Improved method for recovering bromine from bromine-containing wastewater obtained from diafenthiuron production

Abstract

The invention relates to the technical field of diafenthiuron production, in particular to an improved method for recovering bromine from bromine-containing wastewater obtained by diafenthiuron production, which comprises the following steps: pretreatment, filtration and cooling, air floatation and oil removal, ultrafiltration treatment, reduced pressure distillation, bromine extraction, and recovery and application of dichloroethane. According to the method, diafenthiuron production wastewater is heated, molecules of the diafenthiuron production wastewater are enabled to be active, so that coagulant is fully mixed and reacted, and then filtration treatment is carried out in a multi-medium filter, so that large-particle suspended matters and organic pollutants in the wastewater are removed, an air-dissolved water pressure-reducing releaser in air-floating oil removal equipment in a subsequent process is not easy to block, and the air-floating oil removal efficiency is improved. According to the method, the oil removal failure is not easily caused, the bromine recovery efficiency and purity are indirectly improved, and after air flotation oil removal, fine filtration is performed through the ultrafiltration membrane assembly to remove small particles, so that the subsequent oxidizing agent chlorine and bromine ions in wastewater are subjected to sufficient and unobstructed reaction, and bromine with higher purity is obtained through distillation.

Description

Technical Field

[0001] The present application relates to the technical field of diafenthiuron production, and in particular to an improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron. Background Art

[0002] Difenocarb is a new type of thiourea highly effective insecticide and acaricide, which has contact, stomach poison, systemic and fumigation effects, and has a certain ovicidal effect. It is transformed into a substance with insecticidal activity under ultraviolet light, and has strong activity against pests on vegetables that have developed serious drug resistance. It can prevent and control aphids, whiteflies, leafhoppers, noctuid pests and mites on a variety of crops and ornamental plants.

[0003] The conventional synthesis method of dimethoate urea is as follows: 2,6-diisopropylaniline is used as a starting material, dichloroethane is used as a solvent, bromine is slowly added dropwise, and bromine is added at 10-20°C. Then, an aqueous solution of sodium hydroxide is added to neutralize to a weak alkaline state, and the solution is allowed to stand for separation to obtain 4-bromo-2,6-diisopropylaniline and bromine-containing wastewater whose main component is sodium bromide; 4-bromo-2,6-diisopropylaniline is reacted with an acid-binding agent and a catalyst at about 150°C. Phenol undergoes coupling reaction to debrominate, and alkaline water is added to make it weakly alkaline, and filtered to obtain 2,6-diisopropyl-4-phenoxyaniline and bromine-containing wastewater whose main component is sodium bromide; 2,6-diisopropyl-4-phenoxyaniline reacts with sodium thiocyanate using xylene as solvent, and the generated substituted thiourea is thermally split and dehydrated at 155°C and kept warm to obtain 2,6-diisopropyl-4-phenoxyphenyl isothiocyanate, and finally reacts with tert-butylamine to obtain the target product dithiocarbamide.

[0004] In the above-mentioned synthesis reaction, during bromination and debromination, bromide-containing wastewater with sodium bromide as the main component is obtained, which contains a large amount of bromide ions and is directly discharged to pollute the environment. Therefore, enterprises have to consider recovering bromine from wastewater and applying the recovered bromine to the synthesis reaction of diethylcarbamide again, so as to reduce environmental pollution and improve resource utilization.

[0005] For example, a bromine recovery method previously adopted by our unit, as detailed in the Chinese patent application document with application number: 201610872636.4, removes oil substances from bromine-containing wastewater by flotation, then conducts vacuum distillation on the bromine-containing wastewater, and then introduces chlorine into the wastewater to distill bromine. At the same time, the distillate of vacuum distillation is layered, and the obtained ethylene dichloride is used in the production of dithiocarbamide.

[0006] With respect to the above-mentioned related technologies, the inventor believes that there are the following technical defects that need to be improved:

[0007] In the early stage of the synthesis process of diafenthiuron, with the aging and wear of the equipment and the untimely cleaning of the various transmission pipelines, the bromine-containing wastewater obtained from the production of diafenthiuron will be mixed with a large number of particulates and organic matter. These particulates and organic matter will cause a high concentration of suspended matter in the wastewater during the flotation oil removal process, making the dissolved air water pressure relief device in the flotation oil removal equipment easily blocked, which will frequently lead to oil removal failures to a large extent, greatly affecting the subsequent bromine recovery efficiency and purity. Summary of the invention

[0008] The present application provides an improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron to improve the following technical problems:

[0009] In the early stage of the synthesis process of diafenthiuron, with the aging and wear of the equipment and the untimely cleaning of the various transmission pipelines, the bromine-containing wastewater obtained from the production of diafenthiuron will be mixed with a large number of particulates and organic matter. These particulates and organic matter will cause a high concentration of suspended matter in the wastewater during the flotation oil removal process, making the dissolved air water pressure relief device in the flotation oil removal equipment easily blocked, which will frequently lead to oil removal failures to a large extent, greatly affecting the subsequent bromine recovery efficiency and purity.

[0010] The present application provides an improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron, using the following technical scheme:

[0011] An improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron comprises the following steps:

[0012] Step 1, pretreatment: convey the diafenthiuron production wastewater to a heated stirring kettle, heat it to 60-80°C, then add a coagulant and stir it evenly, and initially stand it for more than 3 hours to precipitate to obtain primary pretreated wastewater;

[0013] Step 2, filtration and cooling: the primary pre-treated wastewater is introduced into a multi-media filter for filtration treatment to remove large suspended particles and organic pollutants, and then transported to a heat exchanger for heat exchange and cooling treatment to obtain secondary pre-treated wastewater;

[0014] Step 3, flotation oil removal: preliminarily adjust the secondary pre-treated wastewater to acidity and transport it to the flotation oil removal equipment to remove oil substances to obtain tertiary pre-treated wastewater;

[0015] Step 4, ultrafiltration treatment: The tertiary pre-treated wastewater is filtered through an ultrafiltration membrane assembly to remove tiny particles, thereby obtaining the quaternary pre-treated wastewater;

[0016] Step 5, vacuum distillation: performing vacuum distillation on the fourth-stage pre-treated wastewater, collecting the distillate for standby use, and obtaining the fifth-stage pre-treated wastewater;

[0017] Step 6, bromine extraction: further reducing the acidity of the five-stage pre-treated wastewater and introducing chlorine gas to obtain bromine by distillation;

[0018] Step 7, recovering and reusing the dichloroethane: the distillate collected in step 5 is allowed to stand, and the water layer is removed to obtain dichloroethane, which is then used as a solvent in the production of diafenthiuron.

[0019] In one feasible technical solution of the present application, the flotation oil removal method in step 3 is as follows: the pH value of the secondary pre-treated wastewater is adjusted to 5.5-6.5, passed into a closed flotation oil removal device, and then high-pressure nitrogen is passed into the device, and the pH value is adjusted to 5.5-6.5, and the pH value is adjusted to 5.5-6.5, and the wastewater is passed into a closed flotation oil removal device, and then high-pressure nitrogen is passed into the device, and the pH value is adjusted to 5.5-6.5, and the wastewater ... wastewater is passed into the device, and the wastewater is passed into the device, and the wastewater is passed into the device, and the wastewater is passed into the device, and the wastewater is passed 5 The pressure is maintained under the Pa environment for 10 to 20 minutes, and then the pressure is quickly reduced to normal pressure within 3 to 10 minutes, the oil and water are separated, and the upper oil layer is removed to obtain the tertiary pretreated wastewater.

[0020] In an achievable technical solution of the present application, the reduced pressure distillation method in step five is: steam-heating the fourth-level pretreated wastewater for distillation at a pressure of -0.08 to -0.09 MPa, the heating temperature is 50 to 60°C, the distillation time is 30 to 50 minutes, and the fifth-level pretreated wastewater is obtained.

[0021] In a feasible technical solution of the present application, the method for extracting bromine in step six is: adjusting the pH value of the fifth-stage pretreated wastewater to 3.0-4.8, stirring at a uniform speed, introducing chlorine gas at a rate of 30-40 kg / h at a temperature of 10-20° C. until all bromide ions are converted into bromine, stopping the introduction of chlorine gas, and distilling with steam heating at the same time, collecting a distillate at 60-80° C., removing the water layer from the distillate, and obtaining bromine, wherein the mass percentage of the bromine is greater than 99%.

[0022] In an achievable technical solution of the present application, in step 1, the coagulant is polyacrylamide and / or polyaluminium chloride; based on the volume of the diafenthiuron production wastewater, the dosage of the coagulant is 8-12 ppm.

[0023] In a feasible technical solution of the present application, during the process of adding the coagulant in step one, nitrogen is continuously charged into the diafenthiuron production wastewater in the heated stirring kettle, and the nitrogen is sprayed from the bottom to the top. A plurality of nitrogen spray pipes are arranged at the bottom of the heated stirring kettle, and a nitrogen recovery pipe is arranged at the top of the heated stirring kettle. The nitrogen recovered from the heated stirring kettle is reused in step three for flotation oil removal treatment.

[0024] In an achievable technical solution of the present application, the ultrafiltration membrane used in the ultrafiltration membrane assembly in step four is a polyvinylidene fluoride ultrafiltration membrane, a polysulfone ultrafiltration membrane or a polyethersulfone ultrafiltration membrane, the ultrafiltration membrane is a hollow ultrafiltration membrane, the inner diameter of the ultrafiltration membrane is 0.05-0.1 μm, and the wall thickness of the ultrafiltration membrane is 0.5-1 nm.

[0025] In a feasible technical solution of the present application, the technical means adopted for adjusting the acidity in step three and step six is: gradually adding hydrochloric acid, and the concentration of hydrochloric acid is not less than 10 mol / L.

[0026] In a feasible technical solution of the present application, in step four, the tertiary pretreated wastewater needs to be ultrasonically treated before being filtered through the ultrafiltration membrane assembly: the tertiary pretreated wastewater is transported to an ultrasonic reactor for treatment for 10-15 minutes, and the ultrasonic reactor applies ultrasonic waves with a frequency of 50kHz to 80KHz and a power of 500W to 700W.

[0027] In a feasible technical solution of the present application, in step 2, the temperature of the wastewater after cooling treatment in the heat exchanger is between 25-35°C and consistent with the ambient temperature.

[0028] In summary, the present application includes at least one of the following beneficial technical effects:

[0029] First, the wastewater produced by diafenthiuron is heated to make its molecules active so that the coagulant can fully mix and react. Then, it is filtered in a multi-media filter to remove large suspended solids and organic pollutants in the wastewater. This makes it less likely for the dissolved air water decompression releaser in the flotation oil removal equipment in the subsequent process to be blocked, which will not lead to oil removal failure, and indirectly improve the bromine recovery efficiency and purity.

[0030] After the heat exchanger cools the wastewater, the wastewater can be restored to normal temperature. The phenol impurities in the bromine-containing wastewater are dissolved in water under alkaline conditions and generate phenol under acidic conditions. The pH value of the bromine-containing wastewater is adjusted to acidic conditions to convert the phenol impurities into oily phenol, which is then removed by flotation deoiling.

[0031] After flotation to remove oil, it is inevitable that some tiny particles will be mixed in the wastewater. In view of the above situation, ultrafiltration membrane components are used for fine filtration to remove the tiny particles, combined with a treatment process to further reduce the acidity of the wastewater, so that the subsequent oxidant chlorine and bromide ions in the wastewater can fully and unhindered react, thereby distilling to obtain bromine with higher purity;

[0032] The dichloroethane in the bromine-containing wastewater is recovered by vacuum distillation. The azeotropic properties of dichloroethane and water are utilized to completely recover the dichloroethane in the bromine-containing wastewater. This not only improves the purity of the recovered bromine, but also allows the recovered dichloroethane to be applied to the production of dimethoate, thereby saving production costs, reducing pollution, and being beneficial to energy conservation and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 It is a process flow chart of an improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to an embodiment of the present application.

[0035] Figure 2 It is a schematic diagram of the flow of nitrogen in the heating stirring kettle and the flotation oil removal equipment in the embodiment of the present application.

[0036] Description of reference numerals:

[0037] 100. Heating and stirring kettle; 11. Nitrogen ejection pipe; 12. Nitrogen recovery pipe; 200. Air flotation oil removal equipment. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0040] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0041] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0042] The following is combined with Figure 1-2 This application is described in further detail.

[0043] The present application discloses an improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron. Figure 1 and Figure 2 The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron comprises the following steps:

[0044] Step 1, pretreatment: convey the diafenthiuron production wastewater to a heated stirring tank 100, heat it to 60-80° C., then add a coagulant and stir it evenly, the coagulant is polyacrylamide and / or polyaluminum chloride; the volume of the diafenthiuron production wastewater is used as the calculation basis, the amount of the coagulant is 8-12 ppm, and the wastewater is initially allowed to stand for more than 3 hours to precipitate to obtain primary pretreated wastewater;

[0045] Step 2, filtering and cooling: the primary pre-treated wastewater is introduced into a multi-media filter for filtering to remove large suspended solids and organic pollutants, and then transported to a heat exchanger for heat exchange and cooling treatment to obtain secondary pre-treated wastewater. The temperature of the wastewater after cooling treatment in the heat exchanger is between 25-35°C and consistent with the ambient temperature;

[0046] Step 3, flotation oil removal: preliminarily adjust the secondary pretreated wastewater to acidity (the technical means used to adjust the acidity is: gradually add hydrochloric acid, and the concentration of hydrochloric acid is not less than 10 mol / L), and transport it to the flotation oil removal equipment 200 to remove oil substances, and obtain the tertiary pretreated wastewater. The specific steps of flotation oil removal are: adjust the pH value of the secondary pretreated wastewater to 5.5-6.5, pass it into the closed flotation oil removal equipment 200, and then pass high-pressure nitrogen into it, and at 3-5×10 5 Pa environment for 10 to 20 minutes, then quickly reduce the pressure to normal pressure within 3 to 10 minutes, separate the oil and water layers, remove the upper oil layer, and obtain the tertiary pretreated wastewater;

[0047] Step 4, ultrafiltration treatment: the tertiary pretreated wastewater is transported to an ultrasonic reactor for treatment for 10-15 minutes, the ultrasonic reactor applies ultrasonic waves with a frequency of 50kHz-80KHz and a power of 500W-700W, and the tertiary pretreated wastewater is filtered through an ultrafiltration membrane assembly to remove tiny particles to obtain a quaternary pretreated wastewater, the ultrafiltration membrane used in the ultrafiltration membrane assembly is a polyvinylidene fluoride ultrafiltration membrane, a polysulfone ultrafiltration membrane or a polyethersulfone ultrafiltration membrane, the ultrafiltration membrane is a hollow ultrafiltration membrane, the inner diameter of the ultrafiltration membrane is 0.05-0.1μm, and the wall thickness of the ultrafiltration membrane is 0.5-1nm;

[0048] Step 5, vacuum distillation: vacuum distillation is performed on the fourth-level pretreated wastewater, and the distillate is collected for standby use to obtain the fifth-level pretreated wastewater. The specific steps of the vacuum distillation are: steam heating the fourth-level pretreated wastewater for distillation at a pressure of -0.08 to -0.09 MPa, the heating temperature is 50 to 60° C., and the distillation time is 30 to 50 minutes to obtain the fifth-level pretreated wastewater;

[0049] Step 6, bromine extraction: further reduce the acidity of the five-stage pre-treated wastewater and introduce chlorine (the technical means used to adjust the acidity is: gradually add hydrochloric acid, and the concentration of hydrochloric acid is not less than 10 mol / L), distill to obtain bromine, the specific steps of bromine extraction are: adjust the pH value of the five-stage pre-treated wastewater to 3.0-4.8, stir at a uniform speed, introduce chlorine at a rate of 30-40 kg / h under a temperature condition of 10-20° C., until all bromide ions are converted into bromine, stop introducing chlorine, and distill with steam heating at the same time, collect the distillate at 60-80° C., remove the water layer from the distillate, and obtain bromine, the mass percentage of bromine is greater than 99%;

[0050] Step 7, recovering and reusing the dichloroethane: the distillate collected in step 5 is allowed to stand, and the water layer is removed to obtain dichloroethane, which is then used as a solvent in the production of diafenthiuron.

[0051] In this embodiment, in order to further improve the reaction efficiency and degree of the coagulant in the wastewater, during the process of adding the coagulant in step one, nitrogen is continuously charged into the diethylcarbamide production wastewater in the heated stirring kettle 100, and the nitrogen is sprayed from the bottom to the top, thereby cooperating with the stirring action to disperse the particulate matter and organic matter in the wastewater more evenly so that the coagulant can take effect. A plurality of nitrogen spray pipes 11 are arranged at the bottom of the heated stirring kettle 100, and a nitrogen recovery pipe 12 is arranged at the top of the heated stirring kettle 100. The nitrogen recovered from the heated stirring kettle 100 is reused for flotation oil removal treatment in step three.

[0052] The beneficial technical effects of the improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron in the embodiment of the present application are roughly as follows:

[0053] First, the wastewater produced by diafenthiuron is heated to make its molecules active so that the coagulant can fully mix and react, and then filtered in a multi-media filter to remove large suspended solids and organic pollutants in the wastewater, so that the dissolved air water decompression releaser in the flotation oil removal equipment 200 in the subsequent process is not easy to be blocked, and the oil removal failure is not easy to occur, which indirectly improves the bromine recovery efficiency and purity;

[0054] After the heat exchanger cools the wastewater, the wastewater can be restored to normal temperature. The phenol impurities in the bromine-containing wastewater are dissolved in water under alkaline conditions and generate phenol under acidic conditions. The pH value of the bromine-containing wastewater is adjusted to acidic conditions to convert the phenol impurities into oily phenol, which is then removed by flotation deoiling.

[0055] After flotation to remove oil, it is inevitable that some tiny particles will be mixed in the wastewater. In view of the above situation, ultrafiltration membrane components are used for fine filtration to remove the tiny particles, combined with a treatment process to further reduce the acidity of the wastewater, so that the subsequent oxidant chlorine and bromide ions in the wastewater can fully and unhindered react, thereby distilling to obtain bromine with higher purity;

[0056] The dichloroethane in the bromine-containing wastewater is recovered by vacuum distillation. The azeotropic properties of dichloroethane and water are utilized to completely recover the dichloroethane in the bromine-containing wastewater. This not only improves the purity of the recovered bromine, but also allows the recovered dichloroethane to be applied to the production of dimethoate, thereby saving production costs, reducing pollution, and being beneficial to energy conservation and environmental protection.

[0057] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the application should be included in the protection scope of the present application.

Claims

1. An improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron, characterized in that: The following steps are involved: Step 1, pretreatment: convey the diafenthiuron production wastewater to a heated stirring kettle, heat it to 60-80°C, then add a coagulant and stir it evenly, and initially stand it for more than 3 hours to precipitate to obtain primary pretreated wastewater; Step 2, filtration and cooling: the primary pre-treated wastewater is introduced into a multi-media filter for filtration treatment to remove large suspended particles and organic pollutants, and then transported to a heat exchanger for heat exchange and cooling treatment to obtain secondary pre-treated wastewater; Step 3, flotation oil removal: preliminarily adjust the secondary pre-treated wastewater to acidity and transport it to the flotation oil removal equipment to remove oil substances to obtain tertiary pre-treated wastewater; Step 4, ultrafiltration treatment: The tertiary pre-treated wastewater is filtered through an ultrafiltration membrane assembly to remove tiny particles, thereby obtaining the quaternary pre-treated wastewater; Step 5, vacuum distillation: performing vacuum distillation on the fourth-stage pre-treated wastewater, collecting the distillate for standby use, and obtaining the fifth-stage pre-treated wastewater; Step 6, bromine extraction: further reducing the acidity of the five-stage pre-treated wastewater and introducing chlorine gas to obtain bromine by distillation; Step 7, recovering and reusing the dichloroethane: the distillate collected in step 5 is allowed to stand, and the water layer is removed to obtain dichloroethane, which is then used as a solvent in the production of diafenthiuron.

2. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: The flotation oil removal method in step 3 is as follows: the pH value of the secondary pre-treated wastewater is adjusted to 5.5-6.5, passed into a closed flotation oil removal device, and then high-pressure nitrogen is introduced into the device at 3-5×10 5 The pressure is maintained under the Pa environment for 10 to 20 minutes, and then the pressure is quickly reduced to normal pressure within 3 to 10 minutes, the oil and water are separated, and the upper oil layer is removed to obtain the tertiary pretreated wastewater.

3. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: The reduced pressure distillation method in step five is: steam-heating the fourth-level pretreated wastewater for distillation at a pressure of -0.08 to -0.09 MPa, the heating temperature is 50 to 60° C., the distillation time is 30 to 50 minutes, and the fifth-level pretreated wastewater is obtained.

4. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: The method for extracting bromine in step six is: adjusting the pH value of the fifth-stage pretreated wastewater to 3.0-4.8, stirring at a uniform speed, introducing chlorine gas at a rate of 30-40 kg / h at a temperature of 10-20° C. until all bromide ions are converted into bromine, stopping the introduction of chlorine gas, and distilling with steam heating at the same time, collecting a distillate at 60-80° C., removing the water layer from the distillate, and obtaining bromine, wherein the mass percentage of the bromine is greater than 99%.

5. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: In step 1, the coagulant is polyacrylamide and / or polyaluminium chloride; based on the volume of the diafenthiuron production wastewater, the dosage of the coagulant is 8-12 ppm.

6. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: During the process of adding the coagulant in step one, nitrogen is continuously charged into the diafenthiuron production wastewater in the heated stirring kettle, and the nitrogen is sprayed from the bottom to the top. A plurality of nitrogen spray pipes are arranged at the bottom of the heated stirring kettle, and a nitrogen recovery pipe is arranged at the top of the heated stirring kettle. The nitrogen recovered from the heated stirring kettle is reused in step three for flotation oil removal treatment.

7. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: The ultrafiltration membrane used in the ultrafiltration membrane assembly in step 4 is a polyvinylidene fluoride ultrafiltration membrane, a polysulfone ultrafiltration membrane or a polyethersulfone ultrafiltration membrane, and the ultrafiltration membrane is a hollow ultrafiltration membrane. The inner diameter of the ultrafiltration membrane is 0.05-0.1 μm, and the wall thickness of the ultrafiltration membrane is 0.5-1 nm.

8. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: The technical means used to adjust the acidity in step 3 and step 6 is: gradually adding hydrochloric acid, and the concentration of hydrochloric acid is not less than 10 mol / L.

9. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: In step 4, the tertiary pretreated wastewater is subjected to ultrasonic treatment before being filtered through the ultrafiltration membrane assembly: the tertiary pretreated wastewater is transported to an ultrasonic reactor for treatment for 10-15 minutes, and the ultrasonic reactor applies ultrasonic waves with a frequency of 50kHz to 80KHz and a power of 500W to 700W.

10. The improved method for recovering bromine from bromine-containing wastewater obtained from the production of diafenthiuron according to claim 1, characterized in that: In step 2, the temperature of the wastewater after cooling in the heat exchanger is between 25-35°C and consistent with the ambient temperature.

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