JPH02236292A - Production of carbonaceous electrode plate for electrolytic production of fluorine - Google Patents

Abstract

PURPOSE:To produce the above electrode plate which can stably continue electrolysis without entailing the electrolytic interruption based on an anode effect over the longest possible time by using particles of petroleum coke, etc., of specific grain sizes as a carbonaceous aggregate raw material, kneading a binder thereto and subjecting the mixture to press molding and calcining under prescribed conditions. CONSTITUTION:The articles of the petroleum coke and pitch coke having the grain sizes ranging 74mum to 1mm or the mixture composed thereof are used as the carbonaceous aggregate raw material and the proper binder is added thereto at 8 to 22 parts ratio to 100 parts raw material aggregate, then the mixture is kneaded. The molding is then subjected to the press molding at 95 to 115 deg.C to the desired electrode plate shape and this molding is calcined in the temp. range of 1000 to 1500 deg.C to produce the electrode plate. The molding pressure is preferably about 30 to 250kg/cm<2> in the case of executing the press molding by a compression molding method and the above-mentioned pressure is preferably about 0.03 to 0.5kg/cm<2> in the case of a vibration molding method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a carbonaceous electrode plate for producing fluorine for use in molten salt electrolysis of fluorine. (Prior art) Fluorine is generally used industrially as potassium fluoride (
Using a mixed molten salt of KF) and hydrogen fluoride (HF) as an electrolytic bath, electrolysis is carried out using a carbonaceous electroplating plate explicitly and an iron electrode plate secretly, thereby producing fluorine gas on the surface of the anode electrode plate. It is manufactured by generating During such electrolytic production of fluorine, the inside of the electrolytic tank is in a highly corrosive fluorine gas atmosphere, and especially in the case of an electrolytic tank, one end is immersed in the electrolytic bath and the other end is in a corrosive fluorine gas atmosphere. Since it is exposed to a pervading atmosphere, it has been common to use a high-density carbonaceous electrode material with a relatively dense particle size distribution as an electrode material that can withstand this. (Problem to be Solved by the Invention) However, when obtaining fluorine gas on an anodic plate by fluorine electrolysis, the discharge reaction of fluorine ions on the carbonaceous electrode plate is unique, which is not seen in other electrolytic reactions. When an electrolytic reaction is allowed to proceed at a constant current density, the cell voltage gradually increases over time, and when a certain limit point is reached, the cell voltage suddenly rises.

This phenomenon is called the so-called dipping effect, and if this phenomenon occurs within a short period of time after the start of operation, it will become impossible to continue electrolysis, and the operation of the electrolytic cell will be stopped and replaced with a new electrolytic plate. This was a major hindrance to production efficiency. The present invention provides a method for manufacturing a carbon electrolytic plate for fluorine production, which allows stable electrolysis to be continued for as long as possible without causing interruption of electrolysis due to the sun exposure effect, in the electrolytic production of fluorine as described above. The purpose is to provide the following.

(Means for Solving Problems) In order to achieve the above-mentioned objective, the inventors conducted extensive research and found that one of the most important factors governing the occurrence of the sun effect in electrode plates for fluorine electrolysis is We have discovered that the surface condition of the electrode plate, especially the diameter of the open pores on the surface of the electrode plate, has a significant effect on the time it takes for the scratching effect to occur, or in other words, the life of the electrode plate. In other words, the positive effect in fluorine electrolysis is that a part of the fluorine gas generated in the positive reaction reacts with the positive carbon to produce fluorinated graphite with high electrical insulation, which covers the entire positive surface as the electrolysis progresses. This is thought to occur due to the following. Therefore, in order to delay the occurrence of the stagnation effect as much as possible, it is necessary to suppress the generation of fluorinated graphite, and for this purpose, it is necessary to eliminate the retention of fluorine gas on the conductive surface as much as possible. It must not be. For this purpose, it is necessary to improve the wetting between the electric scraper and the electrolytic bath, and according to the experiments of the inventors, this is significantly influenced by the state of the open pores in the surface layer of the electric scraper.
Most of the pore diameters of the distributed open pores, that is, more than 50%, are 5.
It has been found that wetting can be significantly improved when the thickness is within the range of 0 μm to 150 μm. Therefore, the inventors have completed the present invention as a result of intensive research into a method for manufacturing a carbonaceous electrode plate that can obtain open pores with such a pore size range on the surface of the electric scraper. Petroleum coke 5-pitch coke having a particle size substantially in the range of 74 μm to 1 mm is used as a raw material for carbonaceous aggregate when a caking agent is blended with aggregate, kneaded, pressure-molded, and fired to obtain an electric lump. Alternatively, particles of a mixture of these are used, an appropriate binder is added thereto at a ratio of 8 to 22 parts by weight per 100 parts by weight of the raw material aggregate, and the mixture is kneaded, followed by a desired molding temperature of 95 to 115°C. The molded product is then pressure-molded into a temporary shape, and then heated to 1000-1500°C, preferably 11°C.
00 N A carbon material for fluorine electrolytic production that is characterized by firing in a temperature range of 1400°C? This is a method for manufacturing T-cut boards.

(Function) Generally, carbon'IX is obtained by blending carbonaceous aggregate and caking agent in appropriate proportions and going through the steps of kneading, pressure molding, and sintering.
Electroplated plates usually have numerous open pores ranging in size from several micrometers to several millimeters that occur on their surfaces during the manufacturing process. Electrolysis is performed under special manufacturing conditions, such as keeping the particle size of the material and the blending ratio of the caking agent within a specific range, and adjusting the molding pressure in the pressure molding process after kneading the raw materials to a specific range as necessary. By manufacturing the plate, we succeeded in obtaining a carbonaceous electric scraper with open pores having the desired pore size distribution, that is, 50% of the pores were in the pore size range of 50 um to 150 μm.

In the present invention, as the raw material aggregate, particle size of 74 μm or more and 1 m
Particles of crushed petroleum coke or crushed pitch coke or a mixture thereof whose particle size is adjusted to a range of 100 m or less are used. If the particle size exceeds the upper eyelid in the above range, the opening pore size of the resulting electrode plate will be too large, and if it is less than the lower eyelid, the pore size will become too small, and in either case, the electrode intended for the purpose of the present invention cannot be obtained. I can't get the board.

In this case, there may be cases where the mixing of fine particles with a particle size of 74 μm or less is unavoidable due to operational reasons, but even in such cases, the amount of unavoidable fine particles must be suppressed to a maximum of 5%.

In addition, anthracite is a commonly used carbonaceous material, and according to experiments conducted by the inventors, an electrode plate obtained by crushing anthracite to the particle size range of the present invention was used as an aggregate. was not preferred due to its poor mechanical strength. Next, the above-mentioned aggregates are blended to an appropriate particle size, and 8 to 22 parts by weight of coal tar pitch, petroleum pitch, or a caking agent with coal tar added thereto is added to 10 parts by weight of the raw material aggregate. Mix by mixing. When the amount of the caking agent added is less than 8 parts by weight, the caking agent cannot be evenly sprinkled on the aggregate, making molding difficult. On the other hand, if the caking agent exceeds 22 parts by weight, the carbon content contained in the caking agent will remain considerably after firing, and will block the open pores of the electrode plate, resulting in a reduction in the pore diameter. It's inconvenient.

Next, the carbon material obtained by kneading is pressure-molded to obtain a desired temporary electrode shape. The temperature during pressure molding is suitably in the range of 95 to 115°C. Further, the molding pressure is appropriately determined depending on the pressure molding method to be applied. For example, if a compression molding method is used as the pressure molding method, 30 to 2
It is appropriate to set it in the range of 50 kg/cm2, or in the range of 0.03 to 0.5 kg/cm'' when the vibration molding method is adopted.If the molding pressure is high, the electrically bonded plate after firing The pore diameter of the open pores on the surface tends to increase, and as the molding pressure decreases, the pore diameter tends to decrease, so it is desirable to keep the pressure within the above-mentioned range during pressure molding.

Pressure-molded products are usually produced at a temperature of 1,000 ℃, which is the temperature at which the carbonaceous electrocaking temperature is generally used, that is, the temperature at which the raw carbon material does not graphitize.
An electrode plate for fluorine electrolytic production having a desired surface opening pore size can be obtained by firing in a temperature range of ~150°C, 0~140Q°C. If the firing temperature is less than 1,000°C, the firing will be insufficient and the strength necessary for the electrification temporary will be insufficient;
Exceeding this is undesirable in any case because the carbonaceous material becomes graphitized and a sunburn effect occurs in a short period of time regardless of the pore size distribution.

When the galvanized plate obtained by the manufacturing method of the present invention is incorporated into a fluorine electrolytic cell as a solar cell and fluorine electrolysis is carried out by a conventional method, it is difficult to interrupt electrolysis due to the generation of solar harvesting effect over a long period of time. Therefore, it solves the problem of decreased production efficiency due to the occurrence of sunburn effect during short-time operations, which was traditionally considered the most efficient method for fluorine electrolysis, and makes it possible to continue electrolysis for a long time, which is extremely effective in terms of operational efficiency. It is. Although the reason why the occurrence of the sag effect during electrolysis is delayed when using the electrode plate obtained by the present invention is not fully understood, the carbonaceous electrode plate according to the present invention Most of the carbonaceous electrolyte materials have pore diameters of 5 to 150 μm, which are relatively large for this type of carbonaceous electrolyte material, so during electrolysis, the fluoride electrolytic bath easily penetrates and is retained in the open pores, thereby increasing the electrolyte. Because the surface of the cover plate is sufficiently wetted by the electrolytic bath, the fluorine gas generated on the electrolyte surface does not remain and quickly escapes from the electrolyte surface, which prevents the formation of fluorinated graphite. It seems to be.

According to experiments actually conducted by the inventors, relatively high-density electrode plates, such as those commonly used in conventional fluorine electrolysis, account for most of the open pores existing on the surface of the electrolyte, that is, 5
Since 0% or more of the pores have a pore size of 50 μm or less, when fluorine electrolysis is carried out using such an electric board,
The state of dissipation of fluorine gas on the galvanized surface was poor, and the occurrence of the anode effect occurred within a relatively short period of time, from a few days to a few days after the start of operation, making it difficult to continue the operation for a long time.

(Example 1) As a raw material carbonaceous aggregate, 50% of particles with a particle size of 500-1000 μm, 25% of particles with a particle size of 297-500 μm, 74-2
Medium pitch (J I
Sk2439) Add 1 part of caking agent to 100 parts of aggregate.
9 parts by weight were added and kneaded, and this was compression molded at a molding pressure of 120 kg/cm'' using a compression molding iron equipped with an electrode plate forming mold.Then, this molded product was fired at 1,400°C in a firing furnace to give a long-lasting product. Length 600mm. Medium 350
A carbonaceous power exchange plate with a thickness of 50 mm and a thickness of 50 mm was obtained. When the pore size distribution of the open pores on the surface of this power plate was measured using a porosity measurement method using mercury intrusion method, 20% of the pores had a pore size of 50 μm or less, 75% had a pore size of 50 to 150 μm, and 5% had a pore size of 150 μm or more. %Met. Next, for comparison, we measured the surface opening pore diameter of a commercially available product (Union Carbide product) conventionally used as a plate for fluorine electrolysis using the same mercury intrusion method. 55%, and the remainder consisted of pores with a pore size exceeding 50 μm.

Next, the carbonaceous electrode manufactured by the manufacturing method of the present invention and the conventional commercial product described above were actually incorporated into an electrolytic cell for producing fluorine, and a comparative test was conducted to determine the occurrence of the sun-dried effect.

A practical fluorine electrolyzer was used for the test, and a carbonaceous electrolyte plate was used as the anode, and an iron shade plate was used as the counter.
An electrolytic bath consisting of HF was maintained at 100°C and heated to 250°C.
When a current of A (current density 0.15 A/cm") was supplied and fluorine electrolysis was performed continuously, the electrolytic cell incorporating the carbonaceous electrolyte plate produced by the manufacturing method of the present invention showed that the electrolysis time was 30 minutes after the start of electrolysis. Even after several days had passed, no occurrence of the sludge effect was observed, and the operation continued smoothly and stably.In contrast, in an electrolytic cell incorporating a conventional commercially available product, it took only 9 days after the start of electrolysis.
Within days, a sun exposure effect occurred and electrolysis operations had to be halted.

(Example 2) As raw material carbonaceous aggregate, 45% of particles with a particle size of 500-1000 μm, 30% of particles with a particle size of 297-500 μm, 74-2
Using crushed petroleum coke grains with a particle size distribution consisting of 22% particles of 97 μm (the remaining 3% being unavoidably mixed fine particles of 74 μm or less), medium pitch (JIS)
k2439) Add 20 parts by weight of a caking agent to 100 parts by weight of aggregate, mix and knead, and use a vibration molding machine to form a 0.
The molded product was molded with a molding pressure of 0.04 kg/cm'', and then fired in a firing furnace at 1350°C to obtain a carbonaceous electric plate with a length of 600 mm, a width of 350 mm, and a thickness of 50 mm. When the pore size distribution of the surface pores of the electrode plate was measured by mercury porosimetry, it was found that 31% of the electrode plates had a pore diameter of 50 μm or less, 65% had a 50N150 μm diameter, and 4% had a pore diameter of 150 μm or more. .

Next, we conducted an operation test using a fluorine electrolyzer for this electric cell in the same manner as in Example 1, and found that no positive operation effect was observed even after 45 days had passed since the start of electrolysis, and the operation continued smoothly. I was able to do that.

(Effects of the Invention) As described above, the temporary carbonaceous electrode for fluorine electrolytic production obtained by the production method of the present invention, when fluorine electrolysis is carried out using it, lasts for a long time from the start of electrolysis. This is highly effective because no anode effect is observed and the fluorine electrolyzer can be operated continuously over a long period of time in a stable manner.

Patent applicant: Nikkei Giken Co., Ltd. Procedural amendment (formality) April 1, 1990? Day

Claims (3)

[Claims] (1) Petroleum coke having a particle size in the range of 74 μm to 1 mm as a carbonaceous aggregate raw material when blending a caking agent with raw material carbonaceous aggregate, kneading, pressure molding, and baking to obtain an electrode plate; Particles of pitch coke or a mixture thereof are used, and an appropriate binder is added thereto in an amount of 8 to 2 parts per 100 parts of raw aggregate.
Add 2 parts and knead, then mold at a temperature of 95-11
A method for producing a carbonaceous electrode plate for fluorine electrolytic production, which comprises press-molding it into a desired electrode plate shape at 5°C, and then firing the molded product at a temperature range of 1000 to 1500°C. (2) The method for manufacturing a carbonaceous electrode plate for fluorine electrolytic production according to claim 1, wherein the pressure molding is performed by a compression molding method, and the molding pressure is 30 to 250 kg/cm^2. (3) Manufacture of a carbonaceous electrode plate for fluorine electrolytic production according to claim 1, wherein the pressure molding is performed by a vibration molding method, and the molding pressure is 0.03 to 0.5 kg/cm^2. Law.