and then filter to obtain the m-phenylenediamine product.

[0011] Preferably, the vacuum degree of the ammonia removal and light precipitate removal tower is -0.080 to -0.088 MPa and the reflux ratio is 1 to 2; the vacuum degree of the impurity removal tower is -0.092 to -0.095 MPa and the reflux ratio is 2 to 3; and the vacuum degree of the product tower is -0.096 to -0.099 MPa and the reflux ratio is 4 to 6.

[0012] Preferably, the crude m-phenylenediamine is obtained by low-pressure hydrogenation of isophthalonitrile, and the crude m-phenylenediamine has a purity ≥99.5%, a moisture content ≤0.1%, and an ammonia content ≤0.5%.

[0013] Preferably, the ammonia removal and light nitrate removal tower adopts a floating valve tray, and the number of floating valve trays is 12 to 15 layers.

[0014] Preferably, the packing height of the impurity removal tower is 6-7m, and the packing height of the finished product tower is 9-10m.

[0015] Preferably, the stirring and decolorization time is 1 to 1.5 hours; the amount of modified activated carbon added is 0.3 to 0.5% of the mass of refined m-phenylenediamine.

[0016] Preferably, the modified activated carbon is an amino-functionalized alkaline activated carbon; The preparation methods for amino-functionalized alkaline activated carbon include: Activate the activated carbon at 300~400℃ for 2~3 hours; The activated carbon was immersed in an ethylenediamine solution and stirred at a constant temperature of 60-70℃ for 2-3 hours before drying to obtain amino-functionalized alkaline activated carbon.

[0017] Preferably, the ethylenediamine solution has a mass fraction of 5-8%, and the drying temperature is 120-150°C.

[0018] Preferably, the filtration accuracy of the filter is ≤0.5μm.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By first removing heavy impurities from the crude m-phenylenediamine after deammoniation and light treatment, and then purifying it, this step-by-step method can avoid heavy impurities, i.e. high-boiling-point byproducts, from being mixed into the finished product tower, reducing the burden on the finished product tower and improving purification efficiency and product purity.

[0020] 2. The m-phenylenediamine product prepared by this method has a purity ≥99.8%, moisture ≤0.005%, and color ≤98%; byproducts: 3-cyanobenzylamine mass fraction ≤0.005%, total mass fraction of secondary and tertiary amines ≤0.05%; purification yield ≥98%. The m-phenylenediamine product fully meets the usage requirements of high-end applications such as nylon MXD6 and high-end epoxy curing agents, and can be applied directly without additional treatment; it can be stably stored for ≥12 months under sealed, light-proof conditions at 25℃ without discoloration or degradation, demonstrating significantly improved storage stability. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The materials and instruments used in the following embodiments are all commercially available.

[0022] A method for distilling and purifying m-phenylenediamine, comprising steps S1 to S3.

[0023] S1. Crude m-phenylenediamine is fed into a deammoniation and light-light ... The ammonia and light nitrate removal tower uses floating valve trays, with 12 to 15 layers of trays. The top temperature of the ammonia and light nitrate removal tower is 100 to 110℃, and the bottom temperature is 120 to 130℃. The vacuum degree of the ammonia and light nitrate removal tower is -0.080 to -0.088 MPa, and the reflux ratio is 1 to 2.

[0024] Specifically, ammonia in crude m-phenylenediamine will form an azeotrope with m-phenylenediamine. If it is not removed in advance, it will interfere with the mass transfer efficiency of the subsequent impurity removal tower and the product tower, resulting in incomplete separation of heavy impurities. At the same time, ammonia will affect the purity of the product, resulting in excessive ammonia residue that cannot meet the actual production requirements.

[0025] Light impurities, such as unreacted small molecule nitriles and low-boiling-point byproducts, have boiling points close to those of m-phenylenediamine. If they are mixed into subsequent purification processes, they will increase the burden on the impurity removal tower and the product tower, thus affecting the purity of the product.

[0026] Therefore, this preparation method achieves the removal of ammonia and light impurities from crude m-phenylenediamine through step S1, resulting in an ammonia removal rate of ≥99.9% and a light impurity removal rate of ≥99% in the crude m-phenylenediamine after the removal of ammonia and light impurities. The residual ammonia content in the crude m-phenylenediamine after the removal of ammonia and light impurities collected from the bottom of the removal tower is ≤0.001%.

[0027] Specifically, crude m-phenylenediamine is obtained by low-pressure hydrogenation of isophthalonitrile, and the crude m-phenylenediamine has a purity of ≥99.5%, a moisture content of ≤0.1%, and an ammonia content of ≤0.5%.

[0028] S2. The crude m-phenylenediamine after ammonia and light impurity removal is sent to the impurity removal tower to remove heavy impurities by vacuum distillation, and then sent to the product tower for purification by vacuum distillation to obtain refined m-phenylenediamine. The top temperature of the impurity removal tower is 120~130℃, and the bottom temperature is 250~260℃; the vacuum degree of the impurity removal tower is -0.092~-0.095MPa, and the reflux ratio is 2~3. The top temperature of the finished product column is 128~132℃ and the bottom temperature is 255~265℃; the vacuum degree of the finished product column is -0.096~-0.099MPa and the reflux ratio is 4~6.

[0029] The crude m-phenylenediamine, after being deaminated and lightly treated, is first subjected to the removal of heavy impurities before further purification. This step-by-step approach avoids the mixing of heavy impurities, i.e., high-boiling-point byproducts, into the finished product tower, reducing the burden on the finished product tower and improving purification efficiency and product purity.

[0030] Specifically, both the impurity removal tower and the product tower use stainless steel structured packing. The packing height of the impurity removal tower is 6-7m, and the packing height of the product tower is 9-10m. The temperature fluctuation at the top of the product tower is ≤±0.5℃, and the product collected at the top is refined m-phenylenediamine.

[0031] S3. Add modified activated carbon to the refined m-phenylenediamine, stir and decolorize at 70~80℃, and then filter to obtain the m-phenylenediamine product.

[0032] Specifically, the stirring and decolorization time is 1 to 1.5 hours; the amount of modified activated carbon added is 0.3 to 0.5% of the mass of refined m-phenylenediamine.

[0033] Furthermore, the modified activated carbon is an amino-functionalized alkaline activated carbon; The preparation methods for amino-functionalized alkaline activated carbon include: Activate the activated carbon at 300~400℃ for 2~3 hours; The activated carbon was immersed in an ethylenediamine solution and stirred at a constant temperature of 60-70℃ for 2-3 hours before drying to obtain amino-functionalized alkaline activated carbon.

[0034] Specifically, the ethylenediamine solution has a mass fraction of 5-8%, and the drying temperature is 120-150℃.

[0035] After activated carbon is activated at a high temperature of 300~400℃, a large number of oxygen-containing active groups such as hydroxyl and carboxyl groups will be generated on the surface, providing reaction sites for amine grafting with ethylenediamine. When the activated carbon is immersed in a 5~8% ethylenediamine solution and stirred at a constant temperature of 60~70℃, the amino groups of ethylenediamine will undergo nucleophilic substitution / condensation reaction with the oxygen-containing groups on the surface of activated carbon, realizing covalent grafting of amine groups. Ordinary alkaline activated carbon is modified with alkali, such as NaOH / KOH treatment, to increase the alkaline sites on the surface. The adsorption of quinone pigments is mainly physical adsorption, with weak adsorption specificity and easy desorption. The large number of amino groups grafted on the surface of amino-functionalized alkaline activated carbon can form hydrogen bonds with the carbonyl groups in quinone pigment molecules. The adsorption force is much stronger than physical adsorption, and the adsorption sites are more precise. The modified activated carbon has an increased amine content of over 40%, which can target and adsorb quinone pigments through hydrogen bonding. Its decolorization ability is 30% higher than that of ordinary alkaline activated carbon, and the adsorption equilibrium time is shortened to less than 40 minutes.

[0036] Specifically, after stirring and decolorization, the material is filtered through a precision membrane filter with a filtration accuracy of ≤0.5μm, ensuring that the activated carbon residue is ≤0.001%.

[0037] The m-phenylenediamine product obtained by this preparation method has a purity ≥99.8%, moisture content ≤0.005%, and color ≤98%; byproducts: 3-cyanobenzylamine mass fraction ≤0.005%, and total mass fraction of secondary and tertiary amines ≤0.05%; purification yield ≥98%. The m-phenylenediamine product fully meets the usage requirements of high-end applications such as nylon MXD6 and high-end epoxy curing agents, and can be applied directly without additional treatment; it can be stably stored for ≥12 months under sealed, light-protected conditions at 25℃ without discoloration or degradation, demonstrating significantly improved storage stability.

[0038] This preparation method employs continuous distillation, where the ammonia and light-light ...

[0039] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0040] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, equipment, and materials similar to or equivalent to those described, used, and materials in the embodiments of this invention may be used to implement this invention.

[0041] Example 1 This embodiment provides a method for the distillation purification of m-phenylenediamine, including the following steps: 1. Raw material preparation: Crude m-phenylenediamine obtained by low-pressure hydrogenation of isophthalonitrile is selected as the purification raw material. The quality indicators of the crude m-phenylenediamine are as follows: purity 99.6%, moisture 0.09%, ammonia content 0.4%, which meet the raw material access requirements stipulated in this plan and can be directly used in subsequent purification processes. 2. Ammonia and Light Impurity Removal: Crude m-phenylenediamine is continuously fed into a deammoniation and light impurity removal column for vacuum distillation. The column uses a floating valve tray with 13 trays, a vacuum of -0.085 MPa, a top temperature of 105℃, a bottom temperature of 125℃, and a reflux ratio of 1.5. After vacuum distillation, the ammonia removal rate in the crude m-phenylenediamine is 99.92%, and the light impurity removal rate reaches 99.1%. The deammoniation and light impurity removal crude m-phenylenediamine is collected from the bottom of the column, and the residual ammonia content in the deammoniation and light impurity removal crude m-phenylenediamine is ≤0.001%. 3. Dual-tower purification: Crude m-phenylenediamine is fed into a purification tower, which is filled with stainless steel structured packing with a height of 6.5m, a vacuum degree of -0.093MPa, a top temperature of 125℃, a bottom temperature of 255℃, and a reflux ratio of 2.5. The deweighted liquid collected from the top of the purification tower is sent to the product tower, which is filled with stainless steel structured packing with a height of 9.5m, a vacuum degree of -0.098MPa, a top temperature of 130℃ with temperature fluctuation controlled within ±0.3℃, a bottom temperature of 260℃, and a reflux ratio of 5. Refined m-phenylenediamine is continuously collected from the top of the product tower. 4. Decolorization Stability: Add 0.4% (by mass) of amino-functionalized alkaline activated carbon to refined m-phenylenediamine; heat the mixture to 75℃ and maintain this temperature for 1.2 hours with constant stirring. After decolorization, filter the mixture through a precision membrane filter with a filtration accuracy of 0.5μm to intercept activated carbon particles and obtain the m-phenylenediamine product. The amino-functionalized alkaline activated carbon is activated at 350℃ for 2.5 hours. The activated carbon is then immersed in a 6.5% (by mass) ethylenediamine solution and stirred at 65℃ for 2.5 hours, followed by drying at 130℃ to obtain the amino-functionalized alkaline activated carbon.

[0042] 5. Finished Product Testing: The purity of the m-phenylenediamine product is 99.85%, the moisture content is 0.004%, and the color is No. 8; the content of 3-cyanobenzylamine is 0.004%, and the total content of secondary and tertiary amines is 0.04%; the purification yield is 98.3%; the m-phenylenediamine product is stored in a sealed, light-proof package at a constant temperature of 25°C for 12 months. After testing, the product performance remains stable, the color shows no significant change, and there is no oxidation or deterioration. This embodiment uses a single complete purification unit for industrial production. The actual processing capacity of this single unit is 3.2 t / h, which can meet the needs of large-scale production of tens of thousands of tons.

[0043] Example 2 The difference between this embodiment and Embodiment 1 is that: 1. Raw material preparation: The quality indicators of crude m-phenylenediamine are as follows: purity 99.5%, moisture 0.1%, ammonia content 0.5%; 2. Ammonia and Light Impurity Removal: The ammonia and light impurity removal tower uses a floating valve tray with 12 trays, a vacuum degree of -0.080 MPa, a top temperature of 100℃, a bottom temperature of 120℃, and a reflux ratio of 1. After vacuum distillation for ammonia and light impurity removal, the ammonia removal rate in crude m-phenylenediamine is 99.9%, and the light impurity removal rate reaches 99.0%. 3. Dual-tower purification: The impurity removal tower is filled with stainless steel structured packing with a height of 6m, a vacuum degree of -0.092MPa, a top temperature of 120℃, a bottom temperature of 250℃, and a reflux ratio of 2; the product tower is filled with stainless steel structured packing with a height of 9m, a vacuum degree of -0.096MPa, a top temperature of 128℃, a bottom temperature of 255℃, and a reflux ratio of 4. 4. Decolorization stability: Add 0.3% by mass of amino-functionalized alkaline activated carbon to refined m-phenylenediamine; heat the mixture to 70℃ and stir at this temperature for 1.5h to decolorize; the activation temperature for preparing amino-functionalized alkaline activated carbon is 300℃ and the activation time is 3h; immerse the activated carbon in a 5% by mass ethylenediamine solution and stir at 60℃ for 2h, then dry at 120℃ to obtain amino-functionalized alkaline activated carbon.

[0044] 5. Finished product testing: The purity of m-phenylenediamine is 99.8%, the moisture content is 0.005%, and the color is No. 10; the content of 3-cyanobenzylamine is 0.005%, and the total content of secondary and tertiary amines is 0.05%; the purification yield is 98%; this embodiment uses a single complete purification unit for industrial production, and the actual processing capacity of this single unit is 3t / h, which can meet the needs of large-scale mass production of tens of thousands of tons.

[0045] Example 3 The difference between this embodiment and Embodiment 1 is that: 1. Raw material preparation: The quality indicators of crude m-phenylenediamine are as follows: purity 99.7%, moisture 0.08%, ammonia content 0.3%; 2. Ammonia and Light Impurity Removal: The ammonia and light impurity removal tower uses a floating valve tray with 15 trays, a vacuum degree of -0.088 MPa, a top temperature of 110℃, a bottom temperature of 130℃, and a reflux ratio of 2. After vacuum distillation for ammonia and light impurity removal, the ammonia removal rate in crude m-phenylenediamine is 99.95%, and the light impurity removal rate reaches 99.2%. 3. Dual-tower purification: The impurity removal tower is filled with stainless steel structured packing with a height of 7m, a vacuum degree of -0.095MPa, a top temperature of 130℃, a bottom temperature of 260℃, and a reflux ratio of 3; the product tower is filled with stainless steel structured packing with a height of 10m, a vacuum degree of -0.099MPa, a top temperature of 132℃, a bottom temperature of 265℃, and a reflux ratio of 6. 4. Decolorization stability: Add 0.5% by mass of amino-functionalized alkaline activated carbon to refined m-phenylenediamine; heat the mixture to 80℃ and stir at this temperature for 1 hour to decolorize; the activation temperature for preparing amino-functionalized alkaline activated carbon is 400℃ and the activation time is 2 hours; immerse the activated carbon in an 8% by mass ethylenediamine solution and stir at 70℃ for 3 hours, then dry at 120℃ to obtain amino-functionalized alkaline activated carbon.

[0046] 5. Finished product testing: The purity of m-phenylenediamine is 99.9%, the moisture content is 0.003%, and the color is No. 6; the content of 3-cyanobenzylamine is 0.003%, and the total content of secondary and tertiary amines is 0.03%; the purification yield is 98.5%; this embodiment uses a single complete purification unit for industrial production, and the actual processing capacity of this single unit is 3.5t / h, which can meet the needs of large-scale mass production of tens of thousands of tons.

[0047] Comparative Example 1 The only difference between this comparative example and Example 1 is that conventional activated carbon is used instead of amino-functionalized alkaline activated carbon; all other raw material indicators and process parameters are completely consistent with those of Example 1.

[0048] Finished product testing: The purity of m-phenylenediamine is 99.7%, the moisture content is 0.006%, and the color is 18; the content of 3-cyanobenzylamine is 0.007%, and the total content of secondary and tertiary amines is 0.07%; the purification yield is 97.2%; after the product is sealed and protected from light and stored at 25°C for 6 months, the color increases to 25, and slight oxidation and yellowing occur; the single unit has a processing capacity of 3.2 t / h, but the precision membrane needs to be replaced once a month during the filtration process, resulting in high maintenance costs.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that crude m-phenylenediamine is directly fed into a vacuum distillation column. The packing height of the vacuum distillation column is 10m, the reflux ratio is 3, and conventional activated carbon is used instead of amino-functionalized alkaline activated carbon. All other raw material indicators and process parameters are completely consistent with those of Example 1.

[0050] Finished product testing: The purity of m-phenylenediamine was 99.6%, the moisture content was 0.008%, and the color was 20; the content of 3-cyanobenzylamine was 0.009%, and the total content of secondary and tertiary amines was 0.08%; the purification yield was 96.8%; after the product was sealed and protected from light and stored at 25°C for 5 months, obvious oxidation and deterioration occurred, and the color increased to 30; the single unit has a processing capacity of 3.2 t / h, but liquid deviation occurred during the distillation process, and the product batches varied greatly, with a pass rate of only 95%.

[0051] The following is a comparative analysis of Examples 1, 2, and 3 with Comparative Examples 1 and 2: Table 1 shows a comparison of data from Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2. Table 1 Performance comparison of Examples 1, 2, 3, Comparative Example 1 and Comparative Example 2

[0052] Based on the comparison of the product testing indicators of the above embodiments and comparative examples, it can be seen that the present invention, through the synergistic effect of ammonia removal and light volatile matter removal, dual-tower purification, and amino-functionalized alkaline activated carbon, achieves a m-phenylenediamine product purity of ≥99.8%, moisture content ≤0.005%, and color ≤10, with a purification yield of ≥98.0%. Furthermore, it can be stably stored for 12 months under sealed and light-protected conditions at 25℃. A single unit can process 3.0~3.5 t / h, suitable for large-scale production of tens of thousands of tons, with batch stability and low maintenance costs. Compared with the comparative example, the use of amino-functionalized alkaline activated carbon significantly improves the product's decolorization effect, purity, and antioxidant stability. Dual-tower purification effectively avoids the problems of low purification precision, poor product quality, limited production efficiency, and insufficient resource utilization associated with single-tower batch distillation processes.

Claims

1. A method for purifying m-xylylenediamine by rectification, characterized in that, Includes the following steps: S1. Crude m-phenylenediamine is fed into a deammoniation and light-light ... The temperature at the top of the ammonia removal and light nitrate removal tower is 100~110℃, and the temperature at the bottom of the tower is 120~130℃. S2. The crude m-phenylenediamine after ammonia and light impurity removal is sent to the impurity removal tower to remove heavy impurities by vacuum distillation, and then sent to the product tower for purification by vacuum distillation to obtain refined m-phenylenediamine. The top temperature of the impurity removal tower is 120~130℃ and the bottom temperature is 250~260℃; the top temperature of the product tower is 128~132℃ and the bottom temperature is 255~265℃. S3. Add modified activated carbon to the refined m-phenylenediamine, stir and decolorize at 70~80℃, and then filter to obtain the m-phenylenediamine product.

2. The method for distilling and purifying m-phenylenediamine according to claim 1, characterized in that, The vacuum degree of the ammonia removal and light precipitate removal tower is -0.080 to -0.088 MPa, and the reflux ratio is 1 to 2; the vacuum degree of the impurity removal tower is -0.092 to -0.095 MPa, and the reflux ratio is 2 to 3; the vacuum degree of the product tower is -0.096 to -0.099 MPa, and the reflux ratio is 4 to 6.

3. The method for distilling and purifying m-phenylenediamine according to claim 1, characterized in that, The crude m-phenylenediamine is obtained by low-pressure hydrogenation of isophthalonitrile, and the crude m-phenylenediamine has a purity of ≥99.5%, a moisture content of ≤0.1%, and an ammonia content of ≤0.5%.

4. The method for distilling and purifying m-phenylenediamine according to claim 1, characterized in that, The ammonia and light nitrate removal tower uses floating valve trays, with 12 to 15 layers of floating valve trays.

5. The method for distilling and purifying m-phenylenediamine according to claim 1, characterized in that, The packing height of the impurity removal tower is 6-7m, and the packing height of the finished product tower is 9-10m.

6. The method for distilling and purifying m-phenylenediamine according to claim 1, characterized in that, The stirring and decolorization time is 1~1.5h; the amount of modified activated carbon added is 0.3~0.5% of the mass of refined m-phenylenediamine.

7. The method for distilling and purifying m-phenylenediamine according to claim 1, characterized in that, The modified activated carbon is an amino-functionalized alkaline activated carbon; The preparation methods for amino-functionalized alkaline activated carbon include: Activate the activated carbon at 300~400℃ for 2~3 hours; The activated carbon was immersed in an ethylenediamine solution and stirred at a constant temperature of 60-70℃ for 2-3 hours before drying to obtain amino-functionalized alkaline activated carbon.

8. The method for distilling and purifying m-phenylenediamine according to claim 7, characterized in that, The ethylenediamine solution has a mass fraction of 5-8%, and the drying temperature is 120-150℃.

9. The method for distilling and purifying m-phenylenediamine according to claim 1, characterized in that, The filtration accuracy of the filter is ≤0.5μm.

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