JPS6128493A - Decomposition of halogenated hydrocarbon - Google Patents

Abstract

PURPOSE:To decompose a minute amount of halogenated hydrocarbon present in water in a relatively easy manner, by performing direct electrolysis by using an electrolytic apparatus wherein porous filmy electrode catalyst layers are provided to both surface of a solid electrolyte diaphragm. CONSTITUTION:Porous film like electrode catalyst layers 2 are respectively provided to both surfaces of a solid electrolyte diaphragm demarcating an anode chamber and a cathode chamber to constitute the electrolytic cell to which the catalyst layers 2, the anode collector 3 and the cathode collector 4 were connected and this electrolytic cell is used to electrolyze water containing a minute amount of halogenated hydrocarbon. That is, if the above mentioned electrlytic apparatus is used to perform direct electrolysis, it is unnecessary to add a support electrolyte and application of high current density is enabled and, therefore, a minute amount of halogenated hydrocarbon contained can be easily and rapidly decomposed by a relatively small apparatus without contaminating objective water.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for decomposing halogenated hydrocarbons. More specifically, the present invention relates to a method for decomposing trace amounts of halogenated hydrocarbons present in water by direct electrolysis using an electrolytic device in which a porous membrane electrode catalyst layer is provided on a solid electrolyte membrane.

(Prior Art and Problems) In recent years, treatment with chlorine-based chemicals such as chlorine and sodium hypochlorite has been widely used to sterilize tap water. It has been known for a long time that in this process, many organic chlorine compounds, mainly halogenated hydrocarbons, are generated due to the humic substances contained in natural water. , trihalomethanes such as bromodichloromethane, chlorodibromomethane, bromoform, and rarely trichlorethylene, tetrachlorethylene, 1
,1.1-trichloroethane.

It has been reported that it contains carbon tetrachloride, etc.

In particular, the suspicion of carcinogenicity of trihalomethanes has been reported and has become a social problem, and various studies are being conducted on ways to decompose and remove these halogenated hydrocarbons or prevent their formation.

(Object of the Invention) In view of this situation, the present inventors conducted extensive studies with the aim of relatively easily decomposing halogenated hydrocarbons present in trace amounts in water.

As a result, the inventors discovered that the above object could be fully achieved by using a certain type of electrolytic method, leading to the completion of the present invention.

(Structure of the Invention) The present invention uses an electrolytic cell in which a porous membrane electrode catalyst layer is provided on both sides of a solid electrolyte membrane that partitions an anode chamber and a cathode chamber, and the contact tsW is combined with each current collector. This method of decomposing halogenated hydrocarbons is characterized by electrolyzing water containing a trace amount of halogenated hydrocarbons.

In the electrolysis of the present invention, an oxidation reaction progresses at the anode, ultimately resulting in carbon dioxide and hydrogen halide, and a reduction reaction progresses at the cathode, ultimately resulting in methane and hydrogen halide. .

A diaphragm type is effective as the electrolytic cell type of the present invention, and an organic or inorganic ion exchange membrane, which is a solid electrolyte, is advantageously used as the diaphragm material.

By thermocompressing and bonding porous membrane electrode catalyst layers to both sides of the solid electrolyte diaphragm, direct electrolysis can be performed in the electrode catalyst layers, without the need to supply a supporting electrolyte from the outside.

On the other hand, asbestos diaphragms and m-made diaphragms.

When using a material that does not function as a solid electrolyte, such as a porous polytetrafluoroethylene diaphragm, as a diaphragm material, it is necessary to add a supporting electrolyte, which will contaminate the water to be treated. For example, when used to treat tap water, it becomes suitable for drinking.

Since the solid electrolyte diaphragm electrolysis method used in the present invention can be operated at high current and low voltage, liquid circulation by gas lift is possible, and the time for halogenated hydrocarbons to reach the electrode catalyst layer is fast, resulting in a remarkable decomposition rate. It gets faster. Also,
Since the gas lift also has an aeration effect, the rate of volatilization of halogenated hydrocarbons and their decomposition products becomes faster. Therefore, it can be applied to the treatment of water containing several +1)l) halogenated hydrocarbons.

In contrast, in conventional ion exchange membrane cells, a supporting electrolyte must be added to increase the conductivity of the water to be treated, resulting in contamination of the water. Furthermore, even if a small amount of supporting electrolyte is added, a current of only a few milliamps can flow, and water circulation cannot be expected due to gas lift, so the contact between the halogenated hydrocarbon and the electrode will be slow, and the decomposition rate will be significantly slower. Become.

As the organic ion exchange membrane used in the solid electrolyte diaphragm 1 of the present invention, a perfluorocarbon sulfonic acid type ion exchange membrane is preferably used from the viewpoint of corrosion resistance and service life.

Inorganic ion exchange membranes include zirconium phosphate, zirconium tungstate, ammonium molybdate,
Zirconium molybdate.

Aluminosilicate, polyantimonic acid, etc. can be used. These powders are prepared to have a predetermined particle size range of 1 to 50 microns, and are mixed with 10 to 50% by weight of fluorine-containing polymer powder, if desired. If it is less than 10% by weight, moldability will be poor;
When it exceeds 50% by weight, hydrophilicity is lost. After mixing well, the temperature is 25G~ll5(1'r'! rX++
1. Rin1ay / , J /> /A & AT
)? + m -7+.

It is hot-pressed to a thickness of 100 to 500 microns, preferably 200 to 400 microns.

The porous membrane electrode catalyst layer of the present invention is used by mixing an electrode active component with a fluorine-containing polymer, etc., if desired, and forming the mixture into a membrane by hot-pressing.

Examples of active electrode components include ruthenium, platinum, palladium, iridium, rhodium, cobalt, or oxides thereof for the anode, and nickel, cobalt, iron, ruthenium, rhenium, platinum, rhodium, and palladium for the cathode.

One or more of osmium, iridium, vanadium, or their oxides can be selected and used as appropriate.

Preferably, these are prepared prior to use. For example, to obtain an electrode active component consisting of oxides of ruthenium and iridium, add an excess of sodium nitrate or an equivalent alkali metal salt to both chlorides mixed in the desired weight ratio, Melt at 600°C for about 4 hours. Residues are washed and removed - Sedated acid compounds are removed in 10.
! Adjust to desired particle size range of 'll' 1μ. 10 to 50% by weight of a fluorine-containing polymer is mixed with this thermally decomposed oxide.

If it is less than 10% by weight, moldability will be poor, and if it exceeds 50% by weight, hydrophilicity will be lost. After mixing well, temperature 250
It is formed into a film by hot pressing under the desired conditions of ~350°C and 1 to 20 yen/cjG.

The film is stacked on a predetermined surface of the solid electrolyte diaphragm and heated at a temperature of 250 to 350°C with a weight of 1 to 20 kg/
It is preferable to heat and press the film under ad Q conditions to integrate it and partially embed it in the film surface.

The solid electrolyte membrane provided with the gas- and liquid-permeable catalyst layer is
In order to conduct electricity, it is assembled by using a spring or a screw to bring it into close contact with a current collector, and then pressing the two together with a frame or presser plate.

A fine wire mesh, punched metal, expanded metal, or the like is used as the current collector. As for the constituent material, for example, on the anode side, a valve metal such as titanium, tantalum, niobium, or zirconium whose surface is coated with platinum group metals and their alloys, platinum group oxides and mixtures thereof, etc. is used.
For the cathode side, nickel, stainless steel, iron plated with nickel, etc. are used.

Embodiments will be described below using the drawings. FIG. 1 shows the diaphragm and electrode portion of an electrolytic cell in which a porous membrane electrode catalyst layer 2 is provided on both sides of a solid electrolyte diaphragm 1 of the present invention, and an anode current collector 3 and a cathode current collector 4 are combined. FIG. When electrolysis is performed by supplying water containing halogenated hydrocarbons to the anode and cathode chambers, carbon dioxide gas and oxygen gas are released from the electrode catalyst layer on the anode side, and methane gas and hydrogen gas are released from the electrode catalyst layer on the cathode side. generated and promotes liquid circulation by gas lift,
The halogenated hydrocarbon reaches the electrode catalyst layer quickly,
Therefore, its decomposition rate becomes significantly faster.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Powdered polyantimonic acid 5.01 with a particle size of less than 10μ and polytetrafluoroethylene (hereinafter referred to as PTFE).
A mixture of 1.09 and 1.09 was pressed using a hot press to produce an ion exchange membrane with a thickness of 300 μm, and the membrane was cut into a size of 10×10 cm to obtain a solid electrolyte diaphragm.

PTF containing ruthenium oxide "9 + iridium oxide 3m + 9 with an average particle size of about 30 μ per 1 d on the anode side of this diaphragm.
E thin film (PTFE content: 3) PTFE containing 4 parts of rhodium oxide with an average particle size of 30μ per 1 d on the cathode side of the diaphragm.
Thin 1! (PTFE containing 35% by weight) were bonded together by thermocompression bonding to form a solid electrolyte membrane provided with the gas- and liquid-permeable catalyst layer.

As a current collector, an iridium oxide-coated titanium mesh was used on the anode side, and a nickel-plated 5LI8304 mesh was used on the cathode side.

A titanium spring is used on the anode side to ensure close contact between the current collector and the solid electrolyte membrane with the electrode catalyst layer.

A cathode frame and a holding plate made of 5US304 were used on the cathode side.

500 μe of distilled water to which 0.2 mmol of chloroform was added was supplied to the anode chamber and the cathode chamber, and a current of 10
Electrolysis was carried out in A, and the generated oxygen gas and hydrogen gas were used to circulate the liquid. The sliding voltage was 2.9■.

The chloroform concentration in the electrolyte was measured by gas chromatography.

The chloroform decomposition rate after 10 minutes of electrolysis was 80% on the anode side.
%, reaching 90% on the cathode side, indicating that chloroform is decomposed very quickly.

Example 2 An ion exchange membrane with a size of 110 Cl [Nafion 125J (manufactured by DuPont, USA) was coated with PTF containing 4 iridium oxide particles with an average particle size of about 30 μm per 1 d on both sides.
EIlml (PTFE content: 30% by weight) was bonded together by thermocompression bonding to produce a gas- and liquid-permeable diaphragm provided with the catalyst layer.

As current collectors, platinum-plated titanium mesh was used on the anode side, and nickel mesh was used on the cathode side.

The close contact between the current collector and the solid electrolyte membrane provided with the catalyst layer was the same as in Example 1 above. In exactly the same manner as in Example 1, 500 μm containing 0.2 mmol of chloroform was added.
Distilled water of e is supplied to the anode chamber and the cathode chamber respectively, and a current of 1
Electrolysis was carried out at 0A, and the liquid was circulated using a generated gas lift. The sliding voltage was 2.3■.

The chloroform concentration in the electrolyte was measured by gas chromatography in the same manner as in Example 1.

The chloroform decomposition rate after 10 minutes of electrolysis was 9 on the anode side.
0%, and reached 95% on the cathode side, indicating that chloroform was decomposed very quickly.

Example 3 Electrolytic cells similar to those in Example 2 were used, and the current was 2.
Electrolysis was carried out at 0A. The sliding voltage was 2.4v.

After 30 minutes of electrolysis, the chloroform concentration in the electrolyte reached 0.00029 mmol/R (35μ5/R) on the anode side and 0.00029 mmol/R (21μ971) on the cathode side, which, when converted to decomposition rate, was 85. 5%.

It was 91.0%.

Example 4 Using the same electrolytic cell as in Example 2, 0.01 mmol of i, 1. 500 ■ with addition of it-lichloroethane
Electrolysis was carried out in exactly the same manner as in Example 2, except that distilled water of e was used, and a current of 2 OA was used. The sliding voltage was 2.4■.

The concentration of 1.1.1-trichloroethane in the electrolyte after 10 minutes of electrolysis was 0.0017 mmol/β (227
μ9/1), 0.0011 mmol/1 (
147 μ9/p), and the decomposition rate was 91.5 respectively.
%, 94.5%.

(Effects of the Invention) If direct electrolysis is performed using the method of the present invention using an electrolysis device in which porous membrane electrode catalyst layers are provided on both sides of a solid electrolyte membrane, there is no need to add a supporting electrolyte, and a high current Since density can be applied, trace amounts of halogenated hydrocarbons contained can be easily and quickly decomposed using a relatively small device without contaminating the target water, which is industrially useful.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing a diaphragm and an electrode part of an electrolytic cell used in the present invention.

Claims (1)

[Claims] An electrolytic cell is used in which a porous membrane electrode catalyst layer is provided on both sides of a solid electrolyte membrane that partitions an anode chamber and a cathode chamber, and the catalyst layer is combined with each current collector. A method for decomposing halogenated hydrocarbons, the method comprising electrolyzing water contained in halogenated hydrocarbons.