JPH03221108A - Electrode for use in high density electroosmotic dehydration - Google Patents

Abstract

PURPOSE:To increase carbon density and permit a long time use by a method wherein a mixture of carbon fiber and resin is shaped into the form of an electrode, such shaped product is thereafter baked to carbonize the resin, the resulting electrode is impregnated with resin and baked to carbonize the impregnated resin and this carbonizing step is repeated. CONSTITUTION:The material to be dehydrated is placed between an anode (f) and a cathode (f) facing each other and subjected to compressive dehydration by pressing a compression diaphragm (e) behind the electrode and, at the same time, to electroosmotic dehydration by applying D.C. from behind the electrode. The electrode in this device is formed by a method wherein a mixture of carbon fiber and resin (e.g. polyester) is shaped into the form of an electrode, thus shaped product is baked to carbonize the resin, the resulting electrode is impregnated with phenol resin or the like and baked to carbonize the impregnated resin and such carbonizing step is repeated once or a plurality of times to increase the carbon density. As a result, this method provides a high strength and density and reduces the attrition effect on the electrode accompanying the application of current thereto and, therefore, the electrode can be used for a long period of time and the economics of electroosmotic dehydration can be enhanced with respect to waste liquors and sludge.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is useful in electroosmotic dewatering equipment, particularly filter press type equipment, which promotes dehydration by applying direct current while squeezing sewage sludge for advanced dewatering. Regarding the electrode configuration that exhibits its properties.

(Prior Art) The attached diagram shows the procedure for electroosmotic dehydration using a filter press type device. This device is equipped with synthetic resin filter plates in the form of liquid passage and ventilation passages.

First, as shown in Fig. 1, a pair of filter plates (a) (a)
are closed with filter cloths (b) and (b) sandwiched between them, and the sludge from the material to be dehydrated is passed through the raw solution inlet (C) by a stock solution pump to form between the filter cloths (b) and (b). The filtrate that has been pressurized into the filter chamber and passed through the filter cloth is collected and discharged from the outlet (d), and as much sludge as possible is thrown into the filter chamber without preliminary dewatering by pump pressure filtration. Next, as shown in Figure 2, a flexible compressed membrane (e.
) and pressurize it forward by introducing pressure air behind the electrode (f).
The sludge cake between the filter cloths (b) and (b) is additionally dehydrated by squeezing pressure through the filter cloth (f). The moisture content of the dehydrated cake is reduced to 80 to 85% by this press dehydration, which is the limit of press dehydration. Finally, while continuing compression dewatering, a DC voltage is applied from the power supply unit connected behind the electrodes (f) and (f), and electricity is applied to the sludge through the filter cloth to promote dewatering by electroosmotic action. do. By applying a DC voltage of about 40 V and running it for about 15 minutes, the moisture content of the dehydrated cake will drop to about 50% (1 drop). When the dehydration is finished, open the filter plate and remove the filter cloth as shown in Figure 3. Pull down and remove the dehydrated cake (ε) from the machine and send it for disposal. Dehydrated cake number =
Since the volume and weight are reduced by half and the product is in a solid state, it is easy to dispose of and does not require a burden on the operator.

As an electrode for an electroosmotic water device, as shown in C above, it is exposed to an erosion environment accompanied by the electrochemical action of sludge water that is subjected to a large pressurizing force for pressing dewatering, such as 4J electrolysis, and is also suitable for pressing membranes. Since power must be supplied to the electrode plate from behind the electrode plate in such a way that no voltage drop occurs during that time, the required conditions are severe. Conventionally, electrodes made of various materials and structures such as metal plates and carbon sintered plates have been proposed and used, but each has the problems described in the following section.

(Problems to be Solved by the Invention) In electroosmotic dehydration equipment, the electrodes are electrically conductive, so they not only have excellent electrical functions and sufficient mechanical strength to withstand squeezing pressure, but also are generally expensive. The low resistance to chemical wear and shortening of life is of predominant importance in enabling economical operation. When typical electrodes of the prior art are examined from this viewpoint, the following problems arise.

In terms of mechanical strength, electrodes made of relatively inexpensive corrosion-resistant metal plates such as stainless steel and nickel steel have sufficient strength, but they have a short lifespan because they are ionized by direct current, dissolve into the sludge, and wear out. Furthermore, eluted metal ions, especially chromium, cause secondary pollution problems. Special metal electrode plates made of titanium alloy coated with high-value precious metals such as platinum have low metal elution, low electrode wear, and excellent corrosion resistance, but they are too expensive for practical use and have poor electroosmotic dehydration effects. In order to increase this, it may be useful to reverse the polarity of the DC current during the process, but in this case there is a problem that the platinum coating will peel off when the polarity is reversed.

Electrodes made of non-metallic carbon sintered plates are less likely to elute when energized, but electrochemically, the binder coke is selectively oxidized and consumed by the nascent oxygen, causing physical drop-off of the carbonaceous material. Since there is a lot of wear and tear, the lifespan is not long enough, and there is a problem that it is mechanically weak and can be damaged by compression pressure.

In addition, in order to compensate for the weak points in the strength of nonmetallic electrodes, for example, Japanese Patent Laid-Open No. 147208/1983 discloses an electrode made of a pressure-molded composite of conductive fibers and synthetic resin, but there is no insulation inside the electrode. Because it contains a synthetic resin, the conductivity decreases and the voltage drop inside the electrode becomes large.As a result, the applied voltage must be increased in order to pass the amount of electricity required for electroosmotic dehydration, making it difficult to use. This not only increases costs but also shortens the life of the electrodes, making it uneconomical and, moreover, using high voltages in working environments where water is handled is not desirable because of the risk of electric shock.

In electroosmotic dehydration, the required pressing pressure may be lower than that in a filter press that uses only mechanical compression dehydration. However, filter press type electroosmotic dehydration equipment has the advantage of being able to increase the current-carrying area of the electrodes, but on the other hand, the strength conditions against bending are not as severe, and the structure for supplying power to a large electrode area is disadvantageous. becomes difficult.

The all-carbon electrode made of a carbon material containing carbon fibers disclosed in Japanese Patent Application Laid-Open No. 64-30613 satisfies these requirements, but the electrode wears out due to energization, so it cannot be used for long periods of time. If the electrode becomes thinner due to continued energization, there is a concern that the mechanical strength will be insufficient, and therefore the electrode will have to be replaced sooner.

(Means for Solving the Problems) The present invention provides an electrode made of a carbon material containing carbon fibers as described in JP-A No. 64-30613, which has the optimum characteristics achieved in the prior art as an electrode for electroosmotic dehydration. This was done with the aim of further optimizing the electrode material. In other words, the all-carbon material electrode of this prior art is mainly made of carbon fiber for imparting strength, and a carrier made of short carbon fibers is impregnated with a carbonizable resin that becomes bonded carbon, and after drying, it is hot-pressed. It is made by hardening the resin to shape the bottom into the shape of an electrode, and then firing it at a high temperature of about 2,500°C to carbonize the resin.

Due to the decomposition of the resin part and the escape of components other than carbon due to high-temperature firing, the resin part shrinks in volume and becomes porous. The porosity of this prior art electrode is about 40%.

In the present invention, the pores are filled with bonded carbon to increase the density, and the strength of the electrode body is increased by strengthening the bonding of carbon fibers with the filled bonded carbon, and the conductivity is improved by increasing the density without impairing the total carbon property. We aim to

As a solution to achieve this, the present invention impregnates the carbonaceous electrode, that is, the electrode body formed as described above, with a resin that can be further carbonized, and after drying, it is fired at a high temperature to carbonize the impregnated resin.

This operation is repeated a necessary number of times to obtain the densified electrode for electroosmotic dehydration of the present invention.

That is, in the high-density electroosmotic dehydration electrode of the present invention, the material to be dehydrated is sandwiched between an anode and a cathode that face each other, and the material to be dehydrated is compressed and dehydrated by applying pressure from the compression membrane behind the electrode, and the material is compressed and dehydrated from behind the electrode. This is an electrode for a device that performs electroosmotic dehydration even when DC current is applied by power supply, and the electrode body is impregnated with resin by forming a mixture of carbon fiber and resin into an electrode shape and then firing it to carbonize the resin. It is characterized in that the carbon density is increased by repeating the operation of carbonizing the impregnated resin by firing one or more times.

The mixture of carbon fiber and resin has a length of 2 to 20 mm, for example.
About 10 to 5 m of short carbon fibers and resin are combined.
It can be prepared by mixing it so that it accounts for 0% by weight. Such a mixture can be formed into an electrode shape by heating and pressurizing it using a mold or the like.

The mixture can also be prepared by mixing and stirring the above-mentioned short carbon fibers and a paper-making medium containing a binder for paper-making, and forming the mixture onto a fabric or wire mesh.
It can be prepared by impregnating a dried product with a resin.

The short carbon fibers are dispersed in random directions within a substantially two-dimensional plane by papermaking.

As the binder for papermaking, polyvinyl alcohol, hydroxyethyl cellulose, polyethylene oxide, polyacrylic acid, polyester, etc. are used, and the papermaking medium is obtained by diluting with water or the like. The resin is also preferably used after being diluted with methanol or the like. Such a so-called intermediate base material can be formed into an electrode shape by laminating a plurality of sheets to obtain the required thickness and pressing them together.

As the resin in the composite and the resin impregnated into the electrode body,
Phenol resin, epoxy resin, furan resin, pitch, mixed resins thereof, etc. can be used. All of these resins are carbonized by firing.

Firing to form the electrode body or carbonizing the resin impregnated into the electrode body is performed in an inert atmosphere such as nitrogen or argon or in a vacuum atmosphere, depending on the type of resin, etc. Perform at ~3000″C.

In the present invention, the resin may further contain carbon powder.

(Function) When the densified electrode of the present invention is used in an electro-osmotic dehydration device, the carbon fibers have stronger bonds with more bonded carbon, so they will not bend due to squeezing pressure etc. applied to them during the dehydration operation. In addition, the wear and tear of the electrode due to continued energization is reduced in inverse proportion to the higher density, and the decrease in strength is reduced, so the electrode strength is maintained for a long period of time and the lifespan is extended. In order to further increase the density, the electrode formation facility used in the conventional technology can be used.
There is no additional technical difficulty and the cost increase is small.

(Example) Hereinafter, the characteristics of the high-density electroosmotic dehydration electrode of the present invention will be clarified by comparing it with the conventional electrode for electroosmotic dehydration according to Japanese Patent Application Laid-Open No. 64-30613 using Examples.

Comparative Example Polyacrylonitrile-based carbon fiber (trade name: ``Toreca'' Ta2O) manufactured by Toshi Co., Ltd. was cut into short fibers of 12 mm length, and carbon fiber paper was made by dispersing the short fibers in water. The electrode was impregnated with a phenol resin as a resin that can be carbonized by the method, dried, and then cured by stacking and pressing to form an electrode shape.

Next, this was heated and baked at 2500° C. in a nitrogen atmosphere to carbonize the phenol resin, thereby obtaining a comparative electrode body.

Example A The electrode body of the comparative example was impregnated with a phenolic resin and dried, and then brought to the bottom of the hole again at 2500"C to carbonize the impregnated phenolic resin.
A) was obtained.

Example B The electrode of the comparative example was impregnated with a phenol resin, and after drying, the impregnated phenol resin was carbonized at 800''C to obtain an electrode (B) for high-density electroosmotic dehydration.

Example C Instead of heating and firing at 2500°C in the comparative example,
The electrode body heated and fired at 0''C is impregnated with phenol resin, and after drying, the phenol resin is carbonized by heating and firing at 800°C to obtain the densified electrode for electroosmotic dehydration of the present invention (
C) was obtained.

The following table shows a comparison of the characteristics of the electrodes of the embodiments of the present invention and the electrodes of comparative examples.

As can be seen from this table, the bending strength of the electrode of the present invention is greater than that of the comparative example electrode, and the strength decrease due to wear due to energization is apparently larger, so the wear rate is smaller, that is, the amount of remaining electrode is smaller. It can be seen that there is little influence of strength reduction.

(Effects of the Invention) As described above, the high-density electrode for electroosmotic dehydration according to the present invention has higher strength than the optimal electrode for electroosmotic dehydration made of a carbon material mainly composed of carbon fibers of the prior art. Since it has a high density and is less affected by wear and tear caused by energization of the electrode, it can be used for a long period of time and has the effect of increasing the economic efficiency of electroosmotic dehydration.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the first stage of electroosmotic dehydration using a filter press type device, FIG. 2 is a diagram of the intermediate stage, and FIG. 3 is a diagram of the final stage. (a)...filter plate, (b)...filter cloth, (C)...undiluted solution population, (d)...outlet, (e)...press membrane, (f
)... Electrode, (g)... Dehydrated cake.

Claims (1)

[Claims] An electrode for an apparatus in which a material to be dehydrated is sandwiched between an anode and a cathode facing each other, and the material to be dehydrated is compressed and dehydrated by applying pressure from a compressing membrane behind the electrode, and at the same time, the material is subjected to electro-osmotic dehydration by applying direct current through power supply from behind the electrode. , an electrode body made by forming a mixture of carbon fiber and resin into an electrode shape and then firing it to carbonize the resin is impregnated with resin and firing it to carbonize the impregnated resin, which is repeated one or more times. A high-density electroosmotic dehydration electrode characterized by increasing carbon density.