A pretreatment method for acrylonitrile-containing wastewater

Abstract

The application discloses a pretreatment method of acrylonitrile-containing wastewater, which comprises the following steps: step 1, adding an initiator and a crosslinking agent into the acrylonitrile-containing wastewater to perform a crosslinking polymerization reaction; the reaction temperature is controlled to be 50-90 DEG C; step 2, adding acid into the wastewater after the reaction in step 1 to adjust the pH value to be less than 7, adding a catalyst to perform a catalytic oxidation reaction with the residual initiator; step 3, adding alkali into the wastewater after the reaction in step 2 to adjust the pH value to be more than 6, and adding a flocculating agent to perform a flocculation and precipitation reaction. Compared with the prior art, the application has the following advantages: the biodegradability of the wastewater can be significantly improved, so that the wastewater can enter a biochemical system for treatment; the process flow of the method is simple, and the investment cost is low; the method is simple and easy to operate, and the operation cost is low.

Description

Technical Field

[0001] This invention relates to a method for the pretreatment of chemical wastewater, and more particularly to a method for the pretreatment of acrylonitrile-containing wastewater. Background Technology

[0002] Acrylonitrile is a crucial chemical raw material for the three major synthetic materials (fibers, rubber, and plastics), holding a significant position in synthetic fibers, synthetic resins, and other polymer materials, with broad application prospects. However, wastewater discharged during acrylonitrile production contains acrylonitrile, polymers, and other substances, posing a significant environmental hazard. Furthermore, the biochemical reactions of organic nitrile increase ammonia nitrogen in the water, exacerbating eutrophication. With the continuous expansion of the acrylonitrile market and production scale in recent years, the environmental pollution caused by acrylonitrile wastewater has become increasingly serious. Due to its toxic, harmful, and recalcitrant characteristics, acrylonitrile wastewater has always been a key research focus both domestically and internationally, especially wastewater from the polymerization stage, which is characterized by large volumes and contains acrylonitrile and oligomers such as polyacrylonitrile, making it difficult to treat using conventional biological systems. Currently, the treatment of nitrile-containing wastewater mainly focuses on physicochemical treatment, electrochemical treatment, biochemical treatment, and combinations of multiple methods.

[0003] For example, patent ZL01142858.9 provides a highly efficient activated sludge-microelectrolysis method for treating industrial wastewater containing recalcitrant biodegradable substances, including acrylonitrile fiber wastewater, dyeing and printing wastewater, textile wastewater, and petrochemical wastewater, particularly dry acrylonitrile fiber wastewater. The drawback of this method is that it cannot effectively remove oligomers from the wastewater.

[0004] Patent CN101723523B discloses a membrane treatment method for wastewater from dry acrylonitrile fiber production. This method includes processes such as wastewater homogenization, coagulation and sedimentation, ultrafiltration, and reverse osmosis. This method applies membrane technology to the treatment of dry acrylonitrile fiber wastewater. Targeting the characteristics of the wastewater, it employs appropriate pretreatment measures, adding nano-sized SiO2 powder to the coagulation and sedimentation process to enhance the removal of oligomers from the wastewater and reduce wastewater fouling of the membrane system. However, a drawback is that it is not suitable for treating high-concentration wastewater.

[0005] Although there are many methods for treating acrylonitrile wastewater, each with its own characteristics, the results achieved by the methods currently in industrial application are not ideal. There are many shortcomings in the application of these technologies, such as the risk of secondary pollution, high investment costs, and harsh reaction conditions, which urgently need to be addressed.

[0006] Therefore, it is necessary to adopt practical and feasible methods to pretreat acrylonitrile-containing wastewater so that the treated wastewater can enter the biochemical system for further treatment. Summary of the Invention

[0007] The purpose of this invention is to provide a pretreatment method for acrylonitrile-containing wastewater, especially a pretreatment method for wastewater from the polymerization and recovery process of acrylonitrile fiber plants, which significantly improves the biodegradability of the pretreated acrylonitrile wastewater, thereby facilitating subsequent biochemical treatment.

[0008] A pretreatment method for acrylonitrile-containing wastewater includes:

[0009] Step 1: Add initiator and crosslinking agent to acrylonitrile-containing wastewater to carry out crosslinking polymerization reaction; control the reaction temperature at 50-90℃, preferably 60-80℃;

[0010] Step 2: Add acid to the wastewater after the reaction in Step 1 to adjust the pH to <7, preferably 3-5, add catalyst, and carry out catalytic oxidation reaction with the remaining initiator;

[0011] Step 3: Add alkali to the wastewater after the reaction in Step 2 to adjust the pH to >6, preferably 7-9, and add flocculant to carry out flocculation and sedimentation reaction.

[0012] In step 1 of the present invention, the initiator is selected from persulfate, sodium hypochlorite, hydrogen peroxide, etc., preferably persulfate, and the dosage can be 50-1000 ppm, preferably 100-500 ppm.

[0013] The crosslinking agent can be N,N'-dimethylenebisacrylamide, hydroxyethyl acrylate, benzoyl peroxide, glutaraldehyde, etc., with N,N'-dimethylenebisacrylamide being preferred.

[0014] The amount of crosslinking agent added can be 0.1-80 ppm, preferably 1-10 ppm.

[0015] The crosslinking polymerization reaction time can be 2-200 minutes, preferably 10-100 minutes.

[0016] In step 2 of the present invention, the acid may be hydrochloric acid, sulfuric acid, or phosphoric acid, preferably sulfuric acid.

[0017] The catalyst is a reducing metal compound, which can be selected from ferrous chloride, ferrous sulfate, etc., with ferrous sulfate being preferred; the dosage of the catalyst is 50-5000 ppm, preferably 100-2000 ppm.

[0018] The catalytic oxidation reaction time can be 2-500 minutes, preferably 10-200 minutes.

[0019] In step 3 of this invention, the flocculant can be one or more commonly used flocculants such as aluminum salts, iron salts, polyaluminum chloride, polyferric chloride, and polyacrylamide, preferably a combination of polyaluminum chloride and polyacrylamide. The dosage of polyaluminum chloride is 1-5000 mg / L, preferably 10-200 mg / L; the dosage of polyacrylamide is 0.05-100 mg / L, preferably 1-20 mg / L.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. It can significantly improve the biodegradability of wastewater, enabling it to enter the biological treatment system for processing.

[0022] 2. This method has a simple process flow and low investment cost.

[0023] 3. This method is simple, easy to implement, and has low operating costs. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0025] Table 1 shows the water quality of the polymerization section of a certain acrylonitrile fiber plant.

[0026] Table 1. Wastewater quality from the polymerization and recovery process in the acrylic fiber plant.

[0027]

[0028] As can be seen from the data in Table 1, the wastewater has poor biodegradability, with a B / C ratio of 0.14, which is far from meeting the water quality requirements for entering the biological treatment system.

[0029] For this wastewater, catalytic oxidation, electrochemical oxidation, and iron-carbon internal electrolysis processes have all failed to achieve satisfactory results. After treatment by these methods, the B / C ratio of the wastewater is still less than 0.2. However, by using the method of this invention, the B / C ratio can be increased to above 0.2, or even above 0.3.

[0030] Example 1

[0031] Take 2L of water sample from Table 1, control the temperature at 60℃, add 150ppm potassium persulfate and 3ppm N,N'-dimethylenebisacrylamide, react for 60min, then add 98% sulfuric acid to adjust the pH to 4, add 300ppm ferrous sulfate, react for 60min, then add 30% sodium hydroxide to adjust the pH to 7, then add 60ppm polyaluminum chloride and 2ppm polyacrylamide for flocculation and sedimentation reaction; after the reaction is complete, the B / C ratio of the wastewater is 0.32.

[0032] Example 2

[0033] Take 2L of water sample from Table 1, control the temperature at 60℃, add 300ppm potassium persulfate and 5ppm N,N'-dimethylenebisacrylamide, react for 80min, then add 98% sulfuric acid to adjust the pH to 4, add 300ppm ferrous sulfate, react for 60min, then add 30% sodium hydroxide to adjust the pH to 7, add 80ppm polyaluminum chloride and 4ppm polyacrylamide for flocculation and sedimentation reaction; after the reaction is complete, the B / C ratio of the wastewater is 0.35.

[0034] Example 3

[0035] Take 2L of water sample from Table 1, control the temperature at 70℃, add 150ppm potassium persulfate and 3ppm N,N'-dimethylenebisacrylamide, react for 60min, then add 98% sulfuric acid to adjust the pH to 5, add 500ppm ferrous sulfate, react for 60min, then add 30% sodium hydroxide to adjust the pH to 8, then add 60ppm polyaluminum chloride and 2ppm polyacrylamide for flocculation and precipitation reaction; after 90min of reaction, the B / C ratio of the wastewater is 0.31.

[0036] Example 4

[0037] Take 2L of water sample from Table 1, control the temperature at 60℃, add 150ppm sodium hypochlorite and 3ppm N,N'-dimethylenebisacrylamide, react for 60min, then add 98% sulfuric acid to adjust the pH to 4, add 500ppm ferrous sulfate, react for 60min, then add 30% sodium hydroxide to adjust the pH to 7, then add 60ppm polyaluminum chloride and 2ppm polyacrylamide for flocculation and precipitation reaction; after 90min of reaction, the B / C ratio of the wastewater is 0.21.

[0038] Example 5

[0039] Take 2L of water sample from Table 1, control the temperature at 60℃, add 150ppm potassium persulfate and 5ppm benzoyl peroxide, react for 60min, then add 98% sulfuric acid to adjust the pH to 4, add 500ppm ferrous sulfate, react for 60min, then add 30% sodium hydroxide to adjust the pH to 7, add 60ppm polyaluminum chloride and 2ppm polyacrylamide for flocculation and precipitation reaction; after 90min of reaction, the B / C ratio of the wastewater is 0.23.

[0040] Comparative Example 1

[0041] Take 2L of water sample from Table 1, control the temperature at 60℃, do not add crosslinking agent, add 98% sulfuric acid to adjust the pH to 4, add 150ppm potassium persulfate and 300ppm ferrous sulfate, react for 60min, add 30% sodium hydroxide to adjust the pH to 7, add 60ppm polyaluminum chloride and 2ppm polyacrylamide to carry out flocculation and precipitation reaction; after 90min of reaction, the B / C ratio of wastewater is 0.18.

[0042] Comparative Example 2

[0043] Take 2L of water sample from Table 1, control the temperature at 60℃, add 150ppm potassium persulfate and 3ppm N,N'-dimethylenebisacrylamide, without adding a catalyst, and react for 120min. Then add 60ppm polyaluminum chloride and 2ppm polyacrylamide for flocculation and sedimentation reaction. After 90min of reaction, the B / C ratio of the wastewater is 0.23.

[0044] Comparative Example 3

[0045] Take 2L of water sample from Table 1, control the temperature at 60℃, do not add initiator, add 3ppm N,N'-dimethylenebisacrylamide, react for 60min, then add 98% sulfuric acid to adjust the pH to 4, add 300ppm ferrous sulfate, react for 60min, then add 30% sodium hydroxide to adjust the pH to 7, add 60ppm polyaluminum chloride and 2ppm polyacrylamide to carry out flocculation and precipitation reaction; after the reaction is completed, the B / C ratio of the wastewater is 0.22.

[0046] Comparative Example 4

[0047] Take 2L of water sample from Table 1, without adjusting the temperature, and keep the water sample at room temperature (21.2℃). Add 150ppm potassium persulfate and 3ppm N,N'-dimethylenebisacrylamide. After reacting for 60 minutes, add 98% sulfuric acid to adjust the pH to 4, add 300ppm ferrous sulfate, and react for 60 minutes. Then add 30% sodium hydroxide to adjust the pH to 7. Add 60ppm polyaluminum chloride and 2ppm polyacrylamide to carry out flocculation and precipitation reaction. After the reaction is completed, the B / C ratio of the wastewater is 0.20.

Claims

1. A pretreatment method of acrylonitrile-containing wastewater, comprising: Step 1: adding an initiator and a crosslinking agent to the acrylonitrile-containing wastewater to perform a crosslinking polymerization reaction; controlling the reaction temperature to be 50-90℃, wherein the initiator is selected from persulfate, sodium hypochlorite, and hydrogen peroxide, and the crosslinking agent is selected from N,N'-dimethylene bisacrylamide, hydroxyethyl acrylate, dibenzoyl peroxide, and glutaraldehyde; Step 2: adding an acid to the wastewater after the reaction in Step 1 to adjust the pH to be less than 7, adding a catalyst to perform a catalytic oxidation reaction with the remaining initiator, and the catalyst is selected from ferrous chloride and ferrous sulfate; Step 3: adding a base to the wastewater after the reaction in Step 2 to adjust the pH to be greater than 6, and adding a flocculant to perform a flocculation and precipitation reaction.

2. The method of claim 1, wherein, The initiator is added in an amount of 50-1000 ppm.

3. The method of claim 1, wherein, The initiator is added in an amount of 100-500 ppm.

4. The method of claim 1, wherein, The crosslinking agent is added in an amount of 0.1-80 ppm.

5. The method of claim 1, wherein, The crosslinking agent is added in an amount of 1-10 ppm.

6. The method of claim 1, wherein, The crosslinking polymerization reaction temperature is 60-80℃, and the reaction time is 10-100 minutes.

7. The method of claim 1, wherein, The catalyst is added in an amount of 50-5000 ppm.

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