Electrochemical oxidation polymerization removal method of brominated flame retardants in water system

Abstract

The application discloses a method for removing brominated flame retardant in water system by electrochemical oxidation polymerization, which comprises the following steps: step one, configuring electrolyte containing brominated flame retardant, wherein the solute of the electrolyte comprises TBBPA, supporting electrolyte and alkali, the alkali is NaOH, KOH or LiOH, the supporting electrolyte is NaCl, KCl or LiCl, and the solvent is water; step two, putting cathode material and anode material into an electrolytic cell, and connecting a stabilized DC power supply to carry out electrolysis, in the electrolysis process, TBBPA is electrochemically oxidized and polymerized at the anode to generate solid polymer, so that the purpose of removing TBBPA is achieved. The application can efficiently remove brominated flame retardant in water system in a single-chamber electrolytic cell, and can generate polymer with industrial value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of brominated flame retardant treatment technology in environmental protection, and particularly relates to a method for removing and degrading brominated flame retardants in wastewater by using an electrochemical anodic oxidation method in an alkaline water system. BACKGROUND

[0002] Flame retardants (FRs) are chemicals added to materials to prevent burning and delay the spread of flames after ignition, which have been used in plastic materials of electronic and electrical equipment components since the 1960s (Chemosphere 53 (2003) 1137-1146), and thus a large amount of flame retardants are often contained in waste electronic and electrical equipment, which need to be removed before or during recycling (Environmental Science and Pollution Research (2021) 28: 59190-59213). At present, brominated flame retardants are the largest organic flame retardants in China and even in the world, and the global annual production of TBBPA (tetra-bromobisphenol A) reaches 120,000 tons, accounting for 60% of the global brominated flame retardant market. These lipophilic additive organic flame retardants can easily enter the environment, such as the sediment near the electronic waste disassembly site, because they lack chemical bonds with commodities, and the concentration of TBBPA in the sediment can be as high as 41,200 ng / g (Science of The Total Environment, 2019, 646: 58-67), which seriously threatens environmental safety and human health.

[0003] The common degradation techniques of brominated flame retardants mainly include reduction debromination degradation method, complete mineralization degradation method and polymerization degradation method. Among them, the reduction debromination degradation method includes microbial degradation method (Environment International 174 (2023) 107873), photocatalytic degradation method (Environmental Pollution 271 (2021) 116406) and mechanochemical degradation method (Journal of Environmental Chemical Engineering 11 (2023) 109916) and so on. The complete mineralization degradation method includes potential barrier discharge degradation method (Separation and Purification Technology 240 (2020) 116615) and mesoporous nanostructured BiOBr microsphere catalysis method (Applied Catalysis B: Environmental 107 (2011) 355-362) and so on. The polymerization degradation method can synthesize high molecular weight epoxy resin (Polym. Adv. Technol. 2009, 20 194-208), make composite materials (Manikandan et al. 2020. Int. J. Vehicle Structures & Systems, 12(2), 162-165) and as an epoxy curing agent (ACS Sustainable Chem. Eng. 2022, 10, 2429-2440) and so on.

[0004] The common electrochemical degradation is to realize the process of electrochemical reduction debromination step by step in the cathode by modifying different cathode materials. Using this method to degrade TBBPA will produce four kinds of bromine-containing intermediates, and the final product BPA also has certain biological toxicity (Journal of Environmental Chemical Engineering 11 (2023) 109596). Compared with the electrochemical degradation to generate toxic and harmful intermediates, the electrochemical oxidation method is used in alkaline water system to make the brominated flame retardant in wastewater polymerize, and the polymerized product is recycled and processed into raw materials with industrial value, which can effectively realize the resource utilization of flame retardants.

[0005] The traditional polymerization method uses TBBPA as raw material, and performs ring opening and ring closing reactions with reactant epichlorohydrin in sodium hydroxide aqueous solution to obtain an epoxy resin (Polym. Adv. Technol. 2009, 20 194-208). The reactant epichlorohydrin can be hydrolyzed in a strong alkaline aqueous solution, resulting in low epoxy value and high chlorine content of the product. The electrochemical oxidation polymerization method does not need to add other reactants to realize electrochemical oxidation polymerization of TBBPA, and the generated solid polymer can be recovered by simple filtration, which can effectively solve the environmental pollution problem of brominated flame retardants. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application provides a method for efficiently removing brominated flame retardants in water systems by electrochemical oxidation polymerization, so as to achieve the purpose of degrading brominated flame retardants in wastewater by electrochemical oxidation polymerization of TBBPA.

[0007] Specifically, the present application adopts the following technical solutions:

[0008] A method for removing brominated flame retardants in water systems by electrochemical oxidation polymerization, comprising the following steps in sequence:

[0009] Step 1: configure an electrolyte containing brominated flame retardants, wherein the solute of the electrolyte comprises TBBPA, a supporting electrolyte and a base, the base is NaOH, KOH or LiOH, the supporting electrolyte is NaCl, KCl or LiCl, and the solvent is water; the concentration of TBBPA in the electrolyte is 2 mmol / L to 10 mmol / L, the concentration of the supporting electrolyte is 12 mmol / L to 48 mmol / L, and the concentration of the base is 20 mmol / L to 50 mmol / L.

[0010] Step 2: place the cathode material and the anode material into an electrolytic cell, and connect a stabilized DC power supply to perform electrolysis; during the electrolysis process, TBBPA is electrochemically oxidized and polymerized at the anode to generate a solid polymer, thereby achieving the purpose of removing TBBPA.

[0011] Preferably, the supporting electrolyte is NaCl. Further preferably, the concentration of NaCl in the electrolyte is 48 mmol / L.

[0012] Preferably, the base is NaOH. Further preferably, the concentration of NaOH in the electrolyte is 20 mmol / L.

[0013] Preferably, the concentration of TBBPA in step 1 is 5 mmol / L.

[0014] Preferably, the cathode material is a stainless steel sheet, a zinc sheet, an iron sheet, a copper sheet or a zinc-copper alloy, and further preferably a stainless steel sheet.

[0015] As a preference, the anode is Ti / PbO2.

[0016] As a preference, the electrolysis in step two is preferably carried out at a temperature of 20-50℃, a rotation speed of 100rpm-1500rpm, and a current density of 10mA / cm 2 ~50mA / cm 2 . Further preferably, the electrolysis reaction temperature is 25℃, further preferably the current density is 10mA / cm 2 ~40mA / cm 2 , and most preferably 10mA / cm 2 . Further preferably, the rotation speed is 500rpm-1200rpm, and most preferably 1000rpm.

[0017] Compared with the prior art, the present application has the following advantages:

[0018] 1. The present application provides a treatment method for removing pollutants by electrochemical anodic oxidation of brominated flame retardants in wastewater under alkaline conditions. The brominated flame retardants in water can be efficiently removed in a single-chamber electrolytic cell, and a polymer with industrial value can be generated.

[0019] 2. The cathode and anode materials of the present application do not need to be specially modified and pretreated, are inexpensive and easy to obtain, and the reaction conditions are simple and easy to implement.

[0020] 3. The present application uses electrochemical oxidation polymerization of TBBPA. The polymer floats above the solution, and TBBPA in the wastewater can be removed by simple filtration.

[0021] 4. The present application has high removal efficiency for brominated flame retardants. After 2h of electrochemical oxidation polymerization of 5mmol / L TBBPA, the removal rate of TBBPA is 100%, and the generation rate of solid product is 60.1%. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of the degradation of TBBPA under different supporting electrolytes;

[0023] Figure 2 is a schematic diagram of the degradation of TBBPA under different alkaline solutions;

[0024] Figure 3 is a schematic diagram of the degradation of TBBPA under different cathode materials;

[0025] Figure 4 is a schematic diagram of the initial cell voltage under different cathode materials;

[0026] Figure 5 is a schematic diagram of the solid generation rate under different cathode materials. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the present application more clear to those skilled in the art, the present application is further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0028] Examples 1-3: A method for removing brominated flame retardants in water system by electrochemical oxidation polymerization of TBBPA in wastewater, comprising the following steps:

[0029] Step one: raw material TBBPA (0.0544 g, 5 mmol / L), alkali solution NaOH (0.0160 g, 20 mmol / L), supporting electrolyte is NaCl (Example 1; 0.0561 g, 48 mmol / L), KCl (Example 2: 0.0716 g, 48 mmol / L) and LiCl (Example 3: 0.0407 g, 48 mmol / L) respectively. The reaction solution is added to a 30 ml single-chamber temperature controllable electrolytic cell, a 2x2 cm 2 stainless steel sheet is used as the cathode, a 2x2 cm 2 Ti / PbO2electrode sheet is used as the anode, which is connected to a direct current stabilized power supply, the reaction is started and the cell voltage at the beginning of the reaction is recorded.

[0030] Step two: connect the temperature control jacket of the single-chamber electrolytic cell to the constant temperature bath, set the temperature to 25℃, add a 6mmx10mm stirring bar, set the magnetic stirring to 1000 rpm, start the direct current stabilized power supply to control the current density to 10 mA / cm 2 , respectively, take 0.1 mL of electrolyte at reaction time of 0 h, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, use methanol solution to make up to 1 mL, shake well and then perform high performance liquid chromatography analysis and detection on the reaction solution. Filter and dry the solid material generated by electrolysis for 3 hours, and calculate the generation rate of the solid.

[0031] Detection conditions of the electrolyte: Waters 2695 high performance liquid chromatograph, ODS-SP 5μm 4.6x250mm (UP) as the separation column, the mobile phase is a mixture of 80% methanol and 20% water (volume ratio), and 1 mL of 98wt% formic acid solution is added to adjust the pH (the volume ratio of the mobile phase to the formic acid solution is 1000:1), the detection wavelength is 230 nm, the flow rate is 1 mL / min, and the temperature is 35℃.

[0032] Calculation method of solid product: the solid material after reaction is dried for 12 hours and then weighed, and the generation rate is calculated.

[0033] The samples were detected after electrolysis for 3h, and the degradation rate of TBBPA was more than 99.0%, and the results are shown in Figure 1 It can be seen from the figure that the supporting electrolytes NaCl, KCl and LiCl have little effect on the degradation of TBBPA. Under the action of NaCl, 5mmol / L of TBBPA is almost completely degraded in about 2h. Considering the price and source, NaCl can be preferably used as the supporting electrolyte for the removal of TBBPA by polymerization.

[0034] Example 4-5: A method for removing brominated flame retardants in water system by electrochemical oxidation polymerization of TBBPA in wastewater, comprising the following steps:

[0035] Different from example 1: the alkali solution in step one is KOH (example 4: 0.0224g, 20mmol / L) and LiOH (example 5: 0.0096g, 20mmol / L) respectively, and the rest of the electrolysis conditions are unchanged, and the results are shown in Figure 2 . Figure 2 It is shown that different alkali solutions have a great effect on the removal rate of TBBPA, and in the alkali solution of LiOH, 1h can make the removal rate of 5mmol / L of TBBPA reach 92.4%. In the alkali solution of NaOH and KOH, the removal rate of TBBPA decreases, but in the alkali solution of NaOH, the removal rate of 5mmol / L of TBBPA can reach 99.0% in about 2h. Considering comprehensively, 20mmol / L of NaOH can be preferably used as the alkali solution for the polymerization degradation of TBBPA in water system.

[0036] Example 6-9: A method for removing brominated flame retardants in water system by electrochemical oxidation polymerization of TBBPA in wastewater, comprising the following steps:

[0037] The difference between Example 1 is: the initial concentration of TBBPA in step one is 2 mmol / L (Example 10), 3 mmol / L (Example 11), 4 mmol / L (Example 12), 5 mmol / L (Example 13), 6 mmol / L (Example 14), 7 mmol / L (Example 15), 8 mmol / L (Example 16), 9 mmol / L (Example 17) and 10 mmol / L (Example 18), the supporting electrolyte is NaCl (0.0561 g, 48 mmol / L), and the rest of the electrolysis conditions are unchanged. After 2 h of continuous electrolysis, the solid was dried and weighed, and the solid production rate was 22.9%, 39.9%, 55.2%, 51.5%, 55.7%, 61.2%, 58.1%, 59.2% and 57.8%, respectively. With the increase of the initial concentration of the reaction substrate TBBPA, the production rate of solid product also gradually increased. When the concentration of TBBPA is higher than 5 mmol / L, the time of dissolving TBBPA will also increase; while when the initial concentration of TBBPA is less than 5 mmol / L, the rate of electrochemical oxidation and polymerization is slower. From the comprehensive consideration of energy consumption and reaction time, the initial concentration of TBBPA in water system is preferably 5 mmol / L.

[0038] Examples 10-18: A method for removing brominated flame retardants in water system by electrochemical oxidation and polymerization of TBBPA in wastewater, comprising the following steps:

[0039] The difference between Example 1 is: the initial concentration of TBBPA in step one is 2 mmol / L (Example 10), 3 mmol / L (Example 11), 4 mmol / L (Example 12), 5 mmol / L (Example 13), 6 mmol / L (Example 14), 7 mmol / L (Example 15), 8 mmol / L (Example 16), 9 mmol / L (Example 17) and 10 mmol / L (Example 18), the supporting electrolyte is NaCl (0.0561 g, 48 mmol / L), and the rest of the electrolysis conditions are unchanged. After 2 h of continuous electrolysis, the solid was dried and weighed, and the solid production rate was 22.9%, 39.9%, 55.2%, 51.5%, 55.7%, 61.2%, 58.1%, 59.2% and 57.8%, respectively. With the increase of the initial concentration of the reaction substrate TBBPA, the production rate of solid product also gradually increased. When the concentration of TBBPA is higher than 5 mmol / L, the time of dissolving TBBPA will also increase; while when the initial concentration of TBBPA is less than 5 mmol / L, the rate of electrochemical oxidation and polymerization is slower. From the comprehensive consideration of energy consumption and reaction time, the initial concentration of TBBPA in water system is preferably 5 mmol / L.

[0040] Examples 10-18: A method for removing brominated flame retardants in water system by electrochemical oxidation and polymerization of TBBPA in wastewater, comprising the following steps:

[0041] Different from Example 1 is that: the cathode material in Step 1 is 2x2 cm 2 Zinc sheet (Example 19), iron sheet (Example 20), copper sheet (Example 21) and zinc-copper alloy (Example 22), the rest of the electrolysis conditions are unchanged, the results obtained are shown in Figure 3 Figure 3 It is shown that when the cathode material changes, using 2x2 cm 2 stainless steel sheet, zinc sheet, iron sheet, copper sheet and zinc-copper alloy as cathode material has no effect on the degradation rate of TBBPA. The degradation rate of 5 mmol / L TBBPA can reach 100% after 2.5 hours. However, when the cathode material changes, the voltage between the two electrodes will change. When stainless steel sheet, iron sheet, zinc sheet, copper sheet and zinc-copper alloy are used as cathode material, the cell voltage is 3.7V, 3.9V, 4.2V, 4.2V and 4.2V respectively Figure 4 ). After 3 hours of electrolysis, the reaction solution was filtered and the solid material was dried and weighed, and the results are shown in Figure 5 When stainless steel sheet, zinc sheet, iron sheet, copper sheet and zinc-copper alloy are used as cathode material with the same area, the generated solid mass is 0.0280g, 0.0277g, 0.0327g, 0.0285g and 0.0282g respectively, and the corresponding solid generation rate is 51.5%, 50.9%, 60.1%, 52.4% and 51.8% respectively. From the comprehensive consideration of energy consumption and material price, stainless steel can be preferably used as cathode material for electrolysis reaction for the removal of TBBPA in water system.

[0042] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for electrochemical oxidative polymerization removal of brominated flame retardants in water systems, characterized by: The electrochemical oxidative polymerization removal method of brominated flame retardants in the water system comprises the following steps in sequence: Step one: configure an electrolyte containing brominated flame retardants, the solute of the electrolyte includes TBBPA, a supporting electrolyte and a base, the base is NaOH, KOH or LiOH, the supporting electrolyte is NaCl, KCl or LiCl, and the solvent is water; the concentration of TBBPA in the electrolyte is 4 mmol / L-10 mmol / L, the concentration of the supporting electrolyte is 12 mmol / L-48 mmol / L, and the concentration of the base is 20 mmol / L-40 mmol / L; Step two: put the cathode material and anode material into the electrolytic cell, the cathode material is stainless steel sheet, zinc sheet, iron sheet, copper sheet or zinc copper alloy, the anode is Ti / PbO2, connect the stabilized DC power supply to carry out electrolysis under alkaline condition, the electrolysis is carried out under the condition that the temperature is 20 ~ 50 ℃, the rotating speed is 100 rpm ~ 1500 rpm, the current density is 10 mA / cm 2 ~ 50 mA / cm 2 During the electrolysis process, TBBPA is electrochemically oxidized and polymerized at the anode to generate solid polymer, so as to achieve the purpose of removing TBBPA.

2. The method for electrochemical oxidative polymerization removal of brominated flame retardants in water system according to claim 1, characterized in that: The supporting electrolyte is NaCl.

3. The method for electrochemical oxidative polymerization removal of brominated flame retardants in water system according to claim 2, characterized in that: In the electrolyte, the concentration of NaCl is 48 mmol / L.

4. The method for electrochemical oxidative polymerization removal of brominated flame retardants in water system according to claim 1, characterized in that: The base is NaOH.

5. The method for electrochemical oxidative polymerization removal of brominated flame retardants in water system according to claim 4, characterized in that: In the electrolyte, the concentration of NaOH is 20 mmol / L.

6. The method for electrochemical oxidative polymerization removal of brominated flame retardants in water system according to claim 1, characterized in that: In the electrolyte, the concentration of TBBPA is 5 mmol / L.

7. The method for electrochemical oxidative polymerization removal of brominated flame retardants in water system according to claim 1, characterized in that: The electrolysis temperature is 25 °C, the current density is 10 mA / cm 2 ~ 40 mA / cm 2 The rotation speed is 500 rpm~1200 rpm.

8. The method for electrochemical oxidative polymerization removal of brominated flame retardants in water system according to claim 7, characterized in that: Current density is 10 mA / cm 2 .

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