Treatment method for wastewater containing 2,5-dichloronitrobenzene

Abstract

The present application relates to the treatment method containing 2,5-dichloronitrobenzene wastewater, including the recovery step of 2,5-dichloronitrobenzene, including: in containing 2,5-dichloronitrobenzene wastewater, sodium hydroxide is added for the first time, heated to reflux, reacted 8-10h, sodium hydroxide is added for the second time, reacted 2-4h, regulated ph to be 3.5-4.5, gradient cooling, centrifugation, drying, and obtaining 4-chloro-2-nitrophenols. Also included are the removal steps of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenols in wastewater. Using the treatment method containing 2,5-dichloronitrobenzene wastewater provided by the application, 2,5-dichloronitrobenzene is converted into 4-chloro-2-nitrophenol and then recovered with a high recovery rate, and after treatment, the wastewater contains no or almost no 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol, and the wastewater ph is within the range of 7-9, which is weakly alkaline.

Description

Technical Field

[0001] The patent of this invention relates to a wastewater treatment process, specifically to a method for treating wastewater containing 2,5-dichloronitrobenzene. Background Art

[0002] At present, the domestic production of 2,5-dichloronitrobenzene mainly adopts the mixed acid nitration of p-dichlorobenzene, and the product is obtained through oleic acid separation, alkaline washing, water washing and distillation. A large amount of wastewater is generated in the process. The wastewater contains p-dichlorobenzene, 2,5-dichloronitrobenzene, phenol salts (such as sodium nitrochlorophenol, sodium dinitrochlorophenol, etc.), etc., with the characteristics of high COD concentration and difficulty in biodegradation, which seriously pollutes the environment.

[0003] Regarding the treatment of 2,5-dichloronitrobenzene wastewater, Chinese patent publication number CN101597116A discloses a 2,5-dichloronitrobenzene wastewater treatment process, which uses catalytic micro-electrolysis, catalytic oxidation, activated carbon adsorption, and other methods to reduce the color, COD, and characteristic pollutant content of the wastewater, thereby achieving standard discharge of the wastewater. However, the process involves many steps, and 2,5-dichloronitrobenzene cannot be recycled. In addition, difficult-to-treat iron sludge is generated during the micro-electrolysis and Fenton oxidation process, causing secondary pollution.

[0004] At the same time, 2,5-dichloronitrobenzene and its analogues are important chemical intermediates and are widely used in the pesticide, dye and other industries. Therefore, they have utilization value.

[0005] Therefore, it is necessary to provide a method for treating nitrobenzene-containing wastewater that can recycle 2,5-dichloronitrobenzene and does not cause secondary pollution. Summary of the Invention

[0006] The present invention aims to solve at least one of the problems of the prior art. Thus, the present invention provides a method for treating wastewater containing 2,5-dichloronitrobenzene, comprising a step of recovering 2,5-dichloronitrobenzene. The step of recovering 2,5-dichloronitrobenzene comprises:

[0007] In wastewater containing 2,5-dichloronitrobenzene, sodium hydroxide is added for the first time, heated to reflux, and reacted for 8-10 hours. Sodium hydroxide is added for the second time, reacted for 2-4 hours, the pH is adjusted to 3.5-4.5, the temperature is gradually lowered, centrifuged, and dried to obtain 4-chloro-2-nitrophenol;

[0008] The molar ratio of the sodium hydroxide added for the first time to the 2,5-dichloronitrobenzene is (0.9-1.2):1, the molar ratio of the sodium hydroxide added for the second time to the 2,5-dichloronitrobenzene is (3-4.5):1, and the molar amount of the sodium hydroxide added for the second time is 3-4 times the molar amount of the sodium hydroxide added for the first time.

[0009] The reaction process is shown as follows:

[0010]

[0011] The present application adjusts the process of the recovery step of 2,5-dichloronitrobenzene, specifically including: adjusting the recovery step of the 2,5-dichloronitrobenzene, the molar ratio of the second addition of sodium hydroxide to 2,5-dichloronitrobenzene, the ratio of the molar amount of the second addition of sodium hydroxide to the molar amount of the first addition of sodium hydroxide, the crystallization pH, etc., which can effectively improve the conversion rate of 2,5-dichloronitrobenzene to 4-chloro-2-nitrophenol. Specifically, the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol and then recovered can reach more than 95%, even more than 96%, or more than 97%. The purity of the recovered 4-chloro-2-nitrophenol is more than 99%.

[0012] In a specific embodiment, the molar ratio of the first added sodium hydroxide to the 2,5-dichloronitrobenzene can be 0.9:1, 1.0:1, 1.1:1, or 1.2:1.

[0013] In a specific embodiment, the molar ratio of the first added sodium hydroxide to the 2,5-dichloronitrobenzene can be (0.9-1.0):1, (1.0-1.1):1, or (1.1-1.2):1.

[0014] In a specific embodiment, the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added for the second time can be 3:1, 3.5:1, 4:1, or 4.5:1.

[0015] In a specific embodiment, the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added for the second time can be (3-3.5):1, (3.5-4):1, or (4-4.5):1.

[0016] In a specific embodiment, the molar amount of sodium hydroxide added for the second time can be 3 times, 3.3 times, 3.5 times, 3.6 times, or 3.75 times the molar amount of sodium hydroxide added for the first time.

[0017] In a specific embodiment, the pH can be adjusted to 3.5, 4, or 4.5 during crystallization.

[0018] In a specific embodiment, the pH during crystallization can be adjusted to 3.5-4 or 4-4.5.

[0019] Preferably, the gradient cooling is the first cooling to 58-62 degrees Celsius, stirring for 0.5-1 hour, then the second cooling to 48-52 degrees Celsius, stirring for 0.5-1 hour, and finally the third cooling to 38-42 degrees Celsius, stirring for 0.5-1 hour.

[0020] Through the gradient cooling and the recovery step of 2,5-dichloronitrobenzene, the cumulative conversion amount of 2,5-dichloronitrobenzene into 4-chloro-2-nitrophenol is greater.

[0021] In a specific embodiment, the first cooling of the gradient cooling can be to 58 degrees Celsius, 59 degrees Celsius, 60 degrees Celsius, 61 degrees Celsius, or 62 degrees Celsius.

[0022] In a specific embodiment, the first temperature reduction of the gradient cooling can be to 58-60 degrees Celsius or 60-62 degrees Celsius.

[0023] In a specific embodiment, the second cooling of the gradient cooling can be cooled to 48 degrees Celsius, 49 degrees Celsius, 50 degrees Celsius, 51 degrees Celsius, and 52 degrees Celsius.

[0024] In a specific embodiment, the second cooling of the gradient cooling can be to 48-50 degrees Celsius or 50-52 degrees Celsius.

[0025] In a specific embodiment, the third cooling step of the gradient cooling can be to 38 degrees Celsius, 39 degrees Celsius, 40 degrees Celsius, 41 degrees Celsius, and 42 degrees Celsius.

[0026] In a specific embodiment, the third cooling of the gradient cooling can be to 38-40 degrees Celsius or 40-42 degrees Celsius.

[0027] Furthermore, the inventors discovered that adding sodium sulfite during the recovery step can increase the conversion of 2,5-dichloronitrobenzene to 4-chloro-2-nitrophenol, thereby improving the recovery rate. By adding a certain amount of sodium sulfite at a specific time during the recovery step, the recovery rate of 2,5-dichloronitrobenzene to 4-chloro-2-nitrophenol can reach over 98%, or even over 99%, and the purity of the recovered 4-chloro-2-nitrophenol is over 99%.

[0028] Preferably, sodium sulfite is added after the first cooling of the gradient cooling and before the second cooling.

[0029] More preferably, the mass volume ratio of sodium sulfite to water is controlled to be (1.5-2.5) g:100 mL.

[0030] In a specific embodiment, the mass volume ratio of sodium sulfite to water can be controlled to be 1.5g:100mL, 2g:100mL, or 2.5g:100mL.

[0031] In a specific embodiment, the mass volume ratio of sodium sulfite to water can be controlled to (1.5-2) g:100 mL or (2-2.5) g:100 mL.

[0032] After 2,5-dichloronitrobenzene in the wastewater is converted and recovered, the centrifuged mother liquor in the recovery step still contains 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol and cannot be discharged directly.

[0033] Advanced oxidation technology (ADT) utilizes highly oxidizing species (such as hydroxyl radicals and sulfate radicals) generated during the reaction to oxidize, decompose, and mineralize organic matter and its intermediates in water. Due to the high efficiency and selectivity of sulfate radicals for the removal of recalcitrant organic pollutants, sulfate radicals have a higher redox potential (2.5-3.1 eV) than the hydroxyl radicals (redox potential 1.8-2.7 eV) widely used in traditional ADT. Compared to hydroxyl radicals, sulfate radicals have a better degradation effect on pollutants over a wider pH range. Persulfate-based ADT offers advantages such as stable oxidants, strong oxidizing capacity of the sulfate radicals generated, minimal pH dependence, high oxidant utilization, and non-toxicity.

[0034] Advanced oxidation technology mainly produces free radicals through different pathways. These free radicals can react with difficult-to-degrade pollutants in wastewater through substitution, electrophilic addition, electron transfer, ring opening, bond breaking, etc., causing them to be oxidized and degraded into low-toxic, low-harm and easily biodegradable intermediates, or even directly degraded into water, carbon dioxide and inorganic ions.

[0035] Traditional advanced oxidation technology mainly uses hydroxyl radicals (HO·) as active species to degrade pollutants. However, the latest research has found that sulfate radicals (SO4·-) with a lone pair of electrons have a wider pH value applicability range and a higher oxidation potential than HO·. In theory, they can oxidize more types of organic pollutants and can oxidize and degrade organic pollutants under alkaline conditions.

[0036] Currently, sulfate radicals (SO₄·-) are primarily generated through the reaction of potassium persulfate and potassium peroxymonosulfate. However, using these two oxidants requires a very high oxidant-to-catalyst ratio (generally greater than 100) to achieve effective results, resulting in high costs. Therefore, improvements are needed to generate sulfoxide radicals. A subsequently proposed process using an Fe-sulfite system to generate sulfate radicals can only degrade organic matter in slightly acidic conditions.

[0037] This application uses a colloidal copper hydroxide-sulfite reaction to generate sulfoxide free radicals to further remove 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol from the centrifuged mother liquor after the recovery step. This process eliminates the need for the addition of oxidants or catalysts, is simple to operate, offers high oxidation efficiency, and is rapid. Furthermore, it can remove organic matter under anoxic conditions. The treated wastewater contains virtually no 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol, and has a weakly alkaline pH range of 7-9, requiring no further treatment.

[0038] Thus, further, after the recovery step of the 2,5-dichloronitrobenzene, a step of removing the 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the wastewater is also included, and the removal step comprises:

[0039] Step 1): Prepare a CuCl2 aqueous solution, add sodium alginate, and adjust the pH to 10-11 with sodium hydroxide solution while stirring to obtain a sol;

[0040] Step 2): preparing a sodium alginate aqueous solution, placing zeolite into the sodium alginate aqueous solution, stirring, filtering, and drying to obtain surface-treated zeolite, and adding the surface-treated zeolite to the sol obtained in step 1) to obtain a mixed solution;

[0041] Step 3): Add the mixed solution obtained in step 2) to the mother liquor obtained after centrifugation in the recovery step of 2,5-dichloronitrobenzene to control the Cu 2+ The concentration of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water was determined.

[0042] The inventors adjusted the steps for removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol from wastewater by controlling the CuCl2 concentration, the sodium alginate concentration, the mass ratio of sodium alginate to zeolite in step 2), the mass volume ratio of the surface-treated zeolite to the mixed solution in step 2), and the pH value in step 3), thereby effectively removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol.

[0043] The inventors discovered through experiments that the addition of sodium alginate and zeolite can enhance the stability of copper hydroxide in weakly alkaline conditions. This may be because sodium alginate also forms a sol, and the sodium alginate sol forms a thin layer or semi-encapsulation with the Cu(OH)2 sol. The surface of the surface-treated zeolite has a certain amount of sodium alginate. When the surface-treated zeolite is placed in the sol, the thin layer or semi-encapsulation of the sodium alginate sol and the Cu(OH)2 sol tends to bind to the zeolite with a certain amount of sodium alginate on its surface under stirring. In this way, the Cu(OH)2 molecules are not completely exposed to the weakly alkaline solution. Therefore, they can exist stably in an environment of pH 7-9 for a short period of time.

[0044] Preferably, the concentration of sodium alginate in the sol in step 1) is the same as the concentration of sodium alginate in the sodium alginate aqueous solution in step 2), and the concentration of sodium alginate in the sol in step 1) is 2-8 g / L.

[0045] In a specific embodiment, the concentration of sodium alginate in the sol in step 1) is 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, or 8 g / L.

[0046] In a specific embodiment, the concentration of sodium alginate in the sol in step 1) is 2-3 g / L, 3-5 g / L, or 5-8 g / L.

[0047] In a specific embodiment, the concentration of sodium alginate in the sodium alginate aqueous solution in step 2) is 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, or 8 g / L.

[0048] In a specific embodiment, the concentration of sodium alginate in the sodium alginate aqueous solution in step 2) is 2-3 g / L, 3-5 g / L, or 5-8 g / L.

[0049] Preferably, in step 1), the concentration of the CuCl2 aqueous solution is 80-150 mM.

[0050] In a specific embodiment, in step 1), the concentration of the CuCl2 aqueous solution can be 80mM, 90mM, 100mM, 110mM, 120mM, 130mM, 140mM, or 150mM.

[0051] In a specific embodiment, in step 1), the concentration of the CuCl2 aqueous solution can be 80-100 mM, 100-120 mM, or 120-150 mM.

[0052] Preferably, in step 2), the weight ratio of sodium alginate to zeolite is 1:(10-16).

[0053] In a specific embodiment, in step 2), the mass ratio of sodium alginate to zeolite can be 1:10, 1:12, 1:14, or 1:16.

[0054] In a specific embodiment, in step 2), the mass ratio of sodium alginate to zeolite can be 1:(10-12), 1:(12-14), or 1:(14-16).

[0055] Preferably, in step 2), the mass volume ratio of the surface-treated zeolite to the mixed solution is (5-8) g:100 mL.

[0056] In a specific embodiment, the mass volume ratio of the surface-treated zeolite to the mixed liquid is 5g:100mL, 6g:100mL, 7g:100mL, or 8g:100mL.

[0057] In a specific embodiment, the mass volume ratio of the surface-treated zeolite to the mixed liquid is 5-6 g:100 mL, 6-7 g:100 mL, or 7-8 g:100 mL.

[0058] Preferably, in step 3), the pH is adjusted to 7-8.5.

[0059] In a specific embodiment, the pH can be adjusted to 7, 7.5, 8, or 8.5.

[0060] In a specific embodiment, the pH can be adjusted to 7-7.5, 7.5-8, 8-8.5, 8.5-9.

[0061] In summary, the method for treating wastewater containing 2,5-dichloronitrobenzene provided in this application has the following beneficial effects:

[0062] 1. The method for treating wastewater containing 2,5-dichloronitrobenzene provided in the present application can convert 2,5-dichloronitrobenzene into 4-chloro-2-nitrophenol, efficiently recycle and utilize useful resources, and be green and economical. Specifically, the recovery rate of 2,5-dichloronitrobenzene converted into 4-chloro-2-nitrophenol and then recovered can reach more than 95%, or even more than 96%, more than 97%, more than 98%, or more than 99%, and the purity of the recovered 4-chloro-2-nitrophenol is more than 99%.

[0063] 2. The method for treating wastewater containing 2,5-dichloronitrobenzene provided in this application uses a colloidal copper hydroxide-sulfite reaction to generate sulfoxide free radicals to further remove 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol contained in the centrifuged mother liquor of the recovery step. No oxidant or catalyst needs to be added, the operation is simple, the oxidation efficiency is high, and the speed is fast. After treatment, the wastewater contains no or almost no 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol.

[0064] 3. Sodium alginate and zeolite are further added to the colloidal copper hydroxide-sulfite system of the present application. The addition of sodium alginate and zeolite can improve the stability of copper hydroxide under weak alkalinity. After removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol contained in the centrifugal mother liquor in the recovery step, the pH of the wastewater is in the range of 7-9, which is weakly alkaline and does not require further treatment. DETAILED DESCRIPTION

[0065] The invention provides a method for recycling 2,5-dichloronitrobenzene and a method for removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol.

[0066] The present invention provides a method for treating wastewater containing 2,5-dichloronitrobenzene, comprising a step of recovering 2,5-dichloronitrobenzene. The step of recovering 2,5-dichloronitrobenzene comprises:

[0067] In wastewater containing 2,5-dichloronitrobenzene, sodium hydroxide is added for the first time, heated to reflux, and reacted for 8-10 hours. Sodium hydroxide is added for the second time, reacted for 2-4 hours, the pH is adjusted to 3.5-4.5, the temperature is gradually lowered, centrifuged, and dried to obtain 4-chloro-2-nitrophenol;

[0068] The molar ratio of the sodium hydroxide added for the first time to the 2,5-dichloronitrobenzene is (0.9-1.2):1, the molar ratio of the sodium hydroxide added for the second time to the 2,5-dichloronitrobenzene is (3-4.5):1, and the molar amount of the sodium hydroxide added for the second time is 3-4 times the molar amount of the sodium hydroxide added for the first time.

[0069] Preferably, the gradient cooling is the first cooling to 58-62 degrees Celsius, stirring for 0.5-1 hour, then the second cooling to 48-52 degrees Celsius, stirring for 0.5-1 hour, and finally the third cooling to 38-42 degrees Celsius, stirring for 0.5-1 hour.

[0070] Furthermore, sodium sulfite is added after the first cooling of the gradient cooling and before the second cooling.

[0071] Furthermore, the mass volume ratio of sodium sulfite to water is controlled to be (1.5-2.5) g:100 mL.

[0072] The method for treating wastewater containing nitrobenzene substances provided by the present invention further includes, after the 2,5-dichloronitrobenzene recovery step, a step of removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the wastewater, wherein the removal step includes:

[0073] Step 1): Prepare a CuCl2 aqueous solution, add sodium alginate, and adjust the pH to 10-11 with sodium hydroxide solution while stirring to obtain a sol;

[0074] Step 2): preparing a sodium alginate aqueous solution, placing zeolite into the sodium alginate aqueous solution, stirring, filtering, and drying to obtain surface-treated zeolite, and adding the surface-treated zeolite to the sol obtained in step 1) to obtain a mixed solution;

[0075] Step 3): Add the mixed solution obtained in step 2) to the mother liquor obtained after centrifugation in the recovery step of 2,5-dichloronitrobenzene to control the Cu 2+The concentration of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water was determined.

[0076] Preferably, the concentration of sodium alginate in the sol in step 1) is the same as the concentration of sodium alginate in the sodium alginate aqueous solution in step 2), and the concentration of sodium alginate in the sol in step 1) is 2-8 g / L.

[0077] Furthermore, in step 1), the concentration of the CuCl2 aqueous solution is 80-150 mM.

[0078] Furthermore, in the step 2), the weight ratio of sodium alginate to zeolite is 1:(10-16).

[0079] Furthermore, in the step 2), the mass volume ratio of the surface-treated zeolite to the mixed solution is (5-8) g:100 mL.

[0080] Furthermore, in step 3), the pH is adjusted to 7-8.5.

[0081] The zeolite used in the embodiment is ferrierite, specifically ferrierite ZSM-35 (molecular sieve ZSM-35).

[0082] The present application is further described in detail below in conjunction with Examples 1-27 and Comparative Examples 1-6.

[0083] I. Recycling of 2,5-dichloronitrobenzene

[0084] The recycling and utilization of 2,5-dichloronitrobenzene of the present application will be further described in detail below in conjunction with Examples 1-13 and Comparative Examples 1-3.

[0085] Examples 1-8

[0086] A method for treating wastewater containing 2,5-dichloronitrobenzene, including a method for recycling 2,5-dichloronitrobenzene, wherein the specific steps of the recycling method are as follows:

[0087] Step 1): Take 1000 mL of water containing 30 g (0.156 mol) of 2,5-dichloronitrobenzene, add sodium hydroxide for the first time, heat to reflux, react for 8-10 hours, add sodium hydroxide for the second time, react for 2-4 hours, adjust the pH to 3.5-4.5 with hydrochloric acid, cool gradually, cool to 58-62 degrees Celsius for the first time, stir for 0.5-1 hour, then cool to 48-52 degrees Celsius for the second time, stir for 0.5-1 hour, and finally cool to 38-42 degrees Celsius for the third time, stir for 0.5-1 hour, centrifuge, and dry to obtain 4-chloro-2-nitrophenol.

[0088] The specific conditions of the method for recycling 2,5-dichloronitrobenzene in Examples 1-8 are shown in Table 1.

[0089] Table 1 Specific conditions of the recovery and utilization method of 2,5-dichloronitrobenzene in Examples 1-8

[0090]

[0091] Comparative Example 1

[0092] Comparative Example 1 provides a method for treating wastewater containing 2,5-dichloronitrobenzene, including a method for recycling 2,5-dichloronitrobenzene.

[0093] The only difference between Comparative Example 1 and Example 4 is that the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added for the first time is 1.5:1, and the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added for the second time is 2.5:1.

[0094] Comparative Example 2

[0095] Comparative Example 2 provides a method for treating wastewater containing 2,5-dichloronitrobenzene, including a method for recycling 2,5-dichloronitrobenzene.

[0096] The only difference between Comparative Example 2 and Example 4 is that the crystallization pH is 5.0.

[0097] Comparative Example 3

[0098] Comparative Example 3 provides a method for treating wastewater containing 2,5-dichloronitrobenzene, including a method for recycling 2,5-dichloronitrobenzene.

[0099] The only difference between Comparative Example 3 and Example 4 is that no gradient cooling is adopted, and the temperature is directly lowered to 40 degrees Celsius for crystallization.

[0100] Furthermore, the inventors added sodium sulfite to the reaction system and surprisingly found that it could improve the recovery efficiency to a certain extent. Examples 9-11 are based on Example 4, but sodium sulfite is added after the first cooling and before the second cooling.

[0101] Examples 9-11

[0102] Examples 9-11 respectively provide a method for recycling 2,5-dichloronitrobenzene, the only difference being that sodium sulfite is added after the first cooling and before the second cooling.

[0103] The difference between the above embodiments and embodiment 4 is that sodium sulfite is added after the first cooling and before the second cooling. The amount of sodium sulfite added is shown in Table 2.

[0104] Table 2 Amount of sodium sulfite added in the recovery and utilization method of 2,5-dichloronitrobenzene provided in Example 4 and Examples 9-11

[0105]

[0106]

[0107] In addition, the inventors have studied the timing of adding sodium sulfite, as shown in Examples 12 and 13.

[0108] Example 12

[0109] Example 12 provides a method for treating wastewater containing 2,5-dichloronitrobenzene, including a method for recovering and utilizing 2,5-dichloronitrobenzene.

[0110] The only difference between Example 12 and Example 10 is that sodium sulfite is added before the first cooling.

[0111] Example 13

[0112] Example 13 provides a method for treating wastewater containing 2,5-dichloronitrobenzene, including a method for recovering and utilizing 2,5-dichloronitrobenzene.

[0113] The only difference between Example 13 and Example 10 is that sodium sulfite is added after the second cooling and before the third cooling.

[0114] The mass m of 4-chloro-2-nitrophenol obtained after centrifugation and drying in step 1) of Example 1-13 and Comparative Example 1-3 was measured, and the recovery rate of 4-chloro-2-nitrophenol was calculated.

[0115] The recovery rate is calculated as follows:

[0116] Y = m / (173.57*0.15625);

[0117] Wherein, Y is the recovery rate, and m is the mass of 4-chloro-2-nitrophenol obtained after centrifugation and drying in step 1).

[0118] The recovery rate of 4-chloro-2-nitrophenol and the purity of 2,5-dichloronitrobenzene obtained after centrifugation in step 1) of Example 1-13 and Comparative Example 1-3 were tested, and the results are shown in Table 3 below.

[0119] Table 3 Recovery of 4-chloro-2-nitrophenol and purity test results of 2,5-dichloronitrobenzene obtained after centrifugation in step 1) of Example 1-13 and Comparative Example 1-3

[0120]

[0121]

[0122] According to the experimental results in the examples, when the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added for the first time is (0.9-1.2):1, the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added for the second time is (3-4.5):1, the molar amount of sodium hydroxide added for the second time is 3-4 times the molar amount of sodium hydroxide added for the first time, when the pH is 3.5-4.5, the first cooling temperature is 58-62°C, the second cooling temperature is 48-52°C, and the third cooling temperature is 38-42°C, the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol reaches 95% or more, and the purity of the recovered 4-chloro-2-nitrophenol reaches more than 99%.

[0123] Furthermore, when sodium sulfite is added during the cooling process, the mass volume ratio of sodium sulfite to water is (1.5-2.5) g:100 mL, and the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol reaches 95% or more, and the purity of the recovered 4-chloro-2-nitrophenol reaches 99% or more. When sodium sulfite is added during the second cooling process, the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol reaches 98.5% or more, and the purity of the recovered 4-chloro-2-nitrophenol reaches 99% or more.

[0124] Comparison of Examples 1-4 with Comparative Example 1 shows that when the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added in the first step is too high, and the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added in the second step is too low, with the ratio of the molar amount of sodium hydroxide added in the second step to the molar amount of sodium hydroxide added in the first step being less than 3, the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol is only 92.9%. This may be because the molar ratio of sodium hydroxide to 2,5-dichloronitrobenzene added in the first step is generally around 1:1 to ensure complete reaction. When the molar amount of sodium hydroxide added in the second step is too low, the 4-chloro-2-nitrophenol obtained in the reaction cannot be completely converted to its sodium salt, which is not conducive to further precipitation of 4-chloro-2-nitrophenol.

[0125] Comparison of Examples 4, 5, and 6 with Comparative Example 2 shows that when the pH is 5.0, the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol is only 93.0%, indicating that a high pH is not conducive to the complete precipitation of 4-chloro-2-nitrophenol.

[0126] Comparison of Example 4 with Comparative Example 3 shows that when the crystallization temperature is directly lowered to 40°C without a gradient cooling method, the recovery rate of 2,5-dichloronitrobenzene to 4-chloro-2-nitrophenol is only 91.5%, indicating that a gradient cooling method is more conducive to the precipitation of 4-chloro-2-nitrophenol.

[0127] A comparison of Examples 4, 9, 10, and 11 shows that the addition of sodium sulfite is beneficial to the precipitation of 4-chloro-2-nitrophenol. When the mass volume ratio of sodium sulfite to water is 2 g / 100 mL and 2.5 g / 100 mL, the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol is close to the purity data of 4-chloro-2-nitrophenol. Therefore, the most suitable mass volume ratio of sodium sulfite to water is 2 g / 100 mL.

[0128] Comparing Example 10 with Examples 12 and 13, it can be seen that when sodium sulfite was added before the first cooling step, the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol was only 96.2%. When sodium sulfite was added before the third cooling step, the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol was only 95.1%. Adding sodium sulfite before the second cooling step was more conducive to the precipitation of 4-chloro-2-nitrophenol, possibly because the key to crystallization lies in the second cooling step, and adding sodium sulfite before the second cooling step allows for better control of crystallization.

[0129] II. Removal of 2,5-dichloronitrobenzene and 2,5-dichloronitrobenzene from wastewater

[0130] The recycling and utilization of 2,5-dichloronitrobenzene of the present application will be further described in detail below in conjunction with Examples 14-26 and Comparative Example 4.

[0131] Examples 14-26

[0132] After 2,5-dichloronitrobenzene in wastewater is converted and recovered, the centrifugal mother liquor in the recovery step still contains 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol. The present invention further provides a method for completely removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol from the centrifugal mother liquor.

[0133] A method for treating wastewater containing 2,5-dichloronitrobenzene further includes a method for removing 2,5-dichloronitrobenzene and 2,5-dichloronitrobenzene. The specific steps of the removal method are as follows:

[0134] Step 2): Prepare a CuCl2 aqueous solution, add sodium alginate, and adjust the pH to 11 with sodium hydroxide solution while stirring to obtain a sol;

[0135] Step 3): preparing a sodium alginate aqueous solution, placing zeolite into the sodium alginate aqueous solution, stirring for 10 minutes, filtering, and drying to obtain a surface-treated zeolite, and adding the surface-treated zeolite to the sol obtained in step 2) to obtain a mixed solution;

[0136] Step 4): Add the mixed solution obtained in step 3) to 500 mL of the mother solution obtained after centrifugation in step 1) of Example 10 to control the Cu 2+ The concentration of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water was determined by adjusting the pH to 7-8.5, stirring for 1-2 hours, filtering, and then determining the concentrations of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water.

[0137] The concentration of sodium alginate in the sol in step 2) is the same as the concentration of sodium alginate in the sodium alginate aqueous solution in step 3).

[0138] The specific conditions of 2,5-dichloronitrobenzene and the removal method of 2,5-dichloronitrobenzene in Examples 14-26 are shown in Table 4.

[0139] Table 4 Specific conditions of 2,5-dichloronitrobenzene and the removal method of 2,5-dichloronitrobenzene in Examples 14-26

[0140]

[0141] Comparative Example 4

[0142] Comparative Example 4 provides a method for treating wastewater containing 2,5-dichloronitrobenzene, including a method for removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol.

[0143] The only difference between Comparative Example 4 and Example 15 is that step 3) is not included.

[0144] The details are as follows:

[0145] Step 2): Prepare a CuCl2 aqueous solution, add sodium alginate, and adjust the pH to 11 with sodium hydroxide solution while stirring to obtain a sol;

[0146] Step 3): Add the sol obtained in step 2) to 500 mL of the mother liquor obtained after centrifugation in step 1) of Example 10 to control the Cu 2+ The concentration of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water was determined by adjusting the pH to 8 and stirring for 1-2 hours.

[0147] The concentration of sodium alginate in the sol in step 2) is the same as the concentration of sodium alginate in the sodium alginate aqueous solution in step 3).

[0148] The test results of the concentrations of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water obtained after centrifugation in step 4) of the removal process provided in Examples 14-26 and Comparative Example 4 are shown in Table 5.

[0149] Table 5 Detection results of the concentrations of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water obtained after centrifugation in the removal process step 4) provided in Examples 14-26 and Comparative Example 4

[0150]

[0151] From the experimental results of Examples 14-26, it can be seen that when the CuCl2 concentration is 80-120M, the concentration of sodium alginate is 3-8 g / L, the weight ratio of sodium alginate to zeolite is 1:(10-14), the mass volume ratio of the surface-treated zeolite to the water body is 5-8 g / mL, and when the pH is adjusted to 7.5-8.5 in step 4), 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water body can be completely removed.

[0152] Comparison of Examples 15 and 18-20 shows that when the weight ratio of sodium alginate to zeolite is too small, 0.8 ppm of 2,5-dichloronitrobenzene remains in the wastewater. This may be because when there is too little sodium alginate sol, the Cu(OH)2 colloid cannot be fixed on the zeolite and the contact with the sulfite is not sufficient.

[0153] Comparison of Examples 15 and 21-23 shows that when the mass volume ratio of the surface-treated zeolite to the mixed solution in step 3) is too low, 2,5-dichloronitrobenzene remains in the wastewater.

[0154] From the comparison between Example 15 and Examples 24-26, it can be seen that when the pH value in step 4) is too low, it is not conducive to the removal of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water.

[0155] From the comparison between Example 15 and Comparative Example 4, it can be seen that when the zeolite surface-treated with sodium alginate is not added, 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol remain in the wastewater.

[0156] III. Experimental study on the effect of the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol on the complete removal of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in wastewater

[0157] Furthermore, the inventors selected Example 1, Comparative Example 2, and Comparative Example 3, and removed 2,5-dichloronitrobenzene and 2,5-dichloronitrobenzene from the mother liquor after centrifugation in step 1). The removal method and conditions were the same as those in Example 15.

[0158] Example 27

[0159] The mother liquor after centrifugation in step 1) of Example 1 was used to remove 2,5-dichloronitrobenzene and 2,5-dichloronitrobenzene, and sodium sulfite was added to the mother liquor to make the concentration of sodium sulfite 2g:100mL. The removal method and conditions were the same as those in Example 15.

[0160] Comparative Example 5

[0161] The mother liquor after centrifugation in step 1) of Comparative Example 2 was used to remove 2,5-dichloronitrobenzene and 2,5-dichloronitrobenzene, and sodium sulfite was added to the mother liquor to make the concentration of sodium sulfite 2g:100mL. The removal method and conditions were the same as those in Example 15.

[0162] Comparative Example 6

[0163] The mother liquor after centrifugation in step 1) of Comparative Example 3 was used to remove 2,5-dichloronitrobenzene and 2,5-dichloronitrobenzene, and sodium sulfite was added to the mother liquor to make the concentration of sodium sulfite 2g:100mL. The removal method and conditions were the same as those in Example 15.

[0164] The test results of the concentrations of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water obtained after centrifugation in the removal process step 4) provided in Examples 15, 27, and Comparative Examples 5 and 6 are shown in Table 6.

[0165] Table 6 Detection results of the concentrations of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water obtained after centrifugation in the removal process step 4) provided in Examples 15, 27, Comparative Examples 5 and 6

[0166]

[0167]

[0168] From the comparison of Examples 15 and 27 and Comparative Examples 5 and 6, it can be seen that when the 4-chloro-2-nitrophenol recovered by centrifugation in step 1) is too little, resulting in excessive 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the centrifugal mother liquor, 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the final wastewater cannot be completely removed. Specifically, when the recovery rate of 2,5-dichloronitrobenzene converted to 4-chloro-2-nitrophenol is above 95%, the method provided by the present invention is used. The method for removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol can completely remove 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol from wastewater. When the recovery rate of converting 2,5-dichloronitrobenzene to 4-chloro-2-nitrophenol is lower than 93%, the method for removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol provided by the present invention cannot completely remove 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol from wastewater.

[0169] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for treating wastewater containing 2,5-dichloronitrobenzene, characterized in that: The method comprises a step of recovering 2,5-dichloronitrobenzene, wherein the step of recovering 2,5-dichloronitrobenzene comprises: In wastewater containing 2,5-dichloronitrobenzene, sodium hydroxide is added for the first time, heated to reflux, and reacted for 8-10 hours. Sodium hydroxide is added for the second time, reacted for 2-4 hours, the pH is adjusted to 3.5-4.5, the temperature is gradually lowered, centrifuged, and dried to obtain 4-chloro-2-nitrophenol; The molar ratio of the sodium hydroxide added for the first time to the 2,5-dichloronitrobenzene is (0.9-1.2):1, the molar ratio of the sodium hydroxide added for the second time to the 2,5-dichloronitrobenzene is (3-4.5):1, and the molar amount of the sodium hydroxide added for the second time is 3-4 times the molar amount of the sodium hydroxide added for the first time; The gradient cooling is as follows: the first cooling is to 58-62 degrees Celsius, stirring for 0.5-1h, the second cooling is to 48-52 degrees Celsius, stirring for 0.5-1h, and the third cooling is to 38-42 degrees Celsius, stirring for 0.5-1h; After the first temperature drop of the gradient temperature drop and before the second temperature drop, sodium sulfite was added.

2. The method for treating wastewater containing 2,5-dichloronitrobenzene according to claim 1, wherein: The mass volume ratio of sodium sulfite to water was controlled to be (1.5-2.5) g:100 mL.

3. The method for treating wastewater containing 2,5-dichloronitrobenzene according to claim 1, wherein: After the 2,5-dichloronitrobenzene recovery step, the method further includes a step of removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol from the wastewater, wherein the step of removing 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol comprises: Step 1): Prepare a CuCl2 aqueous solution, add sodium alginate, and adjust the pH to 10-11 with sodium hydroxide solution while stirring to obtain a sol; Step 2): preparing a sodium alginate aqueous solution, placing zeolite into the sodium alginate aqueous solution, stirring, filtering, and drying to obtain surface-treated zeolite, and adding the surface-treated zeolite to the sol obtained in step 1) to obtain a mixed solution; Step 3): Add the mixed solution obtained in step 2) to the mother liquor obtained after centrifugation in the recovery step of 2,5-dichloronitrobenzene to control the Cu 2+ The concentration of 0.1 mM was adjusted to pH, stirred for 1-2 h, filtered, and the concentrations of 2,5-dichloronitrobenzene and 4-chloro-2-nitrophenol in the water were determined; In the step 3), the pH is adjusted to 7-8.

5.

4. The method for treating wastewater containing 2,5-dichloronitrobenzene according to claim 3, wherein: The concentration of sodium alginate in the sol in step 1) is the same as the concentration of sodium alginate in the sodium alginate aqueous solution in step 2), and the concentration of sodium alginate in the sol in step 1) is 2-8 g / L.

5. The method for treating wastewater containing 2,5-dichloronitrobenzene according to claim 3, wherein: In the step 1), the concentration of the CuCl2 aqueous solution is 80-150 mM.

6. The method for treating wastewater containing 2,5-dichloronitrobenzene according to claim 3, wherein: In the step 2), the weight ratio of sodium alginate to zeolite is 1:(10-16).

7. The method for treating wastewater containing 2,5-dichloronitrobenzene according to claim 3, wherein: In the step 2), the mass volume ratio of the surface-treated zeolite to the mixed solution is (5-8) g:100 mL.

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