A continuous washing process for low nitrosamine trifluralin

Abstract

The application belongs to the technical field of herbicide purification, and particularly relates to a continuous washing process of low nitrosamine trifluralin. The washing process comprises the following steps: S1: mixing hydrochloric acid with a bromide salt nucleophilic catalyst and sulfamic acid to obtain a catalytic acid phase; S2: pumping the crude trifluralin and the catalytic acid phase into a static mixer for mixing, and then pumping the mixture into an automatic phase separator to obtain acid-washed crude products and separated catalytic acid phase; S3: pumping the acid-washed crude products and water into a static mixer for mixing and phase separation to obtain wet trifluralin products; and performing post-treatment on the wet trifluralin products to obtain low nitrosamine trifluralin. The application utilizes nucleophilic catalysis to enhance the nitrosamine degradation efficiency, and simultaneously removes nitrous acid active intermediates through sulfamic acid, so that the content of nitrosamine in trifluralin can be less than or equal to 1.0 ppm under mild conditions.

Description

Technical Field

[0001] This invention belongs to the field of herbicide purification technology, specifically relating to a continuous washing process for low-nitrosamine fluroxypyr. Background Technology

[0002] Trifluralin, chemically known as 2,6-dinitro-4-trifluoromethyl-N,N-di-n-propylaniline, is a selective pre-emergence herbicide belonging to the dinitroaniline class. It is commonly used for pre-emergence weed control in fields such as soybeans, cotton, and rapeseed. Industrially, trifluralin crude is mainly prepared by amination of halogenated dinitrotrifluorotoluene with di-n-propylamine. The nitrosamines present in this reaction system can react with the raw material di-n-propylamine, continuously generating N-nitrosamine compounds. The resulting crude trifluralin typically contains 30-50 ppm of nitrosamines. These N-nitrosamine compounds are potent carcinogens and are difficult to degrade in soil, easily remaining in the soil and being absorbed by plants. Therefore, both domestically and internationally, there are strict limits on the nitrosamine content in such herbicides. Thus, the nitrosamines generated in the reaction must be treated to reduce their concentration below a certain level.

[0003] The current mainstream post-processing route mainly involves washing the crude trifluralin with hydrochloric acid at a concentration of 25 wt% or higher. This is intended to neutralize the residual alkali from the reaction process and wash away the N-nitrosamine compounds in trifluralin under a strongly acidic environment. Then, the excess acid is washed away with water to obtain qualified trifluralin.

[0004] For example, Chinese patent application CN101891634A discloses a purification method for dimethyl pendimethalin. This method uses crude dimethyl pendimethalin (a herbicide belonging to the dinitroaniline class) as the target, employing a thiocyanate and 25%~35% concentrated hydrochloric acid system, using sodium thiocyanate / ammonium thiocyanate as a denitrosation aid, and removing N-nitrosamines by reflux at 75~81℃ under normal pressure in an intermittent batch reactor. The product is then obtained by water washing, alkali washing, and vacuum desolventizing. However, under high temperature and strong proton acid system, the dinitroaniline core is sensitive to strong acid. Prolonged high temperature reflux can easily induce side reactions such as nitro hydrolysis, amino dealkylation, and aromatic ring oxidation, directly causing loss of effective components and decrease in purity of the raw material. At the same time, this process relies on intermittent reflux reaction in a reactor, and the reaction time for each batch is relatively long, affecting production capacity. Summary of the Invention

[0005] To address this problem, the present invention provides a continuous washing process for low-nitrosamine fluroxypyr, which, without sacrificing the depth of nitrosamine removal, widens the reaction rate difference between denitrosamine removal and fluroxypyr decomposition, thereby obtaining a high-yield, low-nitrosamine fluroxypyr product.

[0006] To achieve the objectives of this invention, the following technical solution is adopted: In a first aspect, the present invention provides a continuous washing process for low-nitrosamine fluroxypyr, comprising the following steps: S1: Hydrochloric acid is mixed with a bromide nucleophilic catalyst and aminosulfonic acid to obtain a catalytic acid phase; S2: The crude fluroxypyr and the catalytic acid phase are pumped separately into a static mixer for mixing. After mixing, the material flows into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped separately into a static mixer for mixing and phase separation to obtain fluroxypyr wet product; the fluroxypyr wet product is then post-treated to obtain low-nitrosamine fluroxypyr.

[0007] By adopting the above technical solution, a continuous washing system of nucleophilic catalysis-in-situ capture was constructed. A bromide nucleophilic catalyst and an aminosulfonic acid capture agent were introduced into the washing acid phase, enabling the denitrosation reaction to obtain a rate and equilibrium source independent of proton activity. Bromine ions, as highly nucleophilic species, accelerate the rate-determining denitrosation step of protonated nitrosamines, while aminosulfonic acid irreversibly converts the nitrosated species released during denitrosation into inert nitrogen gas. The two work synergistically to efficiently remove nitrosamine impurities from crude trifluralin under mild operating conditions. Simultaneously, it effectively reduces the acid-catalyzed hydrolysis and dealkylation of trifluralin under strong acid and high temperature, balancing the depth of nitrosamine removal and product yield, thus achieving continuous and high-quality purification of trifluralin.

[0008] Further, in step S1, the mass concentration of hydrochloric acid in the catalytic acid phase is 15%~20%, the mass of the bromide nucleophilic catalyst is 0.5%~3% of the total mass of the catalytic acid phase, and the mass of aminosulfonic acid is 0.3%~1.5% of the total mass of the catalytic acid phase.

[0009] By employing the above technical solution, the hydrochloric acid concentration is controlled within a relatively low window of 15% to 20%, maintaining the system's proton activity at a level sufficient to support the pre-equilibrium protonation of nitrosamines, but below the threshold for triggering the nitro hydrolysis and dealkylation side reactions of trifluralin. The bromide and aminosulfonic acid synergistically compensate for the weakening effect of acid reduction on the denitrosation rate within this range, ensuring that the net rate of the target reaction does not decrease, while the decomposition rate of trifluralin decreases with decreasing acidity, thus achieving selective denitrosation.

[0010] Further, in step S1, the bromide nucleophilic catalyst is sodium bromide or tetrabutylammonium bromide.

[0011] By adopting the above technical solution, sodium bromide can provide a high concentration of free bromide ions, which can efficiently accelerate the nitrosamine removal reaction; the tetrabutylammonium bromide quaternary ammonium cation has both nucleophilic catalysis and phase transfer effects, which can enrich the active reaction components at the oil-water interface, realize interfacial localized catalysis, shorten the reaction contact time, and further reduce the probability of trifluralin side reactions.

[0012] Further, in step S2, the mass ratio of the crude trifluralin to the catalytic acid phase is 1:(0.6~1).

[0013] By adopting the above technical solution, on the one hand, it ensures that the catalytic acid phase provides sufficient bromide ions and aminosulfonic acid to match the removal and capture requirements of nitrosamines and maintain sufficient two-phase contact interface; on the other hand, it reduces the amount of acid phase used compared with the existing process, reduces acid consumption, waste acid emissions and subsequent neutralization load, and reduces the phase separation burden caused by excessive dilution of the organic phase by the acid phase, thus adapting to continuous and stable production conditions.

[0014] Furthermore, in step S2, the flow rate of the material in the static mixer is 0.8~2.5 m / s, and the residence time is 10~25s.

[0015] By employing the above technical solution, the high-speed turbulent shearing action within the static mixer enables efficient mixing and mass transfer between the crude trifluralin and the catalytic acid phase within a residence time of seconds. This short residence time ensures the full progress of the denitroso cascade reaction while minimizing the exposure time of trifluralin molecules in the acidic environment, further suppressing decomposition side reactions from a temporal perspective.

[0016] Furthermore, in step S2, the crude trifluralin and the catalytic acid phase are preheated to 45~65°C by heat exchangers before entering the static mixer.

[0017] By adopting the above technical solution, the preheating of the two feed streams avoids the heating waiting and temperature fluctuations of the batch process, so that the materials are in the set optimal reaction temperature zone as soon as they are mixed, and the reaction temperature is stable and controllable along the process. This temperature range avoids the thermal decomposition and oxidation side reactions of trifluralin caused by high temperature conditions while ensuring that the denitrosokinetic kinetics are fast enough, thus achieving a two-way balance between reaction rate and selectivity.

[0018] Further, in step S3, the mass ratio of the pickled crude product to water is 1:(0.3~0.8).

[0019] By adopting the above technical solution, trace amounts of water-soluble impurities such as hydrochloric acid, bromide ions, and residual aminosulfonic acid carried in the pickling crude product can be effectively removed, while avoiding emulsification caused by excessive water and increased load on subsequent dehydration.

[0020] Furthermore, in step S3, the flow rate of the material in the static mixer is 0.8~2.5 m / s, and the residence time is 5~8s.

[0021] By adopting the above technical solution, the water washing section uses a flow rate that matches that of the acid washing section to enhance the two-phase mixing, so that the aqueous phase and the organic phase can fully contact each other and quickly complete the extraction and transfer of impurities; the residence time is shortened to 5-8 seconds. Since water washing is mainly based on physical extraction and has low mass transfer resistance, the washing requirements can be met with a short residence time. At the same time, the contact time of trifluralin is further shortened, ensuring continuous production capacity and product stability.

[0022] Furthermore, in step S3, the mixing temperature is 50~60°C.

[0023] By adopting the above technical solution, this temperature range can reduce the viscosity of the fluroxypyr oil phase, improve the mixing mass transfer and stratification effect of oil and water phases, and is gentle enough to avoid high-temperature hydrolysis, thus taking into account washing efficiency, phase separation effect and product protection.

[0024] Further, in step S3, the post-processing includes the following steps: The wet product of trifluralin was placed at 50-60℃ and the pH was adjusted to 6.5-7.5 with a weakly alkaline aqueous solution. The residence time was controlled to be 1-3 minutes. The phases were separated, the saline phase was discarded, and the trifluralin melt was obtained. After drying, the low-nitrosamine trifluralin was obtained.

[0025] By adopting the above technical solution, the wet product of trifluralin is gently neutralized, which can remove residual acidic species such as hydrochloric acid, hydrobromic acid and sulfate, and prevent them from continuing to catalyze the decomposition of trifluralin and corrode the equipment during subsequent drying and heating. Strict control of pH value, temperature and residence time can ensure that residual acid is neutralized and avoid the introduction of alkaline catalytic decomposition due to excessive alkali or prolonged contact, thereby obtaining a low-nitrosamine trifluralin product with less than 1.0 ppm of nitrosamines, few decomposition impurities and high yield.

[0026] Furthermore, the weakly alkaline aqueous solution is a sodium carbonate aqueous solution with a mass concentration of 2% to 5% or a sodium bicarbonate aqueous solution with a mass concentration of 2% to 5%.

[0027] By adopting the above technical solution, the sodium carbonate and sodium bicarbonate aqueous solution is mildly alkaline and has good buffering properties, which can precisely control the pH value of the system, achieve mild neutralization of acidic impurities, eliminate the risk of strong alkaline side reactions, and make salt impurities easy to remove completely through phase separation and drying without affecting the quality of the fluroxypyr finished product.

[0028] Furthermore, in steps S2 and S3, the static mixers are both SK-type static mixers with an inner diameter ≤170mm.

[0029] By adopting the above technical solution, the SK-type static mixer is composed of spiral twisted blades, which can achieve efficient radial mixing; the inner diameter ≤170mm ensures the turbulence intensity and shear uniformity of the fluid in the mixer, making the two-phase dispersion and contact effect stable, and ensuring the continuous and stable operation of the production line.

[0030] In summary, the beneficial effects of this invention are: 1. This invention introduces a reaction mechanism of bromide nucleophilic catalysis and in-situ capture of aminosulfonic acid, which has no promoting effect on side reactions such as nitro hydrolysis and dealkylation of trifluralin. By adjusting the acidity and temperature of the system, the kinetic rate difference between the main denitrosation reaction and the trifluralin decomposition side reaction is widened, reducing the amount of decomposition impurities generated and effectively improving the yield and purity of trifluralin product. 2. This invention utilizes nucleophilic catalysis to enhance the degradation efficiency of nitrosamines, while simultaneously using aminosulfonic acid to irreversibly remove nitrite-based active intermediates in situ, thus blocking the nitrosamine regeneration pathway. Under mild conditions with a short residence time, nitrosamines in trifluralin can be stably reduced to below 1.0 ppm. 3. The catalytic acid phase of this invention can be regenerated and recycled, resulting in less wastewater generation and no strong acid fluorides, making treatment easier. Compared with traditional high-temperature and high-acid processes, this process has strong controllability, is less affected by fluctuations in the crude nitrosamine raw material, and significantly improves the stability of continuous production quality. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments.

[0032] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples and comparative examples are commercially available.

[0033] Example 1 The specific steps of the continuous washing process for low-nitrosamine fluroxypyr in this embodiment are as follows: S1: Add 1 kg of hydrochloric acid with a mass concentration of 18% to the preparation tank, add sodium bromide (1.5% of the total mass of the catalytic acid phase) and aminosulfonic acid (0.8%), stir and dissolve for 15 min to obtain the catalytic acid phase; S2: The crude trifluralin and the catalytic acid phase are continuously preheated to 55°C via heat exchangers. The outlet temperature fluctuations of both materials are controlled within ±1°C. The crude trifluralin and the catalytic acid phase are continuously pumped into an SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:0.8. The flow rate of the materials in the static mixer is 1.5 m / s, and the residence time is 20 s. After mixing, the materials flow into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped into a static mixer at a mass ratio of 1:0.5 and mixed at 55°C. The flow rate of the material in the static mixer is 1.5 m / s and the residence time is 6s to obtain wet trifluralin. The wet trifluralin is then adjusted to pH 7 at 55°C with a 5% sodium carbonate aqueous solution and the residence time is controlled at 2min. The phases are separated, and the salt water phase is discarded to obtain trifluralin melt. This melt is then dried at 60°C and a vacuum of -0.095MPa to obtain low-nitrosamine trifluralin.

[0034] Example 2 The specific steps of the continuous washing process for low-nitrosamine fluroxypyr in this embodiment are as follows: S1: Add 1 kg of 20% hydrochloric acid to the preparation tank, add 2.5% sodium bromide and 1% aminosulfonic acid (total mass of the catalytic acid phase), stir and dissolve for 15 min to obtain the catalytic acid phase; S2: The crude trifluralin and the catalytic acid phase are continuously preheated to 50°C via heat exchangers. The outlet temperature fluctuations of both materials are controlled within ±1°C. The crude trifluralin and the catalytic acid phase are continuously pumped into an SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:0.7. The flow rate of the materials in the static mixer is 1 m / s, and the residence time is 18 s. After mixing, the materials flow into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped separately into a static mixer at a mass ratio of 1:0.4 and mixed at 52℃. The flow rate of the material in the static mixer is 1m / s and the residence time is 6s to obtain wet trifluralin. The wet trifluralin is then adjusted to pH 7.2 at 60℃ with a 5% sodium carbonate aqueous solution and the residence time is controlled at 1.5min. The phases are separated, and the salt water phase is discarded to obtain trifluralin melt. This melt is then dried at 60℃ and a vacuum of -0.085MPa to obtain low-nitrosamine trifluralin.

[0035] Example 3 The specific steps of the continuous washing process for low-nitrosamine fluroxypyr in this embodiment are as follows: S1: Add 1 kg of 16% hydrochloric acid to the preparation tank, add 0.8% sodium bromide and 1.2% aminosulfonic acid (total mass of the catalytic acid phase), stir and dissolve for 15 min to obtain the catalytic acid phase; S2: The crude trifluralin and the catalytic acid phase are continuously preheated to 55°C via heat exchangers. The outlet temperature fluctuations of both materials are controlled within ±1°C. The crude trifluralin and the catalytic acid phase are continuously pumped into an SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:1. The flow rate of the material in the static mixer is 2.2 m / s, and the residence time is 15 s. After mixing, the material flows into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped separately into a static mixer at a mass ratio of 1:0.4 and mixed at 60℃. The flow rate of the material in the static mixer is 2.2 m / s and the residence time is 8s to obtain wet trifluralin. The wet trifluralin is then adjusted to pH 6.8 at 50℃ with a 2% sodium bicarbonate aqueous solution and the residence time is controlled at 2.5min. The phases are separated, and the saline phase is discarded to obtain trifluralin melt. This melt is then dried at 70℃ and a vacuum of -0.085MPa to obtain low-nitrosamine trifluralin.

[0036] Example 4 The specific steps of the continuous washing process for low-nitrosamine fluroxypyr in this embodiment are as follows: S1: Add 1 kg of hydrochloric acid with a mass concentration of 18% to the preparation tank, add 1.8% of tetrabutylammonium bromide and 0.5% of aminosulfonic acid by mass of the total mass of the catalytic acid phase, stir and dissolve for 15 min to obtain the catalytic acid phase; S2: The crude trifluralin and the catalytic acid phase are continuously preheated to 65°C via heat exchangers. The temperature fluctuations of the two material outlets are controlled within ±1°C. The crude trifluralin and the catalytic acid phase are continuously pumped into an SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:0.6. The flow rate of the material in the static mixer is 2 m / s, and the residence time is 14 s. After mixing, the material flows into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped into a static mixer at a mass ratio of 1:0.7 and mixed at 55℃. The flow rate of the material in the static mixer is 2 m / s and the residence time is 7s to obtain wet trifluralin. The wet trifluralin is then adjusted to pH 7.5 at 55℃ with a 2% sodium bicarbonate aqueous solution and the residence time is controlled at 3min. The phases are separated, and the salt-containing phase is discarded to obtain trifluralin melt. This melt is then dried at 65℃ and a vacuum of -0.095MPa to obtain low-nitrosamine trifluralin.

[0037] Example 5 The specific steps of the continuous washing process for low-nitrosamine fluroxypyr in this embodiment are as follows: S1: Add 1 kg of 15% hydrochloric acid to the preparation tank, add 2.4% tetrabutylammonium bromide and 1.1% aminosulfonic acid (total mass of the catalytic acid phase), stir and dissolve for 15 min to obtain the catalytic acid phase; S2: The crude trifluralin and the catalytic acid phase are continuously preheated to 50°C via heat exchangers. The outlet temperature fluctuations of both materials are controlled within ±1°C. The crude trifluralin and the catalytic acid phase are continuously pumped into an SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:0.8. The flow rate of the materials in the static mixer is 1.5 m / s, and the residence time is 20 s. After mixing, the materials flow into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped into a static mixer at a mass ratio of 1:0.8 and mixed at 58℃. The flow rate of the material in the static mixer is 1.5 m / s and the residence time is 5s to obtain wet trifluralin. The wet trifluralin is then adjusted to pH 6.5 at 55℃ with a 3% sodium carbonate aqueous solution and the residence time is controlled at 1 min. The phases are separated, and the salt water phase is discarded to obtain trifluralin melt. This melt is then dried at 60℃ and a vacuum of -0.095 MPa to obtain low-nitrosamine trifluralin.

[0038] Example 6 The difference from Example 1 is that the bromide nucleophilic catalyst in this example is tetrabutylammonium bromide, and the specific steps are as follows: S1: Add 1 kg of hydrochloric acid with a mass concentration of 18% to the preparation tank, add 1.5% of tetrabutylammonium bromide and 0.8% of aminosulfonic acid by mass of the total mass of the catalytic acid phase, stir and dissolve for 15 min to obtain the catalytic acid phase; S2: The crude trifluralin and the catalytic acid phase are continuously preheated to 55°C via heat exchangers. The outlet temperature fluctuations of both materials are controlled within ±1°C. The crude trifluralin and the catalytic acid phase are continuously pumped into an SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:0.8. The flow rate of the materials in the static mixer is 1.5 m / s, and the residence time is 20 s. After mixing, the materials flow into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped into a static mixer at a mass ratio of 1:0.5 and mixed at 55°C. The flow rate of the material in the static mixer is 1.5 m / s and the residence time is 6s to obtain wet trifluralin. The wet trifluralin is then adjusted to pH 7 at 55°C with a 5% sodium carbonate aqueous solution and the residence time is controlled at 2min. The phases are separated, and the salt water phase is discarded to obtain trifluralin melt. This melt is then dried at 60°C and a vacuum of -0.095MPa to obtain low-nitrosamine trifluralin.

[0039] Example 7 The continuous washing process for low-nitrosamine fluroxypyr in this embodiment differs from that in Example 1 in that the mass of sodium bromide in this embodiment is 3% of the total mass of the catalytic acid phase. The specific steps are as follows: S1: Add 1 kg of 18% hydrochloric acid to the preparation tank, add 3% sodium bromide and 0.8% aminosulfonic acid (by mass of the total mass of the catalytic acid phase), stir and dissolve for 15 min to obtain the catalytic acid phase; S2: The crude trifluralin and the catalytic acid phase are continuously preheated to 55°C via heat exchangers. The outlet temperature fluctuations of both materials are controlled within ±1°C. The crude trifluralin and the catalytic acid phase are continuously pumped into an SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:0.8. The flow rate of the materials in the static mixer is 1.5 m / s, and the residence time is 20 s. After mixing, the materials flow into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped into a static mixer at a mass ratio of 1:0.5 and mixed at 55°C. The flow rate of the material in the static mixer is 1.5 m / s and the residence time is 6s to obtain wet trifluralin. The wet trifluralin is then adjusted to pH 7 at 55°C with a 5% sodium carbonate aqueous solution and the residence time is controlled at 2min. The phases are separated, and the salt water phase is discarded to obtain trifluralin melt. This melt is then dried at 60°C and a vacuum of -0.095MPa to obtain low-nitrosamine trifluralin.

[0040] Example 8 The continuous washing process for low-nitrosamine fluroxypyr in this embodiment differs from that in Embodiment 1 in that the residence time of the material in the static mixer in step S2 of this embodiment is 10 seconds. The specific steps are as follows: S1: Add 1 kg of hydrochloric acid with a mass concentration of 18% to the preparation tank, add sodium bromide (1.5% of the total mass of the catalytic acid phase) and aminosulfonic acid (0.8%), stir and dissolve for 15 min to obtain the catalytic acid phase; S2: The crude trifluralin and the catalytic acid phase are continuously preheated to 55°C via heat exchangers. The outlet temperature fluctuations of both materials are controlled within ±1°C. The crude trifluralin and the catalytic acid phase are continuously pumped into an SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:0.8. The flow rate of the materials in the static mixer is 1.5 m / s, and the residence time is 10 s. After mixing, the materials flow into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped into a static mixer at a mass ratio of 1:0.5 and mixed at 55°C. The flow rate of the material in the static mixer is 1.5 m / s and the residence time is 6s to obtain wet trifluralin. The wet trifluralin is then adjusted to pH 7 at 55°C with a 5% sodium carbonate aqueous solution and the residence time is controlled at 2min. The phases are separated, and the salt water phase is discarded to obtain trifluralin melt. This melt is then dried at 60°C and a vacuum of -0.095MPa to obtain low-nitrosamine trifluralin.

[0041] Comparative Example 1 The continuous washing process for low-nitrosamine fluroxypyr in this comparative example differs from that in Example 1 in that: no aminosulfonic acid is added in this comparative example, and the other operating conditions are completely consistent with those in Example 1.

[0042] Comparative Example 2 The continuous washing process for low-nitrosamine fluroxypyr in this comparative example differs from that in Example 1 in that an equal amount of sodium chloride is used instead of sodium bromide, while the other operating conditions are completely consistent with those in Example 1.

[0043] Comparative Example 3 The specific steps of the continuous washing process for a low-nitrosamine fluroxypyr in this comparative example are as follows: Crude trifluralin was preheated to 90°C with 25 wt% hydrochloric acid and continuously pumped into a SK-type static mixer with an inner diameter of 150 mm at a mass ratio of 1:0.8. The flow rate of the material in the static mixer was 1.5 m / s, and the residence time was 20 s. After mixing, the material flowed into an automatic phase separator to obtain the acid-washed crude product and the separated hydrochloric acid. The acid-washed crude product and water were pumped into a static mixer at a mass ratio of 1:0.5 and mixed at 55°C. The flow rate of the material in the static mixer was 1.5 m / s, and the residence time was 6 s to obtain wet trifluralin. The wet trifluralin was adjusted to pH 7 at 55°C with a 5% sodium carbonate aqueous solution and the residence time was controlled at 2 min. The phases were separated, and the saline phase was discarded to obtain trifluralin melt. The melt was dried at 60°C and a vacuum of -0.095 MPa to obtain low-nitrosamine trifluralin.

[0044] The contents of N,N-di-n-propylnitrosamines in Examples 1 to 8 and Comparative Examples 1 to 3 were determined by GC-MS and are shown in Table 1.

[0045] Table 1. Detection results of N,N-di-n-propylnitrosamine content

[0046] As can be seen from Table 1, the nitrosamine content in the finished products of Examples 1 to 8, which employ the nucleophilic catalysis-in-situ capture cascade continuous washing process of the present invention, is stably controlled within 1.0 ppm, meeting the national standards and export registration standards. Among them, Examples 4 and 6, which use tetrabutylammonium bromide phase transfer catalysis, have the best removal effect and no obvious side reactions under mild operating conditions.

[0047] Compared with Example 1, Comparative Example 1 lost the balance between pull and decomposition pathways after the removal of aminosulfonic acid, resulting in an increase in the content of N,N-di-n-propylnitrosamine, which did not meet the standard.

[0048] Compared to Example 1, Comparative Example 2 showed that the nucleophilicity of chloride ions was much lower than that of bromide ions, and it could not provide a sufficient rate-determining step rate under the mild window. The content of N,N-di-n-propylnitrosamine increased, which did not meet the standard.

[0049] Compared with Example 1, although Comparative Example 3 could suppress nitrosamines by relying on high temperature / high acid and strong proton activity, the yield of trifluralin decreased by 3.6% and the content of decomposition impurities increased during the experiment.

[0050] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A continuous washing process with low nitrosamine fluroxypyr, characterized in that, Includes the following steps: S1: Hydrochloric acid is mixed with a bromide nucleophilic catalyst and aminosulfonic acid to obtain a catalytic acid phase; S2: The crude fluroxypyr and the catalytic acid phase are pumped separately into a static mixer for mixing. After mixing, the material flows into an automatic phase separator to obtain the acid-washed crude product and the separated catalytic acid phase. S3: The pickled crude product and water are pumped separately into a static mixer for mixing and phase separation to obtain fluroxypyr wet product; the fluroxypyr wet product is then post-treated to obtain low-nitrosamine fluroxypyr.

2. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S1, the mass concentration of hydrochloric acid in the catalytic acid phase is 15%~20%, the mass of the bromide nucleophilic catalyst is 0.5%~3% of the total mass of the catalytic acid phase, and the mass of aminosulfonic acid is 0.3%~1.5% of the total mass of the catalytic acid phase.

3. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S1, the bromide nucleophilic catalyst is sodium bromide or tetrabutylammonium bromide.

4. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S2, the mass ratio of the crude trifluralin to the catalytic acid phase is 1:(0.6~1).

5. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S2, the flow rate of the material in the static mixer is 0.8~2.5 m / s, and the residence time is 10~25s.

6. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S2, the crude trifluralin and the catalytic acid phase are preheated to 45~65°C by heat exchangers before entering the static mixer.

7. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S3, the mass ratio of the pickled crude product to water is 1:(0.3~0.8).

8. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S3, the flow rate of the material in the static mixer is 0.8~2.5 m / s, and the residence time is 5~8s.

9. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S3, the mixing temperature is 50~60℃.

10. The continuous washing process for low-nitrosamine fluroxypyr according to claim 1, characterized in that, In step S3, the post-processing includes the following steps: The wet product of trifluralin was placed at 50-60℃ and the pH was adjusted to 6.5-7.5 with a weakly alkaline aqueous solution. The residence time was controlled to be 1-3 minutes. The phases were separated, the saline phase was discarded, and the trifluralin melt was obtained. After drying, the low-nitrosamine trifluralin was obtained.

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