JP2017043846A - Porous carbon electrode for water treatment and waste water treatment method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous carbon electrode which is used for decomposing a hardly decomposable organic compound in water by a promotion oxidation method and has excellent break through property and electrical properties and mechanical strength resistant to long term use or a treatment with water pressure.SOLUTION: There is provided a porous carbon electrode which is used for a water conduction type water treatment by using an electrolytic promotion oxidation method and has communication pores, pore diameter measured by a mercury penetration method (median diameter) of 2 to 90 μm, air permeability of 0.0055 to 0.1000 cm/sec Pa and flexure strength of 10 to 100 MPa.SELECTED DRAWING: None

Description

  The present invention relates to a porous carbon electrode for water treatment and a wastewater treatment method using the same, and more particularly, to electrochemically convert a hardly decomposable organic compound contained in wastewater by water-flowing water treatment using an accelerated oxidation method. TECHNICAL FIELD The present invention relates to a porous carbon electrode used for treatment and a water treatment method using the same.

  Mineral wastewater contains difficult-to-decompose organic compounds such as aromatic compounds and has a problem that it cannot be decomposed and removed by biological treatment or activated carbon treatment. In particular, it is known that oil contained in mineral fuel such as crude oil and shale oil is inferior in biodegradability.

  At shale oil and shale gas drilling sites, which are currently being rapidly developed around the world, 3 to 10 times more oily water is generated than the amount of oil or gas drilled. Since this oily water contains organic compounds that are harmful to the environment and are difficult to decompose, the oily water must be purified and disposed of at the production site. Oil is inferior in biodegradability. In addition, oily water discharged by excavation using seawater or the like is more difficult to treat by biological treatment because of its high salinity. Even if it is purified by a physical method such as adsorption, it is difficult to remove the hardly decomposable organic compound contained in the oily water and the efficiency is poor. For this reason, although oily water is buried in the ground again without being able to be sufficiently purified, or stored in a managed reservoir, there is a strong concern about environmental pollution due to unforeseen circumstances. .

In recent years, a water treatment method using an accelerated oxidation method has been developed as a means for efficiently and inexpensively treating a large amount of water containing a hardly decomposable organic compound. In the accelerated oxidation treatment, OH radicals (hydroxy radicals: .OH) are generated in the treatment apparatus, and the organic compounds are decomposed into low molecules such as CO ₂ , formic acid, and aldehydes by the strong oxidizing power of the OH radicals. .

As a conventional accelerated oxidation method, a method of combining ozone (O ₃ ), hydrogen peroxide (H ₂ O ₂ ), and UV irradiation is generally used, and has been put to practical use for dioxin decomposition treatment. However, this method requires a large cost for special equipment such as an ozone generator, an exhaust gas treatment device, and a UV irradiation device. On the other hand, as a simple method that requires little initial investment and does not require special equipment, a reaction (Fenton reaction) that generates OH radicals from divalent iron ions (Fe ²⁺ ) and hydrogen peroxide as shown in the following formula is used. The Fenton method is known.
Fe ²⁺ + H ₂ O ₂ → Fe ³⁺ + OH ⁻ + · OH

  In addition, an electrolytic Fenton method is known in which both or one of the divalent iron ions and hydrogen peroxide required in the Fenton method are generated and supplied in the same apparatus as the accelerated oxidation treatment. In such an electrolytic Fenton method, In addition to drastically reducing the amount of divalent iron ion source input, depending on the amount of load, it is possible to eliminate the need to input divalent iron ion as a reaction source from the outside if it is initially input. is there. Further, in the method of supplying hydrogen peroxide by electrolytic reduction of oxygen, reduction of the supply cost of hydrogen peroxide can be expected.

For example, Patent Document 1 proposes a wastewater treatment method that performs Fenton treatment while electrochemically reducing Fe ³⁺ . However, it is necessary to use an electrode made of copper, a copper alloy, which is a noble material than Fe as a cathode material, platinum, diamond, or the like as an anode material in the Fenton reaction tank of the waste water treatment apparatus, and such an electrode material is expensive. Therefore, since it is difficult to manufacture a large electrode in terms of cost, it is difficult to efficiently treat a large amount of waste water. In addition, the water treatment using a plate-like or rod-like electrode as in Patent Document 1 has a low supply rate of Fe ³⁺ to the cathode surface, and hydrogen is a competitive reaction when a high voltage is applied to increase the treatment rate. The production reaction becomes advantageous. Therefore, if the Fenton treatment is not performed with very strong stirring in the vicinity of the electrode, there is a problem that the treatment rate of the organic compound in the waste water is remarkably reduced.

  Patent Document 2 discloses a carbon electrode coated with glassy carbon, and Patent Document 3 discloses a method of performing an electrochemical oxidation treatment using the carbon electrode. This is because, after being applied to the porous carbon electrode, the water to be treated containing the microorganisms is polarized in the process of flowing through the fine pores inside the porous carbon electrode. Migration occurs and microorganisms are killed by redox reactions.

  The porous carbon electrodes disclosed in Patent Documents 2 and 3 are made of a material of a porous carbon material on a skeleton surface of a carbon base material that forms pores of a particle-bonded porous carbon material using coke particles and pitch as raw materials. In order to reinforce the strength, it has a composite structure in which dense and hard glassy carbon is coated. However, since coke particles having a large particle size are used as a raw material in order to increase the pore size and increase the water permeability, it is inevitable that the strength is lowered, and is relatively high in order to ensure the water flow rate. It cannot withstand long-term use in water treatment equipment that requires water pressure. Further, since the electrode surface is coated with glassy carbon which is non-graphitizable carbon, there is a problem that the specific resistance of the electrode is increased and the electrode cannot be enlarged.

JP 2004-181329 A Japanese Patent Laid-Open No. 11-139871 JP-A-11-140681

  The present invention provides a continuous water flow using an electrolysis-promoted oxidation method that has high mechanical strength and low specific resistance as an electrode material that can be increased in size, and can withstand long-term use even in environments with high water pressure. An object of the present invention is to provide a porous carbon electrode suitable for mold water treatment.

  As a result of repeated studies to solve the above problems, the present inventor is easy to manufacture, has good liquid permeability, has a low specific resistance value, is light in weight, has high mechanical strength, and promotes electrolytic oxidation. In order to complete the present invention, it is found that by using a porous carbon electrode that can be suitably used for a water-passage water treatment method using a method, wastewater containing a hardly decomposable organic compound can be treated easily. It came.

That is, the present invention relates to a porous carbon electrode used for water flow type water treatment using an electrolysis-promoted oxidation method, having a continuous pore, and having a pore diameter (median diameter) measured by a mercury intrusion method. It is a porous carbon electrode characterized by being ² to 90 μm, an air permeability of 0.0055 to 0.1000 cm ² / sec · Pa, and a bending strength of 10 to 100 MPa.

In the porous carbon electrode, the specific resistance value is preferably 0.1 to 20 μΩm.
In the porous carbon electrode, the electrolysis-promoted oxidation method uses the Fenton reaction, and it is preferable that the water to be treated is used for water-flow type water treatment in which the inside of the electrode flows.

  Further, the present invention is a method for producing the above porous carbon electrode, after kneading and molding a carbonaceous material containing 10 to 80 parts by weight of a binder pitch with respect to 100 parts by weight of graphitizable carbon particles. And a method for producing a porous carbon electrode, characterized by firing and graphitizing.

In the above production method, the graphitizable carbon particles are preferably pitch coke or petroleum coke, and the true density is preferably 1.8 g / cm ³ or more. Further, after firing and graphitization, surface treatment may be performed with hydrogen peroxide or hypochlorous acid.

Further, the present invention provides a method for treating waste water by an accelerated oxidative decomposition method utilizing electrolytic Fenton reaction by flowing waste water containing an organic compound through a reaction vessel in which a cathode and an anode are disposed. At least as a cathode, by applying a voltage to both electrodes while draining water through the pores of the porous carbon electrode as a microchannel, hydrogen peroxide is removed from dissolved oxygen in the drainage water in the pores. It is characterized in that, while producing Fe ³⁺ produced by the Fenton reaction, electrochemically reducing it to Fe ²⁺ , an organic compound in the waste water is continuously subjected to electrolytic Fenton treatment to cause oxidative decomposition. Wastewater treatment method.

When the porous carbon electrode of the present invention is used as an electrode for a water flow type electrolysis-promoted oxidation method, it can stably and efficiently treat a hardly decomposable organic compound for a long period of time. That is, at the interface (contact surface) between the porous carbon electrode and water, the Fe ³⁺ reduction reaction and the H ₂ O ₂ formation reaction are performed, and the Fenton reaction is performed by using the microchannel inside the electrode structure as a reaction field. It is possible to continuously carry out the decomposition of the hardly decomposable organic compound by the above. So far, there has been no porous carbon electrode for water treatment using the Fenton reaction utilizing the internal space of the electrode, and by integrating the electrode and the reaction field, the Fenton treatment can be completed with only the porous carbon electrode, It is a porous carbon electrode that can provide any large electrode and device.

It is a schematic process drawing which shows embodiment of the waste water treatment method using the porous carbon electrode which concerns on this invention. It is the schematic which shows embodiment of the waste water treatment equipment using the porous carbon electrode which concerns on this invention.

The porous carbon electrode of the present invention is a water-permeable porous carbon electrode through which water to be treated flows through the inside of the electrode, and the air permeability as a measure of water permeability is 0.0055 to 0.1000 cm in SI units. ² / sec · Pa (0.55 to 10 cc · cm / cm ² · sec · cmH ₂ O in conventional units), preferably 0.0080 to 0.0500 cm ² / sec · Pa (0.8 to ⁵ . 0 cc · cm / cm ² · sec · cmH ₂ O). If the air permeability is less than 0.0055 cm ² / sec · Pa (0.55 cc · cm / cm ² · sec · cmH ₂ O), the water permeability of the water to be treated will deteriorate, so it takes time for water treatment. It is not suitable. On the other hand, if the air permeability exceeds 0.1000 cm ² / sec · Pa (10 cc · cm / cm ² · sec · cmH ₂ O), the water to be treated flows out of the electrode without being completely treated, which is not suitable.

  The pore diameter (median diameter) of the porous carbon electrode of the present invention is 2 to 90 μm, preferably 3 to 50 μm, more preferably 3 to 25 μm. If the pore diameter is less than 2 μm, the pressure loss when the treated water flows through the electrode will be high, so the liquid permeability will be reduced, leading to an increase in load on the electrode and a decrease in the amount of treated water, and clogging is likely to occur. The problem of becoming. In addition, when the pore diameter exceeds 90 μm, the contact area between the water to be treated and the electrode is reduced, so that it may flow out of the electrode with insufficient treatment, and there is a concern that the mechanical strength of the electrode is lowered.

In the porous carbon electrode of the present invention, since the water to be treated is passed through the electrode through-holes as microchannels for water treatment, it is desirable that the number of pores communicated is large. A large contact area is desirable in terms of processing efficiency. For this reason, the specific surface area of the electrode is preferably 1.0 m ² / g or more, and preferably 4.0 m ² / g or more. The porosity is suitably 10 to 40%, preferably 15 to 30%. When the porosity is 40% or more, the mechanical strength of the electrode is lowered, and when it is less than 10%, the liquid permeability is lowered, so that the treatment efficiency is lowered.

The porous carbon electrode of the present invention preferably has a bulk density of 1.10 to 2.0 g / cm ³ , more preferably 1.25 to 1.90 g / cm ³ , and most preferably 1. It is in the range of ^{30 to} 1.80 g / cm ³ . If the bulk density is low, the mechanical strength is remarkably lowered, and if the bulk density is too high, the air permeability is lowered and it is not suitable as a porous carbon electrode used for water flow type water treatment.

  The porous carbon electrode of the present invention has a bending strength of 10 to 100 MPa. If the bending strength is less than 10 MPa, shape processing cannot be performed with high dimensional accuracy, or damage may occur due to water pressure or external vibration or impact. On the other hand, when the bending strength exceeds 100 MPa, the toughness is lowered and becomes brittle, and there is a problem that precision machining cannot be performed.

  The specific resistance of the porous carbon electrode of the present invention is preferably 0.1 to 20 μΩm, more preferably 0.1 to 15 μΩm. The specific resistance value should be as low as possible. If the resistance exceeds 20 μΩm, the larger the electrode, the more efficiently the current cannot be supplied to the inside, and the efficiency of water treatment decreases. In order to perform a large amount of water treatment using a porous carbon electrode, it is necessary to make the electrode as large as possible. Therefore, an electrode having a low specific resistance is preferable.

  The porous carbon electrode of the present invention having the above characteristics can be produced by a known method. For example, fine carbonaceous coke particles such as pitch coke and petroleum coke are blended with binder pitch such as tar and pitch to make a carbonaceous material, which is put into a kneader and kneaded at a temperature higher than the melting temperature of the binder pitch. It can be manufactured by extruding from a die having an extrusion port of a predetermined shape, followed by firing and graphitization. Further, in place of the above-described extrusion molding, it is also possible to use an embedding molding in which the kneaded product of coke powder and binder pitch is cooled and secondarily pulverized particles are put into a mold having a desired shape and pressure-molded from above. Further, it can also be produced by cold isostatic pressing (CIP) molding in which the secondary pulverized particles are compression molded with a rubber press in water, then fired and graphitized.

In the production of the porous carbon electrode of the present invention, graphitizable carbon having a true density of 1.8 g / cm ³ or more is used as raw coke particles. The raw coke particles are preferably graphitizable carbon particles having a true density of 1.95 g / cm ³ or more. When the true density of graphitizable carbon is less than 1.8 g / cm ³ , the electrical resistance increases and the water treatment efficiency decreases.

  Examples of the binder used for producing the porous carbon electrode of the present invention include tar and pitch. The pitch can be either petroleum pitch obtained from petroleum heavy oil or coal pitch obtained from heavy coal oil, but it can be obtained from raw materials similar to graphitizable carbon particles used as raw coke particles. It is preferable to use the obtained binder pitch because the familiarity during kneading is good.

  The blending ratio of the graphitizable carbon particles and the binder pitch is adjusted depending on the kneading conditions and the molding method, but the blending pitch is 10 to 80 parts by weight with respect to 100 parts by weight of the graphitizable carbon particles. To do. For example, when producing a porous carbon electrode by extrusion molding, the binder pitch is 10 parts to 80 parts, preferably 20 parts to 50 parts, with respect to 100 parts by weight of graphitizable carbon particles. If the binder pitch is less than 10 parts by weight, the mechanical strength is lowered, and the electrode becomes brittle. On the other hand, when the binder pitch exceeds 80 parts by weight, the electrical characteristics are deteriorated. The blending ratio is appropriately adjusted within the above range.

  The kneaded product of graphitizable carbon particles and binder pitch is formed into a desired shape and heat treated (fired) at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere to obtain a porous carbon molded body. By further graphitizing this porous carbon molded body at a temperature of 1500 ° C. or higher, preferably 2000 to 3000 ° C., in a non-oxidizing atmosphere, the porous carbon electrode for water treatment of the present invention is produced. At this time, graphitization is more preferably performed at a temperature of 2000 to 2800 ° C. in order to increase the surface activity of the porous carbon electrode to obtain a predetermined degree of graphitization and crystallinity. In addition, it is preferable that the atmosphere at the time of graphitizing is an inert atmosphere by nitrogen, argon gas, etc., or a vacuum.

  The pore diameter (median diameter) and air permeability of the porous carbon electrode can be controlled by the particle diameter of the graphitizable carbon particles to be used, the amount of binder pitch or impregnation pitch used, the firing temperature, and the like. For example, these numbers increase by increasing the particle size of the graphitizable carbon particles. Further, if firing is performed a plurality of times and impregnation pitch is impregnated at this time, these numbers become small, but the air permeability decreases. Increasing the firing temperature and lengthening the time decreases the specific resistance. Since other characteristics can be controlled by a known method, the above-described conditions are changed so that the desired characteristics are obtained. Specifically, regarding the particle size of the graphitizable carbon particles (coke particles), the particle size of all the particles is preferably 5 mm or less, more preferably 3 mm or less, of which 0.1 mm or less. The grains are preferably present at 10% (by weight) or more, more preferably at least 20%. It is also preferable that the balance between the pore diameter, the air permeability and the mechanical strength (bending strength) is improved by excluding particles having an intermediate particle diameter, for example, about 0.5 to 1.0 mm. . After the graphitizable carbon particles (coke particles) adjusted to a predetermined particle size are kneaded with the binder pitch, the kneaded product or the extruded product may be pulverized and the particle size adjusted again.

  The porous carbon electrode of the present invention preferably has an oxygen content of 0.1 wt% to 10 wt%. If the amount is less than 0.1% by weight, the surface is water-repellent, so that the liquid permeability is deteriorated, and if it exceeds 10% by weight, the electrical characteristics are deteriorated. In addition, the contact angle of the porous carbon electrode with pure water is desirably 110 ° or less, and more preferably 100 ° or less. When the contact angle exceeds 110 °, the wettability of the surface decreases, so that the water repellency increases and the liquid permeability deteriorates. In addition, water treatment using the porous carbon electrode of the present invention, which improves familiarity with organic matter and causes organic matter to accumulate and cause clogging, is treated by an accelerated oxidation reaction while the treated water passes through the electrode. Therefore, the electrode needs to be well wetted with the treated water. For this reason, you may perform the surface treatment of an electrode for the further improvement of the wettability with respect to water.

  As long as the surface modification by the hydrophilization treatment does not affect the pore size and mechanical properties of the porous carbon electrode, the treatment with a strong oxidizing agent such as nitric acid and sulfuric acid or a reactive gas such as fluorine gas, The method is not particularly limited, such as high-temperature air oxidation, but hydrophilic treatment with hydrogen peroxide, hypochlorous acid, or the like, which can be controlled mildly, is preferable.

  The porous carbon electrode of the present invention is an electrode having a low specific resistance and good energization efficiency up to the inside of the electrode. Even if the size is increased, the current loss from the current collector to the inside of the electrode is small, so that the Fenton treatment can be performed even if the current collector is away from the current collector. Moreover, since this material has high mechanical strength, it is a material that can withstand pressure loss of water and backwashing without dropping off the material. It not only has the characteristics as an electrode, but also has design freedom such as an increase in the size of the water treatment device. Furthermore, it is not an electrolysis reaction on the electrode surface such as a non-porous electrode material, but water treatment in a large number of microchannels formed by the continuous pores of the porous carbon electrode. Since it will be moderately disturbed, a separate stirring operation is not required.

  The porous carbon electrode of the present invention is preferably one whose surface is not covered with glassy carbon or the like. Since the whole is integrated, the pores are uniformly distributed, so there is no bias of the water flow inside the electrode, and stable and good water treatment can be performed.

  Since the porous carbon electrode of this invention has high bending strength, it can post-process to an electrode as needed. Examples of post-processing include processing of electrode surface irregularities and groove shapes for the purpose of adjusting water flow, drilling, and the like. In addition, about a drilling process, if it is in the range which can maintain the performance of the porous carbon electrode of this invention, there will be no problem in particular, However, If a hole diameter is 500-1000 micrometers, it will be hard to cause the fall of water treatment performance, and preferable.

When water treatment is performed with a water treatment apparatus using the porous carbon electrode of the present invention, an anode and a cathode made of a porous carbon electrode are disposed in the water treatment apparatus, and the pores communicating with the porous carbon electrode are formed in a microscopic manner. This is done by passing water such as waste water containing organic matter through the channel and applying a voltage. In the case of electrolytic Fenton treatment, when a voltage is applied to both electrodes and a wastewater containing organic matter, iron ions and dissolved oxygen is caused to flow through the microchannel of the porous carbon electrode serving as the cathode, H ₂ derived from the dissolved oxygen in the wastewater. O ₂ and Fe ²⁺ added to the treated water cause a Fenton reaction to generate OH radicals and oxidatively decompose organic matter. Fe ³⁺ produced by the Fenton reaction is reduced to Fe ²⁺ at the interface with the cathode and used again to generate OH radicals by the Fenton reaction. At this time, the total residence time of water passing through the microchannel of the cathode is reduced. By setting the thickness so as to be uniform, the Fenton reaction can be caused continuously, and the treatment of the organic matter can be completed by a single liquid flow. In addition, although the material of an anode is arbitrary, the graphite electrode and noble metal electrode which are excellent in corrosion resistance are suitable.
As described above, the porous carbon electrode of the present invention causes an electrolytic Fenton reaction by applying a voltage and flowing the water to be treated into the micro-channel, purifying the waste water, and performing the water treatment Fenton reaction. The reduction of Fe ³⁺ generated by the above to Fe ²⁺ and the generation reaction of hydrogen peroxide solution are performed.
Furthermore, the porous carbon electrode of the present invention has a low specific resistance, and fine pores are connected to form a complicated micro flow path, so that the treated water is appropriately disturbed during water flow. Therefore, the reducing ability is higher than that of non-porous electrodes. Accordingly, iron (Fe), which is an essential material for the electrolytic Fenton reaction, can be recycled and the amount of hydrogen peroxide (H ₂ O ₂ ) used can be reduced.

The wastewater treatment method using the porous carbon electrode of the present invention will be described in detail below with specific examples.
FIG. 1 is a process diagram showing an embodiment of a wastewater treatment method to which a porous carbon electrode of the present invention is applied. First, an organic wastewater containing an organic compound is added to an Fe ²⁺ compound and hydrogen peroxide for an electrolytic Fenton reaction, and an acid for pH adjustment, and then transferred to a reaction vessel. Next, when the wastewater transferred to the reaction vessel flows through the porous carbon electrode as a cathode installed in the reaction vessel, when a voltage is applied to both electrodes, the communicating pores of the porous carbon electrode are passed through the microchannel. As a result, the organic compound in the waste water is continuously oxidatively decomposed and rendered harmless by the electrolytic Fenton reaction. The waste water detoxified in the reaction tank is neutralized with alkali or the like to remove iron ions so as to be below the regulation value, and finally discharged into the environment as treated water.

In the wastewater treatment method to which the porous carbon electrode of the present invention is applied, when the porous carbon electrode is used as the cathode of the reaction vessel, the main reactions presumed to occur at the cathode are as follows.
Fe ³⁺ + e ⁻ → Fe ²⁺
O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ₂
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O
^{_{H 2 O 2 + Fe 2+ →}} OH · + OH - + Fe 3+

As is apparent from the above reaction formula, in the electrolytic Fenton reaction, hydrogen peroxide and divalent iron ions are required to generate OH radicals, but hydrogen peroxide is discharged from waste water containing dissolved oxygen (O ₂ ) to the cathode. The divalent iron ions can be generated by the cathode reaction from the wastewater containing the trivalent iron ions.

Although iron ion depends on pH, it finally becomes trivalent iron ion (Fe ³⁺ ) or iron hydroxide and is discharged from the reaction tank together with the treated water. Therefore, if the pH of the treated water is raised, the iron component becomes a precipitate of trivalent iron hydroxide and can be separated.

Since hydrogen peroxide (H ₂ O ₂ ) is decomposed on the anode side, it is preferable to supply hydrogen peroxide immediately before the cathode from the viewpoint of suppressing the amount of hydrogen peroxide used. The supply of divalent iron ions, iron hydroxide or trivalent iron ions is not particularly limited as long as it is upstream from the cathode of the reaction tank, and may be added to the drain tank or from the inflow side piping to the drainage layer. Good.

  As shown in the above reaction formula, the Fenton reaction that generates hydroxy radicals (OH.) Occurs mainly on the cathode side. If the structure is as shown in FIG. 2 described later, the waste water continuously flows in one direction from the cathode side to the anode side, so that decomposition of hydrogen peroxide at the anode can be suppressed. The electrode used for the anode may be a known electrode. However, the electrolytic Fenton reaction is acidic on the acidic side and has good reaction efficiency. If the drainage contains chlorine ions, the metal electrode is affected. In view of the durability of the electrode, it is preferable to use the porous carbon electrode of the present invention not only for the cathode but also for the anode.

If the cathode made of a porous carbon electrode is shaped like a plate that matches the cross-sectional shape of the reaction tank and is installed so as to block the flow path of the reaction tank, most of the wastewater flowing through the reaction tank is in communication with the porous carbon electrode. The pores become microchannels and pass through the channel. Various reactions shown in the above reaction formula occur on the cathode side, and an oxidation reaction of the organic compound contained in the wastewater occurs due to the Fenton reaction by the OH radical generated by this reaction. Therefore, since the supply rate of Fe ³⁺ to the cathode surface increases, the reduction reaction near the electrode surface or the pore surface becomes dominant, and the reaction in the microchannel is efficiently generated. Become. As a result, the reaction efficiency is very high compared to the case where an electrode having no communication pores is used.

Waste water treatment by electrolytic Fenton reaction is a method of generating OH radicals from Fe ²⁺ and hydrogen peroxide to oxidatively decompose organic compounds. The amount of the iron compound used in the present invention varies depending on the type and concentration of organic matter in water, the pH of the treated water, the reaction time, etc., but the amount of Fe ²⁺ compound added is preferably 1 to 200 mg / l, preferably Is preferably 5 to 100 mg / l. The higher the concentration of iron, the easier the electrolytic Fenton treatment proceeds, but this concentration is preferable because iron tends to precipitate when the concentration is high. Examples of the Fe ²⁺ compounds that supply divalent iron ions include ferrous sulfate, ferrous chloride, and ferrous nitrate, but ferrous sulfate is the most important in terms of activity and price. Preferably selected.

In the wastewater treatment method to which the porous carbon electrode of the present invention is applied, divalent iron ions (Fe ²⁺ ) necessary for the electrolytic Fenton reaction are added from the outside and used for the Fenton reaction. Then, Fe ³⁺ oxidized by the electrolytic Fenton reaction is electrochemically reduced in the micro flow channel composed of the communicating pores of the porous carbon electrode installed in the reaction tank, and is used repeatedly for the Fenton reaction. The amount of external addition can be reduced.

Hydrogen peroxide necessary for the wastewater treatment method to which the porous carbon electrode of the present invention is applied can also be generated from dissolved oxygen in the wastewater at the cathode. At this time, the amount of dissolved oxygen in the wastewater is 10 mg / l. The above is preferable. The amount of dissolved oxygen in the waste water can be increased by stirring or aeration of the waste water. The hydrogen peroxide necessary for the electrolytic Fenton reaction in the wastewater treatment method of the present invention is supplied from the outside according to the load amount of the wastewater, but the supply amount can be reduced by electrolytic generation from dissolved oxygen in water. Therefore, it is preferable.
When hydrogen peroxide is added from the outside in accordance with the load of wastewater treatment, it is peroxidized at a concentration of 1 to 20 mol times, preferably 5 to 10 mol times the Fe ²⁺ concentration, depending on the organic matter concentration in the wastewater. It is preferred to add hydrogen.

In the wastewater treatment method to which the porous carbon electrode of the present invention is applied, the decomposition of the organic substance by the Fenton method and the reduction of Fe ³⁺ to Fe ²⁺ by the electrochemical method are simultaneously performed in the reaction tank. Accordingly, the water to be treated needs to be maintained in a state in which the above two reactions proceed appropriately. Specifically, the pH is 1.5 to 5.0 at room temperature, preferably 2.0 to 4. It is preferably 0. For adjusting the pH, an arbitrary acid such as hydrochloric acid or sulfuric acid is added. The above pH conditions are convenient for dissolving the iron compound in the sludge again when the sludge is generated.

In this way, the organic matter in the organic wastewater is oxidatively decomposed by the Fenton reaction, and at the same time, Fe ³⁺ generated by the Fenton reaction is reduced again to Fe ²⁺ in the reaction tank and reused for the Fenton reaction. The object can be achieved even if the amount of Fe ^{2+ to be} added is reduced. On the other hand, if the ability to reduce electrochemically is sufficiently large, an Fe ³⁺ compound may be added to the reaction tank instead of the Fe ²⁺ compound.

  The wastewater treatment method to which the porous carbon electrode of the present invention is applied is a method for oxidizing and decomposing an organic compound contained in wastewater using an electrochemical reaction. For this reason, it is necessary to increase the conductivity and improve the processing efficiency by adding a compound serving as an electrolyte to the waste water. The electrolyte compound is not particularly limited as long as it is an ionic compound that is soluble in water, such as sodium sulfate, potassium chloride, sodium chloride, potassium sulfate, or a combination of two or more compounds. Sodium sulfate is preferred because of problems. The amount of the electrolyte added may be a concentration that allows the carbon electrode to be energized, and the concentration is adjusted according to the load of the drainage, but is preferably 0.01 to 3%.

  An example of the embodiment of the waste water treatment apparatus in which the porous carbon electrode of the present invention is installed is shown in FIG. In FIG. 2, an electrolytic Fenton reaction tank 1 has a cathode 2 made of a porous carbon electrode on the drainage supply side and an anode 3 made of a platinum electrode on the drainage outlet side with respect to the flow of water in the reaction tank. So as to be orthogonal to each other. A current collector 4 is in close contact with the cathode 2, and is connected to a DC power source 6 together with the anode 3 by a conducting wire 5. Moreover, in order to make the flow of waste water uniform, a bottom plate or a plastic filler (for example, terralet) may be installed on the waste water supply side of the reaction tank 1 as necessary.

  The waste water 11 containing an organic compound is supplied to the electrolytic Fenton reaction tank 1 after the electrolyte is mixed in the drain tank 8. At this time, it is preferable to further adjust the pH according to the pH of the wastewater, and it is more preferable to adjust the pH to the acidic side in order to prevent clogging due to the generation of iron hydroxide compounds in the electrolytic Fenton reaction tank.

  The drainage supply side of the electrolytic Fenton reaction tank 1 is connected to the drainage tank 8 by a pipe 7 via a water pump 9, and the discharge side is connected to the treated water tank 10 by a pipe 7. When the water pump 9 is operated, the drainage 11 in the drainage tank 8 is supplied to the electrolytic Fenton reaction tank 1.

  In the electrolytic Fenton reaction tank 1, the wastewater containing the organic compound is added with the necessary amounts of hydrogen peroxide and divalent iron ions, and is allowed to flow through the cathode 2 made of a porous carbon electrode that is energized. Decomposes organic compounds contained in the wastewater. At this time, the communicating pores of the cathode 2 made of a porous carbon electrode serve as a microchannel, and when the drainage flows through the microchannel, the organic compounds in the drainage are oxidatively decomposed by OH radicals generated by the electrolytic Fenton reaction. Is done.

  Thereafter, the waste water after the electrolytic Fenton treatment is transferred to the treated water tank 10 from the piping 7 on the discharge side of the reaction tank 1 as treated water 12, but since the treated water 12 contains iron ions or hydrogen peroxide, At the time of discharge, the pH of the treated water is adjusted and the iron ions are removed so as to be lower than the standard value according to laws and regulations. Examples of the removal of iron ions include methods such as collection and separation of iron ions using a chelate resin or the like, and a sedimentation separation method for precipitation as a hydroxide, but the collection and separation of iron ions using a chelate resin or the like may generate sludge. Less preferred.

In the wastewater treatment using the porous carbon electrode of the present invention, the electrolytic Fenton reaction occurs in the microchannel of the porous carbon electrode by the porous carbon electrode having the communicating pores installed in the electrolytic Fenton reaction tank 1. The resulting OH radicals oxidize and decompose organic compounds in the wastewater. At the same time, hydrogen peroxide is also produced from dissolved oxygen in the wastewater, and Fe ²⁺ consumed in the electrolytic Fenton reaction is converted from Fe ³⁺ into electricity. Chemical reduction enables efficient and continuous treatment of wastewater.
For this reason, it is preferable that the electrolytic Fenton reaction tank 1 has a structure in which the entire amount of wastewater supplied into the tank flows through the porous carbon electrode installed in the tank. More preferably, a porous carbon electrode is provided so as to be orthogonal to the flow direction.

  When the waste water 11 containing an organic compound flows through the communicating pores of the porous carbon electrode, the organic compound is oxidatively decomposed by OH radicals generated by the Fenton reaction. The communicating pores of the porous carbon electrode are fine and complex micro-channels, so that the drainage is disturbed appropriately, so stirring operation is not essential, the contact area between the drainage and the electrode is large, flat or rod-like The processing efficiency is higher than that of a reaction tank using electrodes.

Furthermore, when a voltage is applied to the porous carbon electrode, hydrogen peroxide is also generated from dissolved oxygen in the water in the microchannel of the porous carbon electrode simultaneously with the oxidative decomposition of the organic compound in the wastewater by the electrolytic Fenton reaction. In addition, Fe ³⁺ generated by the Fenton reaction is reduced to Fe ²⁺ . For this reason, the waste water 11 can continuously cause an electrolytic Fenton reaction while flowing through the anode 2 and the cathode 3 made of porous carbon electrodes, and the waste water is efficiently discharged using iron ions and hydrogen peroxide. Can be continuously processed by electrolytic Fenton reaction.

  EXAMPLES Hereinafter, although the content of this invention is demonstrated concretely based on an Example, this invention is not limited to the range of these Examples.

Example 1
Pitch coke with a true density of 1.82 g / cm ³ is pulverized to have a particle size blend of 1.000 to 2.380 mm: 40%, 0.074 to 0.297 mm: 35%, 0.074 mm or less: 25% 40 parts by weight of a binder pitch (softening point 97 ° C.) obtained from coal-based heavy oil was added to 100 parts by weight of the pitch coke particles adjusted to the above, and heated and kneaded at 200 ° C. for 20 minutes. This kneaded material was extruded to a size of 20 mmφ × 100 mm. After molding, firing was performed at 1000 ° C., followed by graphitization at 2800 ° C. to obtain a porous carbon electrode A.

Example 2
A porous carbon electrode B was obtained in the same manner as in Example 1 except that the molding method was replaced with mold (formwork) molding and the binder pitch was 30 parts by weight.

Example 3
The same conditions as in Example 1 except that the pulverized pitch coke was replaced with a particle size blend of 0.250 to 1.000 mm: 20%, 0.074 to 0.250 mm: 45%, 0.074 mm or less: 35%. A porous carbon electrode C was obtained.

Example 4
A porous carbon electrode D was obtained by the same process as in Example 3 except that the amount of binder pitch added was 35 parts by weight.

Comparative Example 1
What was baked at 1000 ° C. in the same manner as in Example 1 was immersed in an impregnation pitch (softening point 78 ° C.) heated to 230 ° C., impregnated under reduced pressure, fired again at 1000 ° C., and then Graphitized at 2800 ° C. to obtain a porous carbon electrode E.

Comparative Example 2
The pulverized pitch coke is replaced with a particle size blend of 0.250 to 1.000 mm: 60%, 0.074 to 0.250 mm: 40% (0.074 mm or less: 0%), and the molding method is 0.2 MPa by molding. A porous carbon electrode F was obtained under the same conditions as in Example 1 except that it was molded with a moderately weak load.

Comparative Example 3
The porous carbon electrode F was immersed in an ethanol solution in which a phenol resin was dissolved for 10 minutes under reduced pressure. Thereafter, the excess resin solution is drained, air-dried for 24 hours, heat-treated at 180 ° C. to heat and cure the resin, and subjected to heat treatment at a maximum temperature of 2800 ° C. in a non-oxidizing atmosphere. A porous carbon electrode G coated with was obtained.

Using these porous carbon electrodes A to G, a water passage test was conducted. Table 1 shows the characteristics of the porous carbon electrodes A to G and the results of the water flow test.
[Water flow test]
In the middle of the flow path, a porous carbon electrode processed to 22 mm × 22 mm × 15 mm is arranged so as to be perpendicular to the flow path and block the entire flow path, and at a flow rate of 2 ml / min using a peristaltic pump. A water flow test was conducted by flowing pure water having a water temperature of 20 ° C. In addition, the water flow is acceptable (◯) if the flow rate of pure water can be maintained at 2 ml / min or higher even if the pump output is kept constant for 12 hours with the pump output kept constant, and the pure water that has flowed through the electrode is 5B filter paper. The presence or absence of dropped particles was confirmed by filtering with a filter.

表１において、通気率の括弧内の数値は、ＳＩ単位に換算する前の慣用単位[ｃｃ・ｃｍ/ｃｍ^２・ｓｅｃ・ｃｍＨ_２Ｏ]での値を示す。

In Table 1, numerical values in parentheses of the air permeability indicate values in conventional units [cc · cm / cm ² · sec · cmH ₂ O] before conversion into SI units.

Examples 5-7, Comparative Example 4
The porous carbon electrode was subjected to an iron reduction experiment and a decomposition test of a hardly decomposable organic compound.
In these tests, the porous carbon electrodes A and G and the electrode A1 and the electrode A2 obtained by surface-treating the porous carbon electrode A were used as electrodes.
The electrode A1 is obtained by immersing the porous carbon electrode A in a 30% hydrogen peroxide solution at 50 ° C. for 24 hours for surface treatment, and the electrode A2 is obtained by subjecting the porous carbon electrode A to a 30% order at 50 ° C. The surface treatment was performed by immersing in sodium chlorite water for 8 hours.

[Iron reduction test]
This test verifies whether Fe ³⁺ can be reduced and Fe ²⁺ can be produced by the porous carbon electrode. The apparatus uses a porous carbon electrode processed to 22 mm × 22 mm × 15 mm for the cathode and a platinum electrode for the anode, and the electrolyte is 50 mM Na ₂ while applying a voltage so that the potential difference between both electrodes is 1.5V. The test water prepared by adjusting SO ₄ to Fe ³⁺ so that Fe ₂ (SO ₄ ) ₃ is 0.5 mM is fed into the apparatus at a rate of 1.54 ml / min (the liquid space velocity at the electrode portion is 12.7 h ^{− In 1} ), 250 ml was supplied. The evaluation was carried out by measuring the current value at the time of energization and measuring the Fe ²⁺ concentration in the sample water after the test using an absorptiometric method based on the bathophenanthroline method.

[Decomposition test]
This test verifies whether or not a hardly decomposable organic compound can actually be decomposed by a porous carbon electrode. The apparatus uses a porous carbon electrode processed to 22 mm × 22 mm × 15 mm for the cathode, a platinum electrode for the anode, and 50 mM Na ₂ as an electrolyte while applying a voltage so that the potential difference between both electrodes is 1.5V. Simulated wastewater prepared by using SO ₄ and adjusting dimethyl sulfoxide (DMSO) as a hardly decomposable organic compound to 100 mg / L, hydrogen peroxide 1 mM, and Fe ³⁺ Fe ₂ (SO ₄ ) ₃ to 0.5 mM. 250 ml was supplied into the apparatus at a rate of 1.54 ml / min (liquid space velocity at the electrode part: 12.7 h ⁻¹ ). The evaluation was performed by measuring the amount of DMSO in the sample water after the test using a high performance liquid chromatography (HPLC) method, and calculating the amount of DMSO decomposition.
The test results are shown in Table 2.

  In addition, the measuring method of each physical property is as follows.

[Measurement of pore diameter (median diameter)]
Measured by mercury intrusion method. The measuring device was a micromeritics Auto Pore III manufactured by Shimadzu Corporation, and the mercury pressure was measured under the conditions of 1.9 to 14400 psi.

[Measurement of air permeability]
A cylindrical sample (bottom area A (cm ² ), height L (cm)) is supplied with nitrogen at a pressure P (cmH ₂ O) in the axial direction at room temperature, and the flow rate Q (cm ³ / sec) was measured to calculate the air permeability in conventional units from the following formula and also converted to SI units.
Air permeability in conventional units (cc · cm / cm ² · sec · cmH ₂ O)
= Q (cc / sec) × L (cm) / [A (cm ² ) × P (cmH ₂ O)]
Air permeability in SI units (cm ² / sec · Pa)
= Q (cm ³ / sec) × L (cm) / [A (cm ² ) × 98.0665P (Pa)]

[Measurement of true density, bulk density, resistivity, bending strength]
Each physical property of the material was measured according to JIS R7222 “Method for measuring physical properties of graphite material”.

  The porous carbon electrode for water treatment of the example is composed of a persistent organic compound having an excellent flow-through property and electrical characteristics, and has a mechanical strength that can withstand long-term use and treatment with water pressure, by an electrolysis-promoted oxidation method. It is a material suitable for wastewater treatment electrodes. In addition, according to the water flow experiment and the reduction experiment, it was confirmed that excellent electrical conductivity, liquid permeability and iron reduction reaction, and DMSO, which is actually a hardly decomposable organic compound, could be efficiently decomposed. It is a good material for water treatment by the method, especially the electrochemical Fenton reaction method.

1 Reaction tank 2 Cathode (porous carbon electrode)
3 Anode 11 Drainage 12 Treated water

Claims (7)

It is a porous carbon electrode used for water flow type water treatment using an electrolysis-promoted oxidation method, has a continuous pore, and has a pore diameter (median diameter) measured by a mercury intrusion method of 2 to 90 μm, A porous carbon electrode having an air permeability of 0.0055 to 0.1000 cm ² / sec · Pa and a bending strength of 10 to 100 MPa.   The porous carbon electrode according to claim 1, wherein the specific resistance value is 0.1 to 20 μΩm.   The porous carbon electrode according to claim 1 or 2, wherein the electrolysis-promoted oxidation method uses a Fenton reaction, and is used for water-through water treatment in which treated water flows through the inside of the electrode.   It is a manufacturing method of the porous carbon electrode in any one of Claims 1-3, Comprising: Carbonaceous material which mix | blended 10-80 weight part of binder pitch with respect to 100 weight part of graphitizable carbon particles is knead | mixed. A method for producing a porous carbon electrode, characterized by firing and graphitizing after molding. The method for producing a porous carbon electrode according to claim 4, wherein the graphitizable carbon particles are pitch coke or petroleum coke, and the true density thereof is 1.8 g / cm ³ or more.   The method for producing a porous carbon electrode according to claim 4, wherein the surface treatment is performed with hydrogen peroxide or hypochlorous acid after firing and graphite. The method according to any one of claims 1 to 3, wherein a wastewater containing an organic compound is circulated through a reaction vessel in which a cathode and an anode are disposed, and the wastewater is treated by an accelerated oxidative decomposition method utilizing an electrolytic Fenton reaction. By using a porous carbon electrode as at least a cathode and applying a voltage to both electrodes while passing drainage through the pores of the porous carbon electrode as a microchannel, In addition to producing hydrogen peroxide, the organic compound in the waste water is continuously subjected to electrolytic Fenton treatment to oxidatively decompose, while electrochemically reducing Fe ³⁺ produced by the Fenton reaction to Fe ²⁺ Wastewater treatment method characterized by.

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