Apparatus and method for removing fluorinated organic compounds

Abstract

This invention provides a method for removing fluorinated organic compounds, such as PFAS, which can be decomposed and rendered harmless. [Solution] Activated carbon adsorbing PFAS is transferred from the activated carbon container 102 to the stirring container 105. Methanol is added to the stirring container 105 from the organic solvent container 101 and stirred to disperse the activated carbon in methanol. The activated carbon and methanol are separated using a centrifuge 108. A concentrated sodium hydroxide aqueous solution (1 mol / L or more) is added to the extracted methanol and placed in a bubbling container 118, and ozone 121 is bubbled through a microbubble nozzle 122. The PFAS extracted in methanol is decomposed together with the methanol. Organic matter is decomposed, and the products become sodium fluoride, sodium carbonate, and sodium sulfate, which are dissolved in the sodium hydroxide aqueous solution and removed.

Description

[Technical Field]

[0001] This invention relates to a method and apparatus for safely and efficiently processing persistent organic compounds. [Background technology]

[0002] Fluorine-based organic compounds, known as typical persistent substances, are highly chemically stable and are therefore widely used in various applications such as water repellents, surface treatments, and coatings.

[0003] PFAS (Perfluoroalkyl and Polyfluoroalkyl Compounds) is a general term for organofluorine compounds, and there are said to be over 10,000 types. PFAS have been used in a wide range of applications, such as fire extinguishing agents, frying pan coatings, and water-repellent sprays. However, some PFAS substances have been identified as harmful, including carcinogenic and affecting the development of children, leading to their elimination or restriction under international treaties.

[0004] In Japan, the manufacture and import of two types of PFAS, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), are prohibited by law as of 2021.

[0005] Perfluorocarboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids are used in many industries. However, in recent years, it has become clear that perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are present in wildlife and environmental water.

[0006] Against this backdrop, there is a need for technologies to decompose and neutralize trace amounts of fluorinated organic compounds discharged from factories and other sources. However, fluorinated organic compounds such as PFCAs and perfluoroalkyl sulfonic acids are recalcitrant substances, and PFOS and PFOA in particular are known to be very stable and do not decompose.

[0007] Since PFAS can affect the human body even in extremely small amounts, such as causing cancer, the situation is even more serious than that of the above-mentioned organic compounds containing fluorine or chlorine. In Japan, there are many places where PFAS is used, and groundwater contamination by PFAS flowing out from these places is inevitable.

[0008] According to NHK's broadcast, in several places in Japan, contamination of drinking water with PFAS concentrations exceeding the EPA standards has been reported. As one of the causes, it is said that PFAS has leaked from the place where activated carbon used for treating contaminated water with PFAS was stored.

[0009] The characteristic of organic compounds containing fluorine or chlorine is that they do not burn. On the contrary, different from other organic compounds, heat treatment is difficult, and harmful gases are generated when they decompose. Therefore, a safe treatment method to replace heat treatment is required.

[0010] Patent Document 1 describes that by using two layers, an aqueous layer containing a photocatalyst and a carbon dioxide layer in a supercritical or liquid state, fluorine-based high molecular weight compounds can be decomposed.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] It is necessary to irradiate light while mixing an aqueous layer containing a photocatalyst and a carbon dioxide layer in a supercritical state or a liquid state containing a fluorine-based high molecular weight compound. The price of the treatment device is high, and a long treatment time is required.

Means for Solving the Problems

[0013] The present invention provides a method for removing fluorine-based organic compounds, comprising: a second step of separating activated carbon from an organic solvent in which fluorine-based organic compounds have been adsorbed; a third step of preparing a mixed solution by mixing sodium hydroxide with the organic solvent; and a fourth step of bubbling ozone into the mixed solution. Note that mol / L is sometimes written as M.

[0014] The fluorine-based organic compound removal apparatus of the present invention involves transferring activated carbon adsorbed with PFAS from the activated carbon container 102 to the stirring container 105. Methanol is then added to the stirring container 105 from the organic solvent container 101 and stirred to disperse the activated carbon in the methanol.

[0015] Activated carbon and methanol are separated using a centrifuge 108. A concentrated sodium hydroxide aqueous solution (1 mol / L or more) is added to the extracted methanol and placed in a bubbling container 118, where ozone 121 is bubbling through a microbubble nozzle 122. The PFAS extracted into methanol is decomposed together with the methanol. Organic matter is decomposed, and the products become sodium fluoride, sodium carbonate, and sodium sulfate, which are dissolved in the sodium hydroxide aqueous solution and removed.

[0016] An ion exchange resin contaminated with PFAS is packed into the column. A concentrated sodium hydroxide aqueous solution is added dropwise from the top of the column. PFAS, which has adhered to the ion exchange resin as anions, is flushed out through a filter. The PFAS-containing sodium hydroxide aqueous solution is transferred to a bubbling container 118. [Effects of the Invention]

[0017] It can decompose and remove fluorine-based organic compounds such as PFAS, and detoxify them. [Brief explanation of the drawing]

[0018] [Figure 1] This is a diagram showing the configuration and explanatory diagram of the fluorine compound removal apparatus of the present invention. [Figure 2]This is a diagram showing the configuration and explanatory diagram of the fluorine compound removal apparatus of the present invention. [Figure 3] This is a flowchart illustrating the method for removing fluorinated compounds according to the present invention. [Figure 4] This is an explanatory diagram of the method for removing fluorinated compounds according to the present invention. [Figure 5] This is an explanatory diagram of the method for removing fluorinated compounds according to the present invention. [Figure 6] This is an explanatory diagram of the method for removing fluorinated compounds according to the present invention. [Figure 7] This is an explanatory diagram of the method for removing fluorinated compounds according to the present invention. [Figure 8] This is an explanatory diagram of the method for removing fluorinated compounds according to the present invention. [Figure 9] This is an explanatory diagram of the method for removing fluorinated compounds according to the present invention. [Figure 10] This is an explanatory diagram of the method for removing fluorinated compounds according to the present invention. [Modes for carrying out the invention]

[0019] Ozone rapidly decomposes (on the order of milliseconds) in alkaline aqueous solutions and disappears. However, while ozone disappears in alkaline aqueous solutions, this also marks the beginning of the generation of active radicals.

[0020] Ozone treatment in alkaline aqueous solutions is not due to a reaction by ozone itself, but rather to the active substances generated by the autodecomposition of ozone. Of particular importance is HO2, which is produced in the initial stages of ozone decomposition. - and O2 - (Superoxide). The characteristics of this treatment method are that unreacted ozone is not released into the atmosphere, and fluorine or chlorine, after the decomposition of organic compounds, become sodium fluoride and sodium chloride, respectively, and no harmful substances are released into the atmosphere.

[0021] Figure 4 is a graph showing the absorbance of ozone at its absorption peak of 260 nm. The black circles represent absorbance, and the left vertical axis of the graph shows absorbance. The white circles represent log(As) (t) - As(f) ) It is. The vertical axis is on the right side. The horizontal axis is time (s) (time / sec). Initial concentration of ozone

[03] 0: 3.16 × 10 -3 mol / L Concentration of alkali [OH - : 0.00717mol / L The reaction temperature is 20°C. In Figure 4, the decomposition of ozone is not a simple first-order function, but consists of first-order and second-order terms as follows. -d[O3] / dt = k1[O3] + k2[O3] 2 (1) The second-order term appears because when ozone decomposes, OH radicals are generated, and the OH radicals decompose ozone again. That is,[[]]

[0022] In O3 + OH → product, the concentration of O3 is included in OH. OH is very reactive and difficult to capture directly, but OH is captured. For example, when CO3 2- is added, as shown in Figure 5, the second-order term disappears, and due to the capture of OH radicals at 600 nm, CO3 2- +OH → CO3 - + OH - , and the peak of the generated carbonate radical CO3 - was observed.

[0023] In Figure 5, at the initial stage of the reaction, log(As (t) - As (f) ), indicated by white circles, does not form a straight line. This is because CO3 - decomposes ozone to reach a steady state (the concentration becomes constant), but at the initial stage of the reaction, CO3 - is in the generation process before reaching the steady state. Figure 5 shows the decomposition of ozone in an aqueous solution with a low alkali concentration and is an aqueous solution containing carbonate ions. Concentration of alkali [OH - : 0.00717mol / L Na2CO3: 3 × 10 -3mol / L, reaction temperature 20°C The generation of OH radicals can be attributed to the following reactions involving alkalis. O3+ OH - → O3 - + OH (2) However, this reaction was proven to be incorrect by ozonolysis in highly alkaline aqueous solutions. Figure 7 is a graph showing the decomposition of ozone in a highly alkaline aqueous solution. NaOH: 0.117 mol / L Reaction temperature: 20°C

[0024] Figure 7 shows the change in absorbance at the ozone absorption peak of 260 nm. Figures a and c have different time scales on the horizontal axis. The figure on the right shows the change in absorbance at 430 nm, O3 - It corresponds to the change in concentration.

[0025] In Figure 7, in a concentrated alkaline aqueous solution, ozone decomposes within 0.1 seconds, but a new product appears in the same absorption band. This peak is superoxide O2. - This signifies its appearance. It appears slowly and remains stable even at 0.5s.

[0026] In Figure 9, ozonide ion O3 - It appears in 0.04 s and disappears in 0.1 s. Importantly, in a concentrated alkaline aqueous solution, ozonolysis is slow at first and then accelerates over time, which is due to the breakdown of OH radicals and superoxide O2. - The fact is that it is not generated in the initial stages of the reaction. In other words, OH radical and O2 - It is produced not in the initial stages of the reaction, but in subsequent reactions. Based on the above experimental results, it was concluded that, in an alkaline aqueous solution, the decomposition of ozone begins with the following initial reaction. O3+ OH - → HO2 - + O2(3) HO2 - This triggers the following reactions: The following is a subsequent chain reaction. HO2 - + O3 → O3 - + HO2(4) HO2+ OH- → O2 - + H2O (5) O2 - + O3 → O3 - + O2(6) O3 - + H2O → OH + O2(7)

[0027] In summary, ozone decomposes rapidly in an alkaline aqueous solution. During the decomposition of ozone, HO2 is produced in the initial stage. - This generates HO2 - This induces various reactive radicals. These are O3 - , O2 - And it's an OH radical.

[0028] These radicals decompose organic compounds by extracting or donating electrons from organic bonds. It is important to note that ozone is not only more reactive in alkaline aqueous solutions than in neutral to acidic solutions, but the reaction products are also completely different. In particular, ozone treatment of chlorine-based and fluorine-based organic compounds does not generate harmful gases in alkaline aqueous solutions. The reason for this will be explained below in the context of the decomposition process of carbon tetrachloride.

[0029] It has been revealed that carbon tetrachloride decomposes in an alkaline aqueous solution with ozone. As mentioned earlier, in reality, it is not the reaction with ozone that produces superoxide O2, which is generated by the decomposition of ozone. - This is a decomposition reaction caused by active radicals such as those mentioned above.

[0030] O2 - It cleaves the C-Cl bond of carbon tetrachloride, C + and Cl -It decomposes and disappears itself. The overall reaction is represented as follows. What is noteworthy is that neither chlorine nor carbon is oxidized. In reality, it is decomposed by ozone, but in terms of stoichiometry, ozone is not included. CCl4 + 4NaOH → 4NaCl + CO3 2- +2H + +H2O (8) The following experiment was conducted regarding the decomposition of carbon tetrachloride.

[0031] Carbon tetrachloride is mixed with a concentrated sodium hydroxide solution (for example, 8 mol / L). The solution separates into two layers: carbon tetrachloride in the lower layer and the alkaline solution in the upper layer. While stirring the solution, ozone is generated from an ozone generator under constant conditions. The carbon tetrachloride decomposes, but the NaOH concentration decreases quantitatively due to the reaction described above.

[0032] The change in the amount of carbon tetrachloride is -d[CCl4] / dt = k1[O3][CCl4], but since ozone is constantly bubbling, it is maintained at a constant concentration. The steady-state approximation also holds for active radicals. Therefore, k1[O3] can be rewritten as a constant k, so -d[CCl4] / dt = k[CCl4]. [CCl4] = [CCl4] 0· e(-kt)

[0033] Here, [CCl4]0 is the initial amount of CCl4. Since the same amount of NaOH is consumed as carbon tetrachloride in the above reaction, the reaction can be tracked by measuring the change in NaOH concentration instead of the amount of CCl4. log([NaOH]0- [NaOH] t ) vs. t is a straight line (Figure 10). Here, [NaOH]0 is the initial concentration of NaOH, [NaOH] t is the concentration of NaOH at time t. Similarly, with fluorinated organic compounds, the C-C and CF bonds are cleaved by active radicals.

[0034] Activated carbon is widely used to purify water contaminated with PFAS. While the removal rate varies depending on the type of PFAS, it is considered effective in removing PFAS. Because PFAS have substituents, ion exchange resins are also sometimes used for PFAS removal. This section describes the decomposition treatment of activated carbon or ion exchange resins contaminated with PFAS.

[0035] The detoxification of activated carbon or ion exchange resin contaminated with PFAS is carried out in two stages. First, most of the PFAS is washed out of the activated carbon or ion exchange resin using an organic solvent.

[0036] Any organic solvent that dissolves PFAS will suffice. Methyl alcohol is convenient because it mixes with water. Add a sodium hydroxide aqueous solution of 1 mol / L or higher to the methyl alcohol in which the PFAS has been washed.

[0037] While stirring this mixed solution, blow in ozone. The process is stopped when the PFAS peak disappears in GCMS measurement. Next, immerse the activated carbon or ion exchange resin, from which the PFAS has been washed with an organic solvent, in a sodium hydroxide aqueous solution of 1 mol / L or higher, and blow in ozone. Figure 1 is a diagram illustrating the configuration and method of a fluorine-based organic compound removal apparatus.

[0038] PFAS are absorbed by activated carbon. Depending on the type of PFAS, activated carbon is effective in removing it. Because PFAS has substituents, ion exchange resins are sometimes used to remove PFAS as well.

[0039] In the embodiments of the present invention, examples of adsorbents used include activated carbon and other carbon materials, as well as ion exchange resins. In the following embodiments, activated carbon will be used as an example. PFAS is used as an example, but the invention is not limited to it. Perfluorooctanoic acid (PFOA) or perfluorooctanesulfonic acid (PFOS) may also be used. In this invention, the substance to be removed can be any fluorine-based organic compound. PFAS and similar substances are adsorbed onto activated carbon. This section describes the decomposition treatment of activated carbon or ion exchange resin contaminated with PFAS.

[0040] The detoxification of activated carbon or ion exchange resin contaminated with PFAS is carried out in two stages. First, most of the PFAS is washed out of the activated carbon or ion exchange resin using an organic solvent.

[0041] Activated carbon contaminated with PFAS is recovered and placed in the contaminated material container 102. A fixed amount of activated carbon per hour is added to the stirring container 105 from the contaminated material container 102. The organic solvent container 101 is filled with organic solvent 103. The organic solvent 103 from the organic solvent container 101 is poured into the stirring container 105, and the activated carbon and organic solvent 103 are stirred by the stirring fan 107.

[0042] Any organic solvent that dissolves PFAS, etc., is acceptable. Examples include alcohols, carbon tetrachloride, and oils. Ethyl alcohol and methyl alcohol are preferred because they are miscible with water.

[0043] Add a sodium hydroxide aqueous solution of 1 mol / L or higher to the methyl alcohol in which PFAS and other substances have been washed away. This solution of methyl alcohol in which PFAS and the sodium hydroxide aqueous solution is washed away is called mixed solution 106.

[0044] The stirring fan 107 is operated to equalize the concentration of the mixed solution 106 in the stirring container 105. A pH meter (not shown) is also installed or placed inside the stirring container 102. The pH of the mixed solution 106 is measured using a pH meter 207.

[0045] The mixed solution 106, which is obtained by stirring activated carbon and an organic solvent, is sent to a centrifuge 108. The centrifuge 108 is equipped with multiple separation chambers 111 (separation chamber 111a, separation chamber 111b, separation chamber 111c, separation chamber 111d). The activated carbon and the mixed solution 106 are sequentially injected into the separation chambers 111. A rotating shaft 109 is positioned at the center of the centrifuge 108, and the separation chambers 111 rotate around the rotating shaft 109.

[0046] The activated carbon and the mixed solution 106 are separated by a centrifuge 108. The mixed solution 106 is sent to a bubbling container 118. The activated carbon is placed in a washing container 114, and washing solution 115 is injected, agitated, and washed. The washed activated carbon or ion exchange resin is reused.

[0047] The mixed solution 106 is stirred by a stirring fan (not shown) placed inside the bubbling container 118. The bubbling container 118 has an exhaust duct 119 for exhausting ozone and oxygen. The exhaust from the exhaust duct 119 reduces the pressure inside the bubbling container 118. This reduced pressure improves the stirring of the mixed solution 106 and ozone 121. The activated carbon or ion exchange resin from which PFAS has been washed with an organic solvent is immersed in a sodium hydroxide aqueous solution of 1 mol / L or more, and ozone is blown into it.

[0048] Activated carbon can be reused after treatment. If the PFAS concentration is low, the sodium hydroxide solution is not consumed in large quantities and can be reused. Ozone or the radicals it generates self-decompose within the activated carbon and ion exchange resin, so the efficiency is not very good. It is more effective to wash out as much as possible with a solvent and then treat with ozone.

[0049] When separating PFAS from activated carbon, methanol is preferably used. When decontaminating PFAS using ion exchange resin, a concentrated sodium hydroxide aqueous solution is used to detach or remove the PFAS from the contaminated ion exchange resin. When PFAS is removed using ion-exchange oil (anion exchange resin), decontamination of the ion-exchange resin contaminated with PFAS can be carried out by the following method as one embodiment.

[0050] Pack the column with ion exchange resin contaminated with PFAS. Place a filter at the bottom of the column. Add a concentrated sodium hydroxide solution (2 mol / L or higher) dropwise from the top of the column.

[0051] PFAS, which has adhered to the ion exchange resin as anions, flows out through the filter. As the sodium hydroxide aqueous solution is added dropwise, the PFAS concentration in the filter effluent decreases, and eventually PFAS becomes undetectable. The sodium hydroxide aqueous solution containing the effluent PFAS is transferred to the bubbling container 118, and the subsequent treatment is the same as that for the activated carbon treatment solution described above. Ozone treatment in alkaline aqueous solutions is inexpensive, the equipment is simple, and it can be made cost-effective.

[0052] Ozone 121 is generated by an ozone generator 125 and ejected into the mixed solution 106 from a microbubble nozzle 122. There are three main methods for producing ozone 121: ultraviolet, discharge, and water electrolysis. Industrial-scale ozonizers have primarily used the discharge method, but the water electrolysis method can also be used.

[0053] Ozone 121 is blown into the mixed solution 106 while stirring. The mixed solution 106 is sent to the gas chromatograph / mass spectrometer 123 in real time or at predetermined time intervals by operating the on / off valve 116b.

[0054] The ozone or oxygen after bubbling is sent to the mass spectrometry controller circuit 124, where the ratio of ozone to oxygen, the change in ozone, and the decomposition state of fluorinated organic compounds are measured or evaluated. Based on the measurement or evaluation results, the mass spectrometry controller circuit 124 controls the ozone generator 125 to adjust and set the amount of ozone 121 output from the microbubble nozzle 122, etc.

[0055] Figure 2 is a configuration diagram and explanatory diagram of the gas chromatograph / mass spectrometer 123. In the gas chromatograph / mass spectrometer 123 of the present invention, a mixed solution 106 is injected in real time from the inlet 201 or at predetermined time intervals, the decomposition state of fluorine-based organic compounds such as PFAS is measured or understood by the mass spectrometry controller circuit 124, and the injection amount, injection ratio, and injection stop of ozone 121 output from the microbubble nozzle 122 are controlled.

[0056] The mixed solution 106 is vaporized and introduced into the hollow column 203 of the component separator 202. The components are separated by the difference in affinity between the stationary phase on the inner wall of column 203 and the components in the sample, as well as by their vapor pressure. The separated components are ionized in the ionizer 204 and introduced into the mass spectrometer (MS).

[0057] The mass separator 205 separates the components by mass, and component identification is performed from the mass spectrum pattern, while quantitative analysis is performed from the ion detection intensity or peak area. Based on the results of the quantitative analysis, the mass spectrometry controller circuit 124 controls the ozone generator 125 to adjust and set the amount of ozone 121 output from the microbubble nozzle 122.

[0058] Ozone 121 is bubbling into the mixed solution 106. This treatment decomposes the PFAS and other substances extracted into methanol together with the methanol. The organic matter is decomposed, and the products become sodium fluoride, sodium carbonate, and sodium sulfate, which dissolve in an aqueous sodium hydroxide solution. Since the amount of product is very small, the aqueous sodium hydroxide solution can be reused. This invention makes it possible to measure or understand the decomposition state of fluorinated organic compounds in real time or at predetermined time intervals. The process ends when the peaks such as PFAS disappear during measurement by the mass spectrometry controller circuit 124.

[0059] Since trace amounts of PFAS and other substances remain in the treated activated carbon, a sodium hydroxide solution is added, and the ozone treatment is repeated. The activated carbon and sodium hydroxide solution are separated by centrifugation. Because the activated carbon is not significantly damaged by ozone, it can be reused for the removal of PFAS and other substances. Figure 3 is a flowchart illustrating the method for removing PFAS.

[0060] Activated carbon is used to adsorb PFAS and the like (S01). Next, an alcohol such as methanol is added to the activated carbon contaminated with PFAS and the like, and the mixture is stirred to disperse the activated carbon in methanol (S02).

[0061] The activated carbon and methanol are separated using a centrifuge (S03). A concentrated sodium hydroxide aqueous solution (1 mol / L or more) is added to the separated methanol to make mixed solution 106 (S04). The activated carbon is washed (S06). Since trace amounts of PFAS and other substances remain in the treated activated carbon, sodium hydroxide aqueous solution is added and ozone treatment is performed again. The activated carbon and sodium hydroxide solution are separated by centrifugation. Since the activated carbon is less damaged by ozone, it can be reused in the removal of PFAS and other substances.

[0062] Ozone 121 is bubbling into the mixed solution 106 (S05). This treatment decomposes the PFAS and other substances extracted to methanol together with the methanol. The organic matter is decomposed, and the products are sodium fluoride, sodium carbonate, and sodium sulfate, which are dissolved in the aqueous sodium hydroxide solution. Since the amount of product is very small, this aqueous solution can be reused. [Industrial applicability]

[0063] The present invention makes it possible to detoxify activated carbon or ion exchange resin contaminated with PFAS or the like using ozone. [Explanation of symbols]

[0064] 101 Organic solvent containers 102 Activated carbon container 103 Organic Solvents 104 Injection tube 105 Stirring vessel 106 Mixed solution 107 Agitation fan 108 Centrifugal separator 111 Separation room 114 Washing container 115 Cleaning solution 116 Shut-off valve 118 Bubbling container 119 Exhaust duct 121 Ozone 122 Microbubble Nozzle 123 Gas chromatograph / mass spectrometer 124 Mass Spectrometry Controller Circuit 125 Ozone Generator 201 Inlet 202 Component separator 203 columns 204 Ionizer 205 Mass Separator 206 detectors 207 pH meter

Claims

[Claim 1] A first step involves mixing activated carbon or ion exchange resin on which a fluorine-based organic compound has been adsorbed with an organic solvent, A second step of separating the activated carbon and the organic solvent, A third step involves preparing a mixed solution by mixing sodium hydroxide with the aforementioned organic solvent, A method for removing fluorinated organic compounds, characterized by comprising a fourth step of bubbling ozone into the mixed solution.

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