Defluorination method for perfluorinated compounds using layered double metal oxides or hydroxides

Abstract

The present invention discloses a method for defluorinating perfluorocompounds using a layered bimetallic oxide or hydroxide, and belongs to the technical field of defluorination methods. The method for defluorinating perfluorocompounds using a layered bimetallic oxide comprises adding the layered bimetallic oxide to a solution of the perfluorocompound and performing a hydrothermal reaction at 160°C to 220°C for 30 to 120 minutes. The defluorination method of the present invention has excellent perfluorocompound defluorination effects, mild processing conditions, and a simple processing process, while eliminating complex post-processing steps.

Description

Technical Field

[0001] The present invention relates to the technical field of defluorination methods, and in particular to a defluorination method using layered double metal hydroxides or corresponding layered metal oxides. Background Art

[0002] Perfluoroalkyl substances and polyfluoroalkyl substances (PFASs) are harmful pollutants that are widely present in the environment, wildlife, and humans. The CF bond energy in their structure is high, making defluorination extremely difficult.

[0003] An existing defluorination method is to add an alkali such as sodium hydroxide and then conduct a hydrothermal reaction to achieve rapid degradation and defluorination of perfluorinated compounds through hydroxide nucleophilic substitution. However, this method has high requirements for the hydrothermal reaction temperature and alkali concentration, making it difficult to promote and apply.

[0004] On the other hand, layered double hydroxides (LDHs) are a type of layered structured material composed of layers and intercalated anions. When calcined at high temperatures (e.g., 500°C), they lose interlayer anions and water and transform into corresponding layered double oxides (LDOs). LDOs have a unique structural memory effect. When dissolved in aqueous solution, they reabsorb water molecules and anions, restoring the two-dimensional layered structure of LDHs and leaving behind a large number of OH groups remaining due to the capture of hydrogen atoms. - , increase the pH value of water.

[0005] Based on the above reaction process, another existing defluorination method combines the structural memory effect of LDO with the deprotonation of PFOA in natural water, adsorbing PFOA between the layers of LDO as it restores its two-dimensional layered structure. However, this method does not achieve the mineralization of perfluorinated compounds, converting them into inorganic fluoride ions, or perfluorinated compounds. Furthermore, the resulting PFOA-adsorbed LDHs require difficult and costly post-processing. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention aims to propose a method for defluorinating perfluorinated compounds using layered bimetallic oxides or hydroxides. This method combines and synergizes the structural memory effect of LDO with a hydrothermal reaction. Compared with direct adsorption treatment of LDO or LDH or conventional alkaline hydrothermal treatment, it has better perfluorinated compound mineralization effect and milder treatment conditions, while eliminating the complex post-processing process.

[0007] The technical solutions of the present invention are as follows:

[0008] The invention discloses a perfluoro compound defluorination method using layered bimetallic oxide, which comprises: adding the layered bimetallic oxide into a perfluoro compound solution, and performing a hydrothermal reaction at 160-220° C. for 30-120 minutes.

[0009] The inventors unexpectedly discovered that adding layered bimetallic oxides (LDO) to a solution of a perfluorinated compound and conducting a hydrothermal reaction can effectively combine the structural memory effect of LDO with the hydrothermal reaction. This combination is not a simple case of LDO adsorbing the perfluorinated compound or LDH generated by its rehydration adsorbing the perfluorinated compound and then promoting its thermal degradation by a hydrothermal reaction. Instead, it causes the carbon-fluorine bonds of the perfluorinated compound to break with the participation of LDO, resulting in sufficient mineralization and defluorination of the perfluorinated compound. The defluorination rate is significantly improved compared to direct LDO adsorption treatment or direct thermal degradation of the perfluorinated compound or its thermal degradation under alkaline conditions.

[0010] According to some preferred embodiments of the present invention, the method further comprises: adding the layered bimetallic oxide to a solution of a perfluorinated compound, stirring and mixing the mixture for 5-15 hours, and then performing a hydrothermal reaction at 160° C.-220° C. for 30-120 minutes.

[0011] According to some preferred embodiments of the present invention, the layered bimetallic oxide is a layered bimetallic oxide of magnesium and aluminum, wherein the molar ratio of magnesium to aluminum is 2:1.

[0012] According to some preferred embodiments of the present invention, the temperature of the hydrothermal reaction is 200-220° C.; and / or the time of the hydrothermal reaction is 90-120 min.

[0013] The present invention further provides a method for defluorinating a perfluoro compound using a layered double metal hydroxide, comprising: calcining the layered double metal hydroxide to obtain a layered bimetallic oxide, adding the layered bimetallic oxide to a solution of a perfluoro compound, and performing a hydrothermal reaction at 160° C. to 220° C. for 30 to 120 minutes.

[0014] According to some preferred embodiments of the present invention, the layered double hydroxide is a layered double hydroxide of magnesium and aluminum, wherein the molar ratio of magnesium to aluminum is 2:1, and carbonate ions are present between the layers.

[0015] According to some preferred embodiments of the present invention, the temperature of the hydrothermal reaction is 200-220° C.; and / or the time of the hydrothermal reaction is 90-120 min.

[0016] According to some preferred embodiments of the present invention, the calcination temperature is 450-500°C.

[0017] According to some preferred embodiments of the present invention, the perfluorinated compound is selected from perfluorooctanoic acid and / or potassium perfluorooctane sulfonate.

[0018] According to some preferred embodiments of the present invention, the concentration of the perfluorinated compound solution is 15-25 mg / L.

[0019] The beneficial effects of the present invention include:

[0020] (1) The defluorination method of the present invention can first enrich the perfluorinated compound in the interlayer of the layered bimetallic oxide, and then use the hydrothermal reaction involving the layered bimetallic oxide to completely mineralize the perfluorinated compound. Compared with the traditional hydrothermal reaction treatment of perfluorinated compounds with alkali or the adsorption treatment of layered bimetallic oxide / hydroxide, the defluorination effect is significantly better and the defluorination speed is significantly faster;

[0021] (2) The defluorination method of the present invention has mild reaction conditions, is environmentally friendly, and reduces energy consumption;

[0022] (3) The defluorination method of the present invention reduces the high-cost centralized treatment of the adsorbed materials in traditional adsorption treatment, simplifies the entire process flow, and reduces treatment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The X-ray diffraction comparison diagrams of the raw material Mg / Al-LDH, the Mg / Al-LDO obtained in Example 1, and the redissolved Mg / Al-LDH.

[0024] Figure 2 This is a statistical diagram of the defluorination rate of Example 1.

[0025] Figure 3 This is a statistical diagram of the defluorination rate of Example 2.

[0026] Figure 4 This is a statistical diagram of the defluorination rate of Example 3.

[0027] Figure 5 This is a statistical diagram of the defluorination rate of Example 4.

[0028] Figure 6 This is a statistical chart of the defluorination rate of Comparative Example 1.

[0029] Figure 7 It is the statistical graph of the defluorination rate of comparative examples 2, 3 and 4.

[0030] Figure 8 This is a statistical chart of the defluorination rate of Comparative Example 5. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below through specific embodiments, but this should not be construed as limiting the scope of the present invention to the following examples. Various substitutions or modifications made according to common technical knowledge and customary means in the art without departing from the above-mentioned method concept of the present invention are intended to be included within the scope of the present invention.

[0032] The fluoride ion concentration in the following examples was determined using a fluoride ion electrode (Orion Dual Star pH / ISE dual-channel benchtop meter). The defluorination rate was calculated according to the following formula:

[0033]

[0034] Among them C F is the measured fluoride ion concentration (mg / L), V 液 is the volume of the solution (mL), C0 and V0 are the initial concentration (mg / L) and volume (mL) of the perfluorooctanoic acid or potassium perfluorooctane sulfonate solution, respectively. F It is the ratio of the total amount of fluorine atoms in perfluorooctanoic acid or potassium perfluorooctane sulfonate to the molecular weight.

[0035] Example 1

[0036] Defluorination is carried out by the following steps:

[0037] (1) Mg / Al-LDH was placed in a porcelain boat and then placed in a muffle furnace for calcination to obtain Mg / Al-LDO at a calcination temperature of 500°C for 3 h.

[0038] (2) 5 g of Mg / Al-LDO was added to a 50 mL reactor containing 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution and stirred for 10 h. The mixture was then hydrothermally reacted at 200 °C for 30, 60, 90, and 120 min, respectively, to obtain a reaction solution.

[0039] (3) Add 20 ml of ultrapure water to the reaction solution, sonicate at 100 Hz for 15 min, and then centrifuge at 12,000 rpm for 5 min.

[0040] (4) The supernatant obtained by centrifugation was taken out and filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0041] Meanwhile, reconstituted LDH was obtained by the following steps:

[0042] (1) Mg / Al-LDH was placed in a porcelain boat and then placed in a muffle furnace for calcination to obtain Mg / Al-LDO at a calcination temperature of 500°C for 3 h.

[0043] (2) 5 g of Mg / Al-LDO was added to a 50 mL reactor containing 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution and stirred for 10 h to obtain a reaction solution.

[0044] (3) Place the resulting reaction solution into a centrifuge and centrifuge at 12,000 rpm for 5 minutes;

[0045] (4) The precipitate obtained by centrifugation was placed in a -20°C refrigerator and frozen for 12 h, and then freeze-dried at -50°C for 48 h to obtain the reconstituted Mg / Al-LDH.

[0046] Furthermore, X-ray diffraction comparison was performed on the raw material Mg / Al-LDH (LDH shown in the figure) used in Example 1, the Mg / Al-LDO (LDO shown in the figure) obtained by calcination, and the Mg / Al-LDH obtained after redissolution (re-LDH shown in the figure). The results are shown in the attached figure. Figure 1 shown.

[0047] from Figure 1 It can be seen that LDH has characteristic diffraction peaks at the (003), (006), (012), (015), (018), (110), (113), and (116) planes, which are characteristic of Mg / Al-LDH. After calcination, LDO has characteristic peaks at the (200) and (220) planes, which are characteristic of a MgO-like phase structure. Meanwhile, re-LDH has characteristic diffraction peaks consistent with those of Mg / Al-LDH.

[0048] The above shows that Mg / Al-LDH will turn into the corresponding layered double metal oxide after calcination, and re-dissolving it in water will completely restore the two-dimensional lamellar structure of the layered double hydroxide.

[0049] Further, the filtrate was fixed to 30 ml, the pH was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode. The results are shown in the attached figure. Figure 2 As shown in the figure, it can be seen that only a few carbon-fluorine bonds of PFOA are broken after 30 minutes of hydrothermal treatment, while the defluorination rate reaches 90.55% after 90 minutes of hydrothermal treatment and 100% after 120 minutes of hydrothermal treatment.

[0050] Example 2

[0051] Defluorination is carried out by the following steps:

[0052] (1) Mg / Al-LDH was placed in a porcelain boat and then placed in a muffle furnace for calcination to obtain Mg / Al-LDO at a calcination temperature of 500°C for 3 h.

[0053] (2) 5 g of Mg / Al-LDO was added to a 50 mL reactor containing 16 mL of a 20 mg / L potassium perfluorooctane sulfonate (PFOS) solution and stirred for 10 h. The mixture was then hydrothermally reacted at 200 °C for 30, 60, 90, and 120 min, respectively, to obtain a reaction solution.

[0054] (3) Add 20 ml of ultrapure water to the reaction solution, sonicate at 100 Hz for 15 min, and then centrifuge at 12,000 rpm for 5 min;

[0055] (4) The supernatant obtained by centrifugation was taken out and filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0056] Furthermore, the filtrate obtained in step (4) was diluted to 30 ml, the pH was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode. The results are shown in the attached figure. Figure 3 As shown in the figure, the defluorination rate of PFOS reached 68.95% after 90 minutes of hydrothermal reaction, and 85.89% after 120 minutes. This shows that even though PFOS contains more stable sulfonic acid groups and carbon-fluorine bonds are more difficult to break, the defluorination method of the present invention can still achieve a good defluorination effect.

[0057] Example 3

[0058] Defluorination is carried out by the following steps:

[0059] (1) Mg / Al-LDH was placed in a porcelain boat and then placed in a muffle furnace for calcination to obtain Mg / Al-LDO at a calcination temperature of 500°C for 3 h.

[0060] (2) 0.1 g and 1 g of Mg / Al-LDO were added to a 50 mL reactor containing 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution and stirred for 10 h. The mixture was then hydrothermally reacted at 200 °C for 90 min to obtain reaction solutions.

[0061] (3) Add 20 ml of ultrapure water to the reaction solution, sonicate at 100 Hz for 15 min, and then centrifuge at 12,000 rpm for 5 min;

[0062] (4) The supernatant obtained by centrifugation was taken out and filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0063] Furthermore, the filtrate obtained in step (4) was diluted to 30 ml, the pH was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode. The results were compared with those of the hydrothermal reaction at 200 ° C for 90 min in Example 1. Figure 4 As shown, it can be seen that with the increase of LDO dosage, the defluorination effect is also correspondingly improved.

[0064] Example 4

[0065] Defluorination is carried out by the following steps:

[0066] (1) Mg / Al-LDH was placed in a porcelain boat and then placed in a muffle furnace for calcination to obtain Mg / Al-LDO at a calcination temperature of 500°C for 3 h.

[0067] (2) 5 g of Mg / Al-LDO was added to a 50 mL reactor containing 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution and stirred for 10 h. The mixture was then hydrothermally reacted at 160°C, 180°C, 200°C, and 220°C for 90 min to obtain a reaction solution.

[0068] (3) Add 20 ml of ultrapure water to the reaction solution, sonicate at 100 Hz for 15 min, and then centrifuge at 12,000 rpm for 5 min;

[0069] (4) The supernatant obtained by centrifugation was taken out and filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0070] Furthermore, the filtrate obtained in step (4) was diluted to 30 ml, the pH was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode. The results are shown in the attached figure. Figure 5 As shown, it can be seen that the defluorination effect of PFOA is different at different hydrothermal temperatures. Before 200°C, the defluorination effect increases with the increase of hydrothermal temperature. After exceeding 200°C, the defluorination effect has no further obvious improvement, indicating that 200°C is the optimal temperature for the hydrothermal reaction.

[0071] Comparative Example 1

[0072] Defluorination is carried out by the following steps:

[0073] (1) Mg / Al-LDH was placed in a porcelain boat and then placed in a muffle furnace for calcination to obtain Mg / Al-LDO at a calcination temperature of 500°C for 3 h.

[0074] (2) 5 g of Mg / Al-LDO was added to a centrifuge tube containing 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution and stirred for 10 h to obtain a reaction solution;

[0075] (3) The reaction solution was centrifuged at 12000 rpm for 5 min;

[0076] (4) The supernatant obtained by centrifugation was taken out and filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0077] Furthermore, the filtrate obtained in step (4) was diluted to 30 ml, the pH was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode. The results are shown in the attached figure. Figure 6As shown in the "PFOA adsorption without hydrothermal" bar graph, it can be seen that the defluorination rate calculated when PFOA is directly adsorbed by LDO for 10 h (adsorption rate 97.85%) is only 11.74%. In comparison, when the same dose of LDO is directly stirred with the same volume of ultrapure water for 10 h, a certain amount of fluoride ions can also be detected in the resulting solution. If calculated according to the defluorination rate formula, it is equivalent to a defluorination rate of 11.82% (as shown in the attached figure). Figure 5 This indicates that the fluoride ions in the solution obtained when LDO directly adsorbs PFOA are likely to be the fluoride ions of LDO being exchanged into the solution, rather than the cleavage of the carbon-fluorine bond of PFOA. This is similar to the effect of hydrothermal reaction after LDO adsorbs PFOA under the same conditions (as shown in the attached figure). Figure 5 There are obvious differences in the hydrothermal reaction after PFOA adsorption) and mechanism.

[0078] Comparative Example 2

[0079] Defluorination is carried out by the following steps:

[0080] (1) 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution was placed in a 50 mL reactor and subjected to a hydrothermal reaction at 200°C for 90 min to obtain a reaction solution;

[0081] (2) The reaction solution was filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0082] Furthermore, the volume of the filtrate obtained in step (2) was fixed to 16 ml, the pH was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode.

[0083] Comparative Example 3

[0084] Defluorination is carried out by the following steps:

[0085] (1) 5 g of Mg / Al-LDH was added to a 50 mL reactor containing 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution and stirred for 10 h. The mixture was then hydrothermally reacted at 200 °C for 90 min to obtain a reaction solution.

[0086] (2) Add 20 ml of ultrapure water to the reaction solution, sonicate at 100 Hz for 15 min, and then centrifuge at 12,000 rpm for 5 min;

[0087] (3) The supernatant obtained by centrifugation was taken out and filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0088] Furthermore, the filtrate obtained in step (3) was diluted to 30 ml, the pH was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode.

[0089] Comparative Example 4

[0090] Defluorination is carried out by the following steps:

[0091] (1) 5 g of activated carbon (GAC) was added to a 50 mL reactor containing 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution and stirred for 10 h. The mixture was then hydrothermally reacted at 200 °C for 90 min to obtain a reaction solution.

[0092] (2) The reaction solution was ultrasonicated at 100 Hz for 15 min, and then centrifuged at 12,000 rpm for 5 min;

[0093] (3) The supernatant obtained by centrifugation was taken out and filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0094] Furthermore, the filtrate obtained in step (3) was diluted to 30 ml, the pH was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode.

[0095] The statistical results of the defluorination rates of Comparative Examples 2, 3, and 4 are shown in the attached table. Figure 7 As shown, the results of Comparative Example 2 are shown as "PFOA alone", the results of Comparative Example 3 are shown as "LDH", and the results of Comparative Example 4 are shown as "GAC". Comparing them with the defluorination rate of LDO adsorption and hydrothermal treatment under the same conditions (shown as "LDO"), it can be seen that there is a significant difference in the defluorination effect of PFOA undergoing hydrothermal reaction alone, LDH adsorption followed by hydrothermal reaction, and LDO adsorption followed by hydrothermal reaction. In the presence of LDO, the hydrothermal reaction significantly enhances the defluorination effect of PFOA. Under the same conditions, when granular activated carbon is adsorbed for 10 hours (adsorption rate reaches 100%) and then hydrothermally heated, no fluoride ions are detected in the liquid after hydrothermal treatment (less than 0.2%). This shows that hydrothermal treatment after PFOA adsorption on the surface of conventional adsorbents does not cause the cleavage of carbon-fluorine bonds, and the defluorination effect is not significant. The defluorination treatment of LDO combined with hydrothermal reaction is obviously not achieved by self-hydrothermal degradation of PFOA after adsorption.

[0096] Comparative Example 5

[0097] Defluorination is carried out by the following steps:

[0098] (1) Add 16 mL of 20 mg / L PFOA solution to a beaker and adjust the pH to 12.43, 13.5, and 13.8 with sodium hydroxide, respectively.

[0099] (2) The pH-adjusted solution was transferred into a 50 mL reactor and subjected to a hydrothermal reaction at 200°C for 90 min to obtain a reaction solution;

[0100] (3) The reaction solution was filtered through a 0.22 μm polyethersulfone filter membrane to obtain a filtrate.

[0101] The adjusted pH value of 12.43 in this embodiment is consistent with the pH value of the solution after LDO was rehydrated for 10 hours after the hydrothermal reaction.

[0102] Furthermore, the pH of the filtrate obtained in step (3) was adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration was measured by a fluoride ion electrode. The results are shown in the attached figure. Figure 8 As shown, it can be seen that under the same pH and 90 min hydrothermal conditions of 200°C, LDO has a better defluorination effect than the sodium hydroxide hydrothermal reaction. Even if the pH of the solution is further increased to 13.5 and 13.8, the hydrothermal reaction under the action of sodium hydroxide still cannot achieve a defluorination effect of 90.55%, indicating that the defluorination method of the present invention is better than the conventional alkaline hydrothermal reaction.

[0103] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

[0104] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of protection of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

Claims

1. A method for defluorinating a perfluorinated compound using a layered bimetallic oxide, characterized in that: It includes: The layered bimetallic oxide is added into a solution of a perfluorinated compound and subjected to a hydrothermal reaction at 160-220° C. for 30-120 minutes.

2. The method for defluorinating a perfluorinated compound according to claim 1, wherein: The layered bimetallic oxide is a layered bimetallic oxide of magnesium and aluminum, wherein the molar ratio of magnesium to aluminum is 2:

1.

3. The method for defluorinating a perfluorinated compound according to claim 1, wherein: The temperature of the hydrothermal reaction is 200-220° C.; and / or the time of the hydrothermal reaction is 90-120 min.

4. A method for defluorinating a perfluoro compound using a layered double hydroxide, characterized in that: It includes: The layered double metal hydroxide is calcined to obtain a layered double metal oxide, and the layered double metal oxide is added to a solution of a perfluorinated compound and subjected to a hydrothermal reaction at 160° C. to 220° C. for 30 to 120 minutes.

5. The method for defluorinating a perfluorinated compound according to claim 4, wherein: The layered double metal hydroxide is a layered double metal hydroxide of magnesium and aluminum, wherein the molar ratio of magnesium to aluminum is 2:1, and carbonate ions are present between the layers.

6. The method for defluorinating a perfluorinated compound according to claim 4, wherein: The temperature of the hydrothermal reaction is 200-220° C.; and / or the time of the hydrothermal reaction is 90-120 min.

7. The method for defluorinating a perfluorinated compound according to claim 4, wherein: The calcination temperature is 450-500°C.

8. The method for defluorinating a perfluorinated compound according to any one of claims 1 to 7, wherein: The perfluorinated compound is selected from perfluorooctanoic acid and / or potassium perfluorooctane sulfonate.

9. The method for defluorinating a perfluorinated compound according to any one of claims 1 to 7, wherein: The concentration of the perfluorinated compound solution is 15-25 mg / L.

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