Method for purifying byproduct salt in pesticide production

Abstract

The invention relates to the technical field of pesticide production, in particular to a method for purifying byproduct salt in pesticide production, which comprises the following steps of: dissolving the synthesized pesticide byproduct potassium bromide solid salt with pure water according to the content of 20-50%; hydrobromic acid is added in the dissolving process to adjust the pH value to 3.5-5, and carbonate radicals and bicarbonate radicals in water are removed; after the reaction is completed, stopping aeration and standing, skimming floating glue by adopting an air flotation machine, performing coarse filtration by using a filter bag, and then passing through a ceramic membrane; carrying out coagulative precipitation on the ceramic membrane concentrated water, and carrying out electrochemical experiment to remove COD (Chemical Oxygen Demand) on the supernatant after the coagulative precipitation; electro-catalytic oxidation effluent is returned to the ceramic membrane part for continuous treatment; the pH value of the ceramic membrane clear liquid is adjusted to 7-8 with potassium hydroxide, and then evaporative crystallization is carried out, so that the technical problems that in the prior art, in the process of generating difenoconazole through condensation, the byproduct potassium bromide is difficult to separate, the resource waste is serious, the purity is low, the separation and purification cost is relatively high, and meanwhile, a large amount of wastewater is generated and is difficult to treat are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of pesticide production, and particularly to a method for purifying by-products of pesticide production. Background Art

[0002] Difenoconazole is a triazole fungicide with high safety and belongs to a sterol demethylation inhibitor. It has the characteristics of high efficiency, broad spectrum, low toxicity, low dosage, high safety, etc., and has good therapeutic and protective effects on various fungal diseases.

[0003] Industrially, difenoconazole is mainly prepared by a synthesis method of cyclization, bromination, and condensation. The first step of the cyclization reaction in this route is relatively easy to carry out, with high yield, short reaction time, and high product normalization purity. However, after the formation of the ketal product, the activity of its α-hydrogen decreases, resulting in a decrease in the yield and normalization purity of the bromination reaction.

[0004]

[0005] For example, the prior art patent CN102225935B discloses a method for purifying potassium bromide, a by-product of difenoconazole technical drug. 2,4-dichloroacetophenone and 1,2-pentanediol are used for cyclization, and then bromination is carried out with bromine to generate 2-(bromomethyl)-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolane. A solid heteropolyacid catalyst is added during the cyclization reaction. After the cyclization reaction is completed, the catalyst is filtered and recovered, and then the bromination reaction is carried out. After the bromination reaction is completed, 2-(bromomethyl)-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolane, 1,2,4-triazole, and potassium carbonate are subjected to a condensation reaction to prepare the difenoconazole technical drug. However, in this invention, the separation of the by-product potassium bromide in the condensation reaction uses a single methanol solvent, and the separation and purification effect is not good, and the obtained potassium bromide has a low purity. At the same time, a large amount of organic wastewater is generated during the water washing process, wasting water resources and polluting the environment.

[0006] The prior art patent CN1101277A discloses a production process of by-product potassium bromide in pesticide synthesis. The process includes product desolvation, toluene separation, DMF separation and purification, drying, and high-temperature calcination purification processes. In the production process of by-product potassium bromide in pesticide synthesis disclosed in the invention, after triazole potassium and bromide are condensed to form propiconazole with DMF as a solvent, the solvent DMF is first removed, and then the crude propiconazole is separated by toluene in batches. Then, triazole potassium is separated by DMF solvent. Finally, the remaining solid, that is, potassium bromide, is dried and purified by high-temperature calcination to obtain a potassium bromide solid with a purity of more than 98%. However, in this invention, drying and high-temperature calcination are used for purification, and the obtained potassium bromide has a poor purity, and the energy consumption is high during the production process, and secondary pollutants are easily generated during the sintering process.

[0007] The prior art patent CN103102015A discloses a method for treating pesticide wastewater using immobilized microorganisms, which mainly includes several processes such as strain domestication, carrier preparation, bacterial adsorption, and sewage treatment. Its characteristics are as follows: the domesticated Aspergillus niger is adsorbed onto activated carbon with a diameter of 5 - 8 mm, and then the prepared activated carbon containing saturated Aspergillus niger is put into the wastewater. When the CODcr in each liter of sewage reaches 200 - 10,000, 1% of the sewage volume is added, the temperature is controlled at 5 - 30 degrees, and it is statically immersed for 1 - 6 days. The highest degradation rate can reach 98%. However, in this invention, the treatment using microorganisms has relatively high requirements for the quality of the wastewater, a long treatment time, sludge will be generated during the treatment process, and the treatment effect on some special pollutants is limited.

[0008] In summary, in the prior art, during the process of condensing to produce difenoconazole, the by - product potassium bromide is difficult to separate, there is serious waste of resources, low purity, high separation and purification cost, and at the same time, a large amount of wastewater is generated and difficult to treat. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for purifying by - product salts in pesticide production, aiming to solve the technical problems in the prior art that during the process of condensing to produce difenoconazole, the by - product potassium bromide is difficult to separate, there is serious waste of resources, low purity, high separation and purification cost, and at the same time, a large amount of wastewater is generated and difficult to treat.

[0010] To achieve the above - mentioned purpose, a method for purifying by - product salts in pesticide production adopted by the present invention includes the following steps:

[0011] Step 1: Dissolve the solid salt of potassium bromide, which is a by - product of synthetic pesticides, with pure water at a content of 20% - 50%.

[0012] Step 2: During the dissolution process, add hydrobromic acid to adjust the pH to 3.5 - 5 to remove carbonate and bicarbonate ions in the water.

[0013] Step 3: After the reaction is complete, stop aeration and let it stand. Then, use a flotation machine to skim off the floating colloid, first conduct rough filtration with a filter bag, and then pass through a ceramic membrane to remove fine impurities in the water.

[0014] Step 4: Conduct coagulation and precipitation on the concentrated water of the ceramic membrane, and take the supernatant after coagulation and precipitation for electrochemical experiments to remove COD.

[0015] Step 5: Return the effluent of electro - catalytic oxidation to the ceramic membrane part for further treatment.

[0016] Step 6: Adjust the pH of the clear liquid of the ceramic membrane to 7 - 8 with potassium hydroxide and then conduct evaporation and crystallization.

[0017] Among them, in Step 1, when dissolving the synthetic pesticide by-product potassium bromide solid salt with a content of 20%-50% in pure water, the dissolving method is the way of aeration combined with stirring, and the dissolving time is 60-90 minutes.

[0018] Among them, in Step 2, the concentration of hydrobromic acid added during the dissolving process is less than or equal to 40%.

[0019] Among them, in Step 3, when performing rough filtration with a filter bag, larger impurities in the water can be removed. The water after removing the larger impurities then passes through a ceramic membrane to remove fine impurities in the water, thereby reducing the operating load of the ceramic membrane and improving the flux stability of the ceramic membrane.

[0020] Among them, in Step 3, the ceramic membrane used to remove fine impurities in the water is a ceramic tube membrane element with a pore size of 4-50 nm. It has the advantages of high filtration accuracy, good solid-liquid separation effect, strong anti-pollution ability, and small floor area.

[0021] Among them, in Step 4, the method of coagulation and precipitation for the ceramic membrane concentrated water is to use a coagulant combined with a flocculant for coagulation and precipitation.

[0022] Among them, in Step 5, the ceramic membrane treatment part communicates with the electrocatalytic oxidation part, which is used to treat the effluent of the electrocatalytic oxidation part and further perform solid-liquid separation on the wastewater.

[0023] Among them, in Step 6, most of the concentrated water generated by evaporation and crystallization enters the electrocatalytic oxidation for treatment, and a small amount of concentrated water is discharged. Moreover, the electrocatalytic oxidation part communicates with the evaporation and crystallization part, which is used to treat most of the evaporation mother liquor generated by evaporation and crystallization and further degrade the organic matter in the evaporation mother liquor.

[0024] A method for purifying by-product salts in pesticide production of the present invention is as follows: First, dissolve the synthetic pesticide by-product potassium bromide solid salt with a content of 20%-50% in pure water; add hydrobromic acid during the dissolving process to adjust the pH to 3.5-5 to remove carbonate and bicarbonate in the water; stop aeration after the reaction is complete, let it stand for a period of time, use a flotation machine to skim off the floating colloid, first perform rough filtration with a filter bag, and then pass through a ceramic membrane to remove fine impurities in the water; perform coagulation and precipitation on the ceramic membrane concentrated water, take the supernatant after coagulation and precipitation for electrochemistry experiment to remove COD; the effluent of electrocatalytic oxidation returns to the ceramic membrane part for continuous treatment; adjust the pH of the ceramic membrane clear liquid to 7-8 with potassium hydroxide and then perform evaporation and crystallization. In this way, it solves the technical problems in the prior art that during the process of condensation to form difenoconazole, the separation of the by-product potassium bromide is difficult, the resource waste is serious, the purity is low, the separation and purification cost is relatively high, and at the same time, a large amount of wastewater is generated and difficult to treat.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. Compared with the known purification processes in the prior art, the purification process of by - product potassium bromide in difenoconazole disclosed by the present invention results in a product with high purity, simple process steps, and strong controllability in separation and purification.

[0027] 2. The treatment process for the wastewater generated during the purification of potassium bromide in the present invention effectively removes COD in the wastewater, improves the salt utilization rate, reduces environmental pollution, and increases the utilization rate of the wastewater; 3. The overall yield of the method of the present invention is high, the process is simple, the process flow is short, and it is easy to realize industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following - described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 It is a flow chart of the method for purifying by - product salts in pesticide production of the present invention.

[0030] Figure 2 It is a graph showing the change of flux of 50nm ceramic membrane and 4nm small - pore - diameter ceramic membrane with time in the present invention.

[0031] Figure 3 It is a graph showing the change of nanofiltration membrane flux and temperature with time in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation of the present invention.

[0033] Please refer to Figure 1 , Figure 1 It is a flow chart of the method for purifying by - product salts in pesticide production of the present invention.

[0034] The present invention provides a method for purifying by - product salts in pesticide production, including the following steps:

[0035] Step 1: Dissolve the solid salt of by - product potassium bromide in synthetic pesticides in pure water at a content of 20% - 50%.

[0036] For this specific embodiment, when dissolving the solid salt of by - product potassium bromide in synthetic pesticides in pure water at a content of 20% - 50%, the dissolution method is the way of aeration combined with stirring, and the dissolution time is 60 - 90 minutes.

[0037] Step 2: During the dissolution process, hydrobromic acid is added to adjust the pH to 3.5 - 5 to remove carbonate and bicarbonate in water;

[0038] For this specific embodiment, the concentration of hydrobromic acid added during the dissolution process is less than or equal to 40%.

[0039] Step 3: After the reaction is complete, stop aeration and let it stand. Then, use a flotation machine to skim off the floating colloid, first conduct rough filtration with a filter bag, and then pass through a ceramic membrane to remove fine impurities in water;

[0040] For this specific embodiment, when conducting rough filtration with a filter bag, larger impurities in water can be removed. The water after removing larger impurities then passes through a ceramic membrane to remove fine impurities in water, thereby reducing the operating load of the ceramic membrane and improving the flux stability of the ceramic membrane.

[0041] The ceramic membrane used to remove fine impurities in water is a ceramic tube membrane element with a pore size of 4 - 50 nm. It has the advantages of high filtration accuracy, good solid-liquid separation effect, strong anti-pollution ability, and small floor area.

[0042] Step 4: Coagulate and precipitate the concentrated water of the ceramic membrane, and take the supernatant after coagulation and precipitation for electrochemical experiment to remove COD;

[0043] For this specific embodiment, the method of coagulating and precipitating the concentrated water of the ceramic membrane is to use a coagulant combined with a coagulant aid for coagulation and precipitation.

[0044] Step 5: The effluent of electrocatalytic oxidation returns to the ceramic membrane part for further treatment;

[0045] For this specific embodiment, the ceramic membrane treatment part is connected to the electrocatalytic oxidation part, which is used to treat the effluent of the electrocatalytic oxidation part and further conduct solid-liquid separation of the wastewater.

[0046] Step 6: Adjust the pH of the clear liquid of the ceramic membrane to 7 - 8 with potassium hydroxide and then conduct evaporation crystallization.

[0047] For this specific embodiment, most of the concentrated water generated by evaporation crystallization enters the electrocatalytic oxidation for treatment, and a small part of the concentrated water is discharged. Moreover, the electrocatalytic oxidation part is connected to the evaporation crystallization part, which is used to treat most of the evaporation mother liquor generated by evaporation crystallization and further degrade the organic matter in the evaporation mother liquor.

[0048] Please refer to Figure 2 and Figure 3 , Figure 2 is the graph of the flux of the 50 nm ceramic membrane and the 4 nm small pore size ceramic membrane of the present invention changing with time. Figure 3 is the graph of the flux of the nanofiltration membrane and the temperature of the present invention changing with time. The experimental method for the present invention is as follows:

[0049] (1) Determination and optimization of potassium bromide purification process:

[0050] Example 1: Dissolve potassium bromide at a solid salt content of 30% (300 kg of salt + 700 L of pure water), and use the method of aeration + stirring for dissolution. After dissolution, let it stand for a period of time. Use a flotation machine to skim off the upper floating colloid and then filter bag, and directly evaporate and crystallize the clarified liquid. The purity of potassium bromide can reach 98.43%. The purity is greatly affected by the impurities in the potassium bromide solid salt. Therefore, it is necessary to consider removing the impurities (mainly suspended impurities and alkalinity) in the solid salt.

[0051] Example 2: Dissolve potassium bromide at a solid salt content of 30% (300 kg of salt + 700 L of pure water), and use the method of aeration + stirring for dissolution. After dissolution, let it stand for a period of time. Use a flotation machine to skim off the upper floating colloid and then filter bag, and then filter through a 50 nm ceramic membrane device. Adjust the pH to 7.0 with 40% hydrobromic acid, and the dosage of hydrobromic acid is 32.26 kg / m 3 . According to the experimental results, after adjusting the pH back to about 7, the alkalinity (the sum of CO 3 2- and HCO 3 - in the water) is still about 14000 mg / L. At this time, the purity of potassium bromide after evaporation and crystallization of the ceramic membrane clarified liquid is 98.54%. After adding the ceramic membrane process, the suspended impurities in the water are effectively removed. After adding hydrobromic acid, part of the alkalinity in the water is reduced. However, at this time, there is still some alkalinity in the water that affects the purity of potassium bromide, and the dosage of potassium bromide is relatively high. Considering the economy, consider the feasibility of using the nanofiltration membrane process to remove alkalinity.

[0052] Example 3: Dissolve potassium bromide at a solid salt content of 30% (300 kg of salt + 700 L of pure water), and use the method of aeration + stirring for dissolution. After dissolution, let it stand for a period of time. Use a flotation machine to skim off the upper floating colloid and then filter bag, and then pass through a 50 nm ceramic membrane device. The ceramic membrane clarified liquid passes through a nanofiltration membrane device to further remove the alkalinity in the water. For the nanofiltration product water, adjust the pH of the nanofiltration clarified liquid to 7.0 with 40% hydrobromic acid, and the dosage of hydrobromic acid is 13.08 kg / m 3 . The purity of potassium bromide after evaporation and crystallization of the nanofiltration membrane clarified liquid is 99.2%.

[0053] Example 4: Dissolve potassium bromide at a solid salt content of 30% (300 kg of salt + 700 L of pure water), and use the method of aeration + stirring for dissolution. After the reaction, let it stand for a period of time. Use a flotation machine to skim off the upper floating colloid and then add hydrobromic acid to adjust the pH to about 4.2, and the dosage of hydrobromic acid is 50.12 kg / m 3 , remove carbon and then filter bag, and the clarified liquid passes through a ceramic membrane. After the ceramic membrane clarified liquid is adjusted to pH 7.0, it is evaporated and crystallized. The purity of potassium bromide in the ceramic membrane clarified liquid is 99.5%.

[0054] (2) 0.5 m 2 Continuous experiment of ceramic membrane:

[0055] In the experimental part of the ceramic membrane, the interception effect of ceramic membranes with pore sizes of 50 nm and 4 nm on COD in wastewater and the change of membrane flux were investigated under the same conditions. The removal effect of ceramic membranes with different pore sizes on COD is shown in Table 1. The test results show that the 4-nm small-pore ceramic membrane has a better removal effect on COD. In the potassium bromide purification process, the original water COD is about 44,400 mg / L. After treatment through processes such as acid adjustment, skimmed glue, and filter bag, the COD content of the ceramic membrane inlet water is about 48,600 mg / L. The experimental results show that the interception rate of the 4-nm ceramic membrane on COD is about 50.4%. Under the test conditions of an inlet membrane pressure of 3 bar and a reflux rate of 3.0 m 3 / h, the relationship between the operating flux of ceramic membranes with different pore sizes and time is as Figure 2 shown. The total test time is 5500 min, and the experimental temperature is 30°C. Under this experimental condition, the average flux of the 4-nm ceramic membrane is 75.2 LMH, and the produced water turbidity is <0.3 NTU; the average flux of the 50-nm ceramic membrane is 75.2 LMH, and the produced water turbidity is <0.3 NTU.

[0056] Table 1 Experimental exploration of the removal effect of ceramic membranes with different pore sizes on COD

[0057]

[0058]

[0059] According to the comparison experiment results of ceramic membranes with different pore sizes, this process preferably selects the 4-nm small-pore ceramic membrane for experiments. The average flux of the 4-nm small-pore ceramic membrane is better than that of the 50-nm ceramic membrane. During the operation process, the flux remains stable without attenuation. The 4-nm ceramic membrane has a high removal rate of COD, effectively improving the purity of the potassium bromide salt obtained in the subsequent evaporation and crystallization part, and has high economic value.

[0060] (3) Continuous experiment of nanofiltration membrane:

[0061] The nanofiltration membrane selected is Jiuwu NF1-4040 for pilot-scale tests. Under the test conditions of an inlet membrane pressure of 15 bar and a temperature of 25°C, the relationship between the operating flux of the nanofiltration membrane and temperature and time is as Figure 3 shown. The total test time is 4430 min. Under this experimental condition, the flux of the nanofiltration membrane can be maintained stable for a long time, which is 9 LMH.

[0062] (4) Comparison of the purity of potassium bromide obtained from each experimental route:

[0063] The potassium bromide in Example 4 has the highest purity, which is 99.5%. Followed by Example 3, and the purity of potassium bromide in Example 3 is 99.2%. The product purities of Example 3 and Example 4 are higher than those of Example 1 and Example 2.

[0064] (5) Comparison of operation costs for each experimental route:

[0065] The operation costs mainly include dissolution (water intake cost), skimming (operation cost of air flotation process), filter bag (replacing 2 per cubic meter), ceramic membrane (electricity cost + membrane cleaning cost), nanofiltration membrane (electricity cost + membrane replacement cost: replaced once a week), and pH adjustment reagent cost (hydrobromic acid and potassium hydroxide). The evaporation cost is not included. The comparison of operation costs for different experimental routes is shown in the following table:

[0066] Table 2 Comparison of operation costs for each experimental route

[0067]

[0068] For Example 3 and Example 4, the operation cost of Example 3 is the lowest, which is 542.2 yuan per cubic meter, and the operation cost of Example 4 is the highest, which is 715.78 yuan per cubic meter. In Example 3: Although the operation cost is relatively low, it is found during the experiment that the flux of the nanofiltration membrane is low. Under the same water volume condition, more membranes are used, and more membrane usage will lead to an increase in the one-time cost. Secondly, the fouling rate of the nanofiltration membrane is fast. The fouled nanofiltration membrane in this process cannot be effectively cleaned, and poor membrane cleaning effect will lead to frequent membrane replacement, increasing the operation cost. It is found in the experiment that the membrane performance of the nanofiltration membrane can hardly be maintained for continued use after only one week, and membrane replacement needs to be considered. Finally, the overall process of Example 3 is relatively complex.

[0069] For Example 4, there is a shortage of high operation cost, but its process is relatively simple, the operation difficulty is relatively low, and the product purity is the highest. Considering various reasons, Example 4 is the best choice. The purity of potassium bromide produced in Example 4 can reach 99.5%, meeting the purity standard.

[0070] Using a method for purifying by - products of pesticide production of the present invention, first, the by - product potassium bromide solid salt of synthetic pesticide is dissolved with pure water at a content of 20% - 50%; during the dissolution process, hydrobromic acid is added to adjust the pH to 3.5 - 5 to remove carbonate and bicarbonate in water; after the reaction is complete, aeration is stopped, and after standing for a period of time, the floating colloid is skimmed off by a flotation machine and then coarsely filtered with a filter bag, and then passed through a ceramic membrane to remove fine impurities in water; the concentrated water of the ceramic membrane is subjected to coagulation precipitation, and the supernatant after coagulation precipitation is taken for electrochemical experiments to remove COD; the effluent of electro - catalytic oxidation returns to the ceramic membrane part for further treatment; the clear liquid of the ceramic membrane is adjusted to a pH of 7 - 8 with potassium hydroxide and then subjected to evaporation crystallization. In this way, the technical problems in the prior art are solved, that is, during the process of condensation to produce difenoconazole, the separation of the by - product potassium bromide is difficult, the resource waste is serious, the purity is low, the separation and purification cost is relatively high, and at the same time, a large amount of wastewater is generated and difficult to treat.

[0071] (6) Removal of COD from the concentrated water of the ceramic membrane

[0072] Coagulant (PAC) and flocculant (PAM) are added to the concentrated water of the ceramic membrane. By enabling the particles that are difficult to precipitate in water to aggregate with each other to form colloidal flocs and accompanied by an adsorption effect, impurity removal is achieved, and part of the organic pollutants are removed by sludge discharge. The COD removal rate can reach 5 - 10%, and the concentration of suspended particulate matter can be effectively reduced, reducing the load of the subsequent advanced oxidation part.

[0073] 1. Removal of COD from the concentrated water of the ceramic membrane

[0074] The removal effects of iron - carbon, Fenton, ozone and their combined processes and electro - catalytic oxidation + AAO process on COD in the concentrated water of the ceramic membrane generated in the potassium bromide purification process were explored. The removal effects of different processes on COD are shown in Table 3. The test results show that the electro - catalytic oxidation + AAO process has the best removal effect on COD. The original water COD in the potassium bromide purification process is about 44400 mg / L. After treatment through processes such as acid adjustment, skimming of colloid, filter bag, and ceramic membrane, the COD content of the concentrated water of the ceramic membrane is about 63374.4 mg / L. The concentrated water of the ceramic membrane is respectively taken for iron - carbon micro - electrolysis, Fenton oxidation, ozone and their combined processes and electro - catalytic oxidation experiments. The experimental results show that electro - catalytic oxidation can reduce the water sample COD from 63374.4 to 1330.9 mg / L, and the removal rate is 97.9%.

[0075] Table 3 Exploration experiment on the removal effect of different processes on COD

[0076]

[0077]

[0078] The COD removal rate of the effluent from electrocatalytic oxidation is as high as 97.9%, and the effluent can be returned to the ceramic membrane treatment section in front,

[0079] improve the recovery and utilization rate of potassium bromide salt, and achieve the effect of emission reduction, with high economic and social benefits.

[0080] 2. Operating results of the combined biochemical process:

[0081] Under the conditions of influent COD of 44400 mg / L, total nitrogen of 90 mg / L, ammonia nitrogen of 30 mg / L, and TP of 35 mg / L, a 20-day pilot test was carried out through the combined process of dissolution, air flotation, filter bag, ceramic membrane, coagulation sedimentation, electrocatalytic oxidation, and evaporation crystallization. After each data reached the standard, it was stably operated for 20 days, and the finally produced potassium bromide salt met the purity requirements.

[0082] 3. Estimation of operating costs:

[0083] The estimation of operating costs is shown in the following table, where the electricity cost is calculated at 0.75 yuan per degree, and the sludge moisture content is calculated at 80%.

[0084] Table 4 Estimation of operating costs

[0085]

[0086] About 450 kg of potassium bromide with a purity of 99.2% can be obtained per day by the present invention. Calculated at the market price of potassium bromide of 25000 yuan / ton, the economic benefit of 450 kg of potassium bromide is about 11250 yuan. After removing the operating costs, the net income is 10202.4 yuan, and the annual net income is 3.067 million yuan.

[0087] In summary, by adopting the combined process of dissolution → air flotation + acid adjustment → filter bag + ceramic membrane + coagulation + electrocatalytic oxidation → alkali adjustment → evaporation crystallization, the purity of potassium bromide can be increased to 99.5%. And the concentrated water of the ceramic membrane is returned to the ceramic membrane for further solid-liquid separation after electrocatalytic oxidation treatment, and the evaporation crystallization mother liquor enters the electrocatalytic oxidation part to further remove COD. Both improve the recovery and utilization rate of potassium bromide salt and achieve the effect of emission reduction, with high economic and social value.

[0088] (2) The cumulative time of the ceramic membrane experiment is 5500 min, the average temperature is 30 °C, and the average flux of the 4 nm small pore diameter ceramic membrane is better than that of the 50 nm ceramic membrane. The flux remains stable during the operation process without attenuation. The 4 nm ceramic membrane has a high COD removal rate, effectively improving the purity of the potassium bromide salt obtained in the subsequent evaporation crystallization part, with high economic value.

[0089] (3) The daily operating cost of the present invention is 1,047.6 yuan per day, and the annual income is 3.067 million yuan. The process package can not only effectively remove toxic and harmful environmental pollutants such as COD, but also improve the purity of the by-product potassium bromide in the pesticide production process, with high economic and social benefits.

[0090] The beneficial effects of the present invention are as follows:

[0091] 1. Compared with the known purification processes in the prior art, the purification process of the by-product potassium bromide in the difenoconazole disclosed in the present invention has a high product purity, simple process steps, and strong controllability of separation and purification;

[0092] 2. The treatment process of the wastewater generated during the purification of potassium bromide in the present invention effectively removes COD in the wastewater, improves the salt utilization rate, reduces environmental pollution, and improves the wastewater utilization rate;

[0093] 3. The overall yield of the method of the present invention is high, the process is simple, the process flow is short, and it is easy to realize industrialization.

[0094] The above-disclosed is only a preferred embodiment of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A method for purifying by-product salts from pesticide production, characterized in that: The steps include: Step 1: Dissolve the solid potassium bromide salt, a byproduct of synthetic pesticides, in pure water at a content of 20%-50%; Step 2: During the dissolution process, hydrobromic acid is added to adjust the pH to 3.5-5 to remove carbonate and bicarbonate in the water; Step 3: After the reaction is complete, stop aeration and let it stand. Then use an air flotation machine to skim off the floating glue and then use a filter bag for coarse filtration. Then pass it through a ceramic membrane to remove fine impurities in the water. Step 4: The ceramic membrane concentrated water is coagulated and precipitated, and the supernatant after coagulation and precipitation is taken for electrochemical experiment to remove COD; Step 5: The effluent from the electrocatalytic oxidation is returned to the ceramic membrane for further treatment; Step 6: Adjust the pH of the ceramic membrane clear solution to 7-8 with potassium hydroxide and then evaporate and crystallize.

2. The method for purifying by-product salts from pesticide production according to claim 1, characterized in that: In step 1, when the solid salt of potassium bromide, a byproduct of synthetic pesticides, is dissolved in pure water at a content of 20%-50%, the dissolution method is aeration combined with stirring, and the dissolution time is 60-90 minutes.

3. The method for purifying by-product salts from pesticide production as claimed in claim 2, characterized in that: In step 2, the concentration of hydrobromic acid added during the dissolution process is less than or equal to 40%.

4. The method for purifying by-product salts from pesticide production as claimed in claim 3, characterized in that: In step three, when using filter bags for coarse filtration, larger impurities in the water can be removed. After the larger impurities are removed, the water passes through the ceramic membrane to remove fine impurities in the water, thereby reducing the operating load of the ceramic membrane and improving the flux stability of the ceramic membrane.

5. The method for purifying by-product salts from pesticide production as claimed in claim 4, characterized in that: In step three, the ceramic membrane used to remove fine impurities in water is a ceramic tubular membrane element with a pore size of 4-50nm.

6. The method for purifying by-product salts produced during pesticide production according to claim 5, characterized in that: In step 4, the ceramic membrane concentrate is coagulated and precipitated by using a coagulant combined with a coagulant aid.

7. The method for purifying by-product salts from pesticide production according to claim 6, characterized in that: In step five, the ceramic membrane treatment part is connected to the electrocatalytic oxidation part to treat the effluent from the electrocatalytic oxidation part and further perform solid-liquid separation on the wastewater.

8. The method for purifying by-product salts from pesticide production as claimed in claim 7, characterized in that: In step six, part of the concentrated water produced by evaporation and crystallization enters the electrocatalytic oxidation for treatment, and the other part of the concentrated water is discharged. The electrocatalytic oxidation part is connected to the evaporation and crystallization part to treat most of the evaporation mother liquor produced by evaporation and crystallization, and further degrade the organic matter in the evaporation mother liquor.

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