Method for degrading perfluorocarboxylic acid

Abstract

The invention provides a method for degrading perfluorocarboxylic acid, and belongs to the technical field of environment and chemistry. The method for degrading the perfluorocarboxylic acid comprises the following steps: adding a carbon material into a to-be-treated solution containing the perfluorocarboxylic acid, heating and stirring to degrade the perfluorocarboxylic acid, wherein the carbon material has an oxygen-containing functional group. The carbon material with the oxygen-containing functional group is used as the catalyst, degradation of the perfluorocarboxylic acid can be efficiently catalyzed at low temperature, and secondary pollution is avoided. In addition, the carbon material disclosed by the invention is wide in purchase approach and low in price, and the production cost can be remarkably reduced.

Description

Technical Field

[0001] The present disclosure relates to the fields of environment and chemistry, and particularly to a method for degrading perfluorocarboxylic acids. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are organic compounds with high chemical stability. In recent years, PFAS have been widely used in various industrial and consumer products such as flame retardants, food packaging, paints, etc. However, PFAS enter the environment such as the atmosphere, soil, and water bodies through pollution sources and can persist in environmental media for a long time. Then, they enter the human body through water, food, etc., threatening human health and biosafety. Perfluorocarboxylic acids (PFCA) are an important part of PFAS. Achieving the degradation of PFCA is beneficial to alleviating environmental pollution problems. However, there are still some limitations in the degradation of PFCA in related technologies. Therefore, there is an urgent need for a method that can efficiently degrade PFCA and alleviate environmental pollution. Summary of the Invention

[0003] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present disclosure provides a method for degrading perfluorocarboxylic acids.

[0004] According to an embodiment of the present disclosure, there is provided a method for degrading perfluorocarboxylic acids, including: adding a carbon material to a liquid to be treated containing perfluorocarboxylic acids, heating and stirring to degrade the perfluorocarboxylic acids; wherein, the carbon material has oxygen-containing functional groups.

[0005] According to an embodiment of the present disclosure, using the carbon material as a catalyst, the oxygen-containing functional groups thereon can catalyze the efficient degradation of PFCA at a relatively low temperature, significantly reducing the reaction energy consumption. At the same time, the carbon material has high stability and good environmental protection characteristics, and will not release harmful substances that cause secondary pollution to the environment during the reaction process. In addition, the carbon material adopted in the present disclosure has a wide range of procurement channels and relatively low prices, which can significantly reduce the production cost and simplify the supply chain management of raw materials. Brief Description of the Drawings

[0006] Through the following description of the embodiments of the present disclosure with reference to the drawings, the above and other objects, features, and advantages of the present disclosure will become clearer. In the drawings:

[0007] Figure 1 It is a schematic diagram of the decomposition kinetics of perfluorooctanoic acid (PFOA) according to an embodiment of the present disclosure;

[0008] Figure 2 It is a schematic diagram of the free radical chain reaction of PFOA decomposition according to an embodiment of the present disclosure;

[0009] Figure 3TOF-MS (Time-of-Flight Mass Spectrometry) diagram of the PFOA decomposition reaction intermediate according to an embodiment of the present disclosure;

[0010] Figure 4 Degradation rate diagram of PFOA according to an embodiment of the present disclosure;

[0011] Figure 5 F after PFOA decomposition according to an embodiment of the present disclosure - Yield schematic diagram;

[0012] Figure 6 Degradation rate diagram of PFOA according to an embodiment of the present disclosure;

[0013] Figure 7 F after PFOA decomposition according to an embodiment of the present disclosure - Yield schematic diagram;

[0014] Figure 8 F after PFOA decomposition according to an embodiment of the present disclosure - Yield schematic diagram;

[0015] Figure 9 F after PFOA decomposition according to an embodiment of the present disclosure - Yield schematic diagram;

[0016] Figure 10 F after PFOA decomposition according to an embodiment of the present disclosure - Yield schematic diagram. Detailed implementation manners

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, obviously, one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0018] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The term "including" used herein indicates the presence of features, steps, operations, but does not exclude the presence or addition of one or more other features.

[0019] In the case of using expressions such as "at least one of A, B, and C, etc.", generally, it should be interpreted according to the meaning that those skilled in the art usually understand this expression (for example, "a system having at least one of A, B, and C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", generally, it should be interpreted according to the meaning that those skilled in the art usually understand this expression (for example, "a system having at least one of A, B, or C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0020] In the related art, when realizing the degradation of PFCA, the commonly used methods generally include photocatalytic degradation, electrocatalytic degradation, high-temperature degradation, chemical degradation, and biodegradation, etc. Although these methods have made certain progress in the degradation of PFCA, there are still problems such as relatively harsh reaction conditions, relatively high reaction costs, and possible secondary pollution during the treatment process. In the realization of the inventive concept of the present disclosure, it is found that using a carbon material with oxygen-containing functional groups as a catalyst to degrade PFCA can not only improve the degradation rate of PFCA, but also degrade at a lower temperature, and at the same time, no secondary pollution will be generated during the degradation process. Therefore, the inventor proposes a method for degrading PFCA, which realizes the efficient removal of PFCA at a lower temperature by adding a carbon material with oxygen-containing functional groups.

[0021] Specifically, according to an embodiment of one aspect of the present disclosure, a method for degrading perfluorocarboxylic acid is provided, including: adding a carbon material to a liquid to be treated containing perfluorocarboxylic acid, heating and stirring to degrade the perfluorocarboxylic acid, and the degradation products include fluoride ions (F - ); wherein, the carbon material has oxygen-containing functional groups.

[0022] Hereinafter, taking the degradation of PFOA as an example, the reaction mechanism during the degradation of perfluorocarboxylic acid will be described. As Figure 1 shown, (a) represents the decomposition reaction of PFOA catalyzed by granular activated carbon (GAC) containing COOH functional groups, where (ⅰ) is the free radical product pathway and (ⅱ) is the ionic product pathway; (b) represents the self-decomposition reaction of PFOA, where (ⅲ) is the free radical product pathway and (ⅳ) is the ionic product pathway. The ΔG 4 from PFOA directly to the transition state (PFOA-TS) is 26.76 kcal·mol -1 , and the ΔG 6 from the transition state to the ionic product is -6.09 kcal·mol -1。Since the ionic reaction path is reversible, according to the reaction equilibrium constant formula, the reaction equilibrium constant K of PFOA from the transition state to the ionic product is calculated b to be 6.55, indicating that the equilibrium between the ionic product and the transition state is close. Thus, even if the ionic product is formed, there may be a relatively high probability of the reverse reaction occurring, causing the ionic product to revert to the transition state. Therefore, the system tends to maintain a dynamic equilibrium state, making it difficult for the ionic product to accumulate. It should be noted that the free energy change ΔG³ for the conversion of PFOA from the transition state to the ionic product catalyzed by GAC with a COOH functional group is -34.25 kcal·mol -1 , significantly lower than the ΔG for the direct formation of the ionic product of PFOA 6 , and its reaction equilibrium constant Ka is calculated to be 3.68×10 4 , much larger than K b , indicating that the equilibrium strongly favors the ionic product. Therefore, ion formation is highly favorable, and even in a reversible reaction, the probability of the reverse reaction occurring is extremely low, and the ionic product almost completely dominates. This stability not only reduces the possibility of reverting back to the transition state but also provides favorable conditions for the smooth progress of subsequent reactions, thereby significantly enhancing the overall reaction efficiency. Under the catalysis of GAC with a COOH functional group, the free energy change ΔG¹ for the conversion of PFOA to the transition state is 36.96 kcal / mol, higher than the ΔG for the direct conversion of PFOA to the transition state 4 . Due to the influence of temperature, the system can obtain sufficient energy to overcome this energy barrier. As Figure 2 shown, in addition to the ionic reaction process, the decomposition of PFOA involves a multi-step radical chain reaction, including initiation, recombination, and termination. The addition of GAC accelerates the decarboxylation reaction by reducing the activation energy for the cleavage of the C-C bond linking the carboxyl group in PFOA. In this reaction path, PFOA first generates a non-fluorinated moiety and perfluoroalkyl radicals through decarboxylation. These perfluoroalkyl radicals are highly reactive and can further undergo defluorination reactions or radical chain growth reactions to gradually generate shorter-chain perfluoroalkyl radicals. Eventually, these chain growth reactions terminate after generating extremely short fluorine-containing units. As Figure 3 shown, TOF-MS spectra of reaction intermediates at different reaction times (35 min, 40 min, and 19 h) are detected. (a - c) depict the total ion chromatogram (TIC) curves of the reaction products of PFOA at these time points, and (d - g) represent the mass spectra corresponding to the characteristic peaks in the TIC curves. The various perfluoroalkyl intermediates detected and their mass-to-charge ratios (m / z) are: ·C3F3 (m / z = 92.9), ·C2F5 (m / z = 120.0), ·C3F5 (m / z = 131.0), ·C6F 11(m / z = 281.0), ·C7F 13 (m / z = 331.0), ·C7F 14 (m / z = 351.0). The presence of these perfluoroalkyl intermediates further indicates that the free radical chain reaction is also an important part of this degradation process.

[0023] According to an embodiment of the present disclosure, a carbon material is used as a catalyst, and the oxygen-containing functional groups thereon can catalyze the efficient degradation of PFCA at a relatively low temperature, significantly reducing the reaction energy consumption. At the same time, the carbon material has high stability and good environmental protection characteristics, and will not release harmful substances that cause secondary pollution to the environment during the reaction process. In addition, the carbon material adopted in the present disclosure has a wide range of procurement channels and relatively low prices, which can significantly reduce the production cost and simplify the supply chain management of raw materials.

[0024] According to an embodiment of the present disclosure, the above-mentioned oxygen-containing functional groups include carboxyl groups.

[0025] According to an embodiment of the present disclosure, carboxyl groups are beneficial to improving the catalytic efficiency of the carbon material for PFCA.

[0026] According to an embodiment of the present disclosure, the carbon material includes at least one of coal-based activated carbon and biochar.

[0027] According to an embodiment of the present disclosure, coal-based activated carbon and biochar have good pore structures, rich functional groups and high chemical stability compared with other carbon materials, and will not introduce new pollutants during the reaction process, ensuring the safety and reliability of the reaction.

[0028] According to an embodiment of the present disclosure, the mass ratio of the carbon material to the perfluorocarboxylic acid is 10:5 to 10:1. Preferably, the mass ratio of the carbon material to the perfluorocarboxylic acid is 10:3 to 10:1, such as 4:1, 5:1, 6:1, 7:1, 8:1 and 9:1.

[0029] According to an embodiment of the present disclosure, if the mass ratio of the carbon material to the perfluorocarboxylic acid is too low, the reaction will be incomplete during the degradation process, affecting the degradation effect; if the mass ratio of the carbon material to the perfluorocarboxylic acid is too high, it is not conducive to further improving the degradation effect, and will also cause waste and reduce the utilization efficiency of the reactants.

[0030] According to an embodiment of the present disclosure, the temperature of the heating reaction is 60 to 150 °C. Preferably, the above heating temperature is 80 to 130 °C, such as 90 °C, 100 °C, 110 °C and 120 °C.

[0031] According to an embodiment of the present disclosure, if the temperature of the heating reaction is too low, the reaction rate will be reduced; if the temperature of the heating reaction is too high, it is not conducive to increasing the reaction rate, and will also cause waste of resources.

[0032] According to an embodiment of the present disclosure, the pH of the liquid to be treated is > 12, for example, 12.5, 13, 13.5, and 14.

[0033] According to an embodiment of the present disclosure, controlling the pH of the liquid to be treated > 12 can enable the reaction to proceed in a sufficiently alkaline environment, which is beneficial to the decarboxylation of PFCA, thereby improving the degradation efficiency.

[0034] According to an embodiment of the present disclosure, the liquid to be treated includes a dipolar solvent and water, wherein the volume ratio of the dipolar solvent to water is 3:1 to 10:1, for example, 4:1, 5:1, 6:1, 7:1, 8:1, and 9:1.

[0035] According to an embodiment of the present disclosure, controlling the volume ratio of the dipolar solvent to water in the liquid to be treated to be 3:1 to 10:1 can better adjust the polarity of the reaction system, make the solvent system more homogeneous, and is beneficial to the collision of the substrate and the intermediate as a dispersant, thereby improving the degradation efficiency.

[0036] According to an embodiment of the present disclosure, the dipolar solvent includes at least one of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, hexamethylphosphoramide, acetone, and ethanol. Preferably, the dipolar solvent includes dimethyl sulfoxide, acetonitrile, and dimethylformamide.

[0037] According to an embodiment of the present disclosure, the above-mentioned dipolar solvent has a relatively high polarity compared to other dipolar solvents, can dissolve some substances that are difficult to dissolve in ordinary solvents, and stabilize the reaction intermediate, thereby improving the degradation efficiency.

[0038] According to an embodiment of the present disclosure, the method of the present disclosure further includes: before heating and stirring, the liquid to be treated added with the carbon material is also subjected to ultrasonic treatment.

[0039] According to an embodiment of the present disclosure, performing ultrasonic treatment before heating and stirring can better disperse the substrate and the reactant, thereby improving the degradation efficiency.

[0040] According to an embodiment of the present disclosure, the perfluorocarboxylic acid includes at least one of perfluorobutyric acid, perfluorovaleric acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, and perfluorooctadecanoic acid.

[0041] Furthermore, the concentration of the perfluorocarboxylic acid in the liquid to be treated is not limited, for example, it can be 10 g / L.

[0042] The present disclosure will be further described in detail below with reference to the drawings and specific embodiments.

[0043] Example 1

[0044] 100 mg of perfluorooctanoic acid (PFOA) and 289 mg of sodium hydroxide (NaOH) were added to a polytetrafluoroethylene beaker; 10 ml of dimethyl sulfoxide (DMSO) and 1.25 ml of ultrapure water were added to the beaker; 1000 mg of activated carbon F400 was added to the above beaker and sonicated for 15 s; the sonicated beaker was placed in a heating stirrer and heated and stirred at 120 °C and 500 rpm for 24 h.

[0045] Comparative Example 1

[0046] The difference from Example 1 was that F400 was not added.

[0047] Example 2

[0048] The difference from Example 1 was that F400 was replaced with pyrolytic carbon containing carboxyl (-COOH) modified with nitric acid (pyrolytic carbon - O). The preparation method of pyrolytic carbon - O was as follows: 1000 mg of pyrolytic carbon and 15 ml of nitric acid with a concentration of 10 mol·L -1 were added to a polytetrafluoroethylene beaker and stirred at a speed of 500 rpm for 3 h, and then solid - liquid separation was carried out; the solid obtained in the above reaction was thoroughly washed with deionized water and solid - liquid separated until the conductivity of the supernatant dropped to 50 μS·cm -1 or less; the solid was dried at 110 °C for 12 h to obtain pyrolytic carbon - O.

[0049] Example 3

[0050] The difference from Example 1 was that F400 was replaced with F400 containing carboxyl (-COOH) modified with nitric acid (F400 - O). The preparation method of F400 - O was as follows: 1000 mg of F400 and 15 ml of nitric acid with a concentration of 10 mol·L -1 were added to a polytetrafluoroethylene beaker and stirred at a speed of 500 rpm for 3 h, and then solid - liquid separation was carried out; the solid obtained in the above reaction was thoroughly washed with deionized water and solid - liquid separated until the conductivity of the supernatant dropped to 50 μS·cm -1 or less; the solid was dried at 110 °C for 12 h to obtain F400 - O.

[0051] Example 4

[0052] The difference from Example 1 is that F400 is replaced with a functional group-free PCM polymer PCM0. The preparation method of PCM0 is as follows: Dissolve 3 mmol of 1,3,5-triethynylbenzene, 3 mmol of 1,4-dibromobenzene, 150 mg of tetrakis(triphenylphosphine)palladium(0), and 45 mg of copper(I) iodide in 20 ml of N,N-dimethylformamide and 20 ml of triethylamine to obtain a mixture; Stir the mixture for 30 min under lightless conditions, and then heat it at 80 °C for 72 h in a nitrogen environment; Cool the mixture to room temperature, and wash the obtained product successively with chloroform, water, methanol, and water, and then dry it at 100 °C for 24 h to obtain PCM0.

[0053] Example 5

[0054] The difference from Example 1 is that F400 is replaced with a PCM polymer PCM-OH containing a hydroxyl group (-OH). The preparation method of PCM-OH is as follows: Dissolve 3 mmol of 1,3,5-triethynylbenzene, 3 mmol of 2,5-dibromohydroquinone, 150 mg of tetrakis(triphenylphosphine)palladium(0), and 45 mg of copper(I) iodide in 20 ml of N,N-dimethylformamide and 20 ml of triethylamine to obtain a mixture; Stir the mixture for 30 min under lightless conditions, and then heat it at 80 °C for 72 h in a nitrogen environment; Cool the mixture to room temperature, and wash the obtained product successively with chloroform, water, methanol, and water, and then dry it at 100 °C for 24 h to obtain PCM-OH.

[0055] Example 6

[0056] The difference from Example 1 is that F400 is replaced with a PCM polymer PCM-COOH containing a carboxyl group (-COOH). The preparation method of PCM-COOH is as follows: Dissolve 3 mmol of 1,3,5-triethynylbenzene, 3 mmol of 2,5-diiodobenzoic acid, 150 mg of tetrakis(triphenylphosphine)palladium(0), and 45 mg of copper(I) iodide in 20 ml of N,N-dimethylformamide and 20 ml of triethylamine to obtain a mixture; Stir the mixture for 30 min under lightless conditions, and then heat it at 80 °C for 72 h in a nitrogen environment; Cool the mixture to room temperature, and wash the obtained product successively with chloroform, water, methanol, and water, and then dry it at 100 °C for 24 h to obtain PCM-COOH.

[0057] Example 7

[0058] The difference from Example 1 is that the added mass of F400 is 200 mg.

[0059] Example 8

[0060] The difference from Example 1 is that the mass of F400 added is 500 mg.

[0061] Example 9

[0062] The difference from Example 1 is that the mass of F400 added is 2000 mg.

[0063] The degradation rate of PFCA is expressed by the pseudo-first-order degradation rate constant.

[0064]

[0065] Where K obs is the pseudo-first-order degradation rate constant (min -1 ), C t is the concentration of the reactant at time t (mg·L -1 ), and C0 is the initial concentration of the reactant (mg·L -1 ).

[0066] F - The yield of is calculated by the following formula:

[0067]

[0068] Where, is the final concentration of F - (mol·L -1 ), is the volume of the reaction solution (ml), is the relative molecular mass of PFCA, is the relative atomic mass of F, is the dosage of PFCA (mg), is the number of carbon atoms in the PFCA molecular formula.

[0069] Detect the degradation rate of PFOA over time in Example 1 and Comparative Example 1. As Figure 4 shown, the K obs of PFOA without adding F400 is (2.40 ± 0.12)×10 -2 , and the K obs of PFOA with adding F400 is (4.11 ± 0.22)×10 -2 , and the degradation rate is increased by about 20%, proving that the addition of F400 can significantly increase the reaction rate of degrading PFOA; detect the yield of F - in Example 1 and Comparative Example 1. As Figure 5 shown, the yield of F - of PFOA with adding F400 is increased by about 35% compared with that without adding F400, proving that the addition of F400 can significantly improve the degradation effect of PFOA.

[0070] Detection of F in Examples 1, 2 and Comparative Example 1 - The yield, such as Figure 6 As shown, after the addition of pyrolytic carbon-O, F - The yield of PFCA was increased by about 39%, proving that the increase of oxygen-containing functional groups in carbon materials can significantly improve the degradation effect of PFCA; the F - The yield, such as Figure 7 As shown, after F400-O is added, F - The yield of PFCA was increased by about 18%, proving that the increase in the loading amount of oxygen-containing functional groups in the carbon material can significantly improve the degradation effect of PFCA; the F - The yield, such as Figure 8 As shown, PCM-OH only increases F - The yield of F increased from 50% to 52%, and PCM-COOH increased F - The yield increased from 50% to 67%, proving that the presence of carboxyl groups is more conducive to improving the degradation efficiency of PFCA.

[0071] The degradation rates of PFOA in Examples 1, 7, 8 and 9 were measured. Figure 9 As shown in Figure 2, when the mass ratio of F400 to PFOA is 2, 5, 10, and 20, K obs They are (2.61±0.17)×10⁻², (3.48±0.19)×10 -2 、(4.11±0.22)×10 -2 and (4.24±0.21)×10 -2 It is proved that the reaction rate of PFOA degradation can be improved with the increase of the mass ratio of F400 to PFOA; the F - The yield, such as Figure 10 As shown in Figure 2, with the increase of the mass ratio of F400 to PFOA, - The yield of F400 increased gradually. When the mass ratio of F400 to PFOA reached 10:1, - The yield improvement trend tends to be flat, proving that when the mass ratio of carbon material to PFCA exceeds 10:1, the degradation effect of PFCA is not significantly improved. Figure 9 It can be proved that the mass ratio of carbon material to PFCA in the range of 10:5~10:1 can significantly improve the degradation rate and degradation effect without causing waste.

[0072] The specific embodiments described above further elaborate on the objectives, technical solutions, and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. A method for degrading perfluorocarboxylic acid, comprising: Adding the carbon material to the liquid to be treated containing the perfluorocarboxylic acid, heating and stirring, so that the perfluorocarboxylic acid is degraded; Wherein, the carbon material has oxygen-containing functional groups.

2. The method according to claim 1, wherein: The oxygen-containing functional group includes a carboxyl group.

3. The method according to claim 1, wherein: The carbon material includes at least one of coal-based activated carbon and biochar.

4. The method according to claim 1, wherein: The mass ratio of the carbon material to the perfluorocarboxylic acid is 10:5 to 10:

1.

5. The method according to claim 1, wherein: The heating temperature is 60-150°C.

6. The method according to claim 1, wherein: The pH of the liquid to be treated is>12.

7. The method according to claim 1, wherein: The liquid to be treated includes a dipolar solvent and water; Wherein, the volume ratio of the dipole solvent to water is 3:1-10:

1.

8. The method according to claim 7, wherein: The dipolar solvent includes at least one of dimethyl sulfoxide, dimethylamide, dimethylacetamide, hexamethylphosphoramide, acetone and ethanol.

9. The method according to claim 7, further comprising: Sonication was performed prior to heating and stirring.

10. The method according to claim 1, wherein: The perfluorocarboxylic acid includes at least one of perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid and perfluorooctadecanoic acid.

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