A method for preparing m-xylylenediamine

Abstract

This invention discloses a method for preparing m-phenylenediamine, relating to the field of fine chemical hydrogenation synthesis technology. The method involves preparing a homogeneous feed solution by mixing pretreated isophthalonitrile and anhydrous methanol. A modified Raney Ni catalyst is added to the homogeneous feed solution for low-pressure hydrogenation. The modified Raney Ni catalyst is then separated from the homogeneous feed solution after the low-pressure hydrogenation reaction to obtain a crude m-phenylenediamine solution. The crude m-phenylenediamine solution is then purified by distillation after removing methanol to obtain m-phenylenediamine. The entire process is continuous, and the obtained m-phenylenediamine yield is ≥98.5%, purity is ≥99.5%, and moisture content is ≤0.1%. The modified Raney Ni catalyst is a Mo-Co dual-auxiliary modified Raney Ni catalyst, which can be reused to reduce costs.

Description

Technical Field

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

[0002] m-Phenylenediamine is a key fine chemical intermediate. As a core raw material for high-end epoxy resin curing agents and specialty nylon MXD6, it has irreplaceable application value in high-end manufacturing fields such as electronics, automobile manufacturing, and aerospace. Currently, the mainstream industrial preparation method for m-Phenylenediamine is the hydrogenation method of isophthalonitrile. However, this traditional process has several technical defects, which have become key factors restricting the quality improvement, upgrading, and large-scale development of the m-Phenylenediamine industry.

[0003] The existing isophthalonitrile hydrogenation process employs a high-pressure hydrogenation route, with reaction pressures of 8-15 MPa and temperatures of 80-120°C. Conventional Raney nickel catalysts are used. The technical shortcomings of this process are specifically manifested in four aspects: First, the high-pressure reaction conditions pose an extremely high risk of explosion to the production system, and impose stringent requirements on the pressure resistance and sealing performance of the equipment materials. This not only results in high initial investment costs but also significantly increases subsequent maintenance costs, making it unaffordable for small and medium-sized enterprises and severely limiting the industrial-scale adoption and application of this technology. Second, the reaction selectivity is low, and secondary and tertiary amines are easily generated as byproducts during the process. The presence of byproducts results in a yield of only 95-97% for m-phenylenediamine. This not only increases the difficulty and cost of subsequent product separation and purification processes but also prevents the final m-phenylenediamine product from meeting the purity requirements of downstream high-end applications. Furthermore, conventional Raney nickel catalysts are prone to deactivation, requiring only 2-3 reuses after a single activation, leading to high catalyst consumption and significantly increasing the overall cost of m-phenylenediamine production. Finally, the intermittent production mode results in low efficiency, with a single unit having an annual capacity of less than 4,000 tons, failing to meet the demands for large-scale, continuous production from rapidly developing downstream industries.

[0004] In summary, the existing technical solutions for preparing m-phenylenediamine by hydrogenation of isophthalonitrile cannot simultaneously meet the comprehensive requirements of safety, efficiency, low cost, and large scale for industrial production. Therefore, it is necessary to propose a method for preparing m-phenylenediamine to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing m-phenylenediamine in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention specifically adopts the following technical solution: A method for preparing m-phenylenediamine includes the following steps: S1. Pretreated isophthalonitrile and anhydrous methanol are mixed to prepare a homogeneous feed solution; S2. Add modified Raney Ni catalyst to homogeneous feed liquid to carry out low-pressure hydrogenation reaction; Among them, the modified Raney Ni catalyst is a Mo-Co dual-additive modified Raney Ni catalyst; S3. Separate the modified Raney Ni catalyst after low-pressure hydrogenation reaction from the homogeneous feed liquid to obtain a crude m-phenylenediamine solution; S4. After removing methanol from the crude m-phenylenediamine solution, the solution is purified by distillation to obtain m-phenylenediamine.

[0007] Preferably, the specific method for preparing a homogeneous feed solution by mixing pretreated isophthalonitrile and anhydrous methanol includes: Isophthalonitrile with a purity ≥99.6% and a moisture content ≤0.1% was added to a desiccator and vacuum dried at 100~110℃ for 1~2 hours until the moisture content of the isophthalonitrile decreased to ≤0.01%. Anhydrous methanol is dehydrated in a dehydration tower until the water content of the anhydrous methanol is ≤0.005%; The dried isophthalonitrile and anhydrous methanol were added to the mixing vessel at a mass ratio of 1:3~5, and stirred at 200~300 r / min under 60~70℃ conditions to obtain a homogeneous liquid.

[0008] Preferably, the isophthalonitrile is obtained by continuous low-pressure ammonia oxidation of m-xylene, and the isophthalonitrile has a color of ≤15 and a purity of ≥99.6%.

[0009] Preferably, the modified Raney Ni catalyst has a Ni content ≥90%, a Mo content of 0.5~1.0%, a Co content of 0.3~0.5%, a particle size of 80~120 mesh, and a mass of 2~3% of the mass of isophthalonitrile.

[0010] Preferably, the specific method for the low-pressure hydrogenation reaction includes: The homogeneous feed liquid and the modified Raney Ni catalyst were added to the hydrogenation reactor; After purging the hydrogenation reactor three times with nitrogen, hydrogen gas with a purity ≥99.99% is introduced into the hydrogenation reactor to raise the pressure to 1.5~2.0MPa and the temperature to 70~80℃. The stirring speed is adjusted to 300~500r / min, and the reaction is carried out continuously for 3~4h. During the reaction, hydrogen gas is continuously added to maintain a stable reaction pressure in the hydrogenation reactor, and the reaction pressure fluctuation is ≤±0.05MPa.

[0011] Preferably, the modified Raney Ni catalyst is separated from the homogeneous feed liquid by a filter to obtain a crude m-phenylenediamine solution.

[0012] Preferably, the filter has a particle size cutoff of ≤5μm.

[0013] Preferably, the specific method for obtaining m-phenylenediamine by distillation after removing methanol from the crude m-phenylenediamine solution includes: The crude m-phenylenediamine solution was fed into a desolventizing tower for vacuum distillation to remove methanol, yielding crude m-phenylenediamine. Crude m-phenylenediamine was fed into a purification tower for vacuum distillation to obtain m-phenylenediamine.

[0014] Preferably, the desolventizing tower has a vacuum degree of -0.085 to -0.090 MPa and a temperature of 80 to 90°C, and the purification tower has a top temperature of 128 to 132°C, a bottom temperature of 255 to 260°C, a reflux ratio of 4 to 5, a vacuum degree of -0.095 to -0.098 MPa, and a packing height of 8 to 10 m.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The low-pressure hydrogenation reaction of the present invention has a reaction pressure of 1.5~2.0MPa, which is more than 80% lower than the traditional high-pressure method of 8~15MPa. This fundamentally eliminates the explosion safety hazards caused by high-pressure conditions and greatly improves the safety of the operation process. At the same time, the low-pressure reaction condition reduces the technical requirements of the equipment such as pressure resistance, which not only saves the initial investment in the equipment, but also effectively reduces the maintenance costs of the equipment in the later stage.

[0016] 2. By modifying the Raney Ni catalyst with Mo-Co dual additives and controlling the process parameters, this invention achieves a hydrogenation conversion rate of ≥99% for mesophthalonitrile, a yield of ≥98.5% for m-phenylenediamine, a purity of ≥99.5% for m-phenylenediamine, a content of ≤0.01% for 3-cyanobenzylamine, a total content of ≤0.1% for secondary and tertiary amines, and a color of ≤20. The quality of m-phenylenediamine is improved compared to traditional processes, meeting the requirements of downstream high-end epoxy resin curing agents, special nylon MXD6, and other products.

[0017] 3. The Mo-Co dual-additive modified Raney Ni catalyst used in this invention has high stability and can be reused 5 to 8 times. Compared with the traditional ordinary Raney Ni catalyst, which can only be used 2 to 3 times, the catalyst consumption is reduced by 50%, which greatly reduces the catalyst procurement cost and provides important support for reducing the cost per ton of product.

[0018] 4. This invention adopts a continuous operation mode throughout the entire process, breaking the limitations of intermittent production in traditional processes. The annual capacity of a single hydrogenation unit is ≥8,000 tons, which is more than twice the capacity of traditional intermittent units, and can meet the large-scale needs of downstream industries. Detailed Implementation

[0019] 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.

[0020] This invention provides a method for preparing m-phenylenediamine, comprising the following steps: S1. Pretreated isophthalonitrile and anhydrous methanol are mixed to prepare a homogeneous feed solution; S2. Add modified Raney Ni catalyst to homogeneous feed liquid to carry out low-pressure hydrogenation reaction; Among them, the modified Raney Ni catalyst is a Mo-Co dual-additive modified Raney Ni catalyst; S3. Separate the modified Raney Ni catalyst after low-pressure hydrogenation reaction from the homogeneous feed liquid to obtain a crude m-phenylenediamine solution; S4. After removing methanol from the crude m-phenylenediamine solution, the solution is purified by distillation to obtain m-phenylenediamine.

[0021] This invention pretreats isophthalonitrile and anhydrous methanol to ensure that the purity and moisture content of isophthalonitrile and anhydrous methanol meet the reaction requirements, laying the foundation for subsequent reactions. The pretreated isophthalonitrile and anhydrous methanol are mixed at a specific mass ratio and dissolved at a preset temperature and stirring speed to form a homogeneous liquid, ensuring sufficient contact between the two.

[0022] In step S2 of this invention, a modified Raney Ni catalyst is added to a homogeneous feed solution to carry out a low-pressure hydrogenation reaction. Under mild low-pressure process conditions, the two cyano groups in the isophthalonitrile molecule are reduced to amino groups with high efficiency and selectivity, thereby achieving the directional synthesis of the target product, m-phenylenediamine. At the same time, by modifying the Raney Ni catalyst and matching the process parameters, side reactions such as incomplete reduction and over-reduction are suppressed, the purity of the target product is improved, and the modified Raney Ni catalyst can be efficiently recovered and reused 5 to 8 times, which is suitable for the continuous operation requirements of the process and reduces the equipment and raw material costs of industrial production.

[0023] Specifically, the modified Raney Ni catalyst, as the core active center of this hydrogenation reaction, can efficiently adsorb the cyano group of isophthalonitrile and hydrogen molecules in the homogeneous feed liquid. Through catalytic action, it breaks the triple bond in the cyano group and completes hydrogenation, directionally reducing the -CN group of isophthalonitrile to the -CH2NH2 group of isophthalamide. This is a necessary core step for realizing the conversion from raw material to target product; without this step, the cyano group cannot be reduced under low pressure and mild conditions. Traditional Raney Ni catalysts require high hydrogen pressure to reduce aromatic nitrile compounds, while this invention uses a Mo-Co dual-auxiliary modifier to modify the Raney Ni catalyst, utilizing the electron exchange between Mo, Co, and Ni... The synergistic effect optimizes the hydrogenation activity of the catalyst, enabling the cyano reduction reaction to proceed efficiently under low pressure conditions. This reduces the pressure resistance requirements of the hydrogenation reactor and the safety control costs of the process operation, making it more suitable for continuous industrial production. In addition, side reactions such as incomplete reduction and over-reduction are prone to occur during the dicyano reduction of isophthalonitrile. However, the operation of the Raney Ni catalyst modified with Mo-Co dual promoters in this invention can control the type of active sites and electron density of the catalyst, preferentially catalyzing the complete reduction of cyano and avoiding further hydrogenation of the amino group. Combined with a specific reaction temperature, it effectively inhibits the formation of byproducts such as 3-cyanobenzylamine, secondary amine, and tertiary amine.

[0024] After the hydrogenation reaction, the homogeneous feed liquid contains granular Mo-Co dual-additive modified Raney Ni catalyst. If it is not separated and directly enters the subsequent distillation step, the catalyst will adhere to the distillation column packing / wall, causing packing blockage, reduced heat and mass transfer efficiency, and the introduction of metal impurities, resulting in reduced purity and excessive color of the finished product m-phenylenediamine.

[0025] In step S3 of this invention, the modified Raney Ni catalyst is separated from the homogeneous feed liquid, realizing the recovery and reuse of the modified Raney Ni catalyst without catalyst residue, laying the foundation for subsequent product purification; in step S4, anhydrous methanol is first removed and the anhydrous methanol is directly recycled, and then trace by-products and impurities in the crude product are removed by vacuum distillation, so as to obtain high-purity m-phenylenediamine under the premise of avoiding thermal decomposition of the product, and the finished product indicators meet the requirements of industrial application.

[0026] The specific method for preparing a homogeneous feed solution by mixing pretreated isophthalonitrile and anhydrous methanol includes: Isophthalonitrile with a purity ≥99.6% and a moisture content ≤0.1% is added to a desiccator and vacuum dried at 100~110℃ for 1~2 hours until the moisture content of isophthalonitrile decreases to ≤0.01%; preferably, the vacuum drying temperature can be 105℃ and the vacuum drying time can be 1.5 hours. Anhydrous methanol is dehydrated in a dehydration tower until the water content of the anhydrous methanol is ≤0.005%; The dried isophthalonitrile and anhydrous methanol were added to the mixing tank at a mass ratio of 1:3~5, and stirred at 200~300 r / min under 60~70℃ conditions to obtain a homogeneous liquid. In some embodiments of the present invention, the temperature in the mixing tank can be 60~65℃ or 65~70℃.

[0027] The isophthalonitrile of the present invention is obtained by continuous low-pressure ammonia oxidation of m-xylene, and the isophthalonitrile has a color of ≤15 and a purity of ≥99.6%.

[0028] The modified Raney Ni catalyst of the present invention has a Ni content ≥90%, a Mo content of 0.5~1.0%, and a Co content of 0.3~0.5%. Preferably, the Ni content is 90.5%, the Mo content is 0.8%, and the Co content is 0.4%. The particle size of the modified Raney Ni catalyst is 80~120 mesh. The mass of the modified Raney Ni catalyst is 2~3% of the mass of isophthalonitrile. In some embodiments of the present invention, the mass of the modified Raney Ni catalyst is 2~2.5% or 2.5~3% of the mass of isophthalonitrile.

[0029] The specific method for low-pressure hydrogenation reaction of the present invention includes: The homogeneous feed liquid and the modified Raney Ni catalyst were added to the hydrogenation reactor; After purging the hydrogenation reactor three times with nitrogen, hydrogen gas with a purity ≥99.99% is introduced into the hydrogenation reactor to raise the pressure to 1.5~2.0MPa and the temperature to 70~80℃. The stirring speed is adjusted to 300~500r / min, and the reaction is carried out continuously for 3~4h. During the reaction, hydrogen gas is continuously added to maintain a stable reaction pressure in the hydrogenation reactor, and the reaction pressure fluctuation is ≤±0.05MPa.

[0030] In some embodiments of the present invention, the pressure of the hydrogenation reactor is increased to 1.5~1.8MPa or 1.8~2.0MPa; the temperature of the hydrogenation reactor is increased to 70~75℃ or 75~80℃; the stirring speed of the hydrogenation reactor is adjusted to 300~400r / min or 400~500r / min; and the reaction time in the hydrogenation reactor is 3~3.5h or 3.5~4h.

[0031] The modified Raney Ni catalyst of this invention is separated from the homogeneous feed liquid by a filter to obtain a crude m-phenylenediamine solution. The filter has a particle size cutoff of ≤5μm.

[0032] The specific method of obtaining m-phenylenediamine by distillation after removing methanol from a crude m-phenylenediamine solution according to the present invention includes: The crude m-phenylenediamine solution was fed into a desolventizing tower for vacuum distillation to remove methanol, yielding crude m-phenylenediamine. Crude m-phenylenediamine was fed into a purification tower for vacuum distillation to obtain m-phenylenediamine.

[0033] The vacuum degree of the solvent removal tower is -0.085 to -0.090 MPa and the temperature is 80 to 90°C; in some embodiments of the present invention, the vacuum degree of the solvent removal tower is -0.085 to -0.088 MPa or -0.085 to -0.090 MPa, and the temperature of the solvent removal tower is 80 to 85°C or 85 to 90°C. The purification tower uses wire mesh corrugated structured packing. The top temperature of the purification tower is 128~132℃, the bottom temperature is 255~260℃, the reflux ratio is 4~5, the vacuum degree is -0.095~-0.098MPa, and the packing height is 8~10m. In some embodiments of the present invention, the top temperature of the purification tower is 128~130℃ or 130~132℃, the bottom temperature is 255~258℃ or 258~260℃, the reflux ratio is 4~4.5 or 4.5~5, the vacuum degree is -0.095~-0.097MPa or -0.097~-0.098MPa, and the packing height is 8~9m or 9~10m.

[0034] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0035] 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.

[0036] Example 1 This embodiment provides a method for preparing m-phenylenediamine, including the following steps: 1. Raw material pretreatment: Isophthalonitrile with a purity of 99.7% and a moisture content of 0.08% was vacuum dried at 105℃ for 1.5 hours until the moisture content of the isophthalonitrile decreased to 0.009%; anhydrous methanol was dehydrated to a moisture content of 0.004%. 2. Ingredient dissolution: Dry isophthalonitrile and anhydrous methanol are mixed at a mass ratio of 1:4 and stirred at 65℃ and 250r / min to dissolve and obtain a homogeneous liquid. 3. Low-pressure hydrogenation: The homogeneous feed liquid is fed into the hydrogenation reactor, and 2.5% of the Raney Ni catalyst modified with Mo-Co dual additives is added, wherein the Ni content is 90.5%, the Mo content is 0.8%, and the Co content is 0.4%. After nitrogen purging three times, hydrogen is introduced to pressurize to 1.8 MPa and heat to 75°C. The reaction is stirred at 400 r / min for 3.5 h. Hydrogen is continuously added, with pressure fluctuations of ±0.03 MPa. 4. Catalyst separation: The reaction solution is filtered through a 5μm precision filter, and the catalyst recovery rate is 99.6%, allowing it to be reused 7 times; 5. Solvent recovery: The filtrate is sent to a solvent removal tower to remove methanol at -0.088MPa and 85℃, with a recovery rate of 96%, and the methanol is recycled. 6. Distillation and purification: After solvent removal, the crude product is sent to the purification tower. The vacuum degree in the purification tower is -0.097MPa, the temperature at the top of the tower is 130℃, the temperature at the bottom of the tower is 258℃, the reflux ratio is 4.5, and the packing height is 9m. Finished product specifications: m-phenylenediamine purity 99.6%, moisture 0.09%, 3-cyanobenzylamine content 0.008%, total secondary and tertiary amine content 0.07%, color 18; isophthalonitrile hydrogenation reaction conversion rate 99.5%, m-phenylenediamine yield 98.8%; annual capacity of a single unit is 8,500 tons, and the production cost per ton of product is reduced by 18% compared to traditional processes.

[0037] Example 2 This embodiment provides a method for preparing m-phenylenediamine. The difference between this embodiment and Embodiment 1 is that: Dried isophthalonitrile and anhydrous methanol were mixed at a mass ratio of 1:3 and stirred at 60℃ and 200 r / min to obtain a homogeneous feed solution. The homogeneous feed solution was sent to a hydrogenation reactor, and 2% of the Raney Ni catalyst modified with Mo-Co dual additives was added. After nitrogen purging three times, hydrogen was introduced to pressurize to 1.5 MPa and heat to 70℃. The reaction was stirred at 300 r / min for 3 h. The filtrate was sent to a desolventizing tower to remove methanol at -0.085 MPa and 80℃, with a recovery rate of 95%. The crude product after desolventizing was sent to a purification tower with a vacuum of -0.095 MPa, a top temperature of 128℃, a bottom temperature of 255℃, a reflux ratio of 4, and a packing height of 8 m. Finished product specifications: 99.5% purity of m-phenylenediamine, 99.2% conversion rate of isophthalonitrile hydrogenation reaction, and 98.5% yield of m-phenylenediamine; the annual production capacity of a single unit is 8,000 tons, and the production cost per ton of product is reduced by 15% compared with the traditional process.

[0038] Example 3 This embodiment provides a method for preparing m-phenylenediamine. The difference between this embodiment and Embodiment 1 is that: Dried isophthalonitrile and anhydrous methanol were mixed at a mass ratio of 1:5 and stirred at 70℃ and 300 r / min to obtain a homogeneous feed solution. The homogeneous feed solution was sent to a hydrogenation reactor, and 3% of the Raney Ni catalyst modified with Mo-Co dual additives was added. After nitrogen purging three times, hydrogen was introduced to pressurize to 2 MPa and heat to 80℃. The reaction was stirred at 500 r / min for 4 h. The filtrate was sent to a desolventizing tower to remove methanol at -0.090 MPa and 90℃, with a recovery rate of 97%. The crude product after desolventizing was sent to a purification tower with a vacuum of -0.098 MPa, a top temperature of 132℃, a bottom temperature of 255℃, a reflux ratio of 5, and a packing height of 10 m. Finished product specifications: m-phenylenediamine purity 99.7%, isophthalonitrile hydrogenation conversion rate 99.8%, m-phenylenediamine yield 99.0%; annual capacity of a single unit is 9,000 tons, and the production cost per ton of product is reduced by 20% compared to traditional processes.

[0039] The following is a comparative analysis of Examples 1, 2, and 3: Table 1 Comparison of data from Examples 1, 2, and 3 Examples 1, 2, and 3 all validate the method for preparing m-phenylenediamine of the present invention. Example 1 serves as an intermediate reference example, exhibiting low operational difficulty and strong stability, suitable for routine industrial production. Example 2 is a low-parameter, energy-saving example, suitable for production scenarios with tight raw material supply and low capacity requirements. Example 3 is a high-parameter, optimal example, achieving the best product quality, capacity, and cost advantages, suitable for large-scale industrial production, and is the preferred embodiment of the present invention.

Claims

1. A method for preparing m-phenylenediamine, characterized in that, Includes the following steps: S1. Pretreated isophthalonitrile and anhydrous methanol are mixed to prepare a homogeneous feed solution; S2. Add modified Raney Ni catalyst to homogeneous feed liquid to carry out low-pressure hydrogenation reaction; Among them, the modified Raney Ni catalyst is a Mo-Co dual-additive modified Raney Ni catalyst; S3. Separate the modified Raney Ni catalyst after low-pressure hydrogenation reaction from the homogeneous feed liquid to obtain a crude m-phenylenediamine solution; S4. After removing methanol from the crude m-phenylenediamine solution, the solution is purified by distillation to obtain m-phenylenediamine.

2. The method for preparing m-phenylenediamine according to claim 1, characterized in that, The specific method for preparing a homogeneous feed solution by mixing pretreated isophthalonitrile and anhydrous methanol includes: Isophthalonitrile with a purity ≥99.6% and a moisture content ≤0.1% was added to a desiccator and vacuum dried at 100~110℃ for 1~2 hours until the moisture content of the isophthalonitrile decreased to ≤0.01%. Anhydrous methanol is dehydrated in a dehydration tower until the water content of the anhydrous methanol is ≤0.005%; The dried isophthalonitrile and anhydrous methanol were added to the mixing vessel at a mass ratio of 1:3~5, and stirred at 200~300 r / min under 60~70℃ conditions to obtain a homogeneous liquid.

3. The method for preparing m-phenylenediamine according to claim 1, characterized in that, The isophthalonitrile is obtained by continuous low-pressure ammonia oxidation of m-xylene, and the isophthalonitrile has a color of ≤15 and a purity of ≥99.6%.

4. The method for preparing m-phenylenediamine according to claim 1, characterized in that, The modified Raney Ni catalyst has a Ni content ≥90%, a Mo content of 0.5~1.0%, a Co content of 0.3~0.5%, a particle size of 80~120 mesh, and a mass of 2~3% of the mass of isophthalonitrile.

5. The method for preparing m-phenylenediamine according to claim 1, characterized in that, The specific method for the low-pressure hydrogenation reaction includes: The homogeneous feed liquid and the modified Raney Ni catalyst were added to the hydrogenation reactor; After purging the hydrogenation reactor three times with nitrogen, hydrogen gas with a purity ≥99.99% is introduced into the hydrogenation reactor to raise the pressure to 1.5~2.0MPa and the temperature to 70~80℃. The stirring speed is adjusted to 300~500r / min, and the reaction is carried out continuously for 3~4h. During the reaction, hydrogen gas is continuously added to maintain a stable reaction pressure in the hydrogenation reactor, and the reaction pressure fluctuation is ≤±0.05MPa.

6. The method for preparing m-phenylenediamine according to claim 1, characterized in that, The modified Raney Ni catalyst was separated from the homogeneous feed liquid by a filter to obtain a crude m-phenylenediamine solution.

7. The method for preparing m-phenylenediamine according to claim 1, characterized in that, The filter has a particle size cutoff of ≤5μm.

8. The method for preparing m-phenylenediamine according to claim 1, characterized in that, The specific methods for obtaining m-phenylenediamine by distillation after removing methanol from a crude m-phenylenediamine solution include: The crude m-phenylenediamine solution was fed into a desolventizing tower for vacuum distillation to remove methanol, yielding crude m-phenylenediamine. Crude m-phenylenediamine was fed into a purification tower for vacuum distillation to obtain m-phenylenediamine.

9. The method for preparing m-phenylenediamine according to claim 8, characterized in that, The desolventizing tower has a vacuum degree of -0.085 to -0.090 MPa and a temperature of 80 to 90°C. The purification tower has a top temperature of 128 to 132°C, a bottom temperature of 255 to 260°C, a reflux ratio of 4 to 5, a vacuum degree of -0.095 to -0.098 MPa, and a packing height of 8 to 10 m.

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