JP3937006B2 - Photolysis of fluorinated organic compounds - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for decomposing a fluorine-based organic compound such as refractory trifluoroacetic acid whose concentration in the atmosphere is increasing and becoming an environmental problem.
[0002]
[Prior art]
In recent years, the concentration of water-soluble and hardly decomposable relatively low molecular weight fluorinated organic compounds such as trifluoroacetic acid in the atmosphere has been gradually increasing, which is becoming an environmental problem (A. Jordan et al., Environmental Science and Technology, 33, 522-527, 1999). It is debated whether this source is in nature, or whether it is derived from fluorine-based organic compounds that are widely used as electronic parts, surfactants, medical materials, etc. In addition, these fluorinated organic compounds have been estimated to be harmless to the human body due to their poor reactivity, but perfluoro compounds accumulate in the body and began to point out that they are toxic, May 2000 A major company that manufactured and sold perfluorooctane sulfonic acid (PFOS) stopped producing it and became a big topic in the United States.
[0003]
For these fluorinated organic compounds, an effective treatment technique capable of breaking the carbon-fluorine bond has not yet been developed. At present, titanium dioxide is known and used as a catalyst capable of photodegrading organic matter, but even with this, it is difficult to decompose trifluoroacetic acid, and it is expected that it will become a serious problem in the future. Development of a decomposition treatment technology that disposes of fluorinated organic compounds is desired.
[0004]
[Problems to be solved by the invention]
The present invention has been made based on the above-described actual situation in the prior art, and an object thereof is to provide a treatment method for safely and efficiently decomposing a hardly decomposable fluorine-based organic compound.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors put a water-soluble fluorinated organic compound and a photocatalyst in water containing a photocatalyst, and when irradiated with light under specific conditions, the fluorinated organic compound Has been found to decompose, and the present invention has been completed.
That is, according to the present invention, there is provided a photodecomposition method for a fluorinated organic compound, wherein the fluorinated organic compound is decomposed by irradiating light to an aqueous layer containing the fluorinated organic compound and a photocatalyst in the presence of oxygen. Provided. In that case, as the photocatalyst, using a F heteropolyacid acid compound.
[0006]
In the present invention, the fluorinated organic compound to be decomposed is preferably at least one selected from fluoroalkylcarboxylic acids, fluoroalkylsulfonic acids and fluoroalcohols.
Moreover, according to this invention, the building material characterized by formed using the calcium fluoride obtained from the fluoride ion produced | generated by the said photolysis method is provided.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention contributes to the resolution of environmental problems associated with outflow of fluorine-based organic compounds to the atmosphere by decomposing water-soluble and hardly decomposable relatively low molecular weight fluorine-based organic compounds. Furthermore, the fluoride ions generated by the decomposition are chemically reacted with a compound containing calcium to synthesize calcium fluoride, which is to be reused as a building material, particularly a building material board.
[0008]
In the present invention, the fluorinated organic compound to be decomposed is a water-soluble low molecular weight organic compound having at least one fluorine atom, and is used in a wide range of technical fields such as carboxyl group, hydroxyl group, and sulfonic acid group. One or more selected from fluoroalkylcarboxylic acids having about 1 to 5 carbon atoms, such as trifluoroacetic acid, fluoroalkylsulfonic acids and fluoroalcohols, which are compounds having a functional group having an affinity for water such as It is a fluorinated organic compound.
[0009]
As the photocatalyst used in the present invention, a heteropolyacid compound represented by the formula AMxOy is used , and it is composed of a polyacid ion (M _x O _y ⁿ⁻ ) and a counter ion (A ^{n +} ).
In the above formula, M is a transition metal (elements 4A to 7A), such as molybdenum, vanadium, tungsten, titanium, aluminum, niobium, tantalum and the like. The counter ion ^{An +} is an ammonium ion, a hydrogen ion, or a metal ion (lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, etc.). X and y are the number of atoms, respectively. _{Specifically, H 3 PW 12 O 40 ·} 6H 2 O, H 3 MoO 40, H 6 P 2 W 18 O 62 and the like.
[0010]
About the usage-amount of a photocatalyst and a decomposition target object, although it can select suitably by the difficulty of decomposition, operation conditions, etc., a photocatalyst is 0.0001-100 mol / l normally in a water layer, Preferably 0.001-10 mol / Introduced in the range of l. In this case, the photocatalyst is preferably an aqueous solution sufficiently dissolved in water. The fluorine-based organic compound is introduced in an amount of 1 to 10,000 moles, preferably 1 to 50 moles, of the photocatalyst. Thereafter, oxygen gas may be bubbled under normal pressure, or the inside of the reaction vessel may be filled with oxygen to about 1 MPa.
The temperature of the reaction system is 15 to 90 ° C, preferably 25 to 50 ° C, and the pressure is 0.1 to 30 MPa, preferably 0.5 to 20 MPa.
[0011]
The light irradiation conditions are not particularly limited, but the wavelength of light to be irradiated is usually 200 to 800 nm, preferably 250 to 400 nm, which is the absorption spectrum region of the photocatalyst. The type of the light source is not particularly limited, and a mercury lamp, a xenon lamp, a deuterium lamp, sunlight, or the like may be used as appropriate depending on the desired wavelength of light. Further, the light irradiation time is not particularly limited, but is preferably about 1 to 7 days.
[0012]
Next, the method for carrying out the decomposition reaction of the present invention will be described with examples.
First, water, a photocatalyst, and a fluorinated organic compound are placed in the bottom of a reaction container that can be irradiated with light, and then oxygen is introduced therein. When using a heteropolyacid compound as a photocatalyst, it becomes strongly acidic when dissolved in water. Therefore, it is preferable to use a container made of a pressure-resistant material having acid resistance, for example, made of Inconel, coated with gold or the like. Stainless steel is usually used.
[0013]
The window material provided as a light introduction hole in the reactor is preferably formed of sapphire or the like that can withstand corrosion by the fluoride ions produced. By doing so, the fluorine-based organic compound undergoes photolysis by reacting with the catalyst molecules, and after the light irradiation for a certain time, the decomposition product and the product in the reaction vessel are respectively recovered.
[0014]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
Stainless steel pressure-resistant reactor coated with alumina coated with 1.55 × 10 ⁻⁴ mol of H ₃ PW ₁₂ O ₄₀ · 6H ₂ O, 1.55 × 10 ⁻³ mol of trifluoroacetic acid and 23 mL of water as a heteropolyacid complex with sapphire window (Internal volume 200 ml). Here, oxygen gas was introduced until the total pressure reached 0.5 MPa. While stirring this with a magnetic stirrer, a photodecomposition reaction was performed by irradiating light of 250 nm or more with a high pressure mercury lamp at 25 ° C. for 7 days.
After completion of the reaction, the pressure is returned to normal pressure, and the aqueous layer and residual solids are placed in a volumetric flask. The solution, which is diluted with water and becomes homogeneous, is analyzed by ion exclusion chromatography and remains in the solution. The amount of trifluoroacetic acid was measured. Further, the amount of generated fluoride ions was measured by ion chromatography. As a result, after 85 hours, about 50% of trifluoroacetic acid was decomposed. The results obtained for the remaining amount of trifluoroacetic acid and the amount of fluoride ions generated after light irradiation for a certain period of time are shown in FIG.
[0015]
Comparative Example 1
In Example 1, except that no photocatalyst was introduced, the photoreaction was performed in the same manner as in Example 1, and no decomposition of trifluoroacetic acid was observed.
[0016]
【The invention's effect】
According to the present invention, it is possible to safely and efficiently decompose a hardly decomposable fluorinated organic compound by irradiating a water layer containing a fluorinated organic compound and a photocatalyst in the presence of oxygen. Can contribute to solving environmental problems.
[Brief description of the drawings]
FIG. 1 is a graph showing a decrease in decomposition of trifluoroacetic acid obtained in Example 1 and a state of generation of fluoride ions.

Claims (1)

A method for decomposing a fluorinated organic compound by irradiating light to an aqueous layer containing a fluorinated organic compound and a photocatalyst in the presence of oxygen, wherein the fluorinated organic compound is a fluoroalkylcarboxylic acid or a fluoroalkylsulfonic acid. And a photocatalytic method of a fluorine-based organic compound , wherein the photocatalyst is a heteropolyacid compound .

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