Method for synthesizing pendimethalin through continuous nitration

Abstract

The invention discloses a method for synthesizing pendimethalin through continuous nitration, and belongs to the field of pesticide synthesis. The method for synthesizing the pendimethalin comprises the following steps: respectively metering an N-amylamine solution and nitric acid, and simultaneously conveying the N-amylamine solution and the nitric acid into a tubular reactor for reaction; and the nitrated material flows out from an outlet, and is separated and purified to obtain a pendimethalin product. Compared with the prior art, the synthetic method disclosed by the invention can realize continuous production of pendimethalin, is high in reaction efficiency and good in safety, can greatly reduce the content of a by-product nitrosamine in the product, and has very good popularization and application values.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of pesticide synthesis, and specifically provides a method for continuously synthesizing pendimethalin by nitration. BACKGROUND

[0002] Pendimethalin is one of the most common selective herbicides at present, and can be widely applied to corn, soybean, peanut, cotton, direct-seeded upland rice, potato, tobacco, vegetables and other crop fields.

[0003] On the one hand, the method for synthesizing pendimethalin in the prior art is to add dilute nitric acid to an N-pentylamine solution, heat and react, then separate layers, extract wastewater, and combine oil phases. Concentrated nitric acid is added to the oil layer twice, heat and react, and the oil phase is washed with water, denitrosated, washed with water, and distilled to obtain the product pendimethalin. The method mainly adopts a kettle batch process, which has the following characteristics: 1) in the nitration reaction, high energy consumption is caused by temperature rise and fall, the heat release is large, the heat exchange capacity of the kettle reactor is poor, the temperature and pressure rise sharply, the safety risk is increased, and safety accidents are caused; 2) in the salting and nitration, a K5000L reactor is used, there are many online materials, and dichloroethane, which is flammable and explosive, is used as a solvent, so there is a great safety hazard; 3) in the batch reaction, the reaction time is long, the high consumption time (2 hours for salt addition, 1 hour for heat preservation, 3 hours for nitration drop, and 3 hours for heat preservation) is long, and the production efficiency is low; 4) the degree of automation is low, and the labor intensity of the operator is high. These problems will cause safety hazards and further affect the development of the pesticide industry, therefore, it is an urgent need to develop an efficient and safe continuous technology for producing pendimethalin.

[0004] On the other hand, in the existing method for producing pendimethalin, the yield of pendimethalin based on N-pentylamine is generally about 90.0%, and the content of the raw material is mainly 95%, which does not meet the national standard and the export requirement (the content required for export is greater than 98%), and needs to be further treated and refined, which will increase the production cost. SUMMARY

[0005] The present application is aimed at the deficiencies of the prior art, and provides a safe, efficient and high-quality method for continuously synthesizing pendimethalin by nitration.

[0006] The technical scheme adopted by the present application to solve the technical problem is: a method for continuously synthesizing pendimethalin by nitration, comprising:

[0007] The N-pentylamine solution and nitric acid are respectively metered and simultaneously delivered to a tubular reactor for reaction, and the N-pentylamine is N-(1-ethylpropyl)-3,4-dimethyl aniline;

[0008] The nitration material flows out from the outlet of the tubular reactor, is separated and purified to obtain the pendimethalin product, and the reaction principle is as follows,

[0009] Main reaction:

[0010]

[0011] Side reaction:

[0012]

[0013] As preferred, N-pentylamine and solvent are mixed by metering pump into a mixer to obtain N-pentylamine solution.

[0014] As preferred, the mass ratio of N-pentylamine and solvent in N-pentylamine solution is 1: (1.0-5.0), particularly preferably 1: (1.0-3.0).

[0015] As preferred, the solvent is perfluorohexane, perfluoro (methylcyclohexane), perfluoro-1, 3-dimethylcyclohexane and / or perfluoro-1, 2-dimethylcyclohexane.

[0016] As preferred, the molar ratio of nitric acid and N-pentylamine is 2.0-4.0, the mass concentration of the nitric acid is 45%-75%, particularly preferably 45%-53%.

[0017] As preferred, N-pentylamine solution and nitric acid are sent into a tubular reactor by metering pump, the flow rate of N-pentylamine solution into the tubular reactor is 1200-4000 kg / h, preferably 1200-3200 kg / h; the flow rate of nitric acid into the tubular reactor is 713-1730 kg / h, preferably 850-1600 kg / h.

[0018] As preferred, the flow pressure of N-pentylamine solution and nitric acid in the tubular reactor is 1.0-5.0 MPa.

[0019] As preferred, the reaction temperature is 40-60℃, and the residence time of the material in the tubular reactor is 300-900 seconds.

[0020] As preferred, the tubular reactor is a U-shaped tubular reactor, with a diameter of DN100-500 mm, particularly preferably DN100-250 mm, and a length of 100-500 meters, particularly preferably 300-500 meters.

[0021] As preferred, the nitrated material flowing out of the tubular reactor is continuously layered, the oil phase is subjected to denitrosation, water washing and distillation to obtain the product of pendimethalin.

[0022] As preferred, the water phase obtained by continuous layering is used for the acid preparation of nitrated nitric acid.

[0023] Compared with the prior art, the method for continuously nitrating to synthesize pendimethalin has the following outstanding beneficial effects:

[0024] (1) The pipe reactor is adopted, precise control of the reaction process can be realized, the average residence time is 300-900 seconds, compared with 3 hours of the nitrating kettle type batch process, the reaction efficiency is greatly improved, and the energy consumption is reduced; the whole reaction process is continuous, the risk of flying temperature caused by local overheating is avoided, the online dangerous materials are reduced by more than 50%, thereby the safety of the reaction is improved;

[0025] (2) The ratio of pendimethalin to nitrosamine in the nitration product oil phase reaches (85-90):(15-10), compared with pendimethalin:nitrosamine=(75-80):(25-20) of the batch process, the content of the main nitration product pendimethalin is increased by 10%, and the content of the nitration by-product nitrosamine is reduced;

[0026] (3) The continuous nitration process reduces the content of nitrosamine in the nitration product oil phase to 10-15%, and through the conventional denitrosation and purification treatment, pendimethalin with a content of ≥98.0% and a nitrosamine content of ≤30 ppm can be obtained, which meets the export demand, and the product yield is ≥96.0% based on N-pentylamine, and the cost is lower, and the product has more competitive advantages;

[0027] (4) The dilute nitric acid after nitration is reused for the acid preparation cycle of nitration, and there is no waste water and waste acid discharge. DETAILED DESCRIPTION

[0028] The application will be further described below in combination with specific examples, but not as a limitation to the application.

[0029] Example 1:

[0030] The N-pentylamine and perfluorohexane are respectively punched into the mixer through the metering pump at a flow rate of N-pentylamine 600 kg / h and perfluorohexane 600 kg / h, and are uniformly mixed to prepare N-pentylamine solution.

[0031] N-pentylamine solution and nitric acid with content of 45%, respectively, through the metering pump, according to the flow rate of 1200kg / h, 869.42kg / h, at the same time into the DN100mm, 300m long U-shaped tube reactor, the reaction temperature is 40-50℃, residence time is 300-500 seconds, flow pressure is 1.0-3.0MPa. After the reaction, the nitrated material flows out from the outlet of the U-shaped tube reactor, continuously flows out through the delamination device, the water phase is used to the nitration of nitric acid, the oil phase (pemeton gas chromatography content 88.1%, nitrosamine content 11.7%) is de-nitrosated (oil phase 1700kg, hydrochloric acid 340Kg, heated to 60-65℃ for 2 hours), delaminated after standing, the oil phase is added with 100Kg water, stirred and washed with water, delaminated after standing, the oil layer is removed by vacuum distillation, and the product pemeton 858.34kg is obtained after removing the solvent, with content of 98.0%, nitrosamine content of 15.1ppm, and yield of 96.3%.

[0032] Example two:

[0033] N-pentylamine and perfluoro-methylcyclohexane are respectively pumped into the mixer through the metering pump according to the flow rate of N-pentylamine 700kg / h and perfluoro-methylcyclohexane 1400kg / h, and the N-pentylamine solution is prepared by stirring and mixing.

[0034] N-pentylamine solution and nitric acid with content of 50%, respectively, through the metering pump, according to the flow rate of 2100kg / h, 1141.11kg / h, at the same time into the DN150mm, 400m long U-shaped tube reactor, the reaction temperature is 45-55℃, residence time is 400-600 seconds, flow pressure is 2.5-4.0MPa. After the reaction, the nitrated material flows out from the outlet of the U-shaped tube reactor, continuously flows out through the delamination device, the water phase is used to the nitration of nitric acid, the oil phase (pemeton gas chromatography content 85.1%, nitrosamine content 14.8%) is de-nitrosated (oil phase 2700kg, hydrochloric acid 400Kg, heated to 60-65℃ for 3 hours), delaminated after standing, the oil phase is added with 100Kg water, stirred and washed with water, delaminated after standing, the oil layer is removed by vacuum distillation, and the product pemeton 1000.39kg is obtained after removing the solvent, with content of 98.2%, nitrosamine content of 12.5ppm, and yield of 96.4%.

[0035] Example three:

[0036] N-pentylamine and perfluoro-1,3-dimethylcyclohexane are respectively pumped into the mixer through the metering pump according to the flow rate of N-pentylamine 800kg / h and perfluoro-1,3-dimethylcyclohexane 2400kg / h, and the N-pentylamine solution is prepared by stirring and mixing.

[0037] N-pentylamine solution and 53% nitric acid, respectively, through the metering pump, according to the flow rate of 3200kg / h, 1521.49kg / h, while into the DN200mm, 500 meters long U-shaped tube reactor, the reaction temperature is 50-60℃, residence time is 500-600 seconds, flow pressure is 3.0-5.0MPa. After the reaction, the nitrated material flows out from the outlet of the U-shaped tube reactor, continuously flows out through the delamination device, the water phase is used to the nitration nitric acid acidification, the oil phase (purity of dimethenamid is 90.2%, nitrosamine content is 9.7%) is subjected to denitrosation (oil phase 4000kg, hydrochloric acid 500Kg, heated to 60-65℃ for 4 hours), static delamination, the oil phase is added with 200Kg water, stirred and washed, static delamination, the oil layer is subjected to vacuum distillation, after removing the solvent, the product dimethenamid 1145.65kg is obtained, the purity is 98.1%, the nitrosamine content is 22.8ppm, the yield is 96.5%.

[0038] The above-described embodiments are only the preferred specific embodiments of the present application, and the common changes and replacements made by the person skilled in the art within the technical solution range of the present application should be included in the protection scope of the present application.

Claims

1. A method for continuously nitrating and synthesizing pendimethalin, characterized in that: include: The N-pentylamine solution and nitric acid are measured separately and simultaneously transported to a tubular reactor for reaction, wherein the N-pentylamine is N-(1-ethylpropyl)-3,4-dimethylaniline; The nitrated material flows out from the outlet and is separated and purified to obtain the pendimethalin product.

2. The method for continuous nitration synthesis of pendimethalin according to claim 1, characterized in that: N-pentylamine and solvent are respectively fed into a mixer through metering pumps and mixed to obtain an N-pentylamine solution. The mass ratio of N-pentylamine to solvent in the N-pentylamine solution is 1:(1.0~5.0), The solvent is perfluorohexane, perfluoro(methylcyclohexane), perfluoro-1,3-dimethylcyclohexane and / or perfluoro-1,2-dimethylcyclohexane.

3. The method for continuous nitration synthesis of pendimethalin according to claim 1 or 2, characterized in that: The molar ratio of nitric acid to N-pentylamine is 2.0-4.0, and the mass concentration of nitric acid is 45%-75%.

4. The method for continuous nitration synthesis of pendimethalin according to claim 3, characterized in that: N-pentylamine solution and nitric acid are respectively fed into the tubular reactor through metering pumps. The rate of N-pentylamine solution flowing into the tubular reactor is 1200-4000 kg / h, and the rate of nitric acid flowing into the tubular reactor is 713-1730 kg / h.

5. The method for continuous nitration synthesis of pendimethalin according to claim 4, characterized in that: The flow pressure of the N-pentylamine solution and nitric acid in the tubular reactor is 1.0 to 5.0 MPa.

6. The method for continuous nitration synthesis of pendimethalin according to claim 1 or 2, characterized in that: The reaction temperature is 40-60° C., and the residence time of the material in the tubular reactor is 300-900 seconds.

7. The method for continuous nitration synthesis of pendimethalin according to claim 1 or 2, characterized in that: The tubular reactor is a U-shaped tubular reactor with a diameter of DN100-500 mm and a length of 100 to 500 meters.

8. The method for continuous nitration synthesis of pendimethalin according to claim 1 or 2, characterized in that: The nitrated material flowing out from the outlet is continuously layered, and the oil phase is subjected to denitrification, water washing, and distillation to obtain the pendimethalin product.

9. The method for continuous nitration synthesis of pendimethalin according to claim 8, characterized in that: The aqueous phase obtained by continuous layering is used to prepare the acid for nitrating nitric acid.

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