JPH02267108A - Desulfurization of graphite sheet and desulfurizer therefor - Google Patents

Abstract

PURPOSE:To accomplish the title desulfurization in high efficiency at low cost by heating treatment of a graphite sheet with itself as an exothermic body in a high-frequency induction heating system. CONSTITUTION:A graphite sheet 3 is gradually moved in the arrow a direction through a space between heat resistant, non-electrically conductive partition plates 4,4 made of e. g. ceramic. A high-frequency voltage is then applied from a high-frequency electric source 1 via a current transformer 2 on a high-frequency coil 5 provided externally in proximity to the partition plates 4. Thereby a field current is generated in the graphite sheet 3 to make instantaneous heating and cooling. In this case, the heating temperature is pref. >=1400 deg.C. It is preferable that high-frequency coil 5 be divided into plural parts and the sheet 3 treated at lower temperatures ca.1000-1300 deg.C in the former half and at higher temperatures 1400-1700 deg.C in the latter half, i.e. in a multi- stage temperature-raising manner over heating zones H1-H3 etc. Furthermore, it is preferable that e.g. N2 gas be allowed to flow in the arrow c direction between the partition plates 4,4 to prevent the graphite sheet 3 from oxidation as well as to quickly expel the sulfur-contg. gas generated out of the system. Thus, the objective desulfurization of the graphite sheet 3 can be accomplished in high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] Graphite sheets often contain sulfur components as impurities, and this sulfur content poses a major problem depending on the application. For this purpose, the graphite is desulfurized. Conventional desulfurization methods use ordinary resistance heating elements or heating by gas combustion method to achieve a temperature of 800 to +0
It is heated to about 00'C to decompose or evaporate and remove the sulfur component.

However, in reality, conventional desulfurization methods are insufficient in desulfurization, and a considerable amount of sulfur still remains.

[Problem to be solved by the invention]

The problem to be solved by the present invention is to solve the difficulties of the conventional desulfurization method for this type of graphite sheet. The objective is to develop a method for desulfurizing graphite sheets and an apparatus for use in this process.

[Means to solve the problem]

The present inventor has been conducting intensive research to solve the above problem, and in this research, it was discovered that it might be possible to improve the desulfurization efficiency by heating the graphite sheet to a higher temperature. I came up with a new idea.

Based on this new idea, we experimentally conducted an experiment using a conventional ordinary resistance heating element as shown in Reference Example 1 below.
When heated to 400°C, it was found that the high temperature reliably had a desulfurization effect. However, it has been found that this method has the following problems. That is, although the heating time is only about 10 to 40 seconds,
The graphite sheet reacts with oxygen in the air and exhibits an oxidative consumption rate of about 4 to 6% by weight. In particular, this consumption rate increases rapidly as the temperature increases;
It has also been found that, although it can occur relatively easily up to around 1,400°C, it is almost impossible to use it industrially for a long period of time at higher temperatures, especially at temperatures above 1,400°C.

Although it has been found that heating to high temperatures improves the desulfurization of graphite sheets, the development of means to generate high temperatures has become a major problem, and 1,400 other methods have been developed.
Furnace materials that can withstand high temperatures above ℃, measures to prevent oxidation, and decomposition products or evaporated gases are removed from the heating element inside the furnace, and are they protected? IA+
A. Consideration to prevent damage to heating devices, wiring, etc. has emerged as a new problem when proceeding with low-sulfur treatment of graphite sheets through high-temperature treatment.

As a result of further pushing forward with this research to resolve these issues,
Finally, by using a high-frequency induction heating method to heat the graphite sheet itself as a heating element, we have solved all of the above problems and discovered a method that allows for the continuous production of inexpensive, high-quality graphite sheets on an industrial scale. .

[Structure and operation of the invention]

FIG. 1 shows a schematic diagram of a desulfurization system of the present invention using a graphite sheet itself as a heating element using a high-frequency heating method. In Figure 1, a field current is induced in the graphite sheet (3), which is an electrical conductor, by a loop-shaped high-frequency coil (5), and the sheet (3) is divided into several It becomes red (white) hot at 1000°C to 2000'C in seconds. Since the graphite sheet (3) normally moves slowly in the direction of arrow (A), the red (white) heated zone also moves continuously. In Fig. 1, (1) is a high-frequency power supply, (2) is a current transformer, (4) is a heat-resistant and non-conductive (for example, made of ceramic) partition plate, and ll+, 111°H, also indicates the red (white) fever zone. Also, the arrow (b) indicates the flow direction of the cooling water, and the arrow (c)
indicates an inert gas, usually N, and the direction of gas flow.

Since the graphite sheet (3) has a thickness of about 0.1 to 5 IIl/m, its heat capacity is small, and it is instantaneously heated and instantaneously cooled with a small amount of electric power before being taken out of the furnace.

The time for red (white) heating depends on the moving speed of the graphite belt, but it is approximately 2 to 30 seconds, preferably 3 to 10 seconds. Although the loss due to the oxidation reaction is very small, to ensure completeness, a very small amount of inert gas, such as N2 gas, is supplied from near the electrode (high frequency coil) as shown by the arrow (c). This N
The introduction of gas prevents oxidation of the graphite sheet (3) and also removes sulfur vapor, which is thermally decomposed and discharged from the sheet.
It also has the effect of quickly removing sulfur dioxide gas etc. from the system.

The high frequency coil (5) itself is water-cooled and the temperature is close to room temperature, so a normal hollow steel tube is used. However, in order to prevent wear and tear caused by sulfur compounds removed and discharged from the sheet by heating, and to enhance the replacement effect with N2 gas, a heat-resistant nonconductor was installed between the high-frequency coil (5) and the graphite sheet (3). For example, it is preferable to partition with a ceramic partition plate (4), and to provide a similar ceramic partition plate below.

In order to increase current efficiency, it is desirable that the distance between the graphite sheet (3) and the high frequency coil (5) be as small as possible. The high frequency generator to be used is selected in consideration of the thickness and density of the graphite sheet, but it is usually 10 to 700KH2, preferably 50 to 400KH7, and the required output, power efficiency,
A vacuum tube type, a transistor type, a thyristor type, etc. are appropriately selected in consideration of the equipment cost, etc.

Although the shape and arrangement of the electrodes are not particularly limited, examples include those shown in FIG. 2. In this way, these electrodes are arranged parallel to the sheet (Fig. 2 (a)),
A vertical arrangement ((b) in the same figure) and an oblique arrangement ((c) in the same figure) are adopted, and both cases are effective.

Further, as shown in FIG. 3, it is also possible to arrange the electrodes below the sheet surface. However, Figure 3 is a simulated view of the seat viewed from below. In this case, there is a phenomenon in which the graphite sheet (3) is pushed upward by the effect of magnetic lines of force, and it is possible to prevent scratches on the bottom surface of the sheet due to the feeding movement due to sagging due to gravity in the furnace, and, Even if electrode cooling water leaks, it will not fall onto the graphite sheet exposed to high temperatures, which is safe and effective for quality control.

Furthermore, as shown in FIG. 3 or 4, the electrode can be divided into a plurality of small pieces and the power of each electrode can be controlled. This brings about the following effects. That is, (1) it is possible to heat the entire surface evenly, and (2)
) Also, if necessary, it is possible to perform a so-called programmed heating method in which treatment is performed at a slightly lower temperature in the flow direction at the beginning and at a strongly higher temperature in the latter half, and (3) in the case of desulfurization of graphite sheets, When the rate at which decomposed or vaporized sulfur (compounds) is discharged from the deep part of the sheet to the outside of the sheet is slower than the rate of decomposition (vaporization), bubbles are generated inside the sheet and a swelling phenomenon occurs. If this happens, the quality of the graphite sheet 1- product will be significantly degraded even if roll pressure is applied afterwards.

Therefore, in order to eliminate defects in the sheet due to the generation of internal bubbles, it is desirable to perform heat treatment at a stage when some pore spaces still remain before the sheet itself is completely rolled and densified. Also, even when heating with high frequency, the first half is relatively low temperature, e.g.
Heating at 0°C followed by a relatively high temperature e.g.
It is desirable to carry out multi-stage temperature raising in which heating is performed at 00'C.

The method of arranging multiple small electrode coils shown in Fig. 4 is as follows.
It is ideal for performing such operations.

The graphite sheet to be desulfurized in the present invention is not particularly limited, and includes any conventionally known graphite sheets,
Its thickness is usually 0.1 to 20 m, preferably 0.2 to 10 m
It is about m. These normal graphite sheets before desulfurization are 10
Most of them have a residual sulfur content of about 00 to 1200 ppm. The size of the sheet is not equally limited; in the case of a continuous sheet, it is preferable to perform desulfurization while slowly moving the sheet, and in the case of a continuous sheet, it may be moved, or in a non-moving state. Desulfurization may be performed using

The moving speed may be a speed that allows sufficient desulfurization.

The temperature during desulfurization is preferably higher, but it is usually 1200°C or higher, preferably 1400°C or higher. Further, as already mentioned, it is preferable to combine low temperature and high temperature.

Note that when performing high-frequency heating according to the method of the present invention, it is also possible to provide terminals at both ends of the graphite sheet and to use heating by a direct energization method that utilizes the electrical resistance of the graphite sheet.

[Example] The present invention will be explained in detail by showing Examples and Reference Examples below.

Reference Example 1 Preparation regarding heating temperature and heating time of graphite sheet (a Experiment Graphite sheet (thickness 0.75 m/m, density 0.18 g/m)
c+Il, manufactured by Toyo Tanso) was cut into 5cm x 10cm,
They were held one by one with sample scissors and heated to a predetermined temperature (120°C).
The sample was exposed to a resistance electric furnace maintained at a temperature of 0 to 1600'C for a predetermined period of time (10 to 40 seconds), and then rapidly cooled.

The total sulfur content in the sample pieces before and after treatment was measured, and the results are shown in FIGS. 5 and 6.

However, Figure 5 shows the case where the heating time is kept constant at 30 seconds and the temperature is raised, and Figure 6 shows the case where the heating time is changed at two temperatures, 1500°C and 1600'C. Part (a) shows the case of 1500'C, and part (b) shows the case of 1600'C.

As is clear from FIGS. 5 and 6, the higher the treatment temperature, the longer the treatment time, the lower the wedge sulfur content, and it was found that the influence of the treatment temperature was particularly large.

The gold sulfur content before treatment was about 1200 ppm, but it was found that if the conditions were selected, it could be halved to about 600 ppm.

In these series of experiments, the oxidation loss rate of graphite sheets due to high temperature treatment was approximately 4 to 6%, although there was some variation.
(weight loss).

Example 1 Using the apparatus shown in FIG. 1, the same graphite sheet as in Reference Example 1 was moved horizontally to the center of a flat space surrounded by a ceramic partition plate. A first steel pipe (outer diameter 5 m/m, wall thickness 1 m/m) is placed above the 3 m/m thick ceramic plate.
Rolled up in the shape shown in figure (b) (long side 8 can, short side 5 cm,
A high-frequency coil (double coil) is installed, and a high-frequency current (
280KH2) was applied. (The coil is water-cooled). The graphite sheet is heated almost uniformly to an incandescent state over a width of about 8 cm near the bottom of the coil, and moves while emitting white smoke with a sulfur smell.
It was immediately cooled (blackened). The temperature was measured from the gap between the ceramic plates using an optical thermometer, and was adjusted by controlling the applied high-frequency current and the moving speed of the graphite sheet. The value obtained by subtracting the width of the red (white) tropical zone by the feeding speed was taken as the heat treatment time.

Using this method, the relationship between the heat treatment temperature and heat treatment time and the total sulfur content in the graphite sheet was investigated, and the results are shown in Table 1.

The test samples in Table 1 were manufactured according to the process diagram in Figure 1, and were not subjected to the above high-frequency heat treatment at all (blank test).
The sulfur content in the graphite sheet on the winding roll was 1230 ppm. The sulfur content was measured by the combustion method based on the amount of sulfur dioxide gas produced. The high frequency oscillator is manufactured by Fuji Denpa [Oscillation frequency 280Kl-IZ
Vacuum tube type] was used.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the method of carrying out the method of the present invention, and FIG.
4 are simulated drawings showing the shape of the high-frequency coil and its arrangement. Figures 5 and 6 are graphs showing the results of measuring the sulfur content of graphite sheets. ■... High frequency power supply 2... Current transformer 3... Graphite sheet 4... Partition plate 5... High frequency coil (or more) ゝV

Claims (5)

[Claims] (1) A method for desulfurizing a graphite sheet, which is characterized by subjecting the graphite sheet to high-frequency heating. (2) The desulfurization method according to claim 1, wherein the temperature by high-frequency heating is 1400°C or higher. (3) The desulfurization method according to claim 1, characterized in that the high-frequency heating electrode is separated into a plurality of parts, and the first half is treated at a low temperature and the second half is treated at a high temperature. (4) The desulfurization method according to claim 1, which is carried out while moving the graphite sheet. (5) Graphite sheet desulfurization equipment in which a high-frequency heating electrode is installed at the bottom of the graphite sheet.