Production process method for continuously synthesizing p-phenylenediamine

Abstract

The invention relates to a production process method for continuously synthesizing p-phenylenediamine, and belongs to the field of organic material preparation. The preparation method comprises the following steps: carrying out diazotization reaction on aniline, hydrochloric acid and sodium nitrite serving as raw materials under an ice bath condition, adding a small amount of chelating agent and polymerization inhibitor after the reaction is completed, uniformly mixing, and heating to generate p-aminoazobenzene hydrochloride and a small amount of o-aminoazobenzene solution. And removing redundant hydrochloric acid by using a sodium hydroxide solution, standing, separating into an oil phase and a water phase, enabling the separated water phase to enter a sewage recovery section, and enabling the separated oil phase to enter a trickle bed hydrogenation section. And carrying out reduced pressure rectification on the oil phase after the hydrogenation reaction to recover the chelating agent, the polymerization inhibitor and aniline, and simultaneously obtaining p-phenylenediamine and o-phenylenediamine products. Compared with a traditional benzene nitration method for production, the method provided by the invention belongs to a continuous production process, is more environment-friendly and safer, and is high in reaction process operation continuity, high in product yield and high in purity, so that the method is more suitable for continuous production compared with other methods.

Description

TECHNICAL FIELD

[0001] The application relates to a production process method for continuously synthesizing p-phenylenediamine and belongs to the technical field of organic material preparation. BACKGROUND

[0002] P-phenylenediamine, also known as Ursi D, belongs to aromatic diamine products, and is an important intermediate and is mainly used for preparing azo-based disperse dyes, direct dyes, acid dyes, sulfur dyes, fur dye, anti-aging agent of natural rubber and diene-based synthetic rubber, coupling agent in color photography and hair dye.

[0003] At present, more than 70% of p-phenylenediamine in China is used for preparing acid, nitrogen-based disperse, direct dyes and the like, and a small part is used for preparing para-aramid fiber materials, but with the development of new energy and new materials and the frequent international regional wars, high-performance fiber materials such as bulletproof materials para-aramid are in urgent need, so that researchers gradually pay attention to para-aramid technology. The main production process of p-phenylenediamine in China is the reduction process of p-nitroaniline. In the traditional reduction method of p-nitroaniline, the raw material p-nitroaniline needs to be obtained from chlorobenzene through nitration and ammonolysis, the synthesis process route is complicated, the safety risk in the production process is huge, the pollution in the nitration process is serious, and the proportion of impurities is high. The reduction process of the product after nitration can use iron powder reduction, sulfide alkali reduction and hydrogen reduction. The sulfide alkali reduction method has high safety, and is the mainstream method at present, but there are more wastewater and sludge emissions in the production process, and the conversion rate of the raw material p-nitroaniline is low.

[0004] The patent application No. CN201210492883.3 of the same type of product describes a process for synthesizing p-phenylenediamine by hydrolyzing waste polyester. The patent application No. CN201210234276.7 describes a process for synthesizing p-phenylenediamine by reacting aniline liquid with waste nitrogen oxide, and p-phenylenediamine is only a byproduct. The patent application No. CN201410748155.3 describes a process for preparing p-phenylenediamine by catalytically hydrogenating p-nitroaniline with palladium carbon as a catalyst and 2-methyl-1-propanol and water as a mixed solvent. The patent application No. CN201610552383.2 describes a process for preparing p-phenylenediamine by hydrogenation reaction with p-nitroaniline, a solvent and hydrogen as main raw materials in the presence of a catalyst in a fixed bed reactor or a tube reactor.

[0005] The patent application number CN 02128852.6 describes that aniline is used as a raw material to synthesize 1,3-diphenyltriazene in a reaction kettle, and then the 1,3-diphenyltriazene is directly rearranged into p-aminoazobenzene by heating, and an alkaline solution is used to form oil-water phase separation, and the oil phase of p-aminoazobenzene is separated out, and then a palladium-carbon catalyst is used to carry out hydrogenation reduction in a reaction kettle or a reactor to synthesize p-phenylenediamine and aniline. The patent application number CN 94111111.3 describes a method for producing p-phenylenediamine and aniline by low-pressure hydrogenation of p-aminoazobenzene in a reaction kettle.

[0006] P-phenylenediamine belongs to the upstream of aramid technology, and exploring the preparation method of p-phenylenediamine is one of the key points for breaking through the high-end aramid technology, and is of great significance for realizing clean production substitution. SUMMARY

[0007] In view of the problems that the production process of p-phenylenediamine is intermittent operation at present, the operation needs to switch materials more, the production process continuity is poor, the by-products are more in the nitration process, which leads to poor product purity, and 1,3-diphenyltriazene and p-aminoazobenzene are easy to decompose and easy to precipitate in the solution, the present application develops a p-phenylenediamine production process with strong production continuity and high product purity.

[0008] The production process method of p-phenylenediamine provided by the present application comprises the following steps:

[0009] S1, 3-diphenyltriazene hydrochloride solution: 10-100 parts of aniline, 10-30 parts of concentrated hydrochloric acid with a concentration of 31% are added to a reaction kettle and uniformly mixed; 10-30 parts of sodium nitrite solution is added dropwise to the solution under the condition of ice bath at-20℃-20℃, and the consumption of the three substances is recorded, so that the molar ratio of aniline: hydrochloric acid: sodium nitrite is (1-10):(1-3):1.

[0010] S2 synthesis of p-aminoazobenzene hydrochloride: the synthesized 1,3-diphenyltriazene hydrochloride solution is added with a chelating agent and a polymerization inhibitor, stirred and heated to 40℃-80℃, and the reaction time is 0.5h-5h, to obtain a mixed solution of p-aminoazobenzene hydrochloride and o-aminoazobenzene hydrochloride.

[0011] S3 neutralization reaction and oil-water phase separation: add sodium hydroxide solution (30% to 50% by mass) to the solution of step S2 to neutralize excess hydrochloric acid, adjust the pH to 7 to 14, and the solution of step S2 gradually separates into an oil phase and an aqueous phase. After standing for 6 to 12 hours, separate the aqueous phase with a separatory funnel, and the oil phase enters the trickle bed hydrogenation reaction section, and the aqueous phase enters the wastewater recovery system.

[0012] S4 trickle bed hydrogenation reaction of p-aminoazobenzene and o-aminoazobenzene oil phase: replace the trickle bed hydrogenation reactor with nitrogen 3 to 5 times until the oxygen content is less than 0.5%, then replace the nitrogen in the trickle bed hydrogenation reactor with hydrogen 3 times, and after the replacement is complete, introduce hydrogen, gradually increase the pressure of the trickle bed hydrogenation reactor to 0.5 MPa to 5 MPa, and gradually increase the reaction temperature to 60 to 150°C. The p-aminoazobenzene and o-aminoazobenzene oil phase in step S3 is subjected to a hydrogenation reaction at a reaction temperature of 60 to 150°C, and the residence time of the reaction material is 1 minute to 60 minutes.

[0013] S5 p-phenylenediamine refining: after the hydrogenation reaction is complete, the hydrogenated oil phase enters a vacuum rectification column for rectification, the temperature at the top of the vacuum rectification column is controlled at 60°C, the temperature at the middle section is controlled at 135°C, and the temperature at the bottom of the column is controlled at 195°C. The chelating agent and the polymerization inhibitor are recovered at the top of the vacuum rectification column, the recovered chelating agent and polymerization inhibitor are returned to step S1 as raw materials, the crude aniline is recovered at the middle section and enters an aniline refining column, and the material at the bottom of the column enters an aniline recovery column. Aniline is recovered at the top of the aniline refining column, the recovered aniline is returned to step S1 as raw material, and a mixture of p-phenylenediamine and o-phenylenediamine is obtained at the bottom of the column and continues to enter a p-phenylenediamine separation column for vacuum rectification. o-Phenylenediamine is obtained at the top of the p-phenylenediamine separation column, and crude p-phenylenediamine is obtained at the bottom of the column. The crude p-phenylenediamine enters a p-phenylenediamine refining column, refined p-phenylenediamine is obtained at the top of the column, and the material at the bottom of the column enters the aniline recovery column for continued aniline recovery.

[0014] The above-mentioned synthesis method of p-phenylenediamine has a reaction temperature of -20 to 20°C in step S1 of claim 1, and the molar ratio of aniline:hydrochloric acid:sodium nitrite consumption is (1 to 10):(1 to 3):1. When the reaction approaches the end point, the reaction is stopped when the starch potassium iodide test paper shows blue.

[0015] The above-mentioned synthesis method of p-phenylenediamine has a chelating agent in step S2 of claim 1, which is one or two of DMC, EMC, DMF, MMC, DHF, and TPT.

[0016] The above-mentioned synthesis method of p-phenylenediamine has a polymerization inhibitor in step S2 of claim 1, which is one or two of MeHF, MeQH, MePY, and MEOH.

[0017] The reaction material after neutralization in step S3 of the synthesis method of p-phenylenediamine as claimed in claim 1 is allowed to stand until the oil and water phases are separated, and after separation by a separatory funnel, the oil phase is introduced into a vacuum rectification column for rectification and separation, and the water phase is introduced into a sewage treatment system.

[0018] The reactor in step S4 of the synthesis method of p-phenylenediamine as claimed in claim 1 is a trickle bed reactor, and the catalyst is one or both of a nickel-based molecular sieve catalyst, a nickel-based activated alumina catalyst or a palladium-based activated carbon catalyst.

[0019] In step S5 of the synthesis method of p-phenylenediamine as claimed in claim 1, the pressure of the vacuum rectification column is -90 kPa to -101.3 kPa, the top temperature is 20 to 80 DEG C, the temperature of the middle section is 100 to 145 DEG C, and the bottom temperature is 140 to 200 DEG C; the pressure of the aniline refining column is -90 kPa to 101.3 kPa, the top temperature is 30 to 80 DEG C, the temperature of the middle section is 60 to 100 DEG C, and the bottom temperature is 100 to 180 DEG C; the pressure of the p-phenylenediamine separation column is -90 kPa to 101.3 kPa, the top temperature is 30 to 110 DEG C, and the bottom temperature is 120 to 180 DEG C; the pressure of the p-phenylenediamine refining column is -90 kPa to -101.3 kPa, the top temperature is 80 to 120 DEG C, the temperature of the middle section is 130 to 135 DEG C, and the bottom temperature is 130 to 180 DEG C; and the pressure of the aniline recovery column is -90 kPa to 101.3 kPa, the top temperature is 110 to 170 DEG C, and the bottom temperature is 160 to 240 DEG C.

[0020] The continuous synthesis method of p-phenylenediamine provided by the present application has the following advantages:

[0021] The continuous synthesis method of p-phenylenediamine provided by the present application uses aniline as raw material, and through diazotization reaction, heating rearrangement reaction, neutralization reaction, oil-water phase separation, hydrogenation reaction and continuous vacuum rectification, high-purity product p-phenylenediamine and byproduct o-phenylenediamine can be obtained. The preparation process of the method has high continuity, less reaction byproducts and less wastewater, and meanwhile, the raw material is easy to obtain, the reaction steps are simple and continuous, and the prepared product has high purity, so compared with other methods, the method has good industrial implementation prospect.

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application; based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the protection scope of the present application.

[0023] All other embodiments obtained by those skilled in the art without creative effort belong to the protection scope of the present application.

[0024] The embodiments described above are all within the protection scope of the present application. DETAILED DESCRIPTION

[0025] Example 1:

[0026] S1 Synthesis of 1,3-diphenyltriazene solution: A 500ml flask was charged with aniline (70ml), 31% concentrated hydrochloric acid (30ml), and the system was stirred at room temperature until the aniline was fully dissolved. The flask was then placed in an ice bath to reduce the temperature to 0°C. A 40% aqueous sodium nitrite solution was added dropwise to the system. When the reaction was nearly complete, a blue color was observed on the starch-iodide paper, indicating that the reaction was complete. The sodium nitrite solution was then stopped. The ratio of the reactants was 9:2:1.

[0027] S2 Synthesis of p-aminoazobenzene hydrochloride solution: A certain amount of chelating agent and polymerization inhibitor was added to the 1,3-diphenyltriazene solution prepared in step S1. The mixture was stirred and heated to 65°C for 3 hours to obtain a mixture of p-aminoazobenzene and o-aminoazobenzene hydrochloride.

[0028] S3 Neutralization of excess hydrochloric acid by adding sodium hydroxide solution (30%-50% by mass) to the solution prepared in step S2 to adjust the pH to 13. The solution prepared in step S2 was separated into an oil phase and an aqueous phase. The aqueous phase was separated by a separatory funnel after standing for 6 hours. The oil phase was introduced into a trickle bed hydrogenation reactor, and the aqueous phase was introduced into a wastewater recovery system.

[0029] S4 Hydrogenation of p-aminoazobenzene: The trickle bed reactor was replaced with nitrogen gas until the oxygen content was less than 0.5%. The nitrogen gas was then replaced with hydrogen gas three times. The pressure of the hydrogen gas in the trickle bed reactor was increased to 1 MPa. The mixture of p-aminoazobenzene and o-aminoazobenzene prepared in step S2 was introduced into the hydrogenation trickle bed reactor and reacted with hydrogen gas at 75°C.

[0030] S5 After the hydrogenation reaction was completed, the hydrogenated oil phase was introduced into a vacuum rectification column. The temperature at the top of the column was controlled at 60°C, the temperature of the middle section was controlled at 135°C, and the temperature at the bottom of the column was controlled at 195°C. The chelating agent and polymerization inhibitor were recovered at the top of the column and returned to step S1 as raw materials. The crude aniline was extracted from the middle section and introduced into an aniline refining column. The material at the bottom of the column was introduced into an aniline recovery column. The material extracted from the middle section was introduced into the aniline refining column. Aniline was recovered at the top of the column at 92°C and returned to step S1 as raw materials. A mixture of p-phenylenediamine and o-phenylenediamine was obtained at the bottom of the column at 157°C and introduced into a p-phenylenediamine separation column for vacuum rectification. o-Phenylenediamine was obtained at the top of the column at 85°C, and p-phenylenediamine crude product was obtained at the bottom of the column at 156.5°C. The p-phenylenediamine crude product was introduced into a p-phenylenediamine refining column. P-phenylenediamine refined product was obtained at the top of the column at 132°C, and the material at the bottom of the column was introduced into the aniline recovery column for further aniline recovery. The yield of p-phenylenediamine was 79.4%, and the yield of o-phenylenediamine was 20.5%.

[0031] This example is an implementation of the exploration phase, the main purpose is to explore the production route from aniline to 1,3-diphenyl triazene, and then to p-phenylenediamine by hydrogenation reduction of p-aminoazobenzene and o-aminoazobenzene. Through preliminary exploration, it is found that this method can realize the synthesis of p-phenylenediamine with high purity from aniline, and the synthesis route is correct, but the overall yield of the product is relatively low, and the production parameters of each section need to be further explored and adjusted.

[0032] Example 2:

[0033] S1 Synthesis of 1,3-diphenyl triazene solution: Add aniline (90 mL) and 31% concentrated hydrochloric acid (30 mL) into a 500 mL flask, start stirring, and dissolve the aniline in the system at room temperature. Then place the reaction bottle in an ice bath to reduce the temperature to -5°C. Add 40% (mass ratio) sodium nitrite aqueous solution dropwise to the above system. When the reaction is close to completion, use starch iodine potassium paper to detect blue color, then stop adding sodium nitrite solution, and the ratio is 8:2:1.

[0034] S2 Synthesis of p-aminoazobenzene hydrochloride solution: Add a certain amount of chelating agent and polymerization inhibitor to the synthesized 1,3-diphenyl triazene solution flask, stir uniformly, and heat to 50°C. After 3 hours of reaction, a mixed solution of p-aminoazobenzene and o-aminoazobenzene hydrochloride is obtained.

[0035] S3 Add sodium hydroxide solution (30% to 50% mass ratio) to the solution of step S2 to neutralize excess hydrochloric acid and adjust the pH value to 13. The solution of step S2 gradually separates into an oil phase and an aqueous phase. After standing for 6 hours, the aqueous phase is separated by a separatory funnel, and the oil phase is introduced into the trickle bed hydrogenation reaction section, and the aqueous phase is introduced into the wastewater recovery system.

[0036] S4 Hydrogenation reduction of p-aminoazobenzene: Replace the trickle bed reactor with nitrogen gas to reduce the oxygen content to less than 0.5%, and then replace the nitrogen gas with hydrogen gas three times. Increase the pressure of the trickle bed reactor to 2 MPa with hydrogen gas. Then inject the synthesized p-aminoazobenzene and o-aminoazobenzene mixed solution into the hydrogenation trickle bed reactor and react with hydrogen gas at 80°C.

[0037] After the hydrogenation reaction is completed, the hydrogenated oil phase enters the vacuum rectifying column for rectification. The temperature at the top of the vacuum rectifying column is controlled at 60°C, the temperature at the middle section extraction is controlled at 135°C, and the temperature at the column bottom is controlled at 195°C. The chelating agent and the polymerization inhibitor are recovered at the top of the column, and the recovered chelating agent and polymerization inhibitor are returned to step S1 as raw materials. Meanwhile, the crude aniline is extracted at the middle section and enters the aniline refining column, and the material at the column bottom enters the aniline recovery column. The material extracted at the middle section enters the aniline refining column, and the aniline is recovered at the top of the aniline refining column at 89°C and returned to step S1 as raw material. Meanwhile, a mixture of p-phenylenediamine and o-phenylenediamine is obtained at the column bottom at 136°C and enters the p-phenylenediamine separation column for vacuum rectification. o-Phenylenediamine is obtained at the top of the p-phenylenediamine separation column at 85°C, and the crude p-phenylenediamine product is obtained at the column bottom at 156°C. The crude p-phenylenediamine product enters the p-phenylenediamine refining column, and the refined p-phenylenediamine product is obtained at the top of the column at 133°C. The material at the column bottom at 135°C enters the aniline recovery column for further aniline recovery. The yield of p-phenylenediamine is 85.2%, and the yield of o-phenylenediamine is 14.6%.

[0038] In this example, by adjusting the concentration ratio of each component and adjusting part of the operation parameters, the yield of the target product is greatly improved. In subsequent cases, part of the operation conditions of the neutralization reaction, hydrogenation reaction and vacuum rectification in this example are used for reference. Through the above two experiments, it is found that the amount of sodium hydroxide solution used for neutralization is relatively large. In order to reduce the amount of sodium hydroxide solution, the ratio of concentrated hydrochloric acid and sodium nitrite is adjusted in subsequent experiments.

[0039] Example 3:

[0040] S1 Synthesis of 1,3-diphenyltriazene solution: A 500ml flask was added with aniline (120ml) and 31% concentrated hydrochloric acid (30ml), and the system was stirred at room temperature to dissolve the aniline. Then the reaction bottle was placed in an ice bath to reduce the temperature to 0°C. Sodium nitrite aqueous solution was added dropwise to the above system. When the reaction was close to completion, starch iodide potassium test paper was used to detect blue color, and then the addition of sodium nitrite solution was stopped. Aniline was further added to 6:1.5:1.

[0041] S2 Synthesis of p-aminoazobenzene hydrochloride solution: A certain amount of chelating agent and polymerization inhibitor was added to the synthesized 1,3-diphenyltriazene solution flask, and stirred uniformly. Then the temperature was raised to 55°C, and the reaction was carried out for 3h to obtain a mixed solution of p-aminoazobenzene and o-aminoazobenzene hydrochloride.

[0042] S3 Sodium hydroxide solution (30%-50% mass ratio) was added to the solution of step S2 to neutralize the excess hydrochloric acid, and the pH value was adjusted to 14. The solution of step S2 was gradually separated into oil phase and water phase, and was statically placed for 6h. The water phase was separated by a separatory funnel, and the oil phase entered the trickle bed hydrogenation reaction section, and the water phase entered the sewage recovery system.

[0043] S4 Hydrogenation of p-aminoazobenzene: The trickle bed reactor was replaced with nitrogen gas to less than 0.5% oxygen content, and then replaced with hydrogen gas three times. The pressure of the hydrogenation trickle bed reactor was increased to 3.0 MPa with hydrogen gas. The synthesized p-aminoazobenzene and o-aminoazobenzene mixed solution was injected into the hydrogenation trickle bed reactor to react with hydrogen gas at 75°C.

[0044] S5 After the hydrogenation reaction was completed, the hydrogenated oil phase entered the vacuum rectification tower for rectification. The control temperature at the top of the vacuum rectification tower was 60°C, the control temperature at the middle section was 135°C, and the control temperature at the tower bottom was 195°C. The chelating agent and polymerization inhibitor were recovered at 62°C at the top of the tower, and the chelating agent and polymerization inhibitor recovered at the top were returned to step S1 as raw materials. Meanwhile, the crude aniline was extracted at 89.5°C at the middle section of the tower and entered the aniline refining tower. The material extracted at the middle section entered the aniline refining tower, and the aniline was recovered at the top of the aniline refining tower and returned to step S1 as raw materials. The p-phenylenediamine and o-phenylenediamine mixture was obtained at the bottom of the aniline refining tower and continued to enter the p-phenylenediamine separation tower for vacuum rectification. The o-phenylenediamine was obtained at 85°C at the top of the p-phenylenediamine separation tower, and the crude p-phenylenediamine product was obtained at 156°C at the bottom of the tower. The crude p-phenylenediamine product entered the p-phenylenediamine refining tower, and the refined p-phenylenediamine product was obtained at 133°C at the top of the tower. The material at 134.5°C at the bottom of the tower entered the aniline recovery tower to continue recovering aniline. The yield of p-phenylenediamine was 82.9%, and the yield of o-phenylenediamine was 16.7%.

[0045] After adjusting the concentration ratio of each component, the yield of the target product did not change much, indicating that reducing the amount of hydrochloric acid used would not have a significant impact on the yield of p-phenylenediamine. Therefore, the subsequent cases are based on this ratio.

[0046] Example 4:

[0047] S1 Synthesis of 1,3-diphenyltriazene solution: A 500ml flask was added with aniline (120mL) and 31% concentrated hydrochloric acid (30mL), and the system was stirred at room temperature to fully dissolve the aniline. Then the reaction bottle was placed in an ice bath to reduce the temperature to 0°C. Sodium nitrite aqueous solution was added dropwise to the above system, and when the reaction was close to completion, starch iodine potassium paper was used to detect blue color, and then the addition of sodium nitrite solution was stopped. Continue to add aniline to 6:1.5:1.

[0048] S2 Synthesis of p-aminoazobenzene hydrochloride solution: A certain amount of chelating agent and polymerization inhibitor was added to the synthesized 1,3-diphenyltriazene solution flask, stirred uniformly, and heated to 60°C for 3h to obtain a mixed solution of p-aminoazobenzene and o-aminoazobenzene hydrochloride.

[0049] S3 to the solution of step S2, sodium hydroxide solution (30% ~ 50% mass ratio) is added to neutralize excess hydrochloric acid, and the pH value is adjusted to 13. The solution of step S2 is gradually separated into an oil phase and an aqueous phase, and the aqueous phase is separated by a separatory funnel after standing for 6 hours. The oil phase enters the trickle bed hydrogenation reaction section, and the aqueous phase enters the wastewater recovery system.

[0050] S4 hydrogenation of p-aminoazobenzene: the trickle bed reactor is replaced with nitrogen gas to an oxygen content of less than 0.5%, and then replaced with hydrogen gas three times. The pressure of the trickle bed reactor is increased to 2.0 MPa with hydrogen gas. The mixed solution of synthesized p-aminoazobenzene and o-aminoazobenzene is injected into the hydrogenation trickle bed reactor and reacted with hydrogen gas at 80°C.

[0051] S5 After the hydrogenation reaction is completed, the hydrogenated oil phase enters the vacuum rectification column for rectification. The control temperature at the top of the vacuum rectification column is 60°C, the control temperature at the middle section is 135°C, and the control temperature at the bottom of the column is 195°C. The chelating agent and the polymerization inhibitor are recovered at 61°C at the top of the column, and the recovered chelating agent and polymerization inhibitor are returned to step S1 as raw materials. Meanwhile, the crude aniline is extracted at the middle section and enters the aniline refining column. The material at the bottom of the column at 136°C enters the aniline recovery column. The material extracted at the middle section enters the aniline refining column, and the aniline is recovered at the top of the column at 89°C and returned to step S1 as raw materials. At the same time, a mixture of p-phenylenediamine and o-phenylenediamine is obtained at the bottom of the column at 140°C and continues to enter the p-phenylenediamine separation column for vacuum rectification. o-Phenylenediamine is obtained at the top of the p-phenylenediamine separation column at 80°C, and crude p-phenylenediamine is obtained at the bottom of the column at 156°C. The crude p-phenylenediamine enters the p-phenylenediamine refining column, and the refined p-phenylenediamine is obtained at the top of the column at 133.7°C. The material at the bottom of the column at 134.5°C enters the aniline recovery column for further recovery of aniline. The yield of p-phenylenediamine is 86.6%, and the yield of o-phenylenediamine is 12.7%.

[0052] In this example, higher yields of p-phenylenediamine and o-phenylenediamine are obtained. Based on this example, the conditions for vacuum rectification of the oil phase after hydrogenation are fixed, and the effects of adjusting the reaction conditions in the hydrogenation section on the yield of p-phenylenediamine are tested. The reaction effect is observed by gradually reducing the hydrogenation reaction pressure.

[0053] Example 5:

[0054] S1 Synthesis of 1,3-diphenyltriazene solution: 500ml flask is added aniline (120mL) and 31% concentrated hydrochloric acid (30mL), and the system is stirred at room temperature to dissolve the aniline. Then the reaction bottle is placed in an ice bath to reduce the temperature to 0°C. Sodium nitrite aqueous solution is added dropwise to the above system. When the reaction is close to completion, the blue color appears on the starch iodide potassium test paper, and the addition of sodium nitrite solution is stopped. Then aniline is added to 6:1.5:1.

[0055] Synthesis of p-aminoazobenzene hydrochloride solution: A certain amount of chelating agent and polymerization inhibitor was put into the flask containing the synthesized 1,3-diphenyltriazene solution, and stirred uniformly, and then heated to 60°C for 3h to obtain a mixed solution of p-aminoazobenzene and o-aminoazobenzene hydrochloride.

[0056] S3: Neutralizing the excess hydrochloric acid by adding sodium hydroxide solution (30%-50% by mass) to the solution of step S2, adjusting the pH value to 14, and separating the solution of step S2 into an oil phase and an aqueous phase, standing for 6h, separating the aqueous phase by a separatory funnel, and transferring the oil phase into a trickle-bed hydrogenation reaction section and the aqueous phase into a wastewater recovery system.

[0057] S4: Hydrogenation reduction of p-aminoazobenzene: Replacing the trickle-bed reactor with nitrogen gas to an oxygen content of less than 0.5%, replacing the nitrogen gas with hydrogen gas three times, and increasing the pressure of the trickle-bed reactor with hydrogen gas to 1.4MPa. Then, injecting the synthesized mixed solution of p-aminoazobenzene and o-aminoazobenzene into the hydrogenation trickle-bed reactor to react with hydrogen gas at 80°C.

[0058] S5: After the hydrogenation reaction is completed, the hydrogenated oil phase is transferred into a vacuum rectification column for rectification, the temperature at the top of the column is controlled at 60°C, the temperature of the middle section is controlled at 135°C, and the temperature at the bottom of the column is controlled at 195°C. The chelating agent and polymerization inhibitor are recovered at 61°C at the top of the column, and returned to step S1 as raw materials. Meanwhile, the crude aniline is extracted from the middle section and transferred into an aniline rectification column, and the material at 136°C at the bottom of the column is transferred into an aniline recovery column. The material extracted from the middle section is transferred into the aniline rectification column, and the aniline is recovered at 89°C at the top of the column and returned to step S1 as raw materials. Meanwhile, a mixture of p-phenylenediamine and o-phenylenediamine is obtained at 140°C at the bottom of the column and continuously transferred into a p-phenylenediamine separation column for vacuum rectification. o-Phenylenediamine is obtained at 80°C at the top of the p-phenylenediamine separation column, and crude p-phenylenediamine is obtained at 156°C at the bottom of the column. The crude p-phenylenediamine is transferred into a p-phenylenediamine rectification column, and the refined p-phenylenediamine is obtained at 133.7°C at the top of the column, and the material at 134.5°C at the bottom of the column is transferred into the aniline recovery column for continuous recovery of aniline. The yield of p-phenylenediamine is 86.9%, and the yield of o-phenylenediamine is 12.5%.

[0059] By reducing the reaction pressure of hydrogenation section, the yield of p-phenylenediamine and o-phenylenediamine is not reduced but increased, thus the following optimal production conditions are obtained by multiple comparisons. The optimal molar ratio of aniline: concentrated hydrochloric acid: sodium nitrite is 6:1.5:1, the optimal hydrogenation pressure is 1.4 MPa, the optimal hydrogenation temperature is 80℃, the oil phase after hydrogenation enters the vacuum rectifying column for rectification, the temperature at the top of the vacuum rectifying column is controlled at 60℃, the temperature at the middle extraction is controlled at 135℃, and the temperature at the bottom of the column is controlled at 195℃. The aniline refining column controls the top temperature at 89℃ and the bottom temperature at 140℃. The p-phenylenediamine separation column controls the top temperature at 80℃ and the bottom temperature at 156℃. The p-phenylenediamine refining column controls the top temperature at 133.7℃ and the bottom temperature at 134.5℃. BRIEF DESCRIPTION OF DRAWINGS The intermediate product and the products of p-phenylenediamine, o-phenylenediamine and aniline of the present application are detected by high performance liquid chromatography (HPLC). Figure 1 Figure 1 Figure 1 is the HPLC spectrum of 1,3-diphenyltriazene. Figure 2 Figure 2 Figure 2 is the HPLC spectrum of p-aminoazobenzene. Figure 3 Figure 3 Figure 3 is the HPLC spectrum of p-phenylenediamine and aniline products. Figure 4 Figure 4 Figure 4 is a schematic diagram of the rectification treatment of the oil phase after hydrogenation.

Claims

1. A process for the production of a continuous synthesis of p-phenylenediamine characterized in that, Comprising the following five steps: S1 3-diphenyl triazene hydrochloride solution synthesis: into the reaction kettle aniline, concentrated hydrochloric acid, sodium nitrite mixed, obtained 1,3-diphenyl triazene hydrochloride solution yellow slurry, reaction equation is formula 1: S2 synthesis of p-aminoazobenzene hydrochloride: to the synthesis of 1,3-diphenyl triazene hydrochloride solution added chelating agent and polymerization inhibitor stirring temperature obtained p-aminoazobenzene hydrochloride and o-aminoazobenzene hydrochloride mixed solution, reaction equation 2: S3 neutralization reaction and oil water phase separation: to step S2 solution added sodium hydroxide solution to neutralize excess hydrochloric acid, step S2 solution gradually separated into oil phase and aqueous phase, after standing with separatory funnel separation of aqueous phase, oil phase into the trickle bed hydrogenation reaction section, the aqueous phase into the sewage recovery system; S4 p-aminoazobenzene and o-aminoazobenzene mixed solution trickle bed hydrogenation reaction: nitrogen replacement trickle bed hydrogenation reactor, after replacement into hydrogen, the pressure of trickle bed hydrogenation reactor gradually increased to 0.5 MPa-5 MPa, the oil phase separated from the step S3 hydrogenation reaction, reaction equation is formula 3: S5 p-phenylenediamine refining: after hydrogenation reaction, hydrogenated oil phase into vacuum rectifying column for rectification, vacuum rectifying column top control temperature at 60 DEG C, the middle section of extraction control at 135 DEG C, the column temperature control at 195 DEG C; in the top recovery chelating agent and polymerization inhibitor, the recovery of chelating agent, polymerization inhibitor returns to step S1 as raw material, while in the middle section of crude aniline into aniline rectification column, column materials into aniline recovery column; the middle section of material into aniline rectification column, in the top of aniline rectification column recovery of aniline, the recovery of aniline returns to step S1 as raw material, in the column at the same time get p-phenylenediamine and o-phenylenediamine mixture, continue into the p-phenylenediamine separation column vacuum rectification; in the top of p-phenylenediamine separation column get o-phenylenediamine product, column get p-phenylenediamine crude product; p-phenylenediamine crude product into the p-phenylenediamine rectification column, in the top of p-phenylenediamine rectification column get p-phenylenediamine refined product, column materials into the aniline recovery column continue to recover aniline.

2. A process for the continuous synthesis of p-phenylenediamine characterized in that The temperature of the reaction in step S1 according to claim 1 is -20-20℃, the total consumption of aniline: hydrochloric acid: sodium nitrite is (1-10):(1-3):1, close to the reaction endpoint, when the starch potassium iodide test paper presents blue, the reaction is completed.

3. A process for the production of a continuous synthesis of p-phenylenediamine, characterized by The chelating agent of step S2 according to claim 1 is one or two of DMC, EMC, DMF, MMC, DHF, and the addition of chelating agent accounts for 5%-20% of the mass of 1,3-diphenyl triazene hydrochloride solution.

4. A process for the continuous synthesis of p-phenylenediamine characterized in that The polymerization inhibitor of step S2 according to claim 1 is one of MeHF, MeQH, MePY, MEOH, MEM, and the addition accounts for 0.1%-1% of the mass of 1,3-diphenyl triazene hydrochloride solution.

5. A process for the continuous synthesis of p-phenylenediamine characterized in that After neutralization in step S3 according to claim 1, the reaction is allowed to stand until the oil and water phases are separated, and then the oil phase is separated by a separatory funnel and subjected to rectification in a vacuum rectifying column, while the aqueous phase is subjected to sewage treatment.

6. A process for the continuous synthesis of p-phenylenediamine characterized in that The oil phase mixed solution in step S3 of claim 1 is directly derived from step S2 of claim 1.

7. A process for the continuous synthesis of p-phenylenediamine, characterized in that The hydrogenation reactor in step S4 of claim 1 is a trickle bed reactor, and the catalyst is one of a nickel-based molecular sieve catalyst, a nickel-based active alumina catalyst or a palladium-based active carbon catalyst; wherein the nickel loading in the nickel-based molecular sieve or active alumina catalyst is not more than 5%, the palladium loading in the palladium-based active carbon catalyst is not more than 5%, the hydrogenation reaction pressure is not more than 5 MPa, and the reaction temperature is not more than 150℃.

8. A process for the continuous synthesis of p-phenylenediamine, characterized in that In step S5 of claim 1, low-boiling-point water, chelating agents and polymerization inhibitors are removed from the top of the vacuum rectification tower, the obtained material is extracted from the middle section and enters an aniline refining tower, the material in the tower kettle of the vacuum rectification tower enters an aniline recovery tower, the overhead material of the aniline recovery tower enters the aniline refining tower for further recovery of aniline and products, and the kettle material is sold as heavy components; refined aniline recovered from the top of the aniline refining tower is used as a production raw material, and the kettle material enters a p-phenylenediamine separation tower; refined o-phenylenediamine products are obtained from the top of the p-phenylenediamine separation tower, and the kettle material enters a p-phenylenediamine refining tower. The light component material from the top of the p-phenylenediamine refining tower returns to the p-phenylenediamine separation tower, the material extracted from the middle section is used as a p-phenylenediamine product and enters a product tank area or a melt crystallization section for further refining, and the kettle material of the p-phenylenediamine refining tower returns to the aniline recovery tower for further recovery of aniline.

9. A process for the production of a continuous synthesis of p-phenylenediamine, characterized by In step S5 of claim 1, the pressure of the vacuum rectification tower is -90 kPa to -101.3 kPa, the top temperature is 20℃ to 80℃, the extraction temperature of the middle section is 100℃ to 145℃, and the kettle temperature is 140℃ to 200℃; the pressure of the aniline refining tower is -90 kPa to 101.3 kPa, the top temperature is 30℃ to 80℃, the aniline extraction temperature of the middle section is 60℃ to 100℃, and the kettle temperature is 100℃ to 180℃; the pressure of the p-phenylenediamine separation tower is -90 kPa to 101.3 kPa, the top temperature is 30℃ to 110℃, and the kettle temperature is 120℃ to 180℃; the pressure of the p-phenylenediamine refining tower is -90 kPa to -101.3 kPa, the top temperature is 80℃ to 120℃, the product extraction temperature of the middle section is 130℃ to 135℃, and the kettle temperature is 130℃ to 180℃; and the pressure of the aniline recovery tower is -90 kPa to 101.3 kPa, the top temperature is 110℃ to 170℃, and the kettle temperature is 160℃ to 240℃.

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