Catalytic oxidation process of brominated flame retardant production wastewater

Abstract

The invention provides a catalytic oxidation process of brominated flame retardant production wastewater, and belongs to the technical field of wastewater treatment.The catalytic oxidation process comprises the steps that wastewater discharged in all brominated flame retardant production procedures is uniformly mixed, then mixed liquid is pretreated through flash evaporation, acidification and filtration, and raw wastewater is obtained; raw wastewater is subjected to pH regulation, heat exchange, heating and catalytic oxidation reaction through a conditioning tank, a preheating heat exchanger, an efficient heater and a catalytic oxidation reactor to obtain reaction effluent, reflux regulation or output is performed according to the COD value of the reaction effluent, and after the COD value of the reaction effluent is qualified, the reaction effluent can be discharged to a subsequent comprehensive treatment process. The device has the advantages of continuous effluent, stable water quality, simple treatment mode, small occupied area, low operation cost, no pollution in the process and the like.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and in particular relates to a catalytic oxidation process for wastewater from the production of bromine-based flame retardants. Background Technology

[0002] Industrial wastewater mainly comes from industries such as chemical, pharmaceutical, and petroleum refining. Examples include wastewater from flame retardant production, pharmaceutical production, petrochemical production, and paint production. Industrial wastewater is characterized by high toxicity and poor biodegradability, and usually cannot be treated directly. It requires special treatment processes to meet discharge standards.

[0003] Commonly used wastewater treatment technologies include combined treatments such as settling and clarification, physical adsorption, and biochemical treatment, but their degradation effects are not ideal. The main reason is the high concentration of pollutants in the wastewater, their stable chemical properties, and their difficulty in degradation. For this type of wastewater, catalytic oxidation technology is currently the primary treatment technology used both domestically and internationally. This technology does not produce toxic byproducts or cause secondary pollution during the treatment process. Catalytic oxidation technology is divided into advanced oxidation, ozone catalytic oxidation, and electrocatalytic oxidation. However, regardless of the type used, all suffer from long treatment times, complex equipment, and high energy consumption, resulting in high wastewater treatment costs.

[0004] Therefore, how to achieve good treatment results in wastewater degradation in a short time and at low cost is a problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a catalytic oxidation process for wastewater from the production of bromine-based flame retardants.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a catalytic oxidation process for wastewater from the production of brominated flame retardants, comprising the following steps: S1. Transport the raw wastewater to the conditioning tank for pH adjustment to ensure that the pH value of the adjusted solution is 1~4. S2. The liquid in the conditioning tank is transported to the preheating heat exchanger for heat exchange, and an oxidant is added. Then it is transported to the high-efficiency heater, where the heating medium is used to rapidly heat the liquid. S3. After the high-efficiency heater heats the liquid to 130~170℃, the liquid is then transferred to the catalytic oxidation reactor for degradation reaction under the action of the catalyst. S4. After the reaction is completed, if the COD value of the effluent does not meet the process requirements, adjust the reflux rate of the effluent to dilute the concentration of the feed solution in the conditioning tank through the refluxed effluent, and control the COD value of the wastewater in the conditioning tank within the process requirements range; if the COD value of the effluent meets the process requirements, it is then transported to the subsequent comprehensive treatment process.

[0007] Further, in step S1, the pretreatment of the raw wastewater involves: first, collecting and mixing the wastewater discharged from each production process of the brominated flame retardant, then treating it through flash evaporation, acidification, and filtration, resulting in acidic filtrate as the raw wastewater. This pretreatment removes organic solvents and most water-insoluble organic impurities from the wastewater.

[0008] The wastewater discharged from each process in the production of brominated flame retardants mainly includes: acidic wastewater, alkaline washing wastewater, water washing wastewater, and distillation wastewater, with COD values ​​ranging from 1000 to 20000 mg / L. The collected wastewater has a pH of 6 to 9. Small amounts of organic solvents entrained in the wastewater are removed by flash evaporation at a temperature controlled between 60 and 100°C. Then, dilute sulfuric acid or solid acid is added to the wastewater to control the pH to 1 to 5. Most of the organic insolubles in the wastewater precipitate out. After filtration, most of the solid oxides are retained and recovered. The filtration equipment can be a plate and frame filter press, a precision filter, or a combination thereof.

[0009] Further, in step S2, the oxidant is one or a combination of hydrogen peroxide and sodium persulfate, and the amount of oxidant added is 2% to 10% of the volume of the liquid in the preheating heat exchanger.

[0010] Furthermore, in step S3, the conditions for the catalytic oxidation reaction are: temperature 120~160℃ and pressure 0.2~0.8Mpa. Therefore, the feed liquid needs to be heated with steam before the catalytic oxidation reaction. Then, the oxidant generates hydroxyl radicals with very strong oxidizing power under the action of the catalyst. After the feed liquid comes into full contact with the hydroxyl radicals, it can oxidize and decompose large organic molecules (tetrabromobisphenol A, tribromophenol, etc.) into small molecules. Under the action of sufficient oxidant, the small organic molecules are further oxidized and decomposed into carbon dioxide and water. Inorganic components (sodium sulfate, sodium bromide, etc.) do not participate in the reaction, and the COD value gradually decreases.

[0011] In this process, the catalytic oxidation reactor cuts off energy exchange with the outside world through an insulation layer. After the insulation time reaches the set time, the reaction ends. At this point, the COD value of the effluent decreases by approximately 2000~4000 mg / L. If the decrease is not 2000~4000 mg / L, it is necessary to increase the effluent return flow rate or replace the catalyst in the catalytic oxidation reactor.

[0012] Furthermore, in step S4, when the COD of the effluent after the catalytic oxidation reaction is greater than 2000 mg / L, the effluent is discharged to a buffer tank and then discharged to a conditioning tank at a certain reflux ratio to dilute the liquid in the conditioning tank, thereby controlling the COD value of the liquid in the conditioning tank to be within the range of 4000~8000 mg / L.

[0013] Before being discharged into the conditioning tank, the effluent from the reaction is first heated by a preheating heat exchanger with the liquid output from the conditioning tank.

[0014] Furthermore, in step S4, if the COD of the effluent after the catalytic oxidation reaction is ≤2000mg / L, it will be discharged to the subsequent comprehensive treatment process.

[0015] By adopting the above technical solution, the present invention has the following beneficial effects: (1) This invention utilizes a catalytic oxidation process to oxidize and decompose most of the organic matter in wastewater into harmless components such as carbon dioxide and water, significantly reducing the COD of wastewater and achieving an odorless treatment process. This process does not produce sludge or SO2. X NO X It produces no harmful secondary pollutants, but no secondary hazardous waste, and also has decolorizing, deodorizing, sterilizing and disinfecting effects.

[0016] (2) This invention can adapt to various water qualities and is applicable to the treatment of different industries and different wastewaters. It can be used for the treatment of high-concentration wastewater as well as the deep treatment of low-concentration wastewater.

[0017] (3) The equipment used in this invention has a high degree of automation, a small overall footprint, convenient operation, and stable overall operation of the system (conditioning tank, preheating heat exchanger, high-efficiency heater, catalytic oxidation reactor). The processing method is simple and can be used independently or in combination with other biochemical, physical and other processing methods.

[0018] (4) The present invention can attempt to achieve transparent and colorless or nearly transparent and colorless effluent, which can create favorable conditions for subsequent crystallization of salt, bromine extraction or discharge treatment.

[0019] In summary, this invention has the advantages of continuous water output, stable water quality, simple treatment method, small footprint, low operating cost, and no pollution during the process. Attached Figure Description

[0020] The present invention will be described in detail below with reference to the accompanying drawings and examples. The advantages and implementation methods of the present invention will become more apparent from this description. The accompanying drawings are for illustrative purposes only and do not constitute any limitation on the present invention. In the accompanying drawings: Figure 1 This is a flowchart of the present invention.

[0021] In the picture: 1. Conditioning tank; 2. Preheating heat exchanger; 3. High-efficiency heater; 4. Catalytic oxidation reactor; 5. Buffer tank; 6. Oxidant dosing tank. Detailed Implementation

[0022] like Figure 1 As shown, the present invention provides a catalytic oxidation process for wastewater from the production of brominated flame retardants, comprising the following steps: S1. The raw wastewater is transported to conditioning tank 1 for pH adjustment to ensure that the pH value of the adjusted solution is 1~4.

[0023] In order to reduce the concentration of the liquid in conditioning tank 1, a certain amount of reaction effluent after catalytic oxidation is refluxed into the conditioning tank, and the reflux flow rate is 0%~100% of the feed rate of the conditioning tank; according to the process requirements, 20%~40% sulfuric acid (mass fraction) and 10%~40% caustic soda solution (mass fraction) can be used for pH adjustment.

[0024] The pretreatment of raw wastewater involves first collecting and mixing the wastewater discharged from each production process of the brominated flame retardant, then treating it through flash evaporation, acidification, and filtration. The resulting acidic filtrate is then used as raw wastewater. A transfer pump is used to transport the raw wastewater to conditioning tank 1.

[0025] This step removes organic solvents and most water-insoluble organic impurities from the wastewater.

[0026] The wastewater discharged from each process in the production of brominated flame retardants mainly includes: acidic wastewater, alkaline washing wastewater, water washing wastewater, and distillation wastewater, with COD values ​​ranging from 1000 to 20000 mg / L. The collected wastewater has a pH of 6 to 9. Small amounts of organic solvents entrained in the wastewater are removed by flash evaporation at a temperature controlled between 60 and 100°C. Then, dilute sulfuric acid or solid acid is added to the wastewater to control the pH to 1 to 5. Most of the organic insolubles in the wastewater precipitate out. After filtration, most of the solid oxides are retained and recovered. The filtration equipment can be a plate and frame filter press, a precision filter, or a combination thereof.

[0027] S2. The liquid in the conditioning tank 1 is transported to the preheating heat exchanger 2 by the transfer pump for heat exchange, and a certain amount of oxidant is added. Then it is transported to the high-efficiency heater 3, where the liquid is rapidly heated by the heating medium (steam).

[0028] The oxidant used is 20%~30% (mass fraction) hydrogen peroxide or sodium persulfate, or a combination thereof. The amount of oxidant added is 2%~10% of the volume of the liquid in the preheating heat exchanger 2. The preheating heat exchanger 2 is preferably a shell-and-tube type or a double-tube type, in which the liquid exchanges heat with the reaction effluent after the catalytic oxidation reaction in the subsequent steps.

[0029] S3. After the high-efficiency heater 3 heats the liquid to the set temperature, the liquid is transferred to the catalytic oxidation reactor 4 for catalytic oxidation degradation reaction under the action of the catalyst.

[0030] The conditions for the catalytic oxidation reaction are: temperature 120~160℃ and pressure 0.2~0.8Mpa. Therefore, the feed liquid needs to be heated with steam before the catalytic oxidation reaction. Then, the oxidant generates hydroxyl radicals with very strong oxidizing power under the action of the catalyst. After the feed liquid comes into full contact with the hydroxyl radicals, it can oxidize and decompose large organic molecules (tetrabromobisphenol A, tribromophenol, etc.) into small molecules. Under the action of sufficient oxidant, the small organic molecules are further oxidized and decomposed into carbon dioxide and water. Inorganic components (sodium sulfate, sodium bromide, etc.) do not participate in the reaction, and the COD value gradually decreases.

[0031] In this process, the catalytic oxidation reactor cuts off energy exchange with the outside world through an insulation layer. After the insulation time reaches the set time, the reaction ends. At this point, the COD value of the effluent decreases by approximately 2000~4000 mg / L. If the decrease is not 2000~4000 mg / L, it is necessary to increase the effluent return flow rate or replace the catalyst in the catalytic oxidation reactor.

[0032] S4. After the reaction in step S3 is completed, if the COD value of the effluent does not meet the process requirements, i.e., it does not meet the standard, adjust the reflux flow rate of the effluent. The refluxed effluent will dilute the concentration of the feed solution in the conditioning tank by a certain proportion, and control the COD value of the wastewater in the conditioning tank within the process requirements range.

[0033] If the COD of the effluent after the catalytic oxidation reaction is greater than 2000 mg / L, the effluent will be discharged to buffer tank 5 and then to conditioning tank 1 at a certain reflux ratio to dilute the feed solution in conditioning tank 1, controlling the COD value of the feed solution in conditioning tank 1 within the range of 4000~8000 mg / L. Before being discharged into conditioning tank 1, the effluent will first exchange heat with the feed solution output from conditioning tank 1 through preheating heat exchanger 2.

[0034] If the effluent from the reaction meets the process requirements, i.e., meets the standards, it will be transported to the subsequent integrated treatment process via a transfer pump.

[0035] When the COD of the effluent after the catalytic oxidation reaction is ≤2000mg / L, it can be directly discharged to the subsequent comprehensive treatment process.

[0036] The subsequent comprehensive treatment process mainly includes bromine extraction, neutralization, evaporation and crystallization, separation and drying, etc., to obtain qualified crystalline salts and bromine, and the wastewater can be discharged in compliance with standards. The system operates stably as a whole.

[0037] Example: Pretreatment of raw wastewater: The wastewater discharged from each process in the tetrabromobisphenol A flame retardant production workshop is used as raw material. The wastewater discharged from each process is first collected and mixed. Organic solvents are removed by flash evaporation. Then, acidification and plate and frame filtration are used to obtain acidic filtrate. This acidic filtrate is the raw wastewater. The raw wastewater is transported to conditioning tank 1 by a transfer pump.

[0038] Pretreatment of raw wastewater can remove organic solvents and most water-insoluble organic impurities from the wastewater.

[0039] The raw wastewater has the following characteristics: pH value of 1-5, COD value of 4000-8000 mg / L, specific gravity of 1.04, light yellow color, bromine concentration of 5-20 g / L, and total solids content of 3%-6%.

[0040] Example 1: A catalytic oxidation process for wastewater from the production of brominated flame retardants includes the following steps: S1. The raw wastewater is transported to conditioning tank 1, and the pH is adjusted using dilute sulfuric acid. The pH of the adjusted solution is tested, and the solution has a pH of 2.69 and a COD of 4672 mg / L.

[0041] S2. The liquid in the conditioning tank 1 is transported to the preheating heat exchanger 2 by the transfer pump for heat exchange. Hydrogen peroxide with a concentration of 25.8% is added through the oxidant addition tank 6. The amount of hydrogen peroxide added is 5% of the liquid. Then it is transported to the high-efficiency heater 3. The liquid is heated by steam in the high-efficiency heater 3.

[0042] S3. Under a steam pressure of 0.3 MPa, after the high-efficiency heater 3 heats the liquid to 130°C, the liquid is transferred to the catalytic oxidation reactor 4 and stirred for 40 minutes under the action of the catalyst.

[0043] S4. After the reaction in step S3 is completed, the parameters of the effluent are detected: hydrogen peroxide content is 0%, pH value is 2, and COD value is 1068 mg / L. It can be seen that the COD of the effluent after the catalytic oxidation reaction is ≤2000 mg / L, meeting the process requirements. It can be directly pumped to the subsequent comprehensive treatment process via a transfer pump to finally obtain qualified bromine and white sodium sulfate products.

[0044] Example 2: A catalytic oxidation process for wastewater from the production of brominated flame retardants includes the following steps: S1. The raw wastewater is transported to conditioning tank 1, and the pH is adjusted using dilute sulfuric acid. The pH of the adjusted solution is tested, and the solution has a pH of 2.44 and a COD of 7820 mg / L.

[0045] S2. The liquid in the conditioning tank 1 is transported to the preheating heat exchanger 2 by the transfer pump. Hydrogen peroxide with a concentration of 27.5% is added through the oxidant addition tank 6. The amount of hydrogen peroxide added is 5% of the liquid. Then it is transported to the high-efficiency heater 3. The liquid is heated by steam in the high-efficiency heater 3.

[0046] S3. Under a steam pressure of 0.38 MPa, after the feed liquid is heated to 145°C by the high-efficiency heater, the feed liquid is transferred to the catalytic oxidation reactor and stirred for 50 minutes under the action of the catalyst.

[0047] S4. After the reaction in step S3 is completed, the parameters of the effluent are detected: hydrogen peroxide content is 0%, pH value is 1.85, and COD value is 3885 mg / L. It is evident that the COD of the effluent after the catalytic oxidation reaction is >2000 mg / L, which does not meet the process requirements. The effluent is discharged into buffer tank 5, and then the effluent in buffer tank 5 is returned to conditioning tank 1 for remixing. The return flow rate is 50% of the feed rate to conditioning tank 1. Before being discharged into conditioning tank 1, the effluent first exchanges heat with the feed liquid output from conditioning tank 1 through preheating heat exchanger 2.

[0048] Then, steps S1 to S3 are repeated. After the reaction is complete, the parameters of the effluent are measured: hydrogen peroxide content is 0%, pH value is 2.10, and COD value is 1696 mg / L. It can be seen that the COD of the effluent after the second catalytic oxidation reaction is ≤2000 mg / L, meeting the process requirements. Therefore, it is pumped to the subsequent comprehensive treatment process via a transfer pump to finally obtain qualified bromine and white sodium sulfate products.

[0049] Example 3: A catalytic oxidation process for wastewater from the production of brominated flame retardants includes the following steps: S1. The raw wastewater is transported to conditioning tank 1, and 50% of the reaction effluent reflux liquid is added. After mixing evenly, the pH is adjusted using dilute sulfuric acid. The pH value of the adjusted solution is 2.89 and the COD value is 5528 mg / L.

[0050] S2. The liquid in the conditioning tank 1 is transported to the preheating heat exchanger 2 by the transfer pump. Hydrogen peroxide with a concentration of 28.3% is added through the oxidant addition tank 6. The amount of hydrogen peroxide added is 5% of the liquid. Then it is transported to the high-efficiency heater 3. The liquid is heated by steam in the high-efficiency heater 3.

[0051] S3. Under a steam pressure of 0.35 MPa, after the feed liquid is heated to 138°C by the high-efficiency heater, the feed liquid is transferred to the catalytic oxidation reactor and stirred for 40 minutes under the action of the catalyst.

[0052] S4. After the reaction in step S3 is completed, the parameters of the effluent are detected: hydrogen peroxide content is 0%, pH value is 1.91, and COD value is 3075 mg / L. It is evident that the COD of the effluent after the catalytic oxidation reaction is >2000 mg / L, which does not meet the process requirements. The effluent is discharged into buffer tank 5, and then the effluent in buffer tank 5 is returned to conditioning tank 1 for remixing. The return flow rate is 50% of the feed rate to conditioning tank 1. Before being discharged into conditioning tank 1, the effluent first exchanges heat with the feed liquid output from conditioning tank 1 through preheating heat exchanger 2.

[0053] Then, steps S1 to S3 are repeated. After the reaction is complete, the parameters of the effluent are measured: hydrogen peroxide content is 0%, pH value is 2.26, and COD value is 1189 mg / L. It can be seen that the COD of the effluent after the second catalytic oxidation reaction is ≤2000 mg / L, meeting the process requirements. Therefore, it is pumped to the subsequent comprehensive treatment process via a transfer pump to finally obtain qualified bromine and white sodium sulfate products.

[0054] The test data from the above examples show that each catalytic oxidation reaction can reduce the chemical oxygen demand of wastewater by about 2000-4000 mg / L. This catalytic oxidation process can reduce the color and refractory organic impurities in wastewater to within the acceptable range. No toxic or harmful gases are generated during the reaction process, and the tail gas can be directly discharged. After subsequent comprehensive treatment, most of the bromide ions are converted into bromine, the solid salt is recovered, and the condensate can be directly discharged.

[0055] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A catalytic oxidation process for wastewater from the production of brominated flame retardants, characterized in that: Includes the following steps: S1. The raw wastewater is transported to the conditioning tank for pH adjustment. The pH value of the adjusted solution is 1~4. S2. The liquid in the conditioning tank is transported to the preheating heat exchanger for heat exchange, and an oxidant is added. Then it is transported to the high-efficiency heater, where the liquid is heated to a higher temperature. S3. After the high-efficiency heater heats the liquid to 130~170℃, the liquid is transferred to the catalytic oxidation reactor for degradation reaction under the action of the catalyst. S4. After the reaction is completed, if the COD value of the effluent does not meet the process requirements, adjust the reflux rate of the effluent to dilute the concentration of the feed solution in the conditioning tank through the refluxed effluent, and control the COD value of the wastewater in the conditioning tank within the process requirements range; if the COD value of the effluent meets the process requirements, it is then transported to the subsequent comprehensive treatment process.

2. The catalytic oxidation process for wastewater from the production of brominated flame retardants according to claim 1, characterized in that: In step S1, the pretreatment of the raw wastewater is as follows: the wastewater discharged from each production process of the bromine-based flame retardant is first mixed and collected, and then treated by flash evaporation, acidification and filtration. The resulting acidic filtrate is the raw wastewater.

3. The catalytic oxidation process for wastewater from the production of brominated flame retardants according to claim 1, characterized in that: In step S2, the oxidant is one or a combination of hydrogen peroxide and sodium persulfate, and the amount of oxidant added is 2% to 10% of the volume of the liquid in the preheating heat exchanger.

4. The catalytic oxidation process for wastewater from the production of brominated flame retardants according to claim 1, characterized in that: In step S3, the conditions for the catalytic oxidation reaction are: temperature 120~160℃ and pressure 0.2~0.8Mpa.

5. The catalytic oxidation process for wastewater from the production of brominated flame retardants according to claim 1, characterized in that: In step S4, if the COD of the effluent after the catalytic oxidation reaction is greater than 2000 mg / L, the effluent is discharged into the conditioning tank at a certain reflux ratio to control the COD value of the liquid in the conditioning tank within the range of 4000~8000 mg / L.

6. The catalytic oxidation process for wastewater from the production of bromine-based flame retardants according to claim 5, characterized in that: Before being discharged into the conditioning tank, the effluent from the reaction is first heated by a preheating heat exchanger with the liquid output from the conditioning tank.

7. The catalytic oxidation process for wastewater from the production of brominated flame retardants according to claim 1, characterized in that: In step S4, if the COD of the effluent after the catalytic oxidation reaction is ≤2000mg / L, the effluent will be discharged to the subsequent comprehensive treatment process.

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