JPH0299107A - Electrode for use in electroosmosis dehydration and electroosmosis dehydration process - Google Patents

Abstract

PURPOSE:To improve dehydration rate by causing electrode material composed of carbonaceous material to carry thereon organic compounds which are electrolyzed by energizing them With D.C. current. CONSTITUTION:Electrode material composed of carbonaceous material such as sintered carbon plate, glassy carbon etc., is caused to carry thereon organic compounds which are electrolyzed by energizing them with D.C. current (e.g., preferably, compounds containing carboxyl groups, such as formic acid, acetic acid, oxalic acid, tartaric acid, etc.), whereby oxidation reaction of carbon material due to nascent oxygen generated by electrochemical reactions between carbon material and water or electrolysis of water is reduced, resulting in prolonged life of electrodes, whereby economical electroosmosis dehydration is achieved.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is useful for promoting dewatering by applying direct current between opposing electrodes while sandwiching and squeezing a material to be dehydrated, such as sewage sludge. The present invention relates to a new electrode structure of an electrode made of a carbonaceous material and an electroosmotic dehydration method that enables the implementation of this under advantageous conditions.

(Prior Art) Figures 1 (a), (b), and (c) show the main steps of the operating process when electroosmotic dehydration is carried out using a filter press type dehydrator.

In Figure 1 (a), a pair of filter plates (a) of a filter press are shown.
) (a) Filter cloth 0)) (b) is sandwiched and closed with a compressed membrane (C), and sludge, which is the material to be dehydrated, is forced into the filter cloth from the raw solution inlet (d) using a raw solution pump, The dehydrated liquid that has passed through the filter cloth is discharged to the outside of the machine from the filtrate outlet (e).

In FIG. 1(B), the squeeze membrane on the outside of the filter cloth is expanded by the squeeze pressure introduced behind it, pressurizes the primary dewatered sludge in the front, and squeezes out more water from the solidified sludge cake. In the latter stage of this pressing dehydration, direct current is applied to the material to be dehydrated through the filter cloth between the electrodes (f) on the outside of the filter cloth, and additional dehydration is performed by the electrode osmosis action to increase the dehydration rate. In FIG. 1 (c), the filter plate is opened, the filter cloth is pulled down, and the dehydrated cake (g) is taken out of the machine.

Electroosmotic dehydration can also be carried out using a belt press device, etc.
-61608).

In this way, when a direct current is passed through the sludge in the process of compressing and dewatering sludge that contains a large amount of organic matter that is difficult to dewater, such as sewage sludge, water in the sludge that cannot be dehydrated simply by pressing is transferred to the cathode side by electroosmosis. The water content of the dehydrated cake can be significantly lowered compared to dehydration using only squeezing pressure.

For example, if pre-condensed sewage condensation through coagulation and draining is supplied to a filter press and dehydrated for about 20 minutes at a compression pressure of 3 kgf/c111, the water content of the dehydrated cake will be 80-85%, and if the pressure is higher than this, the moisture content of the dehydrated cake will be 80-85%. However, even if it takes a long time, there is no significant effect on reducing the moisture content of the dehydrated cake. On the other hand, during dehydration, a DC voltage of about 40V is applied to
When electricity is applied for 5 minutes, the moisture content of the dehydrated cake decreases to about 50%, and the volume of the dehydrated cake decreases to 172 or less.

If the electrical conductivity of the sludge is low and it is difficult to apply electroosmotic dewatering, for example, inorganic salts such as common salt, calcium chloride, sodium sulfate, and sodium nitrate may be added to the pre-OI concentrated sludge to increase the electrical conductivity of the sludge. It can be processed by improving the
There are almost no restrictions due to the properties of sludge.

By the way, the electrodes used for electroosmotic dehydration are of various mechanical,
It is necessary to satisfy required electrical and electrochemical characteristics, and conventionally usable electrodes include metal plates and carbon sintered plates, but these are still unsatisfactory in terms of life.

For example, metal plate electrodes made of stainless steel, nickel steel, etc. are ionized by DC current, elute and wear out, and have a short lifespan (in particular, chromium elution poses a problem of secondary pollution.Also, titanium alloys are plated with platinum). The metal electrode used as an anode has low current consumption and good current carrying performance, but it is very expensive and the platinum peels off when reverse polarity current is applied, so it cannot be used. Although the degree of electrochemical corrosion is lower than that of metal plate electrodes such as stainless steel and nickel steel, it still reacts electrochemically with water according to the following reaction formula, c+2L O−+COt +4H” +4 e However, when the binder coke is subjected to oxidative consumption due to oxygen during the generation stage, the binder coke portion is selectively electrolytically eroded, resulting in many physical drop-offs of carbonaceous material, so that the life is still insufficient.

(Problems to be Solved by the Invention) In order to solve the above-mentioned problems of the conventional electrode for electroosmotic dehydration, we first developed a new electrode for electroosmotic dehydration made of a carbonaceous material containing carbon fibers. A patent application was filed (Japanese Patent Application No. 186315-1982). This electrode is an anode,
We have developed a new electroosmotic dehydration method by changing the polarity that can be used for any cathode, and have applied for a patent (Japanese Patent Application No. 186316/1982) in order to maximize the dehydration efficiency. According to the results of the galvanic corrosion test, this electrode has a significantly smaller corrosion loss than either conventional metal plate electrodes or carbon electrodes, which is about 0.03 g/AH. Under the same conditions, the corrosion loss of the stainless steel electrode of the prior art is 0.1175 g/AH, and that of various types of prior art carbon electrodes is about 0.06-0.11 g/AH.

In order to make electroosmotic dehydration economically advantageous, the electrodes that play the main role also account for a large portion of the equipment cost, so further improving the lifespan of the electrodes is important. have sex.

The present invention provides an electrode for electroosmotic dehydration and an electric current which, compared to the prior art and prior art electrodes described above, are not disadvantageous in terms of other properties and which provide improved results with respect to electrode life. It is an object of the present invention to provide an osmotic dehydration method, thereby making it possible to carry out electroosmotic dehydration under economically more advantageous conditions.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an electrode structure for use in electroosmotic dehydration in which an electrode material made of a carbonaceous material supports an organic compound that is electrolyzed by direct current. It is characterized by

Furthermore, as an electroosmotic dehydration method that exhibits the same action and effect, when the material to be dehydrated is sandwiched and a direct current is applied between a pair of anode and cathode made of carbonaceous material for electroosmotic dehydration, electrolysis by direct current is applied. The organic compound is brought into contact with the anode.

As a means of solving the problem, the following matters should be considered in implementation.

It uses organic chemicals that react electrochemically on the electrode surface when energized. As this type of organic compound that is water-soluble and easily available, compounds containing a carboxyl group are preferable, and examples of this type of compound include organic acids such as formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, and succinic acid; Examples include sodium salts, calcium salts, potassium salts, magnesium salts, and ammonium salts.

Furthermore, organic compounds such as alcohols and aldehydes may be added to these. In order to promote the electrochemical reaction of these organic compounds, a catalyst may be present on the electrode surface or may be mixed into the electrode in advance.

Since these are specific examples that are advantageous for implementation, the present invention is not limited by these examples.

The above organic compound can be supported on the electrode material in the following manner.

That is, a porous carbonaceous material or a porous carbonaceous material containing carbon fibers is impregnated with an aqueous solution or emulsion of the organic compound by vacuum and/or pressure. It is preferable to add a binder such as polyvinyl alcohol to the aqueous solution. After impregnating the inside of the carbon porous material, the solvent is removed by drying.

Alternatively, the above-mentioned organic compound powder is mixed with carbon powder into a thermoplastic synthetic resin such as polyethylene or polypropylene resin and shaped into an electrode.

On the other hand, when the organic compound is made separate from the electrode and brought into contact with the surface of the electrode during electroosmotic dehydration, the following example is used.

That is, in the process of pre-concentrating the material to be dewatered such as sewage sludge by coagulating and draining, first compressing it using a filter press type dehydrator equipped with electrodes, and then electro-osmotic dehydration, the above-mentioned substances are added to the pre-concentrated sludge. Add organic compound. In this way, the organic compound comes into contact with the electrode surface as water moves during the compression dehydration process.

Alternatively, after pressing and dewatering, the press is opened, the sludge cake, the filter cloth, and the anode surface are wetted with the aqueous solution of the organic compound, and the press is closed to perform electroosmotic dehydration.

In the present invention, the electrode material made of carbonaceous material is
It is also possible to use carbon sintered plates, grady carbon materials, plastic vibration molded carbon materials mixed with carbon powder to give conductivity, but particularly preferred is the method described in the aforementioned Japanese Patent Application No. 186315/1983. An electrode made of a carbonaceous material containing such carbon fibers, specifically, 10 to 15% by weight of the carbonaceous material has a fiber length of 2 to 20 mm, and is distributed in substantially random directions within a two-dimensional plane. It is preferable to use a carbonaceous electrode in which the carbon fibers are dispersed and laminated, and the carbon fibers are bound by carbon.

Such a carbonaceous electrode is made by using, for example, polyacrylonitrile-based short carbon fibers with a single fiber diameter of 4 to 15 μm and a fiber length of 2 to 20 fibers, mixed with a papermaking medium in which a binder for papermaking such as polyvinyl alcohol is diluted with water, The material is stirred and made into sheets or plates, dried to remove the solvent, and used as an intermediate base material. This is impregnated with a solution of a carbonizable resin such as phenol resin, and hot press molded to harden the resin. , and then heated to 1000 to 3000''C in an inert gas atmosphere to carbonize the impregnated resin.

For carbonaceous electrodes or other porous electrodes obtained in this way, the pores may be impregnated with an aqueous solution of the organic compound by capillary action, for example, after the electrode plate is installed in an electroosmotic dehydration device. .

The present invention does not limit the amount of the organic compound, but for example, when adding it to pre-concentrated sewage sludge, it is recommended to add it in an amount of 10% by weight or more based on the solid content of the sludge. preferable.

(Function) According to the present invention, an organic compound that is electrolyzed by direct current is supported or brought into contact with the surface or inside of the anode made of a carbonaceous material of an electroosmotic dehydrator. The oxidation reaction of carbon materials due to nascent oxygen generated by electrochemical reactions and water electrolysis is reduced,
It is thought that the electrode life will be improved.

(Example) (1) Electrode Example Polyacrylonitrile carbon fiber Torecar T-300 manufactured by Toshi Co., Ltd. was cut into lengths of 12 mm+ and dispersed in an aqueous solution of polyvinyl alcohol to form paper. Next, the paper was impregnated with a phenolic resin, dried, and then hot pressed to harden the resin. Then, the phenol resin is carbonized by heating and baking at 1600°C in a nitrogen atmosphere, and a carbonaceous material containing carbon fibers having a thickness of about 1 cylinder, an apparent density of 1.05 g/crA, and a porosity of about 40% is made. electrode,
That is, a base electrode CB) was obtained. This sample of the base electrode (B) is related to the prior patent application No. 186315/1982, and has a compressive breaking strength of 100 kg/af1 or more,
It has conductivity with an electrical resistance value of 0.015Ωcm.

For this base electrode (B), polyvinyl alcohol 0
．． A carbonaceous material electrode (B) was obtained by repeating the procedure of vacuum impregnation with a saturated solution of tartaric acid as an organic compound that can be electrolyzed by direct current in an aqueous solution containing 5% by weight and drying at 100°C five times. A sample of the electrode (A) of the present invention was obtained by supporting tartaric acid in the pores of the electrode.

I and a cathode (2), in an aqueous solution (3) containing 4 g/l of common salt, and a DC power supply (4) and a voltmeter (5).
．． Current was applied for 3 hours at a current density of 0.02 A/d while changing the polarity at 20 minute intervals.

The amount of electrode consumption was 0.0258/AH.

(n-2) Example (A) Using a sample of the electrode (8) of the present invention, direct current was applied in an aqueous solution containing 4 g/2 of common salt under the same test conditions as in Comparative Example (1).

After energization, the electrode was heat-treated at 500°C in a nitrogen atmosphere to thermally decompose the remaining tartaric acid and polyvinyl alcohol supported on the electrode, and the corrosion loss of only the carbonaceous electrode was measured to be 0.005 g. /AH.

(ll-3) Example (B) A test similar to Comparative Example and Example (1) using a sample of the base electrode (B) in an aqueous solution of 4 g/2 tartaric acid, which is an organic compound that is electrolyzed by direct current. The method of the present invention was carried out by applying direct current under the following conditions.

After the experiment was completed, the tartaric acid concentration in the aqueous solution was electrochemically decomposed and reduced by half to approximately 2 g/l, while the consumption of the carbonaceous electrode was measured to be approximately 0.006 g/8H. Ta.

The amount of consumption of the carbon electrode when an organic compound is used instead of the tartaric acid described above is also shown.

(Effects of the Invention) As described above, according to the present invention, by providing an organic compound that is electrolyzed by electricity on the anode surface in electroosmotic dehydration, the amount of wear and life of the electrode made of carbonaceous material can be significantly reduced. It has the effect of improving and economical electroosmotic dehydration.

[Brief explanation of the drawing]

Figure 1 (a) is a diagram showing the initial operation process of the filter press type electroosmotic dehydration equipment used in the present invention;
B) is a diagram during the operation process, FIG. 1C is a diagram of the final operation process, and FIG. 2 is a diagram showing an outline of the apparatus used for the energization test in the experiment of the present invention. (1)... Anode, (2)... Cathode, (3)... Aqueous solution, (4)... DC power supply, (5)... Voltmeter, (
a)...filter plate, (b)...filter cloth, (C)...squeezed membrane, (d)...stock solution inlet, (e)...filtrate outlet, barb)...electrode , ((2)... dehydrated cake.

Claims (2)

[Claims] (1) An electrode for electroosmotic dehydration, characterized in that the electrode is made of a carbonaceous material and supports an organic compound that is electrolyzed by direct current. (2) When performing electroosmotic dehydration by applying direct current between a pair of anode and cathode made of a carbonaceous material while sandwiching the object to be dehydrated, the organic compound to be electrolyzed by the direct current is brought into contact with the anode. Electroosmotic dehydration method.