Purification method of high-purity p-phenylenediamine
By using water as a solvent for recrystallization and distillation, the problem of purifying crude p-phenylenediamine to high purity has been solved, achieving efficient and low-cost production of high-purity p-phenylenediamine, which is suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SICHUAN NORTH HONGGUANG SPECIAL CHEM CO LTD
- Filing Date
- 2025-12-23
- Publication Date
- 2026-05-08
AI Technical Summary
Existing technologies struggle to efficiently, safely, and cost-effectively purify crude p-phenylenediamine to high-purity polymerization grade (purity ≥99.9%), especially in effectively removing isomer impurities (m-phenylenediamine, o-phenylenediamine) and moisture.
Water was used as a solvent for recrystallization, combined with distillation technology, to purify p-phenylenediamine through high-temperature stirring, cooling crystallization, melting, and distillation steps.
The production of high-purity p-phenylenediamine has been achieved, reaching a purity of over 99.9%. This avoids the use of organic solvents, reduces costs, and simplifies the operation process, making it suitable for industrial production.
Smart Images
Figure CN121990928A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of p-phenylenediamine purification technology, specifically a method for purifying high-purity p-phenylenediamine. Background Technology
[0002] Para-aramid, scientifically known as poly(p-phenylene terephthalamide) fiber, abbreviated as PPTA, is also called aramid 1414 in my country. As a representative of high-performance organic fibers, para-aramid is renowned for its excellent specific strength, specific modulus, heat resistance, and impact resistance, making it a crucial strategic new material. One of the key monomer raw materials for producing para-aramid is high-purity polymer-grade p-phenylenediamine.
[0003] p-Phenylenediamine is typically obtained by catalytic hydrogenation reduction of dinitrobenzene followed by multi-tower continuous distillation, generally with a purity of 99.5%–99.7%. However, the polymer-grade p-phenylenediamine (purity ≥99.9%) required for para-aramid fibers has higher quality requirements, generally requiring a purity of over 99.9%, and strict control over specific harmful impurities, especially isomers (m-phenylenediamine and o-phenylenediamine) and moisture. However, the preparation of polymer-grade p-phenylenediamine is extremely difficult. Improving the purity from 99.5% to over 99.9% requires highly efficient separation of isomer impurities (mainly m- and o-phenylenediamines) with almost identical chemical structures and remarkably similar physical properties. Therefore, developing a simple, low-cost, environmentally friendly method for purifying p-phenylenediamine suitable for industrial production is of significant practical importance.
[0004] Among existing technologies, there are melt crystallization and solution crystallization methods. Melt crystallization uses crude p-phenylenediamine as raw material, employing multi-stage melt crystallization to separate high-purity p-phenylenediamine. The drawbacks of this method are the need for high temperature control precision, long operation time, and low production efficiency. Solution crystallization uses crude p-phenylenediamine as raw material, with NMP and the ionic liquid choline acetate as organic solvents. Under stirring conditions, the mixture is cooled to precipitate crystals. Solid-liquid separation, washing, and drying are then performed at the final crystallization temperature to obtain p-phenylenediamine crystals. The drawbacks of this method are the use of the organic solvent NMP, which is irritating to the skin, eyes, and respiratory tract, requiring protective measures for long-term exposure and posing safety hazards. Furthermore, the use of organic solvents is costly, and subsequent waste treatment processes are complex.
[0005] In summary, there is an urgent need for a purification technology for high-purity polymer-grade p-phenylenediamine that is easy to operate, has high production efficiency, low cost, and is safer and more environmentally friendly. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for purifying high-purity p-phenylenediamine so as to obtain high-purity polymer-grade p-phenylenediamine products with a purity of at least 99.9% from crude p-phenylenediamine as raw material. This method is easy to operate, has high production efficiency, low cost, and is safe and environmentally friendly.
[0007] The objective of this invention is achieved through the following technical solution: A method for purifying high-purity p-phenylenediamine includes recrystallization using water as a solvent.
[0008] In some embodiments, the purification method comprises the following steps: S1: Add water to crude p-phenylenediamine and stir at high temperature to form a homogeneous solution; S2: Cool the solution to crystallize, and obtain crystals and mother liquor; S3: Melt the crystals by heating to obtain a molten liquid; S4: The molten liquid is distilled to obtain the high-purity p-phenylenediamine and the distillation residue.
[0009] In some instances, in step S1, the crude phenylenediamine is prepared by catalytic hydrogenation reduction.
[0010] In some examples, the catalytic hydrogenation reduction method is as follows: using dinitrobenzene as a raw material, in the presence of hydrogen, solvent and catalyst, the nitro group of dinitrobenzene is reduced to an amino group to obtain a diaminobenzene mixture; the diaminobenzene mixture is then subjected to distillation separation to obtain the crude p-phenylenediamine.
[0011] For example, the diaminobenzene mixture includes p-phenylenediamine and isomers such as m-phenylenediamine and o-phenylenediamine, as well as other trace impurities; among which, m-phenylenediamine is the largest component, generally accounting for about 85%, o-dinitrobenzene accounts for about 12%, and p-phenylenediamine has the lowest content but the highest value, accounting for about 3%.
[0012] For example, the solvent is methanol or ethanol; the catalyst is a nickel-carbon skeleton or palladium-carbon.
[0013] For example, the distillation is a multi-tower continuous distillation, so that the purity of the crude p-phenylenediamine reaches 99.5% to 99.7%.
[0014] In some instances, in step S1, the weight ratio of crude p-phenylenediamine to water is 1:2.5 to 3.5.
[0015] In some instances, the high temperature in step S1 is 90°C.
[0016] In some instances, in step S2, the cooling crystallization is performed using a plate-type static crystallizer.
[0017] In some instances, in step S2, the cooling crystallization involves cooling to 25°C.
[0018] In some instances, the melting temperature in step S3 is 90°C.
[0019] In some instances, step S4 includes dehydration and decolorization.
[0020] In some examples, the dehydration operation pressure is 20-30 kPa(A), the operation temperature is 55-65°C at the top of the column and 140-160°C at the bottom of the column; the decolorization operation pressure is 3-4 kPa(A), the operation temperature is 170-175°C at the top of the column and 175-180°C at the bottom of the column.
[0021] In some embodiments, the purification method further includes the following steps: S5: The crystallization mother liquor from step S2 and the distillation residue from step S4 are recovered and used to prepare the crude phenylenediamine.
[0022] In some instances, the crystallization mother liquor and the distillation residue are returned to the distillation stage of the catalytic hydrogenation reduction method for the preparation of crude p-phenylenediamine, and combined with the diaminobenzene mixture for further distillation.
[0023] The beneficial effects of this invention are: 1. This invention uses only water as a solvent, which is simple and avoids the problems of high cost and environmental and safety hazards associated with the use of organic solvents in traditional methods.
[0024] 2. This invention can achieve the high purity requirement of the crystallized product by precisely controlling the amount of solvent water added, without the need for high-precision temperature control equipment in traditional methods, making it easy to automate and suitable for industrial production. Attached Figure Description
[0025] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation
[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.
[0027] The crude p-diphenylamine used in the following examples and comparative examples was prepared by catalytic hydrogenation reduction of dinitrobenzene. Distillation separation yielded 261g of crude m-phenylenediamine, 35g of crude o-phenylenediamine, and 9g of crude p-phenylenediamine. The crude p-phenylenediamine was analyzed by high-performance liquid chromatography (HPLC), and the proportions of each component are shown in Table 1. Table 1. Content of each component in crude p-phenylenediamine
[0028] Example 1 This embodiment provides a method for purifying p-phenylenediamine, the specific steps of which are as follows: 1) Solution preparation: Mix crude p-phenylenediamine and ultrapure water at a weight ratio of 1:3.5 at 90°C to form a homogeneous solution.
[0029] 2) Cooling crystallization: The solution is introduced into a plate static crystallizer. After nitrogen is introduced to replace the air, demineralized water at a temperature of 10-15℃ is used as the internal circulation medium for cooling. When the temperature drops to 25℃, it is kept at that temperature for 1 hour until crystallization is complete.
[0030] 3) Melting: After crystallization, all the crystallization mother liquor is discharged into the mother liquor tank and returned to the distillation process of phenylenediamine production. After the mother liquor is discharged, the p-phenylenediamine crystals in the crystallizer are completely melted by demineralized water at 85-95℃ and then discharged into the crude product tank.
[0031] 4) Distillation purification: The feed liquid in the crude product tank is continuously pumped into the dehydration tower. The top pressure of the dehydration tower is 25 kPa (A), the top temperature is 60°C, and the bottom temperature is 150°C. The dehydrated feed liquid enters the decolorization tower. The top pressure of the decolorization tower is 4 kPa (A), the top temperature is 175°C, and the bottom temperature is 180°C. High-purity polymer-grade p-phenylenediamine product is collected from the top of the tower. The distillation residue is returned to the distillation process for the manufacture of p-phenylenediamine.
[0032] Example 2 This embodiment provides a method for purifying p-phenylenediamine, which differs from Example 1 in that the dehydration and decolorization process parameters are adjusted. The specific steps are as follows: 1) Solution preparation: Crude p-phenylenediamine and ultrapure water are mixed at a weight ratio of 1:3.5 at 90°C to form a homogeneous solution.
[0033] 2) Cooling crystallization: The solution is introduced into a plate static crystallizer. After nitrogen is introduced to replace the air, demineralized water at a temperature of 10-15℃ is used as the internal circulation medium for cooling. When the temperature drops to 25℃, it is kept at that temperature for 1 hour until crystallization is complete.
[0034] 3) Melting: After crystallization, all the crystallization mother liquor is discharged into the mother liquor tank and returned to the distillation process of phenylenediamine production. After the mother liquor is discharged, the p-phenylenediamine crystals in the crystallizer are completely melted by demineralized water at 85-95℃ and then discharged into the crude product tank.
[0035] 4) Distillation purification: The feed liquid in the crude product tank is continuously pumped into the dehydration tower. The top pressure of the dehydration tower is 20 kPa (A), the top temperature is 65°C, and the bottom temperature is 160°C. The dehydrated feed liquid enters the decolorization tower. The top pressure of the decolorization tower is 4 kPa (A), the top temperature is 170°C, and the bottom temperature is 175°C. High-purity polymer-grade p-phenylenediamine product is collected from the top of the tower. The distillation residue is returned to the distillation process for the manufacture of p-phenylenediamine.
[0036] Example 3 This embodiment provides a method for purifying p-phenylenediamine, which differs from Example 1 in that the crystallization endpoint temperature is adjusted. The specific steps are as follows: 1) Solution preparation: Mix crude p-phenylenediamine and ultrapure water at a weight ratio of 1:3.5 at 90°C to form a homogeneous solution.
[0037] 2) Cooling crystallization: The solution is introduced into a plate static crystallizer. After nitrogen is introduced to replace the air, demineralized water at a temperature of 10-15℃ is used as the internal circulation medium for cooling. When the temperature drops to 20℃, it is kept at that temperature for 1 hour until crystallization is complete.
[0038] 3) Melting: After crystallization, all the crystallization mother liquor is discharged into the mother liquor tank and returned to the distillation process of phenylenediamine production. After the mother liquor is discharged, the p-phenylenediamine crystals in the crystallizer are completely melted by demineralized water at 85-95℃ and then discharged into the crude product tank.
[0039] 4) Distillation purification: The feed liquid in the crude product tank is continuously pumped into the dehydration tower. The top pressure of the dehydration tower is 25 kPa (A), the top temperature is 60°C, and the bottom temperature is 150°C. The dehydrated feed liquid enters the decolorization tower. The top pressure of the decolorization tower is 4 kPa (A), the top temperature is 175°C, and the bottom temperature is 180°C. High-purity polymer-grade p-phenylenediamine product is collected from the top of the tower. The distillation residue is returned to the distillation process for the manufacture of p-phenylenediamine.
[0040] Comparative Example 1 This comparative example provides a method for purifying p-phenylenediamine using an organic solvent recrystallization method. The specific steps are as follows: 1) Mix crude p-phenylenediamine and N-methylpyrrolidone at a weight ratio of 1:4 and stir at 90°C under nitrogen protection to form a homogeneous supersaturated solution.
[0041] 2) Introduce the solution into the plate static crystallizer, using demineralized water at 10-15℃ as the internal circulation medium, and begin a slow, programmed cooling process. When the temperature drops to 25℃, maintain the temperature for 1 hour until crystallization is complete.
[0042] 3) After crystallization, the mother liquor is discharged, and the p-phenylenediamine crystals in the crystallizer are completely melted by demineralized water at 85-95℃ and then discharged into the crude product tank.
[0043] 4) The liquid in the crude product tank is continuously pumped into the desolventizing tower. The top pressure of the desolventizing tower is 25 kPa (A), the top temperature is 60°C, and the bottom temperature is 150°C. The liquid after desolventizing enters the decolorizing tower. The top pressure of the decolorizing tower is 4 kPa (A), the top temperature is 175°C, and the bottom temperature is 180°C. High-purity polymer-grade p-phenylenediamine is collected from the top of the tower.
[0044] Comparative Example 2 This comparative example provides a method for purifying p-phenylenediamine. The specific steps are the same as in Example 1, except that the weight ratio of crude p-phenylenediamine to ultrapure water in step 1) is adjusted to 1:2.5.
[0045] Comparative Example 3 This comparative example provides a method for purifying p-phenylenediamine. The specific steps are the same as in Example 1, except that the weight ratio of crude p-phenylenediamine to ultrapure water in step 1) is adjusted to 1:4.5.
[0046] Experimental Example The p-phenylenediamine products obtained in Examples 1-3 and Comparative Examples 1-3 were detected by liquid chromatography, and the specific methods are as follows: The detection method was high performance liquid chromatography (HPLC) with external standard method. The chromatographic column was a C18 column, 250 mm × 4.6 mm, with a particle size of 5 μm. The mobile phase was acetonitrile. The flow rate was 1.0 mL / min, the column temperature was 30 ℃, the detection wavelength was 280 nm, and the injection volume was 10 μL.
[0047] The test results are shown in Table 2: Table 2. Content of each component in p-phenylenediamine products
[0048] Polymerization-grade p-phenylenediamine requires a purity of 99.9% or higher, with m-phenylenediamine and o-phenylenediamine contents not exceeding 0.03%. It can be seen that organic solvents yield p-phenylenediamine products meeting the polymerization-grade requirements. However, when water is used as the solvent, the amount of water significantly affects the purification results. When the water content is 3.5 times that of the crude p-phenylenediamine, the purity can reach over 99.95%, even surpassing the traditional solvent method. This is likely because the water ratio plays a crucial role in controlling intergranular inclusions during the crystallization process, thus further influencing the crystallization effect. Conversely, when the water content is 2.5 and 4.5 times, the m-phenylenediamine content increases significantly, no longer meeting the requirements for polymerization-grade p-phenylenediamine, demonstrating the critical importance of the water addition.
[0049] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.
Claims
1. A method for purifying high-purity p-phenylenediamine, characterized in that, include: Recrystallization was performed using water as a solvent.
2. The purification method according to claim 1, characterized in that, The specific steps are as follows: S1: Add water to crude p-phenylenediamine and stir at high temperature to form a homogeneous solution; S2: Cool the solution to crystallize, and obtain crystals and mother liquor; S3: Melt the crystals by heating to obtain a molten liquid; S4: The molten liquid is distilled to obtain the high-purity p-phenylenediamine and the distillation residue.
3. The purification method according to claim 2, characterized in that: In step S1, the crude phenylenediamine is prepared by catalytic hydrogenation reduction.
4. The purification method according to claim 2, characterized in that: In step S1, the weight ratio of crude p-phenylenediamine to water is 1:3.
5.
5. The purification method according to claim 2, characterized in that: In step S1, the high temperature is 90°C.
6. The purification method according to claim 2, characterized in that: In step S2, the cooling crystallization is carried out using a plate-type static crystallizer.
7. The purification method according to claim 2, characterized in that: In step S2, the cooling crystallization involves cooling the temperature to 25°C.
8. The purification method according to claim 2, characterized in that: In step S3, the temperature at which the temperature is raised and melted is 90°C.
9. The purification method according to claim 2, characterized in that: In step S4, the distillation includes dehydration and decolorization.
10. The purification method according to claim 2, characterized in that, It also includes the following steps: S5: The crystallization mother liquor and the distillation residue are recovered and used to prepare the crude p-phenylenediamine.