Method for defluorinating perfluorinated compound by using layered bimetal oxide or hydroxide

Abstract

The invention discloses a perfluorinated compound defluorination method using layered bimetallic oxide or hydroxide, and belongs to the technical field of defluorination methods. The perfluorinated compound defluorination method using the layered bimetal oxide comprises the following steps: adding the layered bimetal oxide into a solution of a perfluorinated compound, and carrying out hydrothermal reaction at 160-220 DEG C for 30-120 minutes. The defluorination method disclosed by the invention has an excellent perfluorinated compound defluorination effect, mild treatment conditions and a simple treatment process, and meanwhile, a complicated post-treatment procedure is omitted.

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 their 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 bonds in their structures have high bond energy, making defluorination extremely difficult.

[0003] An existing defluorination method is to add an alkali such as sodium hydroxide and then carry out a hydrothermal reaction to achieve rapid degradation and defluorination of perfluorinated compounds through hydroxyl nucleophilic substitution. However, this method has high requirements on the temperature of the hydrothermal reaction and the concentration of the alkali, and is difficult to be promoted and applied.

[0004] On the other hand, layered double hydroxides (LDHs) are a type of layered structural material formed by the assembly of layer plates and intercalated anions. When calcined at high temperatures (such as 500°C), they lose interlayer anions and water and transform into corresponding layered double metal oxides (LDO). LDO has a unique structural memory effect. After dissolving in an aqueous solution, it will reabsorb water molecules and anions, restore the two-dimensional layer structure of LDHs, and leave more OH residues 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 is to combine the structural memory effect of LDO with the deprotonation of PFOA in natural water, and adsorb PFOA between the layers when LDO restores the two-dimensional layer structure. However, this method does not achieve the mineralization of perfluorinated compounds into inorganic fluoride ions, that is, perfluorinated compounds, and the LDHs adsorbed with PFOA obtained need to undergo difficult and costly post-processing. Summary of the invention

[0006] In view of the defects of the prior art, the purpose of the present invention is to propose a method for defluorinating perfluoro compounds using layered bimetallic oxides or hydroxides, which combines and synergizes the structural memory effect of LDO with the hydrothermal reaction. Compared with the direct adsorption treatment of LDO or LDH or the conventional alkaline hydrothermal treatment, the method has better perfluoro compound mineralization effect and milder treatment conditions, while eliminating the complicated post-treatment process.

[0007] The technical solution of the present invention is as follows:

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

[0009] The inventors unexpectedly discovered that adding a layered bimetallic oxide (LDO) to a solution of a perfluoro compound and conducting a hydrothermal reaction can effectively combine the structural memory effect of LDO with the hydrothermal reaction, and the combination is not a simple LDO adsorption of the perfluoro compound or the LDH generated by its rehydration adsorbs the perfluoro compound and then promotes its thermal degradation by a hydrothermal reaction, but rather, the carbon-fluorine bond of the perfluoro compound with the participation of LDO will be broken, so that the perfluoro compound can be fully mineralized and defluorinated, and the defluorination rate is significantly improved compared with direct adsorption treatment of LDO or direct thermal degradation of the perfluoro compound or its thermal degradation under alkaline conditions.

[0010] According to some preferred embodiments of the present invention, it also includes: adding the layered bimetallic oxide to the solution of the perfluorinated compound, stirring and mixing 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 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.

[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 and 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 the treatment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a comparison chart of X-ray diffraction of raw material Mg / Al-LDH, Mg / Al-LDO obtained in Example 1, and Mg / Al-LDH after redissolution.

[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 chart 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 a statistical chart 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. Without departing from the above-mentioned method concept of the present invention, various substitutions or changes made according to common technical knowledge and conventional means in the art should be included in 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 desktop measuring instrument). 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 PFOA or PFOS solution, respectively, P 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. The calcination temperature was 500°C and the calcination time was 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, followed by a hydrothermal reaction 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. The calcination temperature was 500°C and the calcination time was 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) The obtained reaction solution was placed in a centrifuge and centrifuged at 12000 rpm for 5 min;

[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 (shown as LDH) used in Example 1, the Mg / Al-LDO (shown as LDO) obtained by calcination, and the Mg / Al-LDH (shown as re-LDH) obtained after redissolution. 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 belonging to Mg / Al-LDH at (003), (006), (012), (015), (018), (110), (113) and (116) crystal planes. After calcination, LDO has characteristic peaks belonging to the MgO-like phase structure at (200) and (220) crystal planes. And re-LDH has characteristic diffraction peaks consistent with 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 were broken after 30 minutes of hydrothermal treatment, and the defluorination rate reached 90.55% after 90 minutes of hydrothermal treatment. At 120 minutes, the defluorination rate reached 100%.

[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. The calcination temperature was 500°C and the calcination time was 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, followed by a hydrothermal reaction 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] Further, the filtrate obtained in step (4) 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 result is shown in the attached figure. Figure 3 It can be seen that the defluorination rate of PFOS reached 68.95% at 90 minutes of hydrothermal reaction, and reached 85.89% at 120 minutes, indicating that even if 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. The calcination temperature was 500°C and the calcination time was 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, and then subjected to a hydrothermal reaction at 200 °C for 90 min to obtain a reaction solution;

[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] Further, the filtrate obtained in step (4) 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, and compared with the result 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 also increases accordingly.

[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. The calcination temperature was 500°C and the calcination time was 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, followed by hydrothermal reaction 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] Further, the filtrate obtained in step (4) 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 result is 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. The calcination temperature was 500°C and the calcination time was 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) Centrifuge the reaction solution 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] Further, the filtrate obtained in step (4) 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 result is 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 by direct adsorption of PFOA by LDO for 10 h (adsorption rate 97.85%) is only 11.74%. In contrast, 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 obtained 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 different from the effect of LDO adsorbing PFOA and then conducting a hydrothermal reaction 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) placing 16 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution into a 50 mL reactor and performing 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 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, followed by a hydrothermal reaction 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) is fixed to 30 ml, the pH is adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration is 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, followed by a hydrothermal reaction 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) is fixed to 30 ml, the pH is adjusted to 5-6 by hydrochloric acid, and the fluoride ion concentration is 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 Figure 7 As shown, the result of comparative example 2 is shown as "PFOA alone", the result of comparative example 3 is shown as "LDH", and the result of comparative example 4 is shown as "GAC". By comparing them with the defluorination rate of LDO adsorption and hydrothermal treatment under the same conditions (as shown in "LDO"), it can be seen that the defluorination effect of PFOA subjected to hydrothermal reaction alone is significantly different from that of hydrothermal reaction after LDH adsorption and hydrothermal reaction after LDO adsorption. In the presence of LDO, the hydrothermal reaction significantly enhances the defluorination effect of PFOA. Under the same conditions, after hydrothermal treatment using granular activated carbon for 10h (adsorption rate reaches 100%), no fluoride ions (less than 0.2%) were detected in the liquid after hydrothermal treatment. This shows that hydrothermal treatment after PFOA is adsorbed on the surface of conventional adsorbents does not cause the breakage of carbon-fluorine bonds, and the defluorination effect is not significant. The defluorination treatment combined with LDO and 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) transferring the pH-adjusted solution into a 50 mL reactor and performing 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 pH adjustment 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] Further, 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 result is shown in the attached figure. Figure 8 As shown, it can be seen that under the same pH and 200°C hydrothermal conditions for 90 min, LDO has a better defluorination effect than 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 in defluorination.

[0103] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0104] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope 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 the solution of the perfluorinated compound and subjected to a hydrothermal reaction at 160° C.-220° C. for 30-120 minutes.

2. The method for defluorinating a perfluorinated compound according to claim 1, characterized in that: 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, characterized in that: 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 metal 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 into 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, characterized in that: 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, characterized in that: 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, characterized in that: The calcination temperature is 450-500°C.

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

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