Method for removing nitrosamine in trifluralin

Abstract

The invention discloses a method for removing nitrosamine in trifluralin, and belongs to the technical field of carbocyclic compound purification, the removal method comprises the following steps: primary purification of a trifluralin crude product, preparation of an ion mixed solution and photocatalytic decomposition; the photocatalytic decomposition method comprises the following steps: mixing preliminarily purified trifluralin with an ion mixed solution, adjusting the temperature of the solution to be 50-52 DEG C and the pH value to be 3.8-4.2, carrying out ultrasonic dispersion for 15-20 minutes to form a dispersion liquid, transferring the dispersion liquid to a photocatalytic reactor, introducing pure oxygen, carrying out dispersion through a microporous aeration head, turning on an irradiation light source, controlling the reaction temperature to be 54-56 DEG C and the irradiation time to be 35-40 minutes, and carrying out photocatalytic decomposition. And cooling the obtained reaction liquid to 50-52 DEG C, carrying out centrifugal layering through a centrifugal machine, recovering the ionic liquid at the lower layer, and obtaining a trifluralin product at the upper layer. According to the method disclosed by the invention, the removal efficiency of the nitrosamine is high, and the content of the nitrosamine with the content of 10-300ppm can be reduced to 0.1 ppm or below.

Description

Technical Field

[0001] The present invention belongs to the technical field of purification of carbocyclic compounds, and particularly relates to a method for removing nitrosamines in trifluralin. Background Art

[0002] Trifluralin (2,6-dinitro-N,N-dipropyl-4-trifluoromethylaniline), as a broad-spectrum pre-emergence herbicide, is likely to generate the strong carcinogen N-nitrosodipropylamine (nitrosamine) during its synthesis process due to nitration and amination reactions. In traditional processes, the removal of nitrosamines mainly relies on methods such as physical adsorption, chemical pickling, or high-temperature pyrolysis, but there are significant defects.

[0003] The physical adsorption method has certain limitations. In the prior art, adsorbents such as activated carbon and molecular sieves are commonly used to enrich and remove nitrosamines. However, such methods require frequent regeneration of the adsorbent, resulting in an increase in solid waste, and the adsorption efficiency is limited by the specific surface area and pore size distribution of the material, making it difficult to stably control the nitrosamine content below 0.1 ppm.

[0004] Chemical pickling has the risk of secondary pollution. The treatment with strong acids (such as concentrated hydrochloric acid) is the core step of traditional processes, but the cost of treating waste acid accounts for more than 30% of the total production cost. For every 1000 kg of trifluralin produced, about 150 kg of 30% hydrochloric acid is consumed, and 2520 kg of high-COD wastewater is generated, causing serious environmental pollution. In addition, after pickling, a large amount of water washing and alkali neutralization are required, further increasing energy consumption and waste residue discharge. For example, the method for removing nitrosamines in dinitroaniline herbicides disclosed in CN102701989A removes nitrosamines under acidic conditions by adding hydrohalic acid and methanesulfonic acid in an organic solvent, generating a large amount of waste acid and having a high treatment cost; US Patent US5196585A uses hydrochloric acid and sodium sulfite for stepwise treatment. Although the nitrosamine can be reduced to 0.1 ppm, special equipment is required to treat the waste acid, and the reaction time is as long as 9 hours, with extremely high energy consumption.

[0005] The photocatalytic removal technology does not produce waste acid and cause secondary pollution. However, traditional photocatalytic technologies often use catalysts such as TiO2 or Cu / TiO2, which have problems such as high recombination rate of photo-generated carriers and rapid activity decay. For example, the conduction band electrons and valence band holes of TiO2 are prone to rapid recombination, resulting in a high recombination rate of photo-generated carriers. This leads to a low concentration of carriers effectively participating in the reaction and low catalytic efficiency. Moreover, TiO2 is prone to deactivation due to poisoning or a decrease in specific surface area during long-term operation. Traditional catalysts (such as Cu / TiO2-type catalysts) have a large decrease in degradation rate after multiple cycles due to photocorrosion or coverage of active sites. Although fixed-bed reactors can partially recover the catalyst, the carrier stability is insufficient, limiting large-scale application. In summary, the traditional photocatalytic system has a high electron-hole recombination rate and low quantum efficiency, resulting in a generally low degradation rate of nitrosamines below 90%, incomplete removal of nitrosamines, a nitrosamine content > 1 ppm, poor recyclability, insufficient stability, and difficulty in large-scale application.

[0006] In view of the three major pain points of low efficiency, heavy pollution, and high energy consumption in the existing methods for removing nitrosamines from trifluralin, there is an urgent need to develop a green process for efficient degradation, improve the recyclability of raw materials, reduce production costs, and be applicable to large-scale production. Summary of the Invention

[0007] In view of the deficiencies of the existing technology, the present invention provides a method for removing nitrosamines from trifluralin, which can overcome the deficiencies of traditional nitrosamine removal methods, improve the removal efficiency, cause no secondary pollution, reduce energy consumption, lower production costs, and be applicable to large-scale production.

[0008] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: A method for removing nitrosamines from trifluralin includes the following steps: preliminary purification of trifluralin crude product, preparation of an ionic mixture, and photocatalytic decomposition. The method for preliminary purification of the trifluralin crude product is to filter the trifluralin crude product through a 0.45 - 0.6 μm polytetrafluoroethylene filter membrane to remove particulate impurities, and then subject the filtrate to vacuum distillation at 50 - 60 °C and a relative vacuum of -0.08 to -0.10 MPa to remove moisture and low-boiling substances, obtaining the preliminarily purified trifluralin. The content of nitrosamines in the trifluralin crude product is 10 - 300 ppm. The method for preparing the ionic mixture is to add zinc β-monocarboxyl phthalocyanine and sodium tetrachlorobenzoquinone sulfonate to carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate, stir at 50 - 60 °C and 500 - 600 rpm for 20 - 30 minutes, and then perform ultrasonic dispersion for 10 - 15 minutes to form a uniform and transparent ionic mixture. The carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate is 2-carboxyl-1-butyl-3-methylimidazolium trifluoroacetate or 4,5-dicarboxyl-1-butyl-3-methylimidazolium trifluoroacetate; The mass ratio of the carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate, zinc β-monocarboxyl phthalocyanine, and sodium tetrachlorobenzoquinone sulfonate is 100:0.5-0.6:0.1-0.15; The frequency of the ultrasonic dispersion is 40-50 kHz, and the power is 200-300 W; The method of photocatalytic decomposition is as follows: mix the preliminarily purified trifluralin with the ionic liquid mixture, adjust the temperature of the solution to 50-52 °C, the pH to 3.8-4.2, perform ultrasonic dispersion for 15-20 minutes to form a dispersion, transfer the dispersion to a photocatalytic reactor, introduce pure oxygen, disperse it through a microporous aeration head, turn on the irradiation light source, control the reaction temperature at 54-56 °C, and the irradiation time at 35-40 minutes. Cool the obtained reaction solution to 50-52 °C, and centrifuge and layer it through a centrifuge. The lower-layer ionic liquid is recovered, and the upper layer is the trifluralin product; The mass ratio of the preliminarily purified trifluralin to the ionic liquid mixture is 1:2.5-3; The feeding rate of the pure oxygen is 0.5-0.7 L / min; The pore diameter of the microporous aeration head is 10-15 μm; The wavelength of the irradiation light source is 640-660 nm, and the light source power density is 100-120 mW / cm 2 ; The recovery rate of the ionic liquid is greater than 99%; The recovered ionic liquid is treated by activated carbon adsorption, and vacuum distillation is carried out at 80-85 °C and a relative vacuum degree of -0.08~-0.10 MPa to remove the decomposition products. 0.1-0.15 wt% of the photosensitizer zinc β-monocarboxyl phthalocyanine is replenished for every 5 cycles of loss, and the repeated use of the ionic liquid can be realized; The recovered ionic liquid is a carboxyl-functionalized ionic liquid, which has high stability to visible light and is not easily damaged in structure due to light irradiation during multiple cycles. After the ionic liquid is reused 20 times, the content of nitrosamine in the obtained trifluralin product is less than 0.1 ppm, and the nitrosamine removal rate is greater than 99%.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate ionic liquid used in the present invention has a strong nucleophilic carboxyl group (-COOH), and the nitrogen atom in the nitrosamine molecule has a partial positive charge. The two form a stable complex through electrostatic interaction and hydrogen bonding. This complexation causes the nitrosamine to transfer from trifluralin to the ionic liquid, increasing the contact probability between the nitrosamine and the photosensitizer and creating conditions for subsequent photocatalytic degradation.

[0010] Under the irradiation of visible light at 640 - 660 nm, the electrons in the molecule of zinc β-monocarboxyl phthalocyanine absorb photon energy and transition from the ground state to the excited state. The excited zinc β-monocarboxyl phthalocyanine has strong redox ability and can transfer energy to the surrounding molecular oxygen (O2), converting it into singlet oxygen ( 1 O2). Singlet oxygen has strong oxidizing properties and can attack the chemical bonds in the nitrosamine molecule, causing it to undergo an oxidation decomposition reaction, decomposing the nitrosamine into small molecule substances such as carbon dioxide, water, and ammonia, and ultimately achieving the removal of nitrosamine.

[0011] Sodium tetrachlorobenzoquinone sulfonate, as an electron transfer medium, can quickly capture the electrons generated by the excited state of the photosensitizer zinc β-monocarboxyl phthalocyanine, promoting the separation of electron-hole pairs. After the electrons are transferred to sodium tetrachlorobenzoquinone sulfonate, it is reduced, while the holes remain on zinc β-monocarboxyl phthalocyanine, enhancing the oxidation ability of zinc β-monocarboxyl phthalocyanine and continuously generating singlet oxygen to ensure the efficient progress of the photocatalytic reaction. In this process, after being reduced, sodium tetrachlorobenzoquinone sulfonate can be re-oxidized by reacting with oxygen in the system to achieve recycling. (2) The method for removing nitrosamine from trifluralin in the present invention realizes a high removal rate of nitrosamine through the synergistic effect of photocatalysis and ionic liquid, and can reduce the nitrosamine content of 10 - 300 ppm to below 0.1 ppm.

[0012] (3) The method for removing nitrosamine from trifluralin in the present invention recycles the ionic liquid, achieving a 99% recovery rate. It still maintains a high removal ability after being recycled 20 times. The nitrosamine content in the obtained trifluralin product is less than 0.1 ppm, and the nitrosamine removal rate is greater than 99%. This greatly reduces the treatment cost of trifluralin and has no secondary pollution, realizing green production. Specific Embodiments

[0013] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention are now described.

[0014] Example 1 The method for removing nitrosamine from trifluralin includes the following steps: (1) Preliminary purification of crude trifluralin Filter the trifluralin crude product through a 0.5 μm polytetrafluoroethylene filter membrane to remove particulate impurities. The filtrate is distilled under reduced pressure at 55 °C and a relative vacuum of -0.09 MPa to remove water and low-boiling substances, obtaining preliminarily purified trifluralin; The content of nitrosamine in the trifluralin crude product is 100 ppm; (2)Prepare the ionic mixture Add zinc β-monocarboxyl phthalocyanine and sodium tetrachlorobenzoquinone sulfonate to carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate, stir at 55 °C and 550 rpm for 25 minutes, and ultrasonically disperse for 12 minutes to form a homogeneous and transparent ionic mixture; The carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate is 2-carboxy-1-butyl-3-methylimidazolium trifluoroacetate; The mass ratio of the carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate, zinc β-monocarboxyl phthalocyanine, and sodium tetrachlorobenzoquinone sulfonate is 100:0.55:0.12; The frequency of the ultrasonic dispersion is 45 kHz and the power is 250 W; (3)Photocatalytic decomposition Mix the preliminarily purified trifluralin with the ionic mixture, adjust the temperature of the solution to 51 °C and the pH to 4.0, ultrasonically disperse for 18 minutes to form a dispersion. Transfer the dispersion to a photocatalytic reactor, introduce pure oxygen, disperse it through a microporous aeration head, turn on the irradiation light source, control the reaction temperature at 55 °C, and irradiate for 38 minutes. Cool the resulting reaction solution to 51 °C, centrifuge and separate layers through a centrifuge. Recover the lower-layer ionic liquid, and the upper layer is the trifluralin product; The mass ratio of the preliminarily purified trifluralin to the ionic mixture is 1:2.8; The feeding rate of the pure oxygen is 0.6 L / min; The pore diameter of the microporous aeration head is 12 μm; The wavelength of the irradiation light source is 650 nm, and the power density of the light source is 110 mW / cm 2 ; The content of nitrosamine in the trifluralin product is 0.05 ppm; The recovery rate of the ionic liquid is 99.34%.

[0015] Example 2 A method for removing nitrosamine from trifluralin, comprising the following steps: (1)Preliminary purification of trifluralin crude product Filter the trifluralin crude product through a 0.45 μm polytetrafluoroethylene filter membrane to remove particulate impurities. The filtrate is distilled under reduced pressure at 50 °C and a relative vacuum of -0.08 MPa to remove water and low-boiling substances, obtaining preliminarily purified trifluralin; The content of nitrosamine in the technical grade trifluralin is 10 ppm; (2) Prepare an ionic mixture Add zinc β-monocarboxyl phthalocyanine and sodium tetrachlorobenzoquinone sulfonate into carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate, stir at 50 °C and 500 rpm for 30 minutes, and ultrasonically disperse for 10 minutes to form a homogeneous and transparent ionic mixture; The carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate is 2-carboxy-1-butyl-3-methylimidazolium trifluoroacetate; The mass ratio of the carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate, zinc β-monocarboxyl phthalocyanine and sodium tetrachlorobenzoquinone sulfonate is 100:0.5:0.1; The frequency of the ultrasonic dispersion is 40 kHz and the power is 200 W; (3) Photocatalytic decomposition Mix the preliminarily purified trifluralin with the ionic mixture, adjust the temperature of the solution to 50 °C and the pH to 3.8, ultrasonically disperse for 15 minutes to form a dispersion, transfer the dispersion to a photocatalytic reactor, introduce pure oxygen, disperse it through a microporous aeration head, turn on the irradiation light source, control the reaction temperature at 54 °C and the irradiation time at 35 minutes, cool the obtained reaction solution to 50 °C, centrifuge and layer it through a centrifuge, recycle the lower-layer ionic liquid, and the upper layer is the trifluralin product; The mass ratio of the preliminarily purified trifluralin to the ionic mixture is 1:2.5; The feeding rate of the pure oxygen is 0.5 L / min; The pore diameter of the microporous aeration head is 10 μm; The wavelength of the irradiation light source is 640 nm and the power density of the light source is 100 mW / cm 2 ; The content of nitrosamine in the trifluralin product is 0.05 ppm; The recovery rate of the ionic liquid is 99.18%.

[0016] Example 3 A method for removing nitrosamine from trifluralin, comprising the following steps: (1) Preliminary purification of technical grade trifluralin Filter the technical grade trifluralin through a 0.6-μm polytetrafluoroethylene filter membrane to remove particulate impurities, and subject the filtrate to vacuum distillation at 60 °C and a relative vacuum of -0.10 MPa to remove moisture and low-boiling substances to obtain preliminarily purified trifluralin; The content of nitrosamine in the technical grade trifluralin is 300 ppm; (2) Prepare an ionic mixture Add zinc β - monocarboxyl phthalocyanine and sodium 2,3,5,6 - tetrachlorobenzoquinone - 4 - sulfonate into carboxyl - functionalized 1 - butyl - 3 - methylimidazolium trifluoroacetate, stir at 60 °C and 600 rpm for 20 minutes, and then ultrasonically disperse for 15 minutes to form a homogeneous and transparent ionic mixture; The carboxyl - functionalized 1 - butyl - 3 - methylimidazolium trifluoroacetate is 4,5 - dicarboxyl - 1 - butyl - 3 - methylimidazolium trifluoroacetate; The mass ratio of the carboxyl - functionalized 1 - butyl - 3 - methylimidazolium trifluoroacetate, zinc β - monocarboxyl phthalocyanine and sodium 2,3,5,6 - tetrachlorobenzoquinone - 4 - sulfonate is 100:0.6:0.15; The frequency of the ultrasonic dispersion is 50 kHz and the power is 300 W; (3)Photocatalytic decomposition Mix the preliminarily purified trifluralin with the ionic mixture, adjust the temperature of the solution to 52 °C and the pH to 4.2, ultrasonically disperse for 20 minutes to form a dispersion, transfer the dispersion to a photocatalytic reactor, introduce pure oxygen, disperse it through a microporous aeration head, turn on the irradiation light source, control the reaction temperature at 56 °C, irradiate for 40 minutes, cool the obtained reaction solution to 52 °C, centrifuge and separate layers through a centrifuge, recycle the lower - layer ionic liquid, and the upper layer is the trifluralin product; The mass ratio of the preliminarily purified trifluralin to the ionic mixture is 1:3; The feeding rate of the pure oxygen is 0.7 L / min; The pore diameter of the microporous aeration head is 15 μm; The wavelength of the irradiation light source is 660 nm and the power density of the light source is 120 mW / cm 2 ; The content of nitrosamine in the trifluralin product is 0.04 ppm; The recovery rate of the ionic liquid is 99.25%.

[0017] Example 4 Take the recycled ionic liquid in Example 1, after activated carbon adsorption treatment, carry out vacuum distillation at 82 °C and a relative vacuum of - 0.09 MPa to remove the decomposition products. According to the scheme of Example 1, replenish 0.12 wt% of the loss of the photosensitizer zinc β - monocarboxyl phthalocyanine every 5 cycles. After repeating the use for 20 times, obtain the reused ionic mixture. Using this ionic mixture, according to the scheme of Example 1, preliminarily purify and photocatalytically decompose the crude trifluralin containing 100 ppm of nitrosamine. The content of nitrosamine in the obtained trifluralin product is 0.08 ppm, and the nitrosamine removal rate is 99.2%.

[0018] Example 5 The ionic liquid recovered in Example 1 was taken. After being treated by activated carbon adsorption, it was subjected to vacuum distillation at 80 °C and a relative vacuum of -0.08 MPa to remove the decomposition products. According to the scheme of Example 1, 0.1 wt% of zinc β-monocarboxyphthalocyanine, the loss of photosensitizer, was replenished every 5 cycles. After being reused 20 times, a reused ionic liquid mixture was obtained. Using this ionic liquid mixture, according to the scheme of Example 1, the trifluralin crude product containing 10 ppm of nitrosamine was preliminarily purified and photocatalytically decomposed. The content of nitrosamine in the obtained trifluralin product was 0.09 ppm, and the nitrosamine removal rate was 99.82%.

[0019] Example 6 The ionic liquid recovered in Example 1 was taken. After being treated by activated carbon adsorption, it was subjected to vacuum distillation at 85 °C and a relative vacuum of -0.10 MPa to remove the decomposition products. According to the scheme of Example 1, 0.15 wt% of zinc β-monocarboxyphthalocyanine, the loss of photosensitizer, was replenished every 5 cycles. After being reused 20 times, a reused ionic liquid mixture was obtained. Using this ionic liquid mixture, according to the scheme of Example 1, the trifluralin crude product containing 300 ppm of nitrosamine was preliminarily purified and photocatalytically decomposed. The content of nitrosamine in the obtained trifluralin product was 0.09 ppm, and the nitrosamine removal rate was 99.97%.

[0020] Example 7 The method for removing nitrosamine in trifluralin of Example 1 was adopted, except that in the step of preparing the ionic liquid mixture, 30 wt% hydrochloric acid was used instead of carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate, and the other steps were the same. The content of nitrosamine in the obtained trifluralin product was 0.72 ppm; In Example 7, 30 wt% hydrochloric acid was used instead of carboxyl-functionalized 1-butyl-3-methylimidazolium trifluoroacetate, and nitrosamine could not be effectively transferred from trifluralin to the hydrochloric acid solution, resulting in a higher content of nitrosamine in the obtained trifluralin product.

[0021] Example 8 The method for removing nitrosamine in trifluralin of Example 1 was adopted, except that in the step of preparing the ionic liquid mixture, the addition of sodium tetrachlorobenzoquinone sulfonate was omitted, and the other steps were the same. The content of nitrosamine in the obtained trifluralin product was 0.18 ppm; In Example 8, the addition of sodium tetrachlorobenzoquinone sulfonate was omitted, lacking an electron transfer medium. The electron-hole pairs generated by the photosensitizer recombined rapidly, resulting in a decrease in the generation amount of singlet oxygen and superoxide radicals, and a decrease in the decomposition rate of nitrosamine, which affected the content of nitrosamine in the final trifluralin product.

[0022] Example 9 The ionic liquid recovered in Example 8 was taken. After being treated by activated carbon adsorption, it was subjected to vacuum distillation at 82°C and a relative vacuum of -0.09 MPa to remove the decomposition products. The loss of the photosensitizer was replenished with 0.12 wt% of zinc β-monocarboxyl phthalocyanine every 5 cycles. After being reused 5 times, a reused ionic mixed solution was obtained. Using this ionic mixed solution, the technical herbicide trifluralin crude product containing 100 ppm of nitrosamine was preliminarily purified and photocatalytically decomposed according to the scheme of Example 1. The content of nitrosamine in the obtained trifluralin product was 7.61 ppm; For the ionic liquid without sodium tetrachlorobenzoquinone sulfonate used in Example 9, its reuse performance decreased significantly, indicating that the sodium tetrachlorobenzoquinone sulfonate added to the ionic liquid plays a major role in its reuse performance.

[0023] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for removing nitrosamines from trifluralin, characterized in that: The removal method comprises the following steps: preliminary purification of crude trifluralin product, preparation of ion mixture and photocatalytic decomposition; The method for preparing the ion mixture is to add β-monocarboxyl phthalocyanine zinc and sodium tetrachlorobenzoquinone sulfonate to carboxyl functionalized 1-butyl-3-methylimidazole trifluoroacetate, stir at 50-60° C. and 500-600 rpm for 20-30 minutes, and ultrasonically disperse for 10-15 minutes to form a uniform and transparent ion mixture; The photocatalytic decomposition method comprises the following steps: mixing preliminarily purified trifluralin with an ion mixed solution, adjusting the solution temperature to 50-52°C and the pH to 3.8-4.2, performing ultrasonic dispersion for 15-20 minutes to form a dispersion, transferring the dispersion to a photocatalytic reactor, introducing pure oxygen, dispersing the dispersion through a microporous aeration head, turning on an irradiation light source, controlling the reaction temperature to 54-56°C, and irradiating for 35-40 minutes, cooling the obtained reaction solution to 50-52°C, performing centrifugal separation by centrifugation, recovering the lower layer of ionic liquid, and obtaining a trifluralin product in the upper layer.

2. The method for removing nitrosamines from trifluralin according to claim 1, characterized in that: In the method for preparing the ion mixture, The carboxyl functionalized 1-butyl-3-methylimidazolium trifluoroacetate is 2-carboxyl-1-butyl-3-methylimidazolium trifluoroacetate or 4,5-dicarboxyl-1-butyl-3-methylimidazolium trifluoroacetate; The mass ratio of the carboxyl functionalized 1-butyl-3-methylimidazole trifluoroacetate, beta-monocarboxyl phthalocyanine zinc and sodium tetrachlorobenzoquinone sulfonate is 100: 0.5-0.6: 0.1-0.

15.

3. The method for removing nitrosamines from trifluralin according to claim 1, characterized in that: In the photocatalytic decomposition method, the mass ratio of the initially purified trifluralin to the ion mixture is 1:2.5-3.

4. The method for removing nitrosamines from trifluralin according to claim 1, characterized in that: In the photocatalytic decomposition method, The pure oxygen introduction rate is 0.5-0.7 L / min; The pore size of the microporous aeration head is 10-15 μm.

5. The method for removing nitrosamines from trifluralin according to claim 1, characterized in that: In the photocatalytic decomposition method, the wavelength of the irradiation light source is 640-660nm, and the power density of the light source is 100-120mW / cm 2 .

6. The method for removing nitrosamines from trifluralin according to claim 1, characterized in that: The method for preliminary purification of the crude trifluralin product is as follows: filtering the crude trifluralin product through a 0.45-0.6 μm polytetrafluoroethylene filter membrane to remove particulate impurities, and distilling the filtrate under reduced pressure at 50-60° C. and a relative vacuum degree of -0.08 to -0.10 MPa to remove water and low-boiling substances to obtain preliminary purified trifluralin.

7. The method for removing nitrosamines from trifluralin according to claim 6, characterized in that: In the method for preliminary purification of the crude trifluralin product, the nitrosamine content in the crude trifluralin product is 10-300 ppm.

8. The method for removing nitrosamines from trifluralin according to claim 1, characterized in that: The recovered ionic liquid is treated by activated carbon adsorption, and is distilled under reduced pressure at 80-85° C. and a relative vacuum degree of -0.08 to -0.10 MPa to remove decomposition products. The lost photosensitizer is replenished with 0.1-0.15 wt % of β-monocarboxyl phthalocyanine zinc every 5 cycles, so that the ionic liquid can be reused.