A two-step method for removing fluorine-modified polycarboxylic acids from water

Abstract

This invention relates to a two-step method for removing fluorinated polycarboxylic acids from water. The method comprises two steps: first, adding persulfate to the solution containing fluorinated polycarboxylic acids and conducting an advanced oxidation reaction under vacuum ultraviolet irradiation; second, adjusting the pH of the solution to alkaline with NaOH, then sequentially adding sulfite and halide ions, and continuing the advanced reduction reaction under vacuum ultraviolet irradiation. This invention fully considers the chemical structure of fluorinated polycarboxylic acids, utilizes the characteristics of advanced oxidation and advanced reduction technologies, and properly connects different processes, thereby enhancing the defluorination process and achieving effective removal of fluorinated polycarboxylic acids while avoiding the residue of perfluoroalkyl acids.

Description

Technical Field

[0001] This invention belongs to the field of polluted water treatment, specifically relating to a two-step method for removing fluorinated polycarboxylic acids from water. Background Technology

[0002] With the inclusion of perfluorooctane sulfonic acid, perfluorooctane carboxylic acid, and their salts in the Stockholm Convention appendices, an increasing number of alternatives are being synthesized and utilized. Fluoropolymerized carboxylic acids (C...) n F 2n+1 (CH2) m -COO - Perfluoroalkyl acids (PFOAs) are a class of major substitutes and precursors for perfluoroalkyl acids, widely used in textiles, carpets, clothing, and foam fire extinguishing agents. These compounds can be transferred through the food chain, resulting in a bioaccumulation amplification effect. They exhibit a variety of biotoxicities, including hepatotoxicity, neurotoxicity, reproductive and developmental toxicity, endocrine disruption, and carcinogenicity. Their toxicity may be far greater than that of perfluoroalkyl acids, and conversion can increase the potential risk of perfluorooctane carboxylic acid by 40%. They are currently frequently detected in aquatic media.

[0003] Studies have shown that the CH bonds in fluoropolymers enhance the strength of the CF bonds on adjacent carbon atoms, giving them strong chemical stability and limiting the effectiveness of traditional removal methods. While advanced reduction techniques can remove perfluoroalkyl acids, their degradation of fluoropolymers is slow and the defluorination effect is unsatisfactory. In advanced oxidation processes, hydroxyl radicals (·OH) generated from cobalt(II)-activated peroxymonosulfate or thermally activated peroxydisulfate can convert fluoropolymers into PFAAs, but the defluorination rate is limited. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a two-step method for removing fluorinated polycarboxylic acids from water. This method fully considers the chemical structure of fluorinated polycarboxylic acids, utilizes the characteristics of advanced oxidation and reduction technologies, and properly connects different processes to enhance the defluorination process. This achieves effective removal of fluorinated polycarboxylic acids while avoiding the residue of perfluoroalkyl acids.

[0005] To achieve the above effects, the present invention adopts the following technical solution:

[0006] A two-step method for removing fluorinated polycarboxylic acids from water includes the following steps:

[0007] 1) Add persulfate (PDS) solution to the solution containing fluorinated polycarboxylic acid and carry out advanced oxidation reaction under vacuum ultraviolet (VUV) irradiation;

[0008] 2) Adjust the pH of the solution to alkaline with NaOH, then add sulfite solution and halide ion solution in sequence, and continue to carry out advanced reduction reaction under light.

[0009] Furthermore, the perfluorinated telomerase is one or more of 8:3 perfluorinated telomerase, 7:3 perfluorinated telomerase, and 5:3 perfluorinated telomerase.

[0010] Furthermore, the persulfate is one or both of sodium persulfate and potassium persulfate.

[0011] Furthermore, the sulfite is one or both of sodium sulfite and potassium sulfite.

[0012] Furthermore, the halide ion is an iodide ion.

[0013] Furthermore, the wavelength of the vacuum ultraviolet light is 185nm-254nm, preferably 185nm.

[0014] Furthermore, the pH of the advanced oxidation reaction is in the range of 2.0-10.0 and is adjusted with 10mM phosphate buffer.

[0015] Furthermore, the pH value of the advanced reduction reaction is 6.0-12.0.

[0016] Furthermore, the concentration of the perfluorinated telomerase carboxylic acid is 0.1 mg / L to 2 mg / L.

[0017] Furthermore, the concentration of the persulfate solution is 20-500 μM, and the concentration of the sulfite solution is 10 mM.

[0018] Furthermore, the advanced oxidation reaction time is 20 min to 30 min, and the advanced reduction reaction time is 5.5 h.

[0019] The present invention allows the reaction to proceed directly at room temperature without the need for additional heating or cooling.

[0020] This invention employs a two-step "advanced oxidation-advanced reduction" method based on vacuum ultraviolet light to treat fluoropolymeric carboxylic acids in solution. In step I, the H2O2 formed in situ during the VUV / PDS advanced oxidation process is in a dynamic equilibrium with the generated hydroxyl radicals (·OH) and hydroxyperoxy radicals (HO2·), with H2O2 playing a major role in the advanced oxidation process. During this process, after the H is removed from the CH2 at the α-position of the fluoropolymeric carboxylic acid, its intermediate initiates the formation of other intermediates, with the oxidation products mainly being perfluoroalkyl acids. In step II, during the advanced reduction process, under vacuum ultraviolet irradiation, sulfite rapidly removes dissolved oxygen from the water, overcoming the problem of needing to introduce nitrogen gas before adding halide ions, and improving the lifetime of hydrated electrons of reducing radicals. The addition of halide ions improves the utilization rate of sulfite, and the two synergistically accelerate the reaction process, increase the yield of hydrated electrons, and achieve mineralization removal of the target compound under vacuum ultraviolet irradiation.

[0021] Beneficial effects:

[0022] 1. The two-step "advanced oxidation-advanced reduction" technology based on vacuum ultraviolet light adopted in this invention improves the removal rate and defluorination rate of fluorinated polycarboxylic acids, and can achieve complete degradation and thorough defluorination of fluorinated polycarboxylic acids.

[0023] 2. Compared with ultraviolet advanced oxidation, the method of coupling the first and second steps of the present invention has a wider pH range, faster reaction, and lower energy consumption, which significantly improves the degradation and defluorination efficiency of fluorinated polycarboxylic acids and avoids the residue of perfluoroalkyl acids.

[0024] 3. The method of this invention is highly efficient, the reagents are inexpensive, and it does not produce secondary pollution. It can be widely used in the field of advanced treatment of slightly polluted water. Attached Figure Description

[0025] Figure 1 The graph shows the effect of sodium persulfate concentration on the degradation and defluorination of 8:3 fluoropolymerized carboxylic acid in Example 1.

[0026] Figure 2 This is a graph showing the effect of the initial pH in step I of Example 2 on the degradation of 8:3 fluoropolymerized carboxylic acid;

[0027] Figure 3 This is a graph showing the effect of the initial pH in step II of Example 3 on the defluorination of the degradation products of 8:3 fluoropolymerized carboxylic acid.

[0028] Figure 4 The graph shows the degradation effects of different light sources on 8:3 fluoropolymerized carboxylic acid in Example 4.

[0029] Figure 5This is a graph showing the degradation effect of homologues of fluoropolycarboxylic acid with different carbon chain lengths in the VUV / PDS system in Example 5;

[0030] Figure 6 The graph shows the degradation effect of the initial concentration of 8:3 fluoropolycarboxylic acid in Example 6. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these embodiments. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] All equipment and reagents used in this application were purchased from the market and there are no special requirements.

[0033] The solution to be treated in this invention is a spiked sample of pure water.

[0034] Ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS / MS) was used to detect the concentration of fluorinated polycarboxylic acid; a fluoride ion electrode was used to determine the concentration of fluoride ions; and a pH meter was used to determine the pH value of the solution.

[0035] Example 1:

[0036] A two-step method for removing fluorinated telomerase carboxylic acids using an "advanced oxidation-advanced reduction" process includes the following steps:

[0037] 1. Prepare 500 mL of 8:3 FTCA solution with a concentration of 1 mg / L using phosphate buffer. Pour 100 mL of the solution into 5 stoppered quartz test tubes.

[0038] 2. Prepare 100 mL of 50 M sodium disulfate solution.

[0039] Add 0.02 mL of 50 M sodium persulfate solution to test tube 1. The concentration of sodium persulfate solution in test tube 1 is 20 μM.

[0040] Add 0.1 mL of 50 M sodium persulfate solution to test tube 2. The concentration of sodium persulfate solution in test tube 2 is 50 μM.

[0041] Add 0.2 mL of 50 M sodium persulfate solution to test tube 3. The concentration of sodium persulfate solution in test tube 3 is 100 μM.

[0042] Add 0.4 mL of 50 M sodium persulfate solution to test tube 4. The concentration of sodium persulfate solution in test tube 4 is 200 μM.

[0043] Add 1 mL of 50M sodium persulfate solution to test tube 5. The concentration of sodium persulfate solution in test tube 5 is 500 μM.

[0044] 3. Place five test tubes in a vacuum ultraviolet light reaction apparatus with a wavelength of 185nm for irradiation. After reacting for 30 minutes, adjust the pH of the solution to alkaline with 2M NaOH, and then add 1mL of 1M sodium sulfite solution and 0.1mL of 1M I... - The solution was further irradiated for 5.5 hours. Samples were taken at 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, and 6 h to determine the 8:3 FTCA concentration and fluoride ion concentration, and the degradation rate and defluorination rate were calculated. The results are as follows: Figure 1 As shown.

[0045] The degradation efficiency of 8:3 FTCA gradually increased with increasing PDS dosage (20–200 μM), and the increase of PDS increased SO42-. ·- The generation of PDS promotes the formation of ·OH, further accelerating the degradation of the target pollutant. However, as the PDS dosage continued to increase to 500 μM, the degradation efficiency of 8:3 FTCA did not significantly improve. At 30 min of reaction, the defluorination rate remained almost unchanged, but with the onset of the reduction phase, i.e., the addition of sulfite and iodide ions, the defluorination rate reached its maximum when the PDS concentration in the system was 200 μM. When the PDS concentration in the oxidation phase was 500 μM, the defluorination rate decreased, possibly because the remaining PDS in the oxidation phase consumed a certain amount of reducing agent. Therefore, the optimal PDS dosage was determined to be 200 μM.

[0046] Example 2:

[0047] A two-step method for removing fluorinated telomerase carboxylic acids using an "advanced oxidation-advanced reduction" process includes the following steps:

[0048] 1. Prepare 500 mL of 8:3 FTCA solution with a concentration of 1 mg / L using phosphate buffer.

[0049] 2. Prepare 100 mL of 50 M sodium persulfate solution. Add 2 mL of 50 M sodium persulfate solution to the 8:3 FTCA solution, so that the concentration of sodium persulfate solution in the 8:3 FTCA solution is 200 μM.

[0050] 3. Take 100 mL of 8:3 FTCA solution and pour it into 5 stoppered quartz test tubes, and adjust the pH to 2.0, 4.0, 5.0, 6.0, 8.0 and 10.0 respectively.

[0051] 4. Place five test tubes in a vacuum ultraviolet light reaction apparatus with a wavelength of 185 nm for 20 minutes. Samples were taken before and after the reaction to measure the 8:3 FTCA concentration and calculate the degradation rate. The results are as follows: Figure 2The results showed that under different pH conditions of 2.0, 4.0, 5.0, 6.0, 8.0, and 10.0, the degradation rates of the oxidation stage were 24.6%, 36.7%, 55.1%, 97.8%, 90.7%, and 49.7%, respectively.

[0052] The degradation efficiency of 8:3FTCA first increases and then decreases with increasing pH. Compared with strong acid and strong alkaline conditions, weak acid to weak alkaline conditions (pH = 6.0 to 8.0) are more conducive to the removal of 8:3FTCA.

[0053] Example 3:

[0054] A two-step method for removing fluorinated telomerase carboxylic acids using an "advanced oxidation-advanced reduction" process includes the following steps:

[0055] 1. Prepare 500 mL of 8:3 FTCA solution with a concentration of 1 mg / L using phosphate buffer.

[0056] 2. Prepare 100 mL of 50 M sodium persulfate solution. Add 1 mL of 50 M sodium persulfate solution to the 8:3 FTCA solution. The concentration of sodium persulfate solution in the 8:3 FTCA solution is 100 μM.

[0057] 3. Adjust the pH of the 8:3 FTCA solution to 6.0.

[0058] 4. Take 100 mL of 8:3 FTCA solution and pour it into four stoppered quartz test tubes. Place the four test tubes in a vacuum ultraviolet light reaction apparatus with a wavelength of 185 nm for irradiation. After reacting for 30 min, adjust the pH of the solution to 6.0, 10.0, 11.0, and 12.0 respectively with 2 M NaOH. Then, add 1 mL of 1 M sodium sulfite solution and 0.1 mL of 1 M I... - The solution was further irradiated for 5.5 hours. Samples were taken before and after the reaction to determine the concentration of 8:3 FTCA and fluoride ions, and the defluorination rate was calculated. The results are as follows: Figure 3 show.

[0059] As the pH value increases, the defluorination rate gradually increases. At pH = 12.0, the defluorination efficiency is greatly improved, and complete defluorination can be achieved in 2 hours.

[0060] Example 4:

[0061] A two-step method for removing fluorinated telomerase carboxylic acids using an "advanced oxidation-advanced reduction" process includes the following steps:

[0062] 1. Prepare 500 mL of 8:3 FTCA solution with a concentration of 1 mg / L using phosphate buffer.

[0063] 2. Prepare 100 mL of 50 M sodium persulfate solution. Add 1 mL of 50 M sodium persulfate solution to the 8:3 FTCA solution. The concentration of sodium persulfate solution in the 8:3 FTCA solution is 100 μM.

[0064] 3. Adjust the pH of the 8:3 FTCA solution to 6.0.

[0065] 4. Take 100 mL of 8:3 FTCA solution and pour it into three stoppered quartz test tubes. Place the three test tubes in a UV light reaction apparatus for irradiation. The light sources are 185 nm (18 W) and 254 nm (18 W) UV lamps, respectively. After reacting for 30 min, take samples before and after the reaction to measure the 8:3 FTCA concentration and calculate the degradation rate. The results are as follows: Figure 4 The results showed that the removal rates were 97.8% and 91.8% under irradiation with 185nm and 254nm UV lamps, respectively.

[0066] Compared to 254nm ultraviolet light, 185nm vacuum ultraviolet light is more effective in degrading 8:3 FTCA. In addition to direct photolysis, it may also be because the latter produces H2O2, which in turn generates more ·OH free radicals, while UV radiation cannot break the hydrogen-oxygen bonds in water molecules and therefore cannot produce H2O2.

[0067] Example 5:

[0068] A two-step method for removing fluorinated telomerase carboxylic acids using an "advanced oxidation-advanced reduction" process includes the following steps:

[0069] 1. Prepare 500 mL of 8:3 FTCA solutions with concentrations of 0.1 mg / L, 0.5 mg / L, 1 mg / L, and 2 mg / L using phosphate buffer, and adjust the pH of the 8:3 FTCA solutions to 6.0.

[0070] 2. Prepare 100 mL of 50 M sodium persulfate solution. Take 100 mL of 8:3 FTCA solutions of different concentrations (0.1 mg / L, 0.5 mg / L, 1 mg / L, 2 mg / L) and pour them into four stoppered quartz test tubes I, II, III, and IV. Add 2 mL of 50 M sodium persulfate solution to each tube. The concentration of sodium persulfate solution in the 8:3 FTCA solution is 200 μM.

[0071] 3. Place the four test tubes in a vacuum ultraviolet light reaction apparatus with a wavelength of 185nm for irradiation. After reacting for 30 minutes, adjust the pH of the solution to 10 with 2M NaOH, and then add 1mL of 1M sodium sulfite solution and 0.1mL of 1M I... - The solution was further irradiated for 5.5 hours. Samples were taken before and after the reaction to determine the 8:3 FTCA concentration, and the degradation rate was calculated. The results are as follows: Figure 5 The data showed that the degradation rates of tubes I, II, III, and IV were 98.7%, 98.4%, 97.8%, and 86.8%, respectively.

[0072] When the initial concentration of 8:3FTCA decreased from 1 mg / L to 0.1 mg / L, the reaction rate increased, and after 5 minutes, 8:3FTCA was almost completely degraded. However, as the initial concentration increased to 2 mg / L, the degradation rate of 8:3FTCA decreased to 66.0% after 5 minutes, and reached 86.8% after 20 minutes. This is because, with a constant radiation intensity, an increase in the initial concentration means a decrease in the number of photons and free radicals obtained per unit concentration. Overall, however, vacuum UV / persulfate is effective for the degradation of 8:3FTCA within a certain concentration range.

[0073] Example 6:

[0074] A two-step method for removing fluorinated telomerase carboxylic acids using an "advanced oxidation-advanced reduction" process includes the following steps:

[0075] 1. Prepare 200 mL of 8:3FTCA, 7:3FTCA and 6:3FTCA solutions with concentrations of 1 mg / L respectively. Take 100 mL of each solution and pour it into three stoppered quartz test tubes. Adjust the pH of the solution to 6.0.

[0076] 2. Prepare 100 mL of 50 M sodium persulfate solution. Add 2 mL of 50 M sodium persulfate solution to each of three quartz test tubes.

[0077] 3. Place five test tubes in a vacuum ultraviolet light reaction apparatus with a wavelength of 185 nm for irradiation, and react for 30 minutes. Samples were taken before and after the reaction to measure the concentration of fluoropolycarboxylic acid and calculate the degradation rate. The results are as follows: Figure 6 The data showed that the degradation rates of tubes I, II, and III were 93.2%, 97.2%, and 95.6%, respectively.

[0078] The degradability of these homologues in vacuum UV / persulfate is roughly proportional to their chain length, with the degradation efficiency decreasing in the following trend: 8:3FTCA > 7:3FTCA > 6:3FTCA. Almost all of them are completely removed within 20 minutes. The maximum concentration of PFCAs generated by the degradation of 7:3FTCA and 6:3FTCA is one less than the number of fluorine-terminated carbon chains in the parent compound's molecular formula (i.e., the removal of one CF2 atom).

[0079] The above embodiments are merely examples illustrating the explanation, specific implementation methods, and effects of the present invention, and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to the invention without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of the present invention.

Claims

1. A two-step method for removing fluorinated polycarboxylic acids from water, characterized in that, Includes the following steps: 1) Add persulfate to the solution containing fluorinated telomerized carboxylic acid and carry out an advanced oxidation reaction under vacuum ultraviolet irradiation; 2) Adjust the pH of the solution to alkaline with NaOH, then add sulfite and halide ions in sequence, and continue the advanced reduction reaction under vacuum ultraviolet irradiation.

2. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The fluoropolymerized carboxylic acid is one or more of 8:3 fluoropolymerized carboxylic acid, 7:3 fluoropolymerized carboxylic acid, and 6:3 fluoropolymerized carboxylic acid.

3. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The persulfate is one or both of sodium persulfate and potassium persulfate.

4. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The sulfite is one or both of sodium sulfite and potassium sulfite; the halide ion is an iodide ion.

5. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The pH value of the advanced oxidation reaction is in the range of 2.0-10.0; the pH value of the advanced reduction reaction is in the range of 6.0-12.

0.

6. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The wavelength of the vacuum ultraviolet light is 185nm-254nm.

7. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The wavelength of the vacuum ultraviolet light is 185nm.

8. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The persulfate solution concentration is 20-500 μM, and the sulfite concentration is 10 mM.

9. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The concentration of the fluoropolymer carboxylic acid is 0.1 mg / L to 2 mg / L.

10. The two-step method for removing fluorinated polycarboxylic acid from water according to claim 1, characterized in that: The advanced oxidation reaction time is 20 min to 30 min, and the advanced reduction reaction time is 5.5 h.

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